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DEPARTMENT OF THE INTERIOR

Jv
U. 8S. GEOGRAPHICAL AND GEOLOGICAL SURVEY OF THE ROCKY MOUNTAIN REGION
J. W. POWELL 1n CHARGE

WY | >

REPORT

ON THE

GHOLOGY AND REHSOURCES

BLACK HILLS OF DAKOTA
WITH ATLAS 10974

By HENRY NEWTON, E. M., anp WALTER P. JENNEY, EH. M.

WASHINGTON

GOVERNMENT PRINTING OFFICE
18380

Wasuineton, D. C., March 1, 1880.
Sir: I have the honor to transmit herewith the manuscript of the
Report on the Geology and Resources of the Black Hills of Dakota, placed
in my hands for revision.
I am, with respect, your obedient servant,
G. K. GILBERT.
Maj. J. W. Powe 1,
In charge U.S. G. and G. Survey, Rk. M. R., Washington, D. C.

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PREFACE BY THE EDITOR.

At the time of Mr. Newton’s death his manuscript was incomplete. It
was chiefly in the form of a first draft, with much erasure and interlineation,
but by no means perfected. Two important sections were unwritten, and
_ he was engaged in making a re-examination of some parts of his field, for
the purpose of settling certain geological questions that had arisen in his
mind while he was at work upon his report. He regarded no part of his
manuscript as a finished composition, but intended to revise the whole and
recast some portions on his return. The editor has therefore felt called
upon to put himself, in a certain sense, in the place of the author, and make
such emendation of form as seemed necessary to harmonize the whole.
But while he has freely modified the language in such ways as he conceived
the author might have modified it had he been able to revise it, he has,
with a single exception, carefully preserved the substance.

At the time of Newton’s first examination of the Black Hills, gold had
been discovered only in the modern gravels and in a few Archean quartz
ledges. It was natural to assume that all the placer gold originated in the
Archean ledges, and Mr. Newton and Mr. Jenney made that assumption.
The logic of events has shown their error, and Newton was aware of it
before his death, although he had no opportunity to record his later under-
standing. In this single case the editor has modified the substance of the
manuscript so far as was necessary to eliminate the error.

In Newton’s scheme of the third chapter, there were two sections indi-
cated by title but unwritten; the first on “The Quatenary,” the second on the

“Structure and Age of the Black Hills.” It was impossible to supply data
VA

vi PREFACE BY THE EDITOR.

for the first, and it was omitted. The second was largely foreshadowed by
scattered allusions in the preceding sections, and as it must consist in any
event chiefly of simple deductions from the facts set forth in the descrip-
tions of the formations, its composition was undertaken by the editor.
The thoroughness and fidelity of the record of observations and its freedom
from bias made the task an easy and pleasant one. All the data are New-
ton’s, and so are all the principal deductions except those derived from the
drainage system, but he should not be held responsible for the manner of
presentation.

The majority of the wood-cuts illustrating his text were made under
his own direction with the friendly assistance of Mr. J. L. Fitch, and others
were afterwards prepared for the engraver by Mr. Thomas Moran. The
topographic map and the base of the geological map were drawn by Dr.
V. P. McGillycuddy, the topographer of the expedition. The colors of the
geological map, unfortunately, have not the author’s full authority. He
traced the outlines of the formations rudely upon a small and imperfect
map prepared for the preliminary report, but the final map was printed too
late to be used by him. The editor transferred the colors from the small
map to the large, and filled in the details, so far as he was able, to corre-
spond with the descriptions given in the manuscript, but it isto be supposed
that he fell into many errors which the author would have been able to
avoid. The bird’s-eye view, although projected by Newton and drawn
under his supervision, was not engraved until after his death.

The editor’s responsibility does not extend to the chapters which succeed
Mr. Newton’s. Mr. Jenney’s chapters have already been published in a
preliminary report, and are here copied verbatim from that text. In its
separate publication his chapter on the Mineral Resources was introduced
by a general account of the geological structure, which is here omitted
because it is superseded by Mr. Newton’s chapters. Mr. Jenney has sub-
stituted for it a brief classification of the auriferous formations.

At the time of this writing, the editor is called away from Washington,
and confides the general supervision of all the text beyond Chapter III to
Mr. J.C. Pilling, of the Bureau of Ethnology. The proofs of Chapters

oD?

VI, VU, VIII, and IX will be submitted to their authors.

PREFACE BY THE EDITOR. : vii

Besides the papers on Petrography, Paleontology, Botany, and Astron-
omy, it was Mr. Newton’s purpose to include several chapters on the Dakota
Indians, and an account of the topographic work of the survey. The
former were prepared for his use, but have been reserved for a more appro-
priate place in the publications of the Bureau of Ethnology. The latter
does not appear among the papers.

The topographic work was performed by the reconnaissance method.
The topographer traversed the district by numerous and intersecting routes,
sketching and observing the country as he went. His courses were esti-
mated by noting his traveling time. Their bearings and the bearings of
the features of the topography were observed with a prismatic compass.
Sextant observations for latitude were made by the astronomer each night
and at the midday camp. The whole was checked by a triangulation
including the principal peaks. There was no measured base line, but scale
was derived from the astronomical latitudes. The azimuth of the triangu-
lation was determined astronomically. Longitude was at first derived from
chronometers carried with the party, but a telegraphic determination, made
afterward, was adopted in the final map.

Yielding to none in my appreciation of Newton’s noble qualities and
brilliant promise, and sharing as geologist and friend in the regret and grief
at his untimely loss, I yet yield the place of biographer to his early
instructor and life-long friend, Dr. Newberry.

Wasuineton, D. C., May, 1880.

Ve

7

BIOGRAPHIC NOTICE.

New York, February 26, 1880.
Mr. G. K Giipert:

Dear Sir: I take pleasure in complying with your request to furnish
you a brief sketch of the personal character of the late Prof. Henry Newton
and of the work accomplished in his short but busy life. My relations
with him were most intimate for many years, and there is perhaps no one
living who more fully shared his confidence, is more familiar with what he
accomplished, or better capable of judging of the promise of the life upon
which he had but just entered when it was brought to a close.

I fear, however, that I shall hardly find words to do justice to the rare
qualities he possessed, or to express my own affection for him.

Mr. Newton was born in the year 1845 in the city of New York. He
early showed a strong taste for scientific studies, and an unusual mathe-
matical faculty, which he inherited from his father—the late Isaac Newton,
well known from his connection with the growth of the great system of
steam navigation on the Hudson—and shared with his brother Isaac, the
distinguished naval engineer. His academical education was obtained at
the College of the City of New York, from which he graduated in 1866, and
came to us at the School of Mines in the autumn of the same year. During
all his course of study he exhibited the traits which marked his after career.
He was noted for his punctuality, thoroughness, and accuracy of thought,
and success in all the studies pursued, and no less so for his modest, reserved,
and at the same time agreeable manners. No student has left the school
with a better record, and when he graduated, in 1869, he had won the

sincere respect and esteem of all his teachers and associates. The follow-
Ix

xe BIOGRAPHY OF PROFESSOR NEWTON.

ing summer he was appointed an assistant on the Geological Survey of
Ohio, with which he was intimately connected for some years, rendering
important aid in several departments, to which I shall have occasion to refer
again. In 1870 he went to Europe with his intimate friend and classmate,
Prof. W. B. Potter, and spent some months in visiting the principal centers
of iron and steel industry in the British islands and on the Continent.

In 1871 Mr. Newton became assistant in metallurgy at the School of
Mines; in 1872 he was appointed assistant in geology, a position which
he held for two years. During this time we were brought into daily and
hourly communication, and I came to entertain for him not only a sincere
and warm friendship, but an almost paternal affection. Through the
summers of these and succeeding years we were working together on the
Geological Survey of Ohio; in all our intercourse not an unkind word was
ever spoken, and I cannot too highly praise the prompt, punctilious, and
thorough manner in which his every duty was performed. He was always
at his post, courteous and obliging in his manners, doing a great variety of
work, and doing it so well that I ultimately came to feel that whatever
task was committed to him would be done with accuracy and dispatch.

In field geology he was a close observer, and an exact and rapid
worker, and I early learned that ground that he had gone over need not be
revisited unless for a different purpose. Ile wielded a facile pen, and his
notes and reports were at the same time concise and comprehensive.

The subject which lay nearest his heart, however, and that in which
his acquisitions and labors were most important, was the metallurgy of iron
and steel. This he pursued for some years with a devotion which absorbed
all the time he was able to give to it, and with a success that made him at
his death second to no one in this country in his mastery of principles and
practical familiarity with details.

While connected with the Geological Survey of Ohio he made a thor-
ough and exhaustive study of all the resources of the State as regards ores
and furnace fuels, and of the conditions and possibilities of the future devel-
opment of the iron industrp there. This report has not yet been published,
but I have no hesitation in pronouncing it the most complete monograph of
its kind that has yet been prepared in this country.

BIOGRAPHY OF PROFESSOR NEWTON. XI

Of his published reports on iron and steel, the most important are ‘A
Sketch of the Present State of the Steel Industry” (Ohio, Geol. Surv., Report
of Progress for 1870, p. 529) and ‘The Ores of Iron, their Geographical
Distribution and Relation to the Great Centers of the World’s Iron Indus-
tries” (Trans. Inst. Min. Eng’rs, Vol. III, p. 360).

In 1875 the Secretary of the Interior applied to Professor Henry, the
head of the Smithsonian Institution, requesting him to suggest a geologist
to take charge of an exploration of the Black Hills, Dakota, for the purpose
of ascertaining the extent and value of the gold deposits discovered there.
This request was, by Professor Henry, referred to me, and in accordance
with my nominations Mr. W. P. Jenney was appointed geologist and Mr.
H. Newton his assistant The purely geological work of the expedition
was for the most part performed by Mr. Newton, and the report now com-
mitted to you for publication is the result. Although limited to a single
season, the amount of work accomplished by the expedition was surpris-
ingly large and of excellent quality. The topography and geological
structure of the Black Hills were accurately determined and mapped, and
the collection of fossils made by Mr. Newton and described by Mr. Whit-
field contributed a larger amount of new material than that gathered by
any single expedition to the West. Mr. Newton took great pains with his
report, as he had done in the accumulation of facts, and in its preparation
expended about eighteen hundred dollars from his own pocket, when it was
quite uncertain whether this sum would be repaid him by the government
When presented to Congress its publication would have been immediately
authorized except for a selfish and heartless opposition it encountered spring-
ing from the fear that it would betray the inaccuracy of previously published
descriptions of the geology of this region. This opposition cost Mr. New-
ton his life, for when Congress deferred action on his report till another
session he determined to employ a part of the interval in revisiting the
Black Hills, repeating some of his observations and recording the results of
the rapidly-developing mining industry. While engaged in this work he
was attacked by typhoid fever, and died at Deadwood, August 5, 1877.

Previous to his second journey to the West, Mr. Newton had received -
the appointment of professor of mining and metallurgy in the State Uni-

Xl BIOGRAPHY OF PROFESSOR NEWTON.

versity at Columbus, Ohio, a recently organized but already vigorous insti-
tution, and one that promises to be among the strongest of western colleges.
Had he lived this would probably have been the field of his labors for many
years, and we can hardly imagine one better adapted to his tastes and
talents. Columbus is situated but a few miles distant from the Hocking
Valley coal and iron region, which has proved to be one of the richest in
the country, where furnaces are multiplying at a rapid rate, and where
increasing thousands are deriving subsistence, and many wealth, from the
iron and steel industries. Here he would have found immediate application °
for the knowledge gained in years of study and observation, and by bring-
ing to the aid of the Ohio iron masters the last results of progress elsewhere,
and a keen and suggestive intellect for the solution of all new problems, he
would have been to them a most efficient helper, and would doubtless have
gained for himself fame and fortune. It is, of course, useless to speculate
upon what would have been the career of Mr. Newton if he had been per-
mitted to enter upon the life thus opened to him; but when we consider the
keen and logical quality of his mind, his already great acquirement, his
indefatigable industry, and his gentleness and equanimity, which secured
the affection as well as the respect of all who knew him, we cannot but
conclude that it would have been eminently successful.

To his family, by whom he was idolized, and to his friends, who all
loved as well as admired him, his loss is, of course, irreparable. We may
also say that, from his peculiar qualifications to take a leading part in
the development of the great industries which are to be among the most
important elements in our national prosperity, his early death must also be
regarded as a great public calamity.

Yours, very truly,
J. S. NEWBERRY.

CONTENTS.

GEOLOGY OF THE BLACK HILLS, BY HENRY NEWTON.

CHAPTER J.—INTRODUCTION

II.—OBSERVATIONS ON THE ROUTES TO AND FROM THE BLACK HILLS
IIT.—GEOLOGY .... -

Section I.
II.
III.

. The Jura-.
. The Cretaceous
Pe Lhe Menianygeactra sa oe ntas sic cecse sec cl ee beealenceee Hcsckacwoss
we Lhenvolcanie rocks\and yoleanicmpeaks: ---- =. -- see seece esac
pistcucturelandiace of the Black Hills se. 2-32 so ceeree one ween one ee

eee e ne ree eee pe ee ee ee eee ee ee ee ees ce ees wees tee eee wee

Introduction
ANAS SRONE SE 015 JOE eRe SAB ROIS ab on CUES SE SeR oN ae et
RherGranibesessses se

MINERAL RESOURCES OF THE BLACK HILLS, BY WALTER P. JENNEY.

CHAPTER SIVE— MINE RAT YW RESOURCHS ss saan sitcic cies on.cclsietenisieeisre nica e Sisue ou weteccmre oeieecwerlaben

Section I.
If,
Il.

IV.

Vv.
VI.
Vil.
VIIl.
IX.

CHAPTER V.—CLIMATE AND RESOURCES -..------

Section I.
IO

Til.

IV.

Ve

VI.

Introduction -..-.--- -
The French Creek cicenen
Spring Creek district
Whiskey Creek... --
CastlevandsRapidy Creeksrecectc a slscen slo a= os ve etseae seein se
The Castle Creek district
a pidg Cree kee oes aoe aetate aie See tice se wc ae cerenoeeeac ce sa see
Box Elder and Elk Creeks
Spearfish and Bear Butte Creeks
The Bear Lodge country.-..--.
Deposits of auriferous gravels in the foothills. Sect Soncsee Heaaooaoee
Conchnsi Omer merece te se eicaiviee san Saeisiee cic tole Sereisis Scesa/sesiseensaccs

ee eee ewww

wee eee ween cee eee pee eee ce ec ee tee eet cee eee cee eee eee

XIV CONTENTS.

PALEONTOLOGY OF THE BLACK HILLS, BY R. P. WHITFIELD.

Page,
CHAPTER VI.—PALEONTOLOGICAL REPORT ON THE FOSSILS COLLECTED...----.--.------..----. 329
SCO JI; Ler lbrb nay WeNMPRO NS: 66 = 5 coo ccs Cogean oobosd cease coscocsosssobe= 329
eeHossilstromibhey bnimordialsrockssseee eee eee eee see eee eee 331
SH ossilsnom! theJmrassic LockSpeee ese -ee eee ee eee eee eee eee 344
[Vie -Hossils trom the: Cretaceous mocksie=- eee eee eee eae eee eee eee ene 383

VY. Synopsis of species from the Black Hills, noticed in other works,
Mot describedsinthiS ep OL bee ee eeer a= -m ee eee ee eee eee 460
VI. List of fossils described in this report ---.----.-----.-----..-=-5--- 465

MICROSCOPIC PETROGRAPHY OF THE BLACK HILLS, BY JOHN H. CASWELL.
CHAPTER VLI:-—MiIcROSCOPICG;BETROGRAPHY)-252< coco se ce cee Se ne eee eae eee ee ee ee eee 471
Section a. -Quartzites.,./.hs2 5552.28 228d soc ass qsisccs nace e ee eke melee ee 471
I: Mica‘schistsjand'slates:..s- 2 «scce+ca-c22 cise oe os hare eeeeeceeeee 76
Li Skhyolitestrachyte sand, phonoliteeeseeas= sere a aeeee eee eee 483

BOTANY OF THE BLACK HILLS, BY ASA GRAY.

CHAPTER VELL. — BOTANY oes era ce Rain alee y Sie rene nee ae ea oe Se eo ae Tae 531

ASTRONOMY AND BAROMETRIC HYPSOMETRY OF THE BLACK HILLS, BY HORACE P.

TUTTLE.
CHAPTER IX.—ASTRONOMY AND BAROMETRIC HYPSOMETRY -...------.----.---+-----+--------- 543
Sechion le ebherashronomicalawiolkeeseeeeee seer eee eee eee eee ape eae eee 543
JI. Magnetic variation ..........--- deeds oeo6 EpESnaasUsas casaGstSeccecs 547
EL: Barometric works2: a--.-)22ee2> oie occas cr eeiee ernce nee he temoeece 547
Table of positions and altitudes of camps and other points... ..-- 551
TYG, Sh MEIGHT ae cocoecus comGo ooasse casa chan o650 5000 960d conacD Saasse 594

FRONTISPIECE.—-Bear Lodge, looking eastward.

nish On TLE USK ATION S.

Page
Fie. 1. Section through Rawhide Butte..... -....-..-- eo ngéess cee boSeca nobeaotersace cococoas 27
2. Section of uplitt at headwaters of the Niobrara ..-...--.------.---2---+--.---0+-----.- 28
3. Section through outer foothills at Camp Jenney, east fork of Beaver ..-...--..-.-.----- 34
A HeadonmGolden Valley nllustratins packiscenery=cea=. ans c see ose ie mines = see =e 56
5. “‘Saw teeth,” of granite, near Harney Peak..---.....-.---------.-------+------+------ 70
6. Granite forms near Harney Peak......--- SEE SES rE SESE RC nese e ta SNE eae eles negara nae 72
7. Plan and section of schist included in granite -...---. sgonel ¢ Eoeteadoodeerpieaopsogd oevoe 72
SaGroundaplankandisectlontotnGraniier ensue eters arlene eels tere eller sieve iano 74
©): SeGtiom On Syme Cres. pc seosen books sencde sSdeec be eco bouces ceed osenEe ceaeon mace 82
10. Section of the Potsdam sandstone on lower Rapid Creek..-.-.-.-.----.-.--------------- 85
HP Sectionlof theszoisdamionilowerns prim as © reel eet e eee a otrieeletae einen el aire eee == i= 87
12: Section of Potsdam sandstone oni lower French Creel<_-2:-------.------2. .----- +--+ ---- 90
18y, SECON GF Wins 1oyiGleinn in Isforx IDIkolere Creal 8 oso ee deb eeu aeoace sodces Gaede Seseegs case 91
iA Sechioniofibotsdannontlower KapidiCreekee. ease se aee a) | ae selene ail eee sees 94
lowaldealisectiontoimthe Carbomterouss lated Ursa apenas eae eer eieteraiae eteielr ete a 117
16. Ideal section across the Carboniferous Plateau at Camp Jenney.-----.-----.-----.------ 119
Ili, SeetiOm On AMM NON OTE CHAD oo5e5 cons cod dod ones doses pedouc Senseo sseoobobne ches acco 122
18. Section along the lower cation of Rapid Creek-.---...--..----.-.-.------ -c---.-------- 124
19. Ideal section across the Red Valley at Camp Jenney---.-.----.'-----.-----..----.-..----- 140
20. Ideal section across the Red Valley on Amphibious Creek............---.-----.-------- 141
21. Ideal section across the Red Valley on Rapid Creek.-.. ..---- SR CO rR ee SES eer arse 142
22. Ideal section across the Red Valley near Spearfish Creek-...-.-.....----- Pep enewnc ears 144
23. Ideal section across the Red Valley through Sun Dance Hills.........- .-....-----.---- 146
24. Section across the valley of the Belle Fourche near Bear Lodge...--..-....---..--.---- 147
iy, IGE GRSSHEC CON OF WHS IlaGlke JsMIK) 22 -baee oh65 concede seop eHoces cadass sous BuoSesaos 206
26 Contourmaplots obey blacksHalll sidisplacementie een sais == ele eae etna mie oe elae = 208
27. Diagram to exhibit the relation of the drainage system of the Black Hills to the zones
Gir Inehyel CAG! GOs SIMI ooo 5 soos cones cods sedodo sdas ogoSe0 seus bonone Gece cneees eee 214
28: Longitudinal section of the bed of Spring Creek .----. .-- 2-522... «22 20- nne ee eee = 244
IPE ATS) IES.OV1L, Tenleomigloeay s—-s6o cooseebobsies code Goober cueobe 6ooboD ase accbro ueedes Bose baaseE 468
I-II. Microscopic Petrography ..---.-.-.---- Tawra erhcetia! Sesteis Sartesciareie eee lete winis eee 528

U. 8. GEOGRAPHICAL AND GEOLOGICAL SURVEY OF TH ROCKY MOUNTAIN REGION.
J. W. POWELL, IN CHARGE.

; GEOLOGY

OF THE

BLACK HILLS OF DAKOTA.

By HENRY NEWTON, E. M.

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GEOLOGY OF THE BLACK HILLS.

By Henry NEWTON.

CHARI Re
INE ROD CLIO N.

SITUATION AND RELATIONS OF THE BLACK HILLS.—HISTORICAL SKETCH OF EXPLORATIONS IN THE Up-
PER MIssOURI REGION.—DISCOVERIES OF GOLD IN THE BLACK HILLS.—ORIGIN AND ORGANIZATION
OF THE EXPEDITION TO THE BLACK HILLs.

The Black Hills were explored during the summer of 1875, in accord-
ance with the instructions of the Secretary of the Interior. Some little
confusion has arisen in regard to their identity, for the reason that the
mountains adjoining Laramie Peak, in the southeastern part of the Terri-
tory of Wyoming, have been called by the samename. ‘The latter, however,
in the recent surveys of that region, have been more properly designated the
Laramie Mountains; and as a further guard against confusion, the mount-
ains which form the subject of this report are usually called the Black
Hills of Dakota.

The name Black* Hills is said to have been applied to these, the only
mountains of Dakota, from the fact that, as they are approached from the
barren, desert wastes of the Plams, they loom up in the distance as a dark
range, black from the heavy growth of timber they support. They lie
between the 43d and 45th parallels of north latitude, and between the 103d
and 105th meridians of longitude west from Greenwich, occupying an
uregularly shaped area, about 120 miles in length, from north-northwest to
south-southeast, and having a width of from 40 to 50 miles.

The meridian of 27° west from Washington (approximately 104° west
from Greenwich) forms the boundary line between the Territories of Dakota

1 oe 1

2 GEOLOGY OF THE BLACK ILLS.

and Wyoming, and it will be seen by referring to the map accompanying
this report, that by far the greater area of the Hills is m Dakota, and that
but a comparatively small portion of the northern and middle parts is in
Wyoming. The entire Bear Lodge range is in Wyoming.

The area of the Hills proper is about 5,000 square miles—not far from
that of the State of Connecticut.

The whole avea of the main section of the Hills determined to be gold
bearing—the French Creek, Spring Creek, Rapid Creek, Deadwood Creek,
Terry Peak, &c., districts—is in Dakota, while the small and unimportant
gold district of the Bear Lodge range lies in Wyoming.

The Black Hills are embraced between the two forks of the Cheyenne
River, the Belle Fourche and South Fork, which, rising near Pumpkin
Buttes, in eastern Wyoming, spread out, the former northeasterly and the
latter southeasterly, to enfold the Black Hills, and then approaching each
other join about 60 miles east of the Hills in latitude 44° 25’, forming the
Big Cheyenne, which then flows northeast and empties mto the Missouri
River some 15 miles above New Fort Sully. Surrounded on all sides by the
comparatively unbroken sea of the Great Plains, they are entirely separated
from the main chain of the Rocky Mountains on the west, to which system,
however, in character and structure they belong, and rise an island of
rough and rugged mountains complete within themselves.

The elevation of the Hills above the surrounding country—an aver-
age of 2,000 to 3,000 feet—and their heavy growth of timber cause them to
act as condensers upon the water-bearing clouds, and the precipitation of
moisture upon them is much greater than upon the neighboring region of
the Plains. Though they give rise in themselves to no great river or impor-
tant system of drainage, the enfolding branches of the Cheyenne become
augmented to fully double their previous volume by the few running streams
that drain from their heights and valleys. While the region of the Hills
proper is well watered, containing innumerable springs and brooks of clear
and cold water, all the important streams, save about five, sink and disap-
pear in their beds before they reach the regions of the Plains, and though
they occasionally rise and sink again, they carry no running water to the
Cheyenne.

GENERAL FEATURES. 3

There are many parts of the interior area that recall the mountain
scenery of northern New York and New England, and the general char-
acter of the region is exceedingly broken and rugged.

Having passed the barrier of foot-hills surrounding the Black Hills,
and having traversed the broad, red valley that encircles them as a moat,
one gradually ascends the outer slope of the Hills and soon enters, at an
altitude of 4,500 or 5,000 feet, the wooded portion of the region. This
outer slope varies greatly in width, and is underlaid by the older sedi-
mentary rocks, cut in almost every direction by narrow and deep canons.
Usually from the broken interior edge of this slope or plateau of sedi-
mentary rocks one descends a bluff or escarpment and enters the central
area of slates and granites, which is tossed into high ridges and sharp peaks,
cut up by narrow and deep valleys and ravines, and generally thickly tim-
bered with the common pine of the Rocky Mountains (Pinus ponderosa).

In the structure of the Hills there are many points that make them
a miniature representative, compact and wonderfully complete within them-
selves, of the topography and geology of the great Rocky Mountain sys-
tem. In their interior area of sharp ridges of schist and slate and ser-
rated peaks of granite are represented the character and structure of a
large portion of the nucleal regions of the Rocky Mountains; and in the
surrounding sedimentary strata we have, exhibited in a beautifully clear
manner, some of the most interesting features of the composition and_
structure of the sedimentary formations of the Far West.

To the geologist the detailed study of their rocky structure presents
many points of exceeding interest, and, unlike the volume in the East
which is so generally concealed with heavy covers of drift or soil, he has
here the pages of the geological record plainly spread before him, with no
concealing surface accumulations, and with the intimate structure plainly
revealed by bluffs and numerous cross-cutting cations.

The results of the geological observations, which were as carefully
made as the limited time and rapid work of the exploration would permit,
will be given in a somewhat detailed manner in Chapter III. Our small
collections of fossils were made from formations so wonderfully rich that
Professor Whitfield has been enabled to prepare a most important mono-

4 GEOLOGY OF THE BLACK HILLS.

graph on the paleontology of the region, with illustrations of many new
and characteristic forms.

The mineral resources of the country, for the examination of which
the expedition was primarily organized, are not greatly varied in character.
The deposits of auriferous gravels, found in many parts of the Hills, pro-
duced “prospects” sufficient to attract a large influx of miners; and it is
probable that many of the districts will pay a fair remuneration for labor
and outlay. Reports on the discoveries made during the summer were
transmitted from time to time to the department, and fuller accounts, with
analyses since made, will be found in the chapter on Economic Geology.
This chapter, from its immediate importance, was published by resolution
of the Senate, April 18, 1876, in advance of the rest of the report, being
accompanied by a description of the climate and general resources of the
Hills and by a small preliminary map.*

The portion of the Black Hills east of the meridian of 104° lies within
the permanent reservation set aside for the different tribes of the Dakota
or Sioux Indians by the provisions of the treaty of 1858. According to the
terms of this treaty the reservation is bounded ‘‘on the south by the north
line of Nebraska, latitude 43°; on the west by the boundary between Wy-
oming and Dakota, longitude 104° west; on the north by the parallel of
latitude 46° north, and on the east by low water on the Missouri River,” alto-
gether embracing an area of about 40,570 square miles. Beside this area,
by the same treaty, all the country north of the North Platte and east of
the summits of the Bighorn Mountains, is held as unceded Indian terri-
tory, practically granted to them as a hunting reservation. By special
agreement, however, made in 1875, the right of the Indians to hunt in
Nebraska, south of the Niobrara and west of the 100th meridian, was relin-
quished for the sum of $25,000.

This large reservation, excepting the Black Hills, their immediate
vicinity, and the narrow valleys of some of the more important streams, is
a most inhospitable region, desolate and barren, and includes a large area
of the well-known sterile and clayey tracts of “bad lands.” Once abound-

*Forty-fourth Congress, first session, Senate Ex. Doc. No. 51. The Mineral Wealth, Climate and
Rainfall, and Natural Resources of the Black Hills of Dakota, by Walter P. Jenney, E. M., Geologist in
charge. Washington, 1876.

THE DAKOTA INDIANS. 5

ing in buffaloes and smaller game, which afforded an abundant maintenance
for the hunting Indians, it is now deserted, save by a few antelopes and
deer. The buffaloes have been destroyed or driven to the Upper Missouri,
and this large population of 50,000 Indians is held in a tract of country
whose natural resources are utterly inadequate to maintain even a tithe of
the number.

The agricultural possibilities of the Sioux Reservation may practically
be considered as nothing. The soil and climate will admit of farming only
at a few places in the narrow valleys of some of the larger streams, and
even in the most favored spots cultivation is possible only by a systematic
work of irrigation. It is a high estimate to say that one-half of one per
cent of this great country can possibly be irrigated.

Many parts of the reservation afford excellent grazing during the sum-
mer, though water is very deficient, but the rigors of a Dakota winter for-
bid any attempt at a systematic engagement in the grazing of stock, espe-
cially by the improvident Indians. It may be said with truth that the
Black Hills include all the desirable Jand in the reservation and all the
useful timber, and by those who view the treatment and future of the In-
dians in this region in a purely humanitarian spirit the presence of gold in
the Black Hills has been regarded as unfortunate, for if it were not for its
discovery, this beautifully timbered and grassed region would afford them an
excellent retreat during their initiation into the simpler labors of civilization.

By many of the more intelligent of the Dakotas the Black Hills have
been long thought of as the final refuge of their tribe from the encroach-
ments of the whites. They are by far the most powerful Indian nation
within our territories, including, as they do, a population of 50,044*; and
by the absence of game in their country, coupled with its agricultural bar-
renness, they are of necessity thrown upon the bounty of the government,
which has taken all the desirable land they possessed in Minnesota and
elsewhere, leaving them a desolate waste.

Exploration in the region between the Missouri River and the Rocky
Mountains has not been so thorough and complete as in the corresponding

* Report of Commissioner of Indian Affairs, 1875,

6 GEOLOGY OF THE BLACK HILLS.

region south of the Pacific Railway, partly because of the hostile Indians,
the expense of transporting supplies, and the barrenness of the country,
but especially because the more rapid settlement of the south has demanded
the prior exploration and opening up of that part of the Plains. To illus-
trate the progress of exploration in the Upper Missouri Region, and par-
ticularly to show the course of exploration in the area of our last summer’s
work, the different expeditions that have passed over and examined this
northwest territory will be briefly reviewed. Many of the facts relating to
the earlier expeditions are derived from Dr. Hayden’s paper in the report
of General W. F. Raynolds’ ‘‘ Exploration of the Yellowstone and Missouri
Rivers” (1859-1860).

The first authorized expedition made by our government, and the first
intelligent exploration of the Upper Missouri region was conducted in 1804,
’05, and ’06, by Captains Lewis and Clarke of the United States Army, who
were commissioned in 1803 by President Jefferson. They started in the
spring of 1804, following up the Missouri River to its source, and then push-
ed across the Rocky Mountains to the Columbia River and the Pacific. Re-
turning, they descended the Yellowstone to the Missouri and the Missouri to
Saint Louis. Their journal, published in 1814,* contains the first reliable
account of this great northwest territory, and though of exceeding interest,
especially in relation to the Indian tribes they encountered, it contains little
or no information as to the geological structure of the country. They col-
lected a few fossils, however, and from their study Dr. Mortont was able to
establish the presence of the Cretaceous formation on the Upper Missouri.

A long period intervened before the next expedition of note, which
was made in 1832, by Prince Maximilian of Neuwied, who ascended to the
headwaters of the Missouri. The results of his travels were published in a
most elegant manner, profusely illustrated from sketches made ia the field,
which possess much artistic value, beside being truthful pictures of the
country and natives. Maximilian noted more carefully than his predeces-

* History of the expedition under the command of Captains Lewis and Clarke to the sources of the
Missouri, thence across the Rocky Mountains and down the river Columbia, &c., during the years 1804,
05 06, by order of the United States Government. 2 vols, 8vo. Philadelphia, Bradford and Inskeep,
1314.

+ Synopsis of the Organic Remains of the Cretaceous Groups of the United States, etc. ByS. G.
Morton. Philadelphia, 1834,

EARLIER EXPLORATIONS. 7 i

sors the geological features of his route, and mentions the occurrence of
well known Cretaceous fossils from the headwaters of the Missouri to the
mouth of the Big Sioux; and the great geologist Von Bach, from his obser-
vations, was led to state, ‘that this great river flows uninterruptedly from
the foot of the Rocky Mountains, through strata of chalk, at least as far as
the mouth of the Sioux River. This is the result of the accounts and col-
lections of Prince Neuwied and of the report of the celebrated astronomer
Nicollet.” * |

In 1839, the geographer J. N. Nicollet, under the auspices of the War
Department, ascended the Missouri River as far as Fort Pierre, and though
his travels did not extend so far as his predecessors’, from his accurate
observation we obtained the first definite and reliable information of the
geology of that region. Devoting considerable time to the study of this part
of the Missouri Valley, he collected a large series of fossils from the Creta-
ceous formation, and, on his return to Philadelphia, they were described by
Conrad and Morton, and published in the Proceedings of the Academy of
Natural Sciences. The results of his explorations were published by au-
thority of the government. |

Mr. Audubon, in his expedition to the mouth of the Yellowstone in 1843,
was accompanied by Mr. Edward Harris, who had been instructed by the
Philadelphia Academy of Natural Sciences to make observations on the
geology of the region. The committee apointed by the Academy to report
on the notes and collections of Mr. Harris, consisting of Professors Rogers,
Morton, and Johnson, gave the first intimation of the proofs of the fresh-
water origin of certain deposits of the Upper Missouri. Previous explor-
ers, though recording the presence of lignites, &c. on the Missouri River
above Fort Clarke, never recognized the different: character of the deposits
above and below this point; and in the collection of Mr. Harris the first
proofs are presented of the great lignitic and fresh-water Tertiary beds, which
occupy such large areas on the Upper Missouri. Mr. Harris obtained at one
point ‘‘a brown, ferruginous, argillaceous rock, containing three or four
specimens of freshwater, univalve shells, Limnea, Planorbis, etc. One of the
specimens of Planorbis, it is conjectured, may be a form extinct, but the

*Silliman’s Journal, September, 1850,

8 GEOLOGY OF THE BLACK HILLS

mutilated condition of the specimens prohibits a positive opinion.”* In
these collections we have also the first specimens of that great fossil flora of
the Upper Missouri, which has since yielded such rich and valuable stores
of deciduous plants to our paleo-botanists, Newberry, Lesquereux, ete.

It will be noticed that the expeditions mentioned confined their explo-
rations in Dakota and Wyoming almost entirely to the immediate valley of
the Missouri and its branches, and did not penetrate into the great unknown
land beyond the banks of the river. The territory was sterile and disheart-
ening to look upon, and was inhabited then by warlike aborigines. Those
hardy and adventurous pioneers of our earlier civilization, the fur-traders
and voyageurs, had, however, scoured the country far and near, seeking their
peltry and trading with the native tribes in their distant dwelling places.
The employés of the old United States and American Fur Companies and
their powerful rivals in trade the Hudson Bay Company, were familiar with
all points of the great Northwest, but their observations were of little value
from a scientific point of view. Good descriptions of the general features
of the country, of the Indians, and of life in the West, are given in many
of the old books of travels, prominent among which are Irving’s “‘ Astoria”
and “Bonneville.” Specimens, however, brought in from time to time by
these traders gave evidence of interesting deposits, and from this source was
obtained the first information regarding the great bone beds of the “bad
land” Tertiary deposits—the ‘‘Mauvaises Terres” of the White River. An
account of these specimens was first made public in the American Journal
of Science, by Dr. H. A. Prout, in 1847.

In 1849, Dr. D. Dale Owen, who had been intrusted to make a geo-
logical survey of the Chippewa land district, directed his assistant, Dr. John
Evans, to make a trip into the Mauvaises Terres of White River. Dr. Evans
obtained a very excellent collection of Cretaceous shells and vertebrate
remains, and the former were described and published in Dr. Owen’s final
report in 1852, while the latter were described by Dr. Leidy, of Philadelphia.t

In this report of Dr. Owen the first description is given by Dr. Evans}
of these now celebrated ‘bad lands.”

*Proc. Phil. Acad. Sci., May 1845, vol. ii, p. 240.
tProc. Phil. Acad. Sci., vol. vi, 185253, p. 392.
tD, D. Owen’s Final Report, 4to, 638 pp., 27 plates, 16 maps, p. 194, et seq.

EARLIER EXPLORATIONS. . 9

In 1850 the Upper Missouri country was visited by Mr. T. A. Cul-
bertson under the direction of the Smithsonian Institution. He collected
some vertebrate fossils from the White River bad lands and ascended
the Missouri above Fort Union, and though he notes the character of the
country, his report shows that he made no collections and no valuable
observations on the geology of these very interesting formations.

Dr. Evans again, in 1853, passed through this region en route to Ore-
gon Territory, where he was ordered by the government to make a geo-
logical survey. He made here another valuable collection of vertebrate
fossils from the Bad Lands and of Cretaceous fossils from the now well-
known Sage Creek region. Dr. Leidy made a study of the vertebrate re-
mains, publishing the results in the Journal of the Philadelphia Academy
of Natural Sciences, while Drs. Evans and Shumard described the mollus-
can fossils in the Proceedings of the Saint Louis Academy of Sciences.

In the same year, 1853, the region was visited for the first time by
Mr. Meek and Dr. Hayden, to whom so much is due for their study of the
geology of the Northwest, and they have continued to the present time*
among the most voluminous contributors to the geology and paleontology
of the far West. These gentlemen visited the country under the auspices
of Prof. James Hall, of Albany, the veteran American paleontologist, for
the purpose of making a collection of the Cretaceous and Tertiary fossils
of the Bad Land region. The vertebrate remains collected were examined
by Dr. Leidy, and the invertebrate forms of the Cretaceous, studied by
Professor Hall and Mr. Meek, furnished the subject of a memoir published
by the Boston Academy of Science.t In this memoir was a section pre-
pared by Mr. Meek, showing for the first time the order of succession of
the different beds of the Cretaceous in the Upper Missouri Region. The
interesting observations of Meek and Hayden on the geology of the coun-
try from Fort Pierre to Council Bluffs were presented also by Professor
Hall in a paper read before the American Association for the Advancement
of Science, at Providence in 1865.

In 1854 Dr. Hayden, for the most part alone and unaided, again

* Mr. Newton’s MS. was prepared before the lamented death of Mr. Meek, which occurred Decem-
ber 22, 1876.—Ep.
t Proceedings, 1854.

10 GEOLOGY OF THE BLACK HILLS.

visited the Upper Missouri region, in which he spent two years, traversing
it in different directions, often on foot. During this time he passed up the
Missouri River to Fort Benton, and up the Yellowstone to the north of the
Bighorn River, and traversed large portions of the bad lands of the White
River region.

In 1855 an expedition was made into the Dakota country, called the
“Sioux Expedition,” under the command of General W. 8S. Harney. This
was unaccompanied by any scientific observer, and was undertaken primarily
to determine upon routes to the far west and between the frontier military
posts. A report of the exploration was made in a small document, “ xplo-
ration in the Dakota Country,” published by order of the United States Sen-
ate. In 1856 these explorations were continued under the immediate com-
mand of Lieut. (now Major of Engineers and Bvt. Maj. Gen.) G. K. Warren,
of the United States Topographical Engineers, and he was accompanied by
Dr. F. V. Hayden as geologist and naturalist. Starting from Saint Louis,
Lieutenant Warren made a careful survey of the Missouri to Fort Pierre,
at which place the expedition was organized. From this point the Missouri
was ascended in the American Fur Company’s boat to some 60 miles above
the mouth of the Yellowstone River, careful examinations being made en
route. With wagons the Yellowstone was ascended for 100 miles above its
mouth, and with pack mules to the mouth of the Powder River, some 30
miles farther. The expedition returned to Fort Pierre by boats, mapping
the Yellowstone River, verifying the map of the Missouri, and examining
all interesting points. Lieutenant Warren was ordered in 1857 to continue
these explorations, and to determine the best route between the Big Sioux
and Fort Laramie and South Pass, and then to examine the Black Hills as far
as possible. This expedition is of particular interest here, because it obtained
the first reliable information regarding the Black Hills of Dakota, and a
more detailed notice of it will not be out of place.

Leaving Sioux City with wagons, Lieutenant Warren ascended the
Loup Fork to its source, and crossing to the Niobrara ascended it, and
thence reached Fort Laramie. Here his party divided, and one part, under
Lieutenant McMillan, with the wagons, descended the Niobrara, where it
awaited the main party. Lieutenant Warren, accompanied by Dr. Hayden

WARREN’S EXPEDITION. ; 1

as naturalist, with ovly a pack train, proceeded northward from Fort Lara-
mie to the Black Hills. His route passed by Rawhide Butte and down
Old Woman’s Fork to the South Cheyenne, and thence to Beaver Creek, by
the east branch of which he entered the Hills. This is much the same route
as that taken by the expedition of 1875, and Lieutenant Warren’s camp
of September 12 is almost the same as our first camp in the Hills, known
as Camp Jenney. From here Lieutenant Warren proceeded northward to
Inyan Kara, where he was met-by a large force of the Sioux, who were
engaged in herding immense numbers of buffaloes in the Red Water Val-
ley. His party being small and the Indians opposing their progress they
retraced their stéps, and passing around the southern end of the Hills
struck northward on the east side of Bear Butte. Leaving this on October
Ist, they traveled down Warren Creek, and thence southeast to the South
Cheyenne, near Sage Creek, and, ascending the Cheyenne to near French
Creek, crossed over to the White River, meeting Lieutenant McMillan
and the rest of the party on the Niobrara. Fort Randall was reached on
the 1st of November. The preliminary report of Lieutenant Warren,
accompanied by a catalogue of the collections made by Dr. Hayden, was
published by the War Department in 1858.*

Owing to the breaking out of the civil war no final report of Lieuten-
ant Warren’s exploration was ever published, and it is very much to be
regretted that the valuable material collected by this and other surveys
undertaken in the far west about the same time have never been made
public.t .

The results of Dr. Hayden’s observations were combined with those
subsequently made, and published in papers and places hereafter mentioned.

This reconnaissance of the outskirts of the Black Hills was made in a
most rapid manner and with a small amount of instrumental aid, but it has

* Preliminary Report of Explorations in Nebraska and Dakota in the years 1855, 56,57. 8 vo.,
pp. 125, with map. Engineer Department, 1858. Republished in 1875.

tA portion of the material to which Mr. Newton refers has recently been published. The War
Department has brought out the report of Capt. J. H. Simpsen on ‘Explorations across the Great
Basin of the Territory of Utah,” with many scientific appendices, and the report of Capt. J. N. Ma-
comb’s ‘‘ Exploring Expedition from Santa Fé to the Junction of the Grand and Green Rivers,” with a
most valuable geological report by Dr. J. S. Newberry; while an important paper on the ‘“‘ Tribes of
Western Washington and Northwestern Oregon,” by the late George Gibbs, has appeared in the publi-
cations of this survey, ‘‘ Contributions to North American Ethnology, vol. i.”—Ep.

14 GEOLOGY OF THE BLACK HILLS.

been proved by our more detailed survey to exhibit unusual accuracy, and
it remains a most gratifying testimony to the care and precision of the
mapping of Lieutenant Warren. All the subsequent maps of the region,
up to the present time, have been based on his work.

In the year 1859 an expedition under the command of Captain (now
Colonel) W. F. Raynolds, United States Engineers, was organized ‘‘for the ex-
ploration of the region of country through which flow the principal tributaries
of the Yellowstone River, and of the mountains in which they and the Galla-
tin and Madison forks of the Missouri have their sources.” 'This expedition
was accompanied by Dr. Hayden as geologist, and started from Fort Pierre,
on the Missouri, ex route for Fort Sarpy, on the Yellowstone. Passing by
Bear Butte it followed the Red Water Valley westward, and then striking
northwest crossed the Belle Fourche branch of the Cheyenne near its great
northern bend. A passing examination was made of that portion only of the
Black Hills through which their route lay, and a successful scout was made
by Mr. J. D. Hutton, topographer, to the curious peak of the Bear Lodge.
The rest of the season was spent in explorations of the Bighorn and Pow-
der River region, winter quarters being made on the North Platte near Deer
Creek. The following year was occupied by different parties of the expe-
dition in the exploration of the Wind River, Upper Yellowstone, and Upper
Missouri regions, and meeting at Fort Union, at the mouth of the Yellow-
“stone, the main party followed the Missouri to Fort Randall and Omaha on
land, while a division under Lieutenant Maynadier descended the river in
boats The preparation of the reports of the expedition was delayed by
the war of the rebellion, but a report by General Raynolds was issued in
1868,* while the-report of Dr. Hayden on the geology of the region visited
was published in the following year.t

In the interval between the making of this survey and the publication
of the final official reports there appeared numerous valuable publications
on the geology and natural history of the region. In 1857 Dr. Hayden pre-
sented the first map of the geology of the region, in a paper read before the

* Report on theE xploration of the Yellowstone River, by Bvt. Brig. Gen. W. F. Raynolds. 8vo.,
pp. 174, with map. Washington, 1868.

+t Geological Report of the Exploration of the Yellowstone and Missouri rivers, by Dr. F. V.
Hayden. 8vo., pp. 144, with geological map. Washington, 1869.

HAYDEN'S SURVEY. 13

Philadelphia Academy of Natural Sciences,* and in the following year
another map was published by him in the Proceedings of the Philadelphia
Academy, together with the results of his expedition with Lieutenant
Warren to the Black Hills. The most important publication, however,
including all his observations to date, was read as a memoir by Dr. Hayden
before the American Philosophical Society of Philadelphia in 1861,+ being
accompanied by a map. The descriptions by Dr. Leidy of the vertebrate
remains collected in these various expeditions appeared at different times
in the Proceedings of the Philadelphia Academy of Natural Sciences, and
form a most important contribution to our knowledge of these very inter-
esting fossils. Much of the same material, with the addition of that since
collected in other parts of the Far West, appears in a more accessible form
in a quarto publication of the Geological Survey of the Territories.{ The
molluscan collections of the formations of the Upper Missouri have been
described and published through the Philadelphia Academy of Natural
Sciences by Messrs. Meek and Hayden and form the subject of one of the
memoirs issued by the Smithsonian Institution.§

In 1859 Captain (now Colonel) J. H. Simpson, United States Engineers,
made a survey for a wagon road across the Great Basin of Utah, and the
records of the route from Fort Leavenworth to Fort Laramie and South Pass
contain many valuable facts regarding the geology of the southern part of
the Upper Missouri region. The geologist was Mr. Henry Engelmann.||

In 1866 Dr. Hayden again visited the Bad Land region of the Nio-
brara and White Rivers, and in the following year the “‘Geological Sur-
vey of the Territories,” in his charge, was begun under the auspices of
the Commissioner of the General Land Office. The work was commenced
in Nebraska, and in the following year was extended into Wyoming, but
it embraced only the southern portion of that Territory and the northern

* Notes explanatory of a map and section illustrating the geographical structure of the country
bordering the Missouri. May, 1857.

t On the Geology and Natural History of the Upper Missouri, with map. Trans. Am. Phil. Soc.
Philadelphia, July 19, 1861.

} Contribution to the Extinct Vertebrate Fauna of the Western Territories, by Joseph Leidy. 4to,
pp. 358, pl. 37. Washington, 1873. _ ‘

§ Paleontology of the Upper Missouri. Partl. F.B. Meek and F. V. Hayden. Washington, 1865.

|| Exploration across the Great Basin of Utah, 1859, by Capt. J. A. Simpson. (Geology by H.
Englemann.) Sto. Engineer Department, 1876.

14 GEOLOGY OF THE BLACK HILLS

part of Colorado—from Cheyenne and Fort Laramie westward to Fort
Bridger and the South Pass. The results of these two years’ work were
made public in two annual reports issued by the General Land Office.*

The more complete report of the exploration in Nebraska and the parts
of the Territories immediately adjoining, prepared in 1X68, was published
by the Commissioner of the General Land Office in 1872.+

In the following year, 1869, the appropriation for the surveys under
Dr. Hayden’s care was increased, and the work was placed under the im-
mediate direction of the Secretary of the Interior. The field of operations
was transferred to the Territories of Colorado and New Mexico, and the
results of the year’s work were published in a report to the Secretary of the
Interior.t In 1870, 1871, and 1872, the field of survey was once more
north of the railroad, but it included no portion either of eastern Wyoming
or of Dakota. The results were published in annual reports to the Secretary -
of the Interior.§ Since 1872 the field of survey has again been transferred
to the Territories lying south of the railroad.

In 1873 Captain W. A. Jones, United States Engineers, proceeded from
Fort Bridger to northwestern Wyoming, and made a reconnaissance of the
country within that Territory about the headwaters of the Snake, Big-
horn, Grey Bull, Clark’s Fork, and Yellowstone Rivers. This expedition
was accompanied by Prof. T. B. Comstock as geologist, and though much
of the territory examined had already been passed over by Hayden and
other explorers, the report of Professor Comstock affords many valuable
additions to our knowledge of the geological structure of the Wind River
Mountains and the adjoining region, including the headwaters of the Yel-
lowstone and the Yellowstone National Park.||

* First Annual Report of United States Geological Survey of the Territories, embracing Nebraska.
8vo., pp. 64, 1867, and Second Annual Report, &c., embracing Wyoming. 8vo., pp. 36, 1868.

t Final Report of the United States Geological Survey of Nebraska, and portions of adjacent Ter-
ritories. 8vo., pp. 269, plates xi, and Geological Map.

¢ Third Annual Report of United States Geological Survey of Territories, embracing Colorado and
New Mexico. 8vo., pp. 25. Washington, 1870.

§ United States Geological Survey Wyoming and contiguous Territories. 8vo., pp.511. Washing-
ton, 1871. United States Geological Survey Montana and adjoining Territories. 8vo., pp.538. Wash-
ington, 1872. United States Geological Survey Montana, Wyoming, &c. 8vo., pp. 844. Washington,
1873.

|| Northwestern Wyoming, including Yellowstone National Park, Geology, by Prof. T. B. Com-
stock. 8vo., pp. 331, maps 51. Washington, 1875.

CUSTER’S EXPEDITION. ; 15

Lieut. Col. G. A. Custer, in the summer of 1874, was directed by
General Sheridan, of the Department of the Missouri, to organize an expe-
dition at “Fort Abraham Lincoln, Dakota Territory, for the purpose of
reconnoitering a route from that post to Bear Butte in the Black Hills, and
exploring the country south, southeast, and southwest of that point,” and to
“return within sixty days from the time of his departure from it” General
Custer left Fort Abraham Lincoln, and striking southwestward to the val-
ley of the Little Missouri, crossed the Belle Fourche about 10 miles east
of the great northern bend; thence, through the Red Water Valley and
past Sun Dance Hills, he entered the Hills proper near Inyan Kara, and
passing along Floral Valley and Castle Creek encamped on French Creek
near its lower cafon. From this point two scouts were made, one south-
westward to the Cheyenne River, via Red Cation Creek, and another
down French Creek to the Red Valley. An ascent of Harney Peak
was also made. Returning northward the expedition passed over the old
trail to Castle Creek, and then out of the Hills by the valley of the
Box Elder. Passing near Bear Butte, and crossing the Belle Fourche,
they returned to Fort Abraham Lincoln by the valley of the Little
Missouri and the headwaters of Cannon Ball and Heart Rivers, being
absent just sixty days. This was the first expedition that had ever pene-
trated the fastnesses of the Black Hills. In his rapid march General
Custer was accompanied by Capt. Wm. Ludlow, United States Engi-
neers, under whose direction the route was mapped, by Prof. N. H.
Winchell as geologist, and by Mr. G. B. Grinnell as naturalist. The
report of General Custer was published in 1875 in compliance with a Sen-
ate resolution,* while the reports of Captain Ludlow, Professor Winchell,
and Mr. Grinnell form a volume published by the Engineer Department in
the same year.f

General Custer was accompanied by several miners and prospectors,
who were engaged on all possible occasions during their rapid march
through the Hills in examining the region for the existence of mineral de-

* Report of the Expedition to the Black Hills of Dakota, under command of Byt. Maj. Gen. G.
A. Custer. Ex. Doc. No. 32,U.8.Senate. 1875.

t Report of a Reconnaissance of the Black Hills of Dakota, made in the Summer of 1874, by Capt.
William Ludlow, United States Engineers. 4to, pp. 121, maps 3 and plate.

16 GEOLOGY OF THE BLACK HILLS.

posits but more especially in prospecting for gold. In regard to the dis-
coveries. made, the words of General Custer may be quoted from his pre-
liminary report to the Department of Dakota:

It will be understood that within the limits of the Black Hills we were almost
constantly marching, never halting at any one point for a longer period than one day,
except once, and that was near Harney’s Peak, where we remained five days, most of
the command, however, being employed in operations during the halt. * * *
Enough, however, was determined to establish the fact that gold is distributed
throughout the extensive area within the Black Hills. Gold was obtained in numer-
ous localities in what are termed gulches. No discoveries, so far as I am aware, were
made of gold deposits in quartz, although there is every reason to believe that a more
thorough and extended search would have discovered it. No large nuggets were
found; the examination, however, showed that a very- even, if not a very rich, distri-
bution of gold is to be found throughout entire valleys. In other words, the “ pros-
pecting” showed that, while the miner may not in one panful of earth find nuggets of
large size or deposits of astonishing richness, to be followed by days and weeks of
unrewarded labor, he may reasonably expect, in certain localities, to realize from every
panful of earth a handsome return for his labor.

While I feel satisfied that gold in satisfactory quantities can be obtained in the
Black Hills, yet the hasty examination we were forced to make did not enable us to
determine in any satisfactory degree the richness or extent of the gold deposits in that
region. Seeking for gold was not one of the objects of this expedition, consequently
we were but illy prepared to institute or successfully prosecute a search for it even
after we became aware of its existence in the country.

These reports of General Custer, correct in themselves, were magnified
and exaggerated by others until the sensitive imagination of western pros-
pectors and frontiersmen constructed for itself a region of riches and
wealth untold, awaiting only the reaping of the harvest. On the other
hand, it must be recorded that the presence of gold in the Hills, at least
in any quantity, was strongly denied by high scientific authority on the
ground of their supposed general structure, and also by members of the
expedition itself, who would be supposed to have had the opportunity
of practically testing the question. It is proper to mention, too, that the
existence of gold in this region was undoubtedly known long before
to the Indians and some of the old pioneers. The statement of Father de
Smet has often been quoted, and considerable reliance has been placed upon
what he said, but more imagined from what he left unsaid. Father de Smet
was born in Belgium in 1801, and early in life emigrated to this country,
entered the Order of the Society of Jesus, and became a missionary to the

THE GOLD EXCITEMENT. 17

native tribes of the far west. His account may best be given in the words
of a letter written in March, 1875, to General Sherman by General Sheridan,
who was personally acquainted with the holy father and learned from his
own lips the following story:

That while living with the Sioux Indians he was shown by them nuggets of gold,
which they informed him had been obtained at different points in the Black Hills,* sup-
posed to be from the beds of the Bighorn, Rosebud, and Powder Rivers, and from
branches of the Tongue River; and on his representation that such yellow metal was
of the greatest value, they told him they knew where there was a mountain of it. Sub-
sequent investigation, however, proved that the Indian mountain of gold was nothing
more than a formation of yellow mica, such as may be found in the above-described
country.

The reports of General Custer brought this story of Father de Smet
again prominently to light. In the winter of 1874~74 several of the pros-
pectors who had accompanied General Custer in his expedition returned
from Sioux City with others to French Creek. Arriving there about Christ-
mas time, twenty-five in number, with the wife and child of one of the
party, they immediately proceeded to erect a stockade and cabins to protect
themselves from possible Indian attacks and from the severity of the climate
They prospected the valley of the creek in their immediate vicinity, and
although the snow and coldness of the winter prevented a thorough exami-
nation they were satisfied and encouraged. ‘T'wo parties from the camp
returning in February to Cheyenne, fired anew the dormant spirits, ready
for excitement of any kind.

The presence of this party in the Hills and the certainty that others
would follow their footsteps compelled the government to take some notice
of these unauthorized operations within the Indian Reservation, which they
were bound by the terms of the treaty of 1858 to protect from the incur-
sions of the whites A company of cavalry under Captain Mix was there-
fore dispatched from Fort Laramie early in March, and the remainder ot
the stockade party were brought back to Fort Laramie. Measures were
also taken at the various military posts to prevent the starting of others to
the Black Hills.

The reports that had been brought in by the stockade party, in their

*The recent discovery of nuggets weighing several ounces, in the northern parts of the Hills,
renders the knowledge of rich deposits there quite possible.

2BH

eee ae

—

ag

18 GEOLOGY OF THE BLACK HILLS.

true and in their more exaggerated forms, with the addition of others more
or less fictitious, were now spread far and wide over the West, and great
excitement prevailed in the frontier settlements bordering on the reserva-
tion, and extended even into the thickly-settled region of the East. ‘The
great floating population of the frontier, miners and others, suffering from
a dearth for several years of the excitement peculiar to mining discoveries
were now ready to rush into this new E11 Dorado of the West, and the differ-
ent towns of the immediate frontier rivaled each other in the statements of
their superiority as outfitting posts for the Black Hills, while the mere fact
that there was a desire on the part of the government to sustain its part of
the treaty and keep intruders out of the reservation only added new zest to
the enterprise.

It soon became evident that there was a large body of miners ready
to enter the new field, many of whom expressed no wish to transgress the
word of the government given in the treaty, and there was a very general
desire that the right to prospect and mine should be acquired for them by
the government either by purchasing the Black Hills or by obtaining a con-
cession from the Indians, as was endeavored in a subsequent council.

As many of the reports circulated were undoubtedly greatly exag-
gerated, and many persons well informed in regard to this region of the
Northwest, and of high authority, were strong in their denials of the pres-
ence of gold there, at least in remunerative quantities, it became of general
importance to obtain accurate and reliable information on the subject... It
was determined, therefore, that trusty persons should be sent immediately
to examine the region and report to the Secretary of the Interior, so that
the true facts regarding the nature and value of the mineral deposits should
be authoritatively known, and might furnish a basis for any subsequent nego-
tiations with the Indians for the territory.

-As this expedition, both in the territory to be examined and in the
purpose of the examination, was one relating specially to the nghts and
interests of the Sioux Indians, the organization and control were given to
the Bureau of Indian Affairs, under which the work was begun and com-
pleted. Under authority of the Secretary of the Interior, Mr. Walter P.
Jenney was therefore appointed by the Commissioner of Indian Affairs,

ORGANIZATION OF THE JENNEY SURVEY. — I)

March 26, 1875, to undertake the work of the examination, and Mr. Henry
Newton was commissioned to act as his assistant.

At first it was proposed that with his assistant, and with the help of a
small force of miners and laborers, Mr. Jenney should immediately proceed
to the field, make in a few weeks a hasty examination, return, and make his
report. But as much of the value of the labor would be lost without a
reliable map of the region—that of Lieutenant Warren and General Ray-
nolds expressing only the outer rim of the Hills—it was finally arranged
to add to the party a topographer and an astronomer. Dr. V. T. McGilly-
cuddy, late of the Lake and Northern Boundary Surveys, and Capt. H. P.
Tuttle, late of the Cambridge Observatory, were therefore commissioned to
accompany the expedition, respectively as topographer and astronomer.
The personnel of the expedition, as finally organized, consisted of Walter P.
Jenney, EH. M., geologist in charge; Henry Newton, E. M., assistant geolo-
gist; V. T. McGillycuddy, M. D., topographer; Captain Horace P. Tuttle,
A. M., astronomer; C. G. Newberry, M. D., assistant astronomer and natur-
alist; * W. F. Patrick, E. M., and the following corps of miners and laborers:
John Brown, jr.; William H. Root, head mining assistant; William O. Bald-
win, A. J. Bottsford, A. P. Sanders, T. H. Mallory, Thomas Morey, James
Conklin, Robert M. Jones, A. E. Guerin, and George Bowlin, cook.

With all possible haste the plans were matured and the necessary in-
struments and tools purchased, and on April 25 the whole party assembled
at Cheyenne, Wyo. Here an unexpected delay was unfortunately forced
upon us, as the orders for the necessary means of transportation, wagons,
horses, &c., had not been issued by the War Department, as had been sup-
posed. The time, however, was spent in fitting out the numerous little
details of the expedition, and finally, on the 17th of May, all transportation,
&ec. being fully provided for, Cheyenne was left behind. Arriving at Fort
Laramie on May 20 all arrangements were consummated; and crossing the
Platte on the afternoon of the 24th of May we joined the military escort
furnished by the War Department, consisting of Lieut. Col. R. I. Dodge,
Twenty-third Infantry, commanding; Lieut. M. F. Foot, Ninth Infantry,

* From ill health Dr. Newberry was unfortunately compelled to resign at Fort Laramie on the eve
of departure.

——EEEeEe—E—EEEE— ES

20 GHOLOGY OF THE BLACK HILLS.

adjutant; Lieut. J. F. Trout, Twenty-third Infantry, quartermaster; Lieut.
J.G. Burke, Third Cavalry, topographer, and Surgeons Jaquette and Lane ;
with two companies of the Ninth Infantry, under Captains Burt and
Munson and Lieutenant De Lany; two companies of the Second Cavalry,
under Captain Spaulding and Lieutenants Hall, Coale, and Kingsbury; four
companies of the Third Cavalry, under Captains Hawley, Russell, and Wes-
sells and Lieutenants King, Whitman, Lawson, Foster, and Morton, with a
train of 75 wagons.

This large command, numbering fully 400 men, would seem at first
unnecessarily strong for the mere purpose of protecting from Indians those
who were pursuing the investigation in the Hills, but the attitude of the
Indians on the penetration of this, the most cherished spot of their reserva-
tion, could not be foretold, and it was known that they had been not a little
agitated by the incursion of General Custer in the previous year and by the
subsequent visits and operations of miners. Though no bands of Indians
were met during the work, our safety and freedom from their visits were
probably due to the well known magnitude and strength of the expedition.

A great measure of the success of the exploration is due to the hearty
co-operation of the various officers of the command, but particularly to the
commander, Colonel Dodge, whose unwavering interest and determination
to make the work successful, and whose constant assistance and courtesy
were especially valuable and grateful during the entire course of the work.

To Lieutenants Merton and Foster, who were detailed for topographi-
cal work, Dr. McGillycuddy is indebted for assistance in the prosecution of
his mapping.

Reaching the Black Hills on the east fork of the Beaver on the 3d of
June, the work of the survey was soon begun, and a permanent camp was
established on French Creek near the stockade erected by the miners
during the previous winter. In order to pursue the work more rapidly
and thoroughly, a division of the party was made as follows: Mr Jenney,
with a corps of assistants, assumed more particularly the investigations of
the mineral resources of the country, prospecting the gold deposits, &c.;
while the remainder of the party, Mr. Newton, Dr. McGillycuddy, and Cap-
tain Tuttle, continued the topographical and more complete geological study

METHOD OF EXPLORATION. 21

of the Hills. As the work of the survey progressed northward, the main
body of the escort of troops was transferred from one base of supplies to an-
other so as to keep up with the course of the explorations. In this manner,
with scarcely a day’s remission from work, the survey continued until the
entire area of the Black Hills between the forks of the Cheyenne had been
mapped and its geology and mineral resources determined as fully as the rapid
progress would permit. Having passed over the entire country and accom-
plished the object of the expedition, the various parties assembled on the
Cheyenne at the mouth of Rapid Creek, and began the march homeward,
reaching Fort Laramie, via White River and the agencies of Spotted Tail and
Red Cloud, on the 14th of October, after an absence of four months and
twenty days.

Having disbanded the expedition at Cheyenne the officers of the Sur-
vey returned east and assembled in Washington early in November to com-
plete their report.

While in the field, the various discoveries of the presence of gold in
the different districts were announced to the Commissioner of Indian Affairs
at Washington; and a preliminary report by Mr. Jenney on the mineral
resources of the Hills, accompanied by a small preliminary map by Dr.
McGillycuddy, was published in the Annual Report of the Commissioner of
Indian Affairs for 1875. The completed observations on the mineral
resources, climate, &c. (Chapters IV and V of this volume), possessing
immediate and particular interest, were, by resolution of the Senate, called
for in advance of the final report, and with a preliminary map were pub-
lished in the spring of 1876 *

* The Mineral Wealth, Climate and Rainfall, and Natural Resources of the Black Hills of Dakota.
by W. P. Jenney with map. Washington, 1876. 8vo., 71 pp.

CHAPTER II.

OBSERVATIONS ON THE ROUTES TO AND FROM THE BLACK
HILLS.
CHEYENNE TO Fort LARAMIE.—FORT LARAMIE TO THE BLACK HILLS.—RAWHIDE BUTTE AND MONO-

CLINAL RIDGES ON ROAD TO CHEYENNE RIVER.—TERTIARY AND CRETACEOUS ON OLD WOMAN’S

_ ForK.—Fort UNION GROUP ON CHEYENNE RIVER.—HOG-BACKS OR MONOCLINAL RIDGES OF

CRETACEOUS ON WEST SIDE OF THE HILLS.—ROUTE THROUGH THE HILLS.—NOTES ON GEOLOGY

OF EASTERN SIDE OF HILLS.—TERTIARY OR WHITE RIVER GRouUP.—BaD Lanpbs, &C.

The country between Cheyenne, at which place our party was organ-
ized, and Fort Laramie, 96 miles farther north, where the military escort
was added to it, has been so frequently examined and reported upon by
geologists and others, that little need be said concerning its features and
geological structure. Dr. Hayden has repeatedly passed over the route,
and his observations may be found recorded in the annual report of the
Geological Survey of the Territories for 1870.

The government road between these two points runs in a northerly
direction, crossing the valleys of Lodge Pole, Bear, and Horse Creeks to
the Chugwater Valley, which it follows for some 15 miles, and then
strikes northwest to the valley of the Platte and Fort Laramie. It runs its
entire distance along the eastern base of the Laramie Mountains (Black
Hills of Wyoming), whose rugged and snow-capped summits lie some 15
to 18 miles to the west, while to the east spreads the broken, desolate, and
treeless region of the Plains. This great country of the Plains, which on
the Missouri River at Omaha has an elevation above the sea of 1,060 feet,
rises westward, until at Cheyenne, 516 miles distant, it has imperceptibly
reached an elevation of 6,075 feet.

From Cheyenne to Fort Laramie the country is gently rolling, being
cut by the main drainage valleys from the mountains at the west into

22

FROM CHEYENNE TO FORT LARAMIE. AS)

rounded hills and isolated ridges—with numerous dry ravines and arroyos,
the result of surface denudation The general elevation of the surface
appears to vary only a little, but there is a quick descent to the valley of
the North Platte, and at Fort Laramie the altitude is only 4,500 feet,
while the summit point of the mountains, Laramie Peak, 45 miles to the
west, attains an altitude of 10,000 feet above the sea

Of the creeks that we pass on our route, Crow Creek, on which Chey-
enne is situated, and Lodge Pole Creek, bend southward and join the South
Platte, while Horse and Bear Creeks empty into the North Platte, and the
Chugwater joins the Laramie River. With the exception of Crow Creek
and the Chugwater, which are of considerable size, these small, feeble
streams are barely worthy of the name. Their valleys, which are from 4
to 6 miles in width, are almost destitute of trees, but a fair soil, especially
on Horse Creek, supports an excellent growth of grass well adapted for
grazing purposes. The Chugwater, for the distance traversed by the road,
is quite a fertile valley, excavated in the light-colored sandstones and sandy
clays of the Tertiary, which in sharp cliffs line its margins, giving them a
drear and castellated appearance. Many ranches have been established
in these valleys for grazing stock, and considerable hay is cut from their
bottoms, finding a ready market at the neighboring military posts. The
valley of the Chugwater, from its sheltered character, is a favorite place for
wintering stock, which finds -abundant pasturage in its deep and protected
bottoms.

In this region, wherever irrigation can be directed, the common hardy
vegetables and some of the cereals can be cultivated with a good measure
of success. ‘The military post at Fort Russell, near Cheyenne, has suc-
ceeded by a system of irrigation in raising several kinds of vegetables
whose verdant and luxuriant growth presents a most pleasing contrast to
the sere and bare plains around. At the military post of Sidney, 100
miles east of Cheyenne, and at Phillips's Ranch on the Chugwater, gar-
dens have also been maintained by irrigation. At Fort Laramie, where
are present all the facilities for an abundant irrigation, all attempts hitherto
made have been entirely futile, by reason of the poverty of the soil and the
vicissitudes of the climate. Proper irrigation requires very considerable

ee

————

24 | GEOLOGY OF THE BLACK HILLS.

labor and care, and while, perhaps, it has not been persistently followed,
it is the opinion of many of those best capable of judging that though with
great pains hardy vegetables may be cultivated, the usual cold nights of
this high and dry altitude are serious drawbacks. ' Besides, it may be said
that grazing requires so much less labor and produces so much greater
returns, that agriculture offers few charms to the settler.

From Cheyenne to Fort Laramie, and in fact northward to the South
Fork of the Cheyenne River, the country is underlaid by the beds of the
White River Miocene Tertiary, consisting of gray and yellowish sandstones
and sandy clays and marls. These are the deposits from the ancient Ter-
tiary fresh-water lake which overspread so large an area of the Great
Plains, and they are found to cover unconformably the truncated strata of
the Cretaceous, Trias, Jura, and Carboniferous. ‘These older rocks were
nowhere seen on our road to Fort Laramie, as their outcrops are along the
immediate base of the mountains, fifteen miles to the westward, but their
character and occurrence have been repeatedly examined. (See Hayden’s
report for 1870.) Frequent exposures of the composing beds of the Tertiary
are presented in the different valleys, and especially in the cuttings of the
Chugwater, while isolated ridges and buttes on the Plains indicate their
composition, and bear witness to the enormous thickness of material that
has been removed by denudation. ‘The lowest observed rock of the Ter-
tiary is a heavy sandstone, sometimes locally calcareous, with occasional
bands of impure limestone, but more frequently arenaceous and loosely
ageregated, crumbling and weathering rapidly. This is best exhibited in
the Chugwater Valley and on the road between the Chugwater and Fort
Laramie. On the Chugwater it has a thickness of 150 to 250 feet, and
borders the creek valley on both sides like a wall, though often cut up and
weathered into castellated forms like those of the Bad Lands.

Above this soft rock occurs a coarse conglomerate. This is noticeable
on Crow Creek south of Cheyenne, and on Lodge Pole and Horse Creeks,
and on the Chugwater it becomes a very prominent feature in the geology.
Capping the underlying soft rocks, it has protected them from rapid weath-
ering, and where it is wanting, the whole character of the landscape changes,
rounded and rolling hills taking the place of abrupt cliffs and escarpments.

BOWLDER DEPOSITS. 25

‘The thickness of the conglomerate varies from 25 feet to nothing. In
places it graduates from the maximum thickness to a feather edge; elsewhere
it merges imperceptibly into the underlying rocks. In the weathering of
the borders of the Chugwater there are often found buttes or pinnacles,
detached from the face of the cliff and capped by conglomerate. The con-
elomerate contains large quantities of the chalcedonic quartz, which is so
constant an associate of the Tertiary in the West. The agate formations
are often of great beauty and commonly contain the black dendritic dis-
seminations to which the name ‘‘moss” has been applied. In certain places
on the Chugwater the accumulations are large, and many hundreds of
pounds have been collected for ornamental purposes.

On the surface of the Plains along the road south of the Chugwater there
is found a very extensive accumulation of gravel, pebbles, and small bowl-
ders, that have been carried down from the mountains at the west and from
the beds outcropping at their base. On Horse Creek this formation attains
a thickness of 10 to 20 feet and is composed largely of granitic fragments,
while from Lodge Pole to Bear Creek it is peculiar in containing a large
quantity of labradorite fragments. Frequently it is cemented by a calcare-
ous cement. Wherever found, the deposit is largely made up of pieces of
the older sedimentary rocks which underlie the Tertiary and outcrop along
the base of the mountains at the west. Fragments of Carboniferous lime-
stone with its characteristic fossils are numerous. No bowlders nor frag-
ments were noticed with a greater diameter than two feet, and few are more
than six inches in diameter.

So far as our rapid and superficial examination extended, this bowlder
deposit is more strongly developed at or near the margins of the valleys
draining from the Laramie Mountains, as though it was the result of the
denuding and carrying power of streams once larger and filling those
channels, rather than of a more wide-spread and general agent of denunda-
tion and distribution.

Where the road crosses the divide between the valley of the Chug-
water and that of the Laramie, there are cliffs showing from 100 to 200
feet of the soft, light-colored beds of the White River Tertiary, overlying
the conglomerate of the Chugwater Valley.

26 GEOLOGY OF THE BLACK HILLS.

The time spent in the final preparations for a start was occupied by
Captain Tuttle in making observations for the latitude and longitude of
Fort Laramie and in rating the chronometers. By his observations the
flagstaff on the parade ground at the post was found to be in longitude 104°
32’ 01” and latitude 42° 12’ 30”.

All preparations having been concluded the expedition started from
Fort Laramie on the morning of May 25 and thence striking northeast
to Rawhide Creek followed up that creek to the east side of Rawhide Butte,
where it turned northward past the headwaters of the Niobrara to Old
Woman Fork and the Cheyenne River. It followed down the valley of
the Cheyenne for some miles, and then took a northeasterly course to the
west fork of the Beaver, and entered the Hills by the east fork.

The geology of the region between Fort Laramie and the headwaters
of Old Woman Fork is, with the exception of Rawhide Butte and a few
less prominent ridges, very similar in character to that between Cheyenne
and Fort Laramie. In fact it is but a continuation northward of the soft and
somewhat calcareous sandstones of the great Tertiary deposit that follows
along the eastern slope of the Rocky Mountains.

On the Platte and the Rawhide and their numerous dry branches there
are sections showing from 200 to 300 feet of these beds, and to this is to
be added the thickness exposed in the numerous buttes and cliffs, making
the entire thickness of visible Tertiary rocks about 500 feet. They consist of
a soft, more or less incoherent sandstone, light brown, yellow, or drab in
color, and generally more.or less calcareous, with occasional streaks and
concretions of impure limestone. The latter occurrence was specially noticed
on the Rawhide. In some of the limestone nodules fragments of bone
were observed, but no well-preserved fossils were procured from them. In
the bluffs, however, immediately adjoining Rawhide Butte, a complete jaw
of Oreodon was found by Captain Burt, besides numerous fragments of the
bones of the same animal. So far as observed, the strata occupy a nearly
horizontal position, and abut against, or unconformably overlie, the ridges
of elevation of which Rawhide Butte is the most conspicuous.

Rawhide Butte is situated at the head of Rawhide Creek, twenty-five
miles north of Fort Laramie. It is a monoclinal ridge or upheaval, chiefly

RAWHIDE BUTTE. ' rl

of granitoid rocks, and its granite is similar in character to that of the
Laramie Range fifty miles southwest, and to that of the Harney Peak series
of the Black Hills, one hundred miles northeast. The ridge is about three
miles long, and has three principal peaks, the highest of which has an eleva-
tion above the sea of 6,300 feet, or about 1,200 feet above the base. It is,
however, but the southeastern termination of a long range of upheaval on
the headwaters of the Niobrara and Old Woman Fork mentioned in a sub-
sequent place.

In detailed structure the Rawhide Butte consists of a series of black
micaceous schists or gneisses, with alternating strata of a coarse, very feld-
spathic granite. The lat-
ter range from 2 to 20 or
more feet in thickness,
and the whole dip 70° toSw.
75° toward the east, with

Fig. 1.—Section through Rawhide Butte.

sy 2 ° ’
a strike north 40° west. 1. Tertiary sands and clays.
Shies 2. Valley of Rawhide Creek.
The summit is covered 3. Graphic eaniter ae
ahi ° f 4. Schists.
wit common pine oO 5. Feldspathic granite.

good size, and while the slope on the east side is gentle the descent on the
west is very abrupt. The structure is fairly illustrated by the annexed
illustration.

On the extreme southeastern corner, occupying a position beneath all
the other strata of the butte, is exposed a bed of graphic granite (3), whose
junction with the overlying strata is curved irregularly. It is very similar
in character to the graphic granite met with in many places in the Harney
Peak region of the Black Hills. In it were found graphite, rose-quartz, and
tourmaline, and in the gneissic portions of the peak, black mica, red or pink
feldspar, and grains of magnetic iron. Seams or intercalated veins of quartz
are very numerous in the gneissic strata, running always with the stratifica-
tion of the rock.

Around the western portion of the butte numerous fragments of the
Carboniferous limestone were found, but nowhere was it seen in place.

The Tertiary strata which surround the ridge on all sides lie perfectly
horizontal, and in places are seen to lap high up on the ridge itself, while

28 GEOLOGY OF THE BLACK HILLS

several of the cliffs of Tertiary rock near the ridge are curiously capped
with a small thickness of conglomerate of granitic pebbles derived from
the ridge. By these facts it is shown that the elevation of the butte was
prior to the deposition of the Tertiary strata.

The elevation appears to be a monoclinal ridge, such as would have
been formed along a line of faulting where one side of the dislocated series
was elevated considerably above the other, or such as is called by Major
Powell, in his classification of mountain structure, a ‘“monoclinal ridge of
displacement.”* 3

At the springs or headwaters of the Niobrara, twelve miles north or
northeast from Rawhide Butte, there is an elevation exhibiting the older
schists, the Potsdam, and the Carboniferous, as shown in the annexed figure.

The ay of the strata is 20° eastward, and the strike about the same
as that at Rawhide Butte. The

NE. : A
lowest member seen is a mica-

SW.

1 og aS
Fic. 2.—Section of Uplift at Headwaters of the Niobrara. C€OUS QNEISS Or schist ea); contain -

1. Micaceous schist.

2. Coarse, somewhat metamorphosed sandstones (Silu-
rian?); 10 feet. e : ies

Reddish and whitish sandstones (Silurian ?); 125 feet. feldspa1 and seams of feldspathic

White or grayish limestone (Carboniferous ?
. Tertiary sands and clays. e quartz. The dip of the gneissic

ing large quantities of quartz and

gee

strata, though exceedingly variable, is high, the strike having an easterly
course.

Above the gneiss lies a coarse, somewhat metamorphic sandstone 10
feet in thickness, then 2 feet of a highly ferruginous sandstone, and then
50 feet of a whitish and reddish quartzite containing much chalcedonic and
agatiferous quartz. This is capped by 75 feet of reddish sandstone, which
from its character and position is referred to the Silurian, though no fossils
were found in it.

Resting conformably upon the sandstone series is a small thickness of
white limestone, doubtless of Carboniferous age, while surrounding the
elevation are the nearly horizontal beds of the Tertiary, which probably
once covered it as a cloak but have been worn through by erosion expos-
ing the upturned strata.

Again, from the summit of the divide near the headwaters of Old

*The Geology of the Uinta Mountains, by J. W. Powell; Washington, 1876; pp. 16 and 22.

ISLAND RIDGES IN THE PLAINS. __ 29

Woman Fork, from which point was gained our first view of the Black
Hills, there were seen, low down in the northeast horizon, several low ele-
vations of the older rocks, all trending in the same northwest direction
and dipping towards the east, like the monoclinal ridges just mentioned.
Though these ridges were noticed on several occasions along the route, and
seen to extend far to the northwest, the character of our march was such as
to prevent any close or detailed examination of them. At the head of Old
Woman Fork, however, a ridge was examined and found to be composed of
the following strata, beginning at the top: 2. Gray or whitish limestone, in
places showing an interstratification of reddish brown calcareous clays.
Thickness 60 to 75 feet; dip 25° southeast. The limestone contains in
places much flint, chalcedony, and agate, and many fossils of well-known
Carboniferous types—Athyris subtilita, Spirifera camerata, Productus, &c. 1.
Reddish and whitish sandstone, similar in character to that observed pre-
viously, and probably of Silurian age.

Surrounding and overlapping the monoclinal uplift were seen the soft
beds of the Tertiary.

The unconforming relation which the surrounding horizontal Tertiary
bears to these old lines of uplift shows that the latter were upheaved, and
were carved by denuding agencies before the Tertiary beds were deposited,
and that these were spread over them like a sheet, concealing their irregu-
larities. They have again been brought to light by the erosion of the
Tertiary.

Southwest of Rawhide Butte, between it and the Laramie Mountains,
and a short distance northwest from Fort Laramie, several points of
upheaval have been noticed by other observers, exposing granitoid rocks
with overlying Carboniferous and Cretaceous strata, and, as indicated by
the descriptions, they have a similar structure to those already noticed.
These uplifts, with Rawhide Butte and the associated ridges, have been
considered to form a line of connection between the upheaval of the Lara-
mie Mountains and that of the Black Hills. Though less continuous they
have much of the character of the hog-backs, or ridges of sedimentary
rocks, which are so marked a feature of the flanks of the Rocky Mountains.
But unlike the hog-backs, which are the remnants of anticlinal folds of the

30 GEOLOGY OF THE: BLACK HILLS.

strata, now removed from the mountains by denudation, the ridges of which
Rawhide Butte is a type appear to be ridges of displacement following lines
of faulting—monoclinal ridges of displacement. Their trend, so far as
observed, is southeast and northwest, or nearly parallel with the axis of the
Black Hills, but the Laramie Mountains, running from Long’s Peak, Colo-
rado, in a northerly direction to Laramie Peak, there make a great bend
toward the west, and in nearly an east and west direction extend to South
Pass, where they join the Wind River Mountains.

Though the ridges undoubtedly belong to the period of elevation dur-
ing which occurred the main uplifting of the neighboring portion of the
Rocky Mountains and of the Black Hills, they are separate in themselves,
and, except as products of the same forces, form no connection between the

Black Hills and the Rocky Mountains proper.

The valley of Old Woman Fork, along which our route was pursued,
is excavated from the beds of the middle and lower portions of the White
River Tertiary to within twelve or fifteen miles of its mouth, at which place
the underlying Cretaceous beds make their appearance. The Tertiary beds
consist of the same light gray or drab, argillaceous or calcareous sands, and
the banks of the valley are picturesquely sculptured into castellated bluffs
and buttes.

Near Old Woman Butte the upper members of the Cretaceous appear,
well developed and containing’an abundance of characteristic and beauti-
fully preserved fossil forms. The basal portions of the Tertiary are also
well shown, with the characteristic Titanotherium bed, full of vertebrate
remains. A somewhat imperfect section, showing the relation between these
formations near Old Woman Butte, is given below in descending order:

Feet.
7. White sandstone, coarse and incoherent, with quartz pebbles, and at base
6. A bed of coarse greenish sand, containing large quantities of the bones and
teeth of ‘Ttanothervum, Tehinoceros, SoC. . 22-2422 = = eee lee ee . 10-15
5. Yellowish and grayish clay, capping two prominent buttes in the valley. -.... 5-8
AS Bri CksrediGlaygss: oat: stacey ete ik inete ain ciesloeys ee eee ee Ser ee tee eee 5-8
De MCW OWASHICLAY 2522 Piel sie cratic ithe Gu eyes 'se Se - ol Sle tere SIGIR, wiese oe ae ee 10-15
2. Coarse sand and conglomerate, quite ferruginous, with some limestone.

Amount exposed abOvie Creek. i... <1 eerste - | it ace 20-30

CRETACEOUS NEAR THE BLACK HILLS. : 31

~his is probably the base of the Tertiary. Within a short distance to the
west is:

1. Dark gray Cretaceous clays (No. 4 of Meek and Hayden), with many nodules

filled with most beautifully preserved forms—Baculites ovatus, DB. com-

pressus, Inoceramus, Ammonites placenta, &ic....---..---..--+ .200-------- 40-50

Cretaceous No. 5 was not recognized in the immediate vicinity. The
only observed evidence of unconformity between the two systems is the
nature of the coarse stratum (2). The Cretaceous in this vicinity is very
fossiliferous, yielding to our hasty examination many beautiful and some
new forms, and it will undoubtedly afford an abundant harvest to a thorough
and systematic collector. From this point on the creek the Cretaceous
occupies the valley, but at several places there are evidences of a line or
lines of elevation similar to those already mentioned. Thus, at one place
on the northeast side of the creek a few miles below Old Woman Butte,
appears a cliff, 200 feet in height, of coarse yellowish and reddish sandstone,
having all the characteristics of the Dakota or lower Cretaceous sandstone.
Again, between this- point and the Cheyenne several other lines of uplift
were passed, exposing a soft reddish sandstone, dipping 15° to 30° east.
Other points of upheaval in the vicinity of Old Woman Fork have been
noticed by Dr. Hayden, and in one place he records an exposure of the
entire series of the Cretaceous. ,

The entire region seems to be crossed in a northwesterly direction by
upheavals which have involved the Cretaceous rocks. These ridges once
formed islands or reefs in the great Tertiary lake, which has deposited its
sediments around and over them, concealing now nearly all their irregu-
larities and only exposing them occasionally where the cloak of Tertiary
rocks has been removed by denudation.

The valley of the Cheyenne, where it was crossed below the mouth of
Old Woman Fork, is cut to a depth of 250 to 300 feet in soft sandstone,
bearing a few thin seams of lignite.

On the immediate north bank of the river the following section was
exhibited in descending order:
yee UA eb COMMLOMELALC Heo Shae eles) ce Syelsie 5 ate wye gi we oe oye siete ise (feet) . - 5

12. Soit yellowish sandstone...........-... -- eee Sanaa eR ae (feet) .. 35-40
ME Soft. red sandstone... .-. --..--..- eee nite anette ear GPa Oise 2 (feet) . - 4

oe, GEOLOGY OF THE BLACK HILLS.

10. Soft incoherent white sandstone, with bands of harder red sandstone and

small ferruginous coneretions. --2-2--)- == 2-2 er eee ate hie te (feet).. 135

Fa 0 4 ener ee ee aba tS kek a ot mShoo 2.) hin:
(On the south side of the river found with its under clay to be 4 feet thick.)

8. Yellowish and reddish sandstone.............--- Pees 4 Selig aecoen (LECU) ee 8

(. Band of iron-ore ModuUleSe er se ete eee (inches).. 3-10

6. Soft yellowish sandstone, with iron nodules .................--..-. (feet). 2 22

5. Ldenite: . foe 5. tile ee Pe Se ae ees ee ere eh Thin.
4, Brown sandy clay, with much sanomaitnons matter and iron nodules; with

fragmentsiof planitiim pression sapere ae (feet) -: 10

oo LICnbC Ree eee Jed ge Se ea a ee ee (inches).. 8-10

2. Darks fire- clay: is oc, sine i.2 Sa te ee er ea eee pe ee (feet) . - 5

1. Soft whitish sandstone to bed of the Cheyenne River..-...---- pen Leen) ae 15

Total heightof sectione_ Sh eee. = Seen eae eee ee (feet).. 250

These beds are considered to belong to the Fort Union group or Great
Lignitic Tertiary, which contains such large beds of lignite in the Upper
Missouri region. In this locality the beds have a very slight dip toward
the west, about 4° or 5°, which is the same as the angle observed in the
beds of No. 5 Cretaceous exposed a few miles farther east. In other
portions of the northwest the series of Tertiary beds is found resting con-
formably upon the upper Cretaceous and underlying the deposits of the
White River Tertiaries.

From this point on the Cheyenne River northwestward to the Black
Hills one rises gradually to their elevation over a succession of monoclinal
ridges or hog-backs of Cretaceous rocks, which with more or less regularity
are found in parallel and continuous lines surrounding the Hills. The
strata composing them dip from the Hills at varying but low angles—
5° to 10° or 25°. They are monoclinal ridges of denudation, the remnants
of strata which formerly were continuous across the area now occupied
by the Hills; and across their escarped edges, facing the Hills, one passes
from the highest to the lowest strata of the Cretaceous. Definition has been
given to the ridges by the interposition among softer beds of certain more
resistant strata. The most prominent and persistent of these occasions the
range of rampart-like foothills that surrounds the immediate base of the
mountains, forming the outer margin of the remarkable Red Valley, which-
as a moat encircles the Hills. This inner and last of the series of ridges

CRETACEOUS NEAR THE BLACK HILLS. 33

or hog-backs is formed of the sandstone of the lower Cretaceous, directly
overlying the softer Jurassic beds.

From the Cheyenne River northwestward to Camp Jenney on the east
fork of the Beaver, several sections were obtained across the hog-backs.
Thus, on the Cheyenne, two or three miles below the place where the sec-
tion last given was obtained, the following section of the upper Cretaceous
was observed :

5. Red ferruginous sandstone, sometimes conglomeratic, capping the bluff and ce

dipping 5° westward... ... eee ie ee tiny eas) AS cha nie nee Wis eurvans eae ante : 10
Pee aNTe VES MAGS a tse are rae Pita eS Ne op Soothes ore moc de Sa) Eine a Seiwa ae eho aa 40
3. Red sandstone, full of beautifully preserved shellsas 25 see tees ceca 5
Pa Soluyvellowisil SAMUSHONC Es = <-->. 2k aie who os soos oe ee es (exposed) 30
HERO QHECAICH SLOT ASCIOMCMMe rice crs sae ee oe NS Sere vie cee be sete MLL ee 100-150

These beds are shown by their fossils to belong to the Fox Hills group,
or No. 5 Cretaceous. Eastward from these outcrops the surface of the coun-
try fora considerable distance is undulating, exhibiting but few sharp expos-
ures—such a contour as would naturally arise from the soft character of
the underlying dark clays of the Fort Pierre group, No. 4 of the Creta-
ceous. In the valley of Beaver Creek, near the junction of its east and west
forks, are exposed excellent sections, capped by the highly fossiliferous,
calcareous strata of the Niobrara group—No. 3 of the Cretaceous series—

full of fragments of Ostrea congesta and Inoceramus.
Feet.
11. Shaly limestone, filled with fragments of Ostrea and Inoceramus, dipping

POOMMEN ATIC: CAP PIN Ov UNOMD ts 42 fae aie a aes = Gaines an eupcte to cet se 30
10. Gray shale or marl, with small limestone concretions, calcite crystals, and
gypsum in thin layers or seams; becomes reddish and yellow, changing to
STaAy OLldray againvat WASC a2. eso aesce we toe Oe. 3 Se a Se eee 120
9. Shaly limestone, with Gryphea and fish tec hs See EP RBs inte 6 Omaiose a 22
8. Bluish or drab clay shale or marl, becoming seni black below, with much
alkaline matter and several bands of carbonate of iron, 10 or 12 inches thick
ee Peo hes SNe ctc a one ays clei Lew ates we (estimated) 150-200

bo

So. SLE SEIS TICES Boe Re ee Re eee te) Se cg ge ne 9)
6. Sandy and argillaceous shales, with ele Tete. BRAS CS ie ee ee 30
Dep SM AvES AHOSLONO ote soe ey, kee eco code b Shs Perea, Goes PIMC e arr ee ee 20
4. Drab clay shales with cone-in-cone concretions ......-......--..--+-+++- 20
Sa Gray drab clay Or mall: og) ee os) Sek. ee ca ee Pate Sos Be eaten pa 20
2. Shaly Beene Wi eMROCErANUUS IraOMentS. oo. < so. 020+. - 22 sede nee eee ee 8
1. Black alkaline shale, with some shaly sandstone, some iron-ore, limestone

HOMM IES EAICILG, cANG: OY PSUs 92 asia ce moe: ee oe see to Beaver Creek 100

3BH

a

34 GEOLOGY OF THE BLACK HILLS

The greater portion of this would seem to belong to the Niobrara
group, but the lower 200 feet are perhaps referable to the Fort Benton or
No. 2.

Beaver Creek at its forks is a stream of small dimensions, but draining
a large area of these alkaline strata of the Cretaceous it is highly impreg-
nated with salts, which are exceedingly unpalatable and are medicinal in
their effects. It may be remarked here that the streams which rise in or
flow for a long distance through the Cretaceous strata are almost invariably
undrinkable by reason of the large amounts of salts dissolved from these
beds; but the streams that flow ‘hrough long stretches of the Tertiary or
bad land country, generally contain a large amount of suspended clayey
matter with less of soluble salts, and are more endurable.

A section of the rampart foothills, as exposed on the east fork of the

Beaver, is given in annexed figure.

Fic. 3.—Section through outer Foothills at Camp Jenney, East Fork of Beaver.

I Rediclaysioteather keds ed Steere meee ee eee ee eee eee
Or Jurassic sandstones. Clays; eCsm ceca cals ae teal a
3. Massive sandstones, lower part very white. .......-...--.------ )
Ap Thin-pedd edasamOsSton On se persis meee siete ial eerie |
5

\
. Grayish shale or marl, with celenite..-... .2.-...2222.-----+---- ( No. 1 Cretaceous, Dakota group.

6. Massive soft white sandstone, with carbonaceous matter ...-.-- J
7. Black or drab, alkaline shales or marls..:....-....-..----- ---.- \
8. Shaly calcareous sandstone.----------- ------ .- 25 ones o- one [

9. Shaly calcareous sandstones, with impure limestones contain-.-.- -
TG WOH case ccoaso ceeoo sa9e50 Gascan NoDeEC sannudmeoR Gone
HO Citay sinnies ayaGl wWeeHBKS So4660 cece ococascece cote cess saspcsde snes No. 3 (?) Cretaceous.

fae 2 Cretaceous.

From Camp Jenney, after a delay of two or three days, the entire
expedition moved into the Hills proper, establishing the first base of opera-
tions at the stockade on French Creek. Here in order to expedite the
work the corps was divided into two parties: (1) Mr. Jenney, with the
miners, assumed the work of examining the mineral deposits and prospect-
ing the various districts for gold, and (2) Mr. Newton, Dr. McGillyeuddy,
and Captain Tuttle were directed to undertake the more detailed and

MOVEMENTS OF THE PARTIES. oD

thorough topographical and geological study of the country. When the
region of the southern part of the Hills had been worked up as com-
pletely as was practicable the entire expedition moved northward and
established a second camp on Rapid Creek below the forks, from which the
region on each side was in a similar manner explored; a third camp was
made on Bear Butte Creek near Terry Peak, and a fourth on Inyan Kara
Creek about ten miles southeast of Inyan Kara. From this last point the
Bear Lodge range was examined by Mr. Jenney’s party while the other
party descended the Belle Fourche to the mouth of Bear Butte Creek,
where all portions of the expedition again met. The main body of the
escort then skirted the Hills on the east side to Rapid Creek, while Mr.
Jenney’s party crossed southeastward outside of the foothills to the mouth
of Rapid Creek, and the topographical party descended the Belle Fourche
and ascended the South Fork of the Cheyenne to the mouth of Rapid Creek,
where all parts of the expedition met September 22, preparatory to the
homeward march.

The details of the methods pursued in the work of exploring the Hills
can be of no interest in this place. The results of the geological studies, of
the examination of the mineral products, and of the astronomical work are
given with considerable detail in the several chapters referring to those
subjects and in the accompanying maps.

The country on the east side of the Hills has much the same character
as that on the west. Near the Hills is a succession of ridges of the upturned
and eroded Cretaceous rocks, which decrease in inclination and size as their
distance from the Hills increases, till near the borders of the Cheyenne the
country has a flat mesa-like appearance, cut up, however, by numerous dry
ravines.

South of Rapid Creek, two or three miles from its mouth, and occupying
the divides between Rapid, Spring, and French Creeks, are irregular areas
of the lower members of the White River Tertiary, attaining a maximum
thickness of about 200 feet. They possess all the lithological characteristics
of the White River group, but no organic remains were found, even after very
careful examinations. No perceptible unconformity of dip could be detected
between the underlying Cretaceous and these Tertiary strata, but in the

36 GEOLOGY OF THE BLACK HILLS.

presence of avery persistent stratum of quartz conglomerate several feet in
thickness, occupying the base of the Tertiary, we have a strong evidence of
a change of circumstance in the deposition of the sediments. .

These detached areas of Tertiary approach the immediate western
banks of the Cheyenne near French Creek, and on the opposite side of the
river portions of the White River deposits approach equally near, being
separated only by the deeply excavated valley of the river. ‘There can be
no doubt that the two areas were once continuous, and are now separated
only as a result of erosion. The valley of the Cheyenne in the region of
Rapid Creek has a breadth of from one to two miles, and is cut from 150 to
200 feet in the shales and clays of the upper Cretaceous, which in this
vicinity and in the numerous creeks that here join it—Bull Creek, Bear
Creek, Sage Creek, etc.—contain abundant and beautifully preserved fossils,
especially of group No. 4. From this region our collections were enriched
with some of the most beautiful forms obtained on the expedition. The
river itself is shallow and narrow; the water contains much saline matter,
and is milky with fine suspended clay.

Near Rapid Creek the summit of the eastern bank of the Cheyenne
extends eastward in a broad plateau for six or seven miles, when the edge is
suddenly reached, and spread out below in a seeming basin lie the wondrous
bad lands of the White River Tertiary. They are carved into the most
fantastic shapes; castles and pinnacles, domes and minarets, cover the
surface, all hewn in drab and flesh colored clays, and it seems almost as
if they were a ruined city of the dead, rich in the fantasies of a forgotten
architecture. The valleys of the several streams that rise in this bad-land
country and flow into the Cheyenne—Sage Creek, Bull Creek, ete—have a
peculiar funnel-like shape, with their broader parts in the Tertiary and their
narrow portions cut through the Cretaceous to the river.

From the mouth of the Rapid the surveying party ascended the
Cheyenne River to near the mouth of Burntwood Creek, and then, cross-
ing eastward to the White River, joimed the main body of the military
escort, which had crossed through the Bad Lands from near Spring Creek.
Thence following up the White River, via the Indian agencies of Spotted

THE RETURN MARCH. : a0

Tail and Red Cloud, the expedition returned by the agency road to Fort
Laramie.

The geological features of our return route from the White River to
Fort Laramie are very uniform, the underlying rocks belonging entirely
to the White River Tertiary. The typical bad-land arenaceous clays,
destitute of vegetation, already mentioned as lying between the White and
Cheyenne Rivers, are the very lowest members of the White River group,
while the strata found on the immediate banks of the White River, and
especially in the upper portion of its valley, are more recent and belong
to the upper part of the series. Their equivalents probably form the under-
lying rocks on the line of our outward march. Though the whole country
bordering the White River is commonly known as the Bad Lands, the term
is more properly applied solely to the lower clays, which weather in the
fantastic shapes already mentioned, and which contain such abundant
remains of vertebrate animals.

Our march on White River took us across the scene of the distinguished
paleontological discoveries of Dr. Hayden and Professor Marsh, a district
which their labors and those of Dr. Leidy have rendered as famous as the
Sivalik Hills of India; but it was not our privilege to linger.

Between the White River and the Platte the Tertiary is very little
denuded, and presents all the aspects of the geology of our outward route.

CHAPTER III.

CO OG axe
SECTION I.

INTRODUCTION.

It has been remarked by Dr. Hayden that—

The Black Hills of Dakota will form one of most interesting studies on this con-
tinent. There is so much regularity in the upheaval that all obscurity is removed and
all the formations known in the West are revealed in zones or belts around the granite
nucleus in their fullest development. A careful detailed topographical and geological
survey of this range would be a most valuable contribution to science. In all the
western country I have never seen the cretaceous, Jurassic, triassic, or red-beds, the
carboniferous and Potsdam rocks, so well exposed for study as around the Black Hills.*

His statement, founded upon a rapid reconnaissance of the foothills and
extremities of the region during the exploration of Lieutenant Warren in
1857, has been fully corroborated by the more thorough and complete survey
which our party was enabled to make during the past summer. Elevated
as they are like an island above the surrounding sea of the Plains, and
separated by more than one hundred miles from the nearest spur or sub-
range of the Rocky Mountains, the Black Hills are a complete study in
themselves. Iixhibiting in the strata exposed and in the general character
of the elevation most of the principal features of the geology of the Rocky
Mountains, they are a geological epitome of the neighboring portions of that
great range. The geologist therefore finds in this region a monographic
study of universal interest; and by the regularity of the uplift, by the
absence of great faults in the strata, and by the splendid exposures of the

* United States Geological Survey of Wyoming and Contiguous Territory, 1870. p. 98,
33

THE BLACK AILLS AN EPITOME OF: THE ROCKY MOUNTAINS. 39

sedimentary rocks, he is given a piece of mountain geology of great beauty,
simplicity, and ease of elucidation.

Usually in explorations in the West or elsewhere the field of work of
the geologist at any one time or season is but a part, and commonly a very
small part, of a great system that extends over vast areas of country.
Thus, in explorations in the Rocky Mountains, the most assiduous labor of
the geologist can cover thoroughly in one season but a small part of the
great range, and his discussion of results cannot be complete in itself,
but must depend largely upon work in the adjoining regions. Rarely,
then, does the geologist find his work so admirably circumscribed by
nature as did those to whom the exploration of the Black Hills was com-
mitted.

The area of the Hills, to a discussion of whose geological features the
present chapter is devoted, includes only that country between the forks of
the Cheyenne, limited on the north and west by the Belle Fourche, on the
south and west by Beaver Creek and the South Fork, and on the east by
the South Fork. A somewhat detailed account has already been given
in Chapter II of the principal geological features observed in going to and
returning from the Hills—a narration which could not be introduced in this
place without in a measure marring the unity of the plan.

Generally and simply the geological structure of the Black Hills is
as follows: Around a nucleal area of metamorphic slates and schists, con-
taining masses of granite, the various members of the sedimentary series
of rocks, the Potsdam, Carboniferous, Trias or Red Beds, Jura, Creta-
ceous, and Tertiary, lie in rudely concentric belts or zones of varying
width, dipping on all sides away from the elevatory axis or region of the
Hills. From the Hills outward the inclination of the beds gradually
diminishes until all evidence of the elevation is lost in the usual rolling
configuration of the Plains. At numerous points, also, within the area of
the Hills are centers of volcanic eruption of an age probably coincident
with that of the elevation of the mountains themselves.

The succession of the different formations as found in the Hills,
together with their character and approximate thickness, is exhibited in the
following synopsis :

4()

GEOLOGY OF THE BLACK HILLS.

Synopsis of the Rocks of the Black Hills.

|

Ages. Feet. Strata.
E
S)
a Miocene. 200 | White clay, with chalcedony: at base a conglomer-
A ate.
ie)
600 | Clays and shales; gray, yellow, and black; with
some sandstone.
Cretaceous.
3 300 | Coarse yellow sandstone, with sandy shale.
S
4 200 | Gray, white and red, clays and marls, with some im-
S| Jura. 3
pure limestone.
Red Beds. 349 | Red clay, sometimes arenaceous, interrupted by a
single bed of limestone.
425 | Sandstone, red and variegated, somewhat calcareous
and argillaceous.
175 | Alternating sandstone and magnesian limestone.
3 PERITO EO OU 175 | Silicious limestone; silica in nodules and geodes.
S Sores
a 175 | Gray limestone, massive, pure.
re 40 | Shaly limestone, pinkish; in part arenaceous.
ie: 950 | Silicious sandstones, in part quartzitic. Conglomerate
Silurian. usual at base. Caleareous cement and intermin-
(Potsdam.) gled glauconite in upper part. Colors, dark brown
and red, rarely white.
: 2 Slates.
id q F
1e)
Bi 9 | Schists, with lenses of intrusive granite.

|

ARCHAAN AND PALEOZOIC. 4]

The thickness of the highly inclined and distorted schists of the
Archzean is practically impossible to estimate with any degree of accu-
racy. In their present greatly denuded and metamorphosed condition one
cannot determine whether they are the remnants of several great anticlinal
folds among themselves, or whether they are the broken strata of one vast
fold, though the latter, judged from a study of the nature of the rocks,
seems the more probable structure. In that case the total thickness of the
Archean strata must be more than one hundred thousand feet.

The study of these rocks has shown them to be readily divisible into
two groups—Ist, a series of coarsely crystalline micaceous schists, and, 2d,
a series of very fine micaceous clay slates—the latter of which in structure
and associated minerals bears a close resemblance to the Huronian in
the typical localities of its development around the Great Lakes. The
lithological structure of the metamorphic rocks has been examined criti-
cally, both in hand specimens and by a microscopic study of thin sections,
by Mr. Caswell, the results of whose labors will be found in the chapter
on Petrography.

Associated with the schists in the southern portions of the Hills are
immense masses and peaks of highly feldspathic granite, culminating in
the region of Harney Peak; and on the outskirts of the same district are
many smaller masses of the same material. So far as their structure was
made out, each of the bodies has a lenticular shape, and is intercalated
among the strata of the schist. All the observed phenomena of the occur-
rence of the granitic masses have been weighed and studied with care,
and the conclusion that they are of intrusive origin is discussed at length
in the section devoted to them.

In the series of the Paleozoic rocks on the opposite page the facts that
will first attract the attention of a student of the geology of the eastern
portion of our continent are, Ist, that the great Silurian system is represented
only by a sandrock about 250 feet in thickness, referable to the Potsdam
period, and 2d, that the entire Devonian system is absent. The study of
the Potsdam was not surpassed in interest by that of any other formation
of the country. It was in this region that the Silurian in the Far West was
first recognized, and the collections made the last summer have, by the study

42 GEOLOGY OF THE BLACK HILLS.

of Professor Whitfield, added several new species to the fauna of the period.
Of the remaining portions of the Silurian system, which in the eastern United
States reach a maximum thickness of over 20,000 feet, we have no deposits
in the Black Hills, though in other portions of the Rocky Mountain region
equivalent strata have been found.

The Devonian system, as has been said, has no representatives in the
rocky strata of the Hills. Though the exposures are excellent and exami-
nations were carefully made at the proper horizon, no trace of it could be
found. The general thinning of the formation from east to west—from
14,000 or 15,000 feet in the Appalachian region to 1,000 feet in Ohio and_
150 feet in Iowa—culminates in the Black Hills in complete disappearance. -

The Carboniferous system is the most prominent and frequently the
sole representative of the Paleozoic age in the Far West; and while in the
East it is divisible into two periods Sub-Carboniferous and Coal Measures,
the latter bearing the great deposits of coal, in the Far West it contains no
coal and is largely composed of calcareous deposits, in which the two periods
have not usually been distinguished from each other. In the Black Hills
we were not enabled to determine to what period or periods of the Carbon-
iferous age the strata were properly to be referred. Though they were
found highly fossiliferous, sufficiently characteristic forms were not obtained
to decide the question, and it was not possible to give to the study the
necessary careful attention.

Above the beds of undoubted Carboniferous age were found a series
of pink, red, and white sandstones and limestones, with no well-marked
separation from the Carboniferous below, and these pass upward into a
very impure, concretionary or distortedly weathered, reddish sandstone,
above which is the red clay of the Red Beds. In the absence of good fos-
sils, it was difficult to determine to which system these beds should be
referred, whether to the Carboniferous below or to the Red Beds aboye,
but preference was finally given on lithological grounds to the former.

The ‘Trias (?), or Red Beds, the as yet blank leaf in the geology of
the Rocky Mountains, is finely exposed around the Hills, forming in the
Red Valley, or ‘‘Race Course,” one of the most prominent features of the
topography. It consists of three parts—a red clay at base, separated by an

CARBONIFEROUS AND MESOZOIC. 43

impure argillaceous limestone from a similar red clay 200 to 300 feet thick,
containing large quantities of pure white gypsum. Assiduous search, especi-
ally in the limestone, revealed not the slightest trace of organic life in the
series, and there is nothing new to present that will aid in settling the ques-
tion of the true age of the formation.

In connection with the occurrence of the Jurassic formation, the Black
Hills have again a historical interest, for it was first recognized in the geo-
logical series of the West from fossils collected here by Dr. Hayden. Its
separation from the underlying Red Bed series is tolerably well defined by
lithological change, but is especially marked by the occurrence of Jurassic
fossils close to the line of division. From the Dakota sandstone of the
Cretaceous, whose harder strata everywhere form the overlying and pro-
tecting cover to the softer Jurassic beds, the separation of the Jura is less
plainly denoted; for the upper portion of the Jura contains much sandstone
and is usually unfossiliferous. Fortunately we were enabled to make a
large collection of Jurassic fossils, among which are many of the species
described by Professor Meek, upon which he based his determination of the
age of the rocks, besides many new forms.

The Cretaceous rocks were not studied with the care that was given
to the older series, mainly because the opportunities were not so favorable.
The lower member, or Dakota sandstone, is a prominent feature in the topog-
raphy, forming, as it does, the chief stratum of the rampart foothills, but
the separation of the other groups, as established by Meek and Hayden,
was not so clearly made out, though they are exposed on all sides of the
Hills. The general similarity in the nature of the deposits and the scarcity
of good exposures were hinderances to their accurate examination. With
some modifications of thickness, the divisions established by Professor
Meek, and described by Dr. Hayden in various parts of the Upper Missouri
region, are equally applicable in the Black Hills, and to their description
there is little to be added or changed as a result of our examinations. Some
recompense for the insufficiency of our study of the formation is found in
the fine collection of invertebrate fossils which it was our fortune to obtain
from it. The perfection, number, and beauty of the specimens can scarcely
have been excelled by any other collection from this region.

44 GEOLOGY OF THE BLACK HILLS.

Tertiary strata of the White River group are abundantly exposed on
our routes to and from the Hills, as well as on lower Rapid Creek. Many
excellent sections, especially of the lower members, were obtained, though
little of importance was learned in addition to the published results of
observers who have been able to examine the region more thoroughly.
Few fragments of vertebrated fossils, and those of little interest, were
obtained.

The Quaternary deposits have had little interest geologically, as they
consist merely of certain local deposits of gravel along a portion of the
foothills, and the alluvial deposits of bowlders, gravel, sand, and clay,
forming the bottoms or floors of the valleys of the creeks. The latter, how-
ever, are of very considerable moment by reason of the contained gold,
and in certain regions have yielded large returns to the miners. The
deposits all belong to very recent geological time, and are the result of the
wearing and abrading action of existing streams. Of the true glacial drift
we could find no evidence.

The peaks and ejections of volcanic rock which are found at numerous
points in the northern end of the Hills are probably all of similar age, and
consist chiefly of sanidin-trachytes and rhyolites. The effect of the extru-
sion of the volcanic masses on the surrounding strata has been exceed-
ingly local, and if the elevation of the Hills took place synchronously with
their ejection the topography was probably little affected by the accompa-
nying seismic throes. It is possible, however, that the elevation of the
Hills was entirely subsequent to the volcanic extrusions; for we have no
evidence that will define the time of the elevation closer than that it
belongs to a date subsequent to Cretaceous and prior to middle Tertiary
time, while of the age of the volcanic outbursts we can only say that they
were subsequent to the deposition of the Cretaceous.

In this brief résumé an endeavor has been made to give the most
comprehensive view of the formations which constitute the Hills. The
remainder of the chapter will be devoted to a more detailed description of
the same formations, together with a discussion of all peculiar or interest-
ing features and of the general history and origin of the Hills.

Notwithstanding the smallness of our corps, only two members of which

|
+. Jel

THE ARCH ADAN. 45

were engaged in the actual study of the geology of the country, almost
every portion of our large area (over 6,000 square miles) was more or
less carefully examined and the main features of the geology attentively
studied; and if, as is well-nigh inevitable, later study shall convict our
work of errors of omission or of incompleteness, it is hoped that the gravity
of our sentence may be somewhat mitigated by giving consideration to the
rapidity with which the work was necessarily performed. Indeed, it could
scarcely be expected that such a corps in four brief mouths of field work
could unravel without error the geology of a country larger than the State
of Connecticut.

SECTION II.

THE ARCHAAN.

The Archean system as founded by Professor Dana includes the
oldest known rocks—those which lie below all our fossiliferous strata,
and which constitute the ‘“‘only universal formation.” It is for the most
part composed of crystalline and metamorphic rocks—granite, syenite,
eneiss, and micaceous, talcose, hornblendic, and chloritic rocks, with ores
of iron, graphite, etc. It has been divided into two ages, an Azoic, or
lifeless age, and an Kozoic, or age of the dawn of life. Of the former,
the Azoic, we are not as yet accurately informed, either as to its distinc-
tive characters or as to its limits. It has, however, been established as
distinct from the other members of the Archean; first on the philosophi-
cal ground that there must be a series of rocks in the earth’s formation
that existed before the beginning of life on its surface; and, second, to
separate the Archzan rocks containing evidence of life (the Eozoic) from
those in which no evidences of organic existence have been found (the
Azoic.)

The Eozoic has been separated by the Canadian geologists into two
periods, the Laurentian and Huronian, which are well distinguished in
Canada, where they attain a thickness of nearly 50,000 feet, and have been
recognized or separated in various parts of the eastern United States and
in Kurope Where the rocks of both groups are observed in Canada

46 GEOLOGY OF THE BLACK HILLS.

they are found to sustain an unconforming relation to one another, but
elsewhere, where the Kozoic has been divided into these periods, or sup-
posed to be so divisible, the separation rests almost exclusively upon the
slender ground of lithological characters. It is true that to a certain extent
particular rocks or constituent minerals are found to be characteristic of a
particular formation; but such evidence alone cannot be taken as conclusive
in co-ordinating series of rocks, especially where the points of observation
are separated by any considerable distance. At the best, a similarity of
lithological structure is only presumptive evidence as to similarity of age.

In rocks of the Laurentian the Canadian geologists discovered a pecu-
liar structure concerning the character and relations of which there has
been no little discussion. It is considered by Carpenter, Dawson, and_
others to be a fossil, a gigantic foraminifer, and has been described by its
first student, Dr. Dawson, as Hozoon Canadense. A similar structure has
since been recognized from the Hozoic of Bohemia and Scandinavia. This
is the oldest remnant of organic life yet discovered, and it is the main
foundation for the primary division of the Archzean into Azoic and Hozoie.
The presence, however, of large beds of limestone, graphite, apatite, and
iron ore in the Hozoic rocks is strong evidence of the existence of organic
life, for life appears in all observed modern processes to be necessary to the
separation or accumulation of such deposits.

The Laurentian, where best known, is composed chiefly of granitoid
rocks, gneiss, quartzite and crystalline limestone. It is frequently charac-
terized by hornblendic rocks, but is seldom very micaceous; and the pres-
ence of graphite and large beds of magnetic and titaniferous iron ore in
many regions prominently characterizes the series. The system was first
studied by Sir William Logan in a field where it is largely developed—the
Canadian highlands bordering the Saint Lawrence and the Great Lakes and
extending far northwestward. The Archean rocks of the Adirondacks, at
least a portion of those in the Alleghanies, those of the Ozarks in Missouri,
and a portion if not the larger part of the iron-bearing rocks of the Lake
Superior region, are considered to be of Laurentian age, and in all these
regions the system is characterized by immense beds of iron ore.

In Scotland the “fundamental gneiss” has been regarded by Murchison

LAURENTIAN AND HURONIAN. 47

as Laurentian, in Bohemia large areas have been so recognized by Bar-
rande, and in Norway and Sweden the crystalline rocks bearing the iron
ores have also been referred to the same age.

In Canada the Laurentian is subdivided into Lower and Upper, and
the two groups are supposed by Sir William Logan to be separated by
unconformity and by a long interval of time. The upper and less im-
portant group is especially characterized by the abundance of the opalescent
labradorite feldspar, and is particularly well developed in Labrador. It has
been called by Dr. Hunt the Norian or Labradorian series, and it has been
recognized by him in the Adirondack region and elsewhere in the eastern
United States, though it is not yet known to be a persistent member of the
EKozoic of the Appalachian Mountains. |

The Huronian system was first studied on the Canadian border of
Lake Huron, where its rocks are typically developed and are found to
overlie unconformably rocks of well known Laurentian age. They are as
a rule here more silicious in their character than the Laurentian, and con-
sist chiefly of silicious slates and conglomerates, quartzite, jasper, diorite,
and chloritic and epidotic rocks, with ores of iron. The Huronian is less
widely recognizable and distinguishable than the Laurentian, and where its
occurrence is maintained beyond the region of its typical development, the
opinion rests solely upon lithological characters.

The iron-bearing region on the south shore of Lake Superior is in part
regaded as of Laurentian age, but the iron-bearing strata of the Marquette
region are very generally considered to be Huronian. On our eastern coast
the existence of the Huronian is announced as probable. Credner refers
to this age a series of rocks in the Appalachian Mountains from the Saint
Lawrence to Georgia, which includes most of the auriferous rocks of that
region. Hunt also, who has devoted much time and study to the exami-
nation of the Kozoic rocks of Canada and the northern part of the Appa-
lachian Mountains, regards a portion at least of the Green Mountain series
of Vermont as of Huronian age, and believes that they may be traced
southwestward through Pennsylvania to Virginia. Inthe Green Mountain
series the rocks are gneisses (more micaceous than the Laurentian), diorites,

48 GEOLOGY OF THE BLACK HILLS.

epidotic and chloritic rocks, steatites, serpentines, and talcose (or more prob-
ably hydrous mica) schists.

‘Hunt further distinguishes the White Mountain or Montalban series of
rocks, which he regards as newer than the Huronian but Pre-Silurian and
Pre-Cambrian, and he traces them, in a series of deposits parallel to the
Green Mountain rocks, far southward into Pennsylvania. The rocks of this
series in the White Mountains are characterized by mica-schists passing
on one hand into micaceous gneisses and on the other into argillite. They
include beds of micaceous quartzite and concretionary granitic veins with
beryl and tourmaline.

West of the Missouri the Archzean is exposed over large areas in the
axial lines of the Rocky Mountains and its various subordinate ranges, and
includes most of the rocks already enumerated, though the granites, syenites,
and highly feldspathic rocks are more largely developed in many regions, to
the exclusion often of the schists and slates. Until lately no attempt has been
made to draw any line among these Archean rocks and establish the divis-
ions recognized in the East. Such a separation would be based exclusively
upon the lithological structure of the rocks and the presence or absence of
particular mineral species, for no fossil has been found; and by the majority
of geologists such evidence is not admitted in the identification of geologi-
cal formations when, as here, the points of observation and comparison are
widely separated. Mr. King, of the 40th Parallel Survey, has, however,
noticed differences in the rocks of certain of the ranges, which lead him to
regard a separation into Laurentian and Huronian as possible.

The Archean rocks of the Black Hills, as may be seen on the geologi-
cal map, occupy the axial or nucleal area, and their exposure is somewhat
to the east of the center of the uplift. The extent of country occupied by
them is about sixty miles long north and south, and twenty-five miles in its
greatest width east and west, with an area of about 850 square miles.

Rugged and broken as is the entire region of the Hills, the interior
area underlaid by the Archean schists and slates is particularly mountain-
ous and rough. Cut up into peaks, ridges, and valleys, and watered
by numerous brooklets, it has the aspect of many of the picturesque

TOPOGRAPHICAL FEATURES. 49

regions of the Adirondack and Green Mountains, and covered usually with
a heavy growth of timber, but opening out occasionally into grassy park-
like valleys, it often vies in wildness and beauty with those better-known
mountain regions of the East. Viewed from a height, as from Harney
Peak, the area has a billowy appearance—a succession of ridges and peaks,
and at first it reveals no

with now and then a stretch or spot of open park
system of structure, save that it is cut from west to east by the draining
streams which have eroded deep and usually narrow valleys or canons.
Though the strike of the rocks is toward the north or northwest, there at
first appears no feature in the topography due to this fact, but a closer and
more detailed study reveals the presence of a continuous ridge or series of
ridges extending on the east side of the area from southeast to northwest ;
and in the more minute inspection of the geology along the streams these
ridges are seen to have been defined by the presence of particularly hard
strata, quartzites, etc., through which the several draining streams have cut
their way in intricate and deep cations. On the western side of the area a
similar belt of prominent and resistant rocks is observed, through which
many of the streams have cut narrow gorges. Between these ridges the
country, excepting in the region of the Harney Peak granites, is less
rugged, and not unfrequently the banks of the streams widen out into val-
leys broad and gently sloping.

Toward the southern end of the Archzean region is a tract of feld-
spathic granite the most rugged and mountainous in the Hills. It is
characterized by numerous peaks and ridges, of which Harney Peak and
Dodge Peak are the most prominent. South of it and quite in the south-
ern end of the Archzan are many of the park-like expanses already alluded
to, well grassed and devoid of trees, and among them are the largest that
are found in the Hills. Several of the most important have received special
names, as Custer Park, on the headwaters of French Creek, in which is
located Custer City ; Dodge Park, farther southwest, on the headwaters of
Red Canon Creek; and Elkhorn Prairie, on the headwaters of Spring Creek
and the south branch of the Rapid.

The margin of the Archzan area is bordered continuously by an

escarpment more or less abrupt, and usually several hundred feet high,
4 BH

30 GEOLOGY OF THE BLACK HILLS.

formed of the Potsdam sandstone and the Carboniferous limestones. This
escarpment faces inward or toward the Archzean area, and in the cafions
which cut into it the slates and schists are seen beneath the sandstone of
the Potsdam which rests unconformably upon them. With the exception
of Harney and a few of the neighboring peaks, the average elevation of
the schist and slate area is considerably below that of the encompassing
sedimentary rocks. Its relative depression is plainly due to the more rapid
decay and degradation of the schists and slates, while the hard limestones,
being less destructible, remain prominent.

Besides this main area of the metamorphic rocks, there are a number
of minor exposures to the north and northwest of Custer and Terry
Peaks. ‘The country is there underlaid by the Carboniferous limestone,
and this, together with the underlying Potsdam, has been cut through in
deep and narrow canons with innumerable branches, making the country a
perfect labyrinth of canons many of which are 400 to 600 feet in depth.
The main canons have been eroded also many feet deep into the underly-
ing Archeean, and in some places the gold concentrated from its slates and
schists has been collected in very considerable quantities.

The metamorphic rocks of the Black Hills are separable into two dis-
tinct groups, whose lithological. characters are marked and _ persistent.
Their stratigraphy was carefully studied in the hope that it would be pos-
sible to definitely determine the historical relation between them, but the
result was not satisfactory. The great differences, however, in the charac-
ters of the rocks are sufficient to warrant their separation into a western
series or group of schists and an eastern series or group of slates. The line
of separation between them can be only imperfectly indicated. Its trend,
so far as could be ascertained, is a little west of north. Starting just east
of the granitic range of Harney Peak, it curves westward about the north
end of that range, and then turns toward the north-northwest, passing near
the forks of Spring Creek or the present site of Hill City, crossing Castle
Creek in the west canon, and disappearing beneath the Paleozoic rocks in
the vicinity of Custer Peak. ‘To the north of the peak it reappears with a
northerly course.

THE SCHISTS. 51

A distinct discordance of dip between rocks representing the characters
of these two groups was seen by Mr. Jenney in the west canon of Castle
Creek, but in the absence of corroborative observations, the fact of the
unconformity of the two series cannot be insisted upon.

The western series consists of quartzose schist and garnetiferous, quartz-
ose, and ferruginous, mica schists, together with some gneiss, chloritic and tal-
cose (or hydrous mica) schists, hornblendic schist, and quartzite. The whole
series is coarse in texture and highly crystalline, and it contains many
seams or veins of quartz traversing the schists conformably with the strati-
fication and having usually a swelling or lenticular structure. These veins
are interlaminated veins and are not often of any great width; they contain
finely disseminated gold, and have probably afforded by their disintegration
the larger portion of the gold found in the valleys and gulches. The granite
masses are found wholly within the area of the schistose rocks. The east-
ern series is composed of metamorphic rocks distinguished from the western
mainly by their exceedingly fine and compact texture, though, as shown by
Mr. Caswell, their ultimate mineral composition is quite similar. The rocks
are mainly mcaceous clay slate, clay slate, silicious slate, and quartzite.
The last forms persistent strata from 50 to 200 and sometimes 500 feet in
thickness, which may often be traced for long distances with little variation.
The quartzite frequently contains seams or veins of interlaminated or
ribbon quartz, and with them are associated large deposits of hematite or
specular iron ore, also interlaminated with quartz. Frequently the quartz
seams are highly ferruginous and in places they have been found to con-
tain undecomposed pyrites. Unquestionably they are often auriferous.

Micaceous schist is the prevailing and most characteristic rock of the
western series, but its variation in character is very considerable. More
commonly it is a gray, tolerably fine, highly crystalline, uniform, micaceous,
silicious schist, which, from its large proportion of mica, weathers readily
and uniformly. Very frequently, especially in the western part of the area,
it is so highly charged with garnets that it acquires a dark reddish color.
The garnets are well crystallized but of small size, rarely exceeding a
quarter of an inch in diameter. In the weathering down of the garnet-

52 GEOLOGY OF THE BLACK HILLS.

iferous mica schists, the fine material removed and deposited in the creek-
beds consists largely of garnets and mica, the latter showing so brightly on
the creek bottoms beneath the water as often to be mistaken for flakes
of gold. In panning the gravel of upper French Creek and Castle Creek,
when the pan of dirt has been nearly washed, the residue is found to be
composed almost entirely of garnet crystals more or less rounded, beneath
which the particles of gold are collected in the heavier iron sand, while the
light mica is completely washed off. Farther down the streams the mica is
found still finer, while by the abrasive action of the current the garnets have
been worn round and smooth.

The mica schist changes sometimes almost imperceptibly, becoming
finer and containing less and less mica, and passes into a talcose or hydrous-
mica schist, frequently highly garnetiferous, presenting the usual soapy
feeling and general character of talcose schist. The talcose schist being
more coherent than the very micaceous rocks is more prominent in the
topography, and forms harder and rougher ridges.

By a similar gradation the mica schists pass into silicious schists con-
taining but little mica, and then by a more abrupt change into ledges or
strata of hard, dense, and tough quartzite. The quartzites, which are less
developed in the western than in the eastern series, are among the most
durable rocks and in the Hilis generally stand in abrupt, dike-like
ridges, running with the stratification of the rocks. They vary from almost
white to a light or dark grey color, and are bright and glassy on the
fracture, which is usually conchoidal. They commonly contain mica in
small quantities and sometimes are like very silicious mica schists in which
the mica is subordinate and the quartz tough and glassy. They never
in their structure or relations indicate an intrusive origin, but are true
metamorphic strata, differing in character from the associated schists because
of an aboriginal difference in their composition—the latter having been
originally mixed deposits, while the former were more or less purely sili-
cious. They are similar in character to the quartzites of the eastern series.

Sometimes the mica schist passes by almost imperceptible gradations
into true chloritic schist, in which the mica seems to have been replaced by
chlorite. This chloritic schist is usually soft and easily decomposable, of a

QUARTZ VEINS. 53

green color, and with no mica readily visible to the eye. Crystals of
ripidolite may often be picked out from it with a knife, and it frequently.
contains garnets in abundance. In small pieces the rock is flexible, but it
has little or no elasticity.

Associated with the above-mentioned rocks, but of less frequent occur-
rence, is true gneiss—silicious mica schist with feldspar. It was seen on
French Creek near the stockade, in Custer Park, and at several points in
the Harney Peak region. While the occurrence of feldspar in the schist
is probably more common in the vicinity of the great granitic region, there
is nowhere any evidence of a gradation of the gneissic rock into the granite,
but the separation between them wherever observed is sharp and distinct.
Gneiss, however, is not an abundant rock, and though its occurrence is
mentioned as being more pronounced near the granitic areas, it is not by
any means a constant and immediate associate of the granite masses them-
selves, but shares the field with the silicious, micaceous, chloritic, and
hydrous mica schists.

Special descriptions of the veins of quartz found in the schistose rocks
are given in Mr. Jenney’s chapter on Mineral Resources, and little need be
said here further than to mention their general composition and mode of
occurrence. They are very abundant, are always parallel with the stratifi-
cation of the schists, and are what may be termed veins of intercalation. On
Castle Creek, on the headwaters of Spring Creek, and generally in the
western part of the schistose area, they are very numerous, and have
nearly always a lenticular shape, swelling out and narrowing down as
veins so commonly do. They are not usually traceable for great distances,
and are generally narrow, rarely exceeding a few inches in width; a few
have a thickness of several feet. The quartz composing them is usually
bright, vitreous, and translucent, of a pure white, milky, or brown color,
and sometimes very ferruginous. Frequently bunches or lenses of quartz
are found in the schists, but these are not of great extent. Some of them
are evidently true segregations, while others appear to be silicious deposi-
tions coincident in origin with the associated strata.

Where the veins are highly ferruginous they become converted super-
ficially into tolerably pure oxide of iron by the weathering and removal of

54 GEOLOGY OF THE BLACK HILLS.

the quartz. In many instances the quartz veins are undoubtedly aurifer-
ous and the larger portion of the gold found in the gravels of the Hills has
originated from them, but by reason of its sparse dissemination in the vein’
matter, specimens containing visible particles are not often found. Such
specimens, showing thin flakes of gold have, however, been obtained from
some of the ferruginous quartz veins of Custer Park. The very fine state
in which the gold is found in the gravels of the southern end of the Hills is
also an evidence of the fine state of division in which it occurs in the veins.

The gold which since our exploration has been found in the ancient
gravels of the Potsdam formation must be referred, together with that our
party obtained from gravels of the most recent formation, to the quartzes
of the Archean as its source. The fact that the concentration was begun
by the shore action of the Potsdam sea renders it probable that some at
least of the gold of the recent gravels is derived immediately from the Pots-
dam gravels, just as are the associated quartz pebbles.

Hornblendic schist or hornblende rock was found in a few localities.
Near the stockade and on the headwaters of Amphibious Creek a very
silicious schist occurs containing a large proportion of hornblende, and on
French Creek near the point where it leaves the Hills hornblendic masses
were found at more than one place in the bluff of the caton. The latter is
a very compact and close-textured hornblende rock, containing consider-
able silicious matter. The general scarcity of hornblende among the schists
and its entire absence from the slate rocks, except as a microscopic element
in their structure, are facts deserving of remark.

The minerals found in the schists and pertaining to them particularly
are few in number, and with the exception of garnets and mica are not
abundant. Staurotide, well crystallized, was found in one locality in the
schists east of Harey Peak, and a single specimen of crystallized epidote
was brought in for examination. Highly crystalline feldspar and mica are
found in thin veins in the gneissic rocks in some places. Scales of graphite
were found in small quantities in certain of the schists near Harney Peak.

The granites are found only in the schists and gneiss of the western
series, and careful observations nowhere discovered them among the argil-

laceous slates of the eastern series. They occupy a large area entirely in

STRIKE AND DIP. 55

the southern portion of the Archeean district. Their principal mass is in
the Harney Peak region, and has an area twelve miles in diameter north
and south and about seven east and west. Besides this central mass others
of less magnitude are found, diminishing in size as the distance from the
peak increases. ‘The smaller bodies occur at the west and east, but particu-
larly at the south. All of the granite masses whose relations could be
closely examined were found to be parallel with the stratification of the
schistose rocks, and when their structure was readily discernible were seen
to be lenticular in shape.

The strike or trend of the schists is in general north and south, but it
varies from northeast and southwest to northwest and southeast, and south
of Harney Peak in the region of French Creek and in the park country
immediately south of that stream even this range of variation is exceeded.
Here the strata are found to sweep around from a strike on the headwaters
of Castle Creek of north 30° west to an east and west course on Irench
Creek in the vicinity of the stockade, returning again on the east side of the
Harney Peak range to their usual north and south direction. In the
vicinity of the stockade the varying strike is marked by bold ridges of
granite, which bend around and change their strike as indicated.

The dip of the schists is usually very high and often vertical, though
occasionally by local variation it becomes quite low. In several places a
difference of dip was noticed between the schistose rocks on the west and
the slates on the northeast side of Harney Peak, the former being toward
the west and the latter toward the east, but the number of observed points —
of variation was not sufficient to warrant the statement that this difference
is a persistent feature of the relation of the two series of rocks. On Castle
Creek and on the other heads of Rapid Creek the dip is from 55° to 85°
west, but in going southward and eastward there is found a change cor-
responding to the change in strike already noticed on French Creek, and
the dip becomes slightly southward from the vertical. On the headwaters of
Red Cation Creek it is 70° to 80° south; on lower French Creek 45° south.

The vertical position of the schists and their highly micaceous nature
cause them to decompose readily and uniformly, giving a peculiarly
smooth and unbroken surface to the topography and producing those beau-

56 GEOLOGY OF THE BLACK HILLS

tiful expanses of treeless and well-grassed parks that are found in the south-
western and western part of the schist area. The parks occupy irregular and
discontinuous tracts along the western margin of the Archean region, and
extend from Box Elder Creek to the headwaters of French, Red Canon, and
Amphibious Creeks. One of the smaller of them with a granite ridge in
the distance is shown by the view in Golden Valley, Figure 4.

Where the mica of the schists becomes less prominent and quartz takes
its place, or where strata of quartzite or beds of granite predominate among
the schists, the surface of the country becomes more rugged and peaks or
ridges of harder rocks stand out above the surface as rough and soilless
reefs. In the area where granite is the prevailing rock an excessive rough-
ness and ruggedness is given to the surface, which then becomes a mere
succession of sharp ridges and towering peaks.

Characteristic samples of the schistose rocks will be found described in
Mr. Caswell’s report under the numbers 1, 13, 24, 27.

The eastern or slate series occupies probably a larger portion of the
Archean area than do the schists of the western series. Its predominant
rocks are distinguished by their fine and uniform texture, and though they
nowhere have the true slaty cleavage making an angle with the bedding,
they are finely laminated and commonly split on their stratification into
tolerably thin pieces. They are quite distinct in their structure from the
coarsely crystalline schists of the western series, and are fairly distinguished
as slates, although the term does not apply in its more restricted sense.
They do not exhibit the variety of character observed in the rocks of the
western group, but consist mainly of fine silicious slate, clay slate (argilla-
ceous mica slate), argillite, taleose slate and quartzite. With these are inter-
polated many seams of quartz and specular iron ore. Characteristic speci-
mens of the slate have been submitted to Mr. Caswell, and though their
structure and composition are not readily discernible by an inspection with
the naked eye, under the microscope they are in general found to have a
true crystalline constitution and to be distinguished from the rocks of the
western series rather by the fineness and minuteness of their structure than
by a difference of composition. A large portion of the rocks of the eastern

Fig. 4.—Head of Golden Valley, illustrating Park Scenery.

THE SLATES. : 57

series would be classed by Dana as mica slates, but by Von Cotta and Zirkel
as argillaceous mica shists. Rocks of this character are described by Mr.
Caswell from Rapid Creek under numbers 64, 65, 67, and 71.

The argillaceous slates (argillaceous mica schists, Caswell) are among
the most prominent of the slaty rocks, and in color they are usually dark
brown or gray. By reason of their compact and uniform structure they
are less easily decomposed by atmospheric influences than the micaceous
schists of the western group. They are so fine in texture that it is difficult
to detect with the eye the elements of their composition. They appear
generally to contain fine particles or grains of mica, quartz, and argillace-
ous mineral, and they always give an argillaceous odor when moistened
with the breath. Their most argillaceous varieties split readily into thin
sheets, resembling in texture and appearance roofing or school slates, or
become soft and are readily cut like slate pencils. In many places, as on
upper and lower Spring Creek and lower Rapid Creek, the clay slates are
exceedingly dense and fine, and owing to peculiar cleavage planes break
up into slabs or splints, which may be seen in many places piled up like
cord-wood. ‘These pieces are cut with difficulty by a knife and give a
strong metallic ring when struck.

Light gray or drab, fine, soft, talcose, argillaceous slates, containing
minute particles of mica, have been found in some localities, as on middle
Rapid and Box Elder Creeks.

From the distinctive clay slate there is frequently a passage into a
very silicious slate, close-grained and banded with thin lamine of different
colors; and this silicious slate sometimes passes into true quartzite, hard,
uniform, and compact. Silicious slates associated with quartzites are well
exhibited in the cafions of Box Elder, Rapid, and Spring Creeks.

In several localities the silicious slates contain interlaminated with
them immense quantities of iron, almost always specular oxide. On Box
Elder Creek, a ridge some 400 feet in height is composed of a vast deposit
of silicious hematite, which was estimated to be from 800 to 1,000 feet in
thickness across the upturned strata. Occasional bands of almost pure
specular hematite several inches in thickness are found in the mass with

frequent layers of highly crystallized micaceous hematite. The body of

58 GEOLOGY OF THE BLACK HILLS.

the ferriferous strata, however, is highly siliciferous and entirely useless as
an iron ore, consisting of thin strata an inch or less in thickness of specular
hematite alternating with silicious slate or with pure white quartz in seams
or irregular masses, the whole presenting a remarkable resemblance to the
s:licious banded hematite of the Huronian of the Lake Superior region. In
other localities on the same creek hematites were also found in the silicious
slates, but nowhere of any practical value because of their highly silicious
character. The slates associated with these iron deposits are commonly
highly argillaceous as well as silicious, as is indicated by their color, tex-
ture, and strong clayey odor. Similar ferrugineous slates occur also on
the headwaters of Rapid Creek a short distance north of the Elkhorn
Prairie.

The quartzites vary in thickness from seams only a few inches wide to
masses 400 or 500 feetin width, though the more moderate thickness of 75
to 100 feet is more common. Several of these ledges have been traced
long distances, maintaining their regular relations with the adjoming strata
and holding to their own dimensions and character, running across the
country like dikes, bristling suddenly in peaks, or outcropping in the canons
of the creeks in sharp, well-defined walls. A prominent quartzite ledge on
Spring Creek, known as the ‘‘ Mammoth Lode,” has been traced continously
five or six miles in each direction, and others are distinguishable still greater
distances. They seem to be limited in their extent, in thickness as well as
in length, only by changes in the composition of the original deposits from
which they have been formed by metamorphism.

The color of the quartzites is varied, being sometimes an almost pure
white but more often a light or dark gray or an impure blue or pink or,
when much iron is contained, a dark reddish brown. In texture they are
very compact and homogeneous, and on a fresh fracture, which is conchoi-
dal or fragmental, they have a vitreous or glassy luster. They are almost
pure quartz.

Though they are found throughout the entire series of the slates, they
are of greater thickness and more numerous in certain parts of the district.
As has already been mentioned, there extends on the eastern border of the
Archean area a long ridge or succession of prominent peaks and bluffs,

QUARTZITES AND CANONS. | 59

which cuts across all of the creeks north of Harney Peak, occasioning in
each one an intricate, precipitous and exceedingly rough canon. This
ridge and these cations are due to a series of quartzite strata, which by
their hardness and durability preserve the interbedded slates from rapid
erosion, and not only retain their own supremacy in the topography but
restrain the creeks from opening broad valleys.

West of this prominent geological edge there is a stretch of country
which is rolling in character and nowhere very rough. In passing it
the creek bottoms often spread out into valleys of considerable extent,
and the divides between them are neither rough nor steep. Its smooth
character marks it as the outcrop of the soft slates rarely interrupted by
harder strata.

On the west of this strip the headwaters of the various branches of
Spring and Rapid Creeks are secluded in cations precisely similar to those
on their lower courses and due to a similar cause. A series of quartzite
strata resists the wear of the elements and conserves a belt of peaks and
ridges.

Quartz seams of a thickness varying from less than an inch to many
feet are numerous in the more silicious slates. Usually they run parallel
with the stratification but do not have the lenticular, wedging character
noticed in the small quartz veins of the micaceous schists. In many places
the quartz is interlaminated with the slate in thin, alternating seams. Some
of the quartz seams appear to be true veins, formed by the collection of the
quartz along lines of separation of the strata, and such can be traced long
distances. Commonly they run parallel with the bedding, but in a few
instances they have been found cutting across the strata at a right angle,
following cleavage or jointing planes. They are frequently highly ferru-
ginous, so that on their decomposed edges they are made by the weathering
out of the quartz to appear like ledges of brown hematite ore. The quartz
of the seams is highly crystalline, is usually translucent or opaque, and
when unstained by iron is milk-white in color.

A prominent deposit, segregation, or accumulation of quartz is found
two or three miles east of Custer Peak, to which the name of Jasper Hill was
given. It is irregular in shape, about 200 feet in height, and without any

6G GEOLOGY OF THE BLACK HILLS.

clearly defined structure. The silicious materials composing it display
great variety in color and character. Among them are a deep red jasper, a
grayish quartzite and a pure white milky or translucent quartz which in
places has a bright red crystalline iron oxide running through it like the
dendrites in moss-agate.

On Box Elder Creek, south of this deposit and on the summit of a
high elevation, there is found running parallel with the stratification a ledge
of pure milky quartz which from its position attracts the attention of the
passer by. It is some feet in thickness and is traceable for nearly a mile.
Samples were taken from it and tested for gold, but yielded no trace by fire
assay. The quartzites also frequently carry seams of quartz which in
many cases seem to be true veins produced after their formation and con-
solidation. The banded structure already noticed is found also in the seams
in the quartzites. Bands of iron ore, ferruginous strata of the inclosing rock,
and seams of ferruginous quartz are found in the quartzites, and though the
separation between the ordinary quartzite and the ferruginous portions is
generally ill-defined, the latter are sometimes so well marked as to run like
true veins within the body of the quartzite itself. ‘There is, however, no
slickensiding nor other direct evidence of the existence of fissure veins In
many instances the ferruginous quartzite ledges are probably due to the
original dissemination in the quartzite of iron oxides, which in the process
of weathering are oxidized and hydrated to brown hematite. Sometimes,
however, the ferruginous portions arise from the decomposition of iron
pyrites which existed in seams or irregular masses of later date than the
quartzite. The Mammoth Lode, for example, which is highly ferruginous,
owes its iron largely to the decomposition of pyrites, some pieces of which,
unchanged and slightly auriferous, were found in place beneath the level of
the creek.

A fuller exposition of the occurrence and character of the veins is
given by Mr. Jenney in his chapter on the Mineral Resources.

The dip of the strata of the eastern series is always high, 70° to 90°,
and though it varies in amount and direction, it is usually toward the west.
The general strike is about north 30° west, but it swings now in one direc-

MINERALS OF THE ARCHADAN. 61

tion, now in another, ranging freely between the limits of northeast: and
northwest.

In the study of the Archean slates and schists the absence of the
numerous minerals so abundantly found in the metamorphic slates and
schists of the East is peculiarly worthy of remark. With the exception of
garnet, crystallized mica, and hornblende, and in the micaceous schists of
the western series the rare staurotide, epidote, and graphite, none of the
common silicated minerals were met with. Excepting the brown hematite
of the oxidized silicious veins or strata and the specular hematite of the
slates, the metallic minerals were rarely obtained from indigenous rocks.
Galena is said to have been found at one place on Castle Creek, but that it
is not a common mineral is proven by the entire absence of any particles in
the drift or gravel. Pyrites, as a portion of vein matter, was found in several
localities, and though at present not largely found it probably was once
widely distributed in the veins and seams, the oxidation of which has con-
verted it superficially to the brown oxide of iron. Mispickel has also been
found in the same association. |

Gold, originating undoubtedly in the quartz seams, is now found in the
gravel and drift of the valleys and in the basal portions of the Potsdam,
and though there are doubtless many of the seams that carry the gold in
a free state, it is so fine and so sparsely disseminated that gold-bearing
rock with visible particles is rarely met with. The wearing down of the
rocks and the concentrating action of waves and currents have nevertheless
so sifted out and accumulated the precious metal, that in many places it is
now found in tolerable abundance in the ancient and modern gravels.
Quartz seams are so abundant that if they were all, or the larger part of
them, auriferous, the quantity of gold in the gravels would be much larger
than it is actually found.

‘No fossils were found in the Archzean rocks; and marble and serpen-
tine, the metamorphic rocks most likely to yield them, were not seen.

Our examination brought to light no evidence of the duplication of any
parts of the Archean rock system. If the slates or the schists were folded
upon themselves and afterwards worn away so as to leave two or more par-
allel outcrops of the same beds, the folding must have been confined to the

62 GEOLOGY OF THE BLACK HILLS.

homogeneous soft beds; and the presumption is that no such folding took
place within the area exposed in the Hills. The whole system of vertical
beds, with a width of about twenty-five miles, is believed to retain its origi-
nal relation of parts. It has not, of course, its original position, for the
same great process of change which has produced its metamorphic structure
has turned it bodily on edge and either broken away or eroded away its
upward continuation; but it is probable that the system presents the clays
and shales and sandstones from which it was produced by metamorphism
in the same order in which they were originally deposited.

The division of the system into two series, a series of schists and a
series of slates, is based on lithological differences purely, and is fully war-
ranted, whatever may be the structural and historical relation of the two.
The fact that Mr. Jenney discovered an apparent unconformity between
them at one point, although it stands alone, and although the two series
generally conform in strike, is not to be ignored; and coupled with the
great lithological difference gives strong support to the view that the slate
period and the schist period were separated by an interval of time and not
merely distinguished by a change of sediments. Indeed it is questionable
if the original sediments were materially different. Mr. Caswell’s exami-
nations show that the same minerals constitute the typical rocks of both
series, only in the schists they are more coarsely crystallized, so that the
lithological contrast seems to depend more on the degree or character of
their metamorphism than on any difference in chemical constitution. This
fact gives additional support to the view that there was an intervening
lapse of time; for if we assume that the schists are older than the slates, it
is but natural that they should have been subjected to an antecedent and
more powerful metamorphism from which the slates were exempt.

My idea of the history, not by any means as proved, but as most
probable in the imperfect light of the facts now known, is as follows: The
sediments of the western series were first deposited and were altered to the
condition of schists. They were then raised above the ocean, were somewhat
eroded, and sank again. The eastern series were deposited on them with
slight unconformity, and the whole were again subjected to metamor-
phic action, which ceased when the eastern rocks had reached their present

CORRELATION. 63

microcrystalline condition. Then came a great dynamic revolution, fol-
lowed by a great erosion, and the result at the site of the Black Hills was
the exposure at the surface of a broad section of vertical schists and slates.
Of the base of the schists and of the summit of the slates we have no
evidence.

Can we correlate them with the Archzean rocks of the East ?

Primarily the historical order of rocks is shown by the order in which
they overlie each other, and since every change in the character of succes-
sive strata represents a historical change, the geologist always classifies his
section by means of these changes. But when remote sections, the con-
nection between which cannot be traced by the eye, are to be compared,
and their historical relations are to be made out, or, in other words, when
correlation is attempted, the all but universal verdict of geologists is that
evidence from fossils is alone of value and that lithological evidence is not
to be trusted. Nevertheless there are some lithological correspondences so
general that they cannot be accidental, and they must be counted to give
a certain weight to lithological evidence in the absence of paleontological.
Triassic rocks are characterized by a red color the world over. Permian -
limestones are always magnesian. The great limestones of all great rock
systems are Paleozoic. In innumerable localities in all lands the Paleozoic
system begins with a conglomerate and the rocks beneath it are metamor-
phic. These agreements cannot be due to mere coincidences, and if they
are not, then lithological resemblances are not always without meaning,
and they may be taken to afford the basis for a presumption so long as the
better evidence from organic forms is not available. I shall, therefore, give
consideration to the lithological affinities of the Black Hills Archean as
the best available means of judging of their relations.

The rocks of the eastern division of the Archzean—the argillaceous
and silicious slates—have a very similar character to the Huronian rocks
of the south shore of Lake Superior and Canada. They agree in their
partly argillaceous character, in the presence of silicious slates, in the great
abundance of quartzite, and in the occurrence of silicious hematite, banded
quartz, and jaspery formations. We find, however, in the Black Hills no
diorites, conglomerate quartzites, nor limestones, and the iron deposits,

64 GEOLOGY OF THE BLACK HILLS.

though of considerable magnitude, are not frequently recurring. The col-
lection of the typical rocks of the slate series brought in from the Black
Hills have a peculiar resemblance in their general facies to the typical
Huronian rocks, and this fact was immediately noticed by several geolo-
gists to whom the Huronian types are familiar.

In the western series of schists we cannot trace so close a resemblance
to either member of the Archzean of the East. The characters which dis-
tinguish them from the adjacent slate series serve equally to distinguish
them from the typical Huronian. ‘Their rocks are all found in some abun-
dance in the Laurentian, but they are not the characteristic rocks of the
Laurentian. If there is one Laurentian rock more prevalent than another
it is gneiss, but gneiss is almost unknown in the Black Hills; while calca-
reous rocks and magnetic iron ores, the constant associates of the Lauren-
tian schists, do not occur in the Archean of the Hills.

The lithological evidence fails, therefore, to give even its feeble sup-
port to the theory that the two Archean groups of the Black Hills are the
representatives of the two Archzean groups of Canada. The fact that there
are two great groups in each case is a resemblance. A second resemblance
is found when the younger group of the two pairs are compared with each
other. But when the older groups are compared a decided disparity is
brought to light. With evidence of this character nothing short of a full
coincidence could serve to establish even a presumptive correlation, and the
question can only await further light. I have, therefore, abstained from
any provisional assignment of names to the slates and the schists further
than to call the former Newer Archean and the latter Older Archean.

The Archean rocks of the Black Hills, like Archzean rocks elsewhere,
were fully metamorphosed before the dawn of Potsdam time. This is
proved by the Potsdam resting upon their upturned edges unconformably,
and carrying in the conglomerate at its base fragments of slates, schists,
quartzites, etc., of a character precisely similar to that of the underlying
rocks.

A portion at least of the Archean area was above the sea in early
Potsdam time, for the Potsdam conglomerate could only have been formed
by the action of waves on a shore line. The erosion of the Archzean, which

THE GRANITES. ; 65

ceased with the deposition of the Potsdam, was not renewed until after the
Tertiary disturbances which produced the Black Hills uplift.

SECTION III.
THE GRANITES.

The granites occur only within the area of the Archean; but the dis-
cussion of their character and origin and the question of their age present
so many points of interest that it has been thought better to consider them
separately instead of treating them in connection with the slates and schists.

As has been mentioned already, they are wholly confined to the south-
ern end of the Hills; none whatever are found north of Spring Creek. Their
greatest development appears in the accumulation of ridges and summits
about Harney Peak. North of Harney little granite is found and that
merely the ending off of the main range. West, south, and east it becomes
gradually less and less predominant and the schists are more and more
exposed, until at the limit of the Archean exposure it is rarely met with.
West of Harney there are many masses of no little magnitude but they
are more abundant toward the south and southeast. In several of the
canons of the creeks draining the southeastern corner of the Hills granites
appear among the quartzites and schists, while the tops of the cafion walls
are capped by the fossiliferous rocks. Harney thus seems to be an eccen-
tric point in the development, the northern focus of an ellipse whose longer
axis is directed to the southeast and whose area incloses all the outcrops.*

The maximum expansion of the granites around Harney seems to be at
or near the separating line between the two series of metamorphic rocks,
the schists of the western and the slates of the eastern series, and our care-
ful examination found them to be confined entirely to the area of the schists,
none whatever being found in the slates.

It would be a task of no little magnitude to give an adequate idea of the

*NOTE BY THE Ep1TOR.—The reader who compares the distribution of the granite, as described
in the text, with its distribution as given by the geological map, will find discrepancies. The author
drew a few granite areas on a small preliminary map, but attempted no thorough representation, because
the topographical material was not then fully compiled. The editur has transferred these areas to the
final map, but has not attempted to supply the outcrops described in general terms in the text, because
he could not do so without inventing details.

oBH

66 GEOLOGY OF THE BLACK HILLS.

surface features of the rugged and cragey region of the granites, probably
the most difficult of passage of any district in the Hills. A few words,
however, will be devoted to some of the most conspicuous characters of its
topography. Viewed at a distance from the Plains at the west or east, the
Hills appear as a long, low ridge, above which the peaks and ridges of the
interior area raise their sharp and broken summits, and the highest eleva-
tion is readily recognized’ in Harney Peak. Beginning near the extreme
southern end of the Hills, in the high points south of French Creek, there
is seen to be a succession of elevated peaks and ridges, increasing in height
and ruggedness until they culminate in Harney and its retinue of smaller
peaks. These latter are defined, sharp and craggy, against the background
of sky, and even at a great distance Harney Peak with its peculiar cathe-
dral-like summit is easily recognized. By a freak of weathering the highest
point is carved into a seemingly square tower, and joined to this on the south
is a lower ridge forming the body of the edifice. The granite range is cut
off sharply just north of Harney, which stands with its bold front looking
northward over a broad array of lower rolling hills. It rises two thousand
feet above the valleys near its base and several hundred feet above the
other peaks in the Hills, but itis rivaled in height by a point of the limestone
plateau called Crook’s Tower. The latter, however, is an inconspicuous
butte,.rising but little above the general level of the plateau, while Harney,
springing abruptly from lower surroundings, is far the most conspicuous of
the high points.

Approaching Harney from the west, from near the base of the limestone
plateau, we pass over the upturned edge of the schists, and though the
country is occasionally rough no granite is seen until within about ten miles
of the peak. At first we cross a few ridges of granite running parallel with
the stratification of the schists, and ranging in height from a few feet to
several hundred feet. They are extremely rugged, their surfaces being
shattered by weathering and thickly grown with trees, and as we approach
the main range they increase in frequency, size, and roughness. The schists
become at the same time less and less visible, and the little parks and grassy
valleys are less prominent, until at a distance of about five miles from the
peak the schists are no longer seen, and we have reached the unending

ASCENT OF HARNEY PEAK. 67

granite. Beyond us, in a succession of peaks and ridges, or shooting up
vertically in slim pinnacles and points, rounded, grooved, and scarred by
the action of the weather, the summits of the granite masses tower in an
almost endless repetition. Many little drainage valleys, with sides and
bottoms thickly tangled with aspen and pine, wander through the maze of
peaks.

The sides of the peaks are generally covered by a dense growth of
small pine trees, and this extends up to the vertical cliffs. In many places,
however, large areas of the mountain flanks have been burned off, leaving
the blackened trunks; and in others a tornado has covered the slopes with
fallen timber.

Starting from French Creek near the stockade, winding among’ the
granite ridges, which here run east and west, and going northward through
a series of grassy valleys which follow the outcrops of the schists and head
toward the high peaks of the Harney range, the headwaters of Battle
Creek are soon reached. Dammed by the beaver, the creek is spread
out in swampy valleys overgrown with a dense brake of aspen and
willow. Breaking through this undergrowth one is soon compelled to dis-
mount and arduously force his way along, leading his horse as best he
may, while the presence of his comrades is only known by the plunging
and crashing they make in their slow progress. With rugged granite
heights before and on both sides, singling out a prominent peak that
promises most to be Harney, we thither direct our course, and soon find
the tangled valley narrowing, while before us rises the face of a granite
ridge. Mounting its side, rough with broken fragments of rock and per-
haps still further encumbered with a growth of small pines or with fallen
timber, we reach the summit, and exhausted with the exertion of climbing
and pulling up the horses we look eagerly around over the waste of granite,
piled in endless confusion, weathered in fantastic shapes, and cleft with
deep and narrow valleys, to see if Harney is recognizable. Across a
steep-sided valley we think we see it raising its summit in the distance, and
descending several hundred feet over the broken mountain slope, and
crossing the narrow valley, thickly grown with trees and piled with
bowlders, we painfully ascend its farther side, which to our discourage-

68 GEOLOGY OF THE BLACK HILLS.

ment is seen to overlook a similar valley, beyond which is Harney. Thus
ascending rugged mountain slopes and crossing intricate valleys our guid-
ing peak, after almost endless labor, is finally reached and joyously
ascended, only to crown our disappointment with the sight of Harney still
in the far distance, standing high above the surrounding peaks, to reach
which still other and many high ridges and deep valleys must be scaled and
crossed. Such was the experience of several of the officers of our escort,
who thrice attempted the ascent of Harney from the south and southeast,
and each time were foiled by the difficulties of the rugged mountain
region. The triangulation party, however, was more successful, for
approaching the granite range from the west it encountered less difficulty.
Following first one of the grassy valleys of French Creek, and thence
crossing a high ridge from which Harney was visible, a small valley was.
reached, which afterward was found to meander to the very base of the
peak itself. Here encamping, the peak was considered but a slight climb
for the following morning. On the morrow, leaving here the horses, the
ridge bordering the valley was easily mounted, and among the multitude
of peaks in view one was singled out as Harney. This proved to be an
error, but from its summit the true Harney was seen. Following then a
high ridge, along which for a long distance we had to cut a passage
through the undergrowth of pine and aspen and pick our way over fallen
timber and rough crags, the peak was finally reached. At the base of the
tower were found cartridges and other evidence of the presence of General
Custer’s party in 1874, but the tower itself, the summit of the peak, seemed
never to have been ascended. After some struggling and climbing the
highest point was surmounted, from which the whole character of the
country could be studied. A mercurial barometer observed on the top of
the tower gave for its altitude 7,403 feet.

The general character of the view from this point has already been
mentioned in describing the topography of the slate area. Northward the
granite range ends somewhat abruptly, and descends at a high angle for
nearly two thousand feet, while beyond are seen the rounded hills and
scattered valleys of the slate area, with Custer and Terry Peaks in the
distance, and far to the northeast the conical top of Bear Butte. On all

COMPOSITION OF THE GRANITE. 69

sides are the cliffs of the sedimentary rocks, which bound the area of the
crystalline rocks, while near the horizon at the east and west are seen the
bare wastes of the Plains. Immediately around the peak on the east and
south and west rise a myriad of serrated peaks only less than Harney in
height—all weathered and scored and gradually crumbling under the hand
of time. Toward the west and southwest the peaks become less numerous
and prominent as they recede from the granite range, and the country is
seen to open up in little parks and grassy glades; and in the far southwest
it spreads out into Custer Park. East and south the rough and mountainous
character is maintained, though a few openings may be seen on the head-
waters of Battle and French Creeks. In the southeast, however, the rugged
character of the country is most continuous and marked.

The rock of all the granite masses of the hills varies little in character.
Its texture is so extremely coarse that it would scarcely be recognized as
granite by one accustomed to the fine-grained varieties of New England or
the Rocky Mountains. It is granite on a large scale, with all the elements
of that rock—feldspar, quartz, and mica—present, but instead of their being
mixed with tolerable uniformity throughout the mass each constituent is
very highly crystalline and aggregated by itself. Feldspar is the most
abundant constituent and forms 70 or 75 per cent of the whole. It is
always highly crystalline and sometimes exhibits large crystal faces but
no perfect crystal was discovered. It is generally of a pearly white or
grayish white color, having on fresh fractures a bright luster, but it is
occasionally flesh-colored and it often receives a reddish or pinkish stain
from the decomposition of associated ferriferous minerals. This discoloration
is more observable in the southern part of the granite area and in places
where the feldspathic mass is especially weathered and rotten. To the
preponderance of the feldspar is mainly due the rapidity of the decomposi-
tion of the granite, the pinnacled, sharp, and rugged mode of its weather-
ing, and the superficially shattered character of its masses. So readily
does it decompose and crumble that it is in many places difficult to get
even a hand specimen of firm and unchanged rock.

70 GEOLOGY OF THE BLACK HILLS.

The quartz of the granite is commonly glassy and clear, but its varia-
tion in texture and color is great. It is usually crystalline, but no crystals
are found. It is frequently found opaque and white, and sometimes
lightly tinted with pink, while many large ‘masses are of a delicate rose
color. From the decomposition of associated minerals it is often stained
by oxide of iron to a dull red or brown color. It composes approximately
about 20 per cent of the granite, but is distributed with great irregularity.
In many cases the quartz penetrates the feldspar mass in irregular seams or
fragments, which on certain fracture planes produce the figures so suggest-
ive of oriental inscriptions, and which have given to the variety its name
of graphic granite. Sometimes it occurs in large compact bodies, sometimes
in the form of huge veins, and sometimes it forms a more equable mixture
with the feldspar and mica, making a normal and tolerably uniform but
coarse granite.

The mica ranges from silvery white to dark brown in color. It is
always highly crystallized, and well defined hexagonal crystals two inches
in diameter are very common; mica plates six or more inches across have
been found. The mineral forms only about 5 per cent of the granite, and
though sometimes distributed generally through the mass it is more often
found in bunches or segregations. It was observed that it rarely accom-
panies the feldspar alone, but is almost always associated with quartz.

Besides the three minerals essential to the formation of granite the only
ones found in abundance are rose quartz and tourmaline. ‘The latter is
quite common and sometimes composes 3 or 4 per cent of the granite.
It is usually but not exclusively associated with the quartz. It is black
in color, and is generally highly crystallized, though sometimes massive.
At Harney Peak and elsewhere massive pieces of tourmaline were found
weighing several pounds and covered with small well defined crystals.
More generally it occurs in trigonal pyramids, well defined, and sometimes
with beautifully terminated ends. These crystals are often found from three
to eight inches in diameter and nearly a foot in length; but perfect speci-
mens could not be obtained from the weathered surfaces accessible to us.
Though very abundant in the granite it is strictly confined to that rock and
was never seen in either the schists or the slates.

AS;
LENS
\S
WZ si

Fig. 5.—‘‘Saw Teeth” of Granite, near Harney Peak.

CONCENTRIC ARRANGEMENT OF MINERALS. ll

From this brief notice of the components of the granite it is seen to be
exceedingly coarse, feldspathic, and crystalline, and it would probably be
classed by Nauman and Von Cotta as approaching the variety Pegmatite.
In the southern end of the Hills, however, on French Creek and the
headwaters of Amphibious, a fine-grained variety was found which has
more nearly the typical character of granite. In places it has much the
appearance of Scotch granite, though considerably coarser in texture, and
in nearly every hand specimen that may be selected crystals of tourmaline
can be found, but these are neither so large nor so finely crystallized as
those in the coarser rock.

In one of the smaller granite deposits in Custer Park a particular
arrangement of the minerals was observed, which, though interesting, is
quite exceptional. The tourmaline, mica, and quartz have a roughly con-
centric disposition within the general matrix of feldspar. On the exterior
of each aggregation the tourmaline preponderates, with a sprinkling of
quartz. In an intermediate layer the tourmaline is less abundant, and asso-
ciated with quartz are quantities of mica in crystal tablets, while a large
mass of clear, highly crystalline quartz constitutes the nucleus.

In the great peaks and masses of the central nucleus there seems to be
an arrangement in a north and south direction, 7. ¢., their greater diameters
have that trend. There are many cross ridges, it is true, but they appear
to be due rather to an accidental arrangement of the deep eroded valleys
that wander through the granite area than to any primary arrangement of
the granite itself. No distinct marks of stratification were observed even
in a large way. The main peaks are of massive granite, fissured and
cracked, weathered and worn in every direction, but they are longer in a
northeast and southwest direction and comparatively narrow crosswise,
forming in many instances crests or ridges. South and southwest of Har-
ney are some excellent examples of what might be termed weathering
planes, in which granite pinnacles or slabs are weathered out and stand
100 or 200 feet above the mass of the range. ‘These planes have the same
general northwest or north-northwest trend observed in the whole struct-
ure of the granite area. They divide some of the crests into serried pin-

ie, GEOLOGY OF THE BLACK HILLS.

nacles, which near by resemble organ pipes and in the distance saw teeth,
and which contribute greatly to the picturesqueness of the scenery. They
undoubtedly owe their formation to a more readily decomposed material
which has been removed from between their surfaces, but they can hardly
be due to a true stratification in the granite itself. The peculiar pinnacled
topography to which they give rise is confined to a limited area extending
about three miles southwest from Harney Peak and is not generally observ-
able. The saw teeth and the weathering planes are illustrated by Figures
5 and 6, which represent scenery photographed near Harney Peak.

In the summit of Harney Peak a small mass of mica schist was
observed cemented in the feldspathic rock, with its stratification nearly
horizontal. It appears to be an entrapped piece of

ABT REA © AEN TCS
SoS KU by uA Ths fol : : 1 sites
DOI Xeon ab 8c ust enfolded by the granite when the latter was

—ahe< e

YAY Pay Paes P
reer ‘vars, in a plastic state. Mr. Jenney observed near Har-
paw ve
r-N~ ° °
eee, “ay, ney Peak a huge fragment of schistose rock sim-
Buses low, . ‘ : Pate ie
ZI) rA5¢ ilarly entrapped in a mass of granite. This is
Rie ENA , :
QY AN represented in the annexed cut. ‘The mass is about
(6 Se ee A Wee : 5 F : 6
Tasos DY ye 100 by 75 feet in size and lies with its stratification
BLN Ady : ; ‘
ew ANU AEGee vertical. Between the strata of schist is a seam of
ZA SEW A'S MAA

“\ in

SONAL LEN 2 NS

EN” the ferruginous quartz so common in that associa-
tion, and by weathering the rocks have been cut
away in the manner shown in the cross-section.

To study with facility the relation of the granite

FiG. 7_Plan and Section or 10 the Schitose rocks, we must leave the main granite
Schist included in Granite. area and observe those outliers or ridges which run
among the schists and have no immediate connection with the central
mass. In them the character of the granite is similar in all respects
to that of Harney Peak, and we may safely assume that the main range
bears the same relation to the great schist area that we find them to bear to
the schists about them. That relation is in every case the same; they all
run parallel with the stratification, and are perfectly distinct and separate
from the schistose rocks. ‘There is always an absolute and positive line of
demarkation between the two; the transition is sudden, and in no case was
there observed any gradation of one rock into the other, though such facts

—

\

Fic. 6.—Granite Forms near Harney Peake.

SLICKENSIDES. 73

were carefully looked for. Hand fragments may be found anywhere along
the separating line, showing the micaceous schist on one side and the granite
on the other, separated by a line that can be traced with a needle point.

In several instances the contact surface of the granite was found beau-
tifully polished or slickensided, and many others doubtless escaped notice
because of the easy disentegration of the granite. One particular case is
worthy of specification. It was seen near French Creek, as we approached
it from the headwaters of Spring Creek. An exposed surface of one of the
granite masses stands there four or five feet above the incasing schist, and
in fragments extends a distance of twenty feet. This surface is as beauti-
fully smoothed and polished as any glacial planing I have ever seen, and
the resemblance is so striking that it was taken at first to be a glaciated
surface. ‘These smoothed surfaces are produced by the movements of the
rocks against each other, and as the granite is harder than the schist, it
became polished just as a tool of hardened steel is polished on a grindstone.

West of Harney the strike of the rocks is from north and south to
northwest and southeast, and we find the inclosed granite masses running
in the same manner. Southward, on French Creek at and above the stock-
ade, the strike of the schists is changed, and with them the inclosed granite
ridges run nearly east and west. Southwest of the stockade, in Custer
Park, the schists and granite run north and south, and this strike is ex-
changed in the eastern part of the Park region for an east and west, which
bends around on the east side of Harney, becoming the customary trend
toward the north and northwest. These features in the strike of the rocks
have already been noticed in the description of the general features of the
schist area, and need here no further comment. In all the region where the
granites are included in the schists they rise abruptly above the general
level; for though they are somewhat easily disintegrated, they are surpassed
in destructibility by the schists and the latter have been much more rapidly
removed, leaving the granite prominent.

The masses vary greatly in size. Sometimes they are merely veins
an inch or two in thickness and of very limited extent. More commonly,
however, they are 25 or 50 or more feet in width, and several hundred feet
or several hundred yards in length. The larger peaks or ridges are often

74 GEOLOGY OF THE BLACK HILLS.

500 feet in height and several miles in extent. Whatever their size, they
have always a lenticular horizontal section, that is, they are thickest near
the middle and taper off toward each end; but whether this same form
would appear in a vertical section we have no means of ascertaining.
Their form is illustrated in the annexed cut.
Frequently, standing on one of these lenses of granite and

| looking along the strike, the geologist can trace a series of
\\\\! others trending in the same direction and on the same line.
They appear like masses of granite that have filled seams or
separations in the schists, pinching in and swelling out like
fissure veins.

In the canon of French Creek a cliff was observed wherein

a stratum of granite is inclosed between two of quartzite, the
granite mass itself inclosing some gneiss and having distinctly
marked in its short exposure the swelling or lenticular form.

The peculiar granite of the Black Hills resembles but
few of the described granites of the Rocky Mountains proper.
The rock of Rawhide Butte, mentioned in Chapter II, is very
similar in its highly feldspathic and coarse character and in
the abundance of tourmaline and rose quartz.

Laramie Peak, too, presents many of the features of
the granites of the Hills. Dr. Hayden* finds the granite

ria eal Eeuenodies thinner and less abundant at a distance from the main
NS ges peak and the interstratified schistose rocks more prominent,
while the peak itself is composed almost entirely of granite. This he
describes as an ‘aggregation of large crystals of reddish feldspar, with
quartz and mica; the feldspar so predominating that it gives the character
to the rock. The mica usually occurs in small masses and in limited
quantities.”

Dr. Hayden states that the granite of the Wind River Mountains is
very uniform and gray,t and Prof. Theo. R. Comstock remarks a gradual

change from the schists to gneiss, gneissoid granite, and compact fine-

*Geological Survey of the Territories, 1870, p. 18.
tId., p. 37,

GRANITES OF THE ROCKY MOUNTAINS. 75

grained granite, and otherwise does not describe them as similar to those
of the Black Hills.*

In the survey by Mr. Clarence King of the 40th Parallel no granites
were found of the highly feldspathic and coarse character observed in the
Black Hills.

In Colorado the granites and metamorphic rocks of the Middle Park
region have been studied with care by Mr. A. R. Marvinet He finds them
to range from “quartzite through silicious and mica schists to very simple
varieties of gneisses and granites, in which the mica is wholly subordinate,
and the feldspar mostly a tabular and twinned orthoclase, * * * while
the syenitic element and the more basic rocks generally were almost entire-
ly wanting.” Excepting some minor granitic areas of uncertain eruptive
character, Mr. Marvine regards the granites of this region as metamorphosed
shale, which over large areas “‘has reached that last term of metamorphism,
viz, structureless granite.”

The intercalation of granite and gneissic strata with a gradual increase
of the granite ratio in the direction of the main granitic mass is also men-
tioned by Mr. Marvine—an arrangement noticed in the Black Hills. Fre-
quent mention is made of the gradual passage from the schists to the
granites, of their mutual conformity, and of evidences that seem to prove
their metamorphic origin i situ. These granites do not closely resemble
those of the Black Hills in composition, and they differ moreover by con-
taining many metaliferous fissure veins. Dr. J. J. Stevenson,t who has
examined the granites of the southern part of Colorado, finds nowhere the
very coarse, feldspathic granite described in the Hills, and from their study
is firmly convinced that they are metamorphosed strata.

Notwithstanding the study that has been given to the subject, the
origin of granite is still an unsettled problem. There was a time when
it was universally regarded as an igneous or plutonic rock, being at
every locality either a part of the original crust of the earth formed

* Northwest Wyoming, including Yellowstone Notional Park. Jones, United States Engineers.
1873. Geology by T. B. Comstock. p. 103.

t United States Geological and Geographical Survey of Colorado. Hayden, 1873. p. 1389.

{ United States Geographical Surveys west of the 100th Meridian. Vol. iii, p, 345, et seq.

76 GEOLOGY OF THE BLACK HILLS.

when the surface of the molten globe first cooled, and so indigenous, or
else the result of an extrusion of the still molten interior magma, and so
exotic. Later investigations showed that in some places granite passes by
insensible gradations into gneiss, a rock that is universally recognized as
metamorphic, and left no doubt that some granites are the products of the
metamorphism of sedimentary rocks. A school of geologists at once arose
who maintained that all exotic as well as indigenous granites were the
result of the fusion or partial fusion of ancient sediments, and that the
original crust of the earth and the uncongealed substance of the interior
are not illustrated by the rocks accessible to the geologist. Professor Ram-
sey, an advocate of this view, says:

That in one sense it [granite] is an igneous rock; that is to say, that it has been
completely fused. But in another sense it is a metamorphic rock, partly because it is
impossible in many cases to draw any definite line between gneiss and granite, for
they pass into each other by insensible gradations; and granite occupies the space
that ought to be filled with gneiss, were it not that the gneiss has been entirely fused.
I believe, therefore, that granite and its allies are simply the effect of the extreme of
metamorphism, brought about by great heat with presence of water. In other words,
when the metamorphism has been so great that all traces of the semi-crystalline lami-
nated structure has disappeared, a more perfect crystallization has taken place.*

At the present time it is admitted on all hands that there are certain
granites which are merely highly crystalline gneisses, but there are those
who doubt the metamorphic origin of the exotic or intrusive granites.

It has already been intimated that the granite of the Black Hills is
intrusive, and many of the facts by which its relation is proved have been
narrated in describing its distribution; but the latter will be recapitulated
here, in connection with all others that seem pertinent, for the sake of giving
completeness to the demonstration.

First. The feldspar, amounting to 75 per cent of the granite, could
not have been supplied by a simple metamorphism of the schists, which
are not very generally gneissoid, but more commonly micaceous, and in
general may be said to contain 75 per cent of mica. The maximum ratio
of alkalies in the slates and schists is only about 8 per cent, while in
the granite it is fully 15 per cent.

It may be said, by the way, that the granite is chemically very similar

* Physical Geology and Geography of Great Britain. A.E. Ramsey. p.38,2 ed.

BLACK HILLS GRANITE EXOTIC. hrf

to the volcanic rock in the northern part of the Hills, and may perhaps be
closely related in origin. Only a difference in the conditions of cooling
would be needed to produce from the same magma a granite on the one
case and a feldspathic volcanic rock on the other.

Second. The occurrence of pieces of schist rock inciosed in the mass
of the granite is evidence of a plastic condition of the granite coincident
with a non-plastic condition of the schist.

Third. Each granite mass has a long lenticular shape, and several of
them could sometimes be traced in a series along the same line of bedding.
This is the character which veins following the strata of a pliant rock like
mica schist are most apt to assume. ;

Fourth. The coarseness of the crystallization, the thoroughness of the
separation of the several minerals, and the occasional concentric arrange-
ment of the minerals on a large scale, all indicate a condition of the mass
in which there was great freedom of movement among the particles—a
condition of plasticity if not of perfect fluidity.

Fifth. The transition from the schist to the granite is always sudden;
no graded passage of one rock to the other was anywhere observed.

The problem of the age of the granite occupied our attention from the
time of our first examination, and for a while the weight of evidence led
to a conclusion that is now demonstrably erroneous. The history of the
problem is instructive as an illustration of the danger inherent in negative
evidence.

The granite was intruded between strata of the Archean; therefore
it is younger than those strata. Its fragments were found as pebbles of
the conglomerate at the base of the White River Tertiary; therefore it is
older than that formation. There was no considerable disturbance during
the deposition of the strata from the Potsdam to the Cretaceous, inclusive;
therefore the intrusion did not take place in Paleozoic or Mesozoic time.
The granite is coarsely and completely crystalline; therefore it was cooled
slowly and under pressure, and it could not have been intruded after the
Archzean strata were uplifted and eroded and before they were covered by
the Potsdam. There remain two possible dates or epochs, the first in

78 GEOLOGY OF THE BLACK HILLS.

Archean time before the processes of displacement and erosion had brought
the inclosing schists near to the surface, the second in Tertiary time before
the deposition of the White River beds.

This much could be deduced from the positive data of observation
taken in connection with generally accepted principles; but the next step
was taken on the authority of negative evidence. No granite whatever
was found in the conglomerate at the base of the Potsdam sandstone, and
this although definite search was made at every opportunity. The Potsdam
was found to contain a great quantity of quartzitic pebbles easily referable
to the Archean quartzites and occasional specimens of Archzean schists,
but no granite. This conspicuous absence, coupled with the presence of
granite in the Miocene conglomerate and Quaternary gravels seemed to say
that the granite was not a member of the subjacent rock system when the
Potsdam was laid down and pointed to Post-Cretaceous time as the date of
its introduction.

The conclusion thus reached was opposed by the analogy of other
regions, but it was the logical sequent of the premises if weight was to be
given to the negative element, and it was provisionally entertained. Its
hold was soon weakened, however, when attention was directed to certain
other facts of observation, the importance of which was not at first appre-
ciated. As already described, a locality had been seen where a continuous
sheet of the Potsdam passes from a surface of eroded schists to a surface of
granite. There was found no intrusion of the granite along the parting
between the Potsdam and the schists, and there was found no metamorphism
of the Potsdam at the surface of contact with the granite. In these par-
ticulars the relations of the granite are strongly contrasted with those of
the trachyte of the Hills. Wherever the trachyte appears beneath the
Potsdam the latter is uplifted as though by the insertion of the trachyte
between it and the Archean, and its lowest beds are at the same time
metamorphized as though by the heat of the molten intrusion. The fact
that the granite did not at this locality affect the form and constitution of
the Potsdam strata in a manner similar to the trachyte does not well accord
with the idea that it was introduced under similar conditions: and during
the same geological period.

To the same intent are the mineralogical and textural relations of the

AGE OF GRANITE. 79

two igneous rocks. Their mineralogical difference is not great and their
chemical difference is small, but in texture they are widely contrasted.
- The granite is coarse-grained to a degree that is exceptional even for
granite. The trachyte has a fine and uniform texture, and its crystals are
embedded in a paste. All the analogies of modern petrography lead to the
assumption that the conditions under which the two rocks cooled were very
different. The trachyte must have solidified with some degree of rapidity,
else its paste would not have remained. The granite, in order to have
separated its minerals so completely and in masses of such size, must have
congealed with infinite slowness. But if the granite was injected beneath
the Potsdam in the early part of the Tertiary period just as the trachyte
was injected beneath the Potsdam near the beginning of Tertiary time, the
conditions under which the two were consolidated could not have been
vastly different.

The first conclusion having been unsettled by these considerations, the
question was asked whether it was not possible that peculiar atmospheric
conditions in Potsdam time made granite a more perishable rock than it was
during the Tertiary and Quaternary, and thus prevented the preservation
of its bowlders. An examination was made of the descriptions of the basal
beds of the Potsdam in the Northern States and Canada and in the Rocky
Mountain region, and it was found that while silicious pebbles were every-
where observed as predominant and foliated rocks were occasionally noted,
there was but a single record of granitic pebbles. It was seen that the
absence of feldspathic pebbles, from whatever cause it arose, was not pecu-
liar to the Black Hills locality, and the conclusion based upon this absence
was relinquished.

When, therefore, in a subsequent year a feldspathic pebble was obtained
from the Potsdam its discovery occasioned no surprise, for it merely estab-
lished by positive proof a conclusion already entertained as the result of
indirect but cumulative evidence.

The discovery of granitic débris in the conglomerate at the base of the
fossiliferous rock system fixed the age of the granite as nearly as it is likely
ever to be determined. It not only antedates the Primordial sediments, but
it antedates a great division of Archean time. We must count as Archean

80 GEOLOGY OF THE BLACK HILLS.

not merely the time in which the slates and schists and quartzites were
deposited as clay and sand, but also the time in which they were subjected
to the vast displacement and degradation whereby their truncated edges
were finally prepared to receive the later sediments. The intrusion of the
granite took place before those changes were greatly advanced, and possi-
bly before they were begun, for it occurred in the presence of a heat and
a pressure that could not have existed close to the surface of the earth.

SECTION IV.

THE SILURIAN.
THE POTSDAM SANDSTONE.

The members of the great Silurian system, which form such volumi-
nous chapters in the geological history of the territory east of the Missis-
sippi River, attaining along the Appalachian Mountains a thickness of no
less than 38,000 feet, thin out westward. In the Rocky Mountain region
but few of the groups have been recognized, and those occupy but a very
subordinate position when compared with the other members of the Rocky
Mountain rock series. Of the lower Silurian formations, the Primordial,
Canadian, and Trenton, there is found in the Black Hills only the
Primordial, and of the Primordial no group but the Potsdam, while the
different formations of the Upper Silurian—the Niagara, Salina, Helder-

berg, and Oriskany—are entirely absent. In other portions of the Rocky
Mountains beds have been recognized by different geologists as belonging
to the Canadian, Trenton, and Niagara formations, but they are always
inferior in thickness and extent to the more recent formations.

In a few localities in New Brunswick, Nova Scota, and the Eastern
States a series of fossiliferous beds, known as the Acadian or St. John’s
group, have been found underlying the Potsdam, but the latter is the
first in order of time of the widespread, unchanged, fossiliferous strata of
the American geological column. In the great area it is known to underlie,

in its great persistency, and in the uniformity of its character, the Potsdam

THE POTSDAM. siete

formation is one of the most remarkable features of American geology.
It consists generally of a coarse sandstone, usually reddish in color, and
often containing beds of conglomerate. In certain regions it is shaly, in
a few places it embraces beds of limestone, and in the Far West it often
contains beds of quartzite. Where the underlying Acadian formation is
absent, the Potsdam rests unconformably on the upturned edges of the
Archean. Outcropping in immense beds in northern Wisconsin, it skirts
the Archzean area on the south, and flanking the Canadian and Adirondack
Mountains, it is found in great thickness along the entire line of the Appa-
lachians. Though it is exposed nowhere in the great continental basin
between the Alleghanies and the Rocky Mountains, it has been recognized
by its lithological characters in the deep borings at Columbus, Ohio, and
Saint Louis, Mo., and in central Texas it has been investigated by Dr.
Shumard.

The extension of the Potsdam to the region of the Rocky Mountains
was first recognized by Mr. Meek from the fossils collected and observations
made by Dr. Hayden during Warren’s reconnaissance of the Black Hills.
The formation is there very fossiliferous, containing many of the charac-
teristic genera of the Potsdam as found in the east—Lingula, Lingulepis,
Obolella, and Hyolites, with trilobites, fucoids, etc., and from their study the
existence of the Potsdam in the Far West was first announced by Meek
and Hayden in the Proceedings of the Philadelphia Academy of Natural
Sciences for March, 1858. Since the time of Warren’s reconnaissance the
upturned edges of the Potsdam have been found in many places along the
flanks of the Rocky Mountains, and though for long distances apparently
absent, it is probably in most cases merely concealed by overlapping strata
of more recent date. In no place, however, in its western development has
it been found so abundantly fossiliferous as in the area of the Black Hills.
Commonly in the study of Rocky Mountain geology its presence is recog-
nized only by its lithological character and its stratigraphical relations.

In the Black Hills the Potsdam is the lowest member of the fossilif-
erous series, and in its numerous and excellent exposures its character and
relations were easily determined and studied. It everywhere rests uncon-

formably upon the upturned edges of the underlying Archzean slates and
6BH

82 GEOLOGY OF THE BLACK HILLS

schists, filling up irregularities in their surfaces, and its basal member is
generally formed of coarse materials derived from the erosion of the subja-
cent rocks.

Consisting mainly of coarse and friable sandstones, with conglomerates
easily eroded, it covers superficially very limited areas, and its exposures, if
unexaggerated, would be represented on a geological
map by a line rather than by a belt or zone. The
cliffs or bluffs of greater or less prominence that have
already been noticed as surrounding the Archean

area of the Hills on all sides like a wall, and which

NUE: SVCD 5)
Fic. 9.—Section on Spring are broken through here and there by the draining
Creek, showing uncontorm- ne
ity of the Potsdam sand- streams as they escape through narrow cafions, are
stones and underlying

schists. composed of Carboniferous rocks, and at their base,
1. Coarse Potsdam sandstone P i
and conglomerate. between them and the metamorphic slates and schists,

5
a]

2. Schistose rocks, a. Joint- i
ing plane in the schists. lies the Potsdam sandstone. The Potsdam often out-

crops in a bluff or in a series of steps of sandstone with intervening slopes,
but generally the entire exposure is concealed under a talus composed of
the débris of the Carboniferous limestone and of the Potsdam itself. In
many places, however, clean and good sections are presented, especially
in the walls of the canons. Occasionally, near the cliff of fossiliferous rocks,
isolated buttes or hills of Carboniferous limestone, with the underlying
Potsdam, have been left by denudation in the midst of the Archean; but
on account of the friable and easily eroded character of the Potsdam, out-
liers of that formation alone are not frequent. In the northern part of the
Hills, however, in the region north and northeast of Custer Peak, large areas
of the Potsdam are exposed.

West, northwest, and north of Terry Peak, in the wilderness of deep
and intricate canons traversed by the headwaters of Spearfish, and Red-
water Creeks and their branches, many of the cations cut down through the
Carboniferous into the Potsdam, and a few go still deeper, penetrating the
schists beneath. The Potsdam has been examined in several of these canons,
and found to preserve its usual character and its usual relations to the asso-
ciated rocks, but it was not thoroughly studied and no attempt has been
made to map its sinuous outcrop.

DISTRIBUTION OF POTSDAM. 83

Wherever the formation is exposed around the margin of the Archean
area it is found to dip outward from the axial area of the Hills. On the
western side the Potsdam underlying the broad plateau or table-land of
Carboniferous limestone shows little dip along its outcrop, but along the
western margin of the plateau the dip of the overlying and conforming
limestone is away from the axis of the Hills or toward the west. In the
southern, eastern, and western parts of the Hills the dip of the fossiliferous
strata is always well marked, varying from 10° to 25° or 30° from the hori-
zontal. But while the dip of the Potsdam may vary from point to point, it
sustains always the same relation to the underlying slates and schists and to
the overlying Carboniferous series. It ever rests unconformably upon the
former, and it is found always to be entirely and perfectly conformable with
the latter. |

The representatives of these two great systems, Silurian and Carbonif-
erous, which in other parts of our country are separated by many thousands
of feet of deposits, recording zeons of time, are thus found in the Black Hills
in direct and conformable contact.

Around Crow Peak, where the strata have been turned up at a high
angle by the extrusion of the trachyte which composes the mass of the peak,
the Potsdam stands nearly vertical against the mass of volcanic rock, and
has been transformed by the latter into a hard white quartzite. The lime-
stone of the Carboniferous rests conformably against it. In a similar rela-
tion the upturned edges of the Potsdam are found about the volcanic uplift
six miles northeast of Inyan Kara.

Warren Peaks, the prominent points of the Bear Lodge range, consist
of trachytic rocks, and the volcanic force by which they were ejected has
tilted and exposed the various members of the fossiliferous series with the
Potsdam sandstone at their base. The Potsdam is here in many instances
highly metamorphosed, but bears the same stratigraphical relations to the
accompanying rocks.

By a reference to the geological map accompanying this report the
exposures of the Potsdam sandstone will be seen to form a very narrow
band surrounding the Archzean area, and even this is somewhat exaggerated
in width so that the formation may be distinctly represented. Near Terry

84 GEOLOGY OF THE BLACK HILLS.

Peak it forms the surface of a considerable territory, but in other portions
of the Hills it is generally but an outcroping stratum in the face of a cliff
or slope.

Though essentially a sandstone formation it has some variety of com-
position. Usually it carries a conglomerate at the base, but this is some-
times exchanged for a dense quartzite, and in many places there are inter-
stratified beds of quartzite. In a few localities the formation is quite cal-
careous, and in a greater number it contains peculiar greensand deposits.
Its thickness is quite uniform, ranging generally from 200 to 250 feet, but
attaining to 300 feet on the north branch of Redwater Creek.

The basal conglomerate varies in character and thickness in different
parts of the Hills and even within short distances, but is everywhere a well-
rounded shore deposit. Even where it is replaced by quartzite the latter
was determined to contain quartz pebbles. The pebbles and bowlders
forming the conglomerate were examined with minute care, and were found
in all cases to consist of the harder varieties of the rocks composing the
metamorphic series—quartz, the hard blue and gray quartzites, and some
of the harder slates and schists. The latter usually occur as flattened peb-
bles similar to those found in the present streams. The banded or jaspery
quartz, ribbon quartz, ferruginous quartz, etc., of the characters mentioned
in the previous sections, were also found, together with a few feldspathic
pebbles from the granite. In the upper portions of the main conglomerate
and in the occasional fine conglomerates occurring in the body of the forma-
tion the constituent pebbles are almost entirely of quartz.

The discovery of gold in the Potsdam was not made until after the
completion of our field work, nor indeed until after the major part of this
chapter was penned, and I am still unable to give the particulars of its occur-
rence. ‘There is no need, however, to substantiate the announcement of that
which is inherently so probable. ‘The currents that spread the Potsdam sedi-
ments worked over the débris of the veins of the Archean, sorting coarse from
fine and heavy from light, and it might have been anticipated from the
outset (if only the.idea had suggested itself) that they would prove to have
concentrated the gold which then as now was scattered through the ancient
quartzes.

BASAL CONGLOMERATES. 85

Sometimes the bowlders or cobblestones forming the conglomerate are

of considerable size, from one to four feet in diameter.

One of the best

exposures of this character was seen in the canon of lower Rapid Creek,

and is illustrated in the annexed illustration.

The large bowlders shown at the base of the section are perfectly water-

rounded and form a broad talus extending to the bed of the creek. They

Tia. 10.—Section cf the Pots-
dam sandstone on lower
Rapid Creek, showing the
bowlders at its base and
its unconformity with the
underlying schists. Total
thickness, 300 feet.

1. Massive gray limestone
(Carboniferous).

. Thin bedded impure lime-
stone (Carboniferous).

. Reddish sandstone (Pots-
dam).

. Concealed.

. Coarse reddish sandstone
(Potsdam).

. Loose bowlders (Potsdam).

. Schists (Archean).

be hor) Oe ww vo

appear to have had no cementing material, but lie as
loosely as if they had been dumped from a cart.
This is apparently but a local accumulation; at a
short distance on either side no bowlders are visi-
ble, though the underlying slates are still exposed
to view.

A similar heavy,conglomerate formation is found
in many other parts of the Hills, as, for instance, on
the headwaters of Box Elder Creek, where a bowlder
or cobblestone conglomerate with fragments two feet
or more in diameter, rests upon the upturned edges
of the Archean quartzites and slates.

In some places a conglomerate is found above
the base of the formation, in which the pebbles seem
to have been formed from previously existing portions
of the sandstone. A good example may be seen near
the eastern base of Terry Peak. Near Terry Peak
also Potsdam conglomerate was found so thoroughly
metamorphosed that a fracture could be made as
easily across the quartz pebbles and bowlders as in
any other direction, the silicious cement being changed
into quartzite as hard as the quartz pebbles themselves.

The cementing material of the conglomerate is generally silex, and this

is reinforced by the oxide of iron.

Carbonate of lime also has been found

in many localities, and in such cases the interstices are more perfectly filled

and the conglomerate is more compact.

tains the remains of fossils and grains of glauconite.

The calcareous cement often con-
As has been observed,

86 GEOLOGY OF THE BLACK HILLS.

the coarser conglomerates are sometimes scarcely cemented at all, but are
loose aggregations of water-worn fragments.

A description of the character of the Potsdam sandstones of the Black
Hills could be made in almost the same words that have been employed by
various observers in describing the Potsdani in the eastern part of the
United States and in the Rocky Mountains. Thus Professor Emmons
describes the Potsdam of northern New York as of two varieties:

Ist. An even bedded and somewhat porous rock, at many places a distinct white
friable sandstone; in others it is a yellowish-brown sandstone, the particles of which
are compacted together so as to form a firm even-grained mass. 2d. A close-grained,
sharp-edged mass, * * * so closely wedged together that it is with difficulty
quarried. It is in fact a hard quartz rock [a quartzite] scarcely passing for a sand-
stone.*

And again, Professor Whitney, in the Report of the Geological Survey
of Wisconsin, says:

As developed in the northwest and especially in the State of Wisconsin, where it
occupies a large extent of surface, it is made up of an almost chemically pure silicious
sand in minute grains hardly larger than a pin’s head, which are held together by the
minutest possible quantity of calcareous or ferruginous cement. Frequently even this
small quantity of cementing material is wanting, so that the rock can be readily crum-
bled between the fingers like crystallized granular sugar. Where the ferruginous
material, which is the peroxide of iron, becomes more abundant, so as to form two or
three per cent. of the mass, the sandstone acquires a dark brown color * * *.t+

Professor Comstock in the Wind River Mountains finds the Potsdam
to bea “succession of beds of loosely granular almost friable sandstone,
varying in color from red or brown below to white above; in texture, from a
merely loose aggregation of the silicious particles to fairly compact sand-
stone.”{ The wonderful uniformity of the Potsdam will be seen by com-
paring these descriptions with the following.

In the Black Hills the Potsdam formation is a coarse-grained, loosely
granular, often saccharoidal sandstone, composed of small grains of quartz,
more or less rounded, ranging up to the size of a pin-head or small grain

of rice. Sometimes it contains also small scales of mica and grains of the

*Natural History of New York. Geology. Emmons. p. 102.
+ Geological Survey of Wisconsin, 1862. Vol. 1, p. 141.
{ Reconnaissance of Northwest Wyoming, etc. W. A. Jones, United States Engineers. p. 107.

WIDE-SPREAD UNIFORMITY. 87

harder metamorphic rocks, but it generally consists wholly of quartz grains
In texture it varies from an almost incoherent mass of silicious grains,
crumbling on exposure to the weather and easily crushed in the hand, to a
tolerably dense and compact sandstone, which in weathering forms cliffs.
Sometimes it passes almost into a quartzite, the silicious grains being
bedded in a bright glassy silicious cement. The most friable varieties are

at a: light in color and have usually a silicious cement,
x] while the red or brown colored, in which the cement-
ing material is largely oxide of iron, are usually more
compact and durable. It is in places somewhat argil-

[Jat

laceous, and has there a shaly character.

Its color is also quite diverse, varying from a dark
reddish brown, like that of the Triassic red sandstone
of the Atlantic coast, to a light brown and in places a
pure white. The white variety is usually coarse and
saccharoidal; it is found near the top of the forma-
tion, and is well exposed in the northern part of the

Hills on Bear Butte Creek and around Warren
Peaks.

Though the sandstones are coarse in texture they

Par) i

1 os carry in many places abundant remains of fossil forms

in a most excellent state of preservation, and the col-
Fig. 11.—Section of the z : A A : 2
Potsdam on lower Spring lections made in the Black Hills rival in richness and
Creek, with basal por- , f r
tions of the Carboniferous. in the perfection of the specimens the collections from
better known and more thoroughly studied localities of the formation.
Complete sections of the group from base to summit are rarely met
with, both because of its concealment by the broken fragments and talus
of the Carboniferous above, and by reason of the soft and destructible
character of its own beds. In the eastern cation of Spring Creek, however,
a most excellent section is exposed and was carefully measured by Mr.
Jenney. It is illustrated by Figure 11, in which the junction of the Pots-
dam with the Carboniferous and with the slates is also well exhibited.

88 GEOLOGY OF THE BLACK HILLS.

The strata exposed are as follows:
Archean.
Feet.
1. Argillaceous slates, dipping 60° west .-.... ucniot Basel Uaite sate meat the aie Wat eye on ape

Potsdam.

2. Brownish yellow conglomerate, with quartz pebbles, resting unconformably on
1 and dipping.25° northeast (2b ac2 se cece erosion eo eee 25

3. Reddish brown sandstone, thinly bedded at base, and alternating with soft

shaly sandstones, containing large fucoids, Lingulepis, and fragments of

toilobites:...4. ae: aoe ET Ee, BC PA ern bs Sere en aE UM Te 200
Carboniferous.
4. Reddish brown or pinkish, calcareous sandstone, thinly bedded, containing
Spirifera camerata, eyathophylloid corals and crinoid columns .....-.-.-.-- 20
5. Limestone; Spirtfera camerata, Productus, ete ..2-.222522222--.--2--2) 2-22 335

The sandstones are often riddled with small holes perpendicular to
the bedding, one to three or more inches long and about one-eighth of an
inch in diameter, often with rounded terminations. These are especially
characteristic of the white sandstones and occur more frequently in the
upper beds of the formation. Often they are so numerous that a section
of the rocks resembles a piece of perforated card-board. They have been
described by Professor Hall* under the name of Scolithus linearis, and were
long thought to be the casts of a sea-weed. They are now generally con-
sidered the casts of worm borings, and though this explanation is more
acceptable, there is still room to doubt its sufficiency. It has been sug-
gested that they may be the peduncles of brachiopods (Lingula, etc.) or the
borings of the same.

One of the most interesting points in the lithological structure of the
Potsdam is the occurrence of beds of quartzite both at its base and inter-
stratified with its sandstones. Near Warren Peaks, Crow Peak, and
Terry Peak quartzites have been formed from sandstones by the direct
metamorphic action of the volcanic outbursts, and in other portions of
the Hills, particularly in the southern end of the Archean area, there are
quartzites at the base of the formation which may possibly be the result
of metamorphism accompanying the uplift of the Hills. But in many

* Paleontology of New York. Vol. 1, p. 2.

BASAL QUARTZITES. 89

places throughout the Hills beds of hard, compact quartzite are found
interstratified with the ordinary soft sandstones. Some of these localities
are far removed from any evident locus of igneous action, and indeed the
change of particular strata into quartzite while the overlying and under-
lying beds of sandstone are unaffected is an occurrence which can scarcely
be explained upon an igneous theory.

Near the headwaters of Red Canon Creek in the southwestern corner
of the Hills, the Potsdam with its usual soft sandstone character is under-
laid by a bed of quartzite which rests upon the upturned mica schists.
This is a hard, fine-grained, compact quartzite with a glassy fracture, and
is seemingly composed of small grains of quartz sand, cemented by a
glassy quartzose cement into a dense rock. It has a lamellar structure and
breaks with some readiness parallel to the bedding. The color is a deep
brownish or purplish red slightly tinted with green. The entire mass is
filled with fossil remains of Lingula, Lingulepis, Obolella, ete., in a beautiful
state of preservation, altogether yielding the finest collection of fossils
obtained from the Potsdam in the Hills. A similar purplish quartzite was
found on the headwaters of Amphibious Creek, and on the same creek near
the beginning of the limestone canon a heavy bed of grayish quartzite rests
unconformably upon the schists and underlies strata of the usual coarse
sandstone. On Burntwood Creek, on French Creek, and north of Battle
Creek similar quartzites occupy a similar position. So hard and dense
is this rock that it sometimes caps the schists over considerable spaces
where the overlying more friable materials have been entirely removed.
This is particularly well seen on lower Burntwood Creek. On some of
the small streams north of Battle Creek it attains a thickness of about 50
feet. On Burntwood Creek it is not over 15 or 25 feet thick, and on
Amphibious Creek, where it covers several adjoining hills with its hard
and slippery fragments, it has a thickness of fully 50 feet. At these
localities it closely simulates the quartzite of the schists and slates, but it
is usually coarser in texture, betraying on close inspection the sand grains
of which it is composed. Sometimes it is found to contain considerable
portions of fine mica particles, but nowhere were any fossils seen in it. Its

90 GEOLOGY OF THE BLACK HILLS.

color is grayish or sometimes reddish. It is not a persistent stratum, but is
devoloped only in the southern and southeastern parts of the Hills.
The relation of the quartzite in the canon of French
Creek to the other members of the Potsdam and to the
- underlying rocks is shown in Figure 12, where the fol-
lowing strata are exposed.

Carboniferous.
7. White limestone.
6. Impure, pink, shaly and arenaceous limestone with Grnordel
stems.
Potsdam.

>)

. Fine, shaly, calcareous, reddish sandstone, containing green
glauconitic particles and some mica.
4, Yellowish or grayish quartzite, preserving somewhat the lines

FG. 12.—Section of Pots- of stratification but with cracks or fractures perpendicular
dam sandstone on theret
lower French Creek, eTevo- ; . i :
with underlying Arch- 3, Coarse yellowish and red sandstone with Potsdam fossils;

man Tocks: slickensided in places.
2. Hard yellowish quartzite, with quartz pebbles. Has a vertical cleavage. Dip 2°
to 5° east.

Archean.

1. Coarse, red, feldspathic granite, at top very much decomposed and changed into a
soft clay, almost like a fluccan; associated in other places near the creek with
schists, hornblende rock, quartzites, etc., dipping to the southeast at a high angle.
At various places in the Rocky Mountains quartzites are found to oc-

cupy persistently a similar relation to the Archzean, and have been referred

by various observers to the Potsdam formation. Thus on the mountain
ranges of the Gallatin and Madison forks of the Missouri and elsewhere
in the region of Yellowstone Lake, the Teton Range, and the Shoshone

Mountains, quartzites lie unconformably on the metamorphic rocks, and

are referred by Hayden, Peale, and Bradley to the Potsdam.*

They are found also in the Bighorn and in the Wind River Mountains,
where Comstock describes a thick formation of compact red sandstone,
and refers it to the Potsdam.t

The Wasatch Mountains exhibit a great thickness of quartzite—1,500

*Geological Survey of the Territories, 1872. pp. 25, 63, 163, etc.
t Northwest Wyoming and Yellowstone National Park. Jones, 1873, p, 107.

INTERBEDDED QUARTZITES. 91

feet—resting unconformably on the Archean, and underlying Silurian and

Carboniferous limestones; and this is considered by King, Hayden, and

| MAI Wm

Fic. 13—Section of the Pots-

dam on Box Elder Creek.

. Slates inclined at a high
angle.

. Coarse sandstone and

gravel conglomerate.

. Broad talus, no exposure.

. Cliff of coarse red sand-

stone with interstrati-
fied layers of dense,hard,
deep red or purplish
quartzite.

5. Talus with fragments of
the shaly impure lime-
stone of the Carbonifer-
ous.

6. Carboniferous limestone.

Pw WwW

Bradley to be Potsdam,* though no fossils are found
init. The Rocky Mountains of Colorado also con-
tain in many places similar quartzites with the same
relation to the older rocks. Peale has studied them
in the Park range, and besides the basal quartzites
here alluded to finds other beds intercalated with the
sandstones he regards.as Potsdam. In a continua-
tion of the Organ Mountains, near El Paso, Tex.,
Jenneyt found a quartzite 25 feet in thickness, rest-
ing upon the granite and overlaid by beds of Potsdam
well characterized by fossils.

These citations suffice to show the wide-spread
development in the Rocky Mountains of quartzites
at the base of the Paleozoic system, and the una-
nimity with which they have been referred by the
best authorities to the Potsdam sufficiently warrants
the same reference of the basal quartzites in the
southern part of the Hills.

The quartzites found in the body of the forma-
tion differ somewhat in their character from those just
described. They were best observed and studied on
Box Elder Creek in the section illustrated by Fig-
ure 13.

- On the same creek, some eight miles farther west,
a cliff of red sandstone 30 feet in height at the
top of the formation contains six or eight strata of
hard, purplish, glassy quartzite from 6 inches to 1 foot
in thickness.

Intercalated quartzites are also seen on French Creek where the color
is yellowish brown, and the rock seems to be little more than a fine quartz

* Mining Industry, 40th Parallel Survey. King. Chap. vi. Geological Survey of the Territories,
1871. Hayden; p. 15; Ibid., 1872. Bradley. p. 194.
t American Journal of Science. 3d series, vi, 1874, p. 25,

9? GEOLOGY OF THE BEACK HILLS.

sandstone in which the grains are bound together by a clear, glassy,
quartzose cement. They occur also at other localities, but they were best
studied on Box Elder Creek.

Their variations in color are the same as those of the normal sand-
stones of the formation. Their texture at a first glance seems very like the
quartzites of the metamorphic rocks, but a closer examination reveals the
same differences which distinguish the basal quartzites of the formation
from the Archzan. The quartzites of the slates and schists have a very
glassy and uniform fracture, and their texture is homogeneous, resembling
that of quartz. The Potsdam quartzites on the other hand are found by
close examination to consist of an aggregation of small quartz grains, com-
pacted together by a glassy quartzose cement, which at the same time masks
their minute structure. The grains of quartz are generally clear and trans-
parent even in the darker colored varieties, rounded like water-worn sand,
and often brilliantly lustrous like hyalite. In some instances the quartzite
weathers into a coarse sandstone, readily crumbling, from which the sili-
cious cement seems to have been removed by solution. The basal quartz-
ites are usually more compact and durable, but even the quartzite formed
at Crow Peak by the direct metamorphic influence of the heated volcanic
ejection is found to decompose in a similar manner into a coarse sandstone.

An account of the minute structure of the quartzites will be found in
Mr. Caswell’s report. Specimens obtained from the Potsdam are indicated
by the following numbers: 38, 169, 200, 201, 204, 205, 206, 207, 208, 209,
ZLOS and 21

Quartzites similarly interstratified in the Potsdam have been noticed
in many places in the Rocky Mountains, but no theory has, I think, as yet
been propounded for their formation. If only the basal member of the
series assumed this character it would be easy to suppose that there was
some metamorphic action proceeding from below—either an igneous action
connected with the orographic movements by which usually the Potsdam
is brought to light, or else a chemical interchange between the schists and
the sandstones, whereby a silicious cement was supplied to the latter. But
no such explanation will apply to the interstratified quartzites. If we sup-
pose them to have been formed by igneous induration, even accompanied

ORIGIN OF POTSDAM QUARTZITES. 93

by heated waters, the unchanged condition of the intermediate and adjacent
sandstones cannot be accounted for, and the uniformity of the quartzites in
thickness and their marked separation from the associated common sand-
stone are equally difficult to understand. The quartzitic layers are some-
times separated by over one hundred feet of unchanged sandstone from the
underlying schists, while even the basal conglomerate has not been meta-
morphosed in the least particular. In sections of the Potsdam, also, where
the relations to the underlying schists are the same, and where there is no
evidence of greater elevatory or igneous action in the one case than in the
other, the sandstones of one exposure will contain numerous beds of
quartzite and those of another none. Evidently some other explanation is
required, and it appears to me that the true one must involve some peculi-
arity of the original deposition of the strata.

It is well known that many sandstones contain a considerable percent-
age of silica in soluble condition, which on exposure becomes insoluble and
hardens them. Such sandstones when first taken from the quarry may be
cut with ease but become harder on lengthened exposure and are then
worked with much more difficulty. Again, scattered over the country
from Maine to Georgia and westward to Nevada, are found numerous
deposits of infusorial earth (composed largely of the silicious shields of
diatoms) which contain from 2 to 75 per cent of silica in a form readily
soluble in alkalies. The flint found so often in large beds in the Coal
Measures and in masses in other formations often contains fossil diatoms
composed of a soluble form of silica. Besides this, the numerous silicious
deposits of springs on the Arkansas, the Yellowstone, etc., prove that silica
in a soluble state is not an unfrequent ingredient in rocks, nor unusual as a
present natural product. We know, too, that certain acids will throw down
dissolved silica in a gelatinous state, that certain alkalies will precipitate it
in the form of insoluble silicates, and that in the case of quarried sandstone
soluble silica is rendered insoluble by simple exposure to the atmosphere.
May not these quartzites, therefore, be the product of the cementation of
sands by the simple action of waters holding silica in solution, by the
admixture of the silicious portions of organisms, or in a manner similar

94 GEOLOGY OF THE BLACK HILLS.

to the formation of flint, at the time of their deposition as sandstone—the silica
becoming afterwards insoluble?

In many places the Potsdam sandstone is found to contain calcareous
matter and also accumulations of glauconitic grains.
The calcareous condition of the conglomerate at the
base of the formation was frequently noticed and .has
already been mentioned. It is not peculiar to any hori-
zon in the sandstones and does not persist for great
distances, but seems to be a merely local variation or
accident. It was observed to a slight extent on French
Creek, but is more marked on lower Rapid Creek and
on the headwaters of Box Elder Creek.

Figure 14 gives a section of the Potsdam in the
canon of lower Rapid Creek, where this calcareous na-
ture is better exhibited than in any other place. It
exhibits the following beds:

Archean.

F Feot.

1. Argillaceous slates in the bed of the creek; strike, N.

ISD Yo Oly, WEIN, So0 ase coc toeetoses saeend oe

Potsdam.

2. Massive yellow and reddish sandstone, highly cal-
careous, dipping N. H. 20°.--....-...-.-.--...--- 50

3. Impure shaly limestone with some clay shale, yel-
IWMI POMOC Ns <5 6b5q b466d0 GonsescbusoSesas 20

j} 4. Red and brown shale with some thin strata of lime-
; 2 Aas sf stone and large quantities of glauconite....-..----- 80

si. ‘ aes ; Rapid 5. Red and pink impure shaly limestone with green glau-

Creek. conite grains; sandy at bottom.......--.------.-- 50
6. Reddish caleareous sandstone with glauconite .. .. -.-----.---- Hest ees 4

7. Red and yellow sandstone with bright quartz grains, cross-stratified, and
containing at base considerable calcareous matter..... .-.-+--.-------- 70

Carboniferous.

8. Pink shaly limestone, gray at top .--.--.--. -----------+erese rere eee 40

9. Pinkish and yellowish limestone, thin-bedded, containing a few Carbonifer-
ous corals and brachiopod fragments...--. .----------- see eee seers 35
80

10. Gray limestone, stained at base with iron...-.--.+--- --+-+- cesses eeeeeee

GLAUCONITE IN THE POTSDAM. 95

The many peculiar features in the structure and variation of the Pots-
dam and its abundant fossils scarcely exceed in interest the discovery of
its abundant greensand or glauconite grains. In almost every exposure
of the sandstone where careful examinations were made the grains were
found, and in some places they exist in such quantities as to give a green
color to the rock. Though their presence is evidently a persistent feature
of the formation, the reader who may wish to repeat our observations is
referred especially to Castle Creek, to lower French Creek, and to the lower
cation of Rapid Creek. Usually the same portions of the sandstone
are both glauconitic and calcareous, but the association is not invariable.
Ordinarily the glauconitic sandstone is merely speckled with the green
grains, but in some localities the glauconite composes the larger mass of the
rock. The calcareous matter is often not evident until revealed by the touch
of an acid. When the glauconitic sand-rock is treated with acids the lime
matter is dissolved, and the rock readily crumbles into loose grains of sand
and glauconite. The glauconitic grains are rarely over one-tenth of an
inch in their larger diameters, and the majority are not more than half that
size, and from this they range to almost microscopic sand. They are almost
always flattened, and under a low-power magnifying glass appear as disks
or flat flakes of irregular shape, round, oval, reniform, etc., but always
smooth and nicely rounded as though water-worn. Their color is a dark
olive green, sometimes nearly black, and when crushed the powder has a
bright olive-green color. Their hardness is between 4 and 5 of the scale.
Under a microscope of low power they appear perfectly regular in outline,
their surfaces smooth but somewhat pitted, and their color dark olive green,
but over the edges the green color is lighter. They are oqaque except on
very thin edges, and there translucent or semi-translucent. They are only
slightly acted upon by strong hydrochloric acid. Before the blow-pipe
they fuse to a biack magnetic mass, and in salt of phosphoric lead dis-
solve with difficulty, leaving skeletons of silica and giving in the bead the
usual iron reaction. In these blow-pipe characters they resemble perfectly
the greensand grains from the Cretaceous of New Jersey. ‘The latter,
however, are not so hard, and are less smooth and rounded, having botry-
oidal forms as though concretionary in character.

96 GEOLOGY OF THE BLACK HILLS.

Glauconite or greensand is a hydrous silicate of protoxide of iron
and potash, with a variable amount of alumina, but ‘“‘the material is
mostly, if not always, a mixture, and consequently varies much in com-
position.”*

The following analyses will indicate the composition of the min-
eral: Lis from the Greensand of New Jersey; 2 from the Lower Silu-
rian of the Island of Orleans, Canada; and 3 from the Potsdam of the
Black Hills. The first two are by Dr. T. S. Hunt, the last by Dr. P. de P.
Ricketts.

: 1 2 3

Si Cas 2 es J Sea Manes ves soe kote Se So cet wee ts Sere pw aeeeme er 50.70 50.70 54.10
ATTN) 2a se Nee te Secs Sre eee are eign etsy ste ne eee as 8.03 19.80 10.92
Tron ProtOxide sy eee ote) Se Ne ete es cee ae ee Sera 22.50 5.60 22.98
Potash. a9. ee etre at ie pab ee cle crete nortan. a te) 8.20 6.75
Mao NeSiaiasivee <cisicte a sisi Giese een oe ee en ee eee 2.16 3.70 0.82
) Uy 10: eae ea iaet een eee eer TE te MPCs amas Cinta MemS ohn natal 1.36
Sodacs yew vaca ce are A ARES os aay le ed ater tte tete e 0.75 0.50 3.02
Weatere oi eb aaa eis ECR Pee RR ER ree 8.95 8.50 0.04

100.00 100.00 99.99

Greensand has been particularly observed in the Cretaceous, and cer-
tain beds of the formation sometimes contain 70 to 90 per cent. This
feature of the Cretaceous is so persistent, that it has caused the application
of the name ‘‘Greensand” to certain groups of strata. Such strata are
widely recognized in Europe, and in the United States are well developed
in New Jersey, Alabama, and Massachusetts (Gay Head). The mineral
abounds also in the Tertiary rocks, is recognized in various members of
the Silurian system in this country and Europe, and has been found by
Bailey filling the recent shells of Polythalmia (foraminifera) from deep-sea
soundings on the Atlantic coast.t

In the Potsdam of the Rocky Mountains greensand has been found by
Dr. A. C. Pealet in the middle canon of the Madison River; and Dr.

Hayden,§ near the mouth of the Gallatin, finds in the Potsdam “layers of

* System of Mineralogy. Dana. p. 462.

+t American Journal of Science. 2, xxiv, p. 281.

{ Geological Survey of the Territories, 1872. p. 160.
§ Ibid., p. 72.

ORIGIN OF GLAUCONITE. 97

greenish sand and clay with shells and trilobites,” but no particular notice is
made of the occurrence.

Professor Hall* found in the Potsdam of Wisconsin, especially near
the base of the formation, ‘‘extensive beds of a bright green-colored sand,”
and observes ‘‘that the most strongly colored portions contain few or no
fossil remains.” Professor Hall also recognized similar green material in
collections from Texas. |

In Canada the rocks of the Quebec group (Lower Silurian) are in
some localities characterized by grains of a soft green mineral which
closely resembles the more recent glauconites, and analyses and descriptions
of glauconite from more recent formations in America are given at length
by Dr. Hunt in the Report of the Canadian Geological Survey.t

In the lower magnesian limestone (Canadian) of Minnesota, Dr. Owent
describes layers of a green mineral called by him a silicate of iron, an
analysis of which shows its resemblance to recent greensand.

The material is so abundant in many of the geological formations that
it is a matter of surprise that its source was for a long time unknown,
and its mode of formation is still in doubt. To the great microscopist,
Ehrenberg, belongs the credit of discovering that the grains of greensand
are the casts of foraminifera. This he announced from an examination
of the greensand matrix adhering to a bone of Zeuglodon from Alabama,
and (in the Monatsbericht, Berlin, February, 1855) he states that ‘‘ereen-
sand, in all the numerous relations in which I have as yet examined it, has
been recognized as due to the filling up of organic cells.” These observa-
tions were repeated by Professor Bailey, who examined also Cretaceous
ereensand from different parts of the United States, and he arrived at the
same conclusions as Khrenberg. Bailey also, in studying specimens of
deep-sea soundings from the Atlantic coast in which “black sand, probably
ereensand,” was found with globigerina ooze, states: §

That not only is greensand present at the above locality, but at many others, both
in the Guif Stream and Gulf of Mexico, and that this greensand is often in the form

* Geological Survey of Wisconsin. James Hall. Vol. 1,p. 16.
+t Geology of Canada, 1863. p. 488.
{Geological Survey cf Wisconsin, Iowa, and Minnesota. D. D. Owen. p. 60.
§ On the origin of greensand and its formation in the oceans of the present epoch. T. W. Bailey.
American Journal of Science. 2, xxii, p. 280.
7BH

98 GEOLOGY OF THE BLACK HILLS.

of well developed casts of Polythalmia, minute mollusks, and branching tubuli, and
that the same variety of the petrifying material is found as in fossil casts, some being
well defined greensand, others reddish, brownish, or almost white.

Bailey was the first to announce that other forms beside the Polythal-
mia produce greensand. Principal Dawson* calls attention to the fact that
glauconite is akin to materials found filling the pores of Pre-Silurian fossils,
such as the serpentine in the cells of the Eozoon of the Laurentian
formation.

As to the origin of the greensand our knowledge is still deficient.
Whether it is a compound secreted or formed by animal interposition, or
whether it is a fossilizing mineral deposited by a purely chemical process
we have no facts at present to determine.

To complete the observations on the formation, the line of its outcrop
around the margin of the Archzean area will be rapidly passed over, begin-
ning at Castle Creek where it was first seen and noting its appearance at
the points where it was particularly studied. The Carboniferous limestone
plateau which borders the slates on the west has been cut into by the
numerous valleys of the creeks draining eastward, and each valley is a
canon with natural geological sections in its walls. The lower portions of
the Carboniferous stand in cliffs and beneath them are imperfect exposures
of the Potsdam and the schists. The last increase in prominence as we go
eastward down the streams until beyond the serrated and broken edge of
the plateau they alone are exposed.

The limestone always forms bold bluffs 100 or 200 feet in height, and
sometimes stands in isolated buttes or peaks some distance in front of its
main escarpment. From the base of the limestone cliff a broad and gentle
slope descends toward the valleys, and the Potsdam, from its soft and friable
nature, is generally concealed under a grassy slope or covered by limestone
débris, so that cliffs or exposures of the sandstone are not common and a
complete and good outcrop of the Potsdam is but seldom seen.

On Castle Creek the limestone lines both sides of the valley for eight
miles or more in castellated bluffs, standing with their summits 500 or 600
feet above the stream. Though the valley in its lower part is deeply cut in

* The story of the Earth and Man. J. W. Dawson, 1873, p. 229.

THE POTSDAM IN DETAIL 99

the schists, but few and very imperfect exposures were seen of the Potsdam,
which was usually found on the slopes only in fragments or in narrow and
broken outcrops. Near the junction of Castle and Slate Creeks, however,
the base of the formation was seen to be composed of 75 feet of coarse
sandstone, its lower part being a coarse conglomerate of quartz pebbles,
while above it for 200 feet fragments of coarse yellow or brown sandstone,
sometimes calcareous and containing grains of glauconite, were seen scat-
tered over the slope. These are succeeded by small outcrops of the shaly
lower member of the Carboniferous, with crinoidal fragments, Productus,
etc., and then comes the Carboniferous limestone, forming a cliff of 150
feet, the rampart of the valley. The metamorphic rocks, here cut to a
depth of 150 feet by the creek, consist of micaceous, talcose, and chloritic
schists, dipping 80° to 85° west, with a strike nearly northwest and south-
east, while the sedimentary rocks above appear to be almost horizontal.

A few miles south of this point on Slate Creek the following section
was observed by Mr. Jenney:

Carboniferous.
Feet.
8. White, pinkish, and grayish silicious limestone, with Spirifera camerata, Pro-
UWUGUE, GQWSacksbe sosee cobhasdsbocs 665550 be oe ee ood os Se eee eee eae oases 100
7. White compact limestone, containing the same fossils.................----- 100
6. Unexposed slope............ EOE SS Pere SU aes ae Reid E Sey ajaaiowichavete Saicts 250
Potsdam.
5. Soft brown sandstone containing abundant fossils, Lingulepis, Obolella and trilo-
PRICE ELON CLG oe rey PON sino pais iate ee ats Staion (2 caey yc tele cialis Sig aPELN on c nc aimee 50
4. Coarse grained, brownish yellow sandstone, with small quartz pebbles, merg-
SARE GORE CO Reo Maree reat eer ee ste see a Ste ere ay sie ores 3a IS aaa ja gi wis eect ate 50
3. Conglomerate of quartz bowlders and pebbles, cemented by sand and oxide of
SEO TRE WHG ES OTAGO VILINO sere rae re ee arate ie Cent afe ie Bese eisiete Ciseiele bss ase 50
ZUMEXPOSCU> SIOPE 22s ose tine sions eae BEM Mayne ant Nate oi Pras oii oh ier el bie ore oie 35
Archean.

1. Chloritic, talcose, and mica schists; dip, 55° west; strike, north to northwest.

Some five miles southeast from this section a rounded peak, which is
locally a prominent landmark, was found to contain a small but very fossil-

100 GEOLOGY OF THE BLACK HILLS.

iferous outcrop of the Potsdam, and to expose imperfectly the following
strata:

(3) Shaly limestone, 15 feet in thickness, and full of fragments of
erinoidal columns.

(2) Talus of 135 feet with imperfect outcrops of strata of red sandy
conglomerate, and at base a reddish conglomerate with calcareous cement.

(1) An outcrop, 10 to 15 feet in thickness, of reddish and light colored
sandstone, somewhat conglomeratic at base, containing Lingulepis, Obolella,
and trilobite fragments.

From the summit of this butte the edge of the limestone plateau to
the south and west can be seen for a long distance running out eastward
in peninsulas and cut back westward by valleys, with occasional isolated
buttes standing like sentinels along its serrated margin, while eastward is
the rugged area of the slates, with now and then a grassy park, and in the
distance the dark range of Harney.

Southward from these points of observation the Potsdam was not
examined until it was reached between the headwaters of French and Red
Canon Creeks. The exposures are poor, being generally mere fragmentary
outcrops on the slopes below the limestone cliffs. The cliff tops at the head
of Red Canon Creek are 600 feet lower than those on Castle Creek, show-
ing a marked slope of the table toward the southwest. Levels taken at two
places between approximate limits of the Potsdam gave a thickness at each
of 220 feet. At the springs near the head of Red Canon Creek a purplish
quartzite was found at the base of the Potsdam resting on the schists, and
from its abundant fossil remains an excellent collection of Lingulepis and
Obolella was obtained.

Eastward from this point the formation was next examined in the broad
prairie that lies on upper Amphibious Creek. Here the hills, capped with
a cliff of 20 feet of limestone and a fragmentary outcrop of the underlying
lower portions of the Carboniferous, contain along their base imperfect
exposures of a brownish sandstone of the Potsdam with Lingulepis, ete.
Some five or six miles down the creek, at the head of the Great Cafion, are
heavy beds of the gray basal quartzite, and the slope above it is strewn

THE POTSDAM IN DETAIL. 101

with fragments of quartzite to within 150 feet of the capping Carboniterous
limestone.

On Burntwood Creek the coarse sandstones of the Potsdam were not
discovered, but the low hills near the creek are capped by a hard grayish
quartzite lying unconformable upon the schists.

In the canon of French Creek a most excellent exposure of the Pots-
dam is seen and the section there made has already been given. The basal
quartzite is less prominent, but the formation contains an additional bed of
quartzite separated from the basal by a soft coarse sandstone. The granite
approaches the sedimentary rocks on Amphibious, Burntwood, French,
and Battle Creeks more nearly than elsewhere in the Hills, and its prox-
imity may bear some relation to the greater development of the basal
quartzite of the Potsdam in those localities. On French Creek a granite
mass abuts against the lower edge of the Potsdam quartzite for a con-
siderable distance, and its upper two or three feet are decomposed into a soft,
clayey material. With the rapid eastward dip at this place the Potsdam,
from an elevation of 200 feet above the creek, sinks in three miles below its
bed.

Between Battle and Whisky Creeks a peninsula of the Potsdam extends
westward toward Harney Peak, consisting, so far as examined, of a hard
quartzite estimated to be over 50 feet thick. With this peninsula ends the
basal quartzite of the southeastern part of the Hills and on Spring Creek
the Potsdam corresponds more nearly to its western development both in
character and thickness. It may be well to note in this place that the best
sections of the older sedimentary rocks are always exposed in the creek
canons on the east side of the Hills. The vertical cliffs of those cafions,
400 feet or more in height, are often clean walls of the composing for-
mations.

The most interesting feature of the examination on Spring Creek was
the discovery of strata covered with casts of a gigantic spreading fucoid,
Paleophycus occidentalis. ‘The rock is a shaly, argillaceous sandstone near
the middle of the formation, and some of the specimens on its surface are
five or six feet in length, the main stem being nearly an inch in diameter
and dividing into numerous branches three-eighths of an inch in diameter.

102 GEOLOGY OF THE BLACK HILLS.

The stems usually divide into threes or bifurcate, and the smaller branches
frequently terminate abruptly in rounded ends.

Excellent exposures of the Potsdam were found on Spring Creek, and
a section of the strata there found has been given on a preceding page.
On Rapid, the next creek north, the Potsdam presents some of the most
interesting features observed in the Hills—the occurrence of large amounts
of calcareous matter; the presence of great quantities of greensand or
glauconite; and the rapid changes in character and thickness found within
short distances in the canon. A highly arenaceous series with a heavy
bowlder conglomerate at the base changes in three miles to the highly
calcareous series represented in Figure 14, and the section increases in thick-
ness in the same distance fully 100 feet. The Potsdam was evidently
deposited on an uneven bottom of slate, and a local sorting of its material
seems to have been determined thereby. The calcite and glauconite, or the
chemical and organic material, found there way into the depression, while
the purely fragmental material remained in the shallower water. From the
canon of Box Elder Creek northward for ten miles the Potsdam is exposed
at the base of the limestone cliffs which follow the creek. The creek valley
then bends westward and the limestone cliffs run more directly northward
to Bear Butte Creek. From the base of the cliffs there is usually a broad
slope or talus, broken now and then by outcrops and small cliffs of the
Potsdam sandstone, but rarely revealing any well-exposed section of the
formation. Several outcrops of the sandstone exhibit intercalated strata of
quartzite, and the thickness of the formation was found to vary from 200
to 275 feet.

The width of the Archzean area, which near Spring Creek separates
the east and west outcrops of the Potsdam by more than twenty miles, has
narrowed down, until near Custer Peak the outcrops on either side of the
Hills are separated by only five or six miles, while some ten miles directly
north from the same peak, near Black Butte, the eastern outcrop swings
around and joins the exposures of the Potsdam on the western side of the
Hills. In the area north and northeast of Custer Peak there are so many
outlying tracts of Potsdam and even of Carboniferous strata that the imagina-
tion is but lightly taxed to restore them over the whole, and their former

THE POTSDAM AND THE IGNEOUS PEAKS. 103

continuity cannot be doubted. The tract is so broken, carioned, and intri-
cate, that it was almost an impossibility to pass through it at all, except in
the immediate valley of some stream, and its examination was therefore
not so complete as could be desired; but the Potsdam, wherever seen, pre-
sents the same features that were observed in other parts of the Hills.

In some of the valleys in the northern end of the Hills, where such rich
deposits of placer gold have been found since our exploration, the bed-rock
of the stream is Potsdam sandstone. The auriferous gravels may in such
cases have been derived directly from the wearing down of the schists and
slates on the upper courses of the creeks, but it is more probable that they
came indirectly from the same source through the medium of the Pots-
dam. The streams which drain the Archzean area are concentrating the
gold by a method not very dissimilar from that of the Potsdam waves, and
it is reasonable to suppose that dirt which has been first rocked by the
waves and then sluiced by the creeks will hold its gold in a more concen-
trated condition than that which has had the benefit of but one process.

Near Terry Peak, where there have been great outbursts of volcanic
matter, the Potsdam is changed in many places into a quartzite, and
the conglomerate in some places is so metamorphosed that a fracture takes
place as well through the quartz pebbles and bowlders composing it as in
any other manner, the cementing matrix being changed to a rock as hard
as the pebbles themselves.

The Potsdam is exhibited also in an imperfect outcrop around the base
of Custer Peak, which seems to rest upon a foundation of that rock, and
thence we may follow the outcrop southward to Castle Creek, where we
took it up in the beginning of this narration.

In the northwest end of the Hills the Potsdam is brought to view by
the volcanic uplifts at Warren and Crow Peaks. In each place its outcrop
encircles the igneous mass and inclines against it at a high angle, exhibit-
ing more or less metamorphism near the contact. About Warren Peaks
its color is dark brown; in places it is a lamellar shale, and elsewhere it
becomes massive and hard, while locally there were found conglomerates
of brown sandstone pebbles resembling the Potsdam itself. About the
middle of the formation there occurs a thick stratum of shaly, brown or

104 GEOLOGY OF THE BLACK HILLS.

gray, argillaceous sandstone full of fwcoid impressions, and where the rock
is more massive the holes of Scolthus are very abundant, fairly honey-
combing it. These borings (?) are particularly numerous near the upper
part of the sandstone. The base of the formation was concealed at the
pomt of measurement, but the exposed section contains fully 350 feet.
North of the peaks, at the head of the north branch of the Redwater,
the Potsdam is full of the impressions of fucoids or sea-weeds, expecially
near the base of the upper third of the formation. These fossil impres-
sions are not found on merely isolated specimens, but over a large region
almost every fragment of rock that may be picked up is found impressed,
generally in relief, with the branching form of sea-weeds.

Even in the better studied and most fossiliferous localities of the forma-
tion fucoids occur but sparingly, and the great quantity found here and
elsewhere in the Potsdam of the Black Hills indicates an abundance of
vegetable life in the old Potsdam sea that has heretofore not been fully
realized

Before leaving the subject of the Potsdam a few words will be devoted
to the manner of its formation and the physical character of the region at
the time, so far as they have been inferred from a study of the structure
and relations of the rocks.

The whole character of the Potsdam rocks indicates them to be shore
and shallow water deposits. The conglomerate, containing large bowlders
of the Archzean rocks, could only have been produced by the immediate
action of waves on a shore line, breaking against a reef or coast-wall, and
rolling the fragments torn from it to and fro on the shore until they became
smooth and rounded as we now find them. The sand of the sandstones is
the result of the more complete trituration of the same materials by the
shore waves, and being lighter and more easily moved by water currents it
occupied a position some distance from the immediate shore line, but still
at a nearness depending upon the size of the grains and their specific
gravity, the coarser and heavier being deposited nearer and the smaller
and lighter farther from the beach line. The heavy conglomerate is found
only at the very base of the formation and in position nearest the axial line

A REEF IN THE POTSDAM OCEAN. 105

of the Archzean rocks, while the mass of the formation is uniformly a coarse
sandstone, the product still of shore waves, but deposited farther from the
shore. While in the base of the formation fragments may be found of nearly
all of the harder rocks of the Archzean, its mass is composed of quartz
grains without any admixture of other rocks.

We may thus, from a study of the Potsdam rocks and their relations,
infer with a high degree of probability that at this early time the Black
Hills were already marked out, and that they stood above the waves of the
Potsdam shallow sea, probably as a long low reef or island. This reef was
undoubtedly as long as we now find the exposure of the Archean rocks,
and may even have been of greater length, as we do not know the charac-
ter of the unexposed Potsdam of the Hills.

Again, the Archzean rocks were in Potsdam time metamorphosed to
nearly or quite the same extent as now; for the fragments composing the
conglomerate are of the same character as the still unbroken strata of the
metamorphic slates and schists. The slates were also tilted to their present
high inclination, for upon their upturned surfaces the Potsdam rests uncon-
formably, and if any tilting of the metamorphic rocks had taken place
since the deposition of the Potsdam the evidence would be found in great
breakings and fractures in the sedimentary rocks.

At the beginning of the Lower Silurian term we may hence imagine
the Black Hills, and possibly a much more extended region, as an island
(“an island” because the conglomerate is on both sides of the present
axis)—a reef of schists, quartzites, slates, and granites, running northwest
and southeast. Barren and desolate we may picture this island, for we
know of no plants nor land animals that then had their existence. The
only moving things that left their record were the waves that rolled
over a broad and shallow sea and broke the silence by dashing against the
primordial land. Slowly but surely they tore and undermined its cliffs and
rolled away the fragments to form the conglomerates and sandstones of
another age. The inequalities of the Archean shore became gradually
filled up, and as the sea rose higher upon the land all that was not worn
away at last became entirely covered by the Potsdam sea and its sediments.

That the Potsdam stretched completely across the present area of the

106 GEOLOGY OF THE BLACK HILLS.

metamorphic rocks we have undoubted evidence. There is nowhere observed
any thinning out of the formation as we approach the center of the Hills,
but it everywhere maintains within narrow limits the same thickness.

In accounting for the origin of the sands forming the upper part of the
formation, which once concealed the metamorphic rocks entirely, we
start an old problem that has never yet been fully settled by geologists.
What was the derivation of the mechanical deposits, covering now such
wide extents of territory in the West, near which no original land surface
has yet been revealed? The coarse silicious sand of the Potsdam could not
have been derived from a distant shore, for it is not fine enough to be carried
by ocean currents. There was undoubtedly at that time a great area of
exposed land surface, much of which is now buried beneath the land
or the sea, some primordial Archeea which having been worn away to
form our present land surface has vanished from view. ‘The great
extent of Laurentian and Huronian rocks, stretching from Lake Superior
to the Lake of the Woods and thence northwesterly to the Arctic Ocean,
furnished in all probability much of the material; but for the sandstone of
the Potsdam and later formation of the Rocky Mountains there must have
been a land surface farther west, possibly in Pacific regions. The problem
has occurred to Dr. Newberry, who says in his report to Lieutenant Ives*:

The outlines of the western part of the North American continent were ap-
proximately marked out from the earliest Paleozoic times; not simply by areas of
shallower water in an almost boundless ocean, but by groups of islands and broad
continental surfaces of dry land.

Since the erosion of rocks is always subaerial, or at least never takes place more
than 40 feet below the ocean surface, it follows that to form the stratified rocks of only
that portion of the great central plateau which borders the Colorado, an island three
hunded miles in diameter and at least 6,000 feet high, or, what is more probable, a
continent of six times that area and 1,000 feet high was worn down by the action of
waves and rains, and in the form of sediments, sand, gravel, clay, or lime, deposited on
the sea bottom.

When we reflect that, with the exception of narrow wedges of erupted material
in the mountains, an area having, on the 36th parallel, the breadth of the entire dis-
tance between the great bend of the Colorado and the Mississippi (twelve hundred
miles), and a great though yet unmeasured extension north and south, is occupied by
several thousand feet of Paleozoic and secondary strata, we must conclude that these
sediments have not been derived from the erosion of emerged surfaces east of the Mis-

*Colorado Exploring Expedition, Lieut..J. C. Ives, 1861, Geol. Rept., p. 47.

THE CARBONIFEROUS. 107

sissippi, but were fornied by the incessant action of the Pacific waves on shores that
perhaps for hundreds of miles succumbed to their power, and by broad and rapid rivers
which flowed from the mountains and through the fertile valleys of a primeval Atlantis.

In the sea of the Potsdam there was an abundance of life, though of
a low order, huge sea-weeds and delicate brachiopod shells with trilobites
of small size.

The following list gives the names of the genera and species which
have been recognized or described by Professor Whitfield :

Paleéochorda prima. Lingulepis Dakotensis
Paleéophycus occidentalis. Obolus ? pectenoides.
Paleéophycus ———. Obolella polita.

Scolithus ———. Obolella nana.
Lingulepis pinnaformis. Crepicephalus centralis.
Lingulepis cuneolus. Crepicephalus planus.

Lingulepis perattenuatus.

SECTION V.
THE CARBONIFEROUS.

East of the Plains the Carboniferous system is divided into two well-
marked series. ‘The lower, known as the Sub-Carboniferous, is, character-
ized by sandstones and limestones, the former predominating in the neigh-
borhood of the Appalachians and the latter in the Mississippi Valley. The
upper, known as the Coal Measures, is marked by alternations of sand-
stones and shales, with some limestone and some iron ore, and contains
those stores of mineral fuel which have justly given name to the whole
system. It was thought at one time that a third division had been recog-
nized in the Mississippi Valley—a division overlying the Coal Measures
and corresponding to the Permian of European chronology—but the line
of separation from the Coal Measures proved so shadowy that the attempt
to draw it was abandoned. The division is practically ignored at the
present time, although it is not questioned that a fauna allied to the Per-
mian fauna of Europe finds place at the top of the series and is gradually
merged with the Coal Measure fauna below.

108 GEOLOGY OF THE BLACK HILLS.

In the Rocky Mountain region the Carboniferous is the most persistent
and important of the Paleozoic formations. It is found in almost every
great section and is everywhere identified by fossils. Its characteristic
rocks are limestone and sandstone, and are so durable that in the progress
of degradation they have been laid bare over large areas. Nevertheless
the subdivisions known at the East have here received no general recogni-
tion. The prevailing fossils are of Coal Measure types, but with these are
nearly always mingled Sub-Carboniferous forms, and it is but rarely that
any distinctive Sub-Carboniferous strata have been recognized A Permian
has been separated by King in the Uinta Mountains, by Peale in Colorado,
and by other observers far at the south, but in many localities Coal
Measure fossils seem to extend to the top of the system.

In the Black Hills we have established no subdivisions on paleonto-
logical grounds, and are unable to affirm or deny the presence either of
Sub Carboniferous or of Permian The rock series is definitely and con-
tinuously divided into several members, but the lowest and the highest of
these members alike failed to afford us distinctive fossils. It is to be
anticipated that future investigations will correlate them at least with the
several members of the system as known in the neighboring portions of
the Rocky Mountains, but for the present they can only be designated
as Carboniferous.

The local subdivisions are four in number, and they are distinguished

purely by lithological characters. Beginning with the lowest, they are as

follows:
Feet.
1. Shaly limestone-—Thinly bedded, impure, arenaceous limestone, pinkish
in color, often filled with comminuted fragments of crinoidal columns;
contains also Productus, cyathophylloid corals, etc ......- .-..--..---- 20-60
2. Gray limestone—Massive gray or whitish limestone, uniformly pure, con-
taining Spirifera Rocky-montana, Productus, etc.....--. .------- .---- 150-200

3. Silicious limestone—Weathering usually in a peculiar brecciated manner ;
somewhat cavernous and often stained with pinkish and reddish streaks;
containing much flinty and silicious matter, often with a banded struc-
ture; with crystals of calcite lining the interior of weathered crevices
or cavities. Fossils are found, but usually ill preserved and only ex-
posed and obtainable when the rock is much weathered. There have
been recognized Athyris subtilita, Spirifera Rocky-montana, Productus,

COTAIS COCO se Bi Wired ewe et... RnR nyeyee eapteernaiay: toors! See ene 150-175

SUBDIVISIONS OF CARBONIFEROUS. 109

4. The Alternating Series —A series of alternating beds of pink and light

colored sandstones and limestones somewhat argillaceous; the lime-
stones apparently somewhat magnesian and poor in fossils. -.--...---- 150-200

These pass upward into a variegated sandstone, irregularly stained red-

dish, yellowish, and white; somewhat argillaceous and calcareous and

exhibiting little stratification; weathering in peculiar twisted, contorted

(curly) bands... ..- Seis SSS Di Sh ORUIIE Bea tea nn ae me ergo ae 100-150

Wherever the Potsdam sandstone and lower Carboniferous series
are together visible they are absolutely conformable, and the distinction
between the rocks of the two systems is often so perfectly marked that the
blade of a penknife may be inserted at their line of separation. Passing
upward from the coarse brown sandstones of the Potsdam, with Lingulepis,
Obolella, etc., one first meets the thinly bedded pinkish limestones of the
base of the Carboniferous with fossil forms characteristic of that formation,
so that both lithologically and paleontologically the separation between the
Potsdam and the Carboniferous is always distinct and easily traceable.
This lowest member of the Carboniferous weathers easily and is not gener-
ally well exposed, though the separation between it and the heavy limestones
above is very distinct where observable. It has a pinkish or grayish color,
is never a pure limestone, and commonly has an argillaceous appearance.
Its strata rarely exceed eight or ten inches in thickness, and it is often so
thinly bedded as to resemble a calcareous shale. Though it is commonly
very fossiliferous, specimens sufficiently well preserved for specific identifi-
cation were not obtained. The genera Zaphrentis, Spirifera, and Productus
were recognized.

The second member, the massive gray limestone, and the third, the
silicious limestone, are the most persistent features of the formation in the
Hills. They are well seen in nearly all parts of the country examined; in
the western plateau, on the southern border, and on the eastern slope.
Along the eastern edge of the plateau, however, there are considerable
areas from which the silicious limestone and part of the gray have disap-
peared by denudation; and for this reason one who enters the Hills by
crossing the plateau from the west obtains but a very inadequate idea of
the true magnitude and thickness of the Carboniferous formation. Com-
plete and continuous sections of the Carboniferous are found only in the

110 GEOLOGY OF THE BLACK HILLS.

canons cut by the various streams as they pass from the Hills to the Plains,
where by the gradual dip of the strata one member after another is carried
down and out of sight; and even in the cafions it was not always possible
to study them closely in detail.

The gray limestone immediately overlies the thin-bedded pink lime-
stones, and according to many measurements taken in different parts of the
Hills has a thickness of 150 to 200 feet. It is a very uniform, pure lime-
stone, and one of the most prominent members of the Carboniferous series.
It is well exposed in every examined section of the Carboniferous rocks.
Its fossils are numerous, but are not readily separable from the matrix except
where the rock has been so greatly weathered as to destroy their surface
markings. What few species were recognized appear to be equally charac-
teristic of the overlying silicious limestone.

The silicious limestone is a hard, white or grayish, gritty rock, which,
from the oxidation of its iron and perhaps also by percolation from the
overlying rocks, is generally stained irregularly red or pinkish. It contains
much silicious matter concentrated in spots, either as flint, or as crystalline
quartz lining small cavities, or in concretionary or agate-like deposits.
From its silicious and uneven composition it decomposes very irregularly,
often having a brecciated appearance and weathering with cavities or crevi-
ces, and even with caverns of considerable extent. The cavities are usually
lined with crystals of calcite.

The most abundant fossils in the two limestones are Spirifera Rocky-
montana, Athyris subtilita, Productus, Euomphalus, and Streptorhynchus.

While the lower members of the formation are well marked, easily
traced, and readily distinguished from each other and from the underlying
Potsdam, the study of the upper portions was attended with no little embar-
rassment. In the absence of any paleontological assistance of value, the
upper limits of the formation had to be drawn from the lithological nature
of the deposits. While the conclusion here reached is open to question
and is liable to be set aside whenever fossils are brought to bear on the
problem, I am strongly disposed to think that none of the beds here included
in the Carboniferous will ever be relegated to the Trias.

Immediately overlying and conforming to the silicious limestone are

THE ALTERNATING SERIES. 111

the following beds: first, a series of thinly bedded sandstones and impure
limestones, the latter somewhat magnesian, varying in color—pink, white,
yellow, and gray; the limestones containing only traces of fossil remains.
These haye ‘altogether a thickness of 150 to 200 feet, and pass gradually
into (second) a sandstone somewhat argillaceous and calcareous, of a deep
red color, but often streaked or variegated with yellow or pink Fre-
quently on fracture the sandstone has a somewhat lighter color or is almost
white; and while much of the predominating deep coloration is derived
from the oxidation of iron in the rock itself, a considerable portion is also
produced through staining by a downward infiltration from the red clay
above. It generally shows little or no stratification and is massive, but it
weathers in a brecciated or broken manner, with twisted or bent lines of
decomposition parallel with the general stratification of the rocks. It has
a thickness of 100 to 150 feet, making the entire thickness of the upper
or fourth member of the Carboniferous 250 to 350 feet. Detailed and
accurate sections of these rocks are given on another page.

Within the area of the plateau no good exposures of the upper beds
were seen, but along its western edge they appear in a few cafons that
drain westward, especially in those connecting with Beaver Creek. They
are also excellently exhibited in Fanny Peak, which is composed of the
serrated and broken edges of the red sandstones standing vertically.

In the southern end of the Hills in the cafons of Red Camfon and
Amphibious Creeks the silicious limestone (8) is overlaid by over 200 feet
(estimated) of red and pink sandstones, which are somewhat calcareous and
contain occasional beds of limestone. Similar beds at the springs on Minne
Katta Creek have a measured thickness of 300 feet. At the latter place a
few fragments of crinoid stems were found in some of the limestones.

On the eastern side of the Hills, especially in the cations of Rapid and
Box Elder Creeks, where most excellent sections of the entire series are
visible, these upper beds were studied with great care. They are there
more calcareous than on Amphibious Creek and consist of an alternation of
pink and red sandstones and limestones, an accurate measurement of
which is given on a subsequent page. On Box Elder Creek a few fossils
were found in the limestones about 115 feet above the base of the alternat-

12 GEOLOGY OF THE BLACK HILLS.

ing series, and above this fossiliferous stratum the same series continues for
over 200 feet. The fossils, mere fragments, are indeterminable; but among
them are minute gasteropods and small Spirifer-like shells.

Above the alternating series, and therefore, according to our classifi-
cation, above the Carboniferous, there follow in ascending order, first, 75
to 100 feet of red arenaceous clay; second, 15 to 30 feet of purplish im-
pure limestone; and, third, 200 to 250 feet of red clay with gypsum. The
arenaceous tendency of the lower clay allies it to the sandstone at the top
of the alternating series and makes it difficult to draw the line of separation
even here; but, all things considered, the division is more easily made at this
point than elsewhere. Limestone and sandstone are the characteristic
rocks of the Carboniferous throughout the northwest region; and regarding
only lithological evidence, it seems proper to make the separation where
the sandstone and limestone cease and the clay begins. Nevertheless in
Southern Colorado the Carboniferous is known to include in its upper
part large deposits of gypsum and associated beds of a deep red color, and
the same thing may possibly occur in the Black Hills.

In 1857 Dr. Hayden found a few fragments of fossils in the Hills
which he recognized as identical with forms from western Kansas, which
had been studied by Mr. Meek and himself and referred to the Permian.
The rock in which they were found was a bowlder and the material was
not seen in place, but the indication that the Permian is contained in the
Black Hills section may furnish a cue by suggesting a comparison of the
doubtful beds with the nearest rocks for which the title Permian has been
claimed.

Dr. Peale has examined in Colorado, on the Grand River, ete., certain
strata between the Coal Measures and Triassic which Professor Lesque-
reux decided from certain fossil plants found therein to be of Permian
age. Dr. Peale describes the series in words that will apply almost as
well to the lower part of the alternating series of the Black Hills, viz,
‘variegated strata, yellow, pink, and cream colored shales and limestones,
subject to so much change that it was impossible to make any continuous
section.” Similar thin-bedded deposits are also described by him in his
report for 1873, and he has regarded these also as of Permian age.

SEPARATION OF CARBONIFEROUS AND RED BEDS. hes

Though the beds in Nebraska that were referred by Mr. Meek to the
Permian are now considered by him as of upper Coal Measure age, it may
be well to consider their character in this connection. The Sub-Carbonifer-
ous in all the Missouri region consists of massive limestone deposits, while
the upper portions of the Carboniferous, the upper Coal Measures, are com-
posed of more or less thin bedded, alternating deposits of shale, limestones,
sandstones, bituminous shales, and, as far west as eastern Nebraska, thin
coals. Such deposits are called “oscillatory,” as indicating unsteady and
repeated changes in the circumstances of their formation. The alternating
series of the Hills differs conspicuously in the character of its component
beds, but corresponds in the matter of oscillation.

With the very fragmentary and unsatisfactory evidence that is here
brought to bear upon the question of the relation of these upper beds of
the Carboniferous, we can arrive at no more definite conclusion than to say
that they are with little doubt Carboniferous ; that they are probably upper
Carboniferous, and that they may possibly by future investigation be
established as Permian.

In the position I have assigned to the upper limit of the Carboniferous
I differ somewhat from Professor Winchell and Dr. Hayden. The former
places it higher, including the purple limestone which interrupts the red
clays, and the latter places it below the alternating series.

When Dr. Hayden visited the Hills in 1857, he labored under the
disadvantage that always pertains to a rapid reconnaissance, and to this we
must lay his low estimate of the dimensions of the Carboniferous. His
error in this regard was very natural, as the portion of the formation tray-
ersed by him is greatly thinned by denudation. He divided the Carbon-
iferous into two portions, as follows: ‘‘G. Hard, more or less gritty,
yellowish and whiteish limestone, containing Productus, Spirifera, Euom-
phalus, ete., passmg down into a light yellowish calcareous grit, altogether
50 feet;” and, passing downward, ‘“‘H. Very hard, reddish-gray limestone,
containing Syringopora, Productus, Terebratula, etc, * * * 50 feet.”*

His ‘‘G” is our No. 3; his ‘‘H” is our No. 2; our smallest measure-
ment gave them a total of 300 feet. The sandstones, etc., which we have

* Trans. Am. Phil. Soc., 1862. Geology of the Upper Missouri, Hayden.
8 BH

114 GEOLOGY OF THE BLACK HILLS.

included as the upper member of the Carboniferous, together with the red
arenaceous clay underlying the limestone of the Red Beds were placed by
him in the Red Bed series, their thickness being given as 250 to 300 feet.

Professor Winchell, despite the rapidity of his passage through the
Hills (he was in the region less than four weeks), was enabled to make
some interesting observations on the geology. The route by which he
entered them was not, however, a favorable one for geological purposes, and
several of the records and observations made by him are now susceptible of
a different interpretation. He includes in the Carboniferous two elements
which are here placed in the Red Bed series: first the purple limestone, and
‘second the lower red clay, which is not separated by him from the under-
lying variegated sandstone. ‘This sandstone, the upper part of our fourth
member of the Carboniferous, is called by him the “Minne Lusa” sand-
stone, while the underlying sandstones and limestones, 150 to 200 feet in
thickness, do not appear to have been separated by him. Excluding the
beds that are here placed in the Red Beds, the Carboniferous, as estimated
by Professor Winchell, has a thickness of about 300 feet, while the meas-
urements we were enabled to make give the thickness as ranging from 570
to over 700 feet.*

The character and development of the Carboniferous have had a con-
trolling influence in the production of some of the most prominent topo-
graphical features in the Hills) Though limestone is soluble to a certain
extent by ordinary water, it is still one of the most durable of the sedimentary
rocks ‘The Carboniferous limestone is not only durable but thick, and its
influence on the topography is heightened by the softness and incoherence
of the overlying sandstones and clays. The latter have yielded to the
action of the elements and disappeared from all the high places and by so
doing have laid bare the limestone. ‘The limestone stubboruly resists, and
yields only as it is undermined by the disintegration of the shaly and are-
naceous beds at its base. It survives over half of the flat-topped uplift
which constitutes the Hills, forming a great plateau, and surrounds the other
half in a continuous belt of cliffs.

* One of the most serious of Winchell’s errors was the announcement of an unconformity between
the purple limestone and the gypsiferous clay. If that unconformity really existed his separation of
the Paleozoic andl Mesozoic would be preferable to Newton’s.—ED,

THE CARBONIFEROUS PLATEAU. 115

The form of the plateau can be seen by referring to either of the two
maps of the Atlas. In the topographical map it appears as a topographical
feature; in the geological it is marked as the great body of the Carbonifer-
ous exposure. It attains its high elevation by a gradual slope from the
west, from the north, and from the south, while its eastern margin, over-
looking the area of the slates, is a more or less bold escarpment or cliff,
broken and serrated, however, by the penetration of valleys and streams.
It has a width east and west of from fifteen to twenty miles, and a length
north and south of sixty miles, covering altogether between nine hundred
and one thousand square miles, or about one-sixth of the total area of
the Hills. Its surface is generally smooth or gently undulating, but is
sharply cut by the draining streams which traverse it in deep and steep-
sided cafions. Considered in its total mass it is the greatest elevation of
the Hills, and it bears upon its broad back a crag which is second to but
one other summit in height. Crook Tower has an altitude above the sea
of 7,320 feet, and is only 80 feet lower than Harney Peak, while it over-
tops Terry Peak, the next in elevation, by fully 100 feet. It rises only
about 200 feet above the level of the adjacent portions of the plateau.

Approaching from the west, at the headwaters of Beaver Creek, one
ascends from the Red Bed Valley (5,300 feet) by a slope of the Red Beds,
more or less gradual, to the general level of the plateau, here about 7,000
feet high. This general level, varied only by undulation, extends thence
eastward to the margin of the plateau which overlooks the area of the
slates.

From the base of Crook Tower (7,100 feet) the surface of the mesa
spreads southward to the region west of Castle Creek and the headwaters
of Spring Creek with a level varying little from 7,000 feet. From the
headwaters of French Creek, however, there is a visible descent of the
plateau toward the south and southwest. Near the head of Red Canon
Creek the elevation is about 6,000 feet, and at the southwest the mesa soon
ends by the descent of the limestone.

Northward and northwestward from Crook Tower the Carboniferous
rocks extend to the valley of the Redwater in much the same manner as
they spread and disappear southward, except that the plateau character of

116 GEOLOGY OF THE BLACK HILLS.

the surface has been destroyed by the numerous forks and branches of
Inyan Kara, Redwater, and Spearfish Creeks, which have cut canons in
all directions often to the depth of several hundred feet. Still a consider-
able share of the original surface survives, and it is easy to construct from
the many tongues and spurs that remain a clear idea of the original form.
If one views it from a station a little elevated above it, he sees clearly the
plateau character, but may fail to comprehend how great a task lies before
him should he attempt to force a passage across it.

The exposures of the Carboniferous on the eastern margin of the
uplift are comparatively small in extent, and consist entirely of rocks
dipping rapidly to the east. They constitute a monoclinal ridge curving
about the edge of the Archean. The creeks which drain the Archean flow
to the north, east, and south, and cut through this rim of Carboniferous
rocks in canons whose length depends on the rate of dip of the strata.

In the Bear Lodge range the Carboniferous has been tilted and raised
to view, along with the other strata, by the elevation that accompanied the
volcanic outbursts of Warren Peaks. The outcrop is not large and the
strata composing it hardly differ from those in the main portion of the Hills
save in a slight amount of metamorphism due to the voleanism Their dip
is outward from the peaks in all directions, but most strongly towards the
northwest.

The details of the geological structure of the Carboniferous mesa north
of Crook Tower were not studied with much care for lack of the time neces-
sary to penetrate its labyrinth of canons. The dip of the rocks where
they curve down from the table toward the Red Valley is more gradual
than at the south and southwest of Castle Creek. Crossing it in a north-
west direction we found the surface slope, canons excepted, rarely greater
than 6° or 8°; and from well-marked Carboniferous rocks one passes
almost imperceptibly to the Red Bed limestone, which continues the slope
more steeply until it dips under the mass of red clays underlying the great
Red Bed valley that sweeps around the northwestern end of the Hills.
Because of the gentleness of this slope and the ready manner in which
the upper Carboniferous arenaceous strata decompose and form a soil, but
little is seen of them in passing over the slopes, though excellent exposures

THE CARBONIFEROUS PLATEAU. UF

are to be found in the deeper of the canons. On Inyan Kara Creek, and
especially on Redwater Creek and Heron Creek, they are readily
examined ‘The accompanying ideal section, running from the Red Valley
near Inyan Kara eastward across the pla-
teau to Custer Peak, a distance of thirty
miles, though only approximate in its de-

9
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tails, will give a tolerably correct idea of uciowe z
the structure of the mesa at this point. ee Se
Nearly the whole of the northern part ee ee,
of the plateau bears at the surface either the 4 aaa
silicious or the gray limestone (Nos. 2 and eBeeee
3 of the general section), and of the two the a g
a —

gray limestone is more prominently ex-
posed. Crook Tower consists probably of
the gray limestone with a capping of the
silicious, and fragments brought from its
body are filled with Spirifera Rocky-montana.
Considerable portions of the limestones have
been removed by erosion from the surface
of the plateau and a greater amount at the

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eastward. The upper valleys of Inyan
Kara and Redwater Creeks, running from
south to north, are not of very great depth,

and the edges of the bordering rocks are
commonly in whole or part hidden in their sloping soil-covered sides. On
the eastern side of the plateau, however, the northward flowing Spear-

118 GEOLOGY OF THE BLACK HILLS.

fish has cut a cation from 300 to 600 feet deep, often penetrating into and
below the underlying Potsdam. Frequent exposures of the variegated
sandstones of the upper member of the Carboniferous are seen in the west-
ern valleys, where it is a prominent feature, but the intermediate series of
alternating sandstones and limestones were not observed. It is not con-
sidered that they are here absent, but merely that their outcrop is locally
concealed; for they are found farther north on lower Redwater Creek,
farther south in some of the cafons running into Beaver Creek, and on the
eastern hog-back wherever the Carboniferous was carefully examined.

The eastern margin of the plateau where it overlooks the country
around Custer and Terry Peaks has much the same character as farther
south, but it is flanked by more numerous outliers or mesas of Carbonifer-
ous and Potsdam. Northeast of Terry Peak, on the ridges between the
creeks, a series of mesas extends across the slate area.

The plateau south of Crook Tower, so far as examined, is less cut by
the canons of draining streams. From an elevation near Castle Creek of
7,000 feet or a little more it dips off to the south and southwest, until
at the head of Red Canon Creek it is 1,000 feet lower, and thence its
surface soon joins the Red Valley on the south. The extreme southern
end was passed over by some members of the escort, who reported its sur-
face as deeply scored by the canons of streams draining into Beaver Creek
and the Cheyenne, in which character it resembles the extreme northern
end of the plateau. Along the eastern margin of the table near Castle
Creek there is a small southward dip and it increases toward the southern
end. There is also a general dip to the westward, and this, while barely
discernible on the eastern side, increases rapidly toward fhe west and
southwest, until at last the Carboniferous rocks dip steeply under the Red
Valley.

At the western margin of the plateau near Camp Jenney, and for some
distance along the east fork of the Beaver, there is a remarkable and ex-
ceptional dip, which is exceeded only in the rocks immediately surrounding
some of the volcanic peaks at the north. It is illustrated in the accom-
panying section, running from the Red Valley at Camp Jenney eastward
across the mesa to the headwaters of French Creek.

THE CARBONIFEROUS PLATEAU.

18S)

It is impossible on the scale of the section to illustrate accurately this
sudden dip, but it is sufficiently well shown to indicate the main features

of the uplift. The upturned edges of the varie-
gated sandstone forming the peaks (c) are
broken and rugged, and with their brilliant
red color are conspicuous features as seen from
the west.

Another fact worthy of notice is illustrated
by the section. It is observable almost every-
where on the slopes of the Hills, but more strik-
ingly here, that in regions of elevation the in-
clining strata do not make their entire ascent
in one continuous dip, but rise from their nearly
horizontal position to their highest elevation by
steps or waves, between which there may be
considerable intervals with little or no inclina-
tion. This feature is not peculiar to the Hills,
but has been observed in many regions the
geology of which has been accurately studied.
It is characteristic of the district of the Col-
orado plateaus, and is well exhibited in the
Coal Measures in portions of the Alleghany
Coal Field.

The basal member of the Carboniferous
is shown at various places along the eastern
margin of the southern portion of the plateau,
and is distinguished by the great quantity of
fragments of crinoidal columns it contains.
The gray and silicious limestones, just as at
the north, are the surface rocks of the top of the
plateau. The alternating limestones and sand-

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stones are well exposed in cafions across the western edge, and especially
in the vicinity of Fanny Peak, where a number of dry branches of Beaver

Creek score the slope of the plateau.

120 GEOLOGY OF THE BLACK HILLS.

On asmall branch of Castle Creek a section of the eastern cliff was
obtained, as follows:

Feet.
6. Limestone; highly silicious, with no distinct stratification, but breaking irregu-
larly; cavities with much calcedony; color white, with pink and red
blotelhes oe csi b= alee ser Siar te topare eles eich heg lke ae eee ee eee ee 30
5. Talus, Mo @XpOSure’ - Se aii ats oy Soper severed see ie tere ee ene eer ee ener 20
4. Limestone, white and compact, with a few fossils, Productus, a Bryozoan, ete. 30
3. Talus,) with fragments: Of SB 6d 45 eS een eee eee eee eee eer eee 70
2. Limestone, white and compact like 4, with Chonetes, Zaphrentis, etc........ 25
1. Talus to creek, with the Potsdam indicated by a series of springs flowing
from a level about 100 feet above the valley ..-...............-......... 200

Several miles farther down Castle Creek, which is lined with an escarp-
ment of limestone cliffs that render its name very appropriate, a measure-
ment showed the silicious limestone to be 150 feet thick, standing in a steep
bluff, with its top 750 feet above the bed of the creek. It is separated by
a slight talus from a cliff of 100 feet of the white limestone, and from the
base of this, evidently concealing a portion of the limestone, a slope extends
down 400 feet to the schists, which occupy the lower 100 feet of the sides
of the valley. About 75 feet of coarse Potsdam sandstone rest on the
slates, and fragments of Potsdam were found on the slope for 200 feet
higher, above which are numerous pieces of the purple shaly limestone (1)
and rocks from the cliffs above.

From Castle Creek southward to Red Cation Creek the Carboniferous
beds 2 and 3 are continuously seen lining the western border of the schist
area. Red Canon Creek runs in a valley a mile or two in width, and
for about four miles is bordered by cliffs with the limestones above and the
Potsdam below. The increasing dip then brings the limestones in succes-
sion down to the stream level and after them the alternating beds, and
through the latter the creek runs in a cafion to Red Valley. The creek
makes its escape through the southeastern corner of the mesa, and is the
most southerly of the fifteen streams that carry the drainage of the Archzean
district across the encircling belt of Carboniferous.

At this point the plateau may be said to end and the monoclinal
ridge to begin. The ridge runs at first eastward and dips to the sonth; it
then turns toward the north and its dip becomes easterly; and finally to

THE CARBONIFEROUS RIDGE. 121

rejoin the plateau it curves to the northwest and its dip becomes northeast-
erly. Iverywhere on the convex side of the curve it slopes down to Red
Valley. Everywhere on the concave side it presents a cliff face toward the
district of the slates and schists. In the following pages the local details of
the ridge and of the canons which intersect it will be described.

Minne Katta Creek issues from several large springs at the base of a
cliff composed mainly of the upper series of the Carboniferous. A general
section of the cliff by Mr. Patrick is given below, beginning with the cap-
ping Red Bed limestone:

Red Beds.

i Feet,
Bho. LEVIES, LWA a VSS OP EES hee san ESS Cree Gaal le eel pe ait a ce ala oats ans Stosenevenons 40
Swolvediclayis meplacessaisort, redssamdstone ses). 0.2..-. fee... eee ele 140

Carboniferous.

7. A series of colored sandstones, red, yellow, pink, etc., with calcareous layers

DG! MAC MOMNG Sacco dss S See elds o Peele ate ear Ser cae es ieee in ere 285
6. A layer of black, sandy, carbonaceous shale........-..--.~---.-...220-00. Thin.
GL, SEMGISIOIO. 5 Sdd4e, Staci a cis acts © RUNG oe Cpe eee pee aves es Pmt 3
fwAvlayeriot black, sandy, carbonaceous shale: - =. 2... 22.6 22.2 ee eee eee it
DeSAN AS FOES sRededm evel OMe sce e belie aloo Tene eer tse, She aceisis «ea esos 25
2. Silicious and argillaceous limestone, with nodules of flint ....to bed of creek 20
1. Limestone, silicious, weathering irregularly, cavernous; outcropping just at

the level of the creek; probably the silicious limestone, No. 3 of the Carbonif-
CLOUSISCCHIOMMe ae ee yore anys dna eves sae tee ae A Se See Raa SAE, ore Ree

‘ The series 7 of the above section exhibits in a high degree the peculiar
brecciated, wavy manner of weathering characteristic of the upper sand-
stone of the Carboniferous.

Near the head of Amphibious Creek the north-facing bluffs of the
Carboniferous limestone were seen capping an escarpment from 250 to 350
feet in height, and preserving in thickness and character the features of the
Carboniferous as observed near Red Canon Creek. The accompanying
section, Figure 17, was observed along the cafion of the creek from its entry
into the sedimentary rocks to its exit in the Red Beds, a distance of about
nine or ten miles, the larger portion of which is through the Carboniferous
limestones and the red arenaceous beds of the upper Carboniferous.
From the rapidity of our march and the rugged character of the cation, it

122 GEOLOGY OF THE BLACK HILLS.

is necessarily incomplete and wanting in absolute accuracy, but it is believed
to present the character and thickness of the Carboniferous strata with a

P fair amount of exactness. The exposures of
Ww be oe the Potsdam were not sufficiently perfect for
AN a
M 5 measurement.

AK &
|! Ch 8 Carboniferous.
I “\ \ | E Feet.
A \ = 1. Limestone, pink, impure and silicious, con-
MACON x ; taining fragments of crinoid stems (No.
A Ya ey sD fil 190, ores vassevctan Siege eee See exposed. . 20
NG 2. Limestone, white or gray (No. 2)....-...-- 180
% g 4 3. Limestone, silicious, containing much flint
x 3S and colored silicious matter; has a brec-
: o mg ?
3° gad = ciated appearance (No. 3).......-.----- 250
o +o 5 ° .
5 ¢345 4. Alternating limestones and calcareous sand-
a of F F 5
Bie SEs stones; yellow, reddish, white, and pink ;
a HORE near the base a marked stratum of deep
= Ss Sez S red, calcareous sandstone 10 feet thick;
5 fous the top beds a deep red sandstone, with
S Zaz :
a =She much lime in nodules or concretions
° A .

1 OHSS (lower part of No. 4).... -.. estimated... 200
ze 5. Variegated sandstone, distinctly banded in
strata of different colors, red, yellow, and
. white (upper part of No. 4)........-...-. 100
g A)

Pos Pin Red Beds.

Ba H
Bee
S52 6. Red clay, with some soft, red sandstone.... 100
Sas Ja burplevimestone ee asss eee eee eeere : 25
&z- 8. Red clay and gypsum forming the Red Val-
S agt J YI
Us =
E = iS ley POO aE BoD ono DOO oboS Oda ae ooae
a 283
go8 In obtaining the above section, series of
.E. Eg :
< 22° partial measurements were made as follows:
S 2Rtes
Ses84 a . . i 7
S£225 Having measured the first section the canon

2 aN+<5 was followed down until the capping bed of

rz) VE :

a ele the section was seen to reach the creek, when

another section was made, and so on through the carion.

The limestones were not found at any place to be fossiliferous, but the
different beds correspond closely in their lithological characters with the
Carboniferous as described in other parts of the Hills. No. 5 of the local

SINKING OF THE CREEKS 123

section is, however, more silicious in character than the same division on
the east side of the Hills, and its thickness also appears here considerably
greater than elsewhere.

Between the cations which divide the monoclinal ridge good points for
studying the strata are not often met with, for they dip regularly from the
axis of the Hills, and the surface forms an undulating slope on which the
component strata are inseparable.

On Burntwood Creek, which has nowhere cut the older sedimentary
rocks very abruptly, the Carboniferous is poorly exposed, but on French
Creek, the next in order, although the belt of Carboniferous is narrowed,
fair exposures are exhibited. A section showing the junction of the Pots-
dam and Carboniferous and a bluff of the white limestone has already
been given on page 90. A short distance below the place of this section
the dip increases, and the rocks are carried down to the bed of the stream
near the point of its snking. Within a short space the various members of
the Carboniferous are exhibited in the walls of the canon. They are all
readily recognized and distinguished, but their exposures are not well
placed for measurement. Above them in irregular order follow the mem-
bers of the Red Bed series.

In the canons of Battle and Whisky Creeks the Carboniferous lime-
stones are well exposed, and in the cafion of Spring Creek a most excellent
section is cut through the series for a considerable distance, as also on Rapid
Creek. The limestone strata of the gray and silicious divisions are exposed
on Spring Creek in a cliff 335 feet in height, and beneath them are 20 feet
of pink calcareous sandstones, which rest conformable upon the Potsdam
sandstones below. The pinkish, lamellar limestones, or calcareous sand-
stones contain the usual abundance of crinoidal fragments, with cyatho-
phylloid corals, a Spirifera like S. Rocky-montana, and a Productus. The
Carboniferous belt is here about four miles in width, and—a feature com-
mon to most of the creeks of the Hills—the water sinks at a point near
where the massive limestones dip under the creek bed.

The peculiarity of the sinking of the creeks of the Hills is worthy of
remark, for as a rule all the numerous creeks that rise in and flow from the
Hills sink before reaching the Plains. There are but four exceptions—

124 GEOLOGY OF THE BLACK HILLS.

Minne Kaita, Rapid, Spearfish, and Redwater. Some of the streams rise
again at intervals on the Plains, but none of them ever regain their original
volume. Such at least was their character at the time of our visit, but
from numerous signs it would appear that in cer-
tain seasons or during great floods many or all of
them carry water in great volume to the Cheyenne.
This sinking of the water is no uncommon feature
in the western country, and it is due in many cases
to various circumstances of climate which need not

be enumerated here. The sinking of the streams
in the Hills takes place usually within a very small
area, and I surmise that it is caused by a down-
ward infiltration of the water into the limestones,
through which it has dissolved subterranean chan-
nels, and from which it rises again at some distant
place. Sometimes, however, it may find a passage
under the visible bed of the stream among the

. Pink limestone (Red Beds).

5. Alternating sandstones and limestones (Carboniferous).
8. Red clay with gypsum (Red Beds).

6. Red clay (Red Beds).

bowlders filling the channel, and from them it may

yy
d

rise again in the Plains. Minne Katta, which in
the matter of sinking is an exception, issues from
a subterranean channel cut probably in the Car-

Carboniferous).

boniferous rocks; it rises in springs of great vol-
ume within a small area at the base of a cliff of

Fic. 18.—Section along the lower canon of Rapid Creek.

the upper Carboniferous series.
Possibly after the work of active mining has

Carboniferous).

been pursued in the valleys of the Hills for some
time, sending down the creeks large quantities of
fine sand and mud, some of them will become run-
ning streams out into the Plains, their old channels

2. Potsdam sandstones and conglomerate.

4. Gray and silicious limestones (

3. Shaly limestone (

1. Slates.

of subterranean escape being filled up by the débris

carried down from the mining operations.
Returning to the review of the Carboniferous rocks on the eastern side

of the Hills, on Rapid Creek is found one of the best exposures of the

sedimentary rocks that was anywhere examined. ‘The creek runs for some

RAPID CREEK SECTION. 125

five or six miles through a canon whose sides are almost vertical walls of
the sedimentary series. The dip, though varying and increasing in the
lower end of the canon near the Red Beds, is not very great, being 15° or
20°, and the rocks can therefore be studied with considerable ease. The
accompanying section is derived from the walls of the cation.

In ascending order the detailed section is as follows, adhering to the
numbers of the beds as given in the above cross-section :

Carboniferous.

3. Limestone, pink, gray at top and weathering as though slightly argillaceous. 35
Limestone, pink and yellowish, shaly; containing some cyathophylloid corals. 40

4, Limestone, gray or white, very massive; forming cliffs............. ..... 150+
Silicious limestone, pinkish in color, brecciated; weathering in reddish
QUROARS) 00 ASEH SU AR CoS aR BES Su Oa. Beto a Sie Seb el A: oer neie no area r na 175+
5. Silicious limestones pal sandstones alternating in thin beds, pink and red-
GUSTO TI CONOIP 6 AAS Os eee icy tes ee cs Ns ae os Pa ei dra ne ane ee . 200+
impure, massive, white sandstone, stained red’. 2_:...-.-.--.-2.-.-2.--:- 40
Massive: sbrecciated sandstone, stained red 22... (ees sans s.2k eee. so. eee 30

Red sandstone, stratified in well-marked strata............

The section agrees in the main with the typical Carboniferous section,
but the base of the Carboniferous is here thicker than elsewhere in the
Hills, and is at the same time a more massive and pure limestone.

The interstratified sandstones and limestones of the upper Carbonifer-
ous are shown near the mouth of Rapid Creek in great detail, and because
of the interest attaching to these beds a careful section was made of the
exposure as follows, in descending order :

Red Beds.

Feet
19. Limestone, purple ...... che 6 Gy Erp POET CRE LOTS RG IEEE OLS POR ears ES on te ee hae 25
lS Clays deepited! 22.22 22-1... Sod s30CloneenoS aed saennas cUpeaCotOEUUE se aes 100

Carboniferous.
17. Sandstone, white and stained red, distinctly stratified ................-.-- 40
16. Sandstone, variegated, deep red; showing no stratification................ 30
15. Sandstone, white. and. massive, stained red............ 222. -... 2.2222 e0ee0-- 40
ik, JGR OMe. THMMNIK. ote cela Bee SS ae cas nearer Oia Stree eter a ee 3
Sandstone awhteramdsplmid shh ses ee Cetiyaigs Sec ere ete GPs cose Uae ciate ee 3
12. Sandstone, argillaceous and calcareous, becoming a nik and white sand-
GIODUE 5 .cesdesd cscs Wo sadelo Bees dag Mere bie ce ee eee mre ers Rab6 M&S 24 *

ie hunestone, purple impure ‘and arcilaceous. 255 4/122 - ojo ce cece ce cece e 3

126 GEOLOGY OF THE BLACK HILLS.

Feet
10. Sandstone, pink and white, shaly.............. loko: sreihrerareletercae ob gaq5b6000C 3
9), Lamestone, pink... cc 5 fss5 coc aeetcl ote chs oes erste sere ETE et ener 5
8, Limestone; light: pink <2). 22258 Seer sise rete eel o ee ae Ce ee 4
7. Sandstone, coarse, calcareous, pink ........-.. ENE Saas che torate eccectiate age eee ey 3 4
6: Limestone, igray eset. ee a ee ee SE ais ters 2
De Valu escent cists se bts Sareea et en eed diavassl evsiarses pie ese ar ape eaves etetereee ete 40
4.. Limestone, pinks ss 25h S.s: sc ee ie i woe sere eget e eee ea ere 2
3, Juimestone, aroillaceous and siliciousiaee es eraser a eee eee 5
2. Sandstone; white and goin sek are reales er eee een eee eer 3
1. Limestone, gray and pink, in massive bands separated by bands of clay, and
DECOM SAsan dy ws: oe oye eee eae eee pee to the bed of the creek 30

These beds are generally highly colored pink or red, and the majority
of the limestones appear to be more or less magnesian and frequently sili-
cious and flinty. Several of the limestone strata are somewhat fossilferous.
The fossils are poorly preserved casts and are similar in character to those
found in the same series of rocks on Box Elder Creek.

The Box Elder section is more complete, for the underlying silicious
limestone and the purple limestone of the Red Beds both appear in the cliff.
It was carefully measured and examined in detail.

Section of the upper Carboniferous series on Box Elder Creek, in
descending order:

Red Beds.

Feet

45° Purploclimestome se: sree cisieie ces) ta tel tole Noein eebere cre vee ete steele, toy etetevereter etree 25
4A, Red! Clay casita rain tactsroralotel rar orsetie rer creme eter ore aie oeretare ielelarclelclertecite ete 100

Nos. 5 and 4 of the Carboniferous.

43. Variegated sandstone.... . er Pee fore ays ae hha APS oe OM tic A eer mere (0)
2 Wihite and yellowishesandstome ceca terreitoeisisis siete eerie oereieicisistelsetetoieietsie 15
41. Talus with fragments of 42..........-.. RS aes ot as a i Aer ae oh es 10
AD Sandstone, sre dn Cal CarCOusy ers separ setts tere tolerate tler=telehete <ledefalheteyaltelete soles sree aaitt= 5-6
39. Sandstone with limestone fragments, talus .......... ....--..-.-.---..--- 50
38. Sandstone, deep red, calcareous .---.. 0... 2 22-222 es we wees wwe ecn sane 5
Si Conccaled gaan ee eee eee toe aCe eer Ticiseter rr cieetere meee 14
36. Limestone, pink.........-- SP SURO aH aabOnos Neb eet) aire ak aH oaG- Woon Ho 1
ai, (OM INOHG! Se ose basdadcs ocodes Sdasdiedacec BHEOUSoedob Sua obqecscscgooas 10
JA. UM eCSTONe a DULD Oneee male erecta: BE BASS oS On one hobog ooe beg GoscouE 1
33. Sandstone, pink and white, soft and thin bedded..... ..........-...-.--- 8
32) IMeStone wp Inks seta ye eee ee ene al ereetehe cemeeteieteish eat teretteretatat= 6
SL iConcealedict aes kee See ee Cee: cicec ee reer een UAC SES Es CogSead 3)
30. Limestone, gray, stained red ....-. SOME aH Sadodne Shoo damOUD Sb dcLDaNS 4
29. Sandstone; eds 12 wet ace tere ween ces icle cre eaters teeeetererctcls ac caete reiterates 3

ALTERNATING SERIES IN DETAIL, | L227

Feet.
28, Limestone, gray and pink, staimed: red) - <6 ces ec eee een ose ce manne 6
Mis COMOCM EO es J acent Boom edecent oc eo bes BOE CODD ooO SoMa SnoRma oN Coos Ese 6
26, Limestone, gray and pink, stamed red .---.--. ---.----+--.--.--+--.-+.-- 4
215, LDN ORNS, SAN, TOSSES fee ooGs5 coos sooe {see paosedeogHen ec {a ouEots 14
Hil, SPMG ioe, Meloy, NE Soe bo o0 Boose bod seco ooo sodu nome Apo oHooBCaseeaeeo 5
23), JUIMEONE. Gey CNG! jyNlKe Wo oe eocacece Eoaeeeebonee Uoopscdeuo peo sodedor )
22, REMC OOS, wlan, joule Chie weOle oe Gon goes doo ka aeoses ocdonb Gos ossbusacue 6
Bl, nMOS, WiNKe.-os-eosdsscdsegoeoons wooo cse + SuouucecbeDeodse peoknon 14
Al, SPWCRMN@s 55 poonstebunionss avodangnonde Aboodes> coecseauacopaeooue Us oF 2
LO MBUIIMES LOM BOSS MMLC OUS ai sepsis Heit secret val See Pe taint ay shee ayelairerayars)aleyasene¥e) ovsiele elt Mies eve 14
i See imicsanc ered saMmastOMeS- pct. ee er). = = SE Menino peal Sy ae ap ye He UL Sato fails 1s
17. Limestone, gray and hard in strata, 2 feet thick ............-....---.----- 12
1G, JbMNEeSRoMNe, COMMON CE ANG! PII SH obSek ese oneesdeouoodso oe modcooebeneeeoe 3
lomeMestone poray and pinl<thardsandetlimbyscs ss. <2 cecc = dailies c= |e 2
AES ATL SLOMensyelll O Wiese fetter suece ier heist 08 oo op ata non ft ata Tavalre, o's ake ee Stbie cam cers 6
ETTIMES COME ITM POMC ey vam ie set eeeteget f= clin av c/e\ yale ci ate(s e.s1eyanafe e\ciei =) 25 2,0," \sia. 3
12, SAMO SOME Velo WESSIIO 656340 cen 416d5.0500 Gonose ey OadboodooeD bonne ete 4
IL, SAWCISHONS, SNK, Sle seto goa. cod odo nee Bove odes obecEs CouocE Ben eS coed aduk iL
OS SAN SLOTS -pIMASSIVes Ne CaS baled emia as telele sel ee leit (sca) aiel=) = oo eleeialo/s o)< <1) =~) 0/5) =1s 10
O> IITMESHODO, UMN. 66 Hho Rises de dteGsee sees Gua paacond ADO ocEs Coseee nner eae 2
Se OAM SLOME wee SRAM EM Ve LLO Waa ermine eit taearatneic eel silo cheisiencto's c aiavec} <2 cee 6
7. Limestone, gray, silicious, flinty ............. Bio Wy st SeuciAevaralL je eee aciae a eke ake 6
Gh, (COMCSNOC Ks BOE Se Se eee CaaS Ete Ae ee aete ae ee eee BR Re te a acgent ns 3 6
D-PuiIMeEstOne, eray, Compact, fossiliferous* - 2-22... 22. s2------- len arate te 8
APPL AMES COME plIU IN aye OUT Kom sraraece Exe aa peptic nisin Perararct sys tato eve nts > 1e!ahe aicvanatecaicereiaeie © 4
3. Sandstone, pink and yellow, fine grained, weathering red ..............-. 5
2. limestone, silicious, with some sandstone ...:2...--.-..--6----20++--+2 10
1. Limestone, silicious, brecciated ..... p00 SG OD Selonaoey HOODOO ALGO O HOD aad OD 15

No. 3 of the Carboniferous.

The fossils found in the strata marked (*) are few in number and badly
preserved. They are mainly ill-marked casts of very small brachiopods and
gasteropods so poorly defined as to be indeterminable, and though close
search was made, none were found that were of any value in determining
the relationship of the inclosing rocks.

Before entering the canon in which this section was observed Box
Elder Creek flows for eight or ten miles in a southeasterly direction, and
for the most of that distance it skirts the inner base of the monoclinal ridge.
One who follows up the creek valley has at his right, beyond a short slope,
9, vertical cliff 200 to 300 feet in height, formed by the lower Carboniferous.
rocks, which exhibit their usual character and thickness. In the neighboz-

128 GEOLOGY OF THE BLACK HILLS.

hood of Elk Creek and beyond, where the slates carry numerous outlying
patches of Potsdam and Carboniferous, the cliff loses its regularity, but
there is still no difficulty in distinguishing the several beds.

In the cation of Elk Creek, which for several miles cuts a vertical and
tortuous channel 200 or 300 feet in depth through the Carboniferous and
lower Red Beds, excellent sections are exposed of the Carboniferous rocks,
and they were examined at several points as our trail descended into or
wound its way out of the intricacies of the canon. The cross-section
already given of the development and pitch of the Carboniferous on Rapid
Creek would answer almost equally well for a section on Elk Creek. The
alternating bands of colored limestone and sandstone of the upper series
are again well exposed, but the outcrops were not studied with any minute
care.

The four creeks which cross the limestone ridge at the north end of its
bow-shaped curve and flow to the Belle Fourche were not followed through
their canons. The next point examined on the margin of the uplift was the
canon of Spearfish Creek. The Carboniferous is well exposed, but owing
to the presence of several volcanic peaks it is much tilted. Near the mouth
of the canon the intrusion of the volcanic rocks of Black Butte on the south
side of the creek has raised and exposed the lower sedimentary rocks, and
through them the creek flows in a profound canon. The following section
was taken at this place, beginning in the Red Valley.

hed Beds.
Feet
bo ParplisShilimestomeet cerca. cetera er cher ee eres eters eee ve tevereretere repetas 25
4. Crumbling. Soft, sreds Sam Stone yee ete eee teeta lel tte eee - 100
Carboniferous.

3. White, yellow, orange, and dark red, massive, soft sandstone; irregular in
celor, and weathering in fantastic shapes. ....---.-------- Sido does anoase 250
Deel QS ee rie ict ng fens feet d ee see TNS Be ene eames Stans veer Rete: a epeipercts Sees, 200

i Silrciousimestone to: the. bed ofuhemercelaasr seer) ee eer —
Near the butte, resting on the volcanic rock of the peak, fragments of
the metamorphosed Potsdam were seen, and resting upon it in regular order
are the strata of the above section.
Around Crow Peak the Potsdam, altered to a hard quartzite, stands
nearly vertical resting against the trachyte. The Carboniferous also has

THE CARBONIFEROUS AND THE IGNEOUS PEAKS. WAS)

been turned up, and its limestones, unchanged, are found resting upon the
Potsdam, and standing in places in a nearly vertical position. The change
from the normal horizontal position is sudden, and a few hundred feet
away they lie so nearly flat as to give no evidence of their near proximity
to a great cone of eruptive rock.

In a similar manner the Carboniferous is found encircling the volcanic
peak or ridge northeast of Inyan Kara, but here the underlying Potsdam
was not found exposed. The Carboniferous rocks are tilted at a high angle,
and in their elevation are conformably accompanied by the Red Beds, which
are represented most conspicuously by the purple limestone. This lime-
stone wraps the lower part of the elevation, and rises in a gentle slope
some distance upon its sides. Its arching uplift seems like an excrescence
or large bubble upon the main slope, which descends from the Carbonifer-
ous plateau on the east to the valley of the Red Beds.

The only remaining outcrop of the Carboniferous is that which encir-
cles the Warren Peaks, forming the foothills of the Bear Lodge range. It
is the largest of the minor exposures, and like the other minor exposures it
is associated in origin with large masses of volcanic rock.

Though geographically the peaks and elevations of the Bear Lodge
range appear to form a distinct system of mountains, geologically they
belong to the same system as the main range of the Hills. They pertain
to the same epoch of elevation and igneous eruption in which were formed
the numerous volcanic peaks of the northern end of the Hills, and they are
closely identified with them in the character of their rocks and in their
structure. They exhibit, however, a greater localization of the eruptive
force, and the mass of igneous matter is much greater than in any of the
other peaks. The Carboniferous is tilted up on every side just as it is
around Crow Peak, but in several places its beds have become somewhat
metamorphosed by proximity to the igneous rocks. In some localities the
trachyte is found to penetrate between its strata. The strata are also se-
verely dislocated, frequently in an intricate manner.

It is greatly to be regretted that the Carboniferous of the Black Hills
is so loth to yield up its biological record. Consisting almost entirely of

limestone, it is presumably constructed of the very ruins of the life of its
IBH

130 GEOLOGY OF THE BLACK HILLS.

age, and indeed half of the fragments that one picks up betray in some
way an organic origin, but the preservation is so poor that it is only here
and there that a form can be distinguished. Our collections add but four
forms to the list of those gathered by Professor Winchell and Mr. Grinnell
during the Custer expedition of 1874. The forms thus far obtained from
the lower member (1) are—

Zaphrentis centralis ? Spirifera.

Campophylium (or Amplexus). — Productus.

There have been brought from the middle members (2 and 3):

Zaphrentis. Terebratula.

Syringopora multattenuata. Spirifera Rocky-montana.
Athyris subtiita. —— Retzia.

Streptorhynchus. Euomphalus.
Rhynchonella.

On the eastern coast of the United States the Carboniferous period was
followed by an epoch of great disturbance, in which the strata of the Car-
boniferous and the preceding periods were bent, twisted, and plicated in a
grand manner, and the Alleghany Mountains were produced. During this
disturbance there was also an extinction of old organic types and an usher-
ing in of new ones. ‘The Mesozoic strata deposited subsequently are, there-
fore, found resting upon or abutting against the older formations uncon-
formably. In the Far West, too, in the region of the eastern flanks of the
Rocky Mountains, observers have found a similar unconformity between
the Paleozoic and Mesozoic.

In the Black Hills, however, we were able to detect no evidence of un-
conformity between the Carboniferous and the overlying Red Beds. There
is even such a lithological gradation from Paleozoic to Mesozoic that in the
absence of fossils the line between the two cannot be drawn with confidence.
It is true, indeed, that the length of outcrop continuously exposed was not
of sufficient extent to betray a slight discordance of dip, but from the com-
parative study of the strata at many different localities no evidence was
obtained that would warrant us in assuming any want of conformity. For
aught we know the area now included in the Black Hills was the scene of
continuous deposition from the beginning of Paleozoic time to the end of
Mesozoic time.

THE TRIASSIC OR RED BED FORMATION. sul

SECTION VI.

THE RED BEDS.
(Triassic ?)

Resting conformably upon the Carboniferous rocks is a series three or
four hundred feet in thickness of deep red, sandy, and gypsiferous clays,
with an intercalated stratum of limestone. These beds yield no trace of
organic remains, but they underlie conformably a series of lighter colored
clays, marls, limestones and sandstones with abundant and characteristic
Jurassic fossils. Beds of a similar brilliant red color are a conspicuous
element in the structure of the entire Rocky Mountain region, and though
they bear in some localities a few fossils, it is chiefly from their position
between well determined strata of Carboniferous and Jurassic age that they
are usually considered to be Triassic. On account of their prevailing red
color they are also commonly known as the ‘‘ Red Beds,” and that name is
here preferred, for the reason that it implies nothing in regard to their cor-
relation with fossiliferous strata elsewhere. If the name Trias is occasionally
used in these pages it is always with a reservation, for certainly in the Hills
there is nothing to prove its applicability.

The difficulty of ascertaining the position of the base of the series has
already been described in speaking of the Carboniferous. ‘There is no such
doubt about its separation from the Jura. At the top of the Red Beds there
is an unequivocal change in the character of the sediments and immediately
above it are Jurassic fossils in abundance. The Red Beds consist of the

following members in descending order :

Feet.
3. Deep red clay, sometimes becoming soft, shaly, argillaceous sandstone ;
contamineg large quantities of oy PSU: - <1. 1-2-2 ares we we ee oe 200-250
2. einiashsorn purple areilaceous limestone. 2. 24.52.- 22-2 «2 --. 22 ee eee 15-40
1. Deep red clay, sometimes becoming a soft, areillaceous sandstone; contain-
FAI UME MTEL Coke SIM Me eae cll cera eae SE eco Sie ale oad Mayers ig wi ats 75-100

Dr. Hayden, in his general section of the geological formations of the
Hills, includes in the lower portion of the Red Bed series all the strata
between the purple limestone (2 of the above section) and the Carboniter-
ous limestones—‘ brick-red material very similar to the bed D [38 of above

132 GEOLOGY OF THE BLACK HILLS

section], and passing down into a very hard, compact, concretionary sand-
stone, 250 to 300 feet”—thus embracing both the red arenaceous clay (1 of
the above section) and the colored sandstones and occasional limestones
which form the upper member of our section of the Carboniferous.

On the other hand, Professor Winchell (Black Hills of Dakota, Lud-
low, 1874, p. 65), while exaggerating very considerably the thickness of the
purple limestone (2 of the above section), has included it, together with the
underlying red clay and sandstones, whose thickness he greatly underesti-
mates, in the Carboniferous system, indicating, however, their reference to
that formation with some doubt.

The reasons for adopting the division here made between the Car-
boniferous and Red Beds have already been fully expressed in the section
on the Carboniferous. There is one statement by Dr. Hayden which,
if substantiated, would completely overthrow his own classification and
at the same time establish Professor Winchell’s. He speaks of finding in
the purple limestone in the Hills Spirifera (like S. lineata), Plewrotomaria,
Macrocheilus, and Bellerophon. Unfortunately in our most diligent search,
examining and breaking the rock almost by the cart-load and in many
localities, not the least trace of organic remains was found, and it is reluc-
tantly inferred that there was some error in the reference of the fossils to
this limestone.

The purple limestone is very conspicuous in the geological structure
of the Black Hills and an important element in the topography. It
forms the outer slope of the main portion of the Hills, and in a sloping
belt from half a mile to three or four miles in width, dipping outward
from 20° to 30°, completely encircles them. It preserves the underlying
red clay and sandstone from denudation and defines the inner margin
of the great encircling Red Valley. Its inner edge marks with consider-
able accuracy the border of the timbered region of the Hills, though a
few trees are in places scattered over its slope. It is so much harder
than the overlying clay and lies at so steep an angle, that it is swept
clean not only of the clay, but of all soil, and forms a bare and slippery
pavement of rock, which, by its seams and peculiar weathering, has
acquired a tesselated appearance. Were it not for the breaks caused by

THE RED BED LIMESTONE. 3333)

the cutting of the canons of the outgoing drainage one could drive many
wagons abreast entirely around the Hills on this encircling limestone pave-
ment. At Warren Peaks, which exhibit in miniature all the main points of
the geological structure of the Hills, the limestone forms also an encircling
slope.

Underlaid by 75 to 100 feet and overlaid by over 200 feet of soft red
clay, the limestone rests between two cushions, so that in the uplifting of
the rocks at the time of the elevation of the mountains it was not shattered
and dislocated so extensively as if it had been inclosed between more rigid
strata. It is found bending and warping suddenly, especially about some
of the volcanic peaks, and conforming to all the little irregularities of the
outer slope of the Hills, without exhibiting any great fractures or disloca-
tions. Though it is usually very fragmentary in its structure, filled with
eracks and joints perpendicular to its bedding, they seem rather due to its
composition and mode of weathering than to the bending of the strata.

The color of the limestone is grayish, pink, or purple; it is somewhat
mottled and often deeply stained by the red filtration from the overlying
clay. It is hard and gritty, and is rarely massive, but usually thinly
bedded. A qualitative analysis was made by Dr. Ricketts, who reports that
“it contains lime, carbonic acid, iron as protoxide, alumina and silica, in
quantity; and traces of manganese, potash, soda, magnesia, and sulphuric
acid. It consists essentially of carbonate of lime, with some silicate of
alumina and iron (clay); has an odor when ground like Canada petroleum.”
The fetid odor noticed by Dr. Ricketts is plainly discernible whenever the
rock is crushed or a fresh fracture is made. It is a common characteristic
of limestones and is believed to be due to the presence of organic matter
derived from the organisms—plants or animals—that inhabited the water at
the time of their deposition. It is worthy of remark that with this strong
evidence of the presence of life at the time of the formation of this deposit
there should be such an absolute dearth of fossil remains.

The rock appears to be quite soluble in water, for many of the springs
that flow from its base precipitate large quantities of calcareous tufa.

Above this limestone is a great development of brick-red clay, that in
its ordinary exposures exhibits no lamination nor other evidence of sedi-

134 GEOLOGY OF THE BLACK HILLS.

mentary structure. It has, however, in places a sandy phase, and in that
condition it is a plainly laminated shale or shaly sandstone. In the absence
of observable bedding, the thickness had to be determined indirectly by
measuring across the outcrop and combining the result with observations on
the dip and profile of the adjacent strata above and below. From a num-
ber of such estimates a general thickness of 200 or 250 feet was deduced.

The arenaceous phase of the clay was observed chiefly in the Belle
Fourche region near Bear Lodge, in portions of the Redwater Valley, and
on lower Red Canon Creek.

A sample of the material in its typical condition of a fine plastic clay
was submitted to Dr. Ricketts for a qualitative analysis and was found to
contain ‘‘alumina, silica, lime, and iron (as protoxide and peroxide) in quan-
tity, with traces of soda, potash, baryta, and carbonic acid. It is essentially
a silicate of alumina (clay), with some silicate of iron, containing also some
carbonate of lime and colored by sesquioxide of iron.” It does not contain
sufficient carbonate of lime to warrant the title of marl, but critically it may
be considered a clay more or less silicious and colored by peroxide of iron.

Gypsum is found in intercalated beds in great abundance, but its
exposures are not always easily traced The beds have. probably great
variation in thickness, and their outcrops are apt to be covered by thin
layers of clay. They were observed from 2 to 10 feet in thickness, and
could probably be found considerably thicker if excavations were made.
Our examinations did not suffice to determine whether they are more abun-
dant in one portion of the clay than in another, nor to trace for any consid-
erable distance a single stratum. They were found from within 75 feet of
the purple limestone to the very summit of the well distinguished red clays,
lying but a few feet below characteristic Jurassic fossils.

In many places in the vicinity of the gypsum strata the red clay is
found penetrated by a net-work of thin seams of gypsum ranging in width
from an inch to the thickness of a sheet of paper, cutting the clay in all
directions and interlacing in the most intricate manner. These are unques-
tionably a secondary deposition formed by the infiltration in crevices and
cracks in the clay of waters bearing in solution gypsum derived from the
associated beds. The gypsum where exposed has been largely removed by

GYPSUM OF THE RED BEDS. 135

solution, and long-standing outcrops are found to be rotten and crumbling.
In some localities, especially in the Red Valley near Sun Dance Hills, where
the red clay lies nearly horizontal, holes or sinks have been worn in the
gypsum layers, into which the local drainage flows, gradually dissolving the
gypsum and enlarging the sinks.

Its readiness of solution is also shown by its occurrence as an efflores-
ence on surfaces of clay or rock, where it has been deposited by evaporat-
ing waters. The waters which flow through it or in contact with large
surfaces are usually hard and medicinal.

It has a snowy white color, is massive and crystalline in structure
with numerous little sparkling facets, and in outcrops unaffected by the
weather is dense and firm. Occasionally small deposits of a pink, fibrous
gypsum of great beauty are found, but it was never found in crystals.
When long acted upon by the weather it becomes porous and soft and
resembles chalk in texture.

Notwithstanding the enormous quantities in which it occurs, it will
probably never, or at least for very many years, be of any commercial
value There is no market in which it can compete without great disad-
vantage in the matter of transportation.

The brilliant brick-red color of the Red Bed clay, intensified as it often
is by astrong contrast with the snowy white of the included gypsum and
the green of the scanty herbage, makes it one of the most conspicuous
members of the rock system of the Hills. It is easily eroded and washed
away by the action of rains and streams. Limited on each side by a hard
rock, its broad outcrop has been hollowed into a valley between two ridges.
On one side is the underlying Carboniferous series faced by the purple
limestone of the Red Beds, and on the other is the cliff capped by the
lower sandstone of the Cretaceous. Between them is the valley, broad
and open, completely encircling the Hills, and one of the most prominent
features of the topography. Its prevailing red hue distinguishes it from
all others, and it is appropriately entitled the Red Valley. From what-
ever side the Hills are approached the same, or nearly the same, topo-
graphical features are passed over in succession. By a gradual rise from .
the Plains, or sometimes by crossing a series of low cliffs, one reaches the

136 GEOLOGY OF THE BLACK HILLS.

summit of the foothills that encircle like a rampart the fastnesses of the
Black Hills. Looking back from this elevation he commands a broad
stretch of the Plains, a grassy sea, quietly undulating in the distance, but
broken near his feet into rocky billows. Facing about, he finds that he is
standing upon the verge of an escarpment 200 to 500 feet high, and beneath
him is the undulating, treeless Red Valley stretching away to the right and
left until by its curvature it is carried out of sight. Beyond it and two
miles, or four miles, or six miles away, the main mass of the Hills rises
darkly against the sky, timbered and rocky. Just at the base of the Hills,
and parting them from the valley, runs the bare outcrop of the purple lime-
stone, not an even band, but a serrated fringe, divided by every water-course
that descends to the valley and pointing a sharp crag upward in every
interval.

This structure of the Red Valley is indicated in the several cross-cuts
in subsequent portions of this section, Figures 19, 20 and 21. Its course
is shown on the geological map by the brown color which marks the out-
crop of the Red Beds.

Though it is easily distinguishable and traceable around all parts of the
Hills, preserving the same general features, it is subject to variations in
width and in details of structure. Its width depends upon the width of the
outcrop of the upper red clay and that depends on the local dip. It depends
also, but to a less extent, on the thickness of the clay. Where the dip is
slight, the outcrop and the valley are broad; where it is heavy they are
narrow, but there is no place where the valley is less than a mile across.

The Indians, recognizing its continuity and the regularity of its surface,
have followed it with their great trails or routes of travel, and it is known
to them as the ‘‘ Race-course.”

It is generally well covered with the common short grass of the Plains,
but it is entirely destitute of trees, save that an occasional hill may sustain
afew pines. The immediate valleys of the streams and dry washes which
drain across it from the interior of the Hills are narrow and frequently lined
with small groves or seattered individual trees. Their principal tree is the
cottonwood, but there are occasionally dwarfed and stunted oaks and
thickets of willow and wild plum. As already remarked, the majority of

THE RED VALLEY. pa

the streams sink in the cations of the Carboniferous, but many of them rise
again in the Red Valley in unexpected places as springs or pools of water.
They never, however, become again running streams.

Though the surface of the valley is generally undulating, with frequent
wide level expanses, it is often deeply cut and scored by ravines and chan-
nels, and these are especially numerous near the main streams of the Hills,
where the excavated and washed surfaces have an exceedingly bare and
desolate appearance. As has been aptly described by Colonel Dodge,
‘‘sometimes it is really a smooth, beautiful valley; in other places it is a
jumble of low, broken red hills, cut by innumerable ravines and looking
like a Virginian ‘old field’ on a large scale.”

Along the eastern border the valley is narrower than elsewhere, and
all the principal lines of drainage run across it, issuing from the monoclinal
ridge of Paleozoic rocks at the west, and immediately entering the Creta-
ceous rampart at the east. At the southern end the drainage crosses in the
same manner, but the dip is gentler and the valley is broad. At the south-
west it is again narrow, but it has a considerable drainage of its own.
Following its course from Dodge Pass northward, one first ascends for
six or eight miles a water-way that in some seasons must carry a large
volume and then descends through a grassy prairie to the east fork of
Beaver Creek, up which he travels for eight miles without leaving the Red
Valley. Thence to Inyan Kara he finds the drainage longitudinal, though
with no running water, and he crosses but a single divide between the two
forks of the Cheyenne. Approaching Inyan Kara he finds the valley
broader, and it is so broad beyond and so complicated by igneous uplifts
that its typical character is lost. At the north beyond the Bear Lodge
range it resumes its familiar form and for twenty miles it is the broad and
open valley of Redwater Creek.

A small but interesting area of the red clay is exhibited on the Belle
Fourche near Bear Lodge. Here, as also on lower Red Canon Creek and
in places on the Redwater, the clay has so large a proportion of sand that
it becomes a shaly red sandstone, and instead of forming sloping and
rounded surfaces it stands in sharp cliffs.

138 GEOLOGY OF THE BLACK HILLS.

The large percentage of peroxide of iron in the Red Beds, to which they
owe their bright red color, bears an interesting relation to the absence of
fossils. The material of which sediments are formed is derived by the various
processes of denudation from the rocks of older land surfaces. Whatever iron
they contain is dissolved from the land and transported in the condition of
protoxide or some proto-salt, such as the carbonate, and the process is facili-
tated by the presence of carbonic acid in the water. Now iron occurs in
these older rocks as protoxide and peroxide, the former of which is soluble
and the latter insoluble in water. ‘The peroxide, however, by the action of
organic matter, such as is held in solution by boggy waters, may be de-
prived of a portion of its oxygen and converted into protoxide and thus
rendered soluble. If the iron-bearing water is confined as in a shallow
basin and exposed long to the action of the atmosphere the protoxide of
iron absorbs oxygen, and is precipitated as the insoluble red peroxide of
iron. If, however, plant or animal life be present in sufficient quantity this
oxidation is prevented. ,In case but little foreign material—clay or sand—
has been brought by the waters, the deposit will be an iron ore; in the
absence of organic matter the peroxide or brown hematite, or in its pres-
ence the proto-carbonate, such as the iron-ore beds of the Coal Measures.
But in case large quantities of foreign material are deposited from the waters
at the same time there will be produced in the absence of life a brown or
red clay or sandstone, and in its presence a white or light-colored forma-
tion containing the iron as a protoxide. This question of the removal and
deposition of iron has been ably elucidated by Dr. Newberry and others,
and Dr. Hunt ‘‘can hardly conceive of an accumulation of iron, copper,
lead, silver, or gold in the production of which animal or vegetable life has
not either directly or indirectly been necessary.”* The point to be estab-
lished by this seeming digression is this; that reasoning from the condition
in which the iron is found in the Red Beds we must conclude there could
have been little or no life, animal or vegetable, in the water from which
they were deposited. The conclusion is strengthened by the fact of the
presence of large quantities of gypsum, which has been derived from the

* Chemical and Geological Essays, p. 226.

DEARTH OF FOSSILS. 139

evaporation of saline waters The degree of saline concentration which
the precipitation of gypsum indicates would be highly inimical to life

The presence of the gypsum helps to account for the absence of life,
and the absence of life accounts for the brilliant color. The three promi-
nent characteristics of the formation are therefore quite in harmony with

each other.

In passing now to the details of the exposures of the formation there
seems little need to linger. There is so great uniformity of relation and
structure that one or two local sections will illustrate the whole, while
nearly everything of importance has been anticipated by the description of
the several members and of the general topography.

At the headwaters of the east fork of the Beaver the Red Valley is
1,000 feet higher than it is at Camp Jenney, fifteen miles farther south, and it
has a total elevation above the sea of about 5,000 feet. The purple lime-
stone is well exhibited all along the valley, rising to the eastward and lap-

“ping against the side of the plateau, and near the head of the creek it covers a
considerable area. The main stream and several tributaries from the east cut
through it to escape from the plateau to the Red Valley, and in their canons
excellent sections are exposed of the upper Carboniferous and the contiguous
Red Beds. The valley is here three or four miles in width, and its western
rampart—the Cretaceous and Jurassic foothills—is less prominent than
usual. To the southward Beaver Creek cuts a channel of increasing depth
into the red clay; the Red Valley becomes narrower, and the western
escarpment becomes more pronounced, acquiring a height above the valley
of two or three hundred feet. In the vicinity of Camp Jenney and Fanny
Peak the purple limestone shows the double curvature represented in the
section. It laps steeply against the foot of the plateau, sometimes rising a
thousand feet or more above the valley. Then at the base it quickly curves
to the horizontal and in a mile or less it bends down again, disappearing
beneath the gypsiferous clay. Where it disappears its dip is 25° to i0°,
and its eastern edge is upturned to 75° to 85°. Its thickness is 40 feet.

Immediately east of Camp Jenney the lower red clay appears as a
soft sandy clay 50 or 75 feet thick, separating the purple limestone from the —

140 GEOLOGY OF THE BLACK HILLS.

underlying red sandstones which form Fanny Peak. The water of Beaver
Creek issuing largely by springs from beneath the limestone is hard and
limy, and many of the tributaries as they enter the Red Valley and become
exposed to rapid evaporation deposit beds of travertine.

West.

Fig. 19.—Ideal section across the Red Valley at Camp Jenney;, showing the foothills at the left
and Fanny Peak at the right.

1. Carboniferous limestone. 4. Red clays with gypsum (Red Beds).
2. Red sandstone (Carboniferous). 5. Jura.
3. Purple limestone (Red Beds). 6. Cretaceous.

Camp Jenney is at the point where Beaver Creek leaves the Red Val-
ley and cuts through the Cretaceous rampart on its way to the Cheyenne.
To the southward the valley rises gradually in a prairie-like expanse, des-
titute of water and but little broken by the dry channels that traverse it.
Thence to Red Cation Creek it was not examined geologically, but the
account given by the topographical party shows that there are no peculiar
features.

On Red Canon Creek the Red Beds are finely exposed, and the width
of the valley, including the slope of the purple limestone, is fully eight
miles. Here again portions of the red clay are sandy, sometimes becoming
a sandy shale, and in several places a tolerably massive but soft, argillace-
ous red sandstone. This character, as well as the relation of the red clays
to the overlying Jura, is illustrated in the following section taken near
the foothills on the west side of Red Canon Creek.

Jura.
Feet.
5. White ripple-marked sandstone, with a thin calcareous layer at its base full
of Jurassic fossils: Rhynchonella myrina, Pseudomonotis curta, and Trape-
ZUUNUSUDEQUOUIS 2.) abies Ne calc k Mepeic ia tals: Syste Bene eR eae cee ee gee 20
4; Gray shalestormanis et: 05 o<4 02 See ce oe ie SOR OOEL e tae nee eee 15

3. White sandstone, soft, and at bottom shaly, weathering in pot holes.....--. 15

DETAILS OF THE RED VALLEY. 141

Red Beds.
Feet.
2. Soft sandstone, blood red; appears somewhat argillaceous. . Diagn ety: Wika 380
1. Shaly sandstone, deep red, changing into red sandy shales, end ial into
rediclaymwabhyoypSUMn. Lose aed enee kere Hee Sao se cee nce eis (estimated).. 200

The transition from the red sandstones of the Red Beds to the soft
white sandstone and gray marls above is perfectly distinct. Gypsum is
seen in great abundance, and two seams have eacb a thickness of 8 or 10
feet. The locality affords a fine opportunity to study the infiltration veins
of gypsum. The sandy clay in particular is highly suffused, and a laby-
rinth of dry gulches with vertical sides from 10 to 40 feet high expose fine
natural sections.

Our next local examination was made on Amphibious Creek twenty
miles east of Red Cation Creek. The entire width of the valley, including
the slope of the limestone, is between four and five miles, and the red clay,
though well exposed, occupies but a narrow belt along the foothills.

The following ideal section is in direct continuation of the section
already given in Figure 17:

Fic. 20.—Ideal section across Red Valley on Amphibious Creek.

1. Carboniferous. 5. Jura.
2. Red sandstones and clay (Red Beds). 6. Cretaceous sandstone capping the foothills.
3. Purple limestone (Red Beds). 7. Clays of the lower Cretaceous.

4. Red clay with gypsum (Red Beds).

As rudely indicated in the wood-cut the limestone after dipping down
from the north side of the Red Valley warps up again in several places
along the creek. Near the pass of the creek through the foothills there is
exposed a stratum of gypsum 8 or 10 feet thick, lying 175 feet above the
purple limestone; and elsewhere in the vicinity the same mineral shows
numerous outcrops. At the pass the following section was taken; it shows
again the character of the junction between the Red Beds and Jura,
though here there is no evidence from fossils :

142 GEOLOGY OF THE BLACK HILLS.

» Jura.

Feet.

5. Sandstone, red or pink, soft at bottom and hard at top, with numerous ripple
TM ATIES S oisles coche eS re eee: aS oR Oe ae ES Pe A BL ES 8

4, Sandstone, yellowish and greenish, with some tinge

of red; containing some calcareous matter in
thim. bands”: 2s. Ai epee eee eee 10
oy \iMantie SHINGO Hose. gos SsegsosuGcdass boccac 3

Red Beds.

2... Deep red) Clay: i.ccier oe ace cr hie eee 50
EGy psu. pa cece meee to bed of creek. . 8

From Amphibious Creek to Burntwood the
Cretaceous rampart is very prominent, and near the
pass of the latter, called “Buffalo Gap,” it culmi-
nates in high hills. On French Creek, though the
entire Red Bed series is exposed in places, its struc-

Jura.

4. Red clay and gypsum (Red Beds).
6. Cretaceous sandstone.

5.

ture is not well developed, and the Red Valley is
but poorly marked.

From Battle Creek northward past Rapid, Box
Hilder, and Elk Creeks, the Red Valley has again a
fine development, extending to and joining the east-
ern extension of the great Redwater Valley on the
north side of the Hills, and having a width, inelud-

rq. 21.—Ideal section across the Red Valley on Rapid Creek.

aN :

3 ing the outer slope of the purple limestone, of
~s from two to six miles. The profile and cross-
Se section are nearly the same as on Amphibious
23% Creek (Fig. 20). North of Rapid Creek the lime-
[oe stone warps up and creates a ridge in the center of
ae the Red Valley, as shown in the accompanying
oe figure (21). If the uplift be disregarded, an idea

may be derived from the diagram of the general
structure of the Red Valley on the eastern side of
the Hills.

The purple limestone is very prominent on the eastern side of the

Hills. Along the entire margin it forms a gentle slope, rising from the red

DETAILS OF THE RED VALLEY. 143

clay of the Red Valley at an angle of 15° or 20°, and marking closely
with its inner margin the edge of the timbered area. It is frequently cut
by little ravines or gulches that head back a short distance in the Hills,
and from it arise many springs of deliciously cool water. One of these
springs near Elk Creek is of such size that the stream to which it gives
rise flows through and beyond the foothills. The surface of the limestone
is cracked and weather-worn, and is bare of soil for long distances, form-
ing a hard and somewhat slippery pavement.

Near Rapid Creek, immediately above this limestone, the following
strata of the Red Bed series were observed:

Feet.
, Clenys nech \waiilh Soins pay USNS Oo oe ce bon oe See eeaen Eee oo ocee Aono oD oommae es —
B, CSADSUS Won ek, Tees A eee Ae oe SR eh sh ee ae ee eee 8
4, Clay, with several seams of gypsum near the baSe...........-.-----..----- 40
a Ga Vif) SUMMINS WVELL LG rece es epee falhacetel arctaaraye tal wate yee ta a ova alata! <0 haat Soe etn eRe: 8
2 CHER. IRBO ey Wall! SOME) DSI So pecleasne oh eb Pee b ea Soares el oeceD Oo Ceemne ae 75-100
Heme SLONe aD UN Css as eee rae ek eae AS tes 2 5 aha! <2 < si Sinlel wieieie sje 3 ak 25

In the region of Elk Creek and Warren Creek the purple limestone is
tilted at a much higher angle than farther south, inclining 45° to 60° to
the eastward, and the Red Bed valley is correspondingly pinched. At the
same time it is more broken and scored by the minor drainage. Its greatest
constriction is near Crook City,* and beyond that point it opens out through
the valley of Whitewood Creek into the broad valley of the Spearfish and
Redwater, where the upper Red Beds find their greatest expanse. From
the Spearfish the valley runs westward to Sun Dance Hills, with a width
of five to eight miles, and then, bending around the northwestern end of the
Hills, is confluent with the wide expanse near Inyan Kara.

Figure 22 gives a section from the Cretaceous rampart or foothills to
Black Butte, the line running just east of Spearfish Creek.

The purple limestone all about the north end of the Hills has a low dip,
averaging less than 10°, and the exposure of its upper surface is very broad,
sometimes four or five miles. Its surface is frequently warped and bulged,
but it is broken only by erosion. It is not only treeless, but for the most
part soilless and grassless. Around the volcanic peaks—Crow, Sun Dance,

*On the geological map the outcrop of the Red Beds is represented too broad at Crook City. The
colors for Jura and Cretaceous should have been made to follow the contours on the west side of the
creek. Wherever the text and the map are at variance the former is to be preferred; the coloring of
the map was completed after Mr. Newton’s death.—EpD.

144 GEOLOGY OF THE BLACK HILLS.

Warren, the cone northeast of Inyan Kara, and Inyan Kara—it has been
bulged up at a high angle, and through it the igneous masses have been
extravasated. It does not encircle Crow Peak, but it marks out by its
flexure the limit in the Red Valley of the Crow Peak displacement. A
om long, low, rounded ridge, sheathed entirely by
Hills the limestone, extends northward into the val-
ley a distance of three or four miles. The
thickness of the limestone is here from 15 to
25 feet.
On the northwestern exposure it is cut
by the Redwater and its branches, some of
which run for miles in a westerly direction,

Cretaceous sandstone,

7. Jura.
8.
9. Trachyte.

nearly coincident with the strike of the rocks.
One of the western branches heads in the Red
Beds southeast of Sun Dance Hills and enters
the purple limestone from a higher horizon,
while the main branch, rising in Floral Valley
on the Carboniferous plateau, enters the pur-
ple limestone from a lower horizon. The
lower red clay of the Red Beds is often in this
vicinity so sandy as to acquire some degree
of solidity. The upper red clay has a great
development, and gives to this part of the
Red Valley, as seen from an eminence, a
striking appearance not readily forgotten.

Fic. 22.—Ideal section across the Red Valley near Spearfish Creek.

With a rounded, billowy surface, its blood-
red mass deeply gullied in all directions,

2. Red clay and sand (Red Beds).
3. Purple limestone (Red Beds).
4, Red clay and gypsum (Red Beds).

1. Carboniferous.

and with an occasional gash of white gyp-
sum exposed on the red field, the valley

Black Butte

stretches away to the dim line of the distant
rampart.

Occasionally there is a small expanse of grassy surface, but the blades
are scattered and there is scarcely any turf. The only trees are a
few scattered groves that indicate the courses of the creeks. Notwith-

DETAILS OF THE RED VALLEY. ; 145

standing the breadth of the exposure of the red clay—or rather perhaps
because of the breadth—it is impossible to measure its thickness. The
best estimate practicable seemed to indicate a thickness of between 250
and 300 feet. In many places the clay is quite sandy, especially in
the eastern part of the valley where it sometimes becomes a soft argil-
laceous sandstone marked in the topography by hillocks and small buttes
and mesas.

The junction of the Red Beds with the overlying Jura is well seen in
many places along the foothills north of Redwater Creek. Several sec-
tions of the Jurassic rocks, including their relation to the Red Beds, were
measured by Mr. Jenney and Mr. Patrick and will be found in the section
on the Jura.

Southwest of Sun Dance and west and northwest of Inyan Kara there
is a long range of low foothills cut by parallel valleys running north and
south which carry in their bottoms red clay and on their sides the lower
strata of the Jura. At one locality southwest of Sun Dance the following
section was observed: |

Jura.
Feet
7. Slope of hill; no exposure ...... Bohs Obie Ba Aeros Sic RRO Be ete ORD eee 25
6. Sandstone, very soft, white and yellowish; well exposed for 10 feet, in the

remaining distance fragmentary outcrops of soft white sandstones...--.-. 70
5. Shales. brown and yellow, sandy, containing Belemnites, Gryphca calceola,

OLCPineors ee eeeear ee Was aeteh yas) siajeicies eer Se ee ie ed SUSY eee ots es ee ene ee 65
APOANG SCONE: gS Okt wiNUCC zene are iar ajc etnies poie nial iam sie Scat wi wicpeeit o's ao 10
oe Clava or marl; VelOws OLR6ACISH! = els re sei e eicje'= Sores ste c Sietete ae sie eS. <= -. 50-60

Red Beds.
Za Giy, PSU 2 sore ee PO BOOT oie Buel Bid BID OGLE RNS Os TE ER ee ee ee A 6-8

JIS GLEN 5 TRO ee ils 15 aichc'e GB OES ATS oe ee es ETO Iie eet ee nla —

In Figure 23 an attempt is made to illustrate the relation of the Red
Valley and the Red Beds to the volcanic intrusions. The section runs from
Warren Peaks in a southeast direction to the Carboniferous plateau, cutting
on the way one of the Sun Dance Hills. It will be noticed that the Red Beds
rest directly against the trachyte of the Sun Dance Hills, while at Warren
Peaks the Carboniferous and Potsdam are interposed. If the Sun Dance

Hills be omitted and the red clay (5) extended across the space, the sec-
10 BH

146 GEOLOGY OF THE BLACK HILLS

tion will represent the typical synclinal character of the Red Valley at the
northwest angle of the Hills:

The Red Beds in the northern and northwest-
ern part of the Hills contain large quantities of
e@ypsum in strata of considerable thickness as well
as in disseminated seams and veins of small size.

The larger seams are usually 6 or 8 feet in thick-
ness, and though frequent opportunities were taken

a

us}

2)

a

no)

o

S

# 2 to measure them they were not found to exceed 10
Q 3)

= 38 feet.

on ae

= 92 The causes which prevent close measurement
E ‘ss
2é% of the red clay also preclude an accurate placing
Spa 8 ; ch liaaore
=e22 of the gypsum strata in their true position in the
SASS ‘

FSO formation. There appear, however, to be several
ees

well-marked horizons occupied by thick beds.
The first is about 75 or 100 feet above the purple
limestone and the second 40 or 50 feet higher.
A third is at the very summit of the red clay, and

Sun Dance Hilts.

a fourth, less persistent, is a few feet lower. Over
a large area between Redwater and Inyan Kara
Creeks the red clays lie with little or no dip, and

Frc. 23.—Ideal section across the Red Valley through Sun Dance Hills and Warren Peaks.

= in them a continuous seam of gypsum is found

‘ =z which frequently has but a thin stratum of clay

E Be covering it. This thin covering is occasionally

EEE wanting, and then the gypsum is exposed. Under

: Hee such circumstances it is never a firm rock, but its

eege surface is decomposed and undermined by atmos-

cepce pheric action. As one rides over it the feet of his

horse at every step break a thin crust and then

. sink a few inches through the pulverulent product
S of decomposition before striking the more solid bed

below. The latter gives a hollow sound, caused probably by an under-
mining beneath.

There are numerous sink holes in the red clay, and these on close

SINKS IN THE GYPSUM. | 147

examination are traced to seams of gypsum lying generally only a few
feet below the surface. The gypsum by percolation of water has been
decomposed, dissolved, and washed away, forming vertical holes in the seam
and channels of escape for the water to some lower level. These holes
by the action of rain and the drainage from limited areas of the surround-
ing clays become enlarged, and some of them have attained a diameter of
50 feet. The majority are, however, only from 2 to 5 feet in diameter, and
have all the characters of sinks in limestone countries.

East of Sun Dance these sinks are numerous, and between Sun Dance
and Inyan Kara they are met every few hundred feet, dotting the surface
of the red clay.

In the valley of the Belle Fourche, from the vicinity of Bear Lodge
to a point twenty miles northeast, the stream has cut its valley through the
upper Red Beds, here somewhat elevated by the fading extremity of the
uplift which produced the Hills. Above them the Jurassic strata are
exposed in a similar manner and to a greater extent. The cut through the
Red Beds is nowhere more than 200 feet deep, and the width of their out-
crop is not greater than two miles. In some of the side branches and dry
cations, however, the Red Bed exposure penetrates the bluffs for a distance
of several miles.

The following cross-section will give a fair idea of the structure of the
Belle Fourche Valley :

Valley of the
~ Belle Fourche
= ee i Bios they eee
Fig. 24.—Section across the valley of the Belle Fourche near Bear Lodge,
1. Red Beds. 2. 2. Jurassic strata. 3. Dakota sandstone (Cretaceous).

The Red Beds are here so sandy as to form a tolerably coherent shaly
sandstone, but in places they resume their usual clayey character. The
following section, observed at the spot represented by the illustration, shows
the strata from the summit of the lower plateau to the water of the river. —

148 GEOLOGY OF THE BLACK HILLS.

Jura.
Feet.
4, Sandstone, yellowish, sometimes quite red; forming the floor of the lower
plateau in: Pigure:24 25.2.0 ui 28 oo See eee eee eee eee 50
3. Clay or marl, gray or greenish, ali a pink streak near the middle; becoming
in the torre 3 feet an impure shaly limestone, with many Jurassic fossils.
Immediately above the latter layer there is considerable flinty matter... .. 120
fed Beds.
2. Sandstone, deep red, argillaceous and very shaly, containing a bed of gypsum 8
1. Sandstone, deep red, soft and shaly, with several seams of gypsum in its
Upper 4:01 Oteehae aera ae Bi Depa Rs ry cea need re tostream.. 171

The red clays near the junction with the fossiliferous strata were
observed to have a browner color than below. On the opposite side of the
river the same fossiliferous strata were seen, and underneath them, below
60 feet of red clay, is a stratum 20 feet thick made up of seams of gypsum
1 foot thick separated by bands of clay, while below it are the red sandy
clays of the section. Northward, down the river, the Red Beds retain the
characters described In some places they become so firm as to form the
immediate banks of the river for considerable distances, rendering the cross-
ing a matter of difficulty. Where they finally sink beneath the river they
attain their depression by a gradual dip, and give place to the Jurassic
strata, which in turn shortly dip under the river and are replaced by the
lower Cretaceous series.

One other outlying outcrop of the Red Beds remains to be mentioned.
It lies on the west base of Bear Butte, a few miles northeast of Crook City,
and what little is known of its character is detailed in the description of
Bear Butte in the section on the igneous rocks.

In conclusion, a brief notice may be given of the Red Beds or Trias
in other portions of the Rocky Mountain region, for the sake of showing
the more general relations of their development in the Black Hills.

A series of red beds, provisionally referred by most authorities to the
Trias, is found on the eastern slope of the Rocky Mountains almost con-
tinuously from British America to Mexico, and in Indian Territory, Texas,
and New Mexico it covers a large area of country. It occupies the same
eeological position as the series already described in the Black Hills, and is

TRIASSIC PLANTS. . 149

nearly always equally unfossiliferous. Its vivid color renders it a most
conspicuous feature in the geological structure of the region, enforcing the
attention of even the most casual observer. In thickness it ranges from
scarcely 100 feet in some localities to 1,5V0 or 2,000 in others. Wherever
exhibited it carries gypsum in greater or less quantity, and in the southwest
it holds notable amounts of salt.

Near Abiquiu, N. Mex., and in Los Bronces, Sonora, the Red Beds
are found to contain beds of coal, and associated with them a large num-
ber of fossil plants. These have been described by Dr. Newberry who
pronounces them similar to the plants from the Triassic coal basin of
Virginia and North -Carolina and very like the Triassic plants of the
Old World, with which many of the genera and some of the species
appear to be identical. Fossil wood is also frequently found, and in Texas
and New Mexico it is very abundant. It is often saturated with sulphide
of copper, and in some regions this is found in such quantities as to have
been worked in former times by the Spaniards as an ore of copper. Ata
locality in Southern Utah it is similarly saturated with silver ores. This
fossil wood, however, is of little paleontological value, and, with the excep-
tion of the plant leaves just mentioned and a few molluscan forms announced
within two or three years, the beds contain no proof of their age.

With this dearth of fossils the greater part of the evidence for consid-
ering them of Triassic age is derived from their occupying a position
between unquestionable Carboniferous and Jurassic strata. In many
cases, however, the Carboniferous is unrepresented where the Red Bed
series occurs, and in a large part of its development in the Rocky Mount-
ains the overlying Jura is either undistinguishable or wanting.

In Arizona near the Moqui villages Dr. Newberry found resting upon
variegated marls of the Triassic series, and immediately underneath Creta-
ceous sandstones, a stratum of lignite containing fossil plants closely allied
to Jurassic species of Europe.*

In eastern Colorado the series, according to Dr. Stevenson, underlies
unconformably the Jura and Cretaceous,t and since along the eastern

*Ives Colorado Report, pp. 79-82.
t Survey West of the 100th Meridian, Vol. III, p. 379.

150 GEOLOGY OF THE BLACK HILLS.

range the Red Beds overlap greatly the Carboniferous rocks, they must be
quite unconformable also to the Carboniferous.*

In central and northern Colorado the Red Beds have been carefully
studied by the late Mr. Marvine, Dr. Peale, and others. They have there
the normal red sandstone character, varying in thickness from 400 to 1,600
or 2,000 feet, and underlie Jurassic strata, but owing to a general absence
or concealment of the Carboniferous they are found (almost as far north as
the Union Pacific Railroad) to rest directly upon Archean rocks. Mr. Mar-
vine mentions that in the Middle Park region of Colorado the ‘ develop-
ment of the Carboniferous is far more marked, and consists principally of a
second series of red beds of deeper purple hue than those referred to the
Triassic,”> and that in their upper part Dr. Peale found leaves regarded by
Professor Lesquereux as Permian. Northward the Red Beds are found on
the flanks of the Laramie, Wind River, and Bighorn Mountains from Colo-
rado to the British Possessions. North of the Platte they have not yet
been critically examined, but it is known that a red arenaceous series
underlies very fossiliferous Jurassic strata, and rests upon rocks of Car-
boniferous age.

In the Wasatch Mountains Mr. King, of the Fortieth Parallel Survey,
finds the Trias to be composed of quartzites and silicious and dolomitic
limestones capped by the typical red sandstones, and entirely unfossiliferous.

Mr. G. M. Dawson, of the British North American Boundary Survey,
finds on the eastern flanks of the Rocky Mountains, on the 49th parallel,
300 feet of characteristically colored sandstones, which, by comparison with
similar beds in the United States, he regards as of Triassic age.t

The interposition of the Red Beds between Jurassic and Carbonifer-
ous strata cannot be taken as positive proof of their Triassic age; but in the
absence of evidence to the contrary it fully warrants their provisional assign-
ment, and the case is strengthened by the fact that in certain parts of the
Rocky Mountains an unconformity is found on the one hand between the

* Surveys West of the 100th Meridian, Vol. III, p. 499.

t United States Geological Survey of the Territories, 1873, p. 105.

{ Report on the Geology and Resources of the Region inthe Vicinity of the Forty-ninth Parallel, B.
N. A. B. Com., p. 71.

THE JURA. . WI

Carboniferous and the Red Beds, and on the other between the Red Beds
and the Jura. In the Black Hills, however; no such unconformity is to be
found.

SECTION VII.

THE JURA.

The Jurassic system, which is so largely developed in Europe, con-
taining the remains of huge swimming and flying reptiles and holding im-
mense deposits of iron ore that are the foundation of some of the largest
iron industries in England and the Continent, is but sparingly represented
in American geology, and none of the gigantic vertebrates have as yet been »
found here. For along time the Trias of the Atlantic coast, especially in
the coal basins of Richmond and North Carolina, was regarded by some of
our most eminent geologists as in whole or part of Jurassic age, but that
view is now abandoned, and the only developments of undoubted Jurassic —
rocks in our country lie west of the Mississippi.

The first determination of the formation in the Far West was made by
Professor Meek from fossils collected in the Black Hills by Dr. Hayden in
1857, and the discovery was announced by Meek and Hayden in a paper
published in the Proceedings of the Academy of Natural Science of
Philadelphia in March, 1858.

The forms there made known are all molluscan, excepting one crinoid,
Pentacrinus asteriscus, and are closely allied to species of the European
Jura.

Since that announcement it has been found that the formation is very
generally present in the Rocky Mountain system from the extreme north
to New Mexico and from their eastern slope westward in the various ranges
to the Wasatch. It is known, too, in the great interior basin and in the
Sierra Nevada. For the most part, it has been identified by its fossil con-
tents, but there are considerable districts where these guides are wanting
and it has been traced merely by stratigraphical relations and lithological
resemblances. In the mountain chains of the Northwest, the Laramie
Mountains, the Wind River Mountains, the Bighorn Mountains, etc., it is
often richly fossiliferous, but less so than in the Black Hills. In the Hills ©

152 GEOLOGY OF THE BLACK HILLS.

its strata from the base upward are well characterized by fossils, and, except-
ing on the eastern side, they occur in abundance.

The Jura of the Northwest has a very uniform character, consisting
generally of gray or ash-colored marls, marly or arenaceous limestones, and
soft sandstones. The greatest thickness yet found is in the Wind River
Mountains, where the formation is fully 1,000 feet thick, but elsewhere it
ranges from 50 to 100 or 200 feet. In the southwest, however, in southern
Nevada, Utah, Arizona, and New Mexico, though in places absent, it is
found to range as high as 2,000 feet or even more. In the localities of its
maximum development it is composed of highly colored marls, shales, and
soft sandstone, with some limestone and considerable gypsum.

The Jura of the Black Hills consists primarily of gray or ash-colored
clays or marls, with occasional bands of green and red. Interbedded with
these are soft sandstones, more or less argillaceous, and a few restricted
thin bands of impure limestone. The formation is so soft and weathers so
easily that its outcrops are largely covered. by the talus of the overlying
sandstone, and the exposures are generally imperfect. Its study was there-
fore not so satisfactory as that of the other formations; still, by com-
bining the data gathered at many different points the general features
were well made out.

The thickness of the formation in the main region of the Hills is about
200 feet, but it shows a remarkable increase toward the north and north-
west, attaining in the Belle Fourche Valley a depth of nearly 600 feet. Its
strata occupy the greater part of the inner slope of the foothills which
form the outer rim of the Red Valley, and are overlaid by the heavy sand-
stone of the base of the Cretaceous, which everywhere forms the capping
rock of the foothills. In the northwest, where the character and continuity
of the foothills are somewhat interrupted by the Bear Lodge range, the
Jurassic outcrop leaves the margin of the Red Valley and runs over to the
Belle Fourche, where it encircles the outlying outcrop of the Red Beds.

On the north and west, and to a less degree on the south, the forma-
tion is well exposed and characterized by a greater or less abundance of
fossils. On the southeast and east it is less plainly seen, being usually

NO SUBDIVISION OF JURA. 153

covered by a broad talus, and so far as examined it was not found to be
fossiliferous.

The relations of the Jura to the other formations of the Hills and
the place it occupies in their physical structure are indicated in the figures
that have been given in the previous section to illustrate the structure of
the Red Beds and the Red Valley.

Though it was examined in many places and with considerable care,
it was found impossible to base any subdivision of the formation either on
persistent lithological characters or on the distribution of fossil forms.
There is no single bed that was recognized throughout the belt of expo-
sure, and for the most part it was impracticable to correlate, bed by bed,
any two sections.

_ But while the Jurassic strata vary indefinitely among themselves, they
are always easily distinguished from the Red Beds. ‘The change from the
deep red clays below to the pale gray clays above is always abrupt, and
the latter have a marly appearance never seen in the former. The heavy
gypsum strata of the Red Beds are not found above, although the mineral
is not entirely unrepresented. In a few places thin seams of a beautiful
flesh-colored fibrous gypsum were found associated with thin limestone
strata near the base of the formation.

The most marked single bed is a sandstone about 50 feet thick, usually
of a yellow color, but sometimes quite red. On the Belle Fourche this is
about 100 feet above the top of the red clays, and forms the floor of a rude
platform or slope on the borders of the river, extending backward to the
foot of the Dakota cliffs, which at base are formed of Jurassic strata and
at top by the Cretaceous sandstone. Its area may be seen by referring to
the geological map, for it underlies substantially all that part of the Belle
Fourche Valley colored to represent the Jura. <A similar stratum on the
Redwater is probably equivalent to this; it is separated by 50 or 60 feet of
yellowish shale from the red clays below. It is possible, also, that the
same is represented by a thinner sandstone seen on the Beaver, 60 or 70
feet above the red clays; but in the remainder of the visited exposures it
was not recognized.

It is usual to find: this sandstone and others of the formation beauti-—

154 GEOLOGY OF THE BLACK HILLS.

fully ripple-marked—an evidence of the shallowness of the water in which
they were laid down.

The clays or marls do not appear to be more particularly confined
to one part than another, though they perhaps are not so strongly
developed in the extreme upper portion as in the lower two-thirds of the
formation. Their colors are gray or drab and dull green, with an occa-
sional streak of bright red or pink. They often contain seams of limestone
more or less impure, and these are possibly more common in the lower
portion of the formation. The limestones are frequently fossiliferous, but
seem never to be more than a few inches in thickness, and do not constitute,
so far as could be determined, continuous strata.

Everywhere a large proportion of the formation is composed of sand-
stones, which are usually light in color and even sometimes of a snowy
whiteness. As a rule they are very soft or shaly, passing into sandy
shales. Soft incoherent sands are met with at different points on the Red-
water, which are probably the result either of the decomposition of soft fine
sandstone or of the leeching of sandy clays.

Along the Redwater Valley, from Warren Peaks eastward to the
Spearfish, there were found two horizons yielding fossils in abundance;
one at 135 feet and the other at 350 feet above the Red Beds. The latter
horizon is also well marked near Bear Lodge, but was not recognized
elsewhere.

The meagerness and indefiniteness of this general description is due
in part to the variability of the strata, and in part to the imperfection of
the observations. The center of interest in the Hills was in the main body
of the uplift, and what was learned of the periphery was acquired by radial
excursions along the creek valleys. The Jura was crossed at a number of
points, but it was not followed on its line of outcrop. Hach observation is
therefore isolated, and it will probably be best to put each one on record by
itself. In the pages immediately following, the observed sections will be
described in order, beginning with the point on Beaver Creek where the
formation was first observed, and passing in succession to the south, east, and

north sides of the Hills.

DETAILS OF THE JURA. 155

The foothills on the west side of the east fork of the Beaver, for ten
or fifteen miles north of Camp Jenney, reveal along their inner escarpment
frequent exposures of the Jura, giving an excellent idea of the structure of
the formation; and in various places abundant and characteristic fossils
were found. The valley is at bottom an undulating and somewhat rugged
surface of the brick-red clays of the Red Beds, and these in places form
the base of the foothills. Between them and the Cretaceous sandstone at
the top of the cliff the gray clays and sandstones of the Jura crop out at
intervals. About ten miles north of Camp Jenney the following complete

section was procured.
Cretaceous (No. 1).

Teet.
6. Sandstone, white and massive, forming the summit of the cliff.... -......... 85
Jura.

5. Clays or marls, gray or greenish, with a streak of red clay near the middle;
IME EMP PEL ypPALLs Mamiya DELEMMIGESwareicrectey— = sep sichjou <csel= weave ce eines e apse ee 100

4, Sandstones, white and shaly, in places somewhat massive, ripple-marked ; con-
tains fossils near its base (Gryphea calceola,etc.). ..........--.-.-.---! 50

3. Clays or marls, brown or gray, with some gypsum; about 10 feet from base

in a thin and impure limestone, werefound a Gryphea and ammonite frag-
TANG NGS eee etre pee ee TTS ence eis ey aed olin creme Sey eT a can IN atti Con lis ade is alg aie 70

Red Beds

Za GYPSUM ewes aMOLNMOUS ==) set soe eyelet = is Meh OOP aay lta cae t ic 2 8
WM SMRCUGClAY eee ocieeeasetrten since ene anita eat Sota oe to bottom of creek.. 130

The following section was measured near Camp Jenney, on the north-
ern side of the pass which Beaver Creek has opened through the foothills.

Cretaceous (No. 1).

Feet.
6. Sandstone, yellow and white, somewhat lamellar, and containing ripple-marked
SUELACCS ere pihe see crenata rian eG Nat cM Pena Ars cE Laie Gl ouch Mele: aaiard oly w 50
5. Sandstone, yellowish with red stains, heavily bedded....-... Be yee Nene by eiacers 40
4, Sandstone, very white, fine-grained and massive, easily decomposing into fine
white sand ; forms a well-marked cliff, eaten into caverns and holes...... 100
Jura.
3. Covered by talus and not well exposed; at intervals outcrops of gray or green-
ish clays or marls, with occasional bands of limestone containing fossils;
ASOMOMLELOPSOm SAN ShONOs cee a eee e= acces Ge wines cee Reece ee be eee 70
2. Marls or clays, gray and purple, with nodules of impure limestone; base

COMCEG ~ olga ig GSS 0 6 ADA OOS SCIP OCIESC, TS re ree = one ee a a 110
1. Marls or clays, gray and purple, with thin bands of impure limestone, contain-
TIVO LO SSI Sheree ta arene leqsieratencts ienoke le <te) oe icisisle so isiu ls oie. wrale, araie ae to base of cliff.. 20

156 GEOLOGY OF THE BLACK HILLS.

The base of the section is probably some little space above the base
of the Jurassic series. On the opposite side of the creek the red clays with
their inclosed gypsum occupy the bottom of the valley.

In several localities in the vicinity some thin seams of a purple fibrous
gypsum were seen in the purple clays (2), but it exists in no great quantity
and does not appear to be a persistent feature. The massive white sand-
stone (4) is extremely unlike the ordinary coarse and deeply colored sand-
stones of the Cretaceous. It is so very soft that it readily crumbles into
a talus of exceedingly white and fine sand and it was not found at all coarse
or conglomeratic, as is usual with the lower Cretaceous sandstones It is
to such an extent intermediate in character between the Cretaceous rocks
above and the Jurassic below, that its assignment to the upper formation is
made with much hesitation.

In the Belle Fourche Valley a similar soft and white sandstone, about
50 feet in thickness, containing bands of pebbly conglomerate, was found
separated from the overlying undoubted Cretaceous by 5 feet of an impure,
dark calcareous shale.

At Camp Jenney two or three small hills stand in the Red Valley in
front of the main range of the foothills. On the inner side of these hills
are seen isolated exposures of the Jura, which are interesting by reason of
the great abundance of Belemnites in the gray clays, and a recapitulation of
the local section is therefore given.

Crelaceous.
Feet.
3. Sandstone, capping rhe Willy eps ee es re nesta be erate eric erelsitoleiet tae meee 100
Jura.

2. Clays or marls, greenish, grayish, and yellowish, with a streak of red; imper-

fectly exposed, and containing near the base great numbers of Belemnites
CENSUS OSE 5 aoe Oe Ee ToL Oo PE Tet oe gr 165
lcSandstone}white-and: shalye 222 eee er toe ier eee eee exposed. . 5

Then a grassed and undulating surface to the Red Beds and gypsum
below, the base of the Jura being concealed.

The next examination was made on Red Canon Creek, thirty-five miles
south of Camp Jenney. The following section was observed in a small

DETAILS OF THE JURA 157

butte near the foothills and on the west side of the creek. It gives but a
small part of the Jurassic series and that at the base.

Jura.

Feet.

5. Sandstone, white, somwhat lamellar, and filled with ripple marks, containing
at its base a very impure calcareous layer with abundant fossils .....-.-.- 20
4, Marl or clay shale, gray in color, with no fossils......-..... 2... ....-.-.-.- 20
3. Sandstone, white, soft, and somewhat lamellar at base...--.........-. -.- 10

Red Beds.

PP SALOSCOME IN ASSIVIEs GEC PMLCC naire nee ee = Sopra aiapet soci er wale 3 2 Mike ics sie 80

1. Red shaly sandstone changing into red shale and finally passing into red ae
VLU CUVEE OFS Oeste shames teak ey oA me Rm DS ren SER Gears : oe) JID)

The red sandstone (2) belongs undoubtedly to the Red Bed series,
which is in this part of the Hills very arenaceous, having many bands of
sandstone interstratified with the clay and frequently becoming in consider-
able bodies a massive, though soft sandstone. The change is often sudden
from a soft and plastic red clay to a soft and massive red sandstone.

To the northeast of the last section, and within two or three miles, com-
plete exposures were obtained of all the strata of the Jura from base to
summit. The following is the section:

Cretaceous (No. 1).

Feet
10. Sandstone, reddish and yellowish, massive; showing at base a small stratum
Oe (Shy DONS Boing? dns GS BAS oe 6 Regia rs cee nS eae ner nee Eee 150
9. Sandstone, not well exposed.-...-.....-. Sep Peeve winteee ets, Geis c NS opted weniaele.e 50
Jura.
8. Red sandy clay or shaly sandstone, quite soft, with bands of more massive
DUES OLSANOSbON Cer amrereet se eaiesii cot hi shecin ws sean Dente J here we gto os be 60
(ASH AlESLOLSMAL Seco TayeANGsSAM Ol Vacee rye, we veiyer ays ee one la Neyo ca aie ks « 30
6. Sandstone, white, containing near its base a calcareous layer, with fossils
similar to those in 5 of last section (with which stratum this is equiva-
EVIE) ig SS SS AI ES ra ae arenes oe BES eR ED eh 20
Sw ohales onmarls-orayismOr OreemIsh 2 se) |= ent se Gence sce tek ye ce cre eres 45
Red Beds.
4. Sandstones, soft and massive; upper 10 feet white and shaly, lower part
1 HELO les eevenes es he ele) eee ee et ee Pe Rte Set Meee) Smee Sas aies Pasi el eleiepore wines 45
3. Red shales, changing 1@ HOO OAs dk eee cece s So: Ga eee Gre eee ene ee eee 170
ey (Cary OUTTA PLOTS) IMAL TANS YSST NYS) a, Aes ese Noe eta el aie ca 10
1. Red clay, containing much gypsum, in thin ramifying seams; to valley of

158 GEOLOGY OF THE BLACK HILLS.

The next detailed examination of the formation was on Amphibious
Creek, near the canon by which it passes the Cretaceous ridge or ‘“ foot-
hills.” The following section was measured:

Cretaceous (395 feet exposed).

Feet.
16. Sandstone, capping hill; massive, white, stained yellowish and reddish. 300
15. Unexposed.. 22222 ooh Gt Moulage eye nee tate nets Fresemidaoas holst Cie ante agt aan coon 25
14. Sandstone, soft and massive; pinkish in color.......)...............2-... 70
Jura (234 feet).

13. Mostly concealed, a talus overlying soft rocks which at base appear to be a
white or reddish, soft, argillaceous sandstone..-.............-----.-+--- 105
12. Sandstone, light red, soft and incoherent, almost a sand...............-.- 55
.11. Sandstone, greenish and calcareous, thinly bedded ........... .. .....--. 20
10. Sandstone, white or greenish, in thin layers (8-10 inches), with many ripple :
102 2 ey Se tere aR ee et ND rae Te Re RO in Be ay elena a eR At 20
9: Shale, red and gray, and shaly sandstone: --2- = 7225.22 2. see ee ee 8
8 Shale red amd vgraiyin ectes yel= ee tava eee cesar cee ee eer 5
7. Sandstone, red and pink; soft at bottom, hard above; with ripple marks. . 8
6. Sandstone, yellowish, greenish, reddish, a thin brecciated band.......-...-- 10
ba Sandstones wiitecs: chemo sere a peer aaee CRO an cuits ete tan we ens 3

Red Beds (255 feet exposed)

ERMOMER GIS Dike Sag ecaocaRpesonadoe bngonooUbooosooscodDooDododao sD }ous 50
Se CRY PSU kerio ce elon sear rele tect: tale oxo aie stan sate SSieletaha te deetaie Mohs evans ra on ete ane 10
oe: Ole Ia eetely yall et fay NTN Be Boe eee coeses G45 cong osgbosas Hee ar RRR NE 175
LS Limestone; pimk«or purple incr sceretcyete- cc cerec ces ner os eee et we eee careers 20

The Jura was recognized in this section by certain of its beds, but in
the absence of fossils it is hard to say where the separating lines should be
drawn. ‘Taking the demarkation here made the formation has a total of
234 feet, a much greater thickness than was found on Red Cafion Creek,
twenty-five miles to the westward. It will also be noticed that the arena-
ceous materials are here more than usually predominant.

At Buffalo Gap, the pass by which Burntwood Creek breaks through
the foothills, the exposures of the Jura are very imperfect. On lower
French Creek and on lower Spring Creek observations were equally unsatis-
factory. Occasional outcrops of the yellow and drab clays and soft sand-
stones were seen, but no continuous section was anywhere attainable, and
the rocks appeared to be entirely barren of organic remains. Near Rapid
and Box Elder Creeks and north of the latter, frequent exposures of the

DETAILS OF THE JURA. 159

grayish marls were seen, and at one place in the valley of the Red Beds,
where there had been a local uplift, the summit of the red clays, with a bed
of gypsum 6 feet in thickness, was found to be overlaid conformably by 25
feet of greenish and reddish marls and shales and yellow sandstone—a rela-
tion similar to that already described on the western side of the Hills. At
the pass of Rapid Creek through the foothills, the cliffs are capped by a
heavy bed of the Dakota coarse sandstone, about 25 feet thick, stained
deeply red and containing many ferruginous masses. Below this sandstone
are about 200 feet of poorly exposed Jurassic beds resting upon the red
gypsiferous clays of the Red Beds. The Jurassic beds consist in their
upper part of shaly and soft sandstones, with clays or marls, and have
below a greater thickness of greenish, drab and «yellow marls or clays,
with some streaks of deep red, and a snowy white stratum of very soft,
argillaceous sandstone. This sandstone appears to be some 80 or 90 feet
in thickness, and can be traced by its vivid whiteness several miles north-
ward along the foothills. It weathers readily somewhat like a clay, and
is probably a local variation of some of the argillo-arenaceous beds. of
the formation.

-. Near the pass of Box Elder Creek these same beds are seen in frag-
mentary exposures. Atthe pass of Elk Creek through the foothills, beneath
the usual capping of coarse sandstone, here 300 feet in thickness, there are
exposed about 175 feet of gray or greenish clays or marls containing con-
siderable limestone in thin bands but no fossil remains. In the pass of the
north branch of Bear Butte Creek there is a repetition of nearly the same
facts: a capping of Dakota sandstone, here 15 feet in thickness, underlaid
by 50 feet of dark gray and greenish marls or clays with a three-foot seam
of argillaceous limestone, and then a grassy slope with no exposures to the
red clays of the Red Valley below.

From this place around the northeast corner of the Hills to the valley
of Spearfish Creek occasional outcrops of the drab clays are seen, but they
present no good exposition of the structure of the formation and the notes
on their exposures are scarcely worthy of quotation.

In the center of the Red Valley, two miles east of Spearfish Creek,
rises a prominent butte, Joe Peak, capped by Cretaceous sandstone and

160 GEOLOGY OF THE BLACK HILLS.

based upon the Red Beds. The section is imperfect, but is added here to
illustrate the thickness and character of the formation in this part of the
Redwater Valley.

Cretaceous.
Feet.
7. Sandstone, yellow, coarse and massive, fine grained; conglomerate at base. . 70
Jura.
6. Talus, overlying (probably) beds of a soft nature .....-. ein Ree ee ae eee 310
5. Sandstone, white and ireds-— Sipe a eey wis eae ee ee ce eee en : 15
4, Sandstone, yellow, soft; containing calcareous bands 2 or 3 feet thick... 2... 25
3. Clays or marls, aiendslh OF QUAY Heat Se hn Ss Mee etarere Senter acto Re ern 55
Red Beds
ye 6 4 01-1 0111 ee eRe en OM Re eh nA ae EE aS eR A ee OA a ln ena 6
IEE Clay, deep meds wathisovyiy Sum ese ee ee eae to level of creek.. 130

Assuming that the talus (6) is underlaid entirely by Jura, which seems
to be the case, the section gives a thickness of 400 feet to the formation,
and this, though greater than on the eastern side of the Hills, does not
surpass the thickness found a few miles north on the Redwater. As may
be seen by referring to the geological map the Redwater Valley widens
out greatly west of Spearfish Creek, exhibiting the great development of
the Red Beds so frequently mentioned in the discussion of that series.
As the result of a study of the Jura in the foothills on the northern side of
Redwater Creek a number of excellent sections were obtained by Mr. Jen-
ney and Mr. Patrick which will relieve the monotony of the record of
imperfect exposures on the eastern side of the Hills and illustrate the fine
development of the formation on the northern. Here, too, the Jurassic is
quite fossiliferous, especially in two horizons, as will appear by the sections.
Referring again to the geological map it will be seen that the foothills
approach the Spearfish from the east, and turning northward follow its
east bank for some distance. Then crossing the Deepwater, they run
nearly westward for twenty miles, keeping parallel to the course of the
Redwater. The southern flanks of the foothills and frequently a consid-
erable portion of their summits are composed of Jurassic strata, and these
are overlaid by the Dakota sandstone which either caps the bluffs or appears
at some little distance on the northward slopes. Fragments of the Jurassic
rocks, with or without the cap of Cretaceous, are found in isolated buttes in

DETAILS OF THE JURA ; 161

the Red Valley, the sole representatives of the former wide-spread distribu-
tion of those formations. Of this character is the butte near Spearfish, a
section of which has already been given.

On the east side of Spearfish Creek, some two or three miles north of
the section last given, the followmg measurements were made by Mr. Jen-
ney on the escarpment of the foothills.

Cretaceous.

Feet.
9. Sandstone, massive, yellow; the Dakota sandstone.............-—-.... -- 75
Jura (340 feet).

Sree OSC we tee eee rey ea ees. sie alee ae a Ne Serotec Seidieisle ye at sess 50

7. Sands and sandy shales, with a few fossils near the top.......---.----..--- 120

6. Sandstone, soft, crumbling and pinkish ; weathering to a loose reddish sand. 60
5. Sandstone, massive, yellow and pink; laminated with layers of different

shades of red ; containing a few star-fish impressions..... ........-.---- 40

Paes ENG VCO Wi aia coer oe ae, Jee Sao OE Se USE opie Seren se eee 70

Red Beds (exposed 245 feet).

Ss oypsum. white, amorphous... 2. 5.22.20. 228. oLhie BE Menor Sire ea 10

2. Sandstones and sandy clays, deep red; with gypsum.-.............-------- 220

TL, DTUTAYEISS FOL VES] BY ITI Tene Ie ee eS Rem eee 25

The ‘‘ sands” mentioned in this and the following sections are fine and
light colored, produced probably by the decomposition of a friable sandstone,
but a little digging into the outcrop failed to discover a coherent rock.

Westward along the foothills on the north side of the Redwater the
Jura is shown by frequent exposures to occupy the greater portion of the
height of the cliffs, though the red clays encroach more or less upon their
lower part, while the summits are usually capped by the Dakota sand-
stone. The dip of the strata is slight, commonly only 5° or 10°, and in
direction a little east of north. About ten miles west of the junction of
Redwater and Spearfish Creeks (forming the Deepwater) the following
section was obtained by Mr. Jenney:

Jura.
Feet
7. Sandstones, soft, pink, decomposing to a reddish sand ..............--..--- 60
GA SANOStONE MMASSIVE SOL eV OUOW Ee sre 5.2 252 cian de Sst era bic c i foe oe 90
5. Shaly sandstones, yellow in color, containing a few casts of mollusks. ...-... 20
A> Sandstone lamellar, white and crumbling ©:.5:. 2. 2. 0..--22-----2-- ecco 10
3

. Clays or marls, white and gray, full of Belemnites in the upper portion ...... 70
JL eae :

162 GEOLOGY OF THE BLACK HILLS.

Red Beds.
2. Gypsum, whiterand) amorp losses eee ee ene tee ee eae ee 3
In Redielays, andkred: sandy claiys 2 sess sees eee eater to base of hill. . 50
This section represents only the lower portion of the Jura. In the
following section, observed by Mr. W. F. Patrick two miles farther west,
the upper portion is better represented:

Jura (410 feet exposed).

Feet

10. Clay, gray, white and purple; capping the bluff......-........-.....,..-. 35

9. Sandstone, lamellar and yellow; upper layers hard and brown..-......--..-- 30
8. Sands, argillaceous, yellow and greenish, with layers of a calcareous sand-

stone full of fossil mollusks—Belemnites, Ammonites, ete .........--.---- 30

7. Sandstone, white, massive and soft........- sa an ME relent (kA heer NO Nee Aaa 20

6. Sands or sandy marls, white and calcareous, with Belemnites .........-.---- 80
5. Sandstone, pinkish (the same as the summit of the last section) passes into

Hoe (0 ie eee Sa eee Cee es Ais een Ce MN Ra Ome E SSA tie a Sid 60

AISISERUGO I ROLE, avel ONY BRNO WHRISSINV®) Go. ca 5onn 5 55052 o00S55 S005 5505 aie sees iesciaeeye 90

3: Sandstone; amellar andawintegeens..- eae eee eee ee eee eee 10

2 lay, whiteandsorayawibhusandyaelaySeer eoere re sere criie steer eras 50

Red Beds.

Le Redssan dy, claysjswitbhs oy p Sums reo a eee iain eer ee eae —

In this section the cappmg Dakota sandstone is wanting, but appears
some distance down the northern slope of the foothills. The clay at the
summit of the section is shown by a comparison with other sections to be
very nearly the extreme upper portion of the Jura, so that the total of 410
feet represents very closely the full force of the formation at this point.
The bed numbered 8, about 350 feet above the Red Beds, is a marked
fossil-bearing horizon of the Jura in the Redwater and Belle Fourche Val-
leys; it has yielded a large collection, in which Professor Whitfield has
described or identified—

Ostrea strigilecula. Tancredia bulbosa.
Camptonectes bellistriatus. Tancredia postica.
Astarte fragilis. Dosinia TJurassica.
Trapezium Bellefourchensis. Saxicava Jurassica.
Tancredia inornata. Ammonites cordiformis

Tancredia corbuliformis. Belemnites densus.

JURASSIC FOSSILS. 163

One hundred and thirty-five feet above the same datum there is another
horizon, distinguished in the northern part of the Hills by its numerous
fossils, and in the following section, made by Mr. Patrick, one or two miles
west of the last section and immediately north of the forks of the Red-
water, its position in relation to the underlying strata is well shown:

Jura.
Feet

6. Sandstone, white; summit of the hill .... .... -.-...... Sea vere Cyne sete att 60
See SANG SEONE PIMC SMa Mb ett ioe ers Sets las sacra dovai nips as ciaicss! tangs = Peele a wo os 25
4, Sandstone, yellow and white, interstratified with sandy shales; a layer near

the top 14 inches thick (135 feet above the Red Beds) was found to be

highly fossiliferous......- .--. SP An Pere pte Sere ee econ cee cL Ee panne Sey sre 25
3) Sandstone, white, but reddish im places-+-.2 22.025. 2-6-2408 0). eee e 50
Pee lav gO REC LavaSH AS STCCMISH ss eps a hy Ac mele ts el elats Waloya ce inte 2 ayele wich =ceja islelotsio- 60

iar ypsumMeandereduclays tOnvalley 45. a2 seen ene ne cree lee wee Sale waves = =

The same horizon (4) was found to carry many fossils in the exposures
near Crow Peak.

The following section was observed by Mr. Jenney in a butte which
stands in the Red Valley two or three miles south of the forks of the Red-

water:

Jura.

Feet.
6. Sandstone, massive, of a yellowish brown color ......-...-...-... ..------ 5
Dr Shalesior clays. arcllaceous and SIMClOUS. 2 eas. oo. fo oie Soe ace oss 30

4, Conglomerate; pebbles cemented by lime; containing a few fragments of
MNOMMSEAMLOSSIIS wae eee ero che cree ay sinjarsare ala tane eiesne eee etc ac 3
a Shales, sofand sandy, wath Some TOSsilsi.. 2-42.62 oe) este seein se oe ae = 2
By CIENT Be osc s adoclod soc sueodea dd ccoe ane UpHe Daoeae Sud sae SOCS oe Seen 20

Red Beds.

1A INSOM GRAYS. ame cla dan’ udcotsbnS CAOR AS cero OIE Se RIC Ce setae = me en ee me er ere —

Southwest of Sun Dance Hills and west of Inyan Kara there is an
inclining plateau cut into parallel ridges which run northwest and south-
east, parallel with the course of Inyan Kara Creek. These were not
examined critically, but many of them are capped with the Cretaceous
sandstone, below which are the Jurassic strata, while others consist almost
entirely of the Jurassic. They are a direct continuation of the foothills on
the Beaver, but here, owing to the low angle of dip, they spread out and

164 GEOLOGY OF THE BLACK HILLS.

occupy a broader area. Southwest from Sun Dance Hills, and between
them and the foothills, many fragmentary portions of the Jura are seen in
the Red Valley.

Following the Jurassic outcrop westward and northwestward to the
valley of the Belle Fourche one finds there the greatest vertical develop-
ment of the formation in the Black Hills country. Around the main por-
tion of the Hills its thickness, so far as ascertained, is 200 to 300 feet;
along the Redwater Valley it is a little more than 400 feet, and on the
Belle Fourche between 500 and 600 feet.

If the reader will refer to Figure 24 he will readily understand the
structure of the Belle Fourche Valley in the vicinity of Bear Lodge. In
the lowest part is the immediate valley or bottom of the river, carved from
the Red Beds. On each side of this rises a bluff, showing Red Beds at
base and Jura above. Above the bluff is a terrace on each side, floored
by the local hard sandstone of the Jura. Back of this (on each side, though
represented on one only) is a second bluff or cliff exhibiting Jurassic strata
at base and Cretaceous at top. The strata are arched in a direction at right
angles to the line of section, so that if one follows the river far enough in
either direction he will find the Jurassic terrace to gradually descend until
it finally dips entirely beneath the water level. Where this takes place the
cliffs capped by the Cretaceous approach the stream so closely that they
are separated only by the bottom land.

In the illustration the vertical scale is greater than the horizontal. In
reality the face of the lower cliff is 300 feet high and the face of the
upper about 500; the river bottom is one or two miles broad and the ter-
race three or four miles. It must not be understood that the terrace is
regular and continuous. It is indented by numerous lateral valleys and on
the divides between them salients of the upper cliff encroach more or less
on its area.

On the east side of the Belle Fourche, about four miles southeast from
Bear Lodge, the following section was made, beginning with the summit
of the cliffs and their capping of Cretaceous sandstone, and showing the
entire thickness of the Jura:

JURASSIC FOSSILS. 165

Cretaceous. Feet.

13. Sandstone, yellow, with red stains, containing strata of coarse conglomerate. 75

12. Shales, dark gray, calcareous; with impure limestone....-..-.-..----.+-- 5
11. Sandstone, very soft and white, near top pinkish ; massive in places ; contains

LAV ELSlOneMerComMelOMenate weer ears eine ysl ee YE eRe iu 50

Jura (580 feet).
10. Clay or marls, yellow, greenish, and gray, sometimes sandy, with streak of

TOUS ONS TASTE 10) 0) asd Ses ee a adel oe ae ae on ear cae cat Re 140
OP Sanadstonesbrowimlamellansees ue sachets eet Seis eats, aS othe sss s Beales 3
San Claivgomm an eaDLOwmishuan desan diver mic nae see ae cincks om Soae. ces 15

7. Limestone, thin stratum, very fossiliferous; from its equivalent in the vicin-
LEVAMANNOSSIISEWwiere.COlle@tede mist cha cece ns ens Lawak ae nee acvan ete —
6. Clay or marl, yellow; with red sandy clay at base; exposures not complete. 235
5

5. Sandstone, yellow, in places quite red, shaly at the top but lower part massive. 50-7
4, Clay or marl, gray and greenish, with pink streak near the middle; calcare-

ous at base, with much flint; in an impure limestone occur many fossils.... 120

Red Beds.

So Sandstone, redaand sort with much @ypSUMines 56.855 55-5525. 2-22 - 10
2. Gypsum in layers of 12 inches, interstratified with red sandy clay for a space

Oh 'g 5 GAs rae ci ee here Hee OER ia A Se te 15-20
i Sandstone, orsandy clay, soft, red’:.. 22-42 5.-22. 0.22.20 to bed of river.. 150

No. 11 in this section will be seen to correspond in position and char-
acter with a sandstone in the section on Beaver Creek, and it is included
in the Cretaceous, although it has not the common character of the Dakota
sandstone. ‘The fossiliferous stratum (in 7) is probably the same as the
upper fossiliferous stratum of the Redwater section. That stratum is 350
feet above the Red Bed; this, in a thicker series, is 50 feet higher. The
Belle Fourche locality yielded—

Ostrea strigilecula. Tancredia corbuliformis.
Avicula mucronata. Tancredia bulbosa.
Trapezium Bellefourchensis. Tancredia postica.
Pleuromya Newton. Dosinia Jurassica.
Tancredia inornata. Ammonites cordiformis.

At the base of the yellow calcareous clays (4) forming the bottom of
the Jurassic series there is a calcareous layer containing many fossils.
Among them are—

Ostrea strigilecula. Psammobia prematura
Camptonectes bellistriatus. Belemmnites densus.
Pseudomonotis curta.

166 GEOLOGY OF THE BLACK HILLS.

It will be remembered that a similar fossiliferous layer was found on
Red Carion Creek, resting, as here, immediately upon the red clays of the
gypsiferous Red Beds. The list of species at that locality is nearly the
same,

From the southern end of the Hills, where the thickness of the forma-
tion is about 200 feet, there is a great thickening toward the north and
northwest, reaching on the Belle Fourche a maximum of nearly 600 feet.
There seems to be no reasonable cause for suspecting that this thickening is
only apparent and is due to errors of observation. The possibility of
errors of mensuration is negatived by the fact that independent measure-
ments in the same neighborhood were always found to agree as closely as
was to be anticipated. Nor is it credible that any appreciable error was
made in tracing out and identifying the lines of demarkation by which the
formation is separated from the Dakota sandstone above and the Red Beds
beneath. Each of these lines represents a definite lithological change and
could readily be recognized at every point. ‘There was some hesitation in
the selection of the point of separation between the Jura and the Creta-
ceous, but when it was once selected at one place there was no difficulty
whatever in finding it at any other place.

The cause of this thickening toward the northwest is not fully under-
stood, but it is probably a normal increase of depth in the direction of the
source of the material which formed the sediments. East of the Black
Hills the formation is not known. At the southeast end of the Hills area
it is 200 feet thick; at the north end 410 feet; and thirty miles west of the
north end 580 feet. Dr. Hayden found in the Bighorn Mountains (one
hundred and twenty miles west of the Black Hills) a thickness of 800 to
1,000 feet, and Professor Comstock makes the same report of the Wind
River Mountains.

North of the Uinta Mountains in the various ranges of the Rocky
Mountain chain the Jura is well marked by abundant and characteristic
fossils, from which considerable collections have already been made, and the
same is true of the Black Hills. But to the southward very few fossil
forms are known and their localities are rare. In like manner the rocks

CHANGES AT CLOSE OF JURASSIC PERIOD. 167

which compose the Jura in the northern Rocky Mountains are very similar
to their representatives in the Hills, differing chiefly by carrying more car-
bonate of lime, while at the south a considerable portion of the formation
assumes the habit of the Red Beds, abounding in vivid colors and carrying
large quantities of gypsum.

The close of the Jurassic age witnessed great continental and oro-
graphic changes in what is now the western part of the continent. The
Sierra Nevada was uplifted and so were the ranges of the great interior
basin, and the continent was so elevated that the succeeding Cretaceous
made no deposit between the east side of the Wasatch and the west side of
the Sierra Nevada. In the Mississippi Valley, too, there must have been
elevation and erosion either then or before, for Trias and Jura are absent and
the Cretaceous rests on a worn surface of Carboniferous. Butin the region
of the Black Hills there was no emergence. The Dakota sandstone rests
in perfect conformity on the Jura, and although the change in the character
of the sediments is great, it is not abrupt. Probably in the magnitude of
the change from soft calcareo-arenaceous clays below to coarse-grained
sandstone above we have the only local evidence of the revolutions of the
time.

The physical conditions which prevailed during the deposition of the
Jura were a continuation of the shallow water of the Triassic age, with
probably a somewhat deeper submergence. The marine type of the fossil
forms indicates that there was a free communication with the ocean, and
hence that the period was one of a shallow marine submergence over the
Rocky Mountain area.

The fossil fauna of the European Mesozoic (Trias, Jura, and Creta-
ceous) includes so many species and individuals of huge aquatic reptiles
and the reptilian type characterizes so largely the vertebrate remains, that
the age is known as the Reptilian age. The saurians seem to have reached
their maximum development during the Jura, though they are also found
abundantly in the older Trias and the later Cretaceous. In the American
Trias of the Hast have been found those great foot-tracks of the Connecti-
cut Valley, now considered to have been made by huge batrachians; but
in the Jura of the Far West no vertebrate remains have yet been discovered,

168 GEOLOGY OF THE BLACK HILLS.

excepting a single crocodilian bone found in the Uinta, Mountains. Among
plants the European Jura has yielded an abundance of remains of ferns,
conifers, and cycads, bearing a great similarity to the fauna of the Trias;
but in- America no undoubted Jurassic plants have yet been found. The
plants from the Moqui region described by Dr. Newberry are regarded by
him as not distinctive enough to decide whether they are Triassic or Juras-
sic, though they are of Mesozoic types and probably Jurassic.

The following list contains the invertebrate species that have been
described from the Jura of the Rocky Mountain region up to and including
the year 1876. Those marked (*) have been obtained from the Black

Hills:

* Ammonites cordiformis.

*Ammonites Henryt.
Astarte arenosa.

* Astarte fragilis.

* Astarte inornata.

* Asterias dubiumn.

* Avicula mucronata.

* Belemnites densus.

*Camptonectes bellistriatus.

*Camptonectes extenuatus.

Camptonectes pertenustriatus.

Camptonectes platessiformis.
Camptonectes stygius.
* Dosimia Jurassica.
*Gervillia recta.
*Grammatodon mornatus.
Gryphea calceola.
Inma occidentalis.
*Lingula brevivostris.
* Tioplacodus veturnus.
Modiola subimbricata.
* Myacites Nebrascensis.
Myacites subcompressa.

Myophoria lineata.
* Mytilus W hitet.
Natica Lelia.
* Neera longiostris.
Neritina Powell.
*Ostrea Engelmannt
Ostrea procumbens,
*Ostrea strigilecula.
* Pecten Newberry.
* Pentacrinus asteriscus.
*Pholodomya humilis.
Pholadomya King.
*Planorbis veturnus.
*Pleuromya Newton.
* Protocardium Shwnardi.
* Psammobia prematura.
* Pseudomonotis curta.
* Pseudomonotis orbiculata.
Rhynchonella gnathophora.
* Rhynchonella myrina.
Septocardia carditordea.
Septocardia typica.
*Saxicava Jurassica.

THE CRETACEOUS. 169

*Tancredia equilateralis. *Trigoma Conrad.

* Tancredia bulbosa. Trigonia Montanaensis.
* Tancredia corbuliformis. Trigona quadrangularis.
* Tancredia mornata. - *Umo nucalis.
*Tancredia postica. Unio Stewardi.

* Tancredia Warrenana. *Valvata scarbrida.
*Thracia arcuata. *Viwiparus Gilli.

* Thracia sublevis. Volsella formosa.
*Trapezium Bellefourchensis. Volsella isonema.

* Trapezium subequalis. *Volsella pertenuis.

Trigonia Americana.

SECTION VIII.

THE CRETACEOUS.

The rocks of the Cretaceous system surround the Black Hills in an
annular rim of irregular width; and this by means of a belt following the
valley of the Cheyenne is connected with the great Cretaceous exposure of
the upper Missouri. Beyond the border of Cretaceous on the south and
southeast of the Hills stretch the White River Tertiary deposits which
occupy a large area; while on the west and on the north lie the deposits of
the Lignitic or Fort Union Tertiary, extending in one direction to the Wind
River Mountains and in the other to our northern boundary and beyond.

The Cretaceous of the Far West underlies a vast area east of the
mountains, reaching from beyond the Canadian line on the north into Mexico
on the south ; and though its deposits are found nowhere within the great
interior basin, they extend from the southern part of the Plains west-
ward into New Mexico and Arizona, and thence northward into Utah and
Colorado, following around the southern end of the main spurs of the
Rocky Mountains, as though in Cretaceous time the mountain chains had
already received their definition and the Cretaceous sea laved only their
outer slopes. A little north of the Black Hills the Cretaceous occupies
a broad synclinal slope, with a width, from the Rocky Mountains to

170 GHOLOGY OF THE BLACK HILLS.

the western part of Minnesota, of over six hundred miles; but farther
south the width diminishes. The greater portion of this slope, which under-
lies almost the entire area of the Great Plains, is covered and concealed by
the more recent deposits of the Tertiary, but the continuity of these beds
has been interrupted by erosion along some of the principal river valleys
and by uplifts like that of the Black Hills.

The western margin of the Cretaceous area is revealed and readily
studied where the edges of its composing strata are upturned against the
foot-slopes of the Rocky Mountains, while the eastern margin, with a gentler
dip, outcrops through eastern Dakota and western Minnesota, eastern Ne-
braska, and western Kansas. The two are joined in central Colorado.

There are few of the formations of the western rock system that have
been so extensively and thoroughly studied as the Cretaceous, and none that
can vie with it inthe richness, abundance, and beauty of its fossil remains.
Our knowledge of it begins with the explorations of Lewis and Clarke, and
has been extended by subsequent expeditions, as related in the first chapter
of this report. In 1853, Mr. Meek and Dr. Hayden were sent by Professor
Hall, of Albany, to make collections of the Cretaceous and Tertiary fossils
of the bad lands on the White River. They brought back a large collection
of vertebrate remains from the bad lands and Cretaceous fossils from the
Cheyenne and Sage Creek region, as well as from various points on the
Missouri below Fort Pierre. As a result of their exploration, the first
attempt was masle by Mr. Meek to group the different members and forma
general section for the Cretaceous rocks of the West. This section appeared
in a paper by Hall and Meek, entitled ‘Descriptions of new Cretaceous
fossils from the Cretaceous of Nebraska,” which was published in the
Memoirs of the American Academy of Arts and Sciences in 1854. The
thicknesses of the different divisions were given by estimate, and have been
modified by later work, but the order of sequence is essentially the one now
received, and because of its historical interest the section is given below.

i.

MEEK AND HAYDEN’S CRETACEOUS SECTION. 171
SECTION OF THE MEMBERS OF THE CRETACEOUS FORMATION, AS OBSERVED ON
THE MISSOURI RIVER AND THENCE WESL WARD TO THE MAUVAISES TERRES.
Tertiary formation.

Clays, sandstones, etc., containimg remains of Mammalia. The entire thickness
of this formation in the bad lands is from 25 to 250 feet.

Cretaccous Formation.

Feet.

5. Arenaceous clay, passing into argillo-calcareous sandstones ..........-....- 80
4, Plastic clay, with calcareous coneretions, containing numerous fossils. This
is the principal fossiliferous bed of the Cretaceous formation upon the upper

JAS WESSS(OT Ge coe oe, Piel eee ee eee aera ao ane Ra ee ive peace hem oe 250-350

3. Caleareous marl, containing Ostrea congesta, scales of fishes, etc -......-... 100-150

2, Clery, COMBINE A) Tey IROSSIS & Abe Soeebs SAG sa a esinnan Cen Coe ehIneOA oe Abie 80

PE SAM OSCOMCE AMONG ayanteters te Geet tatait iy este cl en ees oie ail aie Sarria clio nae ols. 90

Subsequently the country was visited by Dr. Hayden alone and after-
wards in connection with the reconnaissances of Lieutenant Warren and
Captain Raynolds. From these various explorations the Cretaceous became
better known, and much new material was published by Meek and Hayden
at various times, including descriptions of new fossils and revisions of the
above section, until in their joint paper of December, 1861 (Proc. Acad.
Nat. Sci. Phila.) their final subdivision of the Cretaceous in the West was
presented, with the geographical names which remain now the accepted
nomenclature of the formation in the Northwest.

The following is their section of the Cretaceous of the upper Missouri
country, as given in Professor Meek’s Invertebrate Paleontology of the
United States Geological Survey of the Territories, with the addition of a
short synopsis of the character and estimated thickness of the different
groups as they were found around the Black Hills; the divisions are given

in descending order.
No. 5.—Fox Hills group.

Gray, ferruginous, and yellowish sandstone and arenaceous clays, containing
Belemnitella bulbosa, Nautilus Dekayi, Placenticeras placenta, P. lenticularis, Scaphites
Conradi, S. Nicolleti, Baculites grandis, Pyropsis Bairdi, Piestochilus Culbertsoni, Pyri-
Susus Newberryi, Auchura Americana, Pseudobuccinum Nebrascense, Mactra Warrenana,
Cardium subquadratum, and a great number of other molluscan fossils, together with
the bones of Mosasaurus Missouriensis, ete.

Localities —Fox Hills, near Moreau River; near Long Lake, above Fort Pierre ;
along the base of the Big Horn Mountains, and on North and South Platte Rivers.

Thickness, 500 feet.

172 GEOLOGY OF THE BLACK HILLS.

Black Hills—Well exhibited on the western side of the Hills on the
Cheyenne River near (east of) Old Woman Fork, where it is represented
by ferruginous sandstones with Veniella humilis, Spheriola transversa, Idon-
earca Shumardi, etc. Not well distinguished on the eastern side; appears
lithologically almost inseparable from No. 4.

On the Cheyenne in the vicinity of Rapid Creek, below the base of
the Tertiary deposits, occurs a gray or brown clay with occasional varie-
gated strata, pink, reddish, or ash-colored, containing large quantities of
iron in irregular seams. This has a thickness of about 30 feet, and below
it was found the gray clay with calcareous concretions filled with forms
characteristic of No. 4, but with some also of those peculiar to No. 5.
Besides this deposit the highest well-marked strata of the Cretaceous ob-
served on the eastern side of the Hills are the plastic clays of No. 4, which
occupy by far the larger portion of the valleys of the Belle Fourche and
South Fork of the Cheyenne. North of the Cheyenne No. 5 is reported
to exhibit its usual characters. |

Paleontologically No. 4 and No. 5 are not well distinguished on the
eastern side of the Hills; the fauna appears to show a blending of the -
forms elsewhere found peculiar to each formation.

Thickness, roughly estimated, 100 feet.

No. 4.—Port Pierre group.

(a) Dark-gray and bluish plastic clays, containing, near the upper part, Nautilus
Dekayi, Placenticeras placenta, Baculites ovatus, B. compressus, Scaphites nodosus, Denta-
ium gracile, Crassatella Evansi, Cucullea Nebrascensis, Inoceramus Sagensis, I. Nebra-
scensis, I. Vunuxemi, bones ot Mosasaurus Missouriensis, ete.

(b) Middle zone, nearly barren of fossils.

(c) Lower fossiliferous zone, containing Ammonites complexus, Baculites ovacus, B.
compressus, Heteroceras Mortoni, H. tortum, H. umbilieatum, H. cochleatum, Ptuchoceras
Mortoni, Odontobasis vinculum, Anisomyon borealis, Amauropsis paludiniformis, Inocera-
mus sublevis, I. tenwilineatus, bones of Mosasaurus Missouriensis, ete.

(d) Dark bed of very fine unctuous clay, containing much carbonaceous matter,
with veins and seams of gypsum, masses of sulphuret of iron, and numerous small
scales of fishes. Local; filling depressions in the bed below.

Localities.—(a) Sage Creek, Cheyenne River, and on White River above the Mau-
vaises Terres. (b) Fort Pierre and out to Bad Lands; also down the Missouri on the
high country to Great Bend. (c) Great Bend of the Missouri below Fort Pierre. (d)
Near Bijou Hill, on the Missouri. ;

Thickness of the whole group, 700 feet.

MEEK AND HAYDEN’S CRETACEOUS SECTION. tiie

The Fort Pierre is the most important of the divisions of the Cretace-
ous in the Northwest, alike in the extent of its development, in its influence
on the character of the country, and in the great abundance and beauty of
its fossils. In the number of its fossils it surpasses all the other Cretaceous
groups collectively. Its clays lose by wetting their laminated structure
and become adhesive and pasty, and then by drying become hard and
crumbly, and split or crack from the surface to a depth of several inches.
There is something in its physical or chemical constitution imimical to
vegetation, and over large areas it wears a peculiar black and barren
appearance, scarcely relieved by a shred of vegetable life. In other
regions, however, the surface supports an excellent growth of grass.

Black Hills-—The group is well exposed on Old Woman Fork near the
Cheyenne, and it exhibits there in its fossils a blending with No. 5. It is
in general plainly recognizable entirely around the Hills. It constitutes
the chief Cretaceous exposures on the Belle Fourche and South Cheyenne
from their junction upward to the vicinity of the uplift, and appears again
on the South Cheyenne near the mouth of Beaver Creek.

The upper fossiliferous zone is well exposed along the South Cheyenne
from Rapid Creek downward, and near the mouth of that creek its charac-
teristic fossils occur in great profusion. They are found in calcareous con-
cretions or nodules, often of very large size. Sage Creek and Bear Creek,
which enter the river nearly opposite the mouth of Rapid Creek, are
rendered classic by the collections of Meek and Hayden.

Thickness, estimated, 150 to 250 feet. _

No. 3.—WNiobrara group.

Lead-gray calcareous marl, weathering to a yellowish or whitish chalky appear-
ance above. Containing large scales and other remains of fishes, and many specimens
of Ostrea congesta attached to fragments of Inoceramus ; also several species of Textu-
laria. Passing down into light, yellowish, and whitish limestone, containing great num-
bers of Inoceramus problematicus, I. pseudo-mytiloides, I. aviculoides, and Ostrea congesta,
fish scales, ete.

Localities—Blutts along the Missouri below the Great Bend, to the vicinity of
Big Sioux River; aiso below there on the tops of the hills.

Thickness, 200 feet.

From this formation Professor Marsh and Professor Cope have de-
scribed nearly one hundred vertebrates, including birds, reptiles, and fishes.

174 GEOLOGY OF THE BLACK HILLS.

Black Hills—Exposed around the Hills with its characteristic structure
Well exposed on the west side of the Beaver Creek, where it contains great
quantities of Inoceramus problematicus with adhering Ostrea congesta; on the
Belle Fourche near the Great Bend; and near Bear Butte.

Thickness, roughly estimated, 100 to 200 feet.

No. 2.—fort Benton group.

Dark-gray laminated clays, sometimes alternating near the upper part with seams
and layers of soft gray and light-colored limestones. Inoceramus problematicus, I. ten-
uicostatus, I. latus, I. fragilis, Ostrea congesta, Veniella Mortoni, Pholadomya papyracea,
Ammonites Mullananus, Prionocyclus Woolgari, Mortoniceras Shoshonense, Scaphites
Warrenanus, S. larveeformis, S. ventricosus, S. vermiformis, Nautilus elegans, ete.

Localities —Extensively developed near Fort Benton on the Upper Missouri; also
along the latter, from ten miles above James River to Big Sioux River; and along the
eastern slope of the Rocky Mountains, as well as at the Black Hills.

Thickness, 800 feet.

Four vertebrates are described by Professor Cope from the Fort
Benton clays. .

Black Hills—This group, with its characteristic dark plastic clays,
which usually contain large quantities of alkaline salts and selenite, is a
very persistent feature in the geology of the outer rim of foothills. It is
found resting upon the ferruginious sandstones of the Dakota group, and
forms usually the outer slope to the series of foothills that border the encir-
cling Red Valley. In its upper portion are frequently found thin bedded
caleareous sandstones, containing numerous but fragmentary fossils, Inoce-

ramus, Ostrea congesta, fish teeth, ete.
Thickness, 200 to 300 feet.

No. 1.—Dakota group.

Yellowish, reddish, and occasionally white sandstone, with at places alternations
of various colored clays and beds and seams of impure lignite; also silicified wood, and
great numbers of leaves of the higher types of dicotyledonous trees, with casts of
Pharella? Dakotensis, Trigonarca Siouxensis, Cyrena arenarea, Margaritana Nebracen-
sis, ete.

Localities. —Hills back of the town of Dakota; also extensively developed in the
surrounding country in Dakota county below the mouth of Big Sioux River; and
thence extending southward into Northeastern Kansas and beyond.

Thickness. 400 feet.

CONCENTRIC RIDGES. . 175

Black Hills—Prominently developed, forming the capping rock to the
foothills that surround the Hills on all sides; appears with its characteristic
composition—coarse yellow or red sandstones with discontinuous variegated
clays. At places a considerable thickness of very soft and fine white sand-
stone appears at the base. Hlsewhere considerable portions are of hard,
dense quartzite. No animal fossils were found, but many remnants of
plants—in no case more than mere coaly fragments.

Thickness, 250 to 400 feet.

The rim of Cretaceous strata which encircles the Hills dips outward
on all sides or away from the axis of upheaval. The strata begin with the
foothills that border the outer edge of the valley. The Dakota sand-
stone, resting conformably upon the Jura, forms the capping rock of the
foothill ridge, and dips outward at various angles from 10° to 40°. Just
as the Cretaceous encircles the outcrop of the underlying Jura and Trias,
so the different overlying groups of the Cretaceous—the Fort Benton, the
Niobrara, the Fort Pierre, and the Fox Hills—succeed each other in regular
order, forming a series of concentric ridges that decrease in altitude as the
distance from the Hills increases.

One who journeys from the Hills without following a drainage line
passes over a series of ridges of which each one is lower than the last, but
is composed of strata higher in the geological scale. He finds, too, that the
dip of each ridge-forming stratum is less than the dip of the last, until
finally he reaches one that les nearly or quite horizontal.

It has already been remarked that the concentration of attention on
the main body of the Hills prevented a thorough study of the Jura. Ina
still greater degree it reduced our opportunities for the examination of the
Cretaceous. Very few of our excursions penetrated more than the basal
member, and the only examinations of the entire series were in our rapid
approach to the Hills via Beaver Creek and on our return march. So far,
however, as our observations extended, it was evident that the upper Missouri
section of Meek and Hayden was applicable without essential modification.

Upon the geological map no attempt has been made to distinguish any
individual member of the formation except the Dakota; all the upper -
divisions, from No. 2 to No. 5, inclusive, are represented by one shade.

176 GEOLOGY OF THE BLACK HILLS.

Taking up the groups, now, in order, the first to describe is the Dakota.
Typically it is a coarse sandstone, generally conglomeratic, yellowish in
color and stained red in places by the oxidation of the iron contained in its
nodules. Sometimes the sandstone is white in color and uniform and fine
in texture, and in several places large portions of the formation consist of
intensely hard, glassy, and compact quartzite, white or brownish in color,
and having the density, toughness, sharpness, and conchoidal fracture of
typical flint. The quartzitic development was especially observed at the
southern end of the Hills, where the Dakota expands into a plateau, and
in the region north of Warren Peaks, but it is not confined to those localities.

The quartzitic sandstones are far removed from the possibility of any
igneous action and are to be classed with the quartzites of the Potsdam

already referred to. They consist, like them, of grains of sand cemented.

into a homogeneous mass by a silicious cement, but in many cases they are
more flinty in their appearance and fracture. Just as with the Potsdam
quartzites, there appear to be but two solutions to the problem of their
formation. First, the silicious cement may be derived from the remains of
infusoria, sponges, and other silicious organisms, as it is in the case of the
Coal Measures ahd of the Kuropean Chalk; or, second, it may be derived
from waters containing silica in a soluble condition, either at the time of
the formation of the sandstone or after its deposition.

In several places on the northeastern side of the Hills the usual coarse
yellow sandstone, with a thickness of 300 feet, is overlaid by 25 or 30 feet
of red, yellow, and green variegated clays, 25 feet of white or gray clay,
and 20 feet of yellowish sandstone. On one of the creeks running from the
Hills near Bear Butte 200 feet of the usual coarse sandstones are separated
by a series of light colored clays from another and thinner stratum of sand-
stone, above which come the dark clays of the Fort Benton group; and on
Bear Butte Creek a similar section was seen. These variegated clays are
not a constant feature, for in most sections on the flanks of the Hills they
do not appear; neither are they, in the broad view, exceptional, for such
clays are mentioned by Meek and Hayden in their general section.

Frequent allusion has already been made to the topographical promi-

nence of the Dakota outcrop, and it was impossible in describing the Jura

-!

THE DAKOTA RIDGE. ; lire

and the Red Valley to avoid anticipating a considerable share of that which
belongs most properly here. A certain amount of repetition is therefore
inevitable in presenting the relation of the group to the topography. —

Asa rule every monoclinal ridge contains a hard bed and a soft one.
The hard bed forms one side of the ridge and its crest; the soft bed appears
at the base of the other side and underlies the hard. In the case of the
monoclinal that surrounds the Hills, and to which the title “‘ foothills” has
been applied, the capping hard bed is the Dakota sandstone, and the under-
lying soft bed is partly Jurassic and partly Triassic. But for the hardness
of the sandstone there would be no ridge. But for the softness of the Red
Beds and Jura, it would not be distinguished from the general arch of the
Hills. It is the result, under the laws of erosion, of the contrast between
the two.

Where the dip is great the base of the ridge is narrow and both sides
are steep. Where it is small the base is broad and the side capped by the
sandstone becomes a sloping plateau. On the east and west sides of the
Hills the dip is so great that the ridge character is strongly marked. At
the south end of the uplift the southward dip is very gentle, and the result
is a plateau bounded on the north edge by a cliff. As the ridges approach
the plateau they converge in direction and their lines of strike are continued
as the limiting lines of the plateau until they meet. This gives to the
plateau a triangular form. It is not, however, a plane triangle, but is arched
from east to west. It pictures forth in a most striking manner the slow
sinking of the axis of uplift beneath the quiet strata of the plain. Through
this plateau the South Cheyenne has cut its way from west to east, form-
ing the defile known as the Big Canon.

At the north end of the uplift—or rather at the northwest end, for the
axis of uplift curves around until it has that direction—the structure is
similar in its main points, but it lacks the simplicity exhibited at the south.
The form of the uplift is less regular and it is complicated by volcanic dis-
turbances. It is broader and it is carried a little higher. The Belle Fourche
crosses it just as the South Cheyenne does at the south, but it has eroded
a deep, broad valley instead of a narrow canon, and the symmetry of the
terminal sandstone plateau is thereby destroyed. Nevertheless the plateau

12 BH

178 GEOLOGY OF THE BLACK HILLS.

character of the Dakota outcrop is distinctly marked, and it is clearly seen
to merge at the east and west into the south-trending ‘‘foothill” ridges.

If the reader will refer to the geological map and the bird’s-eye view
in connection with this description, he will obtain a clearer idea of the
topography of the sandstone.

Excepting in the very extremities of the uplift the streams which cross
the Dakota outcrop pass from the central region of the Hills outward toward
the Plains. All of the streams, perennial or occasional, that flow from the
limestone region into the Red Valley, escape from the valley by breaking
through the foothill ridge—either singly or in combination—and the result
is a series of cross-cutting cations in which the composition of the Dakota
group can readily be examined. A few of the succeeding pages will be
devoted to the enumeration of some of the details thus ascertained.

At the Beaver Creek gap the summit of the cliff overlying the Jura
is formed of—
Feet.
1. Sandstone, at base very soft and white, but for the upper 50 feet yellowish
ANG COATSEL,. Ms ba. cgee ts We ciel asin ie OEE icin eS re erence: ee etme 150
This sandstone dips westward 20° to 25°, and near the foot of its slope is a
second low ridge containing at its base, resting upon the above sandstone—

2. Sandstone, whitish and yellowish, thinly bedded, and with many ripple marks. 60
3. Sandy anaes Re ae mA Min ee els Mo Bh a ote cap Lie ee ein reve 20
4. Sandstone, gray and reddish; in places any bedded; with ripple marks... 64
5. Gray clay or marl, with nodules of impure Timestone, strata of siderite, ich
cone-in-conesandsselemite yy y= isreeeny= cee ere reacts ess octet ee renee eer terete 20
6. Sandstone, With’ carbonaceous: atter se ean a ee ere an 10
(ceGrayishalesandpyellowaclayer-- mee cee eee ee Ma cniA oto Gane Sere 15
8., Sandstone = sere cece eee ce ae Spay ate SANA del San eee or 15

No fossils were found in these rocks, but they are all referred to the
Dakota group because they are immediately underlaid by Jurassic strata,
well characterized by fossils, and they immediately underlie the black plastic
clays of the Fort Benton group.

The ridge character of the outcrop continues southward to the gap by
which Red Canon Creek issues from Red Valley, and there ceases. The
southern plateau is included between Red Canon and Minne Katta Creeks.
The next points of examination were on and near the plateau. A section
of the cliff at Red Caton Creek, to be found in the Jurassic division of the

THE DAKOTA RIDGE. 179

chapter, gives the lower part of the Dakota group. Fuller sections, though
still incomplete, were observed in the cation of the Cheyenne, but the com-
ponent beds were not measured in detail. The walls of the cation are in
places from 600 to 800 feet high, and they are composed in chief part of the
sandstones of the Dakota They are perpendicular except at the base, and
are there covered by débris, though a few glimpses are caught of soft
rock, probably belonging to the Jura. The exposed portion of the Dakota
is fully 500 feet in thickness and, allowing for waste above and conceal-
ment below, the group must be estimated to exceed that amount. It has its
usual character in the main, but in the upper part there is a fine example
of the quartzitic phase. In fact, a large portion of the higher part of the
plateau is quartzitic, and the preservation of the table is largely due to this
circumstance.

On the surface of the plateau near Red Caron Creek there is much
fine drift composed largely of quartz grains and garnets.

North of Minne Katta Creek the outcrop resumes its character ‘of a
monoclinal ridge, and so continues all about the east and northeast sides
of the Hills. The dip finds here its maximum and ranges from 20° to 40°
or 45°. The formation exhibits no peculiar features except the occurrence
in the northeast of the variegated clays already referred to

At the north where the Dakota Cliff runs westward parallel to Red-
water Creek the dip is only about five degrees and the exposure takes the
form of a plateau. Farther west it diminishes still more, except in the im-
mediate vicinity of the Bear Lodge range where the strata are upbent
about the trachyte mass. From the summit of Warren Peaks the tabular
character is plainly evident, and the plateau is seen to slope gently to the
east and north and west. It has not, however, a continuous surface, but is
deeply dissected by cafions in every direction. Topographically it is
limited on the west by the valley of the Belle Fourche, but’a dissevered
remnant is to be seen on the farther side, supporting on its surface the vol-
canic cones known as the Little Missouri Buttes.

Wherever examined in this northern portion of the Hills the group has
its typical lithological character, but the thickness was nowhere seen to be
greater than 200 feet. The following section shows so much of the forma-

180 GEOLOGY OF THE BLACK HILLS.

tion as caps the cliffs southeast of Bear Lodge. The top of the cliff is 950
feet above the Belle Fourche.

Feet.
4, Sandstone, yellowish with red stains; containing layers of conglomerate. ... 75
3. Dark gray calcareous shale and dark impure limestone -..... . Boksoesesdcas 5
2. Sandstone, very soft and white, with layers of fine conglomerate............ 50

I. Clays and marls: of the Jira :oo.0< 39) so eee eae ere ee renee —_

Twenty-two miles farther down the river the dip of the sandstone
carries it down to the level of the stream, and it disappears beneath the
overlying clays of the Fort Benton group. At this point the following
section was observed :

Feet.
5. Wandstone, Shalliyy-/se2s cute ths tee ean eee ee ae yee eo eer ea orca Pea eee nee 25
4, Sandstone,ireddish and yellowisheess-. 2-2 so cee ee ee eee 100
3. Shales or clays, gray, yellow, and red .........-...--.....- Bn a eres 50
2.-Sandstones, white and sofbimere sac eee as ete eee ee eee eee 75
1. Jurassic clays or marls, sandy, gray, red, and yellow ...........---.....--- --

Though the Dakota group contains occasional strata of clay or shale
there is rarely any difficulty in separating it from the dark plastic clays of
the overlying Fort Benton.

Of the Fort Benton and upper groups of the Cretaceous no general
study was made, and the little that can be said is a very slight contribution
to their history. They were seen only on a few lines of travel and for the
most part under unfavorable circumstances.

Between Bear Butte and the foothills the undulating country appears
to be underlaid entirely by the black clays of the Fort Benton group (No.
2), but we found no fossils. Hast of the butte No.3 appears, and on the
banks of the Belle Fourche near the mouth of Bear Butte Creek are the —
dark gray clays and shales of the Fort Pierre, No. 4, with a few character-
istic shells, Baculites, Ammonites placenta, ete.

Southward along the base of the foothills the Fort Benton is easily
traced by the fineness and darkness of its clays. ‘They are remarkable for
their large proportion of soluble salts, which contaminate all the streams
that pass through or rise in them, rendering their waters bitter and medic-
inal. In their vicinity it is usual to see a white deposit or crust lining the

banks of the streams, and occasionally alum springs are met with. The

THE UPPER CRETACEOUS GROUPS. 181

same bitter salts are found also in the higher beds but in smaller quantity.
Selenite, in well defined and clear crystals, is very abundant and dots the
exposures of the formation with bright spots that glisten like jewels in the
sunlight.

On Rapid Creek the Fort Benton clays have a thickness of 150 or 200
feet, and dip eastward at about 20°. They rest upon the Dakota sand-
stone, and are covered in turn by a bed of sandstone 10 or 15 feet thick,
which forms a ridge in the topography. Beyond this ridge a furrowed and
rolling surface extends eastward to the Cheyenne, where No. 4 forms the
bank of the stream. On the east side of the river Nos. 4 and 5 are overlaid
by outliers of the White River Tertiary.

At the pass of the foothills on French Creek the Dakota sandstone,
dipping eastward at an angle of 8° or 10°, is overlaid by the following

series :
Feet.
1. Clays of the Fort Benton, dark brown or black. ..............---..-.....- 150
2. Sandstone, white, coarse; somewhat conglomeratic at base ...........---- 40 =
3. Clays, yellow and somewhat arenaceous; with thin shaly limestone near the
LOPE CONLAMINE MNOCETOMUS. wae aa cnc 2 cats voece noe EN cath nc eet 50

Nos. 2 and 3 of this section probably belong to the Niobrara group,
the total thickness of which we could not readily estimate. Professor
Winchell, who enjoyed better opportunities than we at this locality, places
it at 150 feet. In the same vicinity he assigns to the Fort Pierre group a
thickness of 250 feet. 5

The cascade on Minne Katta Creek, which is a little over two miles
from the Cheyenne, is in the gap through which the creek passes the ridge of
Dakota sandstone. The sandstone has a dip to the south and east of about
30°. Above it are the Fort Benton clays about 150 feet in thickness,
which thence form the banks of the creek to the Cheyenne. In this short
space the dip changes so rapidly that at the river the strata lie very nearly
horizontal. Conspicuous hills near the mouth of the creek consist of shales
with some sandstones, and probably exhibit a portion of the Niobrara

- group.

182 GEOLOGY OF THE BLACK HILLS.

At the pass of Red Cation Creek the rocks which immediately overlie
the Dakota sandstone are:

Feet
i. Black clay withamuch selenite’ 22. --seeee soe eee eee eee eee Weeletoe 60
2.. Impure: sandstone: 22 2 saws, . 2 Se oa ear e Cree ceed et see ree 2
do black andlorayiclaysSias eee eee eee SEN eee sn oun eShes 50

At the pass of the east fork of Beaver Creek, the outer slope of the
Dakota, dipping westward at an angle of 35°, is overlaid by the black alka-
line clays of the Fort Benton 150 or 200 feet thick. From these have been
excavated the small valley of the “Bitter Fork,” the waters of which are
highly charged with dissolved salts. A small ridge immediately west of the
valley exposes the following section, resting directly upon the Dakota

sandstone :
- Feet

7. Gray clay SHALES ysis ag Re Pero nso oe ee eye ees eyo ate a eB eee Be eee 20
6. Sandstone, calcareous, lamellar, brown, with a very ‘oauInEnone layer, con-

taining eet specimens of Ammonites, teeth of Lamna, Otodus, etc.. 5
5s Dark; oraiy Clay. oie se. fe avs ee Ea nee ra ees ce eas See a ° 15
44 Sandstone lamellaniand) browitses: sae ese eee aoe eee 4
3. Dark gray-elay Shales a2 <3 niet meee mien he or niat Clo aren ee eee 20
2-qSandstones lamellar anda ronan scree oe ee 10
1. Dark gray or black clay shales with selenite and alkaline salts asa55o500b05¢ 75

Westward from this point to the west fork of the Beaver are frag-
mentary exposures of the gray or yellowish clay of the Niobrara without
discovered fossils, and then, in barren slopes along the Beaver, the colored
clays of the Fort Pierre group, containing many calcareous bowlders or
concretions filled with Inoceramus, Ammonites placenta, Baculites, Scaphites,
Helicoceras, Heteroceras, Ancyloceras, and Ptychoceras.

The Cretaceous exposures on the lower Beaver, on the Cheyenne
above its mouth, and on Old Woman Fork have been described on pre-
ceding pages. On the northwest side of the Hills the Fort Benton and
upper groups were not examined. The most extended and continuous
examination of the formation was made during the exploration of the Belle
Fourche from Bear Lodge to its junction with the south fork of the Chey-
enne, and the ascent of the latter stream to the mouth of French Creek.
For this whole distance the river runs tortuously in a valley from one to
two miles in width, cut in the soft rocks of the different groups of the Cre-

THE UPPER CRETACEOUS GROUPS. | 183

taceous. The low angle of dip, the similarity of the different groups in
lithological character, their too frequent concealment under grassy slopes,
and the absence of fossils for long stretches, rendered a true estimation of
their thickness and extent a matter of difficulty.

From the point where the Dakota sandstone dips under the river and
gives place to the overlying Fort Benton, to the acute northern bend of the
river the following beds are exposed. The section is given in descending

order.
Feet.
4, Gray clay, with many calcareous iron nodules; capping the bluffs at the bend
of the river. (The summit of the bluff carries many water-worn fragments
of sandstone, limestone, and granitic rocks).--..-.-....-. «--.-------- 30
3. Dark gray shales, weathering light gray; stratified in distinct layers, with
bands of white sandstone at the base.......--- SRM NE Sea Fes ane real pveic ala ere Ss 200
Pei lacksOrmeryiO are plashiGiClayiS aria joc ces nace es aie ce tees Se cees cee gees lOO

iD) ATS ATIC FOMO Meee ere arses ee nN aa ESD ne cas thee deere OS Ni Rae =

In the absence of fossil remains a true reference is not easily made.
The bed numbered “2” is evidently the Fort Benton clay; the one
numbered “3” is probably the representative of the Niobrara; while the
capping gray clays with calcareous nodules may indicate the base of the
Fort Pierre.

The river is cut through these beds for a long distance below the bend,
and for some ten miles southeast of the bend ‘‘3” of the above section forms
the immediate banks of the river, the beds being nearly horizontal. By the
southward course of the river the valley east of the bend is cut back upon
the dip, so that at a point about ten miles below the bend the Fort Benton
clays again appear and form the banks for a considerable distance.

About half way between the north bend and the mouth of the Red-
water a local change of dip brings the Dakota sandstone above the surface
of the river, and for a short distance it shows a cliff of 75 feet. This soon
disappears, however, and gives place again to the Fort Benton and Nio-
brara. These dip slightly toward the east and north, and for some distance
above the mouth of the Redwater the valley is cut in the gray clay of the
above section (Fort Pierre group ?).

Judging from the efflorescence on its surface, this clay contains con-

184 GEOLOGY OF THE BLACK HILLS.

sidcrable quantities of soluble salts. Its full thickness was not ascertained,
but a cliff cut in it was found to be nearly 200 feet in height.

The surface of the country north of the river is gently undulating,
and but little scored by branching streams or ravines, so that along almost
the immediate bluff of the valley wagons can be driven for a long distance
without arrest by irregularities of the ground. It is destitute of water, and
for long stretches almost destitute of vegetation. The same clay and the
same surface features characterize the country bordering the river for a long
distance west of the mouth of the Redwater.

Some little distance below Bear Butte Creek the Fort Pierre group is
well distinguished as a gray clay, with calcareous nodules full of charac-
teristic fossils. It was not fully connected with bed 4 of the last section,
but its identity is highly probable. Among the fossils are Ammonites pla-
centa, Baculites, and Inoceramus Sagensis.

Near the forks of the Cheyenne the following beds were found—

Feet
3. Yellow sandonarenaceousiclaye=s2-2- 26:28 ses 00 sce ee eerie eee 20
2, Clay shales, light gray, darker in streaks, withimpure limestones at base and
a few limestone concretions with fossils (No. 4)..............-..-........ 110
1. Dark gray clay shales, with calcareous nodules full of Baculites, Inoceramus,
Ammonites, ete.iG(Nov4)e syne nse tee coe Ieee thickness to river. . 75

Beds 1 and 2 of the above section belong evidently to the Fort Pierre
group, while bed 3 may possibly represent the Fox Hill.

Between the Cheyenne and the Hills a large area of country is under-
laid by the Fort Pierre group, frequently exhibiting its characteristic
barrenness of surface.

From the forks of the Cheyenne up the south branch to and beyond
the mouth of French Creek the river is cut in the dark gray clays of the Fort
Pierre group, and from the abundant limestone nodules we obtained many
fossils. When freshly exposed these concretions are broken with the greatest
difficulty, and in the operation the fossils are generally injured or destroyed.
When, however, they have been exposed for some time and are somewhat
decomposed they are readily broken, and the fossils with their beautiful
nacre and colors are obtained with ease. In the beauty and abundance of

THE UPPER CRETACEOUS GROUPS. . 185

its fossils this region of the lower Cheyenne can scarcely be excelled by any
locality of Cretaceous fossils in the West.

The concretions are not uniformly scattered through the mass of the
formation, but’ are found most abundant along two lines or horizons. One
of these is near the base and the other near the summit of the series, and
the intervening space is barren of fossils. On the South Cheyenne the
greater number of forms collected were from the upper zone, which is here
but a short distance below the base of the Tertiary. Some of the principal
forms are: Cyncyclonema rigida, Pteria linguiformis, P. Nebrascensis, P. pseu-
dopteria, Inoceramus sublevis, I. Sagensis, I Barabini, Nuculana bisulcata, N.
subequilatera, Lucina occidentalis, L. ventricosa, L. subundata, Thracia subgra-
cilis, Neera Moreauensis, Fasciolaria fusiformis, Fusus Cheyenensis, Aporrhais
Meeki, Anchura sublevis, Lunatia concinna, Amauropsis paludineformis, Akera
glans-oryza, Dextalium gracile, Nautilus Dekayi, Scaphites nodosus, and Ancy-
loceras tricostatus.

Between Rapid and Spring Creeks and thence southward to French
Creek and beyond are a series of outlying areas of the White River Ter-
tiary, which rise in white bluffs above the plateau of Cretaceous. The
character of the Cretaceous at their point of junction is illustrated in the
following section observed near Spring Creek:

Tertiary.
Feet.
4, White plastic clays, with impure limestone at base and seams of chalcedony . 150-200
3. Fine, white, quartz gravel, very loosely cemented.......--...-..-.-. ----. 5-8
Cretaceous.

bo

. Plastic clay, gray or brown, with much iron oxide in seams; often variegated

in color, pink, ash, red. ame Drown. «(Hox culls?) 2-22: 30
1. Gray or dab clays, hardly distinguishable from the Clay s at fhe ler el of te
Cheyenne, 600 feet below; containing within 100 feet of the top concretions
full of the characteristic “fossils of the Fort Pierre group, but associated
Nylon some jndicabive Otterbox, ENUIS) 2) 9.5 2. 3 22 nije tanec oe ae -s- —_

The dip of the rocks along the Cheyenne in this vicinity is toward the
south and east, but is low and barely perceptible. The surface of the
country in the vicinity of Rapid Creek is flat, and broken only by the dry
ravines that head back a short distance from the immediate bank of the

186 GEOLOGY OF THE BLACK HILLS.

river. On the east side of the river the Cretaceous strata extend southeast-
wardina broad flat mesa. Crossing it for six or seven miles one reaches the
abrupt edge of the prairie and looks unexpectedly down upon the wonder-
ful and wierd bad land basin of the White River, which falls away from the
plain as though it had been sunk from a higher level by some catastrophe
of nature. It is hard to realize that one has been gradually ascending in
the geological scale while he crossed the even prairie, so that he now looks
down upon a formation higher than any to be seen along the river; but such
is nevertheless the case. The gentle dip of two or three, or perhaps four,
degrees has carried down the Cretaceous until it is no longer visible even
in the deepest water-ways, but is replaced in the topography by the middle
portions of the White River Tertiary.

That the Cretaceous series once extended continuously across the area
which is now elevated to form the Black Hills there can be no reasonable
doubt. The strata have been elevated and tilted and their wasting edges
outcrop around the Hills at various angles, but still they conform perfectly
with the underlying rocks, sharing their curves and inclinations. This
relation could not subsist if they had been deposited after the uplifting ;
and being deposited before it, there could have been nothing to prevent their

continuity across its area.

SECTION IX.

THE THERDTIARY.

There are no Tertiary strata within the area of the Hills, and all men-
tion of the formation might have been omitted at this place but for the
fact that the Tertiary deposits of the vicinity have furnished evidence
bearing on the question of the age of the Hills. A brief account will
therefore be given of the Tertiary of the Plains for the purpose of showing
the general relations of the particular beds that have interest in this con-

nection.

THE TERTIARY OF THE PLAINS. 187

The divisions recognized by Messrs. Meek and Hayden are as follows,
beginning with the highest of the series:

4. Loup RIVER BEDS, Pliocene Tertiary ; consisting of loose sand with some limestone;
all of fresh-water origin, and containing the bones of Mastodon, Equus, Felis,
Castor, Canis, Testudo, etc. These are exposed only on the Niobrara and the
Loup fork of the Platte.

3. WHITE RIVER GROUP, Miocene Tertiary; consisting of light colored clays, often
arenaceous, and sometimes containing beds of limestone; all of fresh-water
origin. They contain many fossil vertebrates, among which are Titanotherium,
Oreodon, Rhinoceros, Testudo, and Equus. They occupy the bad-land country
of the White River and extend over a large area south of the Black Hills and
Cheyenne River.

2. FoRT UNION GROUP, Eocene Tertiary; consisting of clay, sand, and sandstones, with
much iron in ferrnginous concretions and many beds of lignite. The basal
parts are of brackish-water origin; the upper portions contain only fresh-
water remains. These beds contain in places large quantities of leaves of
dicotyledonous plants, Populus, Platanus, Sassafras, ete. The Fort Union
beds occupy a large area, extending from the South Cheyenne on the west
side of the Hills northward to the Missouri and far beyond.

1. JUDITH RIVER BEDS; consisting of sand and clay inclosing some beds of lignite.
They occur only over a small area near the mouth of the Judith River and on
the upper Missouri. The best authorities are very nearly agreed in placing them
at the summit of the Cretaceous series, and they are only added here to com-
plete the joint section of the Cretaceous and Tertiary of the Plains.

Of these divisions the only ones which occur in the immediate neigh-
borhood of the Black Hills are the Fort Union and White River; the former,
according to Dr. Hayden, overlies the Cretaceous at no great distance from
the Hills, on the north, west, and southwest. The latter also overlies the
Cretaceous to the southward and eastward. In a northeastern direction a
belt of Cretaceous outcrop follows the valley of the Cheyenne and separates
the two Tertiary areas. On the opposite or southwest side of the Hills the
Tertiary areas conjoin, and the White River beds were there observed by
Dr. Hayden to overlie the Fort Union.

The precise age of the Fort Union beds has been the subject of much
discussion, and by some inyestigators the propriety of referring them to
the Tertiary rather than the Cretaceous has even been questioned. There
is no need either to recite or to continue that discussion in this place, for
the reason that no relation has yet been determined between the deposition -

188 GEOLOGY OF THE BLACK HILLS.

of the Fort Union beds and the history of the Hills. The White River
beds, however, have been definitely connected with that history, and of
them we are fortunately able to say that their Miocene age is not called in
question. Dr. Leidy and Professor Marsh, who have independently ex-
amined their profuse vertebrate fauna, are at one in their determination of
age, and Professor Meek finds nothing in the scanty fresh-water molluscan
fauna to conflict with their conclusion.

The partial section of the Fort Union group observed by the writer on
Old Woman Fork has been described in the preceding chapter and needs
no further mention. That chapter contains also a description of so much
of the White River group as was seen by our party. In the latter part of
the last section a description will be found of the lower strata of the group
as they appear resting on the Cretaceous near the mouth of Rapid Creek.

The bed of gravel at the base of that exposure of the White River
beds is only one of many evidences that there was an interval of time
between the deposition of the upper Cretaceous beds and the deposition of
the White River. The fact that they are in juxtaposition at this point,
while to the west of the Hills the Fort Union group is interposed between
them, is another evidence, and a third is derived from the disparity of age
of the two formations as shown by .heir fossils. It was during this interval
of time that the principal uplift of the Hills occurred, and one of the chief
witnesses to that fact is the same conglomerate at the base of the upper
series.

The pebbles of the conglomerate are never more than two or three
inches in diameter, and have such a large preponderance of white quartz
that the whole bed has a very light color. It is so loosely cemented that
outcrops are merely piles of loose pebbles, having all the appearance of a
gravel beach on the sea shore. Indeed, it is evidently a shore deposit, the
remains of the beach of the old fresh-water lake, formed before the waters
attained their greatest height and while they were sorting over material
brought by rivers from the neighboring Black Hills. Nearly the whole of
the material seems to have been derived from the quartzes and quartzites
of the various formations now exposed there, but Mr. Jenney succeeded in
finding, mingled with these, not only the rose-quartz which is the com-

THE VOLCANIC PEAKS. 189

panion of the granite of the Harney Peak region, but also a few fragments
of the granite itself. It is thus known not only that the uplift was in
existence at a time near the beginning of the White River lake period, but
also that it had been so long in existence as to permit the wearing away of
its upper portions so as to lay bare the granitic nucleus.

It is worthy of remark that while the deposits of the Cretaceous, from
the demolition of which the White River Tertiaries were evidently largely
formed, are dark, carbonaceous clays or shales, the latter are notable for
their light color. This is probably due to the making over of the sediment
in shallow water, whereby the carbonaceous matter was oxidized, leaving
the accumulation nearly white in color. A similar phenomenon is to be
seen in the work of the modern streams. The two branches of the Chey-
enne, which flow such long distances through the Cretaceous and derive
their drainage largely from its clays, always transport sediment of a light
color. Held in suspense it gives the water a milky color, and precipitated
on the bottom it appears as a white scum. Left on the banks by higher
stages of the water, it takes the form of a light colored clayey material which
dries in the sun to a hard white crust. So fine is it that on a windy day
large white clouds of the material can be seen driving along the valley like
clouds of smokes. The rationale appears to be that the finely divided silt
derived from the Cretaceous clays has by constant exposure to the air had
its carbonaceous coloring matter oxidized and burnt out.

SECTION xX.

THE VOLCANIC ROCKS AND VOLCANIC PEAKS.

Frequent allusion has already been made to the volcanic peaks. Indi-
vidually they are small in extent, but they derive importance from their
number and from the fact that their uniformity of character over a large
area shows the wide distribution of the conditions necessary to their pro-_
duction.

190 GEOLOGY OF THE BLACK HILLS.

They are curiously limited within the region of survey by a parallel
of latitude. The line of 44° 10’ divides the uplifted area
by the outcrop of the Dakota sandstone—into equal parts. South of the

as marked out

line there is no voleanic peak either in the Hills area or in the vicinity.
North of it they dot the country in every direction. They do not seem to
bear toward one another any relation of distribution or intensity of igne-
ous action; and though the maximum effect is seen in Warren Peaks, the
other peaks in that region do not appear to hold toward them any closer
relation, except in position, than they do toward the other igneous peaks.

The main points of eruption are as follows: within the area of the
Hills proper, Custer, Terry, and Crow Peaks and Black Butte; northeast
of the Hills on the edge of the plain, Bear Butte; in the Red Valley on
the northwest side of the Hills, Inyan Kara, Sun Dance Hills, a nameless
-peak northeast of Inyan Kara, and Warren Peaks of the so-called Bear
Lodge range; on the Belle Fourche, Mato Teepee or Bear Lodge; and
near the head of Little Missouri River, the Little Missouri Buttes. Besides
these prominent peaks, all of which are indicated on the geological map,
there are many others, less conspicuous, in the northern part of the main
area of the Hills. Terry is the crowning peak of a group the remaining
members of which lie to the north and to the south of that point. In the
schist area at its northern end, east of Terry Peak, there are probably
several small points of igneous rock. To the east of Black Butte, along
the northeastern margin of the wooded area of the Hills and not far from the
inner edge of the Red Bed limestone, several small peaks supposed to be
igneous were seen from a distance. Farther to the northeast also there
were observed several exposures of igneous rock that had barely penetrated
or disturbed the sedimentary rock, and were only exposed by the denuda-
tion of the overlying formations.

The rocks which form these numerous extrusions have in general a
close resemblance in structure and appearance, and are sometimes almost
identical from several peaks. Specimens from nearly all the prominent peaks
have been critically examined by Mr. Caswell, who finds that they have a
common facies, although some fall into the division of rhyolite and others
into that of sanidin-trachyte. The resemblances are on the whole more

NO IGNEOUS OVERFLOWS. 191

important than the differences, and leave little room to doubt that the peaks
are to be classed together as the result of a single group of conditions and
the product of a single period of eruption.

In the structure of the peaks the first fact that strikes the observer is
their uniformly conical shape. To this rule Bear Lodge is the only excep-
tion, and this, with its symmetrical columnar shape, is the most remarkable
of all. The peaks appear to be merely pointed or conical waves of igneous
rock forced upward through the sedimentary strata, which are found dis-
turbed and turned up around them only in their immediate vicinity. The
metamorphism of the upturned strata is limited in extent, reaching only a
few feet from their contact with the igneous rocks. There was observed no
evidence of any overflow of the igneous matter,* but it is confined exclu-
sively to the cores of the peaks. The view that they are the cores of extinct
volcanoes or centers of igneous overflow is scarcely warranted by the
observed facts. It would be expected, if such were the case, that the sedi-

mentary rocks tilted around them would have been more metamorphosed

by the igneous heat, and even though a large portion of the overflowing
material was removed by denudation, it is scarcely possible that every indi-
cation of such an overflow could have been so completely destroyed. It
would appear therefore that the igneous peaks, instead of being the product
of violent volcanic action, are situated at a great distance from the central
and maximum region of igneous action; and that instead of the material
being ejected with great violence and at such a temperature as to cause it
to overflow readily, it was forced upward through the sedimentary strata
under great pressure and at such a temperature as to make it plastic rather
than fluid. The occurrence of these trachytic peaks appears like a great
pustular outbreak on the surface of the northern end of the Hills whereby
the deep-seated igneous forces were relieved, or like the appearance of
bubbles on the surface of a kettle of boiling tar.

The peaked character of the igneous points seems to be somewhat
peculiar, for in the records of geological explorations in the Rocky Mount-
ains it is not mentioned. Mr. Dawson, however, in his report on the region

* Possibly an exception to this statement should be made, for, as related in the description of -
Terry Peak, rhyolite near the Deer Mountains was seen overlying quartzite belonging probably to the
Potsdam.

192 GEOLOGY OF THE BLACK HILLS.

of the 49th parallel, describes the Sweet Grass Hills as having a similar
peaked structure, around which the sedimentary strata, the Lignitic Tertiary,
have a similar quaquaversal dip.* The rock also of these peaks, a “rhy-
olitic trachyte-porphyry”, passing into ‘“sanidin-trachyte”, seems from the
descriptions to be similar to the igneous rocks of the Black Hills.

The peaks have so little variety that it will not be profitable to describe
them individually. A detailed account will be given only of the principal
ones, viz: Custer Peak, Terry Peak, Bear Peak, Crow Peak, Inyan Kara,
Sun Dance Hills, Warren Peaks, Bear Lodge, and the Little Missouri Buttes.

. Custer Peak stands at the eastern margin of the Carboniferous plateau,
just within the area of the slates. It is a symmetrical, conical mass, and
is a prominent landmark in the northern region of the Hills. Its height
above the valley at its base is 675 feet, and its elevation above the sea is
about 6,950 feet. It is very little higher than the neighboring edge of the
plateau. The mass of the peak is so covered with fragnients of the rock
that neither its intimate structure nor its relation to the prevailing rocks
of the region could be well determined. ‘The slopes of the sides show
only a loose mass of angular fragments, over which the ascent was not a
little difficult. On the extreme summit the rock is exposed in a Y-shaped
ridge, with the stem of the letter bearing north 35° west. The rock has so
perfect a vertical cleavage, following approximately the bearing of the
ridge, that it might readily be taken for a bedded deposit; and in its close
texture, uniformity, and color it so closely resembles the limestone of the
Carboniferous, that it might almost be so mistaken on a superficial examina-
tion. Close inspection, however, reveals its igneous nature. It is a rhyo-
lite of a light bluish gray color, and a fine-grained and uniform structure,
containing occasional crystals of sanidin and bright black hexagonal tables
of biotite.

To the east and northeast of Custer and within a short distance are
two small peaks which appear to consist of igneous rock, but they were
not examined closely. With this exception no other igneous points occur
until the Terry Peak region is reached, about eight miles to the northwest.

* Geology and Resources of the Region in the Vicinity of the 49th Parallel, by G. M. Dawson, p.
122 et seq.

TERRY PEAK. 193

The margin of the plateau west of Custer Peak is exceedingly broken and
the composing rocks are not well exposed. A mile or so directly south,
however, outliers of the Carboniferous limestone were seen in their hori-
zontal position occupying the summits of conspicuous bluffs, and immedi-
ately west of the peak, within a short distance of its base, are small frag-
mentary outcrops of the Carboniferous, undisturbed and unchanged. [ast
of the peak and within a half mile of its base there are outcrops of the
Potsdam along the headwateis of Box Elder Creek, showing the usual
character of the formation, lying nearly horizontal, and so far as observed
entirely unaffected by proximity to the igneous peak.

Terry Peak is the crowning point of an igneous region of considerable
extent, having a maximum development in a northwest and southeast direc-
tion. The region is deserving of careful study, but because of the great
number of the points of exposure and the very rugged nature of the country
it was impossible to wholly examine it even superficially in the time at our
disposal. The peak stands upon the edge of the plateau; the Potsdam is
extensively developed on its eastern side, and with it are occasional outliers
of the Carboniferous. Its sharply pomted summit is the most conspicuous
landmark in the northern region of the Hills and is visible from the Plains
far to the north and east. Its altitude, by mercurial barometer, is 7,230
feet, and there are but two summits in the Hills that outrank it. It rises
fully 1,000 feet from its base.

The igneous group or range of which Terry is the highest point begins
about three miles to the southeast in a cluster of peaks called the Deer
Mountains, and there is a nearly or perhaps quite continuous chain of
trachytic and rhyolitic outcrops all the way to Terry. The same line con-
tinues northward for a few miles beyond Terry.

The disturbance of the sedimentary strata is exceedingly local and
confined to the immediate vicinity of the peaks themselves. Directly east
of Terry Peak, and almost at its base, the Carboniferous limestone lies
undisturbed, while against the ridge that culminates in the peak the Pots-
dam, much metamorphosed, was found at several places inclining at a
high angle. The sides of the ridge and of the peak are for the most part

covered by a talus of angular and slippery fragments of the rock, On the
13 BH

194 GEOLOGY OF THE BLACK HILLS.

summit of the peak the rock is well exposed, and three or four ridges of
outcrop appear to radiate a few hundred feet from the central crest, while
between them the slopes are composed of weathered fragments. The rock
of the summit has a greenish gray color, and contains many conspicuous
crystals of sanidin. In hand specimens it appears like a feldspathic por-
pliyry, but what seems to the unaided eye to be a groundmass is shown
by the microscope to be crystalline and to carry a large amount of quartz
The percentage of silica is so large that Mr. Caswell classes the rock with
the rhyolites.

About a mile and a half to the eastward there is a dike of greenstone
running north and south for some distance, cutting through the sedimentary
rocks. It is probably connected with a small peak northeast of Terry
which was reported to be composed of greenstone.

Near the base of Deer Mountains a rhyolitic rock was observed over-
lying quartzite that was thought to belong to the Potsdam. This may be
either an overflow or an injection between strata, and it is the only case in
which the igneous and sedimentary rocks were seen in this relation. In
several places in the canons contiguous to the igneous masses the Potsdam
sandstone—here the best exposed of the sedimentary series—was found
highly altered by the igneous rocks, which in many places penetrate it. It
is frequently altered into a hard brownish rock with crystals of feldspar
irregularly shot through the mass. Sometimes it is a hard granular rock
with a conchoidal fracture, and in places the conglomerate is so hardened
that it breaks as readily through the composing pebbles as in any other
direction.

The igneous rocks of this region are varied in their appearance and
texture.

Crow Peak is a pustular outbreak of voleanic rock through the Red .
Bed limestone twelve miles northwest from Terry Peak. Though it does
not rank as one of the highest points of the Hills, it springs so abruptly
from its immediate surroundings as to make it locally a very conspicuous
point. Its approximate height above the Red Vailey in its vicinity is 1,500
feet. As seen from the east or west it appears to be composed of two peaks
closely united; the southern one is the rhyolite core, while the northern

BEAR BUTTE. 195

consists of the uplifted sedimentary strata, which are elevated higher on
that side. The rhyolitic point is conical, with, however, a larger develop-
ment in a north and south direction, so that the summit is a ridge several
hundred feet in length. Along this barren ridge the rock crops out promi-
nently. It has a distinct cleavage lengthwise of the ridge, and is divided
thereby into plates which in some places are quite thin. The steep slopes
of the sides are masses of loose and sliding fragments.

The rock is a light gray, compact, tough rhyolite. It has been forced
through the sedimentary strata, which from the Potsdam to the Red Bed
limestone are exposed around the base and are all more or less disturbed.
The Red Bed limestone is least influenced and surrounds the peak in a
gentle slope or bulge, while a long low swell or ridge extends for several
miles northerly into the Red Valley, diminishing and finally dying out
entirely. Within a few hundred feet of the peak the Carboniferous is seen
in a canon lying nearly horizontal, while it laps up against the base at an
angle of 75° or 80°. The Potsdam is exposed at several places in the
canon, having the usual character, while under the Carboniferous against
the peak it stands vertical. It has been more or less completely metamor-
phosed into a hard quartzite, though none of the other sedimentary rocks
appear to be in the least changed by proximity to the igneous mass.

Bear Butte rises from the level of the Plains on the northeastern side
of the Hills about six miles from the edge of the foothills, and though its
total elevation above the sea is but 4,570 feet, its abruptness and its height
above the surrounding plain—1,200 feet—make it a conspicuous landmark.
In structure it resembles Crow Peak, having a similar conical outline, and
being an upburst-of trachytic rock through the sedimentary strata, some of
which are distinguishable all around its base. As seen from the south it
_is a simple cone, but from the east and west the summit appears as a
ridge several hundred feet in length, with a trend about north 40° west.
The summit ridge is narrow and the rock, as in Crow Peak, has a vertical
cleavage running with the length of the ridge. About the ridge are several
bluffs which expose the rock in place nearly to the base, while the inter-
mediate spaces, each like a cul-de-sac, are filled with loose fragments.
These fragments are small, angular, and flat, and are so loosely aggre-

196 GEOLOGY OF THE BLACK HILLS.

gated as to render the ascent of the peak a toilsome task. Where they
cover the side of the peak the entire slope is marked with zigzag paths a
few inches wide that ascend at angles of from 20° to 30°, crossing and.
recrossing each other in a perfect net-work. These are supposed to have
been made by mountain sheep, but none were seen in the vicinity. On
the summit and here and there on the sides of the peak are a few stunted
pines, but its general appearance is barren and has led to the suspicion that
its name was originally and more properly Bare Peak.

The rock is a gray trachyte, with weathering surfaces much darker
than the fresh fracture, giving to the peak a somber appearance. It is hard,
compact, and tough, and has a ring somewhat like phonolite.

The butte stands in the gray shales and clays of the lower Cretaceous,
and around its immediate base are the uplifted strata of the Dakota sand-
stone, with partial exposures of the Jura and Red Beds. The base of the
peak, however, is so much concealed by fragments of the igneous rock and
by grassy slopes that there is little opportunity to examine the lower of the
disturbed strata. A dense quartzite is visible in numerous places at the base
of the peak standing vertical in a prominent ridge, but its continuity is not
perfect around the peak. West from the summit ridge there are a series
of imperfect outcrops, in curves concentric with the peak, which are thought
to belong to the Red Bed scries. On the same side of the peak, close to
the base and underlying the metamorphosed Dakota sandstone, the follow-
ing strata were observed in a deep wash-out. They rise toward the peak

with increasing angles.

Feet

13. Yellow: sandstone ct oy 0 Ss fer rae crece tanersts estes reales tate aerate rer ae ere —
12iGray shale ormarl blaclsabstopee mss) cir ek eels ie eileen eye 20
iis Sandstone mull-of roundedyorain sperms eee ee eae ere iL
ID SITIES lOgOnunn Or \ MOAN <5o565 soo 5sedo5oas .oonsabosHosséousD 25a odooc 15
9); Calcareous ‘marl *=.. 25, Fk2 50 Sa erases set cereter ere rere ote eee 3-4
Su Shale orimark «2,554. 5:5 eerste oe oe ne eee ae ee ete ee aoe 15-20
Tes@alcareous marl si-5.\0.0. cc. Sue. tasers eee ee ete One ee eee : 20
6. MiSlonr MoM) once <= cc SE oe eon geet lee le en on eee 10
5. Yellow, red, and green ale, necomine Sandyiatiases-een = coe soe 30-35
4, Soft white shally Sandstonet e+, sae ee ae A ay eS Pk eh 20-25
3. Greenish shaly sandstone; top somewhat enellleacane Bs SAO nA aS, 5 75
2. Sandstone, yellow and ell Sane PPM PR Fo oe ato tare eM res sO a 3-5
TS Dee peredyclays ft sc..a ot aescectar aera rs Sea erage IA Ce eee exposed. . 8

SUN DANCE HILLS. ; 197

No fossils were discovered in these beds, but, with the exception of the
red clays at the base, they are supposed to belong to the Jura. It is
probable that they are upturned on all sides so as completely to encircle
the uplift, but they are concealed by débris.

A short distance from the base of the butte no evidence can be seen
of the close proximity of an igneous peak.

From this brief description it will appear that Bear Butte is an igneous
extrusion, producing no dislocation or metamorphism in the strata through
which it was protruded, except at its very base. It gives no indication that
its igneous material ever overflowed as a true lava, but rather that, like the
other peaks of this region, it was a huge viscid bubble, breaking through a
- great thickness of superincumbent strata.

Sun Dance Hills.—These two hills are in the northeastern bend of the
great Red Valley, about eight miles southeast from Warren Peaks and
twelve miles due north from Inyan Kara. They are the simplest and best
illustrations of the pustular nature of the igneous ejections of the Black
Hills. They are about three miles apart and are not very prominent except
in the local topography. The higher of the two is 1,!00 feet above the
surrounding valley, while the eastern and smaller hill is, by estimation, not
over 600 feet above its base. The rock is very similar to that of Bear Butte
and Inyan Kara, a hard, gray, compact trachyte. The larger hill was
ascended and found to have a ridge-like summit with its major axis pointing
in a northwesterly direction. Around the bases no more recent strata were
recognized than the red clays and limestone of the Red Beds, and these are
but little disturbed. The limestone surrounds each in a gentle slope very
like the broken edges of a piece of paper that has been punctured bya
sharp pencil but it is in nowise shattered. It seems to conform to the
little irregularities of the uplift almost like a flexible material.

Inyan Kara is the most prominent peak on the west side of the Hills.
It is situated in the Red Valley, west of the limestone plateau. Its name
first appears on the map of Lieutenant Warren, and as translated for him
signifies ‘‘the peak which makes stone.” Jnyan signifies in the Dakota
tongue “stone,” but the word Kara is unknown in the language, and is _
probably a corruption of Ka-ga, ‘to make” The summit of the peak is

198 GEOLOGY OF THE BLACK HILLS.

6,600 feet above the sea, and has an elevation of 1,300 feet above the bed
of Inyan Kara Creek near by. The igneous mass of the peak occupies the
center of what in form resembles a crater, for separated from it by an annular
valley there is an encircling ridge or rim whose top is 500 feet below the
summit of the peak. This rim is formed by the Red Bed limestone rising
up from under the surrounding red clays at an angle of about 40° and
completely encircling the peak except at a narrow break on the northeast
side where the drainage escapes. The limestone wraps around the outer
slope of the peak like a cloak, conforming to all local changes in dip and
bending without fracture. The upper red clays of the Red Beds lap up
against this limestone, which appears as a breakwater raised against the
turbulence of the billowy sea of the Red Valley. On the inside of the rim
is the annular valley, surrounding the igneous nucleus and having a width,
from rim to center of peak, of from one-half to three-fourths of a mile. It
has evidently been formed by the denudation of the easily eroded strata
beneath the limestone.

From the midst of this crater-like depression the peak rises so abruptly
that there is but one side with an easy slope for climbing. The summit is
a broad but very irregular area, whose larger dimension has a bearing
about 30° west of north and upon which the rock is well exposed. It is a
hard, highly feldspathic trachyte, and on weathered surfaces large and
well formed crystals of feldspar were seen in great abundance, giving the
weathered mass a porphyritic appearance. In mass it is notably mag-
netic. The rock shows well marked cleavage or jointing planes, nearly
vertical, in two series. The first runs toward the northwest and the second
toward the west, dividing the rock into prisms and producing a quasi-colum-
nar structure.

Though on a much larger scale, the entire upheaval being probably
two or three miles in diameter, the peak has essentially the structure already
described in Crow Peak and Sun Dance Hills. Among the uplifted beds
surrounding Inyan Kara no strata were recognized excepting the Red Bed
limestone and the underlying, impure, reddish sandstone, and beyond the
immediate base of the outer slope no disturbance was indicated. Indeed,

WARREN PEAKS. 199

the red arenaceous clay is too nearly structureless to retain readily such
evidence.

Warren Peaks are the crowning points of the ‘‘Bear Lodge range,”
an elevated, broken plateau between the Redwater Valley and the Belle
Fourche. The peaks are not remarkably prominent, but their total ele-
vation above the sea, 6,830 feet, is equal that of some of the principal
peaks in the Hills, while their height above the Red Valley immedi-
ately south is about 1,800 feet. The trachyte area to which they belong
is the largest of the whole group, and covers fifteen or twenty square miles.
Around this the strata of the sedimentary series are uplifted and arranged
in concentric circling outcrops, so as to make a sort of miniature copy
of the Hills. The trachytic nucleus has an extension from northeast to
southwest of about eight miles, and a width of two or three miles. Its
surface consists of high, rounded, grass-covered hills, with little or no
timber, and from this rise the two or three more elevated points to which
the name Warren Peaks has been applied. These more central points
are surrounded by smaller and less prominent peaks, which are sepa-
rated by deep ravines or gulches forming the lines of drainage. Besides
this great nucleal mass of igneous rock, several outbursts, very local in
character, were observed in the zone of encircling strata. The rock is a
trachyte, dark gray in color, and containing frequently large and perfect
crystals of sanidin which give it a porphyritic character. Small crystals
of mica and hornblende are also prominent, and the rock yields more to
weathering than that of some of the other peaks. In different portions of
the district the rock varies somewhat in its character, though evidently of
the same general nature. Asa rule itis more highly crystallized than the
trachytes farther south, the large, well formed feldspar crystals being more
common and also the small crystals of mica and hornblende.

A short distance northeast of the central peaks an irregular, ill-defined
ledge was found, traversing the trachyte for some distance in a northwest
direction. It is varied in its composition, but consists mainly of a coarsely
crystallized feldspathic rock, with the crystals imbedded in a fine-grained
feldspathic matrix, the whole mass having a yellowish or reddish brown
color. Near the middle the mass is irregularly intermixed with compact

200 GEOLOGY OF THE BLACK HILLS.

black limonite and manganese oxide, which, though closely associated, seem
to remain distinct These oxides fill the spaces between the feldspar
crystals and irregularly impregnate the rock, giving it a brecciated appear-
ance. They often show a cubodial form, indicating that they are derived
from the decomposition of pyrites, and small pieces of that mineral were
found in the interior of several masses. Though gold is invisible, careful
assays prove its existence in the mass, and from this source is probably
derived a portion at least of the gold found in this region.

The encircling zones of sedimentary rocks include the Potsdam below
and the Jura above. Their dip is quaquaversal and is usually quite regu-
lar, the angle varying from 20° to 30°.

The Potsdam sandstone which immediately overlaps the base of the
igneous mass has been greatly metamorphosed. Where the rock was shaly
it has been changed into a hard fissile slate, scarcely recognizable as of
sedimentary origin; and the pure sandstone strata have been converted
into compact quartzite often of a very white color. In several places the
igneous matter seems to have penetrated between the strata, which are
scarcely distinguishable from the injected rock, and in many cases the
metamorphosis appears to have been performed by the action of heated
waters, for the sandstone was found penetrated irregularly by well formed
crystals of feldspar. On the west side, near the middle of the formation,
were found layers of argillaceous sandstone covered by the large branching
fucoid peculiar to the Potsdam, and some of the upper layers of the sand-
‘stone are pertectly riddled with Scolithus holies. The Potsdam, Carbonifer-
ous, and Red Beds are well exposed in many of the cations which radiate
from the central area carrying the drainage eastward to the Redwater or
westward to the Belle Fourche. On the south and east, facing Sun Dance
Hills, the Red Bed limestone forms the outer slope, dipping under the red
clay of the Redwater Valley. On the north and west, however, the Jura
is well exposed and capping this the Dakota sandstone.

Vhough on a grander scale and exposing a larger area of igneous
rock than the other centers of igneous extrusion, the Warren Peaks show
the same character of pustular eruption.

The Bear Lodge (Mato 'Teepee).—This name appears on the earliest

BEAR LODGE. 201

map of the region, and though more recently it is said to be known among
the Indians as ‘‘the bad god’s tower,” or, in better English, ‘the devil’s
tower,” the former name, well applied, is still retained. It stands on the
immediate western bank of the Belle Fourche, about four miles southeast
from the Little Missouri Buttes. It was not reached by the Warren expe-
dition, but while the Raynolds expedition was in the vicinity of the Little
Missouri River two attempts, the last successful, were made by Mr. Hutton
to reach it. He recorded, however, no particular description of it, so that
when we reached it in 1875 our examination had all the charm of novelty.
Its remarkable structure, its symmetry, and its prominence made it an
unfailing object of wonder. (See frontispiece ) It is a great rectangular
obelisk of trachyte, with a columnar structure, giving it a vertically striated
appearance, and it rises 625 feet, almost perpendicular, from its base. Its
summit is so entirely inaccessible that the energetic explorer, to whom the
ascent of an ordinarily difficult crag is but a pleasant pastime, standing
at its base could only look upward in despair of ever planting his feet on
the top. At a distance it resembles not a little the unfinished Washington
Monument in Washington City, with the difference, however, that Nature
has completed her work.

Within a half mile of the banks of the Belle Fourche the shaft rises
with its broad base of débris from the plateau formed by the lower Jurassic
sandstone. Its dimensions were determined by Captain Tuttle, the astrono-
mer of the expedition, who calculated them from measurements with the
sextant.* The height of the summit above the river was found to be 1,126
feet, while approximately its elevation above the sea is 5,260 feet. The
width of the summit from north to south is 376 feet, and the width at base
is 796 feet. In an east and west direction the diameters are less.

The rock is a coarsely porphyritic sanidin-trachyte of a greenish color,
closely resembling that of Terry Peak. In the mass it has a erystal-like
structure on a grand scale, which from a short distance gives the column
the appearance of a fascicle of gigantic fibers From the base, which is
considerably broader than the body of the peak, each fiber-like crystal or
column rises in a bold curve to the bottom of the vertical obelisk, which it
then-follows to the summit. The columns have generally a rectangular or

202 GEOLOGY OF THE BLACK HILLS.

rhombic section, but are sometimes triangular or hexagonal. With the
exception of an occasional fracture each column or crystal continues to the
very summit. ‘The sides are of various dimensions, but average from two
to four feet at the base. They diminish upward in the same ratio with the
total column. Careful examination at the base shows that the columnar
structure is not continuous below the portion of the peak exposed to view.
The columns differ somewhat in size and position from those characteristic
of basalt. The latter are commonly referred to contraction in cooling,
occasionally combined perhaps with a concretionary action; and they are
always formed perpendicular to a surface of cooling. In a dike they are
perpendicular to the walls, and in an overflow to the atmospheric surface.
They are rarely of any great length, and frequently they extend but a part
of the way through the bed, ending irregularly in a structureless mass. In
the Bear Lodge we have columns over six hundred feet in length rising per-
pendicularly from a seemingly massive base. It is exceedingly difficult to
account for this as a result of cooling by comparison with any known basaltic
phenomena; and, indeed, Bear Lodge, in its shape and structure, appears not
to have been repeated elsewhere by Nature, but stands alone, unique and
mysterious.

The strata from which this igneous column springs are not in the least
disturbed at the nearest points where they could be examined, about 50 or
75 feet from the base, but the sandstones for some distance are converted
into a compact white quartzite.

The Little Missouri Buttes stand on the plateau of Dakota sandstone
about four miles west of Bear Lodge and near the divide between the head-
waters of the Little Missouri River and the Belle Fourche. They are three
in number, occupying three angles of a triangle, and are said to be called
by the Indians ‘‘the buttes which look at each other.” Though prominent
landmarks, they rise only between four or five hundred feet above their
base. They are about one-half or three-fourths of a mile distant from one
another, but they are so thoroughly covered around their bases with débris
that their intimate structure and relation could not well be determined.
The Cretaceous sandstone forming the floor of the surrounding plain could
not be ascertained to exhibit any disturbance or change of structure due to

STRUCTURE AND AGE. 203

proximity to the igneous matter. Hach peak has the same general conical
form so often described, and a similar system of cleavage planes was also
observed. Some cross-planes give locally an appearance of columnar
structure. The rock is a greenish gray trachyte similar to that of the Bear
Lodge, but though it contains many crystals of feldspar it is not so highly
crystallized as the rock from the latter peak. At the base of the buttes in
one or two localities a rock was found exceedingly light and cellular in
structure, yellowish in color, and very like a volcanic tufa. As the result
of a microscopic examination Mr. Caswell designates it a rhyolitic breccia,
including fragments of both sandstone and rhyolite.

SECTION XI.

STRUCTURE AND AGE OF THE BLACK HILLS.

It remains to consider the origin of the topographic forms which con-
stitute the Hills. How and when did the plateaus, and peaks, and cliffs,
and cafions, and valleys that make up its topography come into existence ?
The answer to the question is, in general terms, that the rocks were uplifted,
and that being uplifted they were by the processes of erosion worn away
and carved into the forms we have seen. | If the form of the uplift had
been different, if the order and character of the rocks had been different,
if the date of the uplift had been different, there would have been a differ-
ent topographic result. A complete analysis of the resultant-forms, taken
in connection with the structure of the rocks and viewed in the light of the
natural laws of erosion, should tell, first, the form of the displacement or
uplift and, second, the date of its occurrence./ Our analysis is unfortunately
not so full as to afford either of these results in a satisfactory way, but it
will at least give a fair idea of the methods by which they may be reached.
In presenting the material and deductions the following order will be
observed :

First, the form of the displacement will be considered; second, the
relation of the topography to the form of the displacement and to the rock
structure will be discussed; and third, the evidence which bears upon the

-

204- GEOLOGY OF THE BLACK HILLS.

date of the uplift will be assembled; finally, the age of the igneous masses
will be considered, and the section will close with a summary of the geo-
logical history of the district.

1.—THE FORM OF THE DISPLACEMENT.

If the reader will open the geological atlas at the page which gives a
bird’s-eye view of the Black Hills, he will obtain a clearer idea of the gen-
eral structure than it is possible to convey by words.

Turning his attention first to the Archeean area just to the right of the
middle of the view, he will see that it presents a series of undulations
without any evident system. Around it there is a continuous cliff facing
toward it, so that it is on a grand scale walled in. The rock of this cliff is
the Carboniferous limestone. On the right hand side of the Archzean (the
eastern side) the Carboniferous has a considerable inclination which carries it
at once out of sight. At the left it has a very gentle dip, causing it to form
a plateau instead of a ridge, but at the farther edge of this plateau its dip ~
suddenly increases and carries it out of sight; so too at the north (or in
the distance) and at the south (or in the foreground). The Carboniferous
outcrop is completely surrounded by a line of high dip and its limits are
given thereby. With the aid of the view it is easy to understand that the
same limestone strata once extended completely across the oval area
marked out by the zone of high dip, and that there was no exposure what-
ever of the Archean until it was denuded by the erosion and destruction
of a portion of the Carboniferous. The first step then toward restoring
the form which the rocks acquired by displacement but lost by erosion is
the replacement in imagination of the Carboniferous beds over the area
where now the Archean only is exposed.

Outside of the Carboniferous and completely encircling it is the Red
Valley, marking the outcrop of the soft clays of the Red Bed and Jura
formations, and outside of the Red Valley there is an encircling ridge
popularly known as “the foothills” and carrying the outcrop of the Dakota
sandstone. (The sandstone and the soft beds beneath it conform to each
other and to the Carboniferous limestone and dip in the same direction, so
that the foothills consist everywhere of a monoclinal ridge, having a dip

RESTORATION OF ERODED STRATA. | 205
away from the Hills and toward the Plains. But although the Dakota
sandstone is assumed to be parallel to the Carboniferous limestone beneath
it, its dip is not necessarily the same as that of the nearest outcrop of the
Carboniferous. On the whole its inclination is somewhat gentler, and in the
variations of this inclination we find recorded local details of the form of the
great displacement. | To restore the Dakota sandstone over the whole of the
oval area circumscribed by its outcrop taxes the imagination more heavily
than the restoration of the Carboniferous, and the tax increases with one’s
appreciation of the magnitude of the quantities dealt with. The space to
be filled has a length of nearly ninety miles and a breadth half as great,
and the total thickness of the formations that were removed from it—the
Dakota sandstone, the Jura, and the Red Beds—is about 900 feet. Never-
theless the evidence is such as no geologist would hesitate to accept, and to
restore the uplift to its full proportions we must carry these formations over
the entire area of the Carboniferous, actual and restored, building on every-
where a thickness of from 800 to 1,000 feet. Over the Red Valley the
thickness to be added is not so great, for a part of the Red Beds, and in
some places a part of the Jura also, there survive, so that only the missing
portions need be supplied. The amount to be added varies from 300 feet at
the foot of the Dakota cliff to 900 feet at the margin of the Carboniferous,
and its precise value at any particular point is to be determined by a study
of the local outcrops and the local dip.

The work of restoration does not end with the reconstruction of the
Dakota sandstone. Outside of the foothills the view shows a number of
monoclinal ridges smaller and less persistent than the Dakota ridge, but
agreeing with it in the fact that the composing strata are inclined away
from the uplift. These ridges mark the position of the harder members of
tue upper Cretaceous rocks, and testify to the fact that those rocks were
affected in common with the Dakota sandstone by the upheaval. We do
not know their full thickness, because in the neighborhood of the Hills
they have everywhere lost something by erosion, but whatever that thick-
ness was—and it was not less than 600 feet—it must be rebuilt over the
area of the Hills in order to restore the uplift to its full proportions.

Let us assume that we know the thickness of each of the formations

206 GEOLOGY OF THE BLACK HILLS.

involved in the displacement, and that we know the altitudes of all points
in the Hills. Then by examining the rock at any point and determining to
what part of the stratigraphic series it belongs we can estimate what depth

FIG. fete cross-section of the Black Hills.

The vertical scale is about six times the horizontal. The dotted lines indicate the portion of the
uplift removed by erosion.

1. Archean slates and seats, 6. Jura.

2. Granite. 7. Cretaceous.

3. Potsdam, resting unconformably on 1 and 2. 8. White River Tertiary, resting unconform-
4. Carboniferous. ably on 7.

5. Red Beds, with included limestone.

of rock has been removed, and by adding this to the known altitude of the
point deduce the local altitude of the restored uplift. By repeating this
process at a great number of points we can determine the corresponding
points of the ideal surface and attain to a definite conception of its form

Or if we take into consideration the fact that the inclination or slope of the
ideal surface must be everywhere very nearly identical in direction and
degree with the dip of the visible rock beneath it, then it will suffice to
determine a few points only by the additive method, and fill in the inter-.
vening space by simply copying the slopes observed in the rocks beneath.
I think this latter is the process of reconstruction which the mind employs
when it contemplates such vestiges of erosion, either in nature or in a view
like the one before us.

In the present case we do not know the thickness of all the formations,
but our only conspicuous ignorance is with reference to the highest forma-
tion of all, the upper Cretaceous, and is therefore not serious; for any error
in the estimate of that affects only our determination of absolute height,
and not our determination of form. Each of the formations, too, varies
in thickness at different points of its outcrop, and may be assumed to have
varied within the area from which it has been removed; but these irregu-

FORM OF THE DISPLACEMENT. _ 207

larities, though amounting sometimes to hundreds of feet, are too small to
introduce any serious error in our conclusions. It is unnecessary to burden
these pages by a detailed presentation of the facts we have used in deducing
the form of the uplift; we will merely describe it Many of the facts are
recorded in the geographic and topographic maps and in the bird’s-eye
view, and still others have been detailed in the descriptions of the forma-
tions in the earlier portions of the chapter.

e The first important feature of the uplift is that it is flat-topped. It
belongs to the same order of displacement as the Uinta Mountains and the
Kaibab Plateau.* The top is not absolutely flat, but relatively so, and tlre
inclination all about the periphery is very much greater than any inclina-
tion upon the upper surface. The extent of this tabular top is shown on
the geological map by the combined outcrops of the Carboniferous and
Archean. It is oval in form, with a length of seventy miles and a width of
forty. Its general trend is about 10° west of north, but its axis is not a
straight line; its eastern side is more strongly curved than its western, and
gives an impression, borne out by other evidence, that its median line has
a decided curvature, the concavity of which is toward the west. ) The
highest part of the table is nearer the eastern edge than the western, and
it is perhaps true that the entire top slopes toward the west; certainly that
portion deduced from the study of the Carboniferous plateau does so.

The descent from the tabular summit is steeper at the east and west
than it is at the north and south; that is to say, the table is more definitely
bounded at the sides than it is at the ends. On the east side the surface
bends over gradually until it acquires an inclination of about 30°, and then
curves still more gradually at the base of the uplift until it loses its incli-
nation and merges with the imperceptible slope of the strata of the Plains.
The same is true on the west side, with a single exception. Ata point
near Camp Jenney the descent is, for a short distance, so steep as to be
almost vertical.

At the south end the greatest inclination is not more than 15°, and the
curves which connect this with the table above and with the datum plane
below are exceedingly gentle. / There is a sort of prolongation of the uplift,

208 GEOLOGY OF THE BLACK HAILLLS.

not as a sloping table but as a low anticlinal which gradually descends
and fades away to the southward. The form of the prolongation is realized
by the outcrop of the Dakota sandstone which ceases at that point to be a
simple monoclinal ridge and spreads out into a triangular table sloping to
the southeast and southwest.) Here again a glance at the bird’s-eye view
will give a more definite idea than can be conveyed by a description.

At the north, or rather at the northwest, for that is the direction of the
other extremity of the axis, there is a similar prolongation of the uplift, but
it is on a far greater scale. An anticlinal nearly as broad as the main
tiplift extends for at least forty miles beyond the end of the table, and is
itself somewhat tabular. Where it adjoins the main table it is decidedly
lower, and the two surfaces are connected by a gentle flexure. Thence it
descends slowly to the northwest, and it probably merges gradually with the
datum plane in that direction | Our observations, however, did not extend
to its limit. On its northeastern edge it is limited by a definite flexure,
which in its southward prolongation merges with the eastern flexure of the
main uplift. Its southwestern limit shows no such flexure and is not well
defined.

The extreme height of the uplift as referred to its datum plane—that
is the maximum amount by which a stratum in the arch of the Hills rises
above its prolongation in the surrounding Plains—is estimated to be 6,600
feet. This height is found in the crest of the main uplift, near the eastern
edge of the tabular top. The western edge of the tabular top is about &00
feet lower. The altitude of the southward anticlinal extension, where it is
crossed by the Cheyenne River, is about 1,800 feet above the datum. The
northern prolongation, where it joins the main uplift, has a central height of
about 3,300 feet, just one-half of the full height of the main uplift. Where
it is crossed by the Belle Fourche River its height is 2,200 feet. The total
volume of matter here lifted above the general surface, or, in other words,
the solid contents of the restored dome of rock, is 4,200 cubic miles.

In this description no allusion has been made to the displacements
associated with the igneous rocks. ‘Those displacements modify the form
and destroy the simplicity of the great displacement, but they have no
discernible relation to it except the relation of superposition. Whether

30 40 MILES

Fie. 26.—Contour Map of the Black Hills Displacement.

The vertical interval between contours is 500 feet.
The upper irregular line shows the position of the Belle Fourche River; the lower of the South Fork
of the Cheyenne.

Wiz AAS rae

pad ney - oe 5 7 i

IGNEOUS UPLIFTS. 209

they were formed before or during or after the uprising of the great arch,
there is nothing in their distribution to suggest that they are in any wise
dependent upon it or closely related. Some of them are near the crest of
the arch, some are where the rocks are steeply inclined at the side of the
arch, many are on the gentle slopes of the northern prolongation, and at
least one is entirely outside of the Hills. They are so much smaller than
the protuberance on which they rest that they seem to be merely superficial
phenomena-—a sort of skin disease upon the surface of a tumor.

But however insignificant the volcanic disturbances may appear when
contrasted with their vast orographic associate, they are by no means .
unimportant when considered by themselves. About each of the igneous
cores the upbent strata expose circular outcrops. Evidently their present
condition has resulted from protracted waste under the play of the elements,
and if we could restore the portions which have disappeared to the form
which they had immediately after the upthrust of the molten rock, we
should have mountains of very respectable proportions. It is safe to say
that when the trachyte of Warren Peaks was forced up beneath the Pots-
dam sandstone, it lifted it to a height of 3,500 feet, carrying with it all of
the strata that then rested upon it, and forming a mountain 3,500 feet in
height and six or eight miles in its smailest diameter.

In the accompanying diagram, Figure 26, all uplifts known to be
caused by volcanic action are ignored. |The orographic uplift, pure and
simple, is represented by the method of contours.) It has no pretension to
minute accuracy, but it may be trusted to give a veracious rendering of
the main features of the displacement. ‘The outermost curve of all is
intended to be drawn at the limit of the displacement, and represents the
base of our ideal dome where it joins the plane of reference. The next
curve is the 500-foot contour, and represents the intersection of our ideal
dome with a plane parallel to the datum plane and 500 feet above it. So
of all the other curves, the vertical interval between two adjacent lines
being in each case 500 feet.) The courses of the two forks of the Cheyenne
are marked upon the diagram, partly to aid in giving it a geographical
position and partly to illustrate the fact, to which we shall again have .

14BH

210 GEOLOGY OF THE BLACK HILLS.

occasion to advert, that the rivers flow directly across the mountain instead
of going around it.

In speaking of the elongated dome of strata which we have recon-
structed in the imagination, we have been careful to make use of the adjec-
tive ‘‘ideal,” and to this we have given a double meaning. The dome is
ideal because we have constructed it as a logical deduction from a mass of
observed facts, but it is also ideal because it never had a real existence. |
We have excellent reason to believe that when the uplift began the site of
the Hills was either dry land or the bed of a shallow lake, so that the rising
arch was subject to the attack of the elements either at its inception or
immediately after. The higher it rose the greater was its exposure and the
more rapidly was its summit worn away. When it reached the full
measure of its magnitude as an orographic protuberance, its destruction by
elemental warfare had progressed so far that the magnificence of our ideal
structure was very far from realization. Of the slowness of the uprising
of the mountain we have no evidence in what we were able to glean during
our hurried study. For aught that we learn from local observations the
mountains may have shot up with the speed of a growing vine, but in the
growth of other mountains there are many things to show that their pro-
gress was secular, and upon no plausible theory of the origin of mountains
can it be supposed that their birth-labor is other than exceedingly slow.
The earthquake is but the passing pang that records a unit of progress; it
is only by the combination of many such units, separated often by wide
intervals of time, that the great result is accomplished.

2.—THE RELATION OF THE TOPOGRAPHY TO THE STRUCTURE.

There are two conditions which more than any other determine the
forms of mountains. The first and most important is the rock structure.
The second is the drainage system, or the arrangement of the lines of drainage.
The rock structure always determines the type of the resultant form, and
usually it is largely concerned in the determination of the drainage system.

The rock structure of a mountain is the arrangement of the various
masses which compose it.) When those masses are chiefly sedimentary
rocks, as in the present case, the structure is readily divisible into two

ALTERNATION OF HARD AND SOFT. ate

parts: first, the order of sequence and the thickness of the several strata,
and, second, the position in which they lie, or their altitudes and angles of
dip. The position of the strata of the Black Hills is given by the form of
the displacement. The thickness and character of the several beds have been
described in the preceding sections.

Considering the beds of the conforming series from Potsdam to Cre-
taceous simply with reference to their ability to resist erosion, we have the
following classification:

Feet
Ae SOlus Deas Ol FHO Tp Pel CLEtACCOUS <<: coc'swin ccna =a Sic os se eee cle ce er eeteee 600
Ide lab inils IDEIMO es) SENG +655 caeucsococe sesecpopUbryEede see se nigesa eben = 1, 300
Ce SOtieaed SOtmohe Jura ANG MM ASs-/. 2.) cws se cies fee's e ce dts heceses aac = 540
Dy aelard <sneds, on the upper: Carponiterous j2)-0) ac J. 2 jt = rs io SS Sele ese 300
BH. Very hard; Carboniferous limestone .....-....-..-.-- Skane bow oe Seeder 350
F. Soft; beds of the lower Carboniferous and Potsdam ..........-.....--..--- 290

Here are three zones of soft rock separated by and alternating with
two zones of hard rock. From the summit of the uplift all these rocks
have been removed by erosion. About its flanks each of them outcrops in
aring. The degradation of the dome has been rudely equivalent to the
paring of a slice from its summit, so that the successive envelopes of rock
are laid bare in concentric rings, just as the leaves of an onion bulb are laid
bare when a slice is cut from the side. Here, however, the resemblance
ceases, for the resistance to atmospheric degradation is greater with hard
beds than with soft, and they have not been carried away so rapidly. The
result is that the outcrops of the zones of hard rock have a relatively great
altitude and constitute ridges, while the outcrops of the soft zones are rela-
tively depressed. Taking them in order from circumference to center, we
have the upper soft zone (A) composing the plain from which the Hills
rise; then the first hard zone (B) represented by the ridge of foothills ; then
the second soft zone (C) marked by the Red Valley; then the second hard
zone (DE) constituting the Carboniferous ridge on one side and the Car-
boniferous plateau on the other ; and finally the third soft zone (I) marked
by the central area.

Within the circle of the Potsdam there is exposed an entirely distinct.
series of rocks with a structure of its own, which has no apparent relation

212 GEOLOGY OF THE BLACK HILLS.

to the post-Cretaceous displacement. Here too the contrast of hard and
soft has determined the main features of the topography. The strata have
a nearly vertical position and trend obliquely across the area of their
exposure. Their hard members are quartzites; their soft, slates and schists.
The former stand in ridges; the latter underlie valleys.

Within the newer series of rocks there are masses of trachyte, exotic
bosses, forming no part of the sedimentary series; within the older series
are unstratified masses of granite, lenticular in form and exotic in origin.
The trachyte is harder than any of the sedimentary rocks; the granite
rivals the quartzite in durability. Wherever these intrusive bodies have
been laid bare in the progress of the degradation they form eminences;
peaks in the case of the trachyte, ridges in the case of the granite.

In this manner the main topographic features of the Hills have been
made to give expression to the main faets of the geological structure. The
‘eminences point out the hard rocks; the valleys the soft. The arrangement
of hill and valley betrays to the geologist the character of the displace-
ments and the position of igneous masses. When, however, we leave the
consideration of the main features and descend to details, we find that the
arrangement of the lines of drainage has had much to do with the determi-
nation of the surface features.

The drains as arule cross the strike of outcropping strata at great
angles, often at right angles, and wherever a ridge dependent upon the rock
structure is intersected by a line of drainage it is cleft to its base. The
Carboniferous ridge which curves about the eastern side of the Hills is
jnterrupted in a distance of ninety miles by no less than fifteen creeks.
The Dakota ridge in making the circle of the Hills is crossed by twenty-
seven waterways. At every such intersection the absolute continuity of
the ridge is broken, but the interruption is so brief that the imagination fills
the hiatus without effort, and the structural continuity of the ridge is not
called in question. Indeed, if one who stands at the side of a ridge looks
obliquely down its course he finds it a matter of difficulty to discover the
points where it is divided. So, too, in the Archean district; the streams
intersect the quartzite ridges at high angles and divide them by narrow
canons, interrupting their continuity but not otherwise impairing their ridge

STRUCTURE SHOWN BY TOPOGRAPHY. PONS

character. If the drainage system of the Hills were different the forms
of the surface would be different, but they would still give expression to
the character of the rocks and to the displacements.

On the whole, the drainage system is well adapted to the display of
the intimate relation of rock structure and topography. A great number
of small streams radiate from the Carboniferous plateau, and flow independ-
ently, without combinations among themselves, until they pass beyond
the foothills. These streams are received by the forks of the Cheyenne
which embrace the district of the Hills. As a consequence, the facilities
for the transportation of débris are approximately equal in all directions,
and the rate of degradation by erosion is conditioned almost solely by the
constitution of the rocks. The inequalities of surface therefore—the results
of differential degradation—give a symmetrical and faithful representation
to the rock structure.

In the northwestern extension of the Hills the case is somewhat differ-
ent The low prolongation of the uplift is crossed at right angles by the
north fork of the Cheyenne. A series of outcrops is produced each of
which circles about and returns to itself. On a map this arrangement
might appear very similar to that of the outcrops about the main uplift,
but it is essentially very different, and it depends no more upon the rock
structure than it does upon the disposition of the drainage. The displace-
ment at this point is essentially an anticlinal, and the river in traversing it
first descends stratigraphically, crossing successively lower and lower beds,
and then, having passed the axis, crosses the same beds again in inverse
order. The outcrop of each stratum runs to the right and left from the
point where it is first crossed, rising as it goes and curving in its course until
it becomes parallel to the river on each side of the valley. Then after pass-
ing the axis of uplift the two lines curve again toward the river, and
descending as they approach, finally meet under the water, having com-
pleted the circuit. The river has cut down through the upper soft zone,
the upper or Dakota hard zone, and the greater part of the middle soft zone.
The rocks of the latter alone exhibit complete circuits. The Dakota sand-
stone nearly completes its circuit, but the circle of this outcrop at one point,

214 GEOLOGY OF THE BLACK HILLS.

touches the circle of its outcrop about the main body of the Hills, and each
is broken for a short space at the contact.

3.—THE AGE OF THE HILLS.

The age of the Hills is the age of the uplift.) There is some reason to
suspect, as we have said in another place, that the locality was marked by
an elevation or ridge before the Potsdam sandstone was deposited, but the
present existence of the Hills as an upland district depends upon and dates
from the disturbances which took place after the accumulation of the entire
series of conforming strata. From the base of the Potsdam to the top of
the Cretaceous all of the strata are parallel and conformable, and above the
Potsdam they comprise none of those fragmental deposits which mark the
neighborhood of mountains undergoing erosion. All of the strata are
upbent together in the flanks of the great arch. If the arch had been
formed during the accumulation of the series the beds deposited after the
formation would not conform to the dip of the others, but would either
abut against them or else overlap their worn edges. We are assured there-
fore that the movement did not begin before the end of the period repre-
sented by the Cretaceous strata.

The next formation succeeding the Cretaceous in the region of the
Hills is the Fort Union group, but our single observation of the group
afforded no means of judging whether it shared the movements of the older
beds. Following it in order of time is the White River group, and of this
our knowledge is more satisfactory. The conglomerate which was found
at its base on the east side of the Hills, and only fifteen miles distant from
the foothills, proves by the size of its pebbles that a mountain was under-
going degradation close at hand during its formation, and leaves no doubt
that the Black Hills were then in existence. The discovery by Mr. Jenney
of débris from the granite, mingled with the predominant quartz and
quartzite of the conglomerate, shows further that the degradation of the
uplifted mountain had progressed so far that at some point a water-course
had pierced all the sedimentary beds and laid bare one of the granite masses.
The time consumed by this erosion could not have been inconsiderable and
it preceded the earlier deposits of the White River Miocene lake. The

Fig. 27.—Diagram to exhibit the relation of the Drainage System of the Black Hills to the Zones of
z Hard and Soft Strata.

The central dotted space shows the Archean area of soft rocks. The annular dotted zone shows the
outcrop of the soft Red Beds and Jura. The intervening white zone shows the outcrop of the hard
Carboniferous beds. #

THE CREEKS CATACLINAL. 215

inception of the uplift must therefore have been early in Tertiary time, and
the same evidence shows that by the middle of the Tertiary it was in great
part, if not entirely, completed. For unless the uplift had approached some-
where near its present dimensions the granite would not have stood suffi-
ciently high above the level of the Tertiary conglomerate to render the
transportation of its pebbles practicable.

The evidence derived from the stratigraphy shows, then, that the upris-
ing of the Hills took place either wholly or in chief part during the interval
of time between the completion of the Cretaceous formation and the begin-
ning of the Miocene Tertiary.

Further light upon the history of the displacement is thrown by the
drainage system. An attentive study of the arrangement of the streams shows
that in their relations to the rock structure they fall into two classes. The
first class includes all the creeks which drain the central area of the Hills.
The second includes the two rivers, branches of the Cheyenne, which flow
past the Hills and receive the waters of the creeks. | With slight exception
the creeks flow in the direction of the dip of the strata, or, if we use the classi-
fication of Powell, are “‘cataclinal.”’ Rising for the most part near the center
of the uplift, they run outward in all directions, just as the rocks dip out-
ward in all directions. If the dome of strata were formed under a lake or
sea and then laid bare by the recession of the water, it would be natural
that the drainage system created by the rain upon the rounded surface
should show a descent everywhere in the direction of the dip. If the top
of the uplift appeared above the water before the uprising was completed,
the result would be the same, and it would not be far different if the scene
of the uplift was a plain instead of a sea bed, provided the uprising was
not of exceeding slowness. In either case the arrangement of the drain-
age is a distinct consequence of the uprising and would be classed as “‘con-
sequent.” It is difficult to conceive of any system of drainage except a
consequent system, in which all the streams are cataclinal, and it is there-
fore extremely probable that the creeks of the Hills acquired their positions
and directions either during the formation of the uplift or else when it was
laid bare by a retiring lake. In either case the drainage system is conse-
quent upon the uplift.

216 GEOLOGY OF THE BLACK HILLS.

The relation of the rivers to the rock structure is entirely different.
The Belle Fourche, or North Fork, approaches the uplift from the west, and,
with a northeasterly course, runs directly across it—not at its highest point,
but ata place where the height of the arch is more than 2,000 feet (see
Figure 26). In like manner the South Fork crosses the southern spur of
the uplift, and in its meandering passes in and out of the flank of the arch
in amanner that seems entirely independent of the dip of rocks. If the
reader will turn to the bird’s-eye view, he will see that the South Fork,
which flows from left to right across the foreground, first crosses the series
of hog-backs in a direction opposed to their dip, and then on the opposite
side crosses the hog-backs somewhat in the direction of their dip. In its
middle course it traverses the arching plateau of the Dakota sandstone,
cutting a gorge several hundred feet in depth and passing out on the oppo-
site side; and then, after having escaped completely from the obstruction, it
turns back, and in a loop several miles in length carves a second cation in
the same sandstone.

In their relation to the rock structure these water-ways are manifestly
inconsequent, that is to say, their directions were determined by conditions
entirely independent of the uplift of the rocks. In Powell’s classification
two kinds of inconsequent drainage are recognized, the one called “ante-
cedent,” and the other “superimposed.” Antecedent drainage is produced
when an uplift, occurring in a region the drainage system of which is
already established, progresses so slowly that the corrasion of the streams
keeps pace with it and their positions remain unchanged. Superimposed
drainage is produced when a system of streams which originally pertains
to one rock system is transferred vertically downward to a different and
unconforming rock system, the latter being brought to light by prolonged
denudation.

If the Belle Fourche and the South Fork are antecedent to the Black
Hills uplift, then the region must have been dry land when the uplift began,
and, if subsequently submerged, cannot have received enough sediment to
clog their channels. If, on the other hand, they are superimposed upon the
uplift, we may be equally confident that they acquired their courses on the
surface of a series of sediments laid down subsequent to the uplift and

THE RIVERS SUPERIMPOSED. ; Dalia

reposing unconformably on its flanks. Knowing as we do that the White
River Miocene was deposited after the completion or approximate comple-
ton of the uplift and that it lay against the flanks of the Hills (upon the
south at least), we cannot hesitate to decide that the rivers were superim- .
posed. If they existed before the formation of the Hills they were com-
pletely blotted out by the Tertiary lakes and their sediments, and the
assumption that they did so exist is entirely gratuitous. Whenever the
water of the lakes finally retired from the region of the Hills, the rivers
began to flow in what were then the lowest lines of the surface and there
they have flowed ever since.

The courses of the creeks were fred aud their work of erosion was
commenced when the uplift first exposed its summit to the rain. They
are precisely as old as the Hills, and they have been the agents of the
degradation of the uplift At first they may have descended directly to a
sea or lake, but when the White River conglomerate was formed their
lower courses were upon a plain which bordered a lake. Afterward the
lake rose and carried its shore to the flanks of the Hills, and some or all
of them discharge their water directly into the lake. When at last the lake
was withdrawn, the branches of the Cheyenne River came into existence
upon its bed, receiving the discharge of the creeks and completing the
present drainage system.

The coincidence of the directions of creek courses with the directions
of the dip must be understood to be only approximate. Hach creek in the
course of its history has sunk alternately through soft and hard strata, and
while in the soft strata it has deviated from its original place by the process
of meandering. Ina few cases streams of considerable size have so far
shifted their courses as to form unions with each other before escaping from
the foothills, but such instances are rare. There is, however, one general
exception to the rule of cataclinal drainage which deserves fuller mention.

When the displacement began its summit was necessarily a divide or
water-shed, from which the water flowed in all directions. In the absence
of any disturbing cause this water-shed would remain as steadfast as the
drainage lines all through the period of degradation. Knowing of no dis-
turbing cause, we may assume that the existing water-shed in the Hills holds

218 GEOLOGY OF THE BLACK HILLS.

the same position as the original water-shed, and marks, therefore, the posi-
tion of the summit of the uplift at the time of its inception. An inspection
of the geological map, or of Figure 27, shows that the main water-shed has
a north and south trend and runs near the eastern edge of the Carboniferous
plateau. The summit of the uplift, as shown by the contours of Figure 26,
corresponds very nearly with the central part of the Archean area. Its
trend is parallel with that of the watershed, but it lies fifteen or twenty miles
farther east. Thus it would appear that the portion of the uplift which
took the lead at the start was afterward overtaken and exceeded by another
portion, so that the present summit or axis of upheaval is not the original
axis of upheaval. They both fall within the tabular top of the main uplift,
and the present difference between them is only a few hundred feet.

Notwithstanding the eccentricity of the main water-shed, the creeks of
the Hills afford a rare example of consequent drainage. It does not often
happen upon the slopes of the most symmetrical uplifts that so large a
number of water-ways assume and adhere to centrifugal and independent
courses. So perfect a drainage system could hardly have been established
except under the most favorable circumstances, and this seems to preclude
the idea that the uprising began upon a land surface. If it took place in a
region subject to subaerial conditions, there must have been a pre-existent
drainage system, and that system could not but have an influence upon the
new system inaugurated by the uplift. It seems more probable that the
movement began under water, imparting its curves to a surface smoothed
by the spreading of sediments, so that when it was subjected to meteoro-
logic influences its surface was an exact representation of the displacement
and guided the new drainage in perfect accordance with the dip of the
rocks.

The evidence derived from the drainage system appears to show then,
first, that the Hills began to rise before the desiccation which eventually
succeeded the Cretaceous; second, that the form of the uplift was changed
during its progressive increase, the maximum line shifting from west to
east; and, third, that the flanks were so far buried by Miocene sediments
as to be given a new river system when the lake water was finally with-
drawn.

IGNEOUS EPOCH. 219

This last conclusion has an important bearing in another direction.
The general degradation of the Hills has made little progress since the
time of the Miocene conglomerate. Some drainage line or lines had then
cut so deeply as to touch the granite, and at the present time the bottom of
the deepest valley in the same vicinity is only 2,000 feet lower. Two
thousand feet would be an incredibly small amount of erosion in a mount-
ain district for the indicated interval of time if the conditions of erosion
had always remained as they are now. But the difficulty lessens when it
is known that the erosion was retarded first by a long lake period, during
which the water-ways of the Hills were in part clogged by their own débris,
and second by a long period of slow general degradation, during which the
accumulated lake sediments were little by little casried away and the
‘base level of erosion” was slowly depressed.

4.—THE AGE OF THE IGNEOUS ROCKS.

The igneous masses have so much in common, both in the character of
their material and in their relation to the stratified rocks, that they are
assumed to have a common epoch of formation, and whatever is determined
with reference to one is by analogy ascribed to the whole. Unfortunately
our evidence is not at all precise, and serves only to indicate certain widely
separated time limits, between which the bosses of trachyte and rhyolite
were formed.

In nearly every locality of igneous rock the adjacent sedimentary
rocks were found to have undergone some modification either of character
or of position. Wherever a clay or sandstone was seen in contact with the
intrusive mass it was found to have been more or less metamorphosed by the
original heat ; and about many of the peaks the strata are upturned at con-
siderable angles in such way as to leave no question that their flexure is a
phenomenon of the volcanic event. In all such cases it is evident that the
modified strata are older than the associated intrusives. In different places
all members of the sedimentary series from Potsdam to Dakota were
found upturned around igneous centers, and at a single locality, Bear
Butte, the same influence was found to extend to the Fort Benton group,
No. 2 of the Cretaceous. The higher members of the Cretaceous and the

220 GEOLOGY OF THE BLACK HILLS.

strata of the Tertiary nowhere lie in such proximity to the igneous peaks
that their structural relations could be made out. All, therefore, that we
can learn from the relation of the exotic masses to the strata is that the
epoch of their introduction was later than the Fort Benton Cretaceous.

The opposite limit is shown by the contents of the Miocene conglom-
erate. At the base of the White River deposit Mr. Jenney found not only
granite and quartzite from the Archzean, but pebbles of trachyte, and these
could only have been derived from the Black Hills bosses. The lavas were,
therefore, introduced, solidified, and at some point subjected to erosion
before the beginning of the Miocene.

The indicated interval comprises the Niobrara, Fort Pierre, Fox Hills,
Judith River, and Fort Union epochs; a period of time represented by a
total depth in the upper Missouri region of about 4,000 feet of sediments.
The date of igneous activity is, therefore, very far from established, and
its relation to the uplift of the Hills is not even determined. The trachytes
may have been in place, and even ancient, when the uprising began, or
they may have been forced up while the greater movement was in progress
and well advanced.

A study of the drainage here affords no aid. A rising current of mol-
ten rock cannot flow with secular slowness through colder rocks on account
of the interchange of temperatures and resulting congelation; and for this
reason an uplift of strata by voleanic force is of necessity catastrophic. In
all ordinary cases antecedent drainage is thrown back and turned aside, and
a local system consequent to the new mountain takes its place. The drain-
age of the igneous uplifts of the Hills is essentially, though imperfectly,
consequent, but no conclusion can be drawn from the absence of an ante-
cedent system.

5.—SUMMARY OF THE HISTORY OF THE HILLS.

Putting together the salient events recorded by the character and
arrangement of the rocks, as well as by the arrangement of the drainage
lines, we have the following history :

The older Archean was first laid down. It consisted in chief part of
shales and with these were some sandstones. Over it, and probably after

SUMMARY OF THE HISTORY. | 221

an interval during which some erosion and metamorphism took place, the
newer Archzean was deposited. Its constitution was about the same, but
it was characterized by a greater amount of sandstone. At about the same
time a large quantity of igneous rock was introduced between layers of the
older Archzean, and there solidified, taking the form of granite. The record
is then blank for a period of great duration, and it is only known that at
some time during that period the Archzean strata were altered to the condi-
tion of crystalline schists and quartzite, and were subjected to a vast dis-
placement and erosion, whereby their worn edges were left in a vertical
position over the whole area of their present exposure. In this interval
there may have been many alternating epochs of sedimentation and erosion.
We only know that the closing epoch was one of erosion, and that the local-
ity of the Hills was part of a large tract of dry land.

The next chapter is one of sedimentation. The ocean advanced slowly |
over the sloping land, sorting and rearranging with its waves and currents
the débris that lay upon its surface, and forming the Potsdam conglomerates
and sandstones. For atime a ridge of the Archean seems to have formed
an island in the Potsdam ocean, where the Hills now stand, but it was
eventually overwhelmed and covered by the shifting sand. After this first
advance the waters seemed to have retired for a while, for the Black Hills
show no trace of great formations that were accumulated elsewhere ; but
there was no local displacement and no deep-cutting erosion, and the sedi-
ment of the returning ocean was spread in apparent conformity over that
which marks the Potsdam invasion. The new flood was deeper than the
old, and it deposited at first only limestones, but after a time it became
shallower, and in the latter part of the Carboniferous period many beds of
sand were interpolated among the calcareous deposits.

Up to this time the ocean was full of life, but now the conditions were
changed in some way, and life seems to have been banished. Perhaps
there was a glacial epoch, and all forms that could not migrate perished ;
or perhaps the local waters were by some revolution cut off from the gen-
eral ocean, and, like the Dead Sea, became saturated with a poisonous min-
eral. When life at last returned the sea was so shallow that the (Jurassic)
deposits were ripple-marked, but there was no exposure of land surface.

DOD, GEOLOGY OF THE BLACK HILLS.

Salt water seems to have covered the surface continually to the close of the
Mesozoic, and it was probably succeeded without interval by the fresh water
of a Tertiary lake.

Before the water retired the uprising of the Hills began, and as soon
as the arch of strata appeared above the surface an erosion commenced
which has not yet ceased. Afterward a second Tertiary lake laved the
flanks of the uplift, half buried its foot with sediments, and then disap-
peared. Upon its dry bed the courses of the modern rivers were traced.
The streams that had been transporting detritus from the Hills and casting it
into the lake now found their way to the rivers and transferred their bur-
dens to them. Little by little, but continuously, they have eaten away the
substance of the Hills ever since. The cations they have cut, and which
appeal to our eyes as marvelous monuments of their industry, are the
least of their results. Since their labor began they have demolished and
removed one half of the entire mass of the uplift. Modest and feeble as
they seem, it is their ambition patiently to toil on until no vestige of the
Hills remains.

U. 8. GEOGRAPHICAL AND GEOLOGICAL SURVEY OF THE ROCKY MOUNTAIN REGION.
J. W. POWELL, IN CHARGE.

MINHRAL RESOURCES

OF THE

BLACK HILLS OF DAKOTA.

By WALTER P. JENNEY, E. M.

223

CHAPTER IV.

MINERAL RESOURCES.
By WALTER P. JENNEY.
SECTION I.
ENERO UCL iE OUNe.

The Black Hills are pre-eminently a gold-producing region; the meta-
morphic rocks constituting the gold-field cover an area of nine hundred
square miles, extending north and south through the central portions of
the Hills for a distance of seventy miles, with a breadth of from five to
twenty five miles.

Gold occurs in the following formations:

I. In veins of quartz more or less ferruginous traversing the Archean
schists and slates.

Il. In strata of slate mineralized and altered by the action of waters
depositing silica and iron pyrites.

III. In the conglomerate forming the lower layer of the Potsdam
sandstone, resulting in this case from the denudation of the ledges in the
Archeean rocks.

IV. In trachyte and porphyry intruded at the time ot the elevation of
the Hills in the interval between the Cretaceous and Tertiary periods.

V. In deposits in the slates and sedimentary rocks produced by the
intrusion of the trachyte and porphyry.

VI. In placer gravels resulting from the decomposition and erosion of

the above formations in Tertiary and recent time.

225
15 BH

226 GEOLOGY OF THE BLACK HILLS.

The miners, for convenience in making laws to govern the recording
and locating of claims, have divided the gold-field into different districts,
which division I shall follow as closely as possible in considering the value
and character of the gold deposits.

SECTION II.
THE FRENCH CREEK DISTRICT.

In the French Creek district is embraced all the area of granitic and
schistose rocks surrounding Harney Peak and forming the southern portion
of the Hills, bounded by Spring Creek on the north, and including the
placer gravels in the valleys of Wiwi Creek, Custer Gulch or French
Creek, Amphibious, Minnekata, and Red Cafion Creeks, streams draining
this region and emptying into the south fork of the Cheyenne.

Before discussing the value and extent of the gold deposits it is nec-
essary to describe briefly the topography and geological formation of this
district, which presents, in the immense development of granitic rocks, a
feature peculiar solely to this section of the Black Hills.

The Harney Peak range, and the country included between it and
the foothills on the eastern slope, is an exceedingly rugged and mountain-
ous region, heavily wooded with pine and cut into innumerable deep
ravines by a net-work of smali streams flowing in a general southeasterly
direction, but sinking before they reach the plains. These small creeks are
full of beaver dams, and the bottoms of the gorges are overgrown with a
perfect jungle of oak, elm, birch, elder, and grape-vines, making it almost
impossible to descend the valley of the stream, and compelling the explorer
in this wilderness to travel across the steep and broken rocky ridges, where,
except he be fortunate enough to climb some of the few commanding peaks,
he cannot see but a short distance in any direction, owing to the densely-
wooded and broken character of the region. It is useless to look for any
main divide which can be followed in traversing this mountainous section;
the whole area is broken into innumerable granite peaks and ridges without
any apparent system whatever, except that the drainage is in a general
southeasterly direction toward the open plains. The effects of erosion are

FRENCH CREEK DISTRICT. 227

everywhere strongly marked, and the peculiar topography of the region is
due to the resistance of the hard granite and the yielding of the micaceous
schists to the action of time and water.

The prominence of the granite, which in huge, serrated ridges rises on
every side, is due more to erosion than to any elevation caused by its
intrusion; yet the granite, though so unyielding, shows by the rounded
and pinnacled forms assumed by the peaks that time has affected it as well,
but in a less degree.

To the northeast of Harney Peak is an area of slates, which properly
belongs to the Spring Creek district, but with that exception this section is
almost universally granitic; the schists, wherever they occur, being con-
cealed by the débris resulting from the denudation of the granite ridges
that tower far above the surface of the softer rocks.

Harney Peak, having an altitude of 7,403 feet above the sea, is the -
culminating point of this great intrusion of granite, and forms the most
conspicuous landmark in the Black Hills, visible from the plains to the
south and east for a distance of more than fifty miles from the foothills.

The park region, at the west and southwest of Harney Peak, is a
most agreeable contrast to the inaccesssible wilderness to the east. Broad
glades of level grass land extend between the parallel ridges of granite
and groves of pine cover the rocky hills wherever there is sufficient soil to
support their growth. Isolated peaks of granite, rounded by erosion and
weathering into dome-shaped and castellated forms, rise from the open and
level surface, which everywhere is carpeted with the finest grass, giving a
beautifully picturesque and park-like scenery to the region.

The smooth surface of the parks and the peculiarities in the topog-
raphy are due to the parallel ridges of granite resisting the denudation,
which has excavated the broad swales in the intervening softer schists, and
indicates that the original surface of the formation was far above the present
level.

The granite is comformable to the stratification of the inclosing schistose
rocks, having been intruded between the layers; the only direction in
which the micaceous rocks are readily fractured. This conformability
is not perfect, as it would be were the granite the result of metamorphic

228 GEOLOGY OF THE BLACK HILIS.

action on a layer of the schists, but the eranite ridges often occur travers-
ing the park as a broken range of lenticular peaks on the same line of
fracture, resembling, on an enormously-magnified scale, a well-known
form of segregated quartz-veins. Narrow dikes of granite traverse the
schists, often not more than 2 or 3 feet in width and of regular thick-
ness, continuing uniformly for several hundred yards parallel to the stratifi-
cation, and being harder than the schists, have been left by erosion stand-
ing like walls several feet above the surface of the ground. Where the
surface of contact of the granite and the schists is exposed, the sides of the
dike are seen to be smooth surfaces, often beautifully marked with slicken-
sides exceeding in the polished and striated markings any specimens of the
walls of mineral veins which have ever come under my notice.

The sides of the lenticular masses of granite forming the low ridges
show slickensides and vertical striated surfaces, but not nearly in so marked
a degree as the narrow dikes.

The granite is very coarsely crystalline, largely composed of white or
flesh-colored feldspar, intermixed with quartz and mica (muscovite), with
black tourmaline in large hexagonal crystals as an associated mineral.
Quartz occurs disseminated through the mass of the feldspar in. small grains
and in nodules between the crystals. Segregated veins and irregular
masses of quartz occur in the granite ridges, generally white, vitreous, or
translucent, frequently of a beautiful deep rose-color, but everywhere appar-
ently free from any traces of valuable minerals or any considerable quan-
tity of gold.

The schistose rocks are in great variety, mica-schist being the prevail-
ing form, often garnetiferous, and merging into talcose, chlorite, and quartz
schists.

The minerals found in the schists are few in number. Small garnet-
crystals are very abundant; a few specimens of hornblende, epidote, and
staurotide were seen, but they occur but rarely in these rocks. Veins and
ledges of ferruginous quartz are found traversing the schists between the
granite ridges or dikes to which they are parallel. These ledges are not
true fissure-veins ; that is, they do not intersect the strata at an angle to the
stratification, neither are they segregated veins, but occur filling continuous

THE GRANITE BXOTIC. 229

and regular fissures between the lamellw of the schists formed in the fold-
ing of the rocks, and are in fact interlaminated fissure veins.

The quartz is often mixed with a large proportion of brown and yellow
oxides of iron, resulting probably from the decomposition of pyrites, and
the gold now found in the gravel-deposits along the streams has been
derived from the disintegration and denudation of these ledges in the schists.

But little prospecting could be done in the numerous quartz-veins of
this district for want of time and proper tools. The miners reported gold
in small quantities from several veins which they discovered and opened.

Near the stockade on French Creek.a mass of schist was noticed, about
150 feet in length, upturned on edge and completely inclosed by a broad
rim of granite. This fragment of schist was traversed by a ledge of quartz
and limonite several feet in width, conformable to the stratification, and cut
off at each end by the subsequent intrusion of the granite. From the uni-
formity in the composition and appearance of the granite from all parts of |
the Harney Peak range, the dike character of the ridges, the presence of
slickensides, and the observed instances of inclosed fragments of schists, I
can but regard the granite of this region as injected. ‘There are occurrences
of small, narrow veins of feldspar leading from the granite into the schist,
probably deposited by chemical solutions accompanying the intrusion,
which would seem to indicate that the fluidity of the injected granite was
due more to the presence of water than to the intensity of the heat.

French Creek rises in the level park country southwest of Harney
Peak, among granite, gneiss, and schistose rocks, and flows in a general
easterly and southeasterly course about fifteen miles, until, entering a deep
cation in the limestone formation, it sinks among the bowlders in the bed
of the channel and disappears before reaching the foothills, continuing as
a dry arroyo, with water-holes at intervals, to the Cheyenne. Near its
head it is a sluggish stream with long stretches of slack water; in midsum-
mer, notwithstanding frequent showers of rain, drying up to a chain of
water-holes. A few miles below the stockade it is swelled by springs and
side branches to a creek 10 to 15 feet in width and about 8 to 12 inches
deep, flowing with a moderately-rapid current until it is lost in the canon.

Gold was discovered in gravel bars on French Creek early in August,

230 GEOLOGY OF THE BLACK HILLS.

1874, by Ross and McKay, miners accompanying the expedition under
command of General G. A. Custer, but from want of time they were unable
to ascertain definitely whether the gold existed in paying quantities, although
obtaining by a few days’ work quite encouraging prospects.

About three weeks later this field was visited by the Rey. S. D. Hin-
man, with an escort from the agencies on White River, in search of a suit-
able location for a reservation, but not finding any evidences of gold, on
their return they threw some discredit on the reports of the existence of the
precious metal in the Black Hills.

A party of twenty-five miners from Sioux City reached French Creek
December 23, 1874, and built a stockade and cabins near the location of
General Custer’s camp. They passed the winter prospecting very indus-
triously for gold in the vicinity, opening several quartz ledges in the schist-
ose rocks of the park and sinking pits on the flats and gravel bars along
the stream.

Before cold weather was over and the frost out of the ground, so that
the diggings could be opened on a scale large enough to practically test the
richness and extent of the gravel deposits, these miners were removed by
the military to Fort Laramie. |

When I reached French Creek, June 16, 1875, about fifteen miners
were found camped four miles above the stockade, where they had been at
work for several weeks, and had staked off claims, built small dams, and were
digging ditches preparatory to commencing sluicing on the bars along the
banks of the stream. These miners were very enthusiastic in regard to the
mineral wealth of the gulch; they were reporting from 5 to 27 cents to the
pan from the pay gravel, and made the most extravagant statements as to
the yield which would be obtained as soon as they commenced working
with sluices. But they were working under unfavorable circumstances;
the water-supply was very small, not exceeding 50 miner’s inches, with every
indication that it would soon fail entirely, and the grade of the valley was so
small that it was difficult to get a good head of water for sluicing. On
testing, by washing, the pay gravel from the different prospecting holes
already opened, with a pan, and weighing the gold obtained, it was found
that the usual yield along the stream was from four to eight colors to the
pan (about one-tenth to one-fifth of a cent), and, in favorable and some-

PROSPECTING ON FRENCH CREEK. , 231

what limited localities, from half a cent to as high as one and a half cents
were obtained from the gravel from off bed-rock. The gravel bars were
vich enough in gold to pay if extensively worked under more favorable
circumstances, but too poor to yield a remunerative return for the labor
employed, except in a few limited deposits of gravel near the extreme head
of the stream.

The next day the following dispatch, embodying all the information in
regard to the gold-field that had been obtained to date, was sent by courier
to Fort Laramie and telegraphed to Washington :

CAMP ON FRENCH CREEK, NEAR HARNEY PEAK,

June 17, 1875.
To Hon. E. P. Smiru,

Commissioner of Indian Affairs, Washington, D. C.:

I have discovered gold in small quantities on the north bend of Castle Creek, in
terraces or bars of quartz gravel.

Arrived here yesterday. About fifteen miners have located claims on the creek
above here, and have commenced working. Gold is found from Castle Creek south-
wardly to French Creek at this point; the deposits are almost wholly in Dakota. The
region has not been fully explored, but the yield of gold thus far has been quite small
and the reports from the richness of the gravel bars are greatly exaggerated.

On French Creek the deposits of gravel are very unfavorably situated. The
water-supply is small and failing, and the grade too little to admit of the tailings being
earricd off by the stream.

The prospect at present is not such as to warrant extended operations in mining.

WALTER P. JENNEY, E. M.,
Geologist Exploration of the Black Hills.

The fact of the existence of gold caused considerable excitement among
the soldiers and teamsters of the escort, and quite a number were busily
engaged in prospecting along the creek, sinking holes to the bed-rock
wherever there was the slightest indication of a deposit of gravel, or clean-
ing out old prospecting shafts dug by the miners the preceding winter, and
panning the pay gravel, which had been reported to be so rich in gold. But
the results of their labor were so discouraging—generally only a few small
“colors” would be obtained from a pan of gravel, and rarely more than
three-quarters of a cent to the pan in the richest layer of pay dirt from off
bed-rock—that after a few days they abandoned the search for the pre-
cious metal and did not resume it for more than two weeks, until the dis-

covery of a very encouraging prospect on a bar near the stockade caused

Dan GEOLOGY OF THE BLACK HILLS. -

a renewal of the excitement for a time, an account of which will be given
farther on.

In examining the gravel deposits along the valley of French Creek
advantage was taken of the numerous prospecting shafts already sunk by
the miners, and in the few places remaining untried which gave any indi-
cation on the surface of the existence of valuable underlying gravel beds,
shafts were sunk to bed-rock by the miners assisting me in the work.
The first tests were made by washing several pans of the pay gravel in the
usual manner, and if the result obtained was at all encouraging the deposit
was more extensively tested by washing a measured quantity of the pay dirt
in a rocker and weighing the gold obtained. Finding that the best prospects
in the gulch were from gravel from a prospecting shaft on a dry branch of
French Creek about five miles above the stockade, the following test was
made to determine as accurately as possible the richness of the deposit :

The shaft was first cleaned out and a sufficient quantity of the pay
gravel drifted out from off bed-rock, carefully averaged, measured, and
washed with the greatest care in a rocker, every precaution being taken
to prevent any appreciable loss of fine gold carried over the riffles by the
muddy water. The result was as follows: 9 buckets gravel = 3.12 cubic
feet, gave 0.370 gram of gold in small flat scales and grains; 0.370 gram
= 5.7 grains troy = $0.23, or about one and one-fourth cents to the pan.

This would indicate a yield of $1.87 per cubic yard of the pay gravel
which formed a layer on bed-rock about a foot in thickness.

In the above calculation an average bucket of gravel is taken at 600
cubic inches, or 75 buckets equal one cubic yard. A pan is about half a
bucket, giving 150 pans of dirt to a cubic yard. Ihave estimated the value
of the gold to be $19.40 per ounce in gold coin.

The gravel froma shaft some distance below on the stream, tested in
a similar manner, gave the following result: 10 buckets dirt = 3.42 cubic
feet, yielded 0.020 gram gold; 0.020 gram = 0.3 grains troy = 0.012 cent,
or 9 cents per cubic yard, equal to one-twentieth of a cent to the pan. This
latter gravel was very poor in gold, but that washed in the preceding test
was correspondingly richer than the average of the gravel opened at that
time along the creek. Near the stockade the result of the prospecting

PROSPECTING ON FRENCH CREEK. | 233

showed that the richest gravel was from a hole sunk to bed-rock on the
bank of the creek, four pans of the pay dirt giving ? grain troy = 3 cents
gold, or # of a cent to the pan. Washing twelve buckets of this gravel in
a rocker yielded 44 grains troy of gold =17 cents, or $1.12 per cubic
yard;, nearly the same result as was obtained with the pan.

Most of the prospecting holes had been sunk early in spring, when the
ground was full of water and the locations selected with regard to the rim-
rock, so that the bed-rock might be reached before the depth of the shaft
became so great that it would be flooded with surface water. In order to
test the deeper channels in the flats near the stockade, a place was selected
where the configuration of the surface of the ground indicated an old chan-
nel filled with gravel to the present surface of the bar.

A shaft 5 feet by 7 feet was sunk to bed-rock, which was reached at a
depth of 15 feet, passing through gravel filled with large water-worn bowl-
ders 2 to 3 feet in diameter. Four men were constantly employed for three
days in sinking this shaft; the bowlders had to be broken with sledges and
hoisted out with a windlass, and the water was so troublesome as to require
constant bailing to keep the shaft dry. The bed-rock was found to be
granite. On cleaning up the whole surface the size of the bottom of the
shaft and panning the gravel not a color of gold was obtained, a result
which was unlooked-for by the miners, the gravel passed through having
been quite ‘promising in appearance.

Having forwarded to Washington a written report embodying the
results of the prospecting and exploration made up to date, (June 25), I
left French Creek, and, accompanied by my miners, made an excursion
north, for the purpose of examining the valleys of Spring and Rapid Creeks,
and on my return, July 8, I found that some new discoveries had been
made, and considerable work done by the miners in my absence.

A party of miners about five miles above the stockade had put in a
small sluice, and reported that they obtained by one day’s work 27 penny-
weights of gold, or nearly $27; three men being employed in shoveling
the gravel into the sluice. Unfortunately the work on this bar was stopped
by the stampede to the new discoveries in Spring and Castle Creeks before

234 GEOLOGY OF THE BLACK HILLS.

it could be thoroughly tested and the richness of the deposit proved to be
constant and regular.

John W. Allen, of Cheyenne, an experienced miner, and one of the
best prospectors I ever knew, in a letter to the Chicago Inter-Ocean, gives
the results of this sluicing, in which he assisted the owners of the bar:

CHEYENNE, WYOMING TERRITORY,
August 30, 1875.

To the Editor of the Inter-Ocean:

* * * * ES

I waited last spring for the country to be thrown open by this Indian treaty now
pending, and, becoming impatient, I concluded to do as hundreds of others did, to start
into the Hills, and on the 12th of July landed in Custer Park, and being an expe-
rienced miner, I had doubts in regard to French Creek paying, because of there being
no fall to the creek and scarcely any water. But I found one set of sluice-boxes about
to be set up, and I went to work and helped to fix them, and then worked one day and
weighed the dust, and found that the ground paid $9 per day to the hand of fine dust,

although I am sure this creek will not average that all the way through the gulch.

JOHN W. ALLEN.

John Roberson, an old California miner of the ‘days of 749,” had
discovered very good prospects on an elevated bar near the stockade,
and, building a dam, conveyed the water from the creek in a small ditch to
the face of the drift. In the mean time the soldiers had become quite
excited over the discovery, and were hard at work with pans and rockers
washing the pay dirt from off bed-rock. For several days they were quite
successful. From 16 to 26 colors were obtained to the pan One soldier
found a piece of gold valued at 20 cents; another a small nugget weighing
about a pennyweight, worth 97 cents, and 24 buckets of gravel gave on
washing an average of 12 cents gold. On drifting in on the bar the pay
streak rose, and was found among the bowlders nearly 18 inches above the
bed-rock. The section of this gravel deposit was as follows:

Sollee Ss See ROR Coord RC dc eee eT RS cs i wae moe 1 foot.
Graveltamdsbowlders\e rye yee tele epee wc eaieloie = Naan Slcct Matas erates 4 feet.
Clayey compact gravel containing the gold...... Lp oy arate = ehaiet ay Pein ae oe eee 6 inches.
Decomposed bed-rock and bowlders......-.-.--- Se Oana on Sao 1 foot.

Micaceous schist forming bed-rock.

CHARACTER OF THE GOLD. 235

The sluices were soon in place, and this, bar most thoroughly tested,
under the direction of Mr. Roberson. The result of the first day’s work
of eight hours, four men being employed most of the time, was 2 penny-
weights 8 grains troy of coarse gold, valued at $2.30.

The second day not only the gravel was put through the sluice, but

the whole surface of the bed-rock exposed by both days’ work was most

carefully cleaned up and washed. The return, however, was but 1 penny-
weight 9 grains troy of gold, equal to $1.10.
The work of both days may be summed up:

dere tiple d aye aeSMl Ge sree eee ee A Ss teeter ays = ol afaie era) =a hae ciara ci wsaye! ea ieee $2 30
GRTHE HME ayes Be SU titres Meee ye taht ee Sharad oor eo alsin Se Ug minis ces apm 'ets Ss aleierale 1 10
TD GT UNTER AT ROSUI Ria See Ban OSA Ucine Baers Eis Snes pam a apa Le Sa 3 40

or a yield of 34 cents per day per man.

This result was a disappointment to every one, and seemed to indicate
that the richness of the gravel at first obtained was due to a concentration
of the gold on rim-rock, and that the cleaning of the bed-rock probably
yielded only a very small proportion of the gold, the greater quantity
being derived from the compact gravel.

The gold obtained was in coarse, flat scales, or small, spongy grains,
and was quite deceptive in its appearance, nearly all the miners guessing
the weight of the dust very much too high.

Gold was found in small quantities in gravel deposits along the numer-
ous creeks flowing east from Harney Peak, but the region is so inaccessi-
ble, and so many difficulties are encountered in attempting to prospect it,
that but little could be done by myself and assistants in that area, while
the rush to the discoveries on Spring and Castle Creeks carried all the
miners in the Hills far to the north, and left this region but partly pros-
pected. :

Some prospecting was done on Amphibious, Minnekata, and Red Cation
Creeks, small streams draining the southern portion of Custer Park. On
Amphibious, near its headwaters, a few colors of gold were obtained from
small gravel deposits, but the water-supply was so small, the stream being
dry at the time, that prospecting was very difficult. About five miles below
the head of this creek a number of dry ravines enter it from the east, cut-

236 GEOLOGY OF THE BLACK HILLS.

ting deep into the schists and slates. In these ravines float quartz was
found, showing, on breaking, visible particles of gold, but the quartz was
not traced to the ledge from which it had been originally derived.

Minnekata or “Hot Water” Creek, so named by the Indians from the
warmth of the water, which has a temperature of 74° Fahr., although rising
in large warm springs in the Carboniferous limestone, has a deep deposit of
quartz-gravel on its east bank, about two miles below its source. This
gravel is derived from the wash from the Hills, and is composed of bowlders
of rocks and quartz cemented by sand and lime to a loosely cohering con-
glomerate, forming a bluff on the bank of the stream. Similar deposits are
to be seen at intervals among the foothills at the edge of the plains all
along the eastern slope from this stream as far north as the Box Elder.

On Red Canon Creek several tests were made of the gravel deposits,
but nothing of value found ‘This stream is on the extreme western edge
of the gold-fields, and rises partly in the limestone, contains but little water,
and drains but a limited area of the schistose rocks.

The gravel deposits elevated above the present level of French Creek
showed often a local concentration of gold on the outer edge of the bed-
rock from the repeated washing away of the gravel by floods or heavy
rains, leaving the gold contained in it behind. Though giving a very
encouraging prospect at first, on driving an open cut a few yards into the
bar where the gravel was undisturbed, the richness of the pay dirt rapidly
decreased until it equaled the true average of the whole deposit, thus
showing that the result at first obtained was only a ‘“‘rim-rock prospect.”

The richest layer in the pay gravel was rarely on bed-rock, but usually
from 10 to 20 inches above it, forming the upper surface of the stratum of
compact clayey gravel mixed with fragments of decomposed bed-rock
which had caught and retained the greater portion of the gold.

The gravel-bars along French Creek, for several miles above and
below the stockade, were examined wherever there was the slighest indica-
tion or probability of gold existing in paying quantities with results similar
to those already given, and, as might be expected from the level character
of the valley, the gravel deposits were richest around its head branches,

she TD

GRAVEL OF THE PLACERS. Dot

and proved regularly poorer in gold as the distance below its source in-
creased.

Excepting Castle Creek no stream in the Hills was prospected the past
season to anything like the extent that the gravel deposits on French Creek
were subjected to. The whole bottom of the valley for nearly six miles
was full of prospecting pits. ach new party of miners on arriving in the
Hills first visited Custer Gulch, as it was called, and expended their surplus
energy and enthusiasm in sinking a number of prospecting holes before
proceeding elsewhere in search of gold. But the results obtained by these
miners were very poor, except in a few localities in dry sags and gulches
about the head of the creek and in a limited number of elevated bars
along the stream above the stockade.

The gold obtained from the placer gravels on French Creek was in
small flattened scales and grains, quite uniform in size, mixed with very.
little fine dust, and nearly free from magnetic-iron sand. It showed but
little action of water, and the garnet crystals associated with it were often
quite perfect and scarcely rounded by attrition. The greater portion of the
gold seems to be derived from the quartz ledges in the schistose rocks, and
not from the intruded granite; for in side gulches, where the rocks were
wholly composed of granite, I failed to detect any traces of gold.

The gravel of the placers is a mixture of water-worn quartz mingled
with a less proportion of bowlders from all the rocks at present found in
the region, including granite and fragments of the harder schists and slates.

The pay gravel is composed of the heaviest pebbles, with some clayey
sand and large quantities of red garnet crystals derived from the schists.
It is soft, rarely cemented to a conglomerate, and easily washed in a sluice.
The layers of the gravel are porous and not clayey enough to be impervious
to water, allowing it to pass freely through, and causing considerable incon-
venience in prospecting.

The exploration and prospecting on French Creek, both by the geo-
logical party and the miners, showed, up to the time I left the gulch, a
general diffusion of fine gold in the gravel beds, but little concentrated in
the deposits, and found in small quantities throughout the whole breadth of.
the valley.

238 GEOLOGY OF THE BLACK HILLS.

The water-supply at the head of French Creek was very small and
uncertain, totally inadequate for extensive working of the gulch, while the
flatness of the valley is also a serious obstacle to the successful working
of the gravel bars if water should be brought from Castle Creek for that
purpose; which cannot be done until the richer deposits on that creek are
exhausted.

Above the stockade there are localities where the gravel will pay fair
wages for sluicing, using the limited water-supply of the creek and work-
ing only the richest places in the beds. I regard the poverty of the French
Creek deposits, compared with those afterward discovered on the streams
farther north, to be due to a deficiency in the source of supply, owing to
the small area drained by the stream, the small amount of denudation to
which the ledges in this area have been subjected, and to a want of suffi-
cient grade in the valley to cause a concentration of the gold into a pay
channel.

Had all the gold diffused through the valley of French Creek been
concentrated into a narrow lead or pay channel, it would have made claims
as rich as the most enthusiastic miner would have desired.

SECTION III.

SPRING CREEK DISTRICL:

Spring Creek rises among the parks in the central portion of the Hills
to the west and northwest of Harney Peak, and is formed by the union
of a number of small brooks, some heading in the limestone at the western
edge of the Beaver Creek Plateau, others in the granite of the Harney Peak
range, or with numerous ramifying branches drain the schistose rocks of
the parks.

Just below where the main branch, flowing from the south, rising
among the granite and metamorphic schists of the parks, unites with New-
ton’s Fork, coming from the taleose and quartz schists in the direction of
Castle Creek, a remarkable change is seen in the topography of the region
and the character of the rocks; and Spring Creek, becoming a fine and
rapid stream, heads eastward into a new geological formation—the second

SPRING CREEK DISTRICT. 239

division of the Archeean strata of the Black Hills. We have left to the
south and west a region of feldspathic granite, mica schist, taleose and
quartz schists, with crystalline or rose quartz, mica, garnets, and feldspar
as the characteristic minerals, and enter a parallel belt of massive gray
quartzites, argillaceous and siliceous slates, in which the prevailing minerals
of the schists are no longer seen.

The change in the character of the rocks produces a corresponding
change in the topography of the region; the soft mica-schists had been
worn by erosion into broad parks and valleys, intervening with rounded
peaks and ridges of the harder strata, but the massive quartzites and hard
siliceous slates, resisting denudation, have been left in steep and high rocky
hills, through which the stream, winding and twisting among the peaks, has
cut a narrow gorge several hundred feet in depth.

This ridge of hard slates and quartzites near the contact of the two |
formations is an extension of the line of uplift of the Harney Peak range.
Although the granite does not extend as far north as this point by
several miles, yet the extreme hardness and uniformity in composition
of these rocks, enabling them to resist erosion, may be in part due to the
metamorphic action accompanying the intrusion of the granite forming this
range. Following the course of the stream, which soon enters a cation
among the higher peaks of the ridge, the dip of the formation is observed
to change from a general westerly direction to a well-marked easterly dip.
The sections of the quartzites exposed in the walls of the canon show a
contorted and irregular folding of the strata, but scarcely a quartz vein of
noticeable size occurs in the cliffs, although the composition of the rocks
is extremely siliceous; a most decided contrast to the superabundance of
quartz distributed through the mica-schists of the older formation about the
heads of this stream. Spring Creek, emerging from the cation, winds
through a broad and beautiful valley, bordered by groves of pine for
nearly five miles. Long level tracts of fertile bottom lands, destitute of
trees and covered with a rank growth of the finest grass, extend on either
bank of the stream, while both on the north and south small open valleys
reach far back among the broken and rolling hills, the bright green grass.
of these glades contrasting strongly with the darker color of the pine forest

240 GEOLOGY OF THE BLACK HILLS.

covering the slopes and rocky ridges. For nearly twenty miles this stream
flows in a general easterly course, crossing the slate and quartzite forma-
tion at right angles to the bedding of the strata. Where the hard quartz-
ites predominate in the hills, the creek has cut a deep gorge or cafon
through them; but where the softer clay-slates prevail in extensive belts,
the stream flows through an open valley, inclosed by low rolling hills and
bordered by broad level flats of grass land. Finally, entering a canon in
the limestone formation near the foothills, the water sinks among the
bowlders in the bed of the stream and disappears, from whence a dry
arroyo, fringed with trees, continues to the plains.

In the Spring Creek district I include, for convenience of description,
all the area of the Hills drained by that stream, and also a district of clay-
‘slates northeast of Harney Peak, giving rise to a small branch known as
Whiskey Creek, flowing six to eight miles south of Spring Creek, in the
same direction, and sinking in the foothills.

The head branches of Spring Creek drain an area of nearly one hun-
dred and fifty square miles, elevated about 6,000 feet above the sea, char-
acterized by low, rounded hills and ridges, wooded with pine of medium
size, interspersed with numerous small parks and grassy valleys, well
watered by the springs and brooks forming the sources of this stream. The
prevailing rocks of this region are mica-schists, often garnetiferous and
merging in all gradations into talcose and quartz-schist and strata with thin
slate-like lamellee, containing but traces of mica.

Quartz occurs, distributed abundantly in the schists as thin segregated
veins, parallel to the bedding, or in irregular bunches, not continuous in the
strata. It is found crystalline, white, red, or rose tinted, and, with the
exception probably of gold, appears to be free from any other minerals.

The abundance of quartz forms a serious annoyance in prospecting for
ledges, the whole country being covered with float quartz of every variety,
rendering it difficult to trace fragments found to contain gold to the veins
from which they were derived. The first tests for gold on Spring Creek
were made on a small branch flowing west from Harney Peak and empty-
ing into the main stream about three miles above Newton’s Fork. The
gravel, resulting from the wash of the granite of the Harney Peak range,

ORDER OF STRATA. 241

failed to give a trace of gold on panning, but on descending the branch and
testing the gravel, as soon as we had entered the mica and quartz schists,
small colors of gold were obtained.

The different strata were encountered in the following order in pro-
ceeding down this branch:

1. Coarsely crystalline white feldspar granite of the Harney Peak
range.

2. Metamorphic schist (gneiss).

3. Mica-schist, with segregated quartz veins, containing traces of amor-
phous graphite.

A Quartz-schist, having a slaty structure alternating with strata of
mica-schist; the whole formation dipping 45° west.

In descending Spring Creek, the first gravel bars are seen about five
miles above Newton’s Fork, elevated from 20 to 40 feet above the present
level of the stream on flat points and benches of mica or quartz schist.

On making an open cut into these bars on bed-rock the gravel is found
to be almost exclusively composed of quartz, and to yield, on panning,
small quantities of gold, from one color to half a cent to the pan. Better
results were obtained from dritts run in on bed-rock in the flats near the
edge of the stream. The gravel is full of mica and small garnet crystals,
resulting from the disintegration of the schists, and the gold is associated
with black sand and bright scales of iron ore.

To test the deeper channels in the flat, a shaft 5 by 8 feet was sunk with
considerable difficulty to bed-rock, which was reached at a depth of 134
feet, passing through the following deposits:

Feet
Stele peativges Oil wate eer oe sree mein eee tine Ne RE acs eet! bo A 4
SLOWM-COLOKeU lOOSe Rion hw orTavielere ree ys eet eh. veers cee mtn Ssh Sek 2
Compact enite quartz-gravel, containing about half a cent to the pan of coarse scale
POld eae ee ooo Cida'd BBS Ge See aie Late Ie ean a ea ee 2
Loose quicksands with bowlders, yielding only fine colors of gold .......-....-- 4
Decomposed bed-rock, with colors of coarse scale gold......-..........---4----- 14

Bed-rock; lamellar, taleose-schist.

The quicksand was so loose that water flowed in such quantities into
the shaft as to keep one man employed constantly bailing to enable the

others to work. The gravel was panned regularly for every six inches
16BH

249 GEOLOGY OF THE BLACK HILLS.

depth of the shaft, and the pay dirt and gravel from off the bed-rock tested
by washing a number of pans and comparing the results. Scales of mica
largely composed the lighter gravels and white quartz, and slightly water-
worn garnet crystals were found in the more clayey layers. The pay streak
was not on bed-rock, but nearly 6 feet above it, in the first compact layer
of gravel.

Finding a number of prospecting pits in the vicinity, which had been
sunk by a party of miners from French Creek, I had the pay dirt from
these holes tested, and obtained results similar to the above. Encountering
the miners, they informed me that they had experienced great difficulty in
reaching bed-rock on account of water, and that nothing had been found by
them up to that time better than the deposits in Custer’s Gulch. Spring
Creek at this point was 8 feet wide and 6 inches deep, with a moderate cur-
rent, probably at this time (June 25) affording 250 to 300 miner’s inches
of water. The placer gravels of this portion of the Spring Creek district
may be classed as elevated bars and gulch deposits. The elevated bars are
bank of quartz-gravel, occupying flat points and rocky benches at the
bends of the creek from 10 to 40 feet above the present channel, and
formed by the stream when ages ago, it flowed at that level through the
valley.

The gulch deposits cover the bottom flats of the valleys along every
branch where there is flowing water, and are much more extensive in area
than the higher bars, and include gravel-deposits resting on bed-rock near:
the present water-level, old channels of the stream, filled with gravel and
soil, winding through the flats, and the more recent placers occupying the
present bed of the creek.

The result of prospecting on this branch of Spring Creek seemed to
show a general diffusion of gold in nearly paying quantities through quite
extensive gravel deposits, which in many respects resemble the bars in
Custer’s Gulch. The water-supply was, however, considerably greater, and
the grade or descent of the valley sufficient to enable the deposits to be
worked with much less expenditure of time or labor, so that, were the de-
posits of equal richness, they would be more valuable here than on French
Creek. These head branches were, however, only partially prospected up

MAMMOTH LEDGE. 243

to the time I left the district (August 1), and Newton’s Fork was compara-
tively untouched, the whole attention of myself and miners being given to
practically testing the value of the richer deposits situated some miles below.
While Iam writing hundreds of miners are hard at work prospecting this
region, and the valuable deposits, wherever they exist, will soon be found
and made to give up the gold they contain and have held uselessly locked
up for ages. At this period in the exploration I was camped with a small
party of my miners about a mile below the junction of Spring Creek and
Newton’s Fork for several days. We had been prospecting the head
branches of the stream with results which were not as encouraging as the
appearance and character of the gravel deposits would indicate should be
obtained.

The mountainous region to the north and east, embracing the valleys
of Spring and Rapid Creeks, was unknown and unexplored. The expedi-
tion led by General Custer the preceding summer had passed around this
rugged area to the west and north, following the valley of the Box Elder,
on leaving the Hills, and the miners who were on French Creek had not as
yet attempted to penetrate it in search of gold.

I had noticed to the east the change in the geological formation of the
country, and regarding the belt of clay slates and quartzites as more
favorable to the production of valuable placer-deposits of gold than the
metamorphic mica-schists with their superabundance of crystalline quartz,
I decided to descend the stream far enough to insure the concentration in
the placers of any gold resulting from the denudation of the ledges in the
slate formation, and there prospect and test the richness of the gravel
deposits and prove the value of the district.

Locating in the valley of Spring Creek, about eight miles below New-
ton’s Fork, near where the immense quartz formation known as the Mam-
moth ledge crosses the gulch, a few hours’ prospecting resulted in the
discovery of gold in paying quantities in the placer deposits of this stream.
June 29, 1875, Thomas H. Mallory, one of the best prospectors associated
with me the past season, noticed a line of large bowlders extending across
the stream, forming a dam or riffle, and, suspecting that rocks of that
size and weight must rest on bed-rock, waded into the creek, and turning

244 GEOLOGY OF THE BLACK HILLS.

over a bowlder, dug from beneath it a blue gravelly clay, a shovelful of
which gave on washing six flat scales of gold about a tenth of an inch in
diameter, or five cents to the pan. Putting all my force of miners at work
in this place, several of the bowlders were rolled to one side, affording a
passage for the stream and decreasing the depth of water above the riffle.
On examination the pay gravel was found to be a deposit about 35 feet in
width, crossing the creek and extending into the banks on either side.
resulting from the decomposition of a stratum of soft clay-slate in the bed-
rock, which had caught and retained the gold swept over it by the stream,
The deposit consisted of—

1. Loose gravel of slate and quartz, with small bowlders, containing
“traces of gold; thickness, about 6 inches.

2. “ Pay streak,” a compact gravel, full of small red garnet crystals,
rich in coarse gold; from 3 to 6 inches in depth.

3. Plastic blue clay mixed with rotten slate bed-rock, yielding gold in
paying quantities, but not as rich as the garnet-gravel; thickness, 1 to 2
feet.

4. Lamellar clay-slate, soft and decomposed, forming bed-rock.

The “ Mammoth” quartz ledge crossed the bed of the creek just below
this rich deposit, and subsequently it was found that the line of bowlders
forming the riffle had lodged in the soft slate above the upper side of the
ledge, as shown in the accompanying sketch.

afer i Ferrugwnous
Quartz
44 I tI \ and hard

\ | | i Wy y | ae

Fic. 28. Longitudinal section of the bed of Spring Creek at the point of original discovery.
A. Water of stream.
B. Riffle of large bowlders.
C. Loose gravel and bowlders, poor in gold.
D. Pay streak heavy red garnet-gravel; auriferous.

\
\

DISPATCH TO THE COMMISSIONER. | 245

A number of pans of the pay gravel were washed with a result of from
one to two grains troy of coarse gold, or 4 to 8 cents to the pan. The
average of the whole thickness of clay and gravel was nearly 4 cents to
the pan, while the pay streak would give returns considerably higher if
washed separately. A pit was sunk in the bank of the creek, and the pay
streak found equally rich. Ata depth of 5 feet from the surface several
inches of garnet-gravel overlaid a yellow clay a foot in thickness, resting
on rotten slate and quartz bed-rock The average result on panning the
clay and gravel of this pit was about 4 cents to the pan. Subsequently I
saw the soldiers of the escort obtain from 10 to 15 cents to the pan from
the pay streak in this pit. After prospecting for several days in the vicinity
it became evident that my small force of miners unassisted could not in a
season properly examine the gravel deposits along this section of Spring
Creek, and after exploring Rapid Creek I returned to this locality July 14,
with Captain Burt’s and Captain Munson’s companies of the Ninth Infantry.
The fact that gold had been struck in paying quantities caused the first
stampede in the Hills, and nearly two hundred miners followed me from
French Creek, staked out claims, established a mining district, and rendered
me subsequently great assistance in prospecting the region.

After a few days’ work, comparing my results with those obtained by
the miners who had staked claims for several miles along the creek above
and below my camp, the following dispatch was, through the kindness of
Col. R. I. Dodge, commanding the escort, sent by special courier to Fort
Laramie and telegraphed to Washington:

CAMP ON SPRING CREEK, BLACK HILLS OF DAKOTA,
July 17, 1875.
To Hon. E. P. SMITH,
Commissioner of Indian Affairs, Washington, D. C.:

I have discovered gold in paying quantities in gravel bars on both Spring and
Rapid Creeks, from twenty to thirty miles northeast of Harney Peak.

The deposits are the richest yet found in the Hills, and are very favorably situ-
ated. There is a good head of water in the streams, amply sufficient for working
purposes.

The gold is derived from quartz ledges of enormous dimensions in a belt of clay-
slate and quartzite twenty miles in width, crossing the Hills in a northwesterly direc-
tion at this point. The clay from the bed of the stream near camp yields from 4 to 8 -

246 GEOLOGY OF THE BLACK HILLS.

cents to the pan, and several pieces of about the value of a dollar have been found by

the soldiers. I am engaged in prospecting the value and extent of the region.
* * Ee * * * x

WALTER P. JENNEY, E. M.,
Geologist Exploration Black Hills.

In order to test the richness of the gold deposits in the bed of the
creek, it was necessary to turn the water out of its present channel. With
the assistance of the soldiers a dam was built across the stream above the
point of discovery and the water of the creek conveyed by a ditch 1,000
feet in length across a bend and returned to the channel below the place
we wished to test, leaving comparatively free from water about 400 yards
of the former bed of the stream. Before reporting definitely on the rich-
ness of the new discovery I wished to test on a practical scale the gravel
from the different bars, and for this purpose constructed from rough boards,
whip-sawed from the native pine, a small box sluice 10 to 12 inches in
width, formed of two boxes 14 feet in length. This work had consumed
more than a week. In the mean time the soldiers who were not employed
in assisting me had been hard at work in the bed of the creek above the
riffle washing the clay-gravel in pans and rockers with quite remunerative
results. Several ragged and irregular pieces of gold with oxide of iron
adhering in the cavities had been found, weighing from # pennyweight to
15 pennyweight and worth from 75 cents toa dollar and a half. From 5 to
15 cents to the pan was usually obtained from the pay streak, and the sol-
diers sometimes washed out nearly a dollar’s worth of gold in three or four
hours’ work with a pan. From twenty buckets of dirt taken from the bed
of the stream and washed in a rocker 2 pennyweights of gold, or nearly $2,
was cleaned up, while the pay gravel in places yielded as high as 75 cents
from five buckets of the top gravel—equal to $11.25 per cubie yard.

Working as they did, often waist-deep in the water of the creek, under
many disadvantages from want of skill and tools, letting their tailings fall
back into the holes from which they dug the pay dirt, and, from the pasty
and clayey character of the gravel, obtaining but a portion of the gold
which it contained, the above results are quite remarkable. For, despite all
drawbacks, from an area about twice the size of the floor of a wall-tent (8
by 18 feet), not less than one and a half ounces of gold were obtained.

ENCOURAGING RESULTS. © 247

The water leaking through the dam and that derived from a number
of small springs in the bed of the creek produced a stream of about 30
miner’s inches flowing through the channel from which the creek had been
turned, causing great annoyance and difficulty in working, which could
only be entirely obviated by constructing a bed-rock drain several hundred
feet in length; an undertaking that would consume too much time.

To exclude the water from the strip of pay gravel crossing the creek
at the original discovery, while testing it, a wing-dam was built around the
deposit, and the pit kept moderately dry by continuous bailing. The sluice
was placed in position, the first box into which the gravel was shoveled
being left open, and a longitudinal riffle placed in the second to catch the
gold. A sufficient head of water was brought in a small conduit from the
main ditch, and the gravel, clay, and decomposed bed-rock, covering a
space 8 feet by 9 feet, dug out to a depth of 18 inches, and put through the
sluice. The result, on cleaning up after four hours’ work, was one-third of |
an ounce troy of coarse scale gold, worth $6.48. This was obtained from
four cubic yards of gravel, from which the soldiers had previously taken
the cream of the deposit, and quite a large portion of the material sluiced
was tailings that had been once worked. The next day the sluicing was
continued at the same place, a fresh portion of the creek-bed being inclosed
by a wing-dam. The result of six hours’ work was one-half ounce troy of
gold, equal to $9.72. The result of the work of both days may be summed
up as follows :

4 hours’ work produced 4 ounce troy gold = $6.48
6 hours’ work produced $ ounce troy gold = 9.72

10 hours’ work produced ® ounce troy gold = 16.20

Five men were employed in these tests, one of whom was constantly
at work bailing the water leaking through the wing-dam into the pit, while
the others picked up bed-rock, shoveled the gravel into the boxes, and tended
sluice. They worked, however, under so many disadvantages that, with a
sluice of proper size and a bed-rock drain, two men could have easily
done the same work in the same time, with probably a somewhat increased
yield of gold. But even charging this return of $16.20 with the labor of:

248 GEOLOGY OF THE BLACK HILLS.

five men for ten hours, the result was $3.24 per day per man, and with
economical and skilfull working on a larger scale the clean-up should equal
at least one-half ounce, or $10, to the hand. The soldiers had been panning
previously from this spot for two weeks and worked out the richest of the
gravel, and on weighing the gold in their possession I found that they had
obtained about $32 from the area I had sluiced in both days’ work, which
measured 216 square feet and had been excavated 18 to 20 inches in depth;
or 12 cubic yards of gravel put through the sluice had yielded $16.20 in
addition to that obtained by the soldiers, giving $48.20 as the total yield, or
about $4 per cubic yard.. The water leaking into the pit gavea great deal
of trouble, preventing the bed-rock from being properly cleaned up, and
the blue plastic clay, on being shoveled into the sluice, even after puddling,
rolled into balls and washed through the boxes unchanged, carrying with
it any gold which it contained. - On testing the tailings which concentrated
under the tail of the sluice, I found that considerable gold had in this way
been swept through and lost, the sluice beg too short to properly work
so clayey a gravel. ‘The soldiers rockered the heaviest of these tailings
and the lumps of clay, obtaining about § pennyweight of scale gold from
them. Large quantities of red garnet crystals were caught in the riffles,
together with cubical crystals of iron pyrites and round water-worn pieces
of hematite iron ore. No quicksilver was employed, as I wished to pro-
cure a sample of the gold in its natural state for assay.

The richest layer in the deposit was the lower part of the red garnet
gravel where it rested on the upper surface of the blue plastic clay. Pieces
taken from this contact showed, on breaking, scales and particles of gold
contained in it. The bed-rock, as far as we dug into it, about a foot below
its surface, contained coarse gold in small quantities, probably caught in
crevices in the rock before it decomposed. The soldiers, under the direc-
tion of John Roberson, for two days sluiced the gravel from the bed of the
creek below the riffle, but found the bed-rock either a hard massive quartz-
ite, worn by water smooth and level, or a ferruginous quartz with masses
of crystalline iron pyrites—the outcrop in the creek of the Mammoth ledge.
The gravel was loose and poor in gold, and the character of the bed-rock
prevented it from ever retaining any gold swept over its surface by the

FINENESS OF THE GOLD. 249

stream. Only about 25 cents and $1 were obtained by these tests. After-
ward they put in a wing-dam just above the area I had sluiced out, and
found a few square feet of the clay-gravel, but above that the bed-rock
pitched up stream and changed to a hard quartzite, with loose, poor gravel.
The result of about six hours’ work was $2.70 gold, mostly obtained from
the small quantity of clay-gravel adjoining my pit. No one attempted to
follow this deposit far into the flats on the banks of the stream, though it
gave equally good results at either end, and may have been continuous for
some distance across the bottom. In review of this deposit, it may be
described as a strip of plastic clay crossing the bed of the creek, and result-
ing from the decomposition of a strata of soft clay-slate located on the rise
of the bed-rock, while both above and below was a hard massive quartzite,
smooth and water-worn, but protecting the slate from being rapidly cut
away by the current of the stream. The sample of gold obtained by this
test was submitted to Mr. Ricketts, assayer at the School of Mines, New
York, for the determination of its fineness and value per ounce. The
results of two assays, each made in duplicate, are annexed, showing that
the gold from this district is very pure, being 946, fine, or 22% carats, and,
just as it is washed from the placers, is worth $19.44 to $19.63 per ounce.
Certificate of assay.

SCHOOL OF MINES,
New York, January 6, 1876.

Sir: The sample of placer gold from Spring Creek, Black Hills of Dakota, sub-
mitted to me for examination, contains, by assay of raw dust without previous melting—

CEOS fie oe NS ce MMe CR 8 et CRAY a aaa EG a a ae MOAN Bc a OO 937.8 fine.
SSH AyOVEtA lm Secor dete aed arg ae Me ol ne Aer A Sa 9 Sn ORL irae De a i Oe a 45.9 fine
HS ASE ITT G bal ee eet et ee rm Aral pe, Uae dn Ah Eset ELT oe 16. 30

Ro taller eer ete enor ear Seat ra Geceh cred ig! owed brat 1000. 00

The excess of base metal is due to the presence of oxide of iron adhering to the
particles of gold.

The value in gold coin of one ounce troy of dust is—

COs Sais Ss SW BESO HS SOE SESE OH Beis Ge ERA ee pee ee eee nt ee ee oe $19. 384
Silvers ease See SA CS ie RE he aT 25 fae Bee 0. 057
INO oe 5.66. St 65 Se IS Bb Cie eu eee Cel Fates I a i ep 19. 44

Very respectfully,
P. DE P. RICKETTS, E. M.
WALTER P. JENNEY, E. M.

250 GEOLOGY OF THE BLACK HILLS.

Certificate of assay.
SCHOOL OF MINES,

New York, January 6, 1876.
Str: The sample of placer gold from Spring Creek, Black Hills, submitted to me
for examination, contains, by assay of the melted bar, made by sampling about one
ounce of the raw dust and melting to free it from oxide of iron—

(C0) (teen SeGe Gama hcomohdKods pou ooWOUd eS cebS On baD AOU Ose 946.4 fine
Dilvien ee ses sara ee Ue: Dniesa%ere gfekel a ceed rae /allat ene haters, clio sieyabetn eke ce perry te oes 50.4 fine.
Baseametal: 9. 2p gata ccc Piro e eee ere nie eel ereeic renee Shas sae: CL

otal evel as5 38 BAS Se eee se eee ieee Hace cee Seyarsvacorttenet ete 1000. 00

The value in gold coin of one ounce troy of melted dust is—

Golde Re selene Pe Ae eRe nme fe naeh keene ils BRA: aN sty atopic ao tp aa Se $19. 562
SHIVOD oy Sea cite etek re es tee ie Une ere re Nate syeiy pcm yet orto ate actuate meno 0. 06%

of 00) oN net en eee cre Ree Mire Sec Rit ty teed Smee Ne a ee ema SBS Se cosh 19. 624

Notr.—The value of pure gold per ounce troy is $20. 67; the value of pure sil-
ver per ounce troy is $1. 24.

Very respectfully,
P. DE P. RICKETTS, E. M.
WALTER P. JENNEY, E. M.,

Geologist Black Hills Expedition.

About 100 feet above the original discovery an attempt was made to
test the creek-bed by building a wing-dam to keep out the water and
sinking a prospecting hole inside of it. But after a day of hard work we
were obliged to abandon the working at a depth of 4 feet, springs of water
bursting through the gravel and flooding the pit. From three to four colors
of gold were obtained from the loose gravel.

In a broad gravel flat a quarter of a mile below this point a prospect-
ing hole was sunk to bed-rock, which was reached at a depth of 6 feet, and
found to be hard quartzite, covered with loose gravel, resting on a surface
worn as smooth as a floor by the water. Several pans of dirt were washed
from this pit, but not a color of gold was found. Another pit located in an
old channel had to be abandoned at the depth of 5 feet, quicksand being
struck so fluid that it flowed into the working and caused the walls of the
pit to cave in.

Two prospecting holes in the flat where the Mammoth ledge crossed
the gulch struck a cement of quartz-pebbles and oxide of iron so hard as to
be penetrated with great difficulty. The same cement, several feet in thick-

“ STAND-OFE” BAR. 251

ness, could be seen capping the ledge on the hill near the creek, but on pan-
ning it failed to give a trace of gold. Near my camp a small sluggish
branch entered the creek from the south, and about half a mile above its
mouth a prospecting hole was sunk in the flat. After passing through about
6 feet of soil, gravel, and bowlders, a black, peaty muck was encountered
and penetrated a depth of 7 feet, when the water, bursting in, flooded the
hole, and a pole 5 feet long was easily thrust down through the muck in
the bottom of the shaft, but failed to reach any compact layer of gravel.

A similar experience was the result of a hole put down by ‘Califor-
nia Joe” on his claim below camp. After passing through 6 feet of large
bowlders and compact gravel a deposit of black muck was struck, and
finally an old beaver dam, composed of sticks and mud, was passed through,
resting on another layer of muck, at which point the work was stopped by
the water. The valley below the Mammoth ledge was contracted in width,
and appeared to have been gradually filled up since it had been excavated.
Bed-rock was reached in only two places, although a number of shafts were
sunk by the miners, and in these cases the rock was hard and the gravel
poor in gold.

The hills bordering the stream were composed of thick strata of mas-
sive quartzite upturned on edge, and the narrowing of the valley was doubt-
less due to the hardness of this belt of rocks, resisting denudation and the
forces which excavated it Above the original discovery for nearly five miles
the valley was broad and open, with rolling and broken hills of siliceous
and clay slates, with occasional belts of quartzite. Here the gravel deposits
were very broad and extensive; flats, in places a quarter of a mile wide,
extended along the banks of the creek, while elevated bars were to be found
at the bends of the stream and sides of the valley, which promised to be
very valuable. One of the most noted of these older deposits of the stream,

’ eoncern-

discovered the past season, was the celebrated ‘‘ Stand-off Bar,’
ing the ownership of which there promised at one time to be a serious diffi-
culty, that was only avoided by the determination of its discoverers to
“stand-off” all intruders. John W. Allen, the present recorder of the dis-
trict, im a letter to the Chicago Inter-Ocean, thus describes this deposit,

which proved to be so rich that the owners caved in the drift on leaving the

252 GEOLOGY OF THE BLACK HILLS.

Hills, to prevent any stragglers from working the bar during their enforced

absence :
CHEYENNE, WYOMING TERRITORY,

August 30, 1875.
To the Editor of the Inter-Ocean :

After prospecting a short time in the park we moved to Spring Creek or Jenney’s
Gulch, and on the morning of the 20th of July we commenced prospecting Stand-off
Bar. We did not work more than half an hour until we panned out 25 cents to the
pan, found coarse gold, and ran across the bar about 35 feet. From the last pan of
dirt taken out of the face of the drift we got one pennyweight and three grains, or what
we term a good dollar, to the pan. This is about one mile up Jenney’s Gulch, above
Professor Jenney’s discovery. We panned several pans that weighed from 25 cents to
50 cents and from 78 cents to 93 cents to the pan; it ranged all the way from 10 cents
to $1. * * * We prospected also on Castle Creek, and have proven beyond a
doubt there are good placer-mines there as well as on Spring Creek. We also found
good six-dollar-per-day diggings on Rapid Creek; and had not the military order
arrested our work, we would soon have had plenty of the yellow metal out of the
ground to have shown the world that the Hills are very rich. While we were prepar-
ing sluice-boxes, whip-sawing lumber, &c., preparatory to working our ground, we got
the “ grand military shake,” and had to leave our claims and the Hills. * * *

JOHN W. ALLEN.

Having returned to the Hills after the withdrawal of the military
forces, Mr. Allen writes me, under date January 2, 1876:

Our bar (Stand-off) pays $1 in gold per hour per man employed; have on hand
26 ounces of bankable gold dust taken out inside of three weeks.

Mr. James Allen, of Cheyenne, who visited Spring Creek at that time,
writes :

I prospected ten pans of dirt from Stand-off Bar and got for my trouble $5.35. 1
am perfectly delighted with the country. If anything, it is better and more extensive
than has been represented. A company known as the “ Montana company” had only
been in the gulch three weeks when I got there; during that time they had built two
houses, cut a ditch near a quarter of a mile in length, whip-sawed their lumber for
sluices and set them running, and had taken out near $1,000 in nice, coarse, bankable
dust.

The claims worked by this company are situated below Stand-off Bar,
and I understand that the pay dirt was obtained by a drift run in 50 feet
on the rim-rock of an elevated bar, as high as $110 being obtained in one
day’s work by three men. ‘The companies could not run their sluices more
than six hours during the warmer part of the day, owing to cold and frost,
yet obtained from $6 to $7 per day per man as the result of this limited
work.

ENCOURAGING RESULTS. 253

Owing to the numbers of small springs in the flats, it is doubtful if
they will be worked until covered bed-rock drains can be constructed to
remove the surplus water and admit of dry working. The more elevated
and easily worked bars will first be attacked and made to give up the gold
which they contain. Near the point of original discovery the soldiers
found opposite their camp on the hill-side a small deposit of gravel, 2 to
3 feet deep, which proved to be quite rich, yielding from 12 to 19 cents to
the pan by actual weight.

Just above where the Mammoth ledge outcropped on the south side of
the valley was a hill of cement-gravel which gave colors on rim-rock, and
on sinking a shaft in the center of the hill we passed through a hard cement
of quartz pebbles, gravel, and bowlders, but after a week’s work failed to
get bed-rock at a depth of 22 feet owing to the extreme hardness of the
conglomerate, which was cemented by oxide of iron, probably deposited by
ferruginous springs, the iron of which was derived from the decomposition
of pyrites in the ledge. The gravel from this shaft failed to show gold on
panning, perhaps owing to the particles of gold being inclosed in the hard
lumps of the cement. It promised to be a good deposit to hydraulic, as
that process would break up the cement and set the gold free. Two or
three miles below this point there were some quite extensive gravel deposits,
where a small branch entered the creek from the north, that were reported
to prospect well by the miners who located claims on these bars. But
lower down the stream flowed through a deep rocky gorge cut in the
slates, with gravel deposits at intervals along its course wherever the gorge
was not contracted into a narrow canon. This portion of the stream, ex-
tending from the original discovery to the point where the creek sinks in
an impassable cation in the limestone near the foothills, a distance of ten
or twelve miles, can scarcely be said to have been prospected at all the past
summer. In places the water flowed over the bare slates, and there are no
gravel deposits; but at the bends and forks of the stream bars of consider-
able size were seen.

Below, where the creek sinks in its bed, are bars composed of quartz
and slate gravel intermixed with a large proportion of limestone and sand-
stone bowlders. ‘These deposits undoubtedly contain gold, but I was una-

254 GEOLOGY OF THE BLACK HILLS.

ble to prospect them, there bemg not a drop of water in the vicinity at the.

time of my visit (July 3); but in the spring this stream probably flows out
into the plains, and these dry arroyos and placers can then be worked.

The available water-supply furnished by Spring Creek for working
purposes varies with the season of the year, being probably greatest in
April, May, June, and July, the rainy months, and least in October,
November, and December, when there is little precipitation of moisture.

In turning Spring Creek from its channel a ditch 24 feet wide and 2
feet deep, with a grade of 2 inches in 30 feet, was entirely filled, besides
about 30 miner’s inches which leaked through the dam; and the available
quantity of water at that time (July 25) I estimated at not less than 350
miner’s inches. During the summer months Spring Creek will afford from
300 to 800 minev’s inches of water for mining purposes, the quantity vary-
ing with the season and the yearly rainfall. I had no instruments to accu-
rately measure the grade of the valley of this stream, but by an aneroid
barometer I found that the descent of the main stream from Newton’s Fork
to where the creek enters the limestone is about 1,400 feet in a distance
of nineteen miles, or an average grade of 74 feet to the mile. The descent,
however, is less than this for the more open and broad portions of the val-
ley, probably 50 or 60 feet to the mile, and greater in the narrow, rocky
canons. The gold of this district occurs in the placers in coarse, flat scales,
thick and heavy, intermixed with very little fine dust, and often shows
brown oxide of iron adhering in the cavities of the larger pieces.

The assays made by Mr. Ricketts, of the School of Mines, show that this
gold is 22% carats, or 946 fine, equal to the average of the best Australian
placer gold, and exceeding that from California. It is found associated
with small water-worn red garnet crystals, nodules of hematite iron ore,
magnetic iron sand, and crystals of iron pyrites, but no other minerals were
detected.

The average proportion of gold in the native gold of California, as derived from
assays of several hundred millions of dollars’ worth, is eight hundred and eighty
thousandths, while the range is mostly between 870 and 890. (Prof. J. C. Booth, of
United States mint, in a letter to the author, of May, 1867.) The range of the metal

of Australia is mostly between 909 and 960, with an average of 925. (Dana System
Mineralogy, fifth edition, 1868.)

FINENESS OF THE GOLD: 255

The gold appears to be derived from the decomposition of the slates
and quartzites, as well as from the denudation of the quartz ledges travers-
ing these rocks. The source of supply of the gold is immense. The side
valleys and gulches are often excavated for miles along the outcrops of the
gold-bearing slates, and the quartzites, with their inclosed veins, have acted
as feeders to the placers of the main valley. Over a very extensive area
these rocks have been enormously eroded and the resulting material swept
away. The gold it originally contained has been partly caught and
retained in the gulches; the rest, intermixed with gravel and bowlders
from the metamorphic rocks, and also from the limestone and recent forma-
tions in the foothills, being carried far out on the plains and scattered
broadeast over their surface, so that very little can be ever recovered.
From the results of the prospecting done in this district up to August 1,
1875, when I left the guich, it would be inferred that the character of the
bed-rock strongly influenced the deposition of the gold. Where the bed-
rock was a hard, massive quartzite, the water had worn it smooth, and no
gold was to be found on its surface, while the gravel above it was loose and
poor in the precious metal; but where the bed-rock was soft, easily decom-
posing slates, it had caught and retained the gold swept over its surface by
the stream, and the gravel above, compact from the clay produced by its
decay, was also rich in gold. In the flats and creek bed, when a stratum
of soft slates is found crossing the gulch below, a high and hard bar with
valuable deposits should be sought for.

In discussing the area drained by the headwaters of this stream, the
characteristics of the schistose rocks covering that section have been
already given. The main valley of the creek is excavated wholly in the
rocks of the second division of the Archean, the slate and quartzite
formation extending as a belt fifteen miles in width from the granite on
the eastern slope of the Harney Peak range to the northern part of the
Hills near Crow Peak. On Spring Creek the general strike of the strata is
northwest and southeast, with a dip from northeast 60° to vertical, while
locally the rocks are seen dipping west at high angles. The rocks of this
formation are altered sediments, consisting of hard, massive gray or brown
quartzites, lamellar quartz-slates, and soft clay-slates. By metamorphic

256 GEOLOGY OF THE BLACK HILLS.

action of waters holding silica in solution, or by the preponderance of clay
or sand in the original sediments, these rocks inperceptibly merge into
each other, and the strata of quartzite often cannot be distinguished from
jasper or pure quartz veins except by position and structure. There is a
most remarkable uniformity in the hardness and composition of these rocks,
not only for long distances along the outcrops of the same strata, but
throughout the whole extent of the geological formation of this belt rocks
from widely different localities most closely resembling each other. The
metamorphic action seems to have been the product of the mechanical
force producing the folding and upturning of the strata in Archzean time
The quartz veins are not igneous injections, but chemical precipitations
from waters holding silica in solution, partly, at least, derived from the
wall-rocks of the veins, and undoubtedly formed during the folding of the
strata, at which time the gold must also have been deposited. The lower
layers of the Potsdam prove this, as they contain in places bowlders from
both the veins and the wall-rock identical in hardness and appearance with
the rocks in the immediate vicinity. This chemical deposition of silica
would seem to be similar to the silicification of wood, the solution replacing
the original rock atom by atom, and samples of quartz were seen where
the original rock blended so imperceptibly with the white quartz that it is
difficult to explain the formation of the quartz in any other way. Quartz
occurs in the slates either as interlaminated fissure-veins, coinciding with
the stratification and often quite extensively developed, or as short and thin
veins, following for a few yards the jointing planes of the slates. It is in
the quartzites, however, that the greatest development of quartz is to be
found in this district. Strata of sedimentary rock have, by the action of
water containing silica and iron in solution, been transformed into hard
quartzite intermixed with ferruginous quartz in all proportions throughout
the entire thickness and extent of the bed, until it resembles, on its outcrop,
an immense ledge of quartz and vein matter, traversing the slates for long
distances across the Hills. On examination, however, these peculiar forma-
tions are found to be altered sediments. There is no fluccan or casing to
the ledges, and in the most favorable positions for the existence of slicken-
sides they are seen to be wanting.

ORDER OF THE STRATA. 25%

One of the most remarkable is known as the Mammoth ledge, which
crosses the valley of Spring Creek near the original discovery of gold.
The stream has cut its channel through the formation, leaving a bluff from
20 to 30 feet high on the north side of the valley, exposing a fine section
of the ledge. Near the base of the bluff the quartz is intermixed with a
large proportion of yellow and brown oxides of iron, which has evidently
resulted from the decomposition of iron pyrites. Where the ledge out-
crops in the bed of the creek the quartz is found to be full of masses
of crystallized pyrites, the water having protected it from oxidation.
The ledge is bounded on the west by silicious clay-slates, containing
minute garnet crystals, and having a general northwest and southeast strike,
and a dip, indistinctly marked, about northeast 60°. The section, com-
mencing at the west, is as follows:

1. Quartzite and ferruginous quartz, interlaminated and mixed with
iron ore; width 90 feet

2. Gray, hard, barren quartzite; 50 feet.

3. Ferruginous quartz, mixed with quartzite, clay-slate, and iron ore
(limonite); 200 feet.

4. Hard gray quartzite, forming the eastern boundary of the forma-
tion.

This ledge was a study for a mineralogist. It contains undoubted
segregated veins of milky quartz, changing in 4 short distance into cellular,
rotten quartz, mixed with limonite iron ore. Some of these masses of
vein matter are 10 to 15 feet wide, and continuous for short distances; at
other places the quartzite became ferruginous, and merged into brown
jasper, or, becoming more pure in its composition, changed to white quartz,
as though the silica had replaced, atom by atom, the particles of the original
sediment during the metamorphosis of the strata. This view seemed most
reasonable in viewing the peculiarities of the banded quartz and black
quartzite; each rock, while perfectly distinct, seemed to be the result of
the difference in the capacity of the layers of the original sediment to allow
the silicated solutions to pass through it.

There were no evidences of the comb structure so often seen in.

mineral veins, but everything pointed to segregation as the cause of tho
17 BH

258 GEOLOGY OF THE BLACK HILLS.

formation. This ledge is remarkably persistent and continuous across
the country. It was traced for four miles from Spring Creek in a southeast
direction, and was reported by the miners to extend north to Rapid Creek,
a distance of eight miles, still preserving its great width undiminished. A
small gulch emptying into Spring Creek from the south was excavated its
whole length in the outcrop of this immense quartz formation. The gravel
deposits near its head are entirely made up of the disintegrated fragments
of the ledge. On the south bank of the creek the quartzite is yellow
and brown in color, and resembles impure jasper. On breaking, it showed
sometimes visible particles of gold, but samples of the rock submitted to
Mr. Ricketts, assayer at the School of Mines, proved to contain but traces
of the precious metal. The same result was obtained from iron pyrites
from the bed of the creek. The oxides of iron from portions of this ledge
were bright-yellow in color, resembling plumbic ocher, but on testing with
a blow-pipe they were found to contain neither lead nor silver, but were
merely a variety of limonite. The most promising ferruginous quartz from
this ledge was roughly tested at the time of its discovery by crushing
several pounds in an iron mortar and panning carefully, but only a color
of gold was obtained; and it is doubtful if these immense quartz formations
are of any value except as having furnished gold to the placer gravels.

In the bluff formed by this ledge, on the bank of the stream, are
several small caves, penetrating the rock for 10 to 15 feet, like drifts in
a mine, which proved to have been formed by the decomposition and
washing away of soft clay-slate inclosed in the quartz. There are not
less than three of these quartz formations crossing the valley of Spring
Creek. One, two miles below the Mammoth, is characterized by a great
development of “ribbon-quartz,” thin bands of white quartz, and black
quartzite or slate alternating in the ledge, giving it a banded or ribbon
appearance. In places the rock became a pure white quartz, and, by its
superior hardness resisting denudation, formed the crests of the rocky hills
and ridges, and could be traced for a long distance across the country.

The only minerals besides gold found in the Spring Creek district were
iron pyrites and the oxides resulting from its decomposition. A miner (Mr.
Blake) brought me samples of a rock which he supposed to be black sul-

WHISKEY ORERK. 259

phuret of silver. He had found it while wandering about in the Hills,
having been lost for some time in this vicinity, On testing it with a blow-
pipe, it proved to be only clay-slate, and did not contain a trace of metal.
It was soft, jet-black in color, with a luster resembling very closely the
mineral for which he had mistaken it.

Up to the time I left the gulch (August 1, 1876) no valuable quartz
ledges had been discovered, the attention of every one having been given
to prospecting the placers. The gravel deposits of the Spring Creek dis-
trict, especially for several miles above and below the point of discovery,
are extensive in area and very favorably situated for working. ‘The water-
supply is ample, and the fall of the stream sufficiently great to enable water
to be carried above the tops of the elevated bars without difficulty and
with little expense, while there is room and grade enough in the flats, in
places, admitting of bed-rock flumes being finally put in, and the whole
thickness of the gravel flats, as well as the tailings from the elevated bars,
being economically worked. Timber of suitable size and quantity for the
construction of sluices, flumes, and trestles is to be found growing abun-
dantly in the immediate vicinity, as well as for various house-building pur-
poses and fuel. The gold is coarse, heavy, and easily saved in sluices, and
contains but little silver or impurities to decrease its value. Thus it may
be concisely stated, that the gold-placers of this district, worked by the
systems and processes which the experience of twenty-five years has led
the miners of the Pacific slope to adopt, will pay a handsome return for
the labor required to open the deposits and extract the gold.

WHISKEY CREEK.

A small area of the Spring Creek district remains to be described,
comprising the extreme southern end of the belt of clay-slates and quartzites
included between Spring Creek and the granite ridges and spurs extending
east from Harney Peak. 'The surface of this region is rugged and broken,
though not as mountainous as the granitic area to the south about the
headwaters of Wiwi Creek. The valleys and glades are covered with
groves of burr-oak of medium size, the crests of the hills with pine, while
the bottoms of the ravines and gulches are thickly overgrown with alder,

260 GEOLOGY OF THE BLACK HILLS.

birch, hazel, and hornbeam. The greater portion of this area of slates is
drained by the numerous branches of Whiskey Creek, a small stream with
from 30 to 50 miner’s inches of water (July 20) flowing east from the
Harney Peak range, about six to eight miles south of Spring Creek, and
sinking before it reaches the plains. Near the head of this stream, at the
junction of the granite with the slate formation, a huge mass of slates,
standing on edge, 30 feet in height, was observed projecting from a crag of
feldspar granite. The fragment of slates was only partly inclosed in the
granite, so that the north side of the lenticular peak was composed of slates,
while the south was wholly granite. It was probably a “horse” in the
granite dike. In the southeastern part of this area, near the foothills, is
quite an expanse of Potsdam sandstone and Carboniferous limestone, but
near where the water sinks in Whiskey Creek the limestone belt encircling
the Hills is not more than a mile in width. With the exception of the pres-
ence of granite peaks among the slates, the general character of the rocks
is similar to that of the Spring Creek Valley, and fine crystals of staurotide,
mostly twins in lamellar schists, resembling the specimens of that mineral
from Lancaster, Mass., were found near the granite ridges. In the lower
part of the valley of Whiskey Creek small gravel benches occur along its
banks, but gold was not discovered in paying quantities except below
where the water sinks in the bed of the stream among the limestone Red
Bed formations of the foothills.

From the fact that the area drained by this stream is almost identical
in the character of the rocks with that of the Spring Creek district, although
less extensive, I consider that there are good reasons to expect that, at least
in some localities, gold may be found in paying quantities in the gravel
deposits of Whiskey Creek and its tributaries.

The gold deposits discovered in the dry ravines and arroyos among
the Red Beds where the dry bed of this stream winds through the low hills
at the edge of the plains will be described in the section on The Deposits
of Auriferous Gravel in the Foothills.

DESCRIPTION OF THE STREAMS. = 261

SECTION IV.
CASTLE AND RAPID CREEKS.

Rapid Creek is formed by two main branches—Castle Creek and the
North Fork—each heading in the limestone divide near Crook’s Tower, one
of the most elevated portions of the Black Hills. It is the only stream on
the eastern slope of the Hills flowing a continuous stream of water during
all seasons to the Cheyenne. The other creeks sink among the foothills,
and during the greater portions of the year are marked by dry channels
traversing the plains. Though second in size to Spearfish or Redwater in
volume of water, Rapid Creek is the largest stream rising in the Black Hills.
From its extreme source in the springs issuing from the limestone at the
head of Castle Creek to the point where it empties into the south fork of
the Cheyenne, its length, omitting the minor bends, is not less than one
hundred miles. Throughout its course it is characterized by a rapid current,
the descent of the valley being about 3,200 feet from the source of Castle
Creek to the edge of the plains at the foothills, and nearly 800 feet in
traversing the open plains a distance of forty-five miles to the Cheyenne.
The area drained by Rapid Creek and its tributaries has been divided by
the miners into the Castle Creek and the Rapid Creek mining districts, the
north fork not having been located as a district the past season, although
gold was discovered in considerable quantities on that branch.

3

THE CASTLE CREEK DISTRICT.

Castle Creek, near its source in the limestone, is a small stream fed by
numerous little springs issuing from the sides of the valley, and every few
hundred feet the creek is dammed by the beaver, producing marshy ponds
and boggy tracts of bottom land. At the head of the creek groves of tall
slender spruce cover the hill-sides, separated by narrow open glades of
grass land extending between the low hills, producing most pleasing views ;
but farther down the stream the spruce is replaced by pine, and the valley
is berdered by cliffs of Carboniferous limestone, whose castellated appear- -
ance suggested the name of the stream.

262 GEOLOGY OF THE BLACK HILLS.

The limestone is almost horizontal in its bedding, and the stream grad-
ually cutting deeper throngh the strata as it descends finally exposes the
Potsdam sandstone at its base, resting unconformably on the upturned
edges of schistose rocks. Here the lower layers of the Potsdam are seen
to be a coarse yellow or brown conglomerate, closely filled with pebbles
of white quartz, in places nearly uniform in size, from 1 to 2 inches in
diameter, worn smooth and round by the action of water. The schistose
rocks are exposed in great variety, dipping first west as we descend the
stream and then east at high angles. The strike is in a general north and
south to northwest and southeast direction.

The rocks of this section evidently belong to the first division of the
Archeean, and can be traced south across the park country to the French
Creek district, where they are interlaminated with dikes of feldspar granite;
but no granite is found in this vicinity. The schists are often very mica-
ceous, although a gray talecose quartz-schist, having a slate-like structure,
appears to be the prevailing rock, occurring in broad belts interstratified
with mica-schist. These rocks, though distinct in bedding, insensibly
merge into each other in character; mica-schist, from a preponderance of
mica, becoming a soft, easily-decomposing rock, often highly garnetiferous,
while with a greater proportion of quartz it passes into a fine-grained mica-
schist, or ultimately to a quartzite with only traces of mica.

Chlorite schist and talcose schist are extensively developed on some
of the branches of this stream, and strata frequently are found completely
filled with small red garnet crystals often not more than one-thirty-second
of an inchin diameter. Quartz-occurs as segregated veins, usually not con-
tinuous for any great distance, locally expanding into bunches and irregular
masses of quartz, following the stratification of the schists, but not crossing
the bedding. These irregular deposits of quartz were very abundantly
distributed through the rocks ; often strings of lenticular masses of quartz
followed a line of lamination in the schists, or thin veins could be traced for
short distances coinciding with the stratification. They were not, however,
irue continuous fissure veins, but irregular segregations formed during the
folding and metamorphism of the strata. The quartz is usually milk white
and crystalline, sometimes vitreous, transparent, and stained and coated at

—s ~

CASTLE CREEK. pe 263

its jointing planes and surfaces with oxide of iron, but apparently free from
iron pyrites and metallic minerals. These quartz ledges must, however,
contain, at least, traces of gold, and furnish it to the placer gravels. Small
bright-green crystals of ripidolite in flat scales are inclosed in the mass of
the quartz; and green chlorite, full of red garnet crystals, incases the veins
when traversing the taleose and chloritic schists. Proceeding down the
valley the rocks gradually change in character, becoming less micaceous,
with a greater development of talcose and quartz schists, in places approach-
ing a clay-slate.

Castle Creek, having made a most remarkable bend of eight miles to
the north, the greater portion of the distance through a narrow and deep
canon, resumes its former southeast course in a valley excavated among the
quartzites and clay-slates of the second division of the Archean. An
attempt was made to explore this canon by myself and miners; but owing |
to the prevalence of fallen timber and tangled thickets of small trees and
bushes filling the bottom of the gorge, we were unable to traverse it with
horses beyond a point about seven miles below where Custer’s trail leaves
the creek. The exact line separating the two formations, the schists and
the slates, was not seen, but the dip was observed changing from west to
east, the quartz veins becoming less abundant in the rocks and free from
mica or chlorite, and more continuous and regular in formation. Thin
quartz veins followed the jointing planes of the slates as well as the strati-
fication of the formation. The quartz was locally ferruginous and cellular
from the decomposition of pyrites, and had more of a mineral-bearing ap-
pearance. It is evident from the change in character of the rocks that the
line of contact of the mica-schists and clay-slates must pass in a general
northwesterly direction from Spring Creek, near its union with Newton’s
Fork, across the hills and the cation of Castle Creek until it is concealed
beneath the limestone ridge between Crook’s Tower and Custer Peak. Cas-
tle Creek enters the canon in its north bend among the mica-schists, form-
ing a continuation north of the rocks of the French Creek district, and
emerges among clay-slates and quartzites identical with the rocks of the
lower valley of Spring Creek, and easily traced across the hills to that dis-_
trict. Near the head of a small branch of Castle Creek, entering it from

264 GEOLOGY OF THE BLACK HILLS.

the south just below the canon, the clay-slates were observed, forming the
upper portion of a cliff resting unconformably on the schists at its base.
Both formations were, however, upturned on edge at different angles, and
it is possible that this apparent unconformability of the two divisions of the
Archzean may have been the result of a ‘ fault” formed during the fold-
ing of the schists and slates. The point where this unconformability was
observed was almost exactly on the supposed line of contact between the
two formations. At short distances to the east and west the peculiar char-
acteristics of the rocks of the different divisions were unmistakably exposed
in the cliffs and outcrops of the strata. From the difference in lithological
character in the rocks of the two formations, the resemblance between
specimens of the schists and slates from the Black Hills and samples from
well known Laurentian and Huronian of Canada and Lake Superior, as
well as the observed superposition of the slates and quartzites on the tal-
cose and mica schists, we have been led to regard the clay-slate formation
as of more recent geological age than the mica-schists so extensively devel-
oped on the head branches of Castle, Spring, and French Creeks. This
subject will be found treated more fully in the section on the metamorphic
rocks by Mr. Newton. On examining specimens of the Archean rocks
in the possession of Prof. T. 8. Hunt, I find that schists from the French
Creek district resemble closely the ‘“‘Mont Alban,” or White Mountain
series of Professor Hunt, which he regards as older than the Huronian.

I was informed by Mr. A. H. McKay, one of the miners who accom-
panied the expedition of General Custer, that Ross and himself failed to find
gold in prospecting on Castle Creek ; but on a small branch in the north
part of Elk Horn Prairie they obtained the first “color” of gold from the
Black Hills July 28, 1874, and during the six days the expedition remained
camped on French.Creek they improved the time and got gold enough to
prove its occurrence in the placer gravels of that stream.

Gold was discovered on Castle Creek, above the cation, June 12, 1875,
by the miners assisting me in the work of prospecting. It was found in
small gravel deposits along the creek and in the gulches leading into the
stream from the south. About two or three miles below the point where
Custer’s trail leaves the valley a bar, covering an area of two acres, gave,

PROSPECTING ON CASTLE CREEK. | 265

on prospecting, nearly a cent to the pan of fine gold. This deposit of gravel
was 4 to 5 feet in thickness, composed of quartz and slate pebbles, resting on
bed rock of mica-schists, elevated about 6 feet above the water of the creek,
and so favorably situated for working that the gravel could be sluiced with
very little expense or trouble. Several pits were sunk in the flats near the
channel of the stream, but failed to reach bed-rock, owing to springs of
water, which could not be kept down by bailing. Small gravel benches
were found on the sides of the canon below this bar, which gave four to
six colors of gold to the pan, but were of too limited area to be valuable.

Above the canon on the main creek and its branches are small ele-
vated bars and quite extensive flats of gravel, which were scarcely pros-
pected at all by the miners who staked claims on this creek on the larger
placers below the bend. The gold from this portion of the stream is in
small, flat grains, resembling that of French Creek, and probably similarly
derived from the quartz veins in the schists.

In July, while I was engaged with my assistants in testing the value
of the placers on Spring Creek a party of miners discovered gold in pay-
ing quantities on Castle Creek below the north bend, and quite a stampede
took place to the new diggings. When, three weeks afterward, I visited
the new discovery, I found nearly one hundred and fifty miners camped
along the valley prospecting the claims they had taken. Most of these
men were old Montana miners, and, working together in companies, had
done a surprising amount of work for so short a time. Nearly every claim
had been prospected enough to prove its value, and preparations were being
made to enable them to work with sluices on a large scale. In one place a
bed-rock drain had been dug nearly a quarter of a mile in length, from 3 to
9 feet deep, to drain a gravel flat where the pay dirt gave, by several tests
which we made, from 5 to 15 cents to the pan of coarse rusty gold. The
gravel was at least 80 per cent. water-worn clay-slate, in fragments of small
size, intermixed with quartz bowlders and pebbles from the ledges. The
pay dirt not only was found as a compact clayey gravel on bed-rock, but
also in several pits and drifts occurred in one or more thin layers of clayey
gravel 2 or 3 feet above it. The bed-rock was soft, shelly clay-slate,
easily dug several feet in depth with pick and shovel, and holding gold in

266 GEOLOGY OF THE BLACK HILLS.

its crevices as far below the surface as decomposition had penetrated the
substance of the rock.

Very few large bowlders were seen in the gravel deposits, the pay
dirt, as well as the whole thickness of the bars, being mostly a slate-wash,
easily treated in sluices with a low grade and slow current of water, owing
to the lightness of the material operated upon. The gravel deposits are
flats along the course of the stream, filling the bottom of the valley, and
elevated bars on slate benches, 10 to 30 feet above the creek, often quite
extensive at the bends of the stream. Several pits had been sunk to bed-
rock in the flats, reaching it at a depth of 12 to 15 feet, and in every case
striking on bed-rock pay dirt yielding from 3 to 10 cents to the pan. The
elevated bars showed in places 10 to 12 feet of gravel, and the drifts run in
on rim-rock exposed the bed-rock pitching in toward the center of the bar.
A number of these high bars were tested by my assistants, with a return
from the pay streak of from 3 to 15 cents to the pan. The gold was coarse,
flattened scales and rounded grains, stained a rusty-brown color by a thin
coating of oxide of iron, derived from the presence of iron pyrites in the
slates.

This portion of Castle Creek, extending from the bend to its junction
with the north fork of Rapid Creek, a distance of about eight miles, is in a very
mountainous and broken region. The valley is deep, and in places quite
narrow, and surrounded by high, steep hills of clay-slates, occasionally
intersected by a stratum of ferruginous quartzite mixed with white quartz,
similar to the Mammoth ledge on Spring Creek. It is not necessary to dwell
particularly on the wealth of this district, as there is no doubt that the
gravel deposits on this part of Castle Creek will prove remunerative when
opened. They are very favorably situated for working. The water supply
is quite large, with a grade of at least 76 feet to the mile. The gravel is
easily mined and sluiced, and the gold coarse and readily saved, even
without the use of quicksilver. Castle Creek at this point is a fine rapid
stream of water, averaging in June and July 10 to 12 feet in width, with
a depth of 12 inches, probably yielding 300 to 500 miner’s inches of water.

VALLEY OF RAPID CREEK. 267

RAPID CREEK.

The north fork of Rapid Creek, heading in several small branches just
west of Custer Peak, where the limestone of the divide bounds the area of
slates, is slightly larger than Castle Creek, and near its union with that
stream it winds through a deep and narrow cation in the slates. Gold was
discovered in paying quantities on this branch by the miners, but the
claims were not prospected enough to determine the value of the placers up
to the time I left the Hills. For four miles below the forks Rapid Creek
winds and twists through a deep and contracted cafon, cutting across a
belt of very rugged and broken peaks, an extension of the ridge from
Harney Peak northwest to this point. Vertical cliffs of slates rise several hun-
dred feet on either side of the stream, surmounted by high rocky hills, cov-
ered with pine, the greater portion of which has been killed by fire, leaving
the bare and decaying trunks standing. The bottom of the gorge is choked
with a dense mass of tall spruce trees, tangled with bushes and fallen tim-
ber, making it necessary at the time we first explored the canon to wade
our horses along the channel of the stream. Afterward the miners cut a
trail down the cation, making the journey on horseback along its rocky
bed less difficult. There are a few high bars along the sides of the canon,
covered with dead and fallen spruce trees; but the main gravel deposits
are found in the bottom of the gorge itself.

Below the canon the valley of Rapid becomes more open, and large
and extensive gravel flats and high bars are seen on either bank of the
stream. In places the valley contracts among steep and rocky hills to a
narrow gorge, but does not become a canon until fifteen miles below the
fork, where the stream enters a limestone formation, whence, for a distance
of four miles, it is almost impassable for horsemen. Only near the forks
has the timber been destroyed by fire, and elsewhere through the valley of
this stream the hill-sides are covered with pine of good quality, while near
the foothills small groves of oak and elm grow along the banks of the
creek. Inthe more open portions of the valley broad grass flats skirt its
banks or cover the high gravel bars situated at the numerous bends of the

268 GEOLOGY OF THE BLACK HILLS.

stream. Among the rocky hills these flats are wanting, and the forest
extends nearly to the water's edge.

Rapid Creek flows in a parallel course to Spring Creek, at a distance of
four to eight miles to the north, and cutting through the same belt of clay-
slates and quartzites; the description of the rocks of the Spring Creek
district will apply, with some slight modifications, to the rocks of this
valley.

The immense belts of quartz and quartzite so marked on Spring
Creek are not so prevalent on Rapid Creek, but the soft gray and black
clay-slates, with small ferruginous quartz seams, are here extensively devel-
oped. The clay-slates have a tendency to split, under the action of frost
and the atmosphere, into long, slender prisms, parallel to the bedding of the
rock. In some of the cliffs benches of these slates have weathered out,
and the fragments falling down lie in regular piles like cord-wood along
the face of the rocks. These prisms are about 4 feet long, with an irregu-
lar rhombic section 3 or 4 inches across They readily split into smaller
prismatic fragments an inch wide and afoot or more in length. The slates
contain minute crystals of iron pyrites, and the surfaces of the prisms are
stained with oxide of iron resulting from its decomposition. Other strata
of slates are lamellar in structure, and split into thin plates like roofing
slate. Both forms make excellent bed-rock to catch and retain gold.

A mile above a small branch entermg Rapid Creek from the north, is
a low hill, composed of trachyte intruded between the slates. This was the
only occurrence of igneous rock seen in this geological formation south of
Custer Peak, with the exception of the granite of the Harney Peak range.
On this branch float quartz was found, which on breaking showed small
particles of gold, but it could not be traced to the vein from which it had
been derived.

Samples of quartz brought in by the miners from the hills between Rapid
and Box Elder Creeks gave, on crushing, two or three ounces in a mortar,
and panning from four to six fine colors of gold. Gold was discovered in
paying quantities in a number of places along this portion of the valley;
but the miners who staked claims in this district did not open the placers,
and prospected the bars only enough to prove the presence of gold. ‘These

WATER SUPPLY OF RAPID CREEK. 269

deposits of gravel, including both the high bars and narrow flats in the
canon, are known to be valuable, resembling those of the Spring Creek
district, so closely as to render it unnecessary to again minutely describe
them. Geologically, Rapid, Castle, and Spring Creeks belong to one dis-
trict, as they are characterized by the same prevailing rocks and quartz
veins, and the gravel deposits, being formed by rapid streams, with consid-
erable volumes of water and heavy grades, naturally resemble each other.

Reports from Rapid Creek, December 31, 1875, state that ‘the cation
is located from head to mouth, and 10 cents to the pan is considered a low
average prospect in the pay streak.” The water supply is ample for work-
ing purposes; at least double that of Spring Creek. The current is so rapid
that it is difficult to estimate the volume of the stream without making
accurate measurement. It varies somewhat with the season, probably
between 1,000 and 2,000 miner’s inches; being greatest in May and least
in the fall and early winter months.

The descent of the valley, omitting minor bends, is from 70 to 80 feet
to the mile, measured in straight lines. In places the grade is fully 90 feet;
a most advantageous circumstance in working the placers.

Rapid Creek emerges from the cation in the limestone at the edge of
the plains, and flows through the most beautiful valley in the Hills. Long
flats, covered with a rank growth of bottom grass, line its banks, which are
dotted by groves of oak and elm. The side gorges and ravines cutting
through the Red Beds and the variegated sandstone of the top of the Car-
boniferous expose cliffs several hundred feet in height, pictured with sand-
stone of all shades of color from yellow through pink to the darkest red.
A trail known to the Indians as the ‘Race Course,” following the Red
Valley, and completely encircling the Hills at the edge of the plains, crosses
Rapid Creek a mile below the cation. At this point several large springs
of cold water, free from even traces of gypsum, emerge from the Triassic
limestone, and pour each from 50 to 100 miner’s inches of water into the
creek. Three miles farther down a small branch enters Rapid Creek from
the north, formed by a number of fine springs of water issuing from the
foothills about two miles north of the stream, and affording about 39 miner’s

270 GEOLOGY OF THE BLACK HILLS.

inches of water (August 1, 1875), which will prove useful in working the
gravel bars in that, vicinity.

Rapid Creek, above the springs, is a fine stream of water, from 20 to 25
feet wide and 10 to 15 inches deep, with a very swift current. Probably
the volume or the water is not less than 2,000 minevr’s inches in July, and
below the springs 2,500 inches is not too great an estimate for the available
water. For at least five miles along the valley below the mouth of the
cafion the stream is bordered by the largest gravel bars and flats discovered
in the Hills, reaching out to the low ridges of Jurassic foothills, among the
level plains, and capping broad benches of limestone and Red Beds at the
sides of the valley. The amount of gravel brought down by Rapid Creek
and piled up in these deep and extensive deposits is very large; not only
low hills below the canon are covered by high bars at several different ele-
vations, but the broad flats along the stream are made up of a deep deposit
of gravel, composed mostly of limestone and sandstone, intermixed with
some slate and quartz. Several attempts were made by my assistants to
sink prospect holes on these flats along the banks of the creek, but the pits
had to be abandoned at depths of from 9 to 12 feet before reaching bed-
rock, on account of striking springs of water. The loose gravel from these
holes gave one or two colors of gold to the pan, but it was probably quite
a distance to bed-rock where we stopped working, as the gravel was open
and full of small bowlders. To work these flats, if they are found to con-
tain gold in paying quantities, will require the outlay of considerable labor
or capital to drain the bed-rock, but the grade of the valley will admit of
long covered bed-rock drains being put in for this purpose.

At the mouth of the canon the stream flows along the face of the lime-
stone cliffs, and the largest high bars are on benches on the north side of
the valley, from 20 to 30 feet above the present level of the creek. Open
cuts were driven into these bars on bed-rock, finding nearly 20 feet of gravel
and about a foot of pay dirt on soft limestone bed-rock, giving an average
of three colors of gold, or about half a cent to the pan. Similar results
were obtained in prospecting several smaller gravel points at the bends of
the canon for a mile above these bars; and, taking into account the ease with
which these gravel deposits can be ground-sluiced off, with the great vol-

PROSPECTING ON RAPID CREEE. ° ETA

ume of water available for the purpose so near at hand, I think that it is
possible to work them with a good profit. Where the Indian trail ascends
the hill on the south side of the valley are three large elevated bars. The
lowest, at an elevation of about 40 feet above the creek, covers about four
acres, and appears to be 30 feet in thickness. A drift run in on bed-rock
showed a foot of compact cement gravel full of nodules of hematite iron
ore resting on the soft sandstone of the Red Beds, which gave, on testing,
an average of three colors, or about one-third of a cent to the pan.

The bed rock pitched into the center of the bar, which was com-
posed of bowlders and gravel, at least 50 per cent. being limestcne and
sandstone, the rest slate, quartzite, and quartz in all the varieties found
in the area drained by this stream. Above this bar were two others,
at elevations of 100 and 300 feet above the creek, which have been
described in the chapter on “The Deposits in the Foothills.” A similar
deposit covers the foothills on the opposite side of the ravine, just east of
the lower bar; but with this exception ail the elevated bars are on the
north side of the valley, which extends into the plains a mile and a half
wide, bounded on the south by a bare range of Red Bed hills. On the
north, a continuous bar, 30 feet high above the flats, extends from the
Indian trail down to the small branch heading in the cluster of springs
about three miles below. This bar extends along the valley for three
quarters of a mile, and occupies a triangular area of about two hundred
acres, bounded by the small branch entering from the north. On the top
it is as level as a floor, and on testing the gravel at its edge we obtained
in a number of places three to five colors of quite coarse gold, or at least
half a cent to a cent to the pan, although at the edges of the deposit the
gravel was not over 20 inches thick, resting on soft red sandstone of the
Red Beds. For want of time my assistants were unable to thoroughly
prospect this extensive bar, but it was the opinion of John W. Allen, who
made the discovery, that it would pay well when worked by bringing a
good head of water on top and ground-sluicing the gravel and soft bed-
rock. Several bars of this character intervened between it and the Hills,
which gave equally good results on prospecting. In places the bed-rock
was soft, white, decomposed gypsum. Below the branch before mentioned

22 GEOLOGY OF THE BLACK HILLS.

there were no more elevated gravel bars seen, but along the banks of the
creek gravel flats extend as far at least as the outermost ridge of foot-
hills.

I consider that the Rapid Creek district, including Castle Creek, is
destined to be one of the most productive in the Black Hills. For forty
miles along its course its banks are bordered by deep and extensive
placers, forming the largest gravel deposits on any stream in the Hills.

SECTION V.
BOX ELDER AND ELK CREEKS.

Proceeding north from Rapid Creek, a quite extensive area is passed
over, which, while geologically a continuation of the clay-slate and quartzite
belt, presents in its more level surface a strong contrast to the rocky and
broken region to the south. This section is drained by two small streams,
Box Elder and Elk Creeks, whose largest branches head almost at the very
base of Custer Peak.

A view from the top of Custer shows a comparatively flat country, with
low, rolling hills; in places groups of small broken peaks are noticed; but
the topography is very different from that of the region about the forks of
Rapid and Spring Creeks, where sharp serrated peaks rise, one beyond
another, as far as the eye can reach, only exceeded in height and magni-
tude by Harney itself. It is a desolate-looking country. Most of the
timber has been destroyed by fire and large areas are covered with dead
pines. T’o the east, at a distance of ten or twelve miles, the limestone is
seen crossing the hills in an irregular line in a northwesterly direction, and
many of the slate ridges and peaks are, near the outcrop of the limestone,
capped by it and the Potsdam sandstone—the remnants of the great sheet
of Paleozoic rocks which once covered this area and has since been
removed by erosion.

From the base of Custer Peak the course of each creek can be traced
until it cafions in the limestone, generally flowing through small open
valleys or broad grassy swales, which in places, however, are contracted

into a rocky gorge in cutting across the occasional strata of hard quartzites.

CUARACTER OF THE DISTRICT, : 273

The belt of Carboniferous limestone encircling the area of metamor-
phic rocks is only about four miles in width at the foothills near Spring
and Rapid Creeks, but to the north it becomes broader and extends a
greater distance back from the plains into the hills, its western edge follow-
ing along the north side of the valley of Box Elder as an irregularly broken
cliff or wall. Soon after entering the limestone both Box Elder and Elk
Creeks sink in their beds and disappear from five to eight miles from the
plains. The water must escape through subterranean channels, as, a short
distance below where it sinks among the bowlders, the bare limestone bed-
rock is exposed perfectly dry for some distance across the whole width of
the bottom of the canon.

Contrasted with the Spring or Rapid Creek districts, the area of slates
is comparatively flat, and the grade or descent of the stream much less,
becoming greater in the limestone canon, where for long distances the
Box Elder flows in a swift current over bare bed-rock. Box Elder is not
a single or main powerful stream like most of the other creeks in the Hills,
but an aggregate of numerous small branches formed by insignificant
brooks, which do not unite until the stream enters the limestone. Many of
these head branches are mere threads of water, or contain water only in
occasional deep holes, and are dry during a greater portion of the year,
the largest fork being but 6 to 10 feet wide and very shallow. Small
ponds and broad marshy flats overgrown with a swamp of willows and low
bushes are often encountered on the forks of this stream. They are pro-
duced by the beaver in damming back the water in the level valleys, and
from the same cause large and deep beds of black peaty muck have been
formed by the gradual deposition of vegetable matter in these still pools.

Elk Creek is a stream not quite as large as Box Elder, but resembling
it in other respects. For three miles of its course it flows through a narrow
and crooked canon in the slates, then emerges into an open and flat valley,
with broad grass flats skirting its banks, through which it winds for about
three miles, and, entering the great limestone formation, sinks in the bed of
the canon and disappears. Where the dry ravine of this stream opens
upon the red valley at the edge of the plains, several fine springs of excel-

lent cold water burst out from under the Triassic limestone, and form a
18 BH

274 GEOLOGY OF THE BLACK HILLS.

considerable stream, flowing, however, but a short distance before it sinks
and disappears. On lower Box Elder and on the divides along the valley
of Elk Creek there is considerable pine timber which has escaped the
extensive forest fires. The trees are, however, rarely above medium size,
growing very thickly together in dense groves. The rocks of this section
are clay-slates and quartzites, similar to those of the Spring Creek district.
The occurrence of a broad belt of specular slates containing a large
percentage of hematite iron ore, which extends along Box Elder just above
the point. where Custer’s trail crosses it the second time, is peculiar to this
district. Over quite an extensive tract iron is present in the rocks in quan-
tities sufficient to strongly affect the compass. Thick strata of silicious
slates, on being followed, are gradually found to become more and
more ferruginous, until the rock is finally black and brilliant from
the excess of particles of specular iron. Frequently the hematite occurs
perfectly pure, interstratified in thin layers with white quartz, forming
a peculiar rock, the brilliant black of the bands of iron ore contrasting
strongly with the white stripes of quartz, resembling somewhat the
jaspery specular ore of Lake Superior, except that the interstratified
quartz is white and not red. These iron-bearing strata were upturned on
edge, and often 600 to 800 feet broad, with an unknown extent in the
direction of the strike. The hematite was so completely intermixed with
the quartz as to seriously injure the commercial value of the ore. The
thickest layers of pure specular iron which were seen did not exceed
three inches in width; and, except the presence of large quantities of silica,
the ore seems to be very pure and free from iron pyrites and phosphates.
Near Custer Peak an immense ledge of massive milk-white quartz
extends north and south across the hills, conformable to the slates. Resist-
ing denudation, it caps the ridges for a long distance like a wall, and large
fragments detached from it cover the surface of the hill. Samples of the
quartz from this ledge were assayed by Mr. Ricketts, of the School of
Mines, but not a trace of gold was found in it. Where the slates are
extensively developed the quartz veins are generally thin and inconspicu-
ous. An occasional large ledge is, however, seen of the above character;
but among the belts of quartzites broad strata, transformed into impure

VALUE OF THE ORE. : 275

quartz, are found, similar to the “Mammoth ledge” on Spring Creek.
One of these altered strata contained large masses of limonite iron ore
intermixed with quartz, colored and stained by copper, and resembling
closely some specimens of Colorado gold ores. It was a portion of a
quartzite belt dipping 60° to the south, and could be traced east and west
for a mile across the low hills until the outcrop was concealed beneath the
Potsdam sandstone. Several parallel strata of quartz and quartzite were
found within a few hundred yards. That forming the “lode” was from 20
to 40 feet wide, a mixture of massive milk-white quartz and limonite iron
ore, with considerable ‘‘gossan” ore, resulting from the decomposition of
copper and iron pyrites. Samples were carefully taken from the best-
appearing ore in the outcrop of this ledge and submitted to Mr. P. De P.
Ricketts for assay, who reports that the quartz contains small quantities of
gold, but, unless richer than the samples assayed, the deposit is of little
value. Where the outcrop of this ledge was covered by the Potsdam
sandstone the conglomerate forming the lowest layer of that formation was
full of large rounded bowlders partly derived from it. Some of these
bowlders were 3 to 4 feet in diameter, and contained all the varieties of
rock found in the vicinity, including clay-slate, quartzite, ferruginous and
ribbon quartz, and gossan ore, exactly as they occurred in the adjacent
ledges, proving that very little change had taken place in the slates and the
inclosed quartz veins since the commencement of the Potsdam period.
Previous to the deposition of this conglomerate the slate and quartzite
rocks were subjected to a very great erosion, which must have removed a
great thickness of the strata, but since the elevation of the Black Hills the
Archean rocks in this district have been but little denuded, the remnants
of the Potsdam sandstone capping hills and ridges from 50 to 150 feet
above the present surface; and although the formations which covered this
area at the close of the Cretaceous period have been swept away over
extensive tracts, the erosion has extended but a short distance into the
slates. In the Spring and Rapid Creek districts, however, the slates and
quartzites have been very greatly denuded and furnished a large amount of
material to form the placer gravels.

On Box Elder the gravel deposits seem to be largely composed of

276 GEOLOGY OF THE BLACK HILLS.

pebbles and bowlders from the disintegration of the Potsdam conglomerate,

and only a small portion is derived from the more recent erosion of the_
slates. Partly from this cause and the flat character of the region, there

are few elevated gravel bars on this stream of any practical value. The

slate benches and low hills at the bends and forks of the creek are covered

in places with a thin layer of gravel, which, wherever tested, gave never

more than a color of gold.

There are a few low bars on the larger branches of Box Elder which
may be found to contain gold in workable quantities, but the only gravel
deposits of any size are in the, flats along the stream and its numerous
branches. Several days were spent in prospecting on this stream by a
party of twelve miners who were assisting me at the time, but we failed to
find gold in paying quantities in any of the flats or bars which were tested.
Prospecting in the cafion in the limestone, the bed-rock was found bare in
many places, but not a color of gold was obtained either from the small
gravel deposits or by “crevicing” in the bed-rock, though tests were made
in every favorable-looking place for several miles down the canon.
Below where the water sinks a high bar was found at the forks of two
canons, nearly 100 feet above the present channel, but no gold could be
found in it on panning.

The miners who prospected on Box Elder the past summer before they
were removed from the Hills did not find gold in quantities enough to
encourage them to stake out claims or form a district.

Elk Greek was explored by the topographical party, but was left un-
touched by the miners, very few being aware that such a stream existed.
Gravel flats and low bars are reported on this creek between the canon in
the slates and the canon in the limestone, which promised well as far as
could be judged from external appearances. In reviewing this district,
which it is but justice to state has been only very little prospected, I may
record a small water supply which fails in many places in the smaller
branches after August, a grade hardly greater than that on French Creek,
and gravel deposits which are comparatively of moderate extent and not

found to be rich in gold as far as they have been tested.

eJ

ba |

CHARACTER OF THE DISTRICT. 2

SECTION VI.

SPEARFISH AND BEAR BUTTE CREEKS.

These streams, emptying into the Redwater and the Belle Fourche,
drain the extreme northern section of the main range of the Black Hills.
Rising near the limestone divide between Crook Tower and Custer Peak,
a spur of the great western mesa, they cut through a narrow belt of slate,
quartzite, and igneous rocks before entering the limestone formation en-
circling the Hills. This belt of slates, contracted between the two walls of
Carboniferous limestone, is an extension of the quartzite and clay-slate
formation covering so broad an expanse of territory on Spring and Rapid
Creeks.

From the headwaters of Elk Creek it extends in a direction a little
north of west for twenty miles until terminated by the limestone ridge
between Spearfish and Floral Valley. Covering about one hundred and
fifty square miles, this area of metamorphic rocks has up to the present
time been only partly explored and prospected, owing to the exceedingly
rugged and impenetrable character of the region. It may aptly be called
a ‘‘pathless wilderness”; even game-trails are rarely seen, and the surface
of the country is so cut up by numerous narrow and abrupt canons as to
be impassable for wagons, and extremely difficult and fatiguing to traverse,
even with pack-mules. The bottoms of the canons and gorges are choked
with a tangled jungle of willow and grape-vines, and often beaver-dams
extend from cliff to cliff, producing bogey mud flats, whose depths we tried
to explore, but found no bottom in the fluid black ooze. Only in places
ean the walls of the canons and ravines be scaled, while the ridges and
divides, steep, and broken into innumerable sharp, serrated peaks, are cov-
ered by timber, frequently blown down by the wind and subsequently
overgrown with thickets of aspen. The slow progress made through this
wilderness soon wears out both horse and rider, and the former, instead of
being an assistance, has to be led and pulled along most of the way. To
find yourself at a “jumping-off place,” the end of some sharp ridge between
two streams, to descend hundreds of feet into the bottom of the canon, to

278 GEOLOGY OF THE BLACK HILLS.

slowly climb the opposite side, at last reaching the top of the divide
exhausted and out of breath, only to find that you are on the crest of
another similar ridge ending in a few hundred yards; to continue this
wearisome march for hours and only travel four or five miles in a straight
line; such was one day the experience of the party on Bear Butte Creek.

The more mountainous character of the country and the greater prey-
alence of limestone in the area drained by Spearfish Creek make the cations
on that stream the deepest and longest found in any part of the Hills. One
of the parties exploring Spearfish entered the main canon near its source to
the north of Crook Tower, and, being unable to extricate themselves and
horses, were obliged to force their way through its whole length to where it
opens out into Redwater Valley, some thirty miles from its head. Most of
the distance they waded their horses down the bed of the stream, which in
a swift current flowed over smooth limestone rock. _In places the vertical
cliffs of the cation rose from the water’s edge, and nowhere did they find a
place where the cliffs could be scaled without abandoning the horses. The
party reported that the rocks seen were mostly limestone. A narrow belt
of slates for some distance forms the base of the cliffs, the tops being Pots-
dam sandstone or the limestone of the Carboniferous. This is also true
for those branches of Spearfish rising near Terry Peak, where the Pots-
dam covers quite an extensive area, while the narrow canons are cut
through it into the slates.

Near Black Butte, at the mouth of Spearfish Caron, the limestone
forms the west wall of the main gorge, while the eastern branches drain a
very mountainous track, consisting mainly of igneous rocks. Spearfish
emerges from the canon with a swift current, equaling, if not exceeding,
Rapid Creek in volume of water, and, emptying into the Redwater, forms
by the union a fine river, a branch of the Belle Fourche, known to the In-
dians as Deepwater.

Just above the mouth of the cafion several small streams enter Spear-
fish from the southwest, heading in the ridge between Spearfish and Floral
Valley. On these branches a party of miners discovered rich placer de-
posits the past summer which have since been more fully prospected and
developed. Wishing information in regard to the location of the new dis-

OPINIONS OF THE MINERS. 279

covery, I wrote to Mr. T. H. Mallory, one of the original discoverers of the

district, and received the following reply :
HILL City, January 5, 1876.

DEAR SiR: Iron Creek runs into Spearfish above Crow Peak. Bear Creek runs
into Spearfish lower down and near the buttes. Sand Creek runs into Redwater.
These streams all head nearly together, and they, with their smaller tributaries, make
a large mining district. They are richer, too, than anything on this side of the hills.
One pan of dirt on the discovery of Bear Creek contained $27. I have a report that
another’small stream running into Spearfish from the southeast is still better than any-
thing yet found. How much truth there is in it Bottsford and I will know in a few
days. Isend you a little gold from Sand Creek; it has been retorted and does not

look bright.
THOS. H. MALLORY.

W. P. JENNEY.

The rocks of this new district are reported to be granite (trachyte ?)
near the heads of the creek, and lower down the gulches the bed-rock is
limestone, but equally good gold deposits are found upon it.

The sample of gold sent is quite different from that from Spring Creek,
the particles being much smaller, more ragged and irregular in shape, and
but little water-worn. So large a proportion of the gold is fine dust, that
it is not easily saved without the use of quicksilver in the sluices.

Concerning the Bear Creek discovery, I have received the following
communication from Mr. George W. Corey, of Cheyenne :

CHEYENNE, Wy0., December 20, 1875.

DEAR Sir: I have some fine specimens of Black Hills gold that I will send you.
They were taken out of Bear Gulch by Frank George de Oliver, who would not sell
them, but let me take them to send to you. He took out with a rocker ineight and a
half days $165. One lump which I have weighs one and a half ounces. * * *

GEORGE W. COREY.

WALTER P. JENNEY.

Bear Butte Creek drains the northeastern portion of the Black Hills,
taking its name from a solitary igneous peak near which it flows, some eight
miles from the main range among the open plains. This stream is formed
by two main branches uniting in the Red Valley at the foothills; one, the
east fork, rises to the north of Custer Peak; the other, known as White-
wood, heads near Terry Peak. None of the branches have flowing water
within five miles of the edge of the plain, as they sink even before reaching
the limestone formation. The east fork was only explored by the topo-

280 GEOLOGY OF THE BLACK HILLS.

graphical party; and, for want of time and suitable transportation, my
assistants were unable to properly prospect and explore the branches of this
stream.

Whitewood, heading on the east side of Terry Peak, unites with
Deadwood, a branch rising on the northwest side, forming a swiftly-run-
ning stream flowing nearly 300 miner’s inches of water, but sinking a short
distance below the forks, and thence continuing as a dry canon through the
limestone to the plains.

Whitewood and its branches flow through narrow and deep gorges
excavated in the slates and igneous rocks, with the Potsdam sandstone
capping in many places the tops of the narrow ridges between its numer-
ous branches. The base of the Potsdam is here the usual conglomerate of
round water-worn quartz pebbles and small bowlders. The intrusion of
the igneous rocks has penetrated the Potsdam as well as the slates and
quartzites, and has often metamorphosed the sandstone so that it is unre-
cognizable, except that traces of its stratification are retained, and the strata
are observed resting at a low angle unconformably on the upturned edges
of the slates.

The most common form of this altered Potsdam is a brownish granular
rock, full of feldspar crystals, irregularly distributed through its mass _Lo-
cally, this metamorphosed sandstone is seen as a hard granular rock, break-
ing with a sharp conchoidal fracture, without any traces of crystalline min-
erals, and specimens in their colored and burnt appearance resemble frag-
ments of pottery ware. The slates and quartzites are similar to the rocks
of the Spring Creek district, and broad strata of quartzite, intermized with
limonite and white quartz, resemble closely the Mammoth ledge on that
stream, except that here small ramifying veins of white quartz not more
than half an inch wide intersect the dark-gray quartzite like a net-work;
another evidence that these altered strata are the result of the action of
solutions depositing silica permeating the formation. The strike of the slate
and quartzite belt is observed to be east and west, at a point a few miles
north of Terry Peak. This formation over great areas is concealed by the
intrusion of large masses of igneous rocks, forming the more prominent
peaks in the district, as Terry, Custer, Crow, Black Butte, &e.

IGNEOUS ROCKS. 281

The intrusions of trachyte in the slates usually form dome-shaped
peaks, having penetrated or forced to one side the supermeumbent strata
of Potsdam and Carboniferous. Though in this region trachyte forms in
places quite extensive ridges connecting the peaks and covering large
areas, no narrow dikes were anywhere observed traversing the slates, and
this occurrence of eruptive rocks in dikes so common elsewhere in the
Rocky Mountains seems to be wanting in the Black Hills.

The time of this eruption of igneous rocks appears to have been coeval
with the elevation of the Black Hills at the close of the Cretaceous period;
the intrusion of feldspathic porphyry, forming Crow Peak, has upturned all
the different formations from the Potsdam to the Jurassic; the Cretaceous,
having been removed by erosion, is not seen in the vicinity. These igneous
rocks are very varied in appearance and character, but may be generally
classed either as trachyte or feldspar-porphyry, though merging in all
gradations into each other, so that an exact classification is extremely difh-
cult. Greenstone occurs both as an olive-green rock without any traces of
crystallized minerals and breaking with a fracture-like jasper, and also with
small feldspar-crystals scattered through its mass forming a greenstone-
porphyry. The rock composing Terry Peak seems to be wholly com-
posed of white feldspar, an aggregation of small crystals of that mineral,
resembling a fine-grained granite, without quartz or mica Custer Peak is
formed by the intrusion of a peculiar massive gray rock, with an exceed-
ingly close and uniform texture, resembling a compact gray limestone in
appearance more than an igneous rock. Black Butte, a high peak on the
east side of Spearfish Caton near its mouth, is made up of a genuine
trachyte.

Near Camp Terry, a few miles north of Custer Peak, the prevailing
rocks are garnetiferous mica-schists, resembling the rocks of the French
Creek district. This occurrence of an area of schists in the clay-slate
formation is not easily explained. Possibly the irregular line of contact
between the two divisions of the Archean may here extend a greater dis-
tance to the east. Among these mica-schists on the head branches of the
east fork of Bear Butte Creek the soldiers found gold in the gravel
deposits of the side gulches of the stream, and a piece weighing about half

282 GEOLOGY OF THE BLACK HILLS.

a pennyweight was obtained from one of their prospecting pits near Camp
Terry. Gravel deposits of considerable extent are reported in the valleys
of the branches of the east fork, but have not as yet been prospected by
the miners. The area drained by this fork is more open and less rugged
than the territory to the west, resembling the Elk Creek district, which it
adjoins. Gold has been discovered by the miners on Deadwood and White-
wood Creeks and the numerous gulches running into them in the vicinity
of Terry Peak. The placers are quite extensive, and in most places the
bed-rock is reported to be near the surface, and the gold is doubtless
derived from the disintegration and erosion of the igneous rocks as well
as from slates and quartzites.

Having detected gold in similar trachytes in the Bear Lodge range,
I consider its occurrence in rocks of igneous origin in this district as
extremely probable. The following letter from Mr. T. H. Mallory, formerly
one of my assistants in prospecting the gold field, gives the result of his
explorations on the branches of Bear Butte Creek since the return of the
expedition:

HILL City, DAK., January 31, 1876.

DEAR SiR: Botsford and I have just returned from a trip to the north. We
made locations on Whitewood, a large stream that rises around the northeast side of
Terry Peak and runs down to the Belle Fourche. Starting from the point where the
creek runs into the lowlands not of the cation, forming bars, up it to the west fork, or
Deadwood, as it is called, there are no better paying mines for a poor man in the Hills.
The ground prospects in the creek and on the bars, all the way down to bed-rock, an
average of about two cents to the pan in fine gold. It issaid to be the same on Dead-
wood. The length or extent of locations on these creeks begins at the mouth of White-
wood, and then running thence up Deadwood, makes a distance of twenty-five miles,
all good mining ground.

A small gulch running into Deadwood, called Black Tail, is said to be good.
These mines will certainly pay from $10 to an ounce a day to the man when worked in

the spring. They are easily opened, for the bed-rock is not deep, like it is on Spring,
Castle and Rapid Creeks.

T. H. MALLORY.
W. P. JENNEY.

MATO TIPI. 283

SECTION VII.

THE BEAR LODGE COUNTRY.

Forming the extreme northwestern part of the Black Hills, and sep-
arated from the main range by the broad open valley of the Redwater, the
Bear Lodge country has a geological system and topography which, while
a miniature counterpart of that characterizing the main range of the Black
Hills, is a distinct uplift, produced by the intrusion of the igneous rocks
forming Warren Peaks. Covering an area of nearly one thousand square
miles, mostly included between the Redwater and the Belle Fourche, this
region takes its name from a singularly-shaped trachyte butte, ‘‘ Mato Tipi,”
or “The Bear’s Lodge.” Surmounting a hill near the north bank of the
latter stream, this butte forms the most conspicuous landmark in the region,
resembling the base of a ruined and crumbling column, with its shaft nearly
500 feet in height, and the top 1,127 feet above the water in the Belle
Fourche.

Warren Peaks, a cluster of high rolling hills, grass-covered, and
nearly destitute of timber, are the most elevated points in the Bear Lodge
range, almost equaling Harney Peak in height, their tops being from
6,700 to 6,800 feet above the level of the sea.

Occupying an area about four miles in diameter, these peaks are com-
posed of coarsely-crystallized feldspar-trachyte, apparently destitute of
quartz, but sometimes containing hornblende and mica, and often having in
the arrangement of the crystals of feldspar, in a granular matrix, a struc-
ture-like porphyry. This rock, which is seen of different shades of gray,
yellow, and reddish-brown, seems to be quite readily decomposed by
atmospheric agencies, and, crumbling away, has given rounded surfaces
and outlines to the hills and ridges. Standing on any of the higher of
Warren Peaks, the view shows at once the distant character of the uplift
and the peculiarities produced by it in the topography of the region.

The central peaks are surrounded by others of less elevation, between
which rayines radiate in every direction like the spokes of a wheel from

284 GEOLOGY OF THE BLACK HILLS.

the hub, and give rise to small streams, flowing outwardly from the center,
draining the area. Those to the southeast and south empty into the Red-
water; the rest flow into the Belle Fourche or its branches.

To the north an extensive tract is observed wooded with pine of me-
dium size. Scattered groves occur elsewhere on the ridges and in the
ravines, but large areas are comparatively destitute of timber, and broad
grass-covered divides are seen to the west and northwest between the
streams emptying into the Belle Fourche.

To the east, across the broad valley of the Redwater, excavated in the
gypsum and sandy clays of the Red Beds, Crow Peak is seen, an angular
blue-black butte, forming the most northern peak in the main range of the
Black Hills. Between it and Inyan Kara stretches the great limestone for-
mation so extensively developed on Floral Valley and the head branches
of the Redwater.

To the west (magnetic), some twenty miles away, Bear Lodge Butte
and the Little Missouri Buttes appear in line. From this distance the
former resembles in appearance the huge stump of a tree, its surface
curiously striated vertically from top to base, and, being perched on the
crest of a high, flat-topped ridge, it becomes a very prominent landmark,
which, once seen, is so singular and unique that it can never be forgotten.
Although the Bear Lodge country is an elevated region, and the different
streams have a considerable fall before reaching the Belle Fourche, yet the
topography is quite peculiar in the prevalence of long, flat-topped ridges or
mesas between the narrow and deep valleys and canons of the creeks
This is due to the resistance to erosion offered by hard and continuous
strata of sandstone of the Jurassic and Cretaceous formations, which are
here almost horizontal in their bedding, with a gentle slope away from
Warren Peaks.

In a series of annular belts the different geological formations outcrop
around the central nucleus of Warren Peaks. In passing down any of
the numerous radiating ravines of the streams for three or four miles all
the several members of the section are successfully encountered in the order
of their deposition, from the Potsdam to the Dakota sandstone of the Cre-
taceous. Upturned at an angle of about 20° by the intrusion of the tra-

POTSDAM SANDSTONE. 285

chyte the Potsdam sandstone rests against the slopes of the outer circle of
hills. Its lower layers are so metamorphosed by the heat and chemical
solutions accompanying the upheaval, that they merge imperceptibly into
the igneous rock, until strata which are probably altered sandstone cannot
be distinguished from coarsely-crystalline trachyte. Near the base of the
Potsdam formation, between strata of unmistakable sandstone, a mass of
teldspar-trachyte was observed, which had in the eruption escaped between
the layers and slightly altered the adjacent surfaces of the inclosing rock.
But more frequently the metamorphism seems to have been the result of
the action of heated solutions forced between the layers of the sandstone,
altering the surface of the fracture and transforming the sedimentary rock
into a feldspar porphyry.

Layers of the soft brown sandstone extending horizontally for some
distance had been altered in this manner, the rock being shot full of gray
feldspar crystals, from one-fourth to one-half an inch long, irregularly dis-
tributed through it.

On the west slope of Warren Peaks a layer of blue slate occurred,
inclosed in the trachyte, but conformable in its bedding to well-marked
Potsdam about 50 feet above it, and was probably formed by the action of
heat on a layer of clay-slate in the base of the Potsdam. Here this for-
mation is full of fine specimens of the large fucoids so characteristic of the
Potsdam sandstone in the Black Hills, and great masses of the upper layers
of the rocks are perforated by the borings of marine worms. These fossils
are found unaltered within a few feet of the trachyte, and would seem to
show that the heat accompanying the upheaval of the range and the intru-
sion of the igneous rocks was not very intense. At the south of the peaks
the whole thickness of the Potsdam sandstone has been so metamorphosed
that it cannot be recognized, except by the evidences of an indistinct stratified
structure, and its position under the Carboniferous limestone. The altered
sandstone on that side is a quartzite more or less porphyritic, with feldspar
crystals merging in all gradations into a crystalline rock resembling tra-
chyte. Even here the metamorphism seems to be more from the action of
heated chemical solutions permeating the rock than from the direct action
of heat, producing a semi-fusion of the Potsdam strata. The Carboniferous

286 GEOLOGY OF THE BLACK HILLS.

limestone succeeds the Potsdam, apparently conformable to it, and forms
an eneircling range of low white hills around Warren Peaks, at a distance
of two or three miles. The whole thickness of this formation is at least
600 feet, including the overlying massive sandstones.

The limestone shows but little evidence of metamorphic action, though
in places the trachyte has broken through this formation and appears at
the surface, altering slightly the upper sandstone. Beyond the belt of
Carboniferous, which is nearly two miles wide, the Triassic limestone and
the Red Beds occupy a narrow ring, succeeded by an expanse of sandstone
and clays of Jurassic age, extending for miles across the country. The
tops of the ridges are formed by a ferruginous massive sandstone, probably
the Dakota sandstone, and where it has been removed by erosion the harder
layers of the Jurassic cap the hills and the mesa divides between the
stream.

In the interior area of Warren Peaks no Archzean strata were found,
and the slates, quartzites, and schists so largely developed in the main
range of the Black Hills were here entirely wanting. The rocks of this
district seem to be singularly free from quartz in any form. About five’
miles southeast of Warren Peaks, near the head of a branch of the Red-
water, a fault in the strata exposes a fine section of the Potsdam sandstone,
with its lower layers full of slate and quartzite pebbles, but unfortunately
the base of the formation was covered by a talus, and the rock on which
it rested could not be seen. On the north side of the area of igneous
rocks a trachyte composed of feldspar and black mica was observed, and
near by several large loose bowlders of white quartz were embedded in
the surface of the ground, but the ledge from which they were derived was
not found. Black hornblende also appeared as a constituent mineral, asso-
ciated with feldspar, in the rocks of this district.

Half a mile northeast of the central peaks a gold-bearing ledge was
discovered and traced in a northwest and southeast direction for several
hundred yards. On examination it was found to be irregular in shape,
without any well-defined walls or boundaries, and merging on all sides
into the adjacent trachyte rocks. The rocks composing this peculiar forma-
tion were exceedingly varied in character and appearance, and a score of

GEOLOGY OF THE BEAR LODGE DISTRICT. 2387

different specimens were collected in a radius of as many yards. The
prevailing rock was a very coarsely-crystalline feldspar-porphyry, with a
fine porcelain-like matrix, breaking with a sharp conchoidal fracture. The
feldspar crystals were often very perfect, and from an inch to two inches
long. Flat and thin crystals were common, often joined together, with the
shorter axis of one reversed, as ‘‘ twins.” The specimens varied in color
from light yellow or yellow-brown to gray, and large masses of rock in
the middle of the “ledge” were made up of feldspar intermixed with
irregular masses of limonite iron ore and black oxide of manganese.
Bowlders of iron and manganese which would weigh several hundred
pounds were scattered over the surface of the ground. The mineral was
solid, compact, and exceedingly heavy, but the two oxides were distinct in
the mass, though often closely intermixed. Manganese and limonite
occurred, filling the spaces between the large feldspar crystals and impreg-
nating the rocks irregularly throughout until it resembled a “ breccia.”
Evidences of an octohedral or cubical crystallization in the limonite indi-
cated that it was derived from the decomposition of iron pyrites, and traces
of the latter mineral were found on breaking the rock.

No gold could be detected in this formation by the eye; but, suspect-
ing its presence, the different specimens collected were carefully sampled
and submitted to Mr. P. de P. Ricketts for assay. The result showed the
presence of a decided trace of gold, probably contained in the iron and
manganese oxides.

Prospecting in the dry ravine a‘short distance below this ledge, the
gravel from off bed-rock was found to be largely composed of material
derived from the disintegration of the ledge. Twelve fine colors of gold,
or about half a cent to the pan, was obtained as an average of several
tests, and each time nearly a pint of gravel and pebbles of manganese and
limonite was left in the pan after washing out the lighter clay and feldspar.
It would seem probable that the whole of the gold contained in the gravel
in this ravine had been derived from the decomposition and denudation of
the above ledge. .

The occurrence of gold in trachyte without any quartz being asso-
ciated with it has been previously reported from several mining districts in

288 GEOLOGY OF THE BLACK HILLS.

the West, but this is the first instance that has come under my personal
observation.

Descending the ravine about half a mile traces of previous explorers
were found. Several prospecting holes had been sunk near the stream
and considerable work done in the vicinity, probably by a small party of
miners early in the preceding spring, as small aspen trees which they had
cut down in clearing the ground for working showed half-grown leaves
dead and shriveled, but still clinging to the twigs. A number of these old
prospecting pits were bailed out, the gravel obtained from off bed-rock, and
tested by panning. But in no case did we find gold in paying quantities ;
half a cent to the pan being the highest result of the trials. It is probable
that the miners who dug these holes obtained discouraging prospects, or
they would not have abandoned the district without making it known.

Exploring a number of small streams rising near Warren Peaks, flow-
ing to the north and east, gold was found in gravel deposits in the flats
along the banks of the creeks in several places, but nowhere in paying
quantities, though from want of time we were unable to thoroughly test
all the different ravines in this district. The cluster of hills of igneous
rocks which have yielded the gold are but four to five miles across. The
gravel deposits formed by the creeks extend, however, for some distance
down the valleys, beyond the outcrop of the Potsdam, and are found rest-
ing on limestone bed-rock, so that the district is really elliptical in area and
six to eight miles in diameter, covering an area of from forty to fifty square
miles. The streams being small and the wash not very great, there were
no high-gravel deposits, though one or two bars covering about an acre
were observed occupying flats elevated 3 or 4 feet above the creck.
The gravel was 2 to 5 feet deep, composed wholly of feldspar and the soft
plastic clay resulting from its decomposition, intermixed with considerable
iron and manganese pebbles derived from the ledges. The valleys of the
creeks are not deep, but are narrow, contracted, and overgrown with
thickets of willow, so that only at intervals are gravel flats of any consid-
erable size found along their course. The most extensive of these bars
were found near the outcrop of the limestone, the bed-rock being soft cal-
careous sandstone of the Carboniferous age. These deposits were situated

AURIFEROUS GRAVEL. 289

so that they could be readily worked, but only yielded, on testing, from
one-eighth to one-half a cent to the pan in very fine dust gold.

The gold is derived from the igneous rocks forming Warren Peaks,
most of it apparently from the manganese and limonite ledge on the north-
east slope, as the largest quantities were found in the ravines heading near
that point. The intrusion of the trachyte forming the peaks having dis-
turbed the Cretaceous sandstone and the underlying beds, it is probable
that the Bear Lodge range was coeval with that of the main range of the
Black Hills at the close of the Cretaceous period, and that the gold in the
trachyte was simultaneously deposited. In reviewing this small district,
which is very interesting scientifically, even if the deposits of gold should
not be found of workable richness, it may be stated that the bars are of
limited area, and usually shallow deposits of feldspar gravel. The gold is
fine, and up to the present time has not been found in remunerative quan- |
tities. The water supply is small, but probably sufficient for working pur-
poses during the spring months. The district is remarkable in the occur-
rence of gold without any quartz whatever being associated with it, and in
the fact that the gold is derived from feldspar trachyte-porphyry of so
recent a geological age.

SECTION VIII.

DEPOSITS OF AURIFEROUS GRAVEL IN THE FOOTHILLS.

A belt of gravel deposits, resting usually on the Red Beds near the
edge of the plains, extends from Red Canon Creek, in the extreme southern
end of the Black Hills, all along the southeastern foothills, across the val-
leys of Minnekata, Amphibious, French, Wiwi, Whiskey, Spring, and Rapid
Creeks to Box Elder, where the deposits thin out and disappear. On exam-
ination these gravel beds seem to be river deposits, though in places they
cap hills 300 feet above the present bed of the nearest stream. Where the
divides between the creeks are quite wide, at the edge of the plains, the
gravel is seen to be thickest and most extensively deposited near the valleys
of the streams, and to thin out toward the crests of the divides. The gravel

appears to have been deposited by the water at the point where the power
19 BH

290 GEOLOGY OF THE BLACK HILLS.

of the stream became insufficient to transport farther in large quantities
bowlders of this size and weight, and the beds resemble somewhat shore or
estuary deposits, such as are formed near the mouth of a stream emptying
into a lake or sea. These gravel banks have been formed since the eleva-
tion of the Black Hills, and the great Tertiary sea which gave rise to the
extensive beds of that age in the valleys of White River and the South
Cheyenne may have reached to the foothills of this range. A gravel
“wash” from the Black Hills is found all over the surface of the plains to
the north, east, and south of the range. Near the Cheyenne this gravel
forms a conglomerate 6 feet in thickness between the top of Cretaceous No.
5 and the base of the White River Tertiary, and also occurs as scattered
gravel and bowlders on the tops of the Tertiary hills, showing that it has
been deposited since the close of the Cretaceous period, both before and
after the later Tertiary. These gravel beds are made up of a mixture of
bowlders and pebbles from all the harder rocks found in the different geo-
logical formations on the eastern slope of the Black Hills, including granite,
trachyte, schist, slate, quartzite, and quartz in all its varieties, mixed with
a variable proportion of sandstone and limestone from the disintegration of
the Potsdam, Carboniferous, and Red Beds.

The preponderance of any particular rocks in the gravel seems to be
the result of the position of the deposits and the circumstances of influencing
the erosion which produced it. The more elevated beds contain a less pro-
portion of limestone and sandstone bowlders, mingled with those from the
Archean rocks, than the deposits at lower levels, formed after deep gorges
had been cut by the streams through the recent formations. A layer of
gravel a few inches in thickness covered the lower foothills near Box Elder
Creek, but the deposits were thin and spread out over a considerable area.
It was impossible to prospect them for gold, as there was not a drop of
water in the bed of the stream for several miles up the cation. This pecu-
liar formation of high gravel-capped hills does not become extensively
developed north at the valley of Rapid Creek, although a thin wash of lime-
stone and sandstone bowlders, mingled with a little quartz and slate, covers
the foothills as far to the north and west as the forks of Spearfish and
Redwater.

AURIFEROUS GRAVEL. 291

Where Rapid Creek bursts through the foothills and flows out on the
plains are very extensive gravel beds of this character, evidently deposited
by the stream at different periods as they cover the tops of hills at three
distinct elevations, respectively, at about 50 feet, 100 feet, and 300 to 350
feet above the present bed of the creek. The lowest of these deposits occu-
pies benches and flat-topped hills formed of the soft red sandstone of the
Red Beds. The gravel was mostly composed of limestone and sandstone
bowlders, mingled with quartz, slate, and ferruginous quartzite. The next,
also resting on the Red Beds, was of similar character; not more than 50
per cent. of the gravel was derived from the metamorphic rocks. Both of
these deposits were on the side hills of the valley, in places forming banks
or terraces 20 to 30 feet in height, and should properly be classed as high
bars. The gravel from off bed-rock, obtained by drifting into the face of
these bars a distance of 4 or 5 feet, gave one to two colors of gold to the
pan. The highest gravel deposits were in places 30 to 40 feet in thickness,
capping the tops of the hills of Carboniferous and Triassic limestones, often
at a considerable distance from the present valley of the stream ; the lower
layers contained water-worn bowlders, 1 to 2 feet in diameter, of quartz,
slate, quartzite, granite, and trachyte, both feldspathic and hornblendic, but
scarcely a trace of limestone or sandstone rocks are found in these more
elevated deposits. Wherever tested the gravel from off bed-rock gave small
quantities of gold on panning.

On Spring Creek, below the limestone cafion, prospecting was out of
the question for want of water, though it is probable that in the early spring
months this stream flows out into the plains.

In the dry side ravines of Whiskey Creek, among the Red Beds, gold
was discovered by a party of miners entering the Hills. Prospecting up a
dry gulch, they obtained twenty-five colors of gold from the dirt shaken
from the roots of a small bush growing in a narrow crevice in the bare
sandstone bed-rock at the bottom of the ravine. This locality, known as
the ‘‘ Rosebush diggings,” derived its gold from the gradual washing down
into the ravines of the gravel deposits capping the hills by the action of
occasional heavy rains, when for a short time a stream of water would flow
through the gulch and sluice the gravel accumulated in it, the gold being

292 GEOLOGY OF THE BLACK HILLS.

caught in the crevices of the bed-rock, while the dirt was swept away.
Prospecting in one of these side gulches, about half a mile from the main
stream, the dirt from the crevices in the bed-rock was found to yield from
5 to 15 cents to the pan. The gold was in fine particles, associated with
small red garnet crystals, derived from the schists in the neighborhood of
Harney Peak. This ravine was excavated about 200 feet in depth through
the Red Beds. Its bottom was formed of a pavement of the upper layers
of the Carboniferous sandstone, while the hills on both sides were covered
with a deposit of slate and quartz gravel which had furnished the gold.

A mile below, the small side gulches in the Red Beds afforded in places
5 to 10 cents to the pan of gold, but the supply of water at this time (July
20) was so small that the miners decided to give up prospecting in the
vicinity and abandon the diggings until the spring rains should fill the
water-holes and make it possible to work the pay dirt in rockers, if any
deposits rich enough for that purpose should be discovered.

About five miles south of Whiskey Creek, at the edge of the plains, a
conglomerate 30 feet in thickness caps hills 100 to 150 feet in height, of the
soft sandstone of the Red Beds. The conglomerate is composed of granite,
quartz and slate bowlders, cemented by sand and lime into a loosely-coher-
ing “cement,” the lower layers of which contain quartz bowlders 1 to 4
feet in diameter. The small gulches in the vicinity are full of the quartz
gravel, resulting from the decomposition of the conglomerate, and undoubt-
edly contain gold; but unfortunately there was not a drop of water any-
where to be found in the neighborhood, and I was obliged to relinquish the
attempt to prospect them. Similar gravel deposits encircle the foothills,
crossing the valleys of French, Amphibious, and Minnekata Creeks, and
in this connection it would seem not inappropriate to give a tradition relat-
ing to the gold deposits in this portion of the Hills.

Toussaint Kensler, a half-breed Indian, who had worked in the gold
mines of Alder Gulch, Montana, was confined in prison under sentence of
death for murder. Escaping, he was not heard from for a long time; when
he appeared at the agencies, having in his possession several goose-quills
filled with gold dust, and a fossil skull which he had found in the Bad Lands
on his way from the diggings he reported he had discovered. Being rear-

DISCOVERY OF GOLD IN THE BLACK HILLS. 293

rested, he was taken back to prison, and hung for the crime for which he
was originally sentenced; but before the execution he drew a map of the
locality where he claimed to have discovered gold, and the routes traveled
in going to and from the agencies, with the distances and names of the
principal streams marked unmistakably in the sketch. He stated that he
followed down Hat Creek to the south fork of the Cheyenne, crossed that
stream, and on the second creek of any size entering the Cheyenne from
the north below the mouth of the Hat Creek he discovered gold about ten
miles from the Cheyenne, among low hills, but outside the main range of
the Black Hills. He described the locality as among hills capped with high
and thick gravel bars of large size. Here he found rich gravel, and in a
short time obtained his sample of gold by washing the pay dirt in a small
tin dish.

A tracing of the map drawn by Kensler is before me while I am
writing. On comparing it with the map drawn by Dr. M’Gillyeuddy, topo-
grapher of the expedition, I find that it agrees very closely with the latter
in regard to distances, directions, and the bends of the Cheyenne, and that
the stream on which Kensler discovered gold was either Amphibious Creek
or French Creek, probably the former. Quite extensive gravel deposits are
known to occur in the vicinity, and it is probable that Kensler was the first
discoverer of gold in the Black Hills, obtaining his pay dirt from the small
ravines and gulches among these gravel beds, where the gold had been
concentrated by heavy rains. Should these elevated gravel deposits on
further exploration be found to contain throughout their thickness sufficient
gold to warrant working by the hydraulic process, water can be conveyed
from the streamsin the Hills to them in many places under a considerable
head, as they are elevated only about 3,800 feet above the sea, while the
streams, fifteen miles in the interior, are flowing through valleys at an ele-
vation of 5,000 feet. On Rapid Creek, a large volume of water, at least
2,000 minevr’s inches, under a head of 75 feet to the mile, can be made
available for working these high bars above the valley, at a moderate
expenditure of capital and labor required to construct the flumes. Only
two streams, Rapid and Minnekata, having gravel deposits of this character
in their valleys, form a continuous stream of water to the Cheyenne; tlie

294 GEOLOGY OF THE BLACK HILLS.

rest all sink in their beds among the foothills, several miles from the plains.
Among some of these dry ravines, cutting through the gravel deposits,
miners in the future may make good wages washing the earth from the
bottoms of the gulches in rockers during the early spring months, when
there is sufficient supply of water in the vicinity.

SECTION Ix.

CONCLUSION.

Very few minerals were found during the exploration, and until the
quartz ledges have been more thoroughly prospected and opened it is pre-
mature to discuss the occurrence or non-ocecurrence of any of the valuable
minerals or ores in the Black Hills.

A number of samples of quartz were taken from ledges in different parts
of the gold field, and submitted to Mr. P. De P. Ricketts for assay, but were
found to contain only traces of gold. The following is Mr. Ricketts’s report

in detail :
SCHOOL OF MINES, COLUMBIA COLLEGE,
New York, January 24, 1876.
Certificate of assay.
Sir: The samples of ores from the Black Hills, marked as below, submitted to me
for examination, contain no silver, but gold as follows :

Gold
No; 1.) Jasper, trom) Jasper alla ox eB der= se aerrecce terete lalate et ioye None.
No. 2. Porphyry ledge, Warren Peaks —- 7.22) 22. --. SER ey oR ne Trace.
No. 3. Empress lode, Box Elder............ eis pooooosooddtioassones Heavy trace.
No» 4. Great Quartz led se, Box HIden Ane emer leet easier None.
Now Ds bee Annarlode Springs Cree ke seein ener peters aa Trace.
No? 6: Sullivan’s lode,@astlei@reekiy-2 54ers eee eieei rile Heavy trace.
No.7. ode on: Rapid Creek 2.2. 0 Sees cies Sacre eee iice ee ees Trace.
Now 28. [ron pyrites trom Spring Oreck me. was ae ee eee seers aay. Trace.
No. 9. Lode on Rapid Creek—quartz.......-.......... .....+-.--.---Heavy trace.
No. 10. Lode on Rapid Creek—quartz.................-..-+.---- aera Heavy trace.
Noite Empress| lode) Box Mlder—quartz.. 2. cats e\-.ee ete rite erie None.
INowl2: sloderoneRapide Creek: cass sect cr cor a =: aio taetere sc natare eee eee ee ete Trace.

The amount of gold found in each case was too small to weigh, although the charges
of ore were large.

Very respectfully,
P. DE P. RICKETTS, E. M.
WALTER P. JENNY, EH. M.,

Geologist Black Hill Expedition.

ANALYSIS OF ORES. 295

Hematite iron ore exists in extensive deposits in the slates on Box
Elder, but is so intermixed with quartz as to greatly deteriorate its value.

“Blue block” iron ore (siderite), weathering to limonite, was found of
good quality in the black clay-shales of the Cretaceous on Beaver Creek.
The deposit covered quite a large area, and consisted of three horizontal
layers, respectively, 8 inches, 3 inches, and 5 inches thick, separated by a
few feet of clay-shales. This ore closely resembles the block ores of the
Coal Measures of Kentucky and Pennsylvania, which are worked in the
small charcoal iron-furnaces scattered through the timbered districts.

Gypsum is found in beds from 5 to 12 feet in thickness, interstratified
with the red clays of the Red Beds. Usually there are three or four of
these layers of massive white or gray gypsum in the formation, but in places
they seem to be wanting and to be replaced by sandy clays.

These Red Beds entirely surround the Black Hills, but are so exposed
by uplift on the southern and eastern sides as to conceal partially the gyp-
sum beneath the dcebris of the clays.

In Redwater Valley, in the northwestern portion of the Hills, and in
the vicinity of Inyan-Kara and Sun Dance Hills, the gypsum beds are very
prominent, and the mineral occurs in extensive strata, so exposed as to be
easily mined should there ever be a demand for it.

The Carboniferous limestone which covers a large area of the Black
Hills is very pure, and when burnt will make an excellent white lime suit-
able for building purposes. Building stone is everywhere abundant in the
Hills, and of good quality, including granite, slate, quartzite, sandstone of
all shades of color and degrees of hardness, limestone both white and gray,
and many varieties of trachyte and altered sedimentary rocks.

Some of the soft variegated sandstone of the Red Beds is very orna-
mental, embracing every shade of color from yellow, through orange and
pink, to the darkest red.

Springs, issuing from the black clay-shales of the Cretaceous on Beaver
Creek, were found to be strongly acid and astringent to the taste, turning
blue litmus red, and probably containing alum and free sulphuric acid.
Similar springs were reported to be found near Buffalo Gate, on the south-
eastern side of the Hills. A yellow efflorescence resembling flowers of sul-

296 GEOLOGY OF THE BLACK HILLS.

phur in appearance is often seen on the surface of these clay-shales. On
testing, it was found to be a basic sesquisulphate of iron, probably identical
with a yellow salt of similar composition used in medicine.

In reviewing the gold deposits in the Black Hills, there are some
peculiarities in the occurrence which require to be specially noticed.

The gold contained in the trachytes of the northern part of the Hills
and the Bear Lodge range has been deposited in these rocks at the time of
the intrusion, which was probably coeval with the elevation of the range at
the close of the Cretaceous period. But the gold ledges in the schists and
slates are of Archean age, and formed during the folding of the metamor-
phie rocks.

‘There seems to have been no volcanic disturbance in the Black Hills
since the elevation, and the occurrence of basalt capping gravel deposits, so
common a feature in the California and Australian gold fields, is here
entirely wanting. No fossil plants or the bones of extinct animals have as
yet been found in the placers, whereby their age might be determined, but
from their position they have been deposited not later than the Tertiary,
and since the elevation of the Black Hills.

Very few minerals have been found associated with the gold, except
garnets and magnetic iron sand. The occurrence of zircon, topaz, or plati-
num, so conmon in the gold-washings in other parts of the world, has not
been observed in the Black Hills.

With the exception of a few of the gravel deposits in the foothills,
which may be of shore formation, no deep leads or old channels filled with
gravel were found, which could not be referred to the present streams and
system of drainage, assuming only a greater rain-fall than at present, as
numerous gravel beds occur in dry sags and gulches, where water rarely, if
ever, forms now a running stream.

There are evidences of four distinct erosions having taken place in the
geological history of the Black Hills. The first at the close of the Archzean,
the second during the early Tertiary, the third in the Drift or Glacial
period, and the fourth, the result of the action of the present streams and
drainage in recent times.

After the elevation and folding of the schists and slates, the formation

EROSION. 297

of the auriferous quartz veins, and probably the intrusion of the granite of
the Harney Peak range, a most enormous denudation of the metamorphic
rocks occurred, and the greater portion of the resulting material was swept
away and lost. Only water-worn bowlders of quartz and the harder rocks
remain, forming the conglomerate at the base of the Potsdam.

Most, if not all, of the area of metamorphic rocks was at one time cov-
ered by this conglomerate, and it is probable that the advancing Silurian
ocean, at least in part, produced this erosion of the slates and schists. The
conglomerate is often found to contain huge bowlders of quartz and quartzite
derived from the ledges in the slates in the immediate vicinity, but nowhere
were we able to find any pebbles of granite in the Potsdam, though frag-
ments of soft clay, slate, quartzite, and quartz from its lower layers, and
scales of mica are easily seen with a magnifying glass in the compact layers
of this sandstone. Granite occurs abundantly in the Tertiary and more
recent conglomerate, and I can only account for this absence of granite in
the conglomerate of the Potsdam by supposing that the feldspar yielded
more readily to decomposition by the atmospheric agencies of the Silurian
period than it has from the same forces since the elevation of the Black Hills.

The Potsdam commences with the coarse conglomerate, a deposit formed
by a shallow and advancing sea, which seems to have gradually deepened,
as the sediments forming the sandstone regularly become finer in grain as
we ascend.

Since the Cretaceous, the Black Hills have been above the ocean-level,
probably attaining their present altitude by a slight additional elevation at
the close of the Tertiary, strata of that age, on the Cheyenne, having a dip
of 8° to 5° from the direction of this range. From the Archean to the
Cretaceous, these sedimentary rocks are an evidence of denudation; of a
wearing down of some continent, furnishing the enormous mass of material
which now composes the extensive strata of slate, sandstone, limestone, and
clay-shales.

The second great erosion succeeded immediately the elevation of the
Black Hills, and occurred during. the early part of the Tertiary period.
The resulting material forms the conglomerate between the top of No. 5
Cretaceous and the base of the Miocene or White River Tertiary. Only

298 GEOLOGY OF THE BLACK HILLS.

on the Cheyenne, between the mouths of Rapid and Spring Creeks, where
this conglomerate, about 6 feet in thickness, caps hills of Cretaceous shales
500 feet in height, can the result of this erosion be identified. There the
conglomerate is made up of small bowlders, round and water-worn, of
granite, trachyte, slate, quartzite, and quartz, in all the varieties in which it
is now found in the Black Hills, together with chert nodules from the Carbon-
iferous limestone, and fragments of hard quartzite from the Cretaceous.

The third erosion occurred during the Glacial or Drift period, when
thin beds of gravel, with occasional large bowlders, were strewn over the
surface of the plains for a distance of fifty miles from the foothills, and
rest equally on the surface of the different members of the Cretaceous and
cap hills of the White River Tertiary. Some of these traveled bowlders
are 2 feet in diameter, and are most abundant on the Cheyenne to the
southeast of the Black Hills. They have evidently been transported by
the agency of floating ice. Any current of water sufficiently powerful to
carry bowlders of this size and weight would entirely remove and sweep
away the soft clay-shales on which they rest. There was no evidence
found that during the Quaternary period any extensive glaciers occurred
in the Black Hills. Even the tops of the highest peaks showed no glacial
scratches where the hardness of the rocks would insure their preservation.
A few large bowlders of granite, 8 to 10 feet in diameter, were observed
perched on the tops of rocky benches at the bends of the small streams flow-
ing southeast from Harney Peak. They resemble those referred to glacial
action in the Eastern States, but were possibly only the result of a peculiar
weathering of the granite.

While there is little evidence of the presence of extensive glaciers in
the Black Hills, the occurrence of large quantities of ice and snow in this
elevated region during the Glacial period, with the necessary accompani-
ment of increased rainfall and river action, have probably been the agents
which have caused this immense denudation of the sedimentary strata. And
it seems almost necessary to assume the occurrence of an extensive lake sur-
rounding the Hills during the Quaternary period, when the bowlders result-
ing from the erosion were transported by the agency of the floating ice to
the places where they are now found.

EROSION. ; : 299

The whole area of the gold field in the Black Hills was, at the time of

the upheaval of the range, covered by the Potsdam and subsequent forma-
tions. It is probable that the Potsdam conglomerate, formed by the pri-
mary erosion of the metamorphic rocks and their inclosed auriferous quartz
ledges, contains considerable quantities of gold, and, by the disintegration
and denudation of this conglomerate since the elevation of the Hills, the
gold which it contained has been set free and concentrated anew in the
placer gravels. This may in part account for the richness of some of the
older and more elevated gravel deposits along the valleys of the present
streams.
The fourth erosion in the Black Hills has taken place in comparatively
recent times—since the Glacial period—and is still in progress, modifying
the effects of the previous denudation, and often removing and redepositing
the gravel beds resulting from them.

This last erosion is solely the work of time, frost, rainfall, and river
action, as they occur at the present time, all working extremely slowly, but
gradually wearing down the rocks, deepening the valleys and canons of the
streams, and, by working over the older auriferous gravels, increasing the
richness of the bars and flats along the present beds of the streams. But
the amount of gcld swept into the valleys by the present forces and rain-
fall must be inappreciable, compared with that resulting from the enormous
tearing down of metamorphic rocks and quartz ledges by the previous ero-
sions. The placer miners have a saying that “Gold does not go down
stream at the present day,” else we would look for it in beaver dams and
other similar places. Though it is true that fine gold will sluice through a
cation over bare bed-rock, and be deposited in the bars below the mouth,
it being only a question of time how long a particle of gold is making the
journey, no matter how many times it may be caught on bed-rock, only
to be liberated by the wearing away of the rock or by freshets. Some of the
richest placers found in the Hills the past season were thus situated below
the mouths of the canons of the streams, where the valleys widened out,
allowing permanent gravel deposits to form, retaining the gold.

In conclusion, in reviewing the gold placers of the Black Hills, it
should be noted that at best the gold field has been but partly prospected,

300 GEOLOGY OF THE BLACK HILLS.

and that it is extremely difficult to predict, even approximately, the value
of any particular gulch or district until the gravel deposits have been com-
pletely opened and nearly worked out.

The causes and circumstances which have influenced the concentration
of the gold in the placer gravels are but little understood, and erosion has
often removed entirely the ledges which were the source of supply of the
gold now found in the gulches.

The deposits of auriferous gravel in the Black Hills may generally be
said to be favorably situated for working, and that the gold can be very
cheaply extracted, with the expenditure of but comparatively little time or
capital in opening the deposits.

Compared with some of the world-renowned districts in California and
Australia, the placers at present discovered are not remarkably rich, yet
there are claims already opened and worked which are yielding a very good
return for the labor employed.

At Cheyenne the railroad is not more than two hundred and fifty
miles from the gold fields; the roads over which machinery and supplies are
transported are excellent, the grades usually easy, and the drives not long
between water.

The climate of the Black Hills is wonderfully healthy and invigorat-
ing; wood, water, and grass are everywhere abundant and of the best
quality.

There is gold enough to thoroughly settle and develop the country,
and, after the placers are exhausted, stock-raising will be the great business
of the inhabitants, who have a world of wealth in the splendid grazing of

this region.

CHAPTER V.

CLIMATE AND RESOURCES.

By WALTER P. JENNY, EH. M.
SECTION I.
CLIMATE.

It is extremely difficult, in fact almost impossible, to determine defi-
nitely the climate of the Black Hills from observations extending over a
portion of a single year, especially as we were continually changing our
location and altitude during the progress of the exploration, never being in
any place more than a few weeks; but I have tried to give the facts as I
observed them, with all the possible collateral evidence based on the growth
of plants and trees and the experience of previous explorers in this region.
Naturally many obvious contradictions will be noticed, which I have in
some cases tried to reconcile. In most instances I have given simply all
the information that was collected concerning the climate and rain-fall of
the Hills, that others, who have had greater and more extended experience
than myself in the Western country, might digest my data and judge for
themselves, should they not feel inclined to concur with my deductions.

During the growing season heavy dews were of regular occurrence at
night, especially in the low bottom-lands along the streams, where the grass
in the morning would be as wet as if it had rained hard for an hour. By
experience we found it best to locate our camps on some slight elevation
above the flats of the valley, to obviate the annoyance of having tents and

camp equipage saturated with dew on breaking camp early in the morning.
: 301

302 GEOLOGY OF THE BLACK HILLS.

It is doubtful if there is a heavy snow-fall in the Black Hills. The
miners who remained in the Hills during the winter of 1874~5 report that
there was never more than six inches of snow on the ground until April,
when a heavy fall eccurred at the time they were removed by Capt. John
Mix.

In a few localities in the interior of the Hills I saw small trees which
had been bent down by snow-drifts, but the streams showed no traces of
freshets caused by snow melting in the spring. There was no drift- wood
along their banks, and the bridges built by General Custer the previous
summer were still in place, which a rise of a few inches would have swept
away. The snow must be sometimes deep enough to hide trails and land-
marks, as the main Indian trails leading through the Hills were marked by
stones placed in the forks of the trees or by one or more sets of blazes, the
oldest almost overgrown by the bark.

No hail-storms occurred in the Hills the past summer, which caused
an injury to vegetation. Often during thunder-storms it would hail for a
few minutes, owing to some sudden change of temperature in the storm. The
central portion of the Hills is elevated from 2,000 to 3,000 feet above the
foothills, or an altitude of 5,000 to 7,000 feet above the sea, and necessarily
the weather is sensibly cooler. The thermometer seldom stands above 85°
Fahrenheit in the shade. In this elevated region thin ice formed occasion-
ally at night in open dishes of water left exposed to the sky even in mid-
summer, and after September 1 thin ice formed nearly every night in still
pools. This low temperature occurred just before daylight and was of
short duration. It was owing to the great radiation and evaporation, due
to the rarity of the air and the clearness of the sky, causing no correspond-
ing reflection of heat back to the earth. It seemed to have no bad effect
on vegetation, which flourishes bright and green until about September 8,
when the first frosts began to change the color of the leaves of the plants.

The growing season in this elevated region is necessarily but a few
months. June 10 the aspen trees at the head of Floral Valley, at an alti-
tude of 6,600 feet, were just bursting into leaf, the grass was green but
quite short, and by September 8 the plants in this same valley were col-

CLIMATE. 303

ored by the frost, and vegetation, except the evergreens and grass, had
ceased to grow.

From the equable temperature and pure air, the climate was found to
be remarkably healthy. Scarcely any one was sick in the whole command
during the time we remained in the Hills.

The temperature of many springs of water issuing from the Carbonif-
erous limestone and the granite and metamorphic rocks in the central and
elevated portion of the Hills was found to average 42° Fahrenheit even in
midsummer. The springs bursting out among the foothills at the edge of
the plains were not tested with a thermometer, but apparently the water
was not as cold by several degrees.

Col. Richard I. Dodge, commanding the escort of the expedition, a
close observer of nature, publishes the following article on the climate of the
Black Hills, which is so excellect, that I take pleasure in quoting it entire :

The climate is sufficiently varied to suit the tastes of almost any person or class.
We have no knowledge of the winter climate, except from the reports of the miners
who built the stockade and passed several months of last winter on French Creek.
These unite in commendation. The winter was cold, butclear; the temperature remark-
ably equable. There were no storms of any disagreeable magnitude, and the first serious
snow-storm occurred just before they were brought out, in March.

It is hardly fair to judge even of spring and summer climate by the experiences
of a single year, more especially since we were almost continually moving; changing
not only our position, but our altitude. If, however, the experiences gained under such
cireumstane¢es are to be regarded even as approximate tests, I can pronounce the cli-
mate of the Black Hills well-nigh perfect. Scarcely a day was too hot; scarcely a
night so damp or cold that we could not sit out and enjoy ourselves around the camp-
fire.

There is no such thing as a hot night. Though extremely susceptible to heat, I
slept not a single night in the Hills under less than the equivalent of two blankets, and
many times, even in midsummer, I required more.

I have already mentioned that on the 10th day of June we encountered, in the ele-
vated gorge named by Custer “ Floral Valley,” a sharp snow-storm, alternating with
sleet and rain. This valley is more than 6,000 feet above tide-water. On French Creek,
at an elevation of 5,800 feet, we had a severe, killing frost on the night of the 10th of
August. There is abundant evidence that the season, in these very high altitudes, is
too short for an agricultural country.

For five weeks, from 14th June to July 20, Camp Harney, on French Creek, was
the center of operations of our exploring and surveying parties. We had, therefore, a
much better knowledge of its climate than of any other portion of the Hills. It is 5,620
feet above tide-water. The climate is superb. Though it sometimes felt hot by day
and damp and cold by night, the thermometer was never above 78° nor below 54°. “A

\

304 GEOLOGY OF THE BLACK HILLS.

series of observations (not so regular as might be wished) gave a mean temperature of
62° and a daily variation of 14°. A fewsimilar observations at Camp Crook, on Rapid
Creek, in the latter part of July, resulted in a mean temperature of 64°, with a daily
variation of 20°. On the 24th of July, on Rapid Creek, a severe hail-storm sent the
mercury from 84° to 62°, 22° in half an hour. Camp Cook is at least a thousand feet
lower in altitude than Camp Harney.*

The past winter of 1875~76 has been unusually mild all through the
Northern and Western States, and reports from the miners in the Black
Hills speak in glowing terms of the delightful weather they have experienced,
very little snow having fallen before February, the grass being green at
the roots, and the stock, when not overworked, keeping fat and in good
condition. The winter of 1874—75 was correspondingly extremely severe ;
yet the Sioux City party of miners, who built the stockade and cabins on
French Creek in December and January, report that the cold was not
intense, and that their cattle kept fat on the grass in the vicinity, where the
altitude is 5,600 feet above the sea.

The Black Hills, with their copious rain-fall, rise like a high wooded
island from an ocean of grass-covered and treeless plains, watered by occa-
sional and scanty rains. ‘The rain-fall on the plains, far from yielding a
constant and uniform supply of moisture, unfortunately is very uncertain
and irregular, both in quantity and occurrence, and sometimes falls so far
below the average that the grass almost perishes from the drought.

This arid character of the plains is not peculiar to the region immedi-
ately about the Black Hills, but is equally true in a general way for this
whole belt of elevated plains, nearly five hundred miles in width, extending
along the eastern slope of the Rocky Mountains from Mexico to the British
Possessions. And the reason for the treeless character of this immense
tract of country is to be sought in its location with respect to the adjacent
ranges of the Rocky Mountains and to the oceans on both side of the con-
tinent.

From the north the winds, coming from the colder regions in the British
Possessions, bring with them scarcely any moisture; while from the south,
the direction of the prevailing winds and the character of the country is
such that any supplies of rain from that direction are cut off. The winds

* The Black Hills, by Richard Irving Dodge, Lieutenant-Colonel, United States Army. New York:
James Miller, publisher, 647 Broadway, 1876.

RAIN-FALL. 3505

which sweep over the Pacific Ocean are chilled by contact with the ele-
vated ridges and snow-clad peaks of the Rocky Mountains, and precipitate
the moisture which they contain as rain or snow. Passing on, these winds
descend on the heated surface of the level plains, where in summer the
temperature is often as high as 100° Fahrenheit in the shade. Becoming
heated and ravrified, they sweep eastward to the Missouri, having their
capacity for holding moisture greatly increased, and no ordinary change of
temperature will cause these winds to part with the little moisture which
they possess. Thus it will be seen that, practically, these plains have to
depend for their rain-fall on the supply of moisture derived from easterly
winds coming from the Atlantic Ocean and the Gulf of Mexico. These
winds, in passing over the Alleghanies and the Mississippi Valley, have
been subjected to innumerable changes of temperature, and robbed of the
ereater portion of the moisture they originally contained, to the serious detri-
ment of this immense belt of country. As would be expected from the |
above, it was noticed the past season in the Black Hills that the rain-storms
of long duration were preceded by, or occurred during, the prevalence of
easterly winds, which were chilled by contact with the colder and more
elevated portion of the Hills, precipitating the moisture which they carried.

While encamped on Rapid Creek, near the edge of the plains on the
eastern slope of the Hills, I had an excellent opportunity to observe the
formation and condensation of rain-clouds during the succession of rainy
days in July. The wind was blowing gently from the east and southeast.
Out on the level plains it scarcely rained at all, though dense banks of
clouds hung over them and detached masses of mist and fog were sweeping
low over the more elevated foothills. The clouds would form over the
plains and, drifting on to the Hills, conceal from view the highest peaks and
ridges, chill, settle down to the level of the valleys, and immediately rain
until the excess of moisture was precipitated, then rise and drift away ;
when a short interval would occur before the clouds would again sweep in
and produce a shower.

On examining the accompanying maps of the Black Hills, it will be
seen that nearly all the streams rise in the central or western portion and
flow east, the slope of the country being in that direction. I think that

20 BH

306 GEOLOGY OF THE BLACK HILLS.

this eastern slope of the Hills has a greater rain-fall than the western, judg-
ing from the growth of plants and trees, a fact which would coincide with
the theory that the rain-producing winds came from the east and precipi-
tated their moisture on that slope.

But the showers of rain and the thunder-storms which we so frequently
experienced seemed to be independent of the easterly winds as a source of
their moisture, and to be local in their origin and occurrence. Generally
of short duration, they came usually from the west and passed rapidly by,
raining hard for ten to twenty minutes, and leaving the grass and trees
dripping with moisture and refreshed by their passage.

The winds which blow on the Hills from any direction pass over the
plains for a great distance, and, gathering some moisture, part with it on
being chilled by contact with the cold and elevated peaks in the interior.
Thus the Black Hills may be said to have a local and limited rain-fall not
directly dependent on the easterly winds, which, nevertheless, furnish the
greater supply of moisture.

The rain-fall experienced in the Hills during the progress of the survey
was very remarkable for the frequency and regularity of the showers and
their short duration. It was varied by the occurrence of occasional long,
steady rains, and damp, drizzly, or foggy days. From June 1 to August 1
it rained more or less at least twenty days in the month. Usually the sky
would be overcast by clouds about 3 or 4 o’clock in the afternoon. A smart
shower, lasting from a quarter to half an hour, would rapidly pass by from
the west, and the sun would shine again and quickly dry up the ground.
On one occasion I experienced, near Harney Peak, four distinct showers,
accompanied by thunder and lightning, in a single day, which was otherwise
warm and pleasant, the sun shining brightly except when it was raining.
It was not unusual to have a shower during the day followed by another
after midnight. After August 1 the showers were not so numerous and the
rain-fall was appreciably less, although several rainy days occurred in both
August and September.

Referring to my note-book, I find the following record of the rain-fall
observed while prospecting on Rapid and Spring Creeks :

June 26, rained steadily all the afternoon.

RAIN-FALL. 307

June 27, a shower in the afternoon.

June 28 and 29, no rain where we were camped.

June 30, rained steadily all day, preventing any work being done.

July 1, two showers during the day.

July 2, 3, did not rain.

July 4, rained hard all day.

July 5, rained hard for half an hour in the afternoon.

July 6, showers all around on the Hills, but did not rain where we were.

July 7, 8, no rain.

July 9, 10, 11, 12, 13, 14, 15, one or more showers each day, usually
after 2 p. m.

From the above it will seem that it rained fifteen days out of twenty-
two. Referring to the published reports of the expedition to the Black Hills
under command of Gen. G. A. Custer, in 1874, I find that Colonel Ludlow
mentions this fact of the frequent occurrence of showers in the afternoon,
under date of July 27, while encamped on the head of Castle Creek, a
branch of Rapid Creek.

This portion of the Black Hills never suffers from drought. No arid places are
seen except on the summits of the limestone ledges. Springs are numerous, and very
cold and pure. The soil is everywhere moist, and vegetation marvelously luxuriant
and fresh. The warm currents of air from the plains condense as they ascend the
slope of the hills, and robbed of their moisture in fog, rain, and heavy dews, which
occur nightly. The clouds almost invariably formed in the afternoon, and interfered
greatly with astronomical observations. (Report of a reconnaissance of the Black
Hills of Dakota, made in the summer of 1874, by William Ludlow, captain of Engineers,
&c., page 13.)

Gen. G. A. Custer and Major Forsyth also mention, in their reports of
the expedition, the refreshing showers of rain which were frequently
encountered, and also the thick fogs, prolonged rains, and severe thunder-
storms experienced while in the Hills. That this remarkable rain-fall,
which was observed throughout the Black Hills during the progress of the
exploration, was not the exhibition of a peculiarly wet season, I can only
judge from the evidence given above by previous explorers during the
preceding year and by such observations as I was enabled to make on the
growth of plants and trees. In many places I noticed plants whose habits
of growth I was well acquainted with, which require a considerable and

308 GEOLOGY OF THE BLACK HILLS.

regular supply of moisture for their maintenance, growing on dry, rocky
hill-sides, exposed to parching winds and the heat of the sun, and flourish-
ing and producing flowers and seed in perfection. On the tops of the
mountains, near Harney and Custer Peaks, far above the level of any
springs of water, I found patches of wild raspberries growing so thickly
that the ground was covered with them. The bearing-canes, which are of
a previous year’s growth, were of full size and loaded with fruit, showing
that the previous season had been equally favorable to their development.
All along the eastern slope of the Hills burr-oak and elm trees, which
require an abundance of moisture to sustain their growth, attain at least a
medium size, and are found not only along the banks of the running
streams, but growing in small grooves on the hill-sides and in the swales and
valleys. On examining the pine timber in different parts of the Hills I
found that the annual rings of growth were uniform in width. The coarse-
ness of the grain of the timber, its softness, and the regular appearance of
the full-grown trees, all indicate, independent of the species of tree, a
uniform yearly growth, and consequently a regular rain-fall. From these
evidences I think I may safely draw the conclusion that the season of 1875
in the Black Hills which I witnessed was not an unusually wet one,
although the rain-fall may have been somewhat above the average. The
average amount of rain for the plains surrounding the Black Hills does not,
probably, exceed 15 inches for the whole year. To the north, in the
valley of the Upper Missouri, it is about 12 inches.

From the nature of the work the past season it was impracticable to
definitely determine the amount of rain-fall; but the presence of trees indi-
cates conclusively that it must be at least 25 inches; and not much below
that amount for more than a single successive season, or many of the trees
would perish from want of moisture. The following tables, giving the rain-
fall in inches for the nearest localities to the Black Hills where observations
have been made, are from the Smithsonian Institution tables and the records
of the Signal Service of the United States Army:

PRECIPITATION OF MOISTURE. _ 309

Mean amount of precipitation of moisture, as rain and melted snow, for each month in the year.

’ | |
: m E

re b >) 3) 3S

> : 2 5 2 >

Name of station. ae Sp lid : | @ a | & a |g

Pletal re Beet Wee lcm ce te (Ne. |e

= SS = = a | 5 ° 2

Brel site eal ory os Aa oe| a | A
Xi od eG bie IDE ic ek Pe Soe eres 0.49 | 0.42 | 0.99 | 1.10 | 2.67 | 2.30 | 1.76 | 2.56 | 2.43 1.09 | 0.41 | 0.30
Fort Pierre, Dak ..---..-- sseosessscer cases 0.50 | 1.18 | 0.46 | 1.63 | 2.19 | 0.48 | 1.18 | 1.66 | 1.29 | 1.08 | 1.39 | 0.47
Fort Abercrombie, Dak.-..-..--.-.-..- .----- 0.52 | 0. 66 | 1.03 | 1.82 | 1.82 | 2.18 | 3.01 | 2.30 | 1.07 | 1.30 | 0.99 | 0. 64
Hontrlaramie Way Oe sane renee eae eee 0.61 | 0.46 | 0.84 | 1.06 | 3.74 | 1.90 | 1.63 | 1.37 | 1.17 | 0.97-| 0.84 | 0.57

|

Mean amount of precipitation of moisture, as rain and melted snow, for the season and the whole year.

Extent of ates
~ q series.
Name of station. eh z = 8 Year.
& E E Ss Years. |Mo.| Beginning. and)
|
Eto rtsFeara dls] PRED es a een ete ak ier 4.76 | 6.64 | 3.90 | 1.21 | 16.51 8 | 10 1857 1867
MwortrPiecre talc-ss ste ete ee ener es ee out ee 4.28 | 3.32 | 3.76 | 2.15 | 13.51 1 | 10 1855 | 1857
orb sAtberceom Dies Wakes oe ae aan sees ae | 4.67 | 7.49 | 3.36] 1.82 | 17.34] 6 | 11 1860 1867 |
jeeMontilarainies Way 0 e228 == 5 (ones se we eee e eokn. 5.64 | 4.90 | 2.98 | 1.64 | 15.16 | 12 6 1849 | 1864
feGhoyennepWiy orm seen ot oes eens ee eet 3.11 | 5.56 | 1.98 | 0.37] 10.02 | 4 4| 1871 1875
Rorisbutord wl lakwyeioe meer sos eee een Roe ee mer |e cae 6.49 | Bees | eoee 11.75 8 0 1867 1874

It will be noticed from a comparison of the above tables that the
rain-fall for the whole Upper Missouri region follows the same general law,
being greatest in the spring and summer months, from May to September,
and least in autumn and winter, coinciding with the observations made in
the Black Hills the past season. ‘The season of 1875 was remarkably wet
generally throughout the United States. At Cheyenne and North Platte,
on the Union Pacific, 220 miles south of the Black Hills, the rain-fall was
not above the average, but at Yankton and Bismarck, Dakota, situated
nearly an equal distance north and east, it was unusually great, as is shown
in the following table, compiled from the records of the Signal Service,
United States Army:

: g a) | =
~ ° al
Pal Needles <i Sibi eae leet ee
Name of station. z = = ae ; : Z a 2 A 2
| = mI = = 5 ¢ B =p = ° Caer: 6
Roo ewe oldie): fee |) S- | oo) | ou,
SE ey ese a SS eet Bl eye ers
| ‘Cheyenne, Wyola. --c28<--eece canon | 0.42 | 0.06 | 0.23 | 0.50 | 1.20 | 0.29 | 4.47 | 2.12 | 1.34 | 0.60 | 0.84) 12.07
| Yankton, Dak .......-.22-...-2..---2------| 107 | 1.51 | 1.79 | 5.26 | 2.04 | 9.21 | 5.53 | 4.95 | 5.33 | 0.14 | 0.12 | 36.95
Bismarck, Dak 26. ves (eee Se Boe 1.05 | 1.32 | 2.06 | 4.22 | 3.40 | 5.02 | 1.53! 2.89] 1.85 | 2.37] 1.33 | 27.04
Nortly Platte, Nebr sass se 0 sees -c eee 0.24 | 0.26 | 0.40 | 6.21 | 1.69 | 1.62 | 2.12 | 0.66 | 1.40 | 0.14 | 0.52 | 15.26

310 GEOLOGY OF THE BLACK HILLS.

Severe thunder-storms prevail in the Black Hills during the summer
months. The clouds, instead of floating high in the air, sweep low over
the elevated ridges, and the lightning is consequently peculiarly liable to
strike the ground rather than to pass from one portion of the cloud to
another and harmlessly expend its force. This causes some damage to the
timber of the region. Often, in riding through the Hills, trees showing
unmistakable marks of lightning would be seen, generally with the top
shattered and a strip of bark about an inch wide torn out in a straight or
spiral line from the top of the tree to the ground. Sometimes, however,
only the splintered stump of what had once been a large tree remained,
while the ground all around was strewed with fragments of the trunk,
branches, and limbs.

It would seem that the pines growing in certain portions of the Hills
were peculiarly liable, for some unknown reason, to be struck by lightning.
On a hill near the headwaters of Spring Creek I counted twelve trees,
growing on about two acres of ground, that were marked by lightning, and
in a small park near by, among about one hundred trees, fourteen had been
struck in previous years; some of them more than once. ‘The most severe
thunder-storms came from the west and traveled in an easterly or south-
easterly course, the storm commencing with gusts of wind from the west,
shifting to the north and northeast in the height of the tempest, and finally,
as the storm passed by, blowing from the east or southeast.

A most terrific thunder-storm was encountered by myself and a small
party of miners while camped on Box Elder Creek, August 7. The day had
been pleasant but somewhat warmer than usual. About 3 o’clock in the
afternoon a dense black cloud, extending like a wall across the valley, and
rapidly advancing from the west, warned us of the approaching storm.
Hardly had we completed our preparations to protect ourselves and provis-
ions from the rain, when, preceded by violent gusts of wind that nearly
prostrated every tent, the storm burst upon us. The rain, impelled by the
violence of the wind, descended almost horizontally, and beat in torrents
against the sides of the tents for about five minutes. Then, suddenly the
wind shifted to the north, and came in sudden squalls of cold, piercing
wind, chilling us through in a moment, and changing the rain instantly to

THUNDER STORMS. 311

hail, which was piled in winrows against every projection on the ground.
Quickly veering back again to the west, the rain came, mixed with hail,
driving before the blast. And then the storm raged with all its fury; flash
after flash of chain-lightning followed in quick succession, extending verti-
cally from the low, overhanging cloud to the ground, and striking at nearly
every discharge among the trees on the surrounding hills. The thunder
was incessant, and the crashing, increased by the reverberations from the
surrounding rocky cliffs, was so continuous that it could not be referred to
any particular flash. The wind shifted nearly all around the compass in
the direction of the motion of the hands of a watch. The storm passed by
in half an hour, the last rain coming from the southeast. The sun shone
brightly once more, while to the east, down the valley, the cloud could be
seen hiding everything from view, but illuminated every moment by flashes
of lightning extending to the ground On examining several dishes which
had been left out in the rain, I found that in about twenty to thirty minutes
an inch of water had fallen. One of the miners came into camp shortly
afterward and reported that he had been caught out on the top of a neigh-
boring hill during the storm, and that two trees near him were struck by
lightning and thrown to the ground in fragments. The Indians are said to
desert the Hills in the summer on account of the lightning, and I can easily
understand that a band of superstitious Indians, after experiencing such a
storm, especially if any of their number were injured by lightning, would
forever forsake the locality.

SECTION II.
WATE Bebo OU PP Ve.

To a settler in a new country no question is of greater importance
than the purity and abundance of the supply of water, and in this respect
the Black Hills are unequaled by any region in the ‘‘Great West.”

A glance at the map shows, by the innumerable branches of the creeks
and the intricate nature of the topography, that it is an extremely well-
watered country. Springs are found in almost every ravine. Nearly all
the small head-branches of the creeks are running brooks of pure water,

312 GEOLOGY OF THE BLACK HILLS.

and streams of considerable size, and but a few miles apart, drain this
region, affording a constant and regular supply of water for both stock-
raising and mining purposes.

The creeks which drain the gold field rise in numerous small springs,
issuing from the granite and metamorphic rocks, and the water is conse-
quently remarkably pure and free from mineral or organic matter. Those
branches which head in the great Carboniferous limestone yield water
suitable for most domestic purposes, the only drawback being a slight
“hardness,” due to the presence of carbonate of lime, which does not in
the least affect the health of those using it.

Only among the foothills, where the gypsum of the Red Beds or the
“alkali” derived from the Jurassic and Cretaceous shales has contaminated
the streams draining these formations, is the water found to be unfit for
cooking purposes and possessing purgative properties. Elsewhere through-
out the whole area of the Black Hills included within the timber-line at the
edge of the surrounding plains the water, both of the springs and running
streams, is clear, cold, delicious to the taste, and extremely healthy. Early
in June the temperature of the springs at the head of Floral Valley was
found to be 39° F., the elevation being 6,600 feet above the sea. In mid-
summer the water of a number of springs in the interior of the Hills was
tested with an accurate thermometer, and found to vary between 42° and
44° F. After August 1, the past summer, the volume of all the streams in
the Black Hills was somewhat diminished by the partial cessation of the
heavy rains, but none of the creeks stopped running, except that portion of
French Creek above the Stockade, where the springs supplying the water
are small and the grade very slight. From the character of the geological
formations outcropping in the foothills and along the edge of the plains, all
the streams rising in the Black Hills sink in their beds and disappear before
passing through the belt of Carboniferous limestone, with the exception of
Rapid Creek, which flows into the Cheyenne, and Spearfish and Redwater,
which empty into the Belle Fourche. Large springs of good cold water
burst out from under the Triassic limestone in the Red Beds at intervals
along the inner rim of the broad Red Valley encircling the Black Hills.

These springs will be very valuable to the future stock-raisers in this region,

WATER SUPPLY. 3 3) 113)

affording watering-places for the stock grazing in the open plains or among
the foothills.

Spearfish and Redwater Creeks united pour a large volume of excellent
water into the Belle Fourche, but the shales of the Cretaceous formation
through which the river flows soon contaminate the water with alkali, giving
it a slightly unpleasant taste, and causing it the past autumn to seriously
affect the health of the escort. Probably at other seasons the water of the
Belle Fourche deserves its name and reputation, but at the time we were
camped on its banks (September 20) the stream was comparatively low and
the water contained its maximum of impurities. The south fork of the
Cheyenne is like most of the rivers in the plains, shallow, with a moderate .
current flowing through a broad level bottom, yet subject to sudden rises in
spring and early summer. In places it cannot be forded on account of quick-
sands, even when the river is so low that the water is but a few inches deep.

The water of the Cheyenne is full of suspended mud, and contains
traces of alkali derived from clays along its banks.

SHCTION IIl.
SOIL.

There is no better way to judge of the fertility of the soil of a new and
unsettled region, where the rain-fall is abundant, than to examine the growth
and character of the vegetation which it supports.

The Black Hills are an oasis of verdure among the open and Jevel
plains. A luxuriant growth of grass spreads over the whole region; even
on the rocky hill-sides grass is found growing in the crevices in the rocks
wherever there is a particle of soil for its support. A heavy forest covers
the greater portion of this area, the trees growing thickly together and
attaining full size, not only on the rich bottom lands of the valleys, but on
the tops of the level limestone ‘‘mesas”; and the steep rocky ridges are
clothed with pine of good size to their very crests The soil on the main
divides and ridges is not so deep as it is in the parks and valleys which

have received the wash from the neighboring hill-sides, and these elevated

314 GEOLOGY OF THE BLACK HILLS.

tracts being most valuable for grazing purposes, will not be used for cul-
tivation.

Even a casual examination shows that the soil of the valleys, the broad
swales of the parks, and the bottom lands along the creeks is exceedingly
rich and deep, being a dark-colored loam, resulting from the decomposition
of the granite, limestone, and schistose rocks occupying the central area of
the Hills. Often in sinking prospecting pits along the valleys in search of
gold, the soil would be found to be a black peaty loam, from 2 to 3 feet in
thickness, and frequently in the bottom-lands the soil was 4 feet in depth,
resting on a gravelly subsoil.

In the parks and along the elevated limestone divide near Crook’s
Tower are numerous swales of rich grass-land between the low hills and
ridges. The soil is deep and fertile, supporting a rank growth of herba-
ceous plants, but owing to the elevation above the sea and the short grow-
ing season of not more than three months the value of these tracts for cul-
tivation has yet to be proved by experiment. In the valleys of Spring and
Rapid Creeks are extensive bottom-lands, which would be excellent for
farming purposes did not the underlying gravel contain gold in quantities
sufficient to cause it to be mined out in the next few years, to the ruin or
serious detriment of the land.

The whole valley of Rapid Creek, a mile and a half wide, from the
foot-hills to the Cheyenne, a distance of 45 miles, is susceptible of irriga-
tion from the stream, which carries at least 3,000 miner’s inches of water in
midsummer. The soil of this valley is deep and fertile, except near the
Cheyenne, among the clay-shales of the Cretaceous, where the presence of
alkali makes the grass thin and poor.

There are extensive tracts of good farming lands on the Redwater and
Spearfish where they unite to form the Deep Water, a branch of the Belle
Fourche. Colonel Dodge, the commander of the escort, regarded this
locality as admirably suited for a military post.

The soil of the upper valley of the Belle Fourche, from Bear Lodge
Butte to the point where it suddenly bends to the southeast, is reported by
the topographical party to be excellent, and that broad flats of grass-land
skirt its banks for miles. The valley of this stream below where it is joined

SOTL. 315

by the Deep Water is injured by the prevalence of black Cretaceous clays
and the usual accompaniment of alkali.

The South Fork of the Cheyenne has a broad level bottom, but gen-
erally so little elevated above the water in the stream as to be liable to
inundate from floods. In places, however, some very good land is to be
found in the extensive flats along that stream. Were the Blacks Hills as
densely populated as the State of New Hampshire or Vermont, which they
resemble in the character of the vegetation and climate, a very considerable
proportion of the area would be subjected to cultivation. But the amount of
arable land, or rather land that will in the next quarter of a century be cul-
tivated in this region, is small compared with the whole area of fully six
thousand square miles embraced in the Black Hills There is good land
enough in the bottoms of the streams suitable for cultivation to amply
support the population which will remain in the Hills after the present
excitement shall have subsided and stock-raising become an established
occupation.

Including the bottom-lands of the Cheyenne and the Belle Fourche
and the arable land along the valleys of the streams issuing from the Black
Hills, I estimate that not less than one-twentieth of the whole area is sus-
ceptible of cultivation, the remainder being covered by forest or forming
stock-ranges of the finest description.

SECTION IV.
Webi DD HE ULES:

The fruits found growing wild in the Black Hills are an evidence of
the adaptability of the country for raising the more valuable cultivated
varieties, and hence I propose to consider the wild fruits which were found
in this region much more in detail than they would otherwise deserve.
The most useful is the red raspberry, which was found in large patches in
the vicinity of Terry Peak, at an elevation of 6,500 feet above the sea.
The plant is rather dwarf in size, the bearing canes being about 2 feet high,
and August 15 were loaded with delicious fruit, resembling very closely the
cultivated variety “‘ Knevit’s Giant” in size, flavor, and productiveness. _

A variety of black gooseberry was abundant on the western side of the

316 GEOLOGY OF THE BLACK HILLS.

Hills, near Inyan-Kara; the fruit was of a pleasant acid flavor and of
good size, only differing from the ordinary western wild gooseberry in being
blue-black in color instead of dark-red.

Several species of currants, including the black, red, and fetid varieties,
were occasionally seen, but are valueless.

The wild western strawberry grows throughout the Hills. It is a very
shy bearer, and the fruit is deficient in flavor

The bunch-berry, or cornel (Cornus canadensis), was found in the ex-
treme northern part of the Hills. I have never seen it elsewhere, except in
Maine and Nova Scotia.

Service-berries (Amelanchier canadensis) were quite plenty on Spring
and Rapid Creeks in July. The common wild red plum grows in patches
among the foothills, along the bottoms of the ravines The fruit was ripe
about September 20

The only variety of grape noticed was a kind of frost-grape, found
along the banks of the streams, near the edge of the plains.

Quite extensive patches of the two varieties of hazel-nuts were observed
in the southeastern part of the Hills, associated with alder, white birch,
iron-wood, white elm, burr-oak, sumac, the poison ivy (hus toxicodendun),
the Virginia creeper, and many other plants of wide range and distribution.

Wild flax and wild hops attain a rank and luxuriant growth on the
bottom-lands along the streams, and the soil and climate seem to be remark-
ably well suited to the growth of these plants.

The flora of the Black Ilills bears quite a resemblance to that of South-
ern Maine and New Hampshire in the same latitude, and it is probable that
many of the agricultural productions, fruits, and vegetables which can be
grown in perfection there will also succeed in favorable portions of this
region. The luxuriance with which the heavily seeded grasses known
commonly as wild rye, cheat, and wild oats grow on the rich bottoms
along the eastern slope, would indicate that an equally rank growth
of the cultivated cereals and grasses is to be expected. Except at a low
elevation among the foothills near the edge of the plains, the nights will
probably be found too cool for the successful growth of Indian corn, which
is a tropical plant, but oats, rye, barley, and wheat should yield well, and

potatoes of the best quality may be produced in the fertile valleys.

PASTURE LANDS. 317

SECTION V.
GRAZING.

The grazing in the Black Hills is most excellent. Nine-tenths of the
whole area is covered by a thick growth of the finest wild grasses. It con-
stitutes the great future wealth of this region, and its value can hardly be
overestimated.

Every one who visited the Hills the past season was enthusiastic over
the luxuriance of the grass, which in the brightest green spreads over the
surface of the parks, hill-sides, and valleys, adding greatly to the beauty of
the scenery.

Cavalry officers, herders, scouts, and miners all were united in praise
of the grazing. ‘California Joe” said of the valley of Spring Creek:
‘““There’s gold from the grass roots down, but there’s more gold from the
grass roots up.” And no matter how rich the gold-placers in the Black
Hills may prove to be, the great business in this region in the future will
be stock-raising and dairy-farming.

Owing to the heavy dews at night during the growing season, to the
frequent thunder showers, and the occurrence of occasional long and heavy
rains, the grass grows all over the Black Hills wherever it can obtain a
particle of soil for its support and a few hours’ sunshine during the day.

Even in the clefts of the rocks, the sides of the steep ridges, and in the
bottoms of the deep canons, grass is found growing, depending on the
scanty soil for its sustenance, and the little sunlight that pierces through
the dense branches of the trees or penetrates for a short time the depths of
the gorge..

Unlike the grass on the plains, which springs up in May and by July
has turned yellow and cured to a natural hay, the grass in the Black Hills,
stimulated by the abundance of moisture, continues growing all through
the summer, remaining always fresh and green until its growth is checked
by the frosts of autumn.

When the expedition reached the Hills, about June 1, spring was well
advanced. The trees on the foothills were in full leaf, and the grass had

BS GEOLOGY OF THE BLACK HILLS.

evidently been growing for several weeks. On the top of the Beaver Creek
plateau, at an elevation of 6,000 feet above the sea, the grass (June 5) was
six inches high, and covered the whole surface of the level mesa, growing
thickly ander the shade of the pine forest, even to the very roots of the
trees, giving the region the appearance of a smooth, well-kept lawn, with

tall pines rising from the green carpet of grass. .

The grasses in the Black Hills are almost endless in variety, every
condition being so extremely favorable to their growth. In the interior of
the country the shorter grasses prevail. But among the foothills on the rich
bottom-lands of Rapid Creek the taller grasses, known as wild rye, crow’s
foot, cheat, and wild oats, attain a luxuriant growth. The grama, or
buffalo grass, covers the valleys at the edge of the plains to the exclusion
of the other varieties. It is considered the most nutritious wild grass in the
Western country, curing to hay on the ground. But, when growing in an
alkaline soil, it seems to rapidly lose its nutritive qualities after the seed
ripens. Along the banks of the streams, where the soil is marshy, large
patches of the scouring rush are found growing. It forms an excellent food
for stock, for which they will desert the finest grasses, and feed upon it
until they are full and can eat no more.

I had previously been engaged in explorations in Western Texas and
New Mexico, but I was surprised at the quality of the grazing we found in
the Black Hills, which resembled the grass growing in the oak openings in
Central Texas, except that it was finer and freer from weeds and the coarser
and less nutritious grasses. The escort of the expedition remained camped
on French Creek for six weeks, and grazing for nearly one thousand horses
and mules and three hundred head of cattle was found during that time
within a mile and a half of camp, the grass commencing to grow again as
soon as it was eaten off by the stock. or the requirements of the popula-
tion that the Black Hills will support in the next twenty years enough hay
can be procured from the wild grasses; and should the demand in the future
increase, an ample supply can be raised by sowing timothy or other culti-
vated varieties on the bottom-lands of the valleys. The best localities for
hay are in the southeastern part of the Hills, on Amphibious, French, Spring,
and Rapid Creeks, and in the valley of Rapid, between the foothills and the

GRAZING. 319

Cheyenne, where the taller grasses are abundant on the moist bottoms of
the streams and side valleys.

On the plains in the valleys of the Cheyenne and the West Fork of
Beaver Creek there are localities where sage brush and ‘prickly pears”
cover the alkaline soil, and grass is only to be found in patches. But gen-
erally throughout the area of the Black Hills the grass uniformly covers the
land, wherever there is soil for its support and the shade is not too dense
for its growth. Except among the Red Beds in the foothills, sage-brush is
never seen and cactus but rarely met with.

Over thickly-wooded areas, and in the mountainous and rocky region
about Harney Peak, the grass is found only in patches in the few localities
favorable for its existence. A similar region, comparatively destitute of
grass, occurs in the northern part of the Hills between Terry and Crow
Peaks, where the whole surface of the country is cut into innumerable
canons, and a species of ground ivy, called “kinnikinick,” a plant probably
of the dog-wood family, replaces the grass.

I estimate the total area of country destitute of grass, or where it only
occurs in isolated patches, to be not more than six hundred square miles,
or one-tenth the whole area of the Black Hills, the remaining five thousand
five hundred square miles constituting some of the best ranges for cattle,
horses, and sheep to be found in the whole Western country.

Cattle frequently perish on the plains in large numbers during the
severe winters, not so much from the low temperature or intensity of the
cold as from the piercing winds, accompanied by sleet or snow, that sweep
with resistless fury over the level and unbroken surface of the ground,
chilling the animals more than any ordinary degree of cold could possibly
affect them in a more sheltered locality. In the Black Hills the wind may
blow a gale over the mountain-tops and exposed ridges, but in the valleys
the air will be comparatively at rest, the timber covering the hill-sides
and ridges materially contributing toward making the valleys warm and
sheltered. This will be of great advantage to the stock which may be
wintered in the Hills, shelter being found everywhere from sudden or
severe storms. ‘The grass exposed on the hill-sides by the snow blowing

320 GEOLOGY OF THE BLACK HILLS.

away or melting, as well as the green twigs of the bushes and trees, will
afford subsistence for the cattle during any heavy fall of snow.

The miners who have passed the winters of 157475 and 1875~76 in
the Black Hills report that the grass remained green at the roots, and
afforded good grazing, keeping the stock in good condition, if it were not
overworked. Little snow was experienced until the early spring months,
when the first heavy falls of snow occurred.

From the secluded and sheltered character of the valleys, the abun-
dance of water, and the fine quality of the grazing, the Black Hills are
well adapted for dairy-farming, the establishment of cheese and butter
factories, and the raising and breeding of fine breeds of cattle and sheep.

The Black Hills are remarkably free from noxious insects, and grass-
hoppers and locusts are rarely met with in numbers sufficient to cause any
appreciable damage to the grazing or vegetation. Only in one locality
were they at all numerous. On Beaver Creek, in the southwestern portion
of the Hills, near the plains, early in June grasshoppers were just hatching,
and in a few weeks had grown large enough to strip the leaves from the
bushes. Gnats and mosquitoes were sometimes found in the Hills, but
never in numbers to cause any annoyance. Large flies were quite trouble-
some during a few weeks in July and August, but the first cool nights
caused them to disappear.

SECTION VI.
TIMBER.

The Black Hills are a well-wooded country. The plenteous rains and
showers in summer keep the vegetation growing unchecked by drought:
The density of the forests clothing the hill-sides have from their somber
hue, when viewed from a distance, given the name to this region, the
‘Black Hills,” by which it is known also in the Indian dialects.

The following trees will yield timber in this section:

The heavy pine (Pinus ponderosa), often known as yellow or Norway
pine, the most abundant and vaiuable tree in the Hills.

TIMBER. 321

Black and white spruce, found among the valleys in the central and
‘northern portions of this region, covering a considerable area.

Burr-oak (Quercus macrocarpa), in small groves on the eastern slope,
near the foothills.

White elm (Ulmus Americana), associated with the burr-oak, occurs
along the valleys of the streams near the eastern and southeastern foot-
hills.

Aspen, white birch, ash, mulberry, box-elder (segundo), iron-wood
(horn-beam), and juniper grow sparingly in different parts of the Hills,
but are of little comparative value.

The pine forests cover so extensive an area and will yield so large a
proportion of the timber, that all the other trees combined may be neglected
in comparison, though they will be found valuable in the future develop-
ment of the country. The Norway pine is a tall, straight tree, free from
limbs for one-half its height from the ground. The wood is white, soft,
with a straight, somewhat coarse grain, free from knots, and splitting
readily into ‘“‘ shakes,” shingles, or other similar forms. The sap is more
resinous than that of the white pine, and in this respect this variety
approaches more nearly the pitch-pine of North Carolina, a tree which it
somewhat resembles in its style of growth.

The transverse strength of the wood is not so great as that of white
pine, but by proper care in using it in construction this deficiency can be
compensated for and practically obviated.

On the bottom-lands in the lower valley of French Creek specimens
of this pine were seen that were fully 100 feet in height, and would
measure 35 to 40 inches through at the ground. Trees of these large
dimensions are, however, rare in the Hills. Timber of from 12 to 24
inches diameter is common, while extensive tracts are covered by a dense
forest of small slender pines from 50 to 60 feet high, and rarely less than 8
or more than 12 inches through at the ground.

The pine forests in the Black Hills, where the trees are of mature
growth and uninjured by wind or fire, will furnish good straight saw logs
from 30 to 50 feet in length and very uniform in thickness, with a gradual
taper, averaging in diameter from 12 to 20 inches.

21 BH

399 GEOLOGY OF THE BLACK HILLS.

The tall slender pines will be very useful to the settlers in this region,
being well adapted for fencing and house-building purposes. The resinous —
character of the wood makes it a most excellent fuel, burning with a long
smoky flame, giving out an intense heat, almost equaling in this respect
the pitch-pine of the Southern States.

On the tops of the ridges and hills, where the trees are exposed to the
violence of the storms, the timber is wind-shaken and injured in quality;
but on the more sheltered hill-sides, the broad level mesas, and in the
numerous valleys and parks, the trees are free from this evil, and are remark-
ably straight and regular in growth. Pines were sometimes encountered,
blown down by the wind across the narrow ravines, the trunk of the tree,
even when 1 to 2 feet in diameter, being broken short off by the violence
of the fall on the rocks. This rarely happens with the spruce under similar
circumstances, owing to the greater transverse strength of the wood.

The Black Hills have been subjected in the past to extensive forest-
fires, which have destroyed the timber over considerable areas. Around
Custer Peak and along the limestone divide, in the central portion of the
TIills, on the headwaters of the Box Elder and Rapid Creeks, scarcely a
living tree is to be seen for miles. The timber, deadened by the fire and
the trees left standing, their decaying trunks stripped of bark by weather
or prostrated by the wind, cover the ground, crossing each other at all
angles, forming an impassable abattis.

Some portions of the parks and valleys, now destitute of trees, show
by the presence of charred and decaying stumps that they were once
covered by forest, but generally the pine springs up again as soon as it is
burnt off, though sometimes it is succeeded for a time by thickets of small
aspens.

Along the eastern and northeastern slopes of the Black Hills, at a
distance of not more than ten miles from the edge of the plains, the pine is
partly replaced by burr-oak and white elm of moderate size. These trees
are found in groves in the valleys and swales between the hills, and
associated with white birch in the ravines of the streams. Neither the oak
nor elm attains a large size, the trees averaging 30 to 40 feet in height and
10 to 15 inches through.

TIMBER. . due

The wood of the white elm is well known; that of the burr-oak resem-
bles white oak, is strong and tough, and will prove valuable for many pur-
poses.

In the elevated portion of the interior of the Hills, especially along
the valleys in the limestone formation, extending from Custer Peak to
Floral Valley, and on the headwaters of Rapid, Castle, Elk, Bear, Butte,
and Spearfish Creeks, two varieties of spruce, resembling the black and
white spruce of the Northern States, are quite abundant. The trees are
tall, growing thickly together, and will furnish logs quite uniform in diam-
eter throughout their whole length. In the canons, where the soil is rich,
the white spruce attains a height of 100 feet, and is occasionally 2 feet in
diameter at the ground. Usually, however, these trees are from 8 to 15
inches through, and will prove very valuable in constructing trestles and
small bridges on account of the strength of the timber. The wood is white,
fine-grained, and remarkably tough and elastic. The small slender spruce-
trees are much sought after by the Indians, who visit the Hills in the spring
for the purpose of procuring them for lodge-poles.

It is difficult to estimate accurately the area covered by valuable tim-
ber in the Black Hills. Taking into consideration that the foothills are
but sparsely wooded; that there are extensive parks and valleys in the
interior destitute of trees, or where there are only scattered groves of pine;
that over an aggregate area of several hundred square miles the timber has
been destroyed by fire, I estimate that one-half the surface included within
the timber-line is covered by forest of more or less mature growth.

By careful measurements of the map, the area within the timber-line
or outer boundary of the forest at the edge of the plains is three thousand
eight hundred square miles. One-half of this, or one thousand nine hun-
dred square miles, is covered by woods, including the large forests of young
trees, as well as the sections of valuable timber.

Portions of this area are difficult of access, or the timber is wind-shaken
and injured in quality, and the forests of small pine are relatively more
extensive than the tracts of timber of a mature growth. Hence I estimate
that one-fifth the above area of the Black Hills, or nearly eight hundred

324 GEOLOGY OF THE BLACK HILLS.

square miles, equal to 500,000 acres, is covered by timber of merchantable
quality, suitable for cutting and sawing into lumber.

Col. R. I. Dodge, commanding the escort, by an entirely independent
series of observations, estimates the merchantable timber at only about four
hundred square miles, and comparing it with the pine forests of North Caro-
lina, he says:

I estimate that there are in the two sections something over four thousand square
miles of country more or less covered with pine. Of this, including the Red Valley,
the parks, the bare bottoms, and valleys of creeks, I estimate that four-tenths are
entirely without timber. Another four-tenths is composed of young forests, excellent
for railroad ties, small buildings, fencing, &c., but not yet fit for the saw-mill. One-
tenth is wind-shaken or injured by lightning or fire, and one-tenth is good lumber. In
other words, I think that this four thousand square miles will furnish not more than
one-tenth of the merchantable lumber that would be obtained from an equal area of the
virgin pine forests of Michigan or North Carolina. There is an abundance of lumber
for all purposes of the country itself, but, except ties, it will not furnish any very large
quantity for exportation.*

*The Black Hills, by Richard Irving Dodge, lieutenant-colonel, United States Army. James
Miller & Co., New York, 1876, p. 102.

U. S. GEOGRAPHICAL AND GEOLOGICAL SURVEY OF THE ROCKY MOUNTAIN REGION.
J. W. POWELL, IN CHARGE.

neal OUN LOLOG Y

OF THE

BLACK HILLS OF DAKOTA.

By R. P. WHITFIELD.

325

van

Aupany, N. Y., December 10, 1876.

Dear Sir: I herewith submit to you the following report on the fos-
sils collected by the United States Geological and Geographical Explora-
tions in the Black Hills of Dakota during the summer of 1875, and placed
in my hands for determination.

The report contains figures and descriptions of the fossils of the Pri-
mordial, Jurassic, and Cretaceous formations only, those of the Carbon-
iferous not being deemed of sufficient interest to warrant the expense.

I have been under obligations to the officers of the Smithsonian Insti-
tution for the opportunity of making comparisons with their collections from
the same formations, and to Dr. C. A. White for personal courtesies while
so doing. I have also availed myself of the very valuable work of F. B.
Meek, esq., on the fossils of that region, lately published by the Department
of the Interior, a copy of which was sent to me at his request at the earliest
moment it could be obtained.

Very respectfully, yours, &c.,
R. P. WHITFIELD.
W. P. Jewnney, E. M.,
In charge Exploration of the Black Hills.

327

CHAPTER VI.

PALEONTOLOGICAL REPORT ON THE FOSSILS COLLECTED
BY THE UNITED STATES GEOLOGICAL AND GEOGRAPH-
ICAL SURVEY OF THE BLACK HILLS.

By. R. P. WHITFIELD.
SECTION I.
PRELIMINARY REMARKS.

The species described in the following pages were collected in and
around the Black Hills during the expedition, and represent the different
formations recognized, except the Carboniferous; from which, the fossils
obtained were few and of little interest.

The horizon of the Potsdam formation of the Black Hills appears to
be, so far as the fossils will serve to determine, about the same as that of
Wisconsin and the neighboring States, and of some of the layers the litho-
logical features are so nearly the same, that it would be difficult.to distin-
guish between specimens from the two localities. The purplish-green
quartzitic rock from the head of Red Canon Creek, containing Lingulepis
pinniformis Owen, sp., and several other Brachiopodous shells, appears to
hold nearly the same relation to the rest of the group as does that at the
Falls of the Saint Croix, from which the species was originally described,
namely, near the base, the Red Cafion Creek beds resting immediately on
the slates of older date (probably Huronian), while the Trilobitic beds and

the soft friable layers occur at a horizon of about 100 feet below the Car-
329

330 GEOLOGY OF THE BLACK HILLS.

boniferous. The entire fauna of the Black Hills beds closely resemble
that from Wisconsin; although the species are nearly all distinct, the
generic fasces is the same throughout. Among the fossils from the higher
parts of the formation there are quantities of Plante remains belonging to’
the genus Palcophycus, which I am informed cover the surface of the rocks
over large areas where exposed, being densely matted together. These
beds also hold a position similar to the plant beds of other localities.

The Jurassic formations seem also to be well represented in this region,
and many of the beds are highly fossiliferous. The species are not numer-
ous, but the individuals are extremely abundant, many of the slaty calca-
reous layers being so largely composed of organic remains, mostly Lamel-
libranchiates, as to be quite friable and easily broken in the hand, and some
of the sandy layers have their surfaces densely covered with the separated
shells of one or two species. The absence of Gasteropoda is a noticeable
feature at all localities from which specimens have been brought, no
example of this class of mollusks being present in the entire collection
from this formation. The few species of Fresh-water Gasteropoda described
as probably from this horizon in the Smithsonian contributions (Paleon-
tology of the Upper Missouri) being still doubtfully referred. This same
absence of Gasteropoda is also noticed in all the collections of Jurassic age
we have seen from the western countries, not more than three or four
species having been obtained beyond those above referred to.

Among the Cretaceous fossils there are many forms of great interest,
especially among the Inocerami and Cephalopoda. Among the former the
forms described under the new generic name of Hndocostea are interesting as
affording light on a group of shells which, although long known, have not
been fully understood, probably owing to the want of more and better
material which this collection has afforded, the feature there described hav-
ing previously been seen only on isolated poorly preserved specimens. _

Among the Cephalopods of the Cretaceous there are some fine exam-
ples of the aberrant forms of the Ammonite Group, which show very conclu-
sively that a rich field awaits the future collector in this region In some
of the localities of this formation from which collections have been brought
there appears to be a difficulty in recognizing the divisions of the group

PRIMORDIAL FOSSILS. 331

proposed by Messrs. Meek and Hayden, as the fossils of two of the divisions
are found intermingling at the same place and in the same layers. The
specimens brought from the locality on Old Woman Fork of the Chey-
enne are of this character; and there seems to be the same trouble among
those from certain parts of Beaver Creek. The collection affords no speci-
mens belonging strictly to the Divisions No. l and No. 3, though the beds
were observed, but not collected from.

SECTION Il.

‘ FOSSILS FROM THE PRIMORDIAL ROCKS.

LAs AL..

Genus PALAZZOCHORDA.
PALA OCHORDA PRIMA.

Plate 1, fig. 2.
Paleochorda prima Whitf., Prelim. Rept. Pal. Black Hills, 1877, p. 7.

Plants, the remains of which, as preserved on the surface of the rock,
consist of narrow, linear, grass-like stipes, coiled or twisted without any
regular order, leaving by their removal or decomposition flattened depres-
sions of from one line to two lines in width and of an indefinite length,
with rounded or obtusely-pointed extremities.

The examples in the collection before us are coiled, forming irregular
curves, usually enrolled, but sometimes sigmoidal. The surfaces are smooth
and structureless, presenting no marking whatever, although the substance
is usuaily. of a somewhat lighter color than the surrounding rock. The ter-
minations are usually sharply rounded, and the whole appearance is more
that of the impression of an Annelid than of a plant; though it is difficult
to conceive of the preservation of anything other than a plant to leave such
markings. We have referred them to the above genus, presuming them to
be congeneric with those figured by Professor McCoy in his Synopsis of
British Paleozoic Fossils, Plate 1 A, Fig. 3, although they are not elevated
or rounded bodies, but flattened stipes. :

332 GEOLOGY OF THE BLACK HILLS.

Formation and locality—In the plant-beds of the Potsdam formation
(probably Upper Potsdam or Calciferous). Head of Redwater Valley,
Black Hills.

Genus PALAZOPHYCUS Hall.
PALAIOPHYCUS OCCIDENTALIS.
Plate 1, fig. 3.
Paleophycus occidentalis Whitf., Prelim. Rept. Pal. Black Hills, 1877, p. 7.

Remains consisting of strong, subcylindrical, flexuous stems or roots,
covering the surface of the sandstone. ‘The stems are more or less rounded,
although frequently quite flattened, and varying in diameter from one-fourth
of an inch to one inch, frequently bifurcating and sometimes dividing into
threes. They are commonly interlaced with each other, but do not appear
to coalesce, but are simply overlapped; the surfaces, although sometimes
quite smooth, are generally marked by indistinct, longitudinal pits and
ridges of greater or less extent, frequently occurring of an inch in length,
while many are merely short, roughened depressions, which give a corru-
gated surface to the stems.

Judging from the specimens in the collection, we should suppose they
often attain considerable length, as on a specimen measuring nearly ten
inches the variation in diameter is scarcely perceptible, but occasionally
one will be found to terminate in an obtuse point.

This species bears some resemblance to Fucoides duplex Hall (Foster and
Whitney Lake Superior, p. 226, Plate A 23, Fig. 1), but does not present the
longitudinal depression along the middle, as in that one, except near a bifur-
cation. It is very similar to P. tubularis Hall, from the Calciferous sand-
stone of New York; but is less ridged, and has a somewhat different mode
of bifurcation from any of the specimens of that species which we have
seen. Ifa larger number of the New York species were examined, how-
ever, it is possible that the resemblance might be much greater than at
present supposed. ;

Formation and locality—In the plant-beds of the Potsdam formation
(probably Upper Potsdam or Calciferous). Head of Redwater Valley,
Black Hills.

PRIMORDIAL FOSSILS. Bore

PALZZOPHYCUS, sp. ?

Plate 1, fig. 1.

Besides the foregoing species of Paleophycus in the plant-beds at the
head of Redwater Valley, there are layers covered in places with disjointed
and almost characterless stems or rootlets of various sizes, ranging from a
twentieth of an inch to those of nearly or quite one-fourth of an inch in
diameter, and of various lengths. Some of them are straight and ridged, as
though they had been hard cylindrical bodies; while many are more or
less flexuous, and others have clavate terminations; but among them there
are none preserving enough of form to characterize them as a species, or to
place them positively in any established genus of value; we have therefore
represented them only, leaving them doubtfully under the above genus, but
without specific designation. Attention being thus directed to them may
lead others to collect and examine them still further, by which means some
light may be gained as to their nature and origin.

Very similar forms are common on certain layers of the Clinton Group
of Oneida County, New York, where very similar conditions have existed ;
but so far as we are aware no positive determination has been reached as
to their exact nature. Figures of these latter are given by Professor Hall
in Vol. I, Paleontology of New York, Plate 9, Fig. 4, and others of cor-
responding character are common on the Portage sandstones of Western
New York.

INCERTAISE DES.

ARENICOLITES, sp.?

Plate 2, fig. 25.

Some specimens of a hard white sandstone of the Potsdam Group, col-
lected near Warren Peaks, in the northern part of the Black Hills, are filled
with cylindrical perforations of an undetermined length, but measuring
about two inches on the specimen in hand, were supposed to represent
the existence of the genus Scotiraus. The tubes are about one line in
diameter, but are slightly variable in this respect, and have a somewhat
rigid character, although by no means parallel to each other, and some-

304 GEOLOGY OF THE BLACK HILLS.

times slightly curved; still they give no evidence of bifureating or anas-
tomosing with each other, as is the case with Scolithus linearis. In these
features they differ from that genus, and we are strongly inclined to consider
them as having had quite a different origin. It has been suggested that
they might have been the perforations or sheaths of the peduncles of lin-
guloid shells, and the same suggestion was made by the writer some years
ago to Professor Morse concerning some perforations in the sandstones of
the same formation at Trempeleau, Wis.; but in this latter case the tubes
are often found surrounded, or lined, by the fragmentary shells of Lingulas,
and the sandstones contain on their surfaces shells of Lingula or Obolella;
but these specimens furnish no such remains, nor are there any such brought
from the localities from which these tube-bearing specimens were obtained.
This fact would be rather against their linguloid origin, although they seem
to be all vertical to the bedding of the rock. This latter feature, together
with their rigid and somewhat uniform character, leads us to consider them
as the burrows of some species of Amnelid, rather than the cavities left by
the removal of the remains of plants.* Another block of sandstone from
Custer Peak, near the central portion of the Black Hills, has vertical tubes
of a similar form, but of larger size; while a block of reddish sandstone,
from the head of Redwater Canon, is filled with irregular cavities of vari-
ous sizes and shapes, being neither uniform in size or position, but which
have all the appearance of broken drifted stems of plants. These latter,
coming from the same locality as the species of Cruziana contained in the
collection, it is more natural to suppose may be the remains of vegetable
organisms. ‘These latter specimens are exactly similar to those figured by
Dr. D. D. Owen in the Geological Report of Wisconsin, Iowa, and Minnesota,
Plate 1 C1, Figs. 1-8.

* Since writing the above I have seen and described, in the Geological Report of Wisconsin,
specimens of a similar form that present indisputable evidence of their annelid character.

PRIMORDIAL FOSSILS. 300

BRACHIOPODA.

LINGULIDA.

Genus LINGULEPIS Hall.
LINGULEPIS PINNAFORMIS.
Plate 2, figs. 1-4.

Lingula pinnaformis Owen, Geol. Rept. Wis., lowa, and Minnesota, p. 583, Pl. 1 B, figs.
4, 6, and 8.

Lingula pinnaformis Owen, Repts. of Wisconsin, vol. 1, p. 21, fig. 3, and p. 435.
Lingula antiqua Hall, Foster & Whitney’s Lake Sup., part 2, p. 204, Pl. 23, fig. 2.
Tingulepis pinnaformis (Owen) Hall, 16th Rept. State Cab., p. 129, Pl. vi, figs. 14, 16.

Shell elongate-spatulate, rounded in front and on the sides, becoming
narrowed and attenuate toward the beak, especially on the ventral valve,
the cardinal slopes of which are long and slightly concave; apex of the
valve very slightly truncate; width about three-fifths as great as the length
in the most perfect individuals; surface of the ventral valve beautifully
rounded over the body of the shell, becoming proportionally more sharply
elevated along the middle on the narrowed portion, and almost subangular
on the upper part of the beak. Dorsal valve shorter than the ventral, more
broadly truncate at the upper end, and less regularly rounded on the sur-
face, sometimes being slightly flattened in the lower part.

Surface of the shell polished, but presenting decided lines of growth,
which, on weathered or partially exfoliated specimens, show a tendency to
a lamellose structure; they are also marked in the latter condition by fine
radiating lines, which are not apparent on the more perfect specimens.

The examples of this species before us are so exactly similar in their
form and characters to those from the Falls of Saint Croix, that it is impos-
sible to point out any differences that can be described.

Formation and locality—In greenish-purple sandstone of the Potsdam
formation, at the headwaters of Red Cafion Creek, Black Hills, Dakota.

336 GEOLOGY OF THE BLACK HILLS.

LINGULEPIS CUNEOLUS.
Plate 2, figs. 5, 6.
Lingulepis cuneolus Whitf., Prelim. Rept. Pal. Black Hills, 1877, p. 8.

Shells small, rather below the medium size, triangularly ovate in out-
line, or sometimes subcuneate; ventral valve triangularly ovate, with a sharp
somewhat pointed beak, the width and length about as three and four, and
the point of greatest width near the lower third of the length of the valve;
cardinal slopes abrupt, scarcely convex; basal line rounded at the sides,
but nearly straight in the middle; surface of the valve strongly convex,
becoming almost subangular in the upper part; dorsal valve much shorter,
proportionally, than the ventral, the length but little exceeding the width;
side and base more rounded and the beak truncate; surface distinctly
convex.

Surface of the shell apparently smooth, but usually exfoliated, in
which condition a few fine radiating lines are visible.

This shell differs from L. pinnaformis Owen in size and in the more
distinctly cuneate form of the ventral valve. At first sight it might be
taken for the young of that species, but a little critical examination soon
reveals marked distinctions in the truncation of the front margin, and
especially in the form of the cardinal slopes, which are rounded and never
concave, as in almost all ventral valves of that species. In consequence of
this latter feature the beak does not appear so attenuated as in that one,
although proportionally quite as long. In the general surface characters
and form of the valves it corresponds with the genus Lingulepis, although
we have not been able to distinguish the muscular impressions.

Were it not for the difference in the size of the shells, we should be
inclined to think this might be the species figured by Messrs. Meek and
Hayden (Paleontology of the Upper Missouri, p. 3, Plate 1, Fig. 1 a and 6)
as L. dakotensis; but as their figures appear to be of the natural size, we
should suppose it to be very distinct, as all the specimens of our shell
noticed have been small, none exceeding one-fourth of an inch in length.

Formation and locality—In soft, friable sandstone of the Potsdam Group,
at Red Canton Creek, in the Black Hills, Dakota.

PRIMORDIAL FOSSILS. aol

LINGULEPIS PERATTENUATUS.
Plate 2, figs. 7-9.
Lingulepis perattenuatus Whitf., Prelim. Rept. Pal. Black Hills, 1877, p. 9.

Shell spatulate or elongate-ovate, becoming acutely pointed toward
the beak; sides below the middle of the length of the ventral valve
rounded; front margin very regularly curved; cardinal slopes straight, or
sometimes slightly convex; greatest width a little more than half the
length of the ventral valve and sometimes nearly two-thirds as great.
Surface of the ventral valve depressed convex, very slightly subangular
alone the middle above the lower third of the length, and a little more
distinctly so in the upper part. Apex scarcely truncate. Dorsal valve
considerably shorter than the ventral, broadly truncated at the upper end,
the line of truncation being distinctly arched. Surface evenly convex.
Structure of the surface of the shell polished, with fine, somewhat lamellose,
lines of growth. |

The shell, in many points, closely resembles LZ. pinnaformis Owen, but
is a proportionally longer shell, and not exceeding one-half the size of the
adult specimens of that species. When compared in shape, it is more
elongate in front, the lower end of the shell forming a section of an ellipse
rather than of a circle, as in that one; the cardinal slopes are convex and
the valves proportionally longer, the apex being more elongated in propor-
tion to the size of the body of the shell, but not so narrow. The two spe-
cies are associated in the same blocks, and the dissimilarity between exam-
ples of the same size is so perceptible, that there will not be the slightest
difficulty in recognizing them as distinct.

Formation and locality.—In greenish-purple sandstone of the Potsdam
formation, at the headwaters of Red Canon Creek, Black Hills, Dakota.

LINGULEPIS DAKOTENSIS.

Plate 2, figs. 10, 11.
Linguelepis pinnaformis (Owen) M. & H., Pal. Upp. Missouri, p. 2, Pl. 1, fig. 1.
Linguelepis dakotensis M. & H., Pal. Missouri, p. 3.
“Shell subovate or ovate-subtrigonal, rounded in front and angular at

the beaks, moderately convex ; sides converging to the beaks with straight
22 BH

338 GEOLOGY OF THE BLACK HILLS.

or concave outlines. Beaks more or less produced, that of the larger valve
attenuate and acutely pointed. Surface marked by rather obscure con-
centric strize, which are sometimes crossed by faint radiating lines, usually
most apparent on exfoliated surfaces, and generally quite distinct near the
front, on the interior surface, and on internal casts.”

Although there are a number of fragmentary individuals of this spe-
cies in the collection, there are none in a condition to figure or describe ;
we have, therefore, copied the original description, and also the figures
from the Paleontology of the Upper Missouri, in order to give as perfect an
exposition as possible of the fauna of this period, represented in this
interesting region. The species differs from L. pinnaformis Owen, as it
occurs at the Falls of the Saint Croix, and also from the same locality in
its straight sides or cardinal slopes; in the more broadly rounded front,
and in the somewhat more regularly convex valves.

Formation and locality—In brown, somewhat ferruginous and friable
sandstones of the Potsdam formation, at Castle Creek, Black Hills, Da-
kota.

OBOLIDA.
Genus OBOLUS Eichwald.

OBOLUS? PECTENOIDES.
Plate 2, figs. 18, 19.

Obolus pectenoides Whitf., Rept. on a Reconnaissance of the Black Hills of Dakota, by
Capt. W. Ludlow, 1875, p. 103, Pl. —, figs. 1-3.

Shell rather small, transversely oval or broadly ovate, the length and
breadth being subequal; apex of the larger valve very obtusely pointed ;
cardinal margins sloping from the beak, and inclosing an angle of from
110° to 120° in most cases, but often a much greater angle, or in many
specimens the cardinal margin forms a segment of an elliptical curve ;
sides and base somewhat regularly rounded, the latter often being broadly
rounded. Dorsal valve shorter than the ventral and proportionally more
transverse. Exterior surface of the shell strongly lamellose; substance
comparatively thick,

PRIMORDIAL FOSSILS. 339

The specimens present in the collection are in a coarse friable sand-
stone and very imperfect, or in a harder band packed so closely together
that it is impossible to isolate a perfect valve from those surrounding, so
that the features are much obscured. The substance of the shell is the
same as those used in the original description of the species, loc. cit, and
on exfoliation presents the same peculiar radiating lines there indicated.
The imperfect material has not afforded any further knowledge of the
interior structure or muscular makings than there given.

Formation and locality.—In dark brown sandstone layers of the Pots-
dam formation, on Castle Creek, Black Hills, Dakota.

Genus OBOLELLA Billings

OBOLELLA POLITA.
Plate 2, figs. 12, 13.
Obolus apollinus ? Owen (not Hichwald), Geol. Surv. Wiscon., Iowa, and Minn., p. 501,
etc., Tab. 1 B, figs. 9, 11, 15, 20.
Tingula ? polita Hall, Ann. Geol. Rept. Wisconsin, 1860, p. 24.
' Obolella ? polita Hall, 16th Rept. State Cab., p. 103, Pl. vi, figs. 17-21.

Shells small, short-ovate, being much the broadest below the middle
of the length and narrowing above, somewhat abruptly so to the small, rather
pointed beak of the ventral valve; basal line broadly but regularly rounded;
surface convex, rather strongly rounded, most abruptly so in the upper
part and becoming prominent and highly rounded toward the beak on the
ventral valve, and more evenly rounded on the dorsal; surface of the
shell smooth, or showing lamellose lines of growth on the weathered or
partially exfoliated specimens. Interior of the shell not observed in any
of the specimens present in the collection.

The shells referred to this species among the collections from the
Black Hills differ very little from those from Wisconsin; they are rather
more regularly ovate, not so wide below, nor so regularly narrowing
toward the beaks, as the generality of those from that locality; the surface
is slightly more lamellose and not so. polished; but the specimens are all
more or less weathered and less perfectly preserved, and are few in num-

340 GEOLOGY OF THE BLACK HILLS.

ber, so that the comparison is not a favorable one; still there is no doubt
of the correct identification, as the differences are no more than might
result from local causes.

Formation and locality.—In friable sandstone of the Potsdam forma-
tion, at the head of Redwater Canon, Black Hills.

OBOLELLA NANA.
Plate 2, figs. 14-17.

Obolella nana M. & H., Proc. Acad. Nat. Sci. Phil., Oct. 1861, p. 435.
Obolella nana M. & H., Pal. Upp. Missouri, p. 4, PI.-1, fig. 1.

‘Shell very small, subcircular or transversely suboval; moderately
convex; rather thick; front broadly rounded; sides more narrowly rounded.
Beak of dorsal valve short and obtuse. Ventral valve proportionally a
little longer than the other, or about as wide as long, and having a slightly
more prominent beak; without a distinct mesial ridge within; scar of
anterior adductor muscle? located behind the middle; impressions of
sliding muscles narrow; cardinal area rather narrow and flattened; groove
for the passage of the peduncle shallow. Surface marked by a few con-
centric grooves or impressed strie; exfoliated specimens showing small,
regularly disposed radiating strize.”

The above is the description of the species as given by its authors in
the Paleontology of the Upper Missouri, and agrees well with the many
specimens before us from the same region of country. But we notice
among them considerable diversity of form; different individuals varying
from transversely oval to elongate triangular-ovate, as will be seen by refer-
ence to the figures on Plate II. The specimens vary very much also in
the degree of convexity, many of them being flattened-discoid, while others
are highly ventricose or become quite gibbous in the vicinity of the umbones.
It is possible there may be more than one species among the specimens
referred by us to this one; but as on many blocks, bearing an,ageregate
of several hundred individuals, the general similarity is so great, while the
individual characteristics are so variable, we should not hesitate for a
moment to consider them all as of the same species. One feature is quite
noticeable, however, among them, that the transversely broad-oval speci-

PRIMORDIAL FOSSILS. 341

mens are almost always depressed-convex, while the narrower forms
are more highly convex. But among them there are all grades of outline
between the two extremes, and the variation in the convexity of the indi-
viduals is as gradual as the change in form; while the texture of the shell
and the surface markings are the same throughout the whole. The shells
are all minute, seldom attaining more than a line in length by a little less
in width, or length and breadth subequal; some of the larger individuals,
which are of the transversely broad-oval form, will measure about a line
and half in width by a length somewhat less. We have not been able to
satisfactorily see the internal muscular impressions, and have therefore
copied Messrs. Meek and Hayden’s figure showing these features.

Formation and locality—In a hard quartzitic sandstone, of the Potsdam
formation, of dark greenish-purple color, at the headwaters of Red Canon
Creek, Black Hills, Dakota.

ARTICULATA.

TRILOBITA.
CALYMENIDA,.
Gexus CREPICEPHALUS Owen (? LOGANELLUS Devine.)

CREPICEPHALUS CENTRALIS.

Plate 2, figs. 21-24.
Orepicephalus (Loganellus) centralis Whitf., Prelim. Rept. Pal. Black Hills, 1877, p. 10.

Species recognized only by the glabella and fixed cheeks, with a few
imperfect fragments of the movable cheeks. The former parts, when
united, are somewhat quadrangular in outline, broadest at the base and
gently narrowing in front; glabella round-conical, higher than wide,
the anterior end somewhat sharply rounded; surface highly convex and
marked by three pairs of distinct lateral furrows, which are strongly
directed backward in their direction from the margin, and on the larger
specimens the posterior pair almost unite in the middle. Occipital furrow
distinct, extending entirely across the base of the head; occipital ring

342 GEOLOGY OF THE BLACK HILLS.

strong, rounded, and in the older individuals supporting a short spine;
dorsal furrows well pronounced, extending with equal clearness in front of
the glabella. Fixed cheeks broad, more than equaling one-half the width
of the glabella; palpebral lobes small and slightly angular, situated oppo-
site the middle of the glabella; ocular ridges distinct, directed anteriorly
in passing from the eye to the dorsal furrow. Frontal limb short, not more
than one-third as long as the glabella, one-half of its length formed by the
strong, rounded marginal rim and furrow. Facial suture directed gently
inward from the front of the eye lobe to the anterior margin, with but little
curvature ; behind the eye it is directed backward and outward at an angle
of from 35° to 40° with the occipital line of the head, with a slightly
sigmoidal curvature, giving an elongate triangular form to the postero-
lateral limbs.

There is considerable variation in the form and proportions of the
glabella among the different individuals in the collection, the larger speci-
mens being proportionally broader and the lateral furrows much more
distinctly marked. On the smaller one figured the furrows are not distinct
enough to indicate without exaggeration. The presence or absence of an
occipital spine is also noticed, dependent apparently on the same cause.
It is possible that the two individuals may belong to different species, but
from their great similarity in other respects we feel confident that this is
not the case.

This species resemble in some of its characters C\(Bathyurus?) angulatus
H. and W., from the same formation on the west side of Pogonip Mountain,
White Pine, Nevada, described in the Geological Exploraton of the Fortieth
Parallel, vol iv, p. 220, Plate 2, Fig. 28, but lacks the angular frontal limb of
that species, and the facial sutures converge in front of the eye, while in that
one they are slightly divergent. We know of no other species with which
it is closely related, unless it should prove to be more nearly related to
Agraulus Oweni M. & H., Paleontology of the Upper Missouri, p. 9, Figs.
A, B, C, than we are inclined to believe; there are several particulars in
which it differs very materially from their figures and also from the descrip-
tion given, that would at once mark it as distinct, if it were not that the
imperfect material in both cases tend to lead to error. The difference in

PRIMORDIAL FOSSILS. , 343

the width of the occipital lobe is a very marked one, and also the length
of the frontal limb; while the form of the glabella varies much in being
more distinctly conical than in that species..

Formation and locality——In coarse sandstones of the Potsdam formation,
at Castle Creek, Black Hills, Dakota.

CREPICEPHALUS PLANUS.

Plate 2, fig. 20.
Orepicephalus (Loganellus) planus Whitf., Prelim. Rept. Pal. Black Hills, 1877, p. 11.

Glabella and fixed cheeks, when united, subquadrangular in outline,
narrowest across the eyes and slightly expanding in front, and more
abruptly so posteriorly. Glabella very depressed convex, slightly conical
and somewhat squarely truncate in front, the width across the base being
equal to about three-fourths of the height above the occipital furrow, and that
of the anterior end equal to about half the height; lateral furrows very faintly
marked, oblique, and extending about one-third of the width from the
margin. Occipital furrows not strongly marked, extending entirely across
the base of the head; ring narrow and without spine. Dorsal furrows
distinct, but not deep, extending around the front of the glabella. Fixed
cheek wide, more than half as wide opposite the eye as at the middle of the
glabella. Frontal limb of moderate length, at least as long as the width of
the anterior end of the glabella, but its entire extent and anterior margin
lias not been fully ascertained. Facial suture cutting the anterior border
at right angles to the margin of the head and directed slightly inward to
the eyes, behind which it is directed obliquely backward, at an angle of
about 60° with the base of the head, to the occipital furrow, behind which
itruns more directly outward. Ocular ridges distinct. Palpebral lobes
small and situated behind the middle of the head.

The species is only known by the glabella and fixed cheeks, and is
remarkable only for its general flatness and want of prominent characters.
There is no known species from the same formation either in the Wisconsin
locality or from the more western regions that is so closely related to it as
to be readily mistaken. C. (L.) quadrans H. & W., Geological Exploration

344 GEOLOGY OF THE BLACK HILLS.

of the Fortieth Parallel, vol. iv, p. 238, Plate 2, Figs. 11-18, from the slates
above Call’s Fort, North Wasatch Mountains, is perhaps as closely related
as any, but differs in having the glabella more rounded in front and propor-
tionally broader.

Formation and locality—Associated in the same beds and locality with
the preceding species.

SECTION IIl.

FOSSILS FROM THE JURASSIC ROCKS.

RADIATA.
ECHINODERMATA.

ASTEROIDEA.

Genus ASTERIAS Linn.
ASTERIAS ? DOUBIUM.

Plate 3, fig. 3.
Asterias? dubium Whitf., Prelim. Rept. Pal. Black Hills, 1877, p. 15.

Several impressions of a species of Starfish, apparently of the genus
Asterias, are present in the collection from a bed of light-red sandstone
which occurs at a horizon of from 80 to 100 feet above the red Triassic beds.

The specimens are not in a condition to afford a full description of
their specific characters. They are of small size, the rays being from
three-fourths of an inch to one and one-fourth inches long,
the center of the body. The rays are slender and flexuous, most of them

measuring from

being more or less curved in their direction and elevated along the middle,
as shown on a gutta-percha cast taken in a natural mold of a group of
three individuals. The upper surface is subangular, and in structure they
are apparently composed of small nodiform plates, placed in longitudinal
rows. The center of the body or disk is marked by an obscurely pentan-
gular depression on the upper surface. None of the specimens show the
under side of the body or rays, so that the characters of these parts are
entirely unknown.

JURASSIC FOSSILS. ; 345

The species appears to have been somewhat abundant, judging from
the condition in which they are grouped on the sandstone, and although
the specimens are obscure and too imperfect for positive determination and
description, it has been thought best to designate them by name, as they
will undoubtedly prove a characteristic form over a certain region and of
a limited horizon. The sandstone is marked on the layers in which they
are found, by ripple or wave marks, having a width of about three inches, and
indicates a near proximity to a shore-line over the area where they were
obtained, and that the individuals are probably stranded specimens. A
single very imperfect impression of a Lamellibranchiate shell is present
on the same fragments of rock, but too imperfect for determination.

Formation and locality—In red sandstones of Jurassic age, 70 feet
above the red beds, on the east side of Spearfish Creek, near its junction
with the Redwater, Black Hills, Dakota.

CRINOIDEA.
PENTACRINIDA.

Genus PENTACRINITES Miller.

PENTACRINITES ASTERISCUS.
Plate 3, figs. 1, 2.

Pentacrinus asteriscus M. & H., Proc. Acad. Nat. Sci. Phil. March, 1858, p. 49, ibid., Oct.
1860, p. 419.

Pentacrinites asteriscus M. & H., Pal. Upp. Missouri, p. 67, Pl. i, fig. 2.

Pentacrinites asteriscus (M. & H.) White, Pal. Rept. Lieut. Wheeler’s Rept. U. S. Geol.
Surv. 100th Meridian.

Pentacrinites asteriscus? (M. & H.) H. & W., Geol. Expl. Fortieth Parallel, vol. iv, p.
280, Pl, 6, fig. 16.

Messrs. Meek and Hayden describe this species from rocks of Jurassic
age at the southwest base of the Black Hills, but none of them appear to
have been obtained in the collections of Mr. Jenney’s expedition. The fig-
ures on Plate 3, are from examples from the Big Horn Mountains, and are
given for the purpose of presenting the form, which is so characteristic a
fossil of this formation in the western part of the continent.

346 GEOLOGY OF THE BLACK HILLS.

BRACHIOPODA.
LINGULIDA.

Genus LINGULA Brug.
LINGULA BREVIROSTRIS.

Plate 3, figs. 4, 5.

LTingula brevirostris M. & H., Proc. Acad. Nat. Sei. Phil. 1858, p. 50.
Ibid., Oct. 1860, p. 419.
Lingula brevirostris M. & H., Pal. Up. Missouri, p. 69, Pl. 3, fig. 3.

“Shell subovate, varying to spatulate-ovate, very thin; lateral margins
nearly straight or somewhat convex, generally converging a little towards
the beaks; front subtruncate or abruptly rounded; cardinal extremity nar-
rowly rounded. Beaks obtuse and apparently not extending beyond the
cardinal margin.”

The above is the author's description of the species as given in the
Paleontology of the Upper Missouri, so far as it relates to the general form
of the shell. The specimens which we have examined correspond very
closely with their figures above cited, except that they are not usually as
broad, proportionally, as their Fig. 3, but with Fig. 3 a they agree. The
sides of the shells are slightly converging above the lower third of the
length to the commencement of the cardinal slopes; the beak is obtusely
pointed and short; the base rather sharply rounded than otherwise—that
is, the curve is not that of a true circle, but rather paraboloid; but we
have seen none of them which might be called subtruncate. The surface
of our shells are not polished, being somewhat decomposed or exfoliated
by the separation of the rather soft sandstone in which they are embedded.
The shells are rather highly convex and somewhat inclined to angularity
from the beak to near the middle of the length, below which they become
slightly flattened on the central portion, though not enough to modify the
form of the front outline. Fine concentric lines mark the surfaces on all

the specimens.

JURASSIC FOSSILS. 347

Formation and locality—In red sandstones of Jurassic age, from 80 to
100 feet above the red beds referred to the Triassic, on the east side of
Spearfish Creek, near its junction with the Redwater, Black Hills, Dakota.

RHYNCHONELLIDA.

Genus RHYNCHONELLA Fischer.

RHYNCHONELLA MYRINA.
Plate 3, figs. 6, 7.
Rhynchonella sp.? M. & H., Pal. Up. Missouri, p. 71, Pl. 4, fig. 3.
Rhynchonella myrina H. & W., Geol. Expl. Fortieth Parallel, vol. iv, p. 284, Pl. 7, figs. 1-5.

Shell ot moderate size, subcircular or subtriangular in general outline,
with moderately convex valves. Ventral valve depressed-convex in the
middle portions, more sharply rounding upward along the cardinal slope,
and marked by a broad, shallow depression along the middle in the anterior
half of the shell, becoming somewhat more abrubtly bent upward in front ;
beak moderately large, pointed, and incurved. Dorsal valve more convex
than the opposite and more generally rounded, the beak appressed and
incurved within that of the ventral; middle portion of the valve elevated
forward of the center, forming a broad mesial elevation corresponding to
the depression of the other valve.

Surface marked by from twenty to twenty-eight distinct, rather angu-
lar, radiating plications, from four to eight of which are depressed in the
sinus of the ventral valve, and a corresponding number elevated on the fold
of the dorsal. These are crossed by distinct, often strongly-marked, con-
centric lines of growth and finer concentric striz, which arch across the
plications more or less abruptly according as they are more or less angular.

The shells under consideration are doubtless the same as those referred
to by Messrs. Meek and Hayden loc. cit., and are also identical with those
described under the name Lt. myrina H. & W. loc. cit., but are quite distinct
from those given under the name of R. gnathophora Meek, Geological Sur-
vey California, Pal., Vol. I, Plate 8, Fig. 1, being proportionally broader,
less equally convex, and much more finely plicated.

Formation and locality.—In white limestones of Jurassic age, above the
red beds referred to the Triassic, at Red Canon Creek, Black Hills, Dakota.

348 GEOLOGY OF THE BLACK HILLS.

LAMELLIBRANCHIATA.
OSTREID A.
Genus OSTREA Linn.

OSTREA STRIGILECULA.
Plate 3, figs. 8-12.

Gryphea calceola var. nebracensis M. & H., Pal. Upp. Missouri, Pl. 3, fig. 1 a-f.

Not Gryphea calceola var. nebracensis M. & H., loc. cit., p. 75, figs. A-E.

Gryphe calceola var. nebracensis (M. & H.) H. & W., Geol. Expl. Fortieth Parallel, p.
268, Pl. 7, fig. 11.

Ostrea strigilecula White, Geol. Surv. 100th Meridian, ete.

Shells of moderate size or smaller, very variable and irregular in form,
but usually somewhat curved or subreniform in outline. Lower valve often
attached to foreign bodies by nearly its entire external surface, and when
separated shows a broad, irregular cicatrix, from the edge of which the
sides and basal margins rise at a considerable angle, and form the cup of
the valve of greater or less depth The posterior or cardinal portion of the
valve is often quite shallow, while the basal or front border rises to a height
equal to more than two-thirds of the entire length of the valve. Cardinal
end of the valve narrow, triangular, and with a ligamental area of propor-
tionally large size. Upper valve flattened or very depressed-convex. Sur-
face of the valves strongly lamellose or concentrically ribbed and wrinkled ;
muscular impression large in most examples.

The shells of this species are extremely variable in character, it being
quite difficult to select two specimens of the same form from a collection of
a moderate number. The shell has been referred to Gryphea; but, as has
been remarked under the observations on the species in vol. iv, Geologi-
cal Exploration Fortieth Parallel, p. 287, it presents, at many localities,
the features of a true Oyster, and not those ascribed to the genus Gryphea.
Since those remarks were written, Dr. C. A. White has described it under
the name Ostrea strigilecula, considering it entirely a distinct species from

the forms given by Meek and Hayden, Paleontology of the Upper

JURASSIC FOSSILS. 349

Missouri, p. 75, Figs. A-E, as the normal forms of their G. calceola vay.
nebracensis, with which opinion we entirely agree. We have examined a
large number of individuals from several widely-separate localities, and
also masses of rock composed almost entirely of the shells, but find no
specimens among them having the characters of the genus Gryphea, or
with the specific features ascribed to the var nebracensis.

Formation and locality—tIn rocks of Jurassic age, at a horizon of 350
feet above the red beds referred to the Triassic, east of the Belle Fourche
. River; also at an elevation of 300 feet at the same place, and at an eleva-
tion of 20 feet above the same horizon at the Belle Fourche; also at Sun
Dance Hill and near Beaver Creek, Black Hills. The localities near the
Belle Fourche are nearly opposite Bear Lodge Butte.

Genus GRYPHAA Tenn

GRYPHA#A CALCEOLA var. NEBRASCENSIS.
Plate 3, figs. 13-16.

Gryphea calceola var. nebracensis M. & H., Proc. Acad. Nat. Sci. Phil., Dec. 1861, p. 437.
Gryphea calceola nebracensis M. & H., Pal. Upp. Missouri, pp. 74 and 75, figs. A-E.
Shells of moderate size, very inequivalve, and but slightly oblique;
lower valve the largest, somewhat ovate in outline, strongly arcuate, and
showing a tendency to trilobation in the lower part of the larger individ-
uals; beak strong, incurved, and sometimes enrolled, but not truncated at
the apex by any cicatrix of attachment, its substance much thickened by
the solidifying or filling up of the rostral portion of the valve. Anterior
side of the valve rather rapidly spreading for some distance from the beak,
and below rounding abruptly to the narrow basal border; posterior side of
the valve less expanded above, but often more so below, and distinctly lobed
by a sulcus which marks the exterior from a little below the beak to the
postero-basal border, which is in consequence sometimes strongly emargi-
nate; ligamental area of moderate size, triangular, and concave; muscular
impressions not very large and rather faintly marked, elongate-paraboloid
or truncate-ovate, and situated behind the middle of the shell. ‘Upper
valve ovate, nearly flat on the outside, or a little convex near the beaks,

350 GEOLOGY OF THE BLACK HILLS.

and more or less concave near the middle, usually concave on the inner
side toward the cardinal extremity, which is thick and truncate; surface
with rather distinct concentric marks of growth.” (M. & H.)

Exterior surface of the larger valve often marked by distinct and some-
times wiry, irregular, longitudinal striz, which radiate from the apex and
continue to below the middle of the valve. —

Messrs. Meek and Hayden formerly united this and the preceding
species (Ostrea strigilecula), under the same name, as a variety of Quen-
stedt’s G. calceola. It appears to us, however, from an examination of spec-
imens, that they are clearly distinct, generically as well as specifically, and
that if the same variations of form occur associated with each other in the
European localities, it is very probable that the two genera are also there
represented as well as in our American formations.

Formation and locality—tIn rocks of Jurassic age, Wind River Mount-

ains.

PECTENID A.

Genus PECTEN Bruguieres.
PECTEN NEWBERRYI.
Plate 4, figs. 12-15.
Pecten newberryi Whitf., Prelim. Rept. Pal. Black Hills, 1877, p. 16.

Shell of moderate size, suborbicular in outline, erect, and subequilat-
eral, the height and length nearly equal. Valves depressed-lenticular in a
transverse section when united; their surfaces .depressed-convex, except
along the sides of the valves near the cardinal slopes, where the surface is
elevated so as to form a broad, rounded, fold-like border on this part, with
a broad, undefined, shallow depression separating it from the body of the
valve. Hinge line short; that of the left valve less than half as long as the
shell below; straight, or a very little sloping outward from the apex of the
valve, which is small, appressed, and not projecting above the line of the
hinge Anterior side of the hinge a little longer than the other, the ante-
rior wing being rounded at the extremity, more than as long again as the
height above the body of the valve at its widest part; separated from the
shell below by a very shallow, rounded byssal notch, and along the surface

JURASSIC FOSSILS. : 351

by a searcely perceptible groove bordering the body of the valve. Poste-
rior wing smaller, triangular, a little obtuse at the outer upper angle, and
proportionally somewhat higher or longer on the lateral border than the
anterior wing. Surface of the left valve marked, except on the fold and
depression bordering the cardinal slopes, by strong, flattened radii, which
are variable in strength, size, and distance, and are separated by flattened
interspaces, usually of greater width than the ribs themselves. The sur-
face is also marked by closely-arranged, distinctly-elevated, regular, lam-
ellose, concentric lines, parallel to the outer margin, and coincident with the
lines of growth, and are slightly arched backwards in crossing the radii.
These latter markings also cover the surface of the folds of the cardinal
borders and the cardinal auriculations.

A single right valve of small size, associated with a number of left
valves on the same block, has the same general form and the same fold-like
feature of the cardinal slope, but appears to be entirely destitute of the
radii on the body of the valve, and the concentric markings are also much
less distinct and regular than on the opposite valve. ‘The anterior wing is
also very small and obtusely triangular, but may have been somewhat
mutilated. There can be little if any doubt, however, that this right valve
belongs to the same species.

This species may be readily distinguished by the peculiar fold-like
feature of the cardinal slopes and the character of the concentric mark-
ings; being entirely different in these respects from any other of the genus
described from rocks of this age.

Formation and locality.—-In reddish and buff-colored argillaceous lime-
stones of Jurassic age, at T—— Springs, west of the Black Hills of Dakota.

Genus CAMPTONECTES Agassiz.
CAMPTONECTES BELLISTRIATUS.
Plate 4, figs. 6-11.

Pecten bellistriatus Meek, Proc. Acad. Nat. Sci. Phil. July, 1860, p. 311.
Camptonectes bellistriatus M., Smithsonian Cat. N. A. Jurassic Foss., 1864.
Camptonectes bellistriatus M. & H., Pal. Upp. Missouri, p. 77.

Shells large, circular or slightly oblate in outline; valves depressed-
convex, or when united lenticular; the left valve perceptibly the most

352 GEOLOGY OF THE BLACK HILLS.

convex; hinge line nearly straight, varying from a little more than one-
third to nearly one-half as long as the body of the shell below; posterior
ear very short, usually not more than half as long as the anterior one, the
extremity very obtusely angular, the posterior margin sloping rapidly
backward to the junction with the body of the shell; anterior ear on the
left valve flattened, of moderate size, the margin very slightly obtuse, and
more rapidly sloping near the body of the valve. That of the right valve
is separated from the body of the shell by a deep triangular notch or sinus,
extending fully one-half the length of the wing; surface of the auriculation
marked by a single strong, flattened, and gradually widening rib, at a dis-
tance below the hinge line equal to its own width, and crossed by strong,
somewhat lamellose lines parallel to the outer margin. Surface of the
shell marked by very fine radiating lines or striz, which diverge from the
median line and curve rapidly in their direction toward the margin, and
on the upper part of the shell are strongly recurved, so as to have an
upward direction along the margin below the beak. The striz are rapidly
increased both by bifurcation and implantation, and are crossed by a few
moderately strong concentric lines of growth, and by finer, regular, con-
centric striz, only strongly marked on the interspaces of the radii, where
they form transverse puncta along the depressions.

On the interior of the right valve, the space on the hinge line above
the strong rib marking the anterior ear is crossed by rather strong vertical
lines, which seems to be a character pertaining to the articulation of the
valves, and on the posterior side the border is elevated, forming a distinct
ridge similar to those on the hinge of Plewronectia Swainson.

The shells of this species vary considerable in outline and degree of con-
vexity; many of the right valves are somewhat squarish on the upper side
below the auriculations, as in the interior of the right valve figured, in
which case they are usually unsymmetrically curved along the basal bor-
der, while most are regularly orbicular, and occasionally they are slightly
elongated. The degree of strength of the surface striz is alse a point in
which they differ in different localities; those from the Big Horn Mountains,
which are usually of large size, are the most finely marked, and many
smaller specimens from the Black Hills region having the strize twice as

JURASSIC FOSSILS. . 300

strong. It is possible that there may be several species confounded under
this name, but with the insufficient material yet brought in, it is impossible
to separate them satisfactorily.

Formation and localities —In rocks of Jurassic age, near Bear Lodge, on
the Belle Fourche River, 20 feet above the Red Beds; on Spearfish Creek,
300 feet above the Red Beds; in Redwater Valley, 350 feet above the Red
Beds; and in the Big Horn Mountains.

CAMPTONECTES EXTENUATUS.
Plate 4, figs. 4, 5.

Camptonectes extenuatus M. & H., Proc. A. N. Sci. Phil., May, 1860, p. 184.

Camptonectes extenuatus M. & H., Pal. Upp. Missouri, p. 78, Pl. 3, fig. 6.

Camptonectes (?) pertenuis M. & H., ibid., Explan., Pl. 3, fig. 6.

Camptonectes (?) extenuatus (M. & H.) Meek, Smithsonian Check List Invert. Foss., p. —.

Camptonectes (?) extenuatus (M. & H.) Hall & Whitf., Geol. Expl. Fortieth Parallel, p.
290, Pl. 7, fig. 18.

Shell varying from small to rather above a medium size, somewhat
ovate or suboval in outline, exclusive of the auriculations. Hinge line of
the left valve straight, equal to a little more than half the greatest length of
the body of the shell in an antero-posterior direction; posterior side short,
but little more than half as long as the anterior. Auriculations large, tri-
angular, the posterior one obtusely angular behind, the margin sloping
rapidly backward to the junction with the body of the shell. Anterior
auriculation convex on the surface between the cardinal line and the body
of the shell below; lateral margin nearly at right angles to the hinge, its
surface marked only by concentric lamellose lines. Body of the shell four-
fifths as great in an antero-posterior line as the height from hinge to base,
the anterior and posterior borders nearly equally rounded, the posterior
side forming a little the longest curve; basal border more sharply curved.
Beak small, rather sharply rounded, and somewhat appressed, not projecting
above the hinge line. General surface of the valve strongly convex, most
ventricose between the beak and the middle of the valve, and in some
cases approaching angularity (perhaps from compression). Surface of the
shell marked by fine radiating striee, which diverge from the median line
and are strongly curved as they approach the lateral border, and still more:

23 BH

354 GEOLOGY OF THE BLACK HILLS.

strongly toward the line separating the auriculations from the bedy of the
shell. Also by finer concentric strize crossing the radii, which are lamellose
in their structure in the depressions between the ribs, with deep pits between
them, giving a punctate character to the interspaces. Right valve of the
species not observed.

The shell differs from C. bellistriata M. & H. in the more elongate
form, greater size of the auriculations, and coarser strize of the left valve.
We have no doubt, in our own minds, in regard to the proper reference
of this species. The uniform small size of the type specimens is no reason
why larger individuals might not occur, and there are also large numbers
of individuals in the collection of the size of Fig. 5, and smaller, having
exactly the same features as the type. It has been suggested that it might
be C. platissiformis White (Geology of the Uinta Mountains, p. 93,) but
that species is said to have the outline of C. stygius White, which this cer-
tainly has not.

Formation and locality—In shaly limestones of Jurassic age about
twenty feet above the red beds, east of the Belle Fourche River, near Bear
Lodge, Black Hills.

AVICULIDA.
Genus PSEUDOMONOTIS Bronn.

PSEUDOMONOTIS (EUMICROTIS) CURTA.
Plate 3, figs. 20-25.
Avicula curta Hall, 1852, Stansb. Rept. Great Salt Lake, p. 412, Pl. 2, fig. 1.
Avicula (Monotis) tenuicostata M. & H., Proce. Acad. Nat. Sci. Phil., 1858, p. 50.
Monotis curta M. & H., Proc. Acad. Nat. Sei. Phil., 1860, p. 418.
Humicrotis curta (Hall) M., Smithsonian Check List Jurassic Foss., 1864.
Eumicrotis curta (Hall) M. & H., Pal. Upp. Missouri, p. 81, Pl. 3, f. 10.
Humierotis curta (Hall) H. & W., Geol. Expl. Fortieth Parallel, p. 289.
Pseudomonitis (Eumicrotis) curta (Hall) Meek, Geol. Surv. Mont. Idaho, Wyom. and
Utah, 1872, p. 473.

Shell of moderate size, suborbicular in outline, very slightly oblique,
and nearly equivalve, generally a little higher than wide; beaks subcenéral
or nearest to the anterior end; hinge short, usually less than half the length
of the shell below, longest on the posterior side; left valve the most rotund

JURASSIC FOSSILS. 300

and the beak small, but often approaching tumid, the apex incurved and
extending a little above the hinge-line; anterior wing small, abruptly
rounded toward the beak, its surface strongly curved toward the opposite
valve near the cardinal margin, so as to leave a small byssal opening, or gap-
ing at the anterior margin; posterior wing longer and somewhat flattened
toward the extremity; surface of the valve marked by raised radiating lines,
which are very variable in number and character on different individuals,
and also by concentric lines which often form slight asperities or nodes in
crossing the radii, especially on the sides and near the basal border of well-
preserved specimens; right valve slightly less convex than the left, with a
smaller and less conspicuous beak, which does not extend beyond the cardi-
nal line; anterior side characterized by a short and very narrow wing, sep-
arated from the body of the shell by a sharp, deep, and very narrow groove,
the actual sinus scarcely extending within the limits of the wing, while the
anterior margin of the valve below extends considerably beyond the ex-
tremity of the wing in a nearly parallel direction; posterior wing propor-
tionally larger and compressed, the extremity angular and sometimes almost
pointed, the posterior border of the valve running nearly at right angles to
the hinge line, or slightly sinuate below; surface of the valve marked by
strong concentric lines of growth, and on the body of the shell by obscure
radii, which are often obsolete. Each valve is further characterized by a
narrow, longitudinally striated ligamental area, extending nearly or quite
to the extremities of the hinge line; and in the right valve the area is nar-
rowed anteriorly, for the accommodation of the internal, slightly oblique
fold of the shell, forming the depressed groove between the ear and the
body of the shell. On the left valve there is a slight depression or break
in the ligamental area beneath the beak, and an apparent depression on the
right valve (these features of the area are obscure and a little uncertain on
account of the small size of the specimen). Muscular impression as seen
on a right valve rather large, and subcentrally situated.

We have considerable doubt as to any very close relations of this spe-
cies to the genus Pseudomonotis, as typified by Monotis speluncaria Munster,
or P.hawnt M. & H. All the Upper Carboniferous specimens of the latter
species which we have examined appear to have a distinct notch or sinus

356 GEOLOGY OF THE BLACK HILLS.

between the anterior ear of the right valve and the body of the shell below.
In this species there is no true notch, at least no sinus, the depression or
groove separating the wing from the body of the shell being simply a fold
of the shell projecting on the interior surface in form of a strong fold below
the hinge area, just as it does in some specimens of the right valve of the
the genus Meleagrina Lam., to which shell we are inclined to think them
closely related. If the genus Pseudomonotis Bronn, must be retained for
the M. speluncaria group, it seems to us it might be well to retain the name
Eumicrotis, proposed by Meek and Hayden for that same group for this
section, as it is equally applicable to these shells.

Formation and localities.—In rocks of Jurassic age, two miles south of
the Belle Fourche River, near Bear Lodge Butte; on Beaver Creek; on Red
Canon Creek, near the Cheyenne; and in Redwater Valley, Black Hills.

PSEUDOMONOTIS (EUMICROTIS) ORBICULATA.
Plate 3, figs. 17-19.

Pseudomonotis (Eumicrotis) orbiculata Whitf., Prelim. Rept. Pal. Black Hills, 1877, p. 17.

Shell of moderate size, orbicular in outline, nearly equilateral, and sub-
discoid. Left valve depressed convex, most rotund just below and anterior
to the beak; beak small, full, slightly incurved, and projecting somewhat
above the cardinal border. Anterior wing very short, almost obsolete, the
anterior end regularly rounded from its extremity to and along the basal
margin; posterior wing of moderate size and compressed, shorter than the
shell below, the posterior margin rounding backward from its extremity to
near the middle of the length of the valve, thence somewhat regularly
rounded to the base. Surface of the valve marked by numerous unequal,
slender, and slightly elevated radii, which are separated by wider flattened
interspaces, also by irregular concentric strize of growth, which often give
a knotty or roughened surface to the radii where crossing them, especially
toward the posterior border and near the outer margin. Right valve less
convex than the opposite one, with a smaller inconspicuous beak, which
does not project beyond the cardinal line. Anterior side of the hinge line
characterized by a small and very obscure wing, which is reduced to a mere
point, reaching to not more than one-third of the length of the very short

JURASSIC FOSSILS. Br

anterior side of the hinge. The wing is separated from the body of the
shell below, as in others of this division of the group, by a narrow and
rather deep groove, but not by a distinct sinus. Posterior wing longer and
compressed, but not extending to more than half the length of the body of
the shell below. Surface of the valve marked, in all cases observed, by
fainter radii than the left valve, but otherwise of similar character.

This species is closely related to P. (E.) curta Hall, but is much larger,
several of the individuals measuring seven-eighths of an inch in length;
and one specimen measures nearly an inch, while those of that species
seldom attain to more than two-thirds of that size. The shell is also much
less oblique, less convex, the radii sharper and not usually so distinct,
although in this latter feature they both differ very materially among the
different individuals; and the right valve is also distinctly marked by the
radii, which is not the case in that one.

Formation and locality—In calcareous clays of Jurassic age, ranging
about 20 feet above the red beds, in Redwater Valley, Black Hills.

GENUS AVICULA Lam.
Supcenus OXYTOMA Meek.

AVICULA (OXYTOMA) MUCRONATA.
Plate 4, figs. 1, 2.

Pteria (Oxytoma) munsteri (Bronn) M. & H., Pal. Upp. Missouri, p. 80, f. A. B.
P. or Avicula (Oxytoma) mucronata M. & H., loc. cit., p. 81.

Shell rather below the medium size, moderately oblique, the axis of
the shell forming an angle of a little more than 45° with the posterior
hinge line, although somewhat variable in this respect. Body, exclusive of
the wings, rather broadly and obliquely ovate, the greatest transverse diam-
eter being obliquely across the shell a little below the middle of the height.
Hinge-line very slightly declining on each side of the beak and somewhat
shorter than the length of the shell below; posterior wing on the left valve
about twice as long as the anterior, flattened or compressed on the surface
and mucronate at the extremity, separated from the body of the shell below
by a broad, but not very deep, sinus; anterior wing small, slightly rounded

358 GEOLOGY OF THE BLACK HILLS.

at the extremity and ventricose on the surface; beak moderately large,
pointed, incurved, and extending above the cardinal line; body of the shell
quite prominently convex, especially on the umbo; anterior margin of the
shell slightly projecting in the upper part so as to leave a faint sinus below
the anterior wing, and regularly rounding obliquely backwards and down-
ward to the basal border below, with which it forms an almost regular curve
to near the posterior basal extremity, which is sharply rounded. Right
valve smaller than the left, very depressed-convex, becoming’ distinctly
flattened toward the posterior margin and wing; beak small, pointed, but
not projecting beyond the hinge line; posterior wing large; anterior wing
small, and separated from the body of the shell by a depressed groove.

Surface of the right valve faintly marked by a few distinct radii.
That of the left valve marked by a varying number of distant, elevated,
raised radii, flattened on their surfaces and separated by interspaces of
twice or thrice their width, bearing finer lines.

Messrs. Meek and Hayden refer this species with doubt to Avicula mun-
steri Bronn, and at the same time suggest the name A. (0.) mucronata, which
we have adopted on the evidence of their suggestion, not having been able
to compare them with European specimens.

Formation and locality—In shaly limestones of Jurassic age, on the
tops of the highest hills, two miles south of the Belle Fourche River, near
Bear Lodge Butte, Black Hills.

Genus GERVILLIA De France.
GERVILLIA RECTA.

Plate 4, fig, 3.
Gervillia recta Meek, U.S. Geol. Surv. Terr., vol. ix, p. 66.

A single small right valve of a species of Gervillia occurs in the
collection, which, so far as we can judge, appears to belong to the above-
named species. ‘The valve is very triangular'in form, oblique and depressed
convex, the body of the shell being scarcely distinct from the rather large
posterior wing, and entirely destitute of any surface markings other than
the ordinary lamellose concentric lines common to all the species of the

genus; hinge line straight and about two-thirds as long as the extreme

JURASSIC FOSSILS. 359

length of the body of the shell, measuring from the beak to the base with
the obliquity of the valve. Anterior ear very small and barely perceptible;
beak not rising above the cardinal line, small, and somewhat compressed ;
outer margin of the posterior wing nearly at right angles to the hinge line
for some distance below, then directed backward to the extremity of the
basal line; anterior margin very oblique to the hinge and parallel to the
body of the shell

Having only a single right valve of the species, and that of small size,
it is somewhat difficult to satisfactorily identify it; but there appears no
feature on the shell that would contradict the reference.

Formation and locality—In sandy limestone of Jurassic age, associated
with Ostrea strigilecula and Mytilus whitei, near Sun Dance Hills, Black
Hills.

ARCIDA.

Genus GRAMMATODON M. & H.
GRAMMATODON INORNATUS.

Plate 5, figs. 16-18.
Arca (Cucullea) inornata M. & H., Proc. Acad. N. Sci. Phil., March, 1858, p. 51.
Grammatodon inornatus M. & H., ibid., Oct. 1862, p. 419.
Grammatodon inornatus M. & H., Pal. Upp. Missouri, p. 90, Pl. iii, fig. 9.

Shell small, arciform, subrhomboidal in outline, with ventricose, arcu-
ate valves, sometimes quite gibbous on the umbonal region. Valves a little
less than twice as long as high between the cardinal and basal borders;
hinge line straight, somewhat shorter than the shell below; anterior end
rounded, extending a little beyond the antero-cardinal extremity ; posterior
end obliquely truncate, the longest point being at the extremity of the
posterior umbonal ridge; basal line forming a broad semielliptical curve,
being most strongly rounded at each end. Beaks large, strong, slightly
incurved, strongly projecting above the body of the valve, subapproximate,
and situated just behind the anterior third of the length of the shell ; pos-
terior umbonal ridge somewhat angular, most distinctly so in the upper
part, becoming more obtuse below; posterior cardinal slope abrupt and very
gently concave between the ridge and the cardinal line; anterior umbonal |
region rounded.

360 GEOLOGY OF THE BLACK HILLS.

Cardinal area narrow, slightly arcuate and apparently extending to
the extremities of the hinge line. Surface of the shell marked by fine,
irregular, concentric lines of growth, and also by a few indistinct radiating
strize, which are very faint and sometimes obsolete.

Interior of the hinge marked by two or three slightly oblique lateral
teeth, which gradually increase in strength toward the posterior extremity,
and on the anterior end by several, more oblique, shorter cardinal teeth.
Muscular impressions small and somewhat obscure.

The shell is decidedly arciform in its general appearance, but the
character of the hinge teeth at once separate it from the genus Arca, and
the absence of the elevated crest or ridge bordering the muscular impression
equally distinguishes it from the genera Cucullea Lam. and Idonearca
Con. Its relations to the genus Macrodon Lycette, are more intimate, and
it is difficult, in the specimen which we have examined, to see where any
distinct generic difference exists.

Formation and locality—tIn rocks of Jurassic age, near the Black Hiils;.
exact locality not given.

MYTILIDA.

Genus MYTILUS Linn.
MYTILUS WHITEI.
Plate 5, figs. 9-12.
ilytilus whitei Whitf., Prelim. Rept. Pal. Black Hills, 1877, p. 18.

Shell of moderate size, trapezoidal in outline, very oblique; hinge line
slightly arcuate, as long or a little longer than the distance from the apex
to the postero-basal extremity; anterior or byssal border long, distinctly
concave from the apex of the beak to the junction of the basal border, the
general direction being at an angle of about 45°, or within 45° with the
cardinal line; posterior margin a little more than half as long as the shell
and nearly parallel to the anterior border, or slightly converging toward
the base; basal margin short and more or less rounded, somewhat variable
in different individuals. Beaks small, pointed, terminal, and incurved, with
a short but distinct area-like space beneath them; umbones prominent,

JURASSIC FOSSILS. 361

subangular, and with a slightly flattened or concave space on the anterior
side, just below the apex of the beak. Umbonal ridge elevated, strongly
arcuate and subangular, the surface of the shell sloping rapidly to the pos-
terior and postero-cardinal margins. Anterior slope of the shell nearly or
quite vertical, or sometimes a little concave near the middle of the length.

Surface of the shell marked by numerous strong but very irregular
varices of growth, which give to the shell an extremely rugose appearance.
Between the varices the surface is marked by fine lines of growth. No
radiating lines or other surface markings beyond those described can be
detected. Substance of the shell thick and strong.

The shell is a strongly marked and very characteristic species, and
judging from the fragments in the hand specimens of rock must have been
an abundant form in a certain layer at the locality where collected. We
know of no American species of the genus having any close resemblance to
this one.

Formation and locality—tIn rocks of Jurassic age, associated with
Jurassic fossils, near Sun Dance Hills, Black Hills.

Genus VOLSELLA Scopoli.

VOLSELLA (MODIOLA) FORMOSA.
Plate 5, fig. 15.

Modiola (Perna) formosa M. & H., Proc. Acad. Nat. Sci. Phil., Dec. 1861 p. 439.
Volsella formosa Meek, Smithsonian Check List Jurassic Foss. N. A., 1864, p. 28.
Volsella formosa M. & H., Pal. Upp. Missouri, p. 86.

Shell ventricose, very elongate-ovate or subelliptical, widest across the
shell at the end of the cardinal line, slightly arcuate, and becoming more
curved with increased growth. Cardinal line rather more than half the
length of the shell, slightly curved; beaks small, nearly terminal and
appressed; anterior end broad, extending but little beyond the beaks, and
sharply rounded below the middle of the width to the basal border, which
is slightly concave; posterior margin convex, gradually declining from the
extremity of the hinge line to the postero-basal extremity, where it is sharply
rounded. Body of the shell highly convex, somewhat subangular along

362 GEOLOGY OF THE BLACK HILLS.

the umbonal ridge and flattened on the lower side of the beak and anterior
end, cardinal slope slightly convex and abrupt.

Surface of the shell marked by fine lines or strize, which are regularly
radiating along the umbonal ridge and on the cardinal slope, while on the
ventral region they strongly diverge from the umbonal line and reach the
ventral border at right angles to the margin. The latter strize are consid-
erably finer than those of the cardinal slope and do not extend to or radiate
from the anterior extremity of the shell, but have their origin along the
umbonal ridge, thereby forming an entirely different system of strize from
those of the cardinal slope.

The specimens of the species which we have examined are of smaller
size than those figured by Messrs. Meek and Hayden, and the umbonal ridge
is more angular, while the surface of the valve below the beak for some
distance from the anterior extremity is more compressed than shown in their
figures. These are probably, however, only individual differences, though
in the specimens examined are quite marked.. The authors of the species
compare it with Mytilus cancellatus Goldf. of Europe, and state that it may
possibly prove to be identical; but specimens of that species which we have
- seen do not possess, at least do not show, the striations on the ventral side
of the umbonal ridge as seen on those of this species.

Formation and locality—In rocks of Jurassic age, near Big Horn Mount-
ains.
VOLSELLA PERTENUIS.

Plate 5, figs. 13, 14.
Mytilus pertenuis M. & H., Proc. Acad. Nat. Sci. Phil., March, 1858, p. 51.
Volsella pertenwis Meek, Smithsonian Check List N. A. Jurassic Foss., 1864.
Yolsella pertenuis M. & H., Pal. Up. Missouri, p. 86, Pl. 3, fig. 5.

“Shell small, very thin and fragile, narrowly oblong-oval, slightly
arcuate; valves convex along the middle, from near the beaks obliquely
backward in the direction of the lower part of the posterior end. Extremi-
ties narrowly rounded, the anal end being a little broader than the other;
base slightly arched behind the middle. Hinge nearly straight, and appar-
ently rather less than half the length of the shell; dorsal margin forming a
broad descending curve from the back extremity of the hinge posteriorly.
Beaks small, subangular, and located at the anterior end, scarcely projecting

JURASSIC FOSSILS 363

beyond the margin. Surface marked by fine, rather obscure, lines of
growth. |

‘Length, 0.73 inch; breadth, 0.26 inch; height, 0.30 inch.”

The specimens of this species in the collection are internal casts in a
fine red sandstone, associated with Lingula brevirostris M. & H., and do
not show the entire external features of the shell, although the concentric
lines are preserved. The specimens agree pretty well with the above
description and figures, except that the shell is not so arcuate as represented,
nor so angular along the umbonal ridge, and the anterior end is somewhat
narrower and less full on the buccal portion. In any of these features,
however, shells of this class are very liable to vary very much among the
different individuals of a species, as we plainly see in nearly all of the
living species. Messrs. Meek and Hayden compare it with Modiola minuta
as figured by Queenstedt (Des. Jura, Tab. 1, Fig. 36), and observe that they
are at a loss to point out characters by which to distinguish it. As a
general rule, we do not agree with the almost indiscriminate identification

of species from our American formations with those of Europe, especially

among the non-migratorial forms of life, but with shells of this class, which
are frequently moored to floating wood or other substances, that are apt to
be transported to great distances without material injury to the animals,
we see no reason why the same species might not be an inhabitant of
distant countries, and therefore think it even more than probable that this
may be identical with the above-named species of Europe.

Formation and locality—In fine-grained red sandstone of Jurassic age,
at from 80 to 100 feet above the red beds referred to the Trias, east side of
Spearfish Creek, near its junction with the Redwater, Black Hills.

CRASSATELLIDA.

Genus ASTARTE Sowerby.
ASTARTE (?) FRAGILIS.
Plate 5, figs. 32, 33.

Astarte fragilis M. & H., Proc. Acad. Nat. Sci. Phil., May, 1860, p. 183.
Astarte fragilis M. & H., Pal. Up. Missouri, p. 94, Pl. iv, fig. 7.

Shell small, thin, and fragile, transversely oval in outline, nearly two-
thirds as high as long, with depressed convex valves, most ventricose at the

364 GEOLOGY OF THE BLACK HILLS.

anterior third of the length, and gradually decreasing in convexity poste-
riorly. Beaks scarcely elevated above the cardinal line, small, pointed,
strongly directed forward, and situated rather within the anterior fourth of
the entire length of the shell. Anterior end short and rounded, the longest
point opposite or a little below the middle of the height; basal line regularly
and gently arcuate; posterior end more sharply rounded than the anterior,
longest below the middle, the cardinal line sloping with a gentle convex
curvature from the beaks to the longest point. No appearance of escutcheon
or lunule exists on the examples under consideration. Ligament very
small and external.

We have no hesitation in referring the specimens under consideration
to the above-named species, but they certainly are not congeneric with the
recent forms of Astarte. They seem to us to be much more nearly related
to some of those referred to the genus Cyrena, especially such as C. papua
Prime; but as the internal features of the hinge have not been observed, it
is impossible to fully determine their generic relations; and we have there-
fore left the generic reference as originally given by the authors of the
species.

Formation and locality—In shaly limestones of Jurassic age, at a
horizon 350 feet above the Red Beds, at Redwater Valley, Black Hills.

Genus TRAPEZIUM Humph. (= CYPRICARDIA Lam.)

TRAPEZIUM BELLEFOURCHENSIS.
Plate 5, figs. 1-4.
Trapezium bellefourchensis Whitf., Prelim. Rept. Pal. Black Hills, 1877, p. 18.

Shell small, transversely elongate quadrangular, the length being from
two and a half to three times greater than the height: dorsal and basal
margins subparallel, the former very slightly arched and the latter scarcely
concave, except in the older individuals, the smaller and medium-sized
individuals being usually a little curved upward toward the posterior end;
beaks small, nearly terminal, rounded on the umbones and very slightly
incurved; posterior extremity truncate in the older specimens, rather
squarely so below and rounding forward to the extremity of the hinge line

JURASSIC FOSSILS. 365

above. In the smaller individuals it is narrower, somewhat sloping from
- above or obliquely truncate. Anterior end very slightly prolonged below
the middle of the height and excavated beneath the beaks. A narrow
linear escutcheon of considerable length is seen on many of the separated
valves. Anterior muscular impression rather large and strongly impressed,
as shown by the strong markings on internal casts; posterior impression
not distinguishable; pallial line faint, and the space within its limits often
marked by radiating lines, as in the recent forms of the genus.

Surface of the valves ventricose, with a distinctly angular umbonal
slope in the larger specimen, but often obtusely rounded in the smaller
ones. A broad but rather faint depression runs obliquely backwards from
the beak to the middle of the basal border on many individuals, but is not
always present. Surface of the shell marked by one concentric lines
of growth parallel to the margin of the valve.

The species is closely allied to a form described by Mr. Meek Gn MS.)
under the name of Trepezium (Pachymya) truncata, but is proportionally
very much more elongated than the specimens which are so labeled in the
collection at the Smithsonian Institution. The shells have been exceedingly
abundant in certain layers, being densely packed together, so that it is im-
possible to separate the individuals. They are quite variable in form at
different stages of growth, the younger shells being transversely elongate-
ovate, narrowed and rounded, or very obliquely truncate from above
posteriorly, and becoming almost squarely truncate behind in the older
specimens, the slight sinuosity of the basal margin being hardly noticeable
until they attain to near their adult size.

Formation and locality—In a hard and somewhat silicious limestone of
reddish color, at a level of 350 feet above the Triassic beds east of the
Belle Fourche River, near Bear Lodge Butte, Black Hills.

TRAPEZIUM SUBEQUALIS.
Plate 5, figs. 5-8.
Trapezium subequalis Whitf., Prelim. Rept. Pal. Black Hills, 1877, p. 19.

Shell small, transversely elongate, subelliptical, about twice and a half
as long as high, or nearly so. Valves somewhat ventricose, with large

366 *sKOLOGY OF THE BLACK HILLS.

tumid beaks situated a little nearest to the anterior end, and projecting
above the general line of the hinge; hinge line, posterior to the beaks,
about half as long as the entire length of the shell, straight, but gradually
declining to the extremity; posterior end of the shell very obliquely trun-
cate, being much the longest below the middle at the postero-basal angle;
anterior end shorter, slightly contracted in front of the beaks, but rounded
at the extremity and broader than the opposite end; basal margin straight
or very slightly convex in the middle and strongly rounded upward toward
each extremity. Body of the shell often distinctly angular along the pos-
terior umbonal ridge and the postero-cardinal slope quite abrupt; some
individuals, however, are obtusely rounded on the umbonal ridge. Surface
of the shell marked by rather strong concentric ridges of growth, which
are crossed on the rounded anterior end and middle of the valve by
extremely fine radiating strize, only detected near the basal portion of the
larger individuals by the aid of a moderate magnifying power.

There may be some little doubt as to the true generic relations of this
shell, but it possesses so many of the features of 'Trapezium that we have
not hesitated to refer it to that genus; the almost subcentral and somewhat
prominent beaks forms the strongest point of difference. It differs in this
respect from the preceding species, as also in the general form of the valves
and in the surface markings. The shells of the two species have nearly the
same dimensions, and in their mutilated and imperfect condition, as seen —
imbedded in the rock, may readily be confounded, but the more prominent
beaks and longer anterior end of this one will at once distinguish them.

Formation and locality—In a hard white sandstone of Jurassic age,
associated with Pseudomonotis curta, just above the Triassic red beds at Red
Cation Creek, Black Hills, Dakota.

JURASSIC FOSSILS. / 367

FAMILY uncertain.*
Genus PLEUROMYA Agassiz.
PLEUROMYA NEWTONI.
Plate 5, figs. 19, 20.
Pleuromya newtoni Whitf., Prelim. Rept. Pal. Black Hills, 1877, p. 20.

Shell of moderate size, transversely subovate or triangularly ovate, the
greatest height being across the valve nearly on a line with the beaks.
Valves strongly convex near the anterior end, and in a cardinal view acutely
wedge-shaped, thickest opposite the beaks and rapidly decreasing posteriorly.
Beaks large, strong, enrolled, and approximate, situated at or within the
anterior third of the length of the shell, and projecting largely above the
cardinal line. Hinge line not exceeding one-half the length of the shell,
distinctly arched ; anterior end obliquely subtruncate, longest below at its
junction with the basal margin, and in some cases the anterior slope is dis-
tinctly flattened. Posterior end narrowed, the postero-cardinal margin
rapidly declining from the extremity of the hinge line to the longest point
of the valve, which is narrowly rounded and at about the middle of the
height; basal margin very slightly constricted or emarginate, just within
the anterior third of the length, by a faint sulcus, which passes from the
surface of the umbo to the base of the shell; posterior to this it is strongly
convex, and as it approaches the posterior third of the length is more
strongly rounded upward to the extremity. Body of the valve convex,
most ventricose on the umbones and along the middle of the valve; ante-
rior umbonal ridge obtusely angular; anterior slope abrupt and sometimes
flattened obliquely; posterior umbonal ridge scarcely defined or broadly
rounded. Immediately behind the anterior umbonal ridge a broad unde-
fined sulcus passes across the valve, slightly modifying the direction of the

*The family relations of this shell, as well as some others herein described, are not yet satis-
factorily determined; and we do not like to refer them to a family to which we feel certain, from their
characters as far as known, they have no resemblance or affinity; we rather prefer to leave them in
doubt, and as subjects for future investigation. The reference of Pleuromya and Myacites to the same
family with Anatina, we deem unnatural, as from the character of the shell and the consequent habits
of the animal they must have been very far removed from each other in structural features, and thesé
we deem the only sure and reliable means of classification.

368 GEOLOGY OF THE BLACK HILLS.

concentric lines. No appearance of escutcheon or lunule exists, nor of an
external ligament.

Surface of the shell marked by numerous irregular concentric undula-
tions, which are usually broad and undefined, but on some individuals have
a slightly sharper character. The general surface beyond these undefined
undulations appears to have been smooth, and we should suppose from its
character that it had been semi-polished. Substance of the shell moder-
ately thick. The features of the hinge and interior have not been fully
ascertained. There appears, however, on the left valve a strong tooth-like
process of considerable height, and in front of it a deep triangular pit,
probably ligamental.

This species differs from Myacites (Pleuromya) subcompressa Meek (Sixth
Annual Report United States Geological Survey of the Territories, 1872, p.
472), in being proportionally longer; more distinctly ovate or less triangu-
lar, the anterior end being of greater length in proportion to the rest of
the valve; the beaks are larger and project farther above the cardinal
line; the body of the shell is less flattened and the surface less strongly
marked.

Formation and locality—In shaly limestones of Jurassic age, on top of
the highest hills two miles south of the Belle Fourche River, near Bear
Lodge Butte, Black Hills.

TANCREDIIDA.
Genus TANCREDIA Lycett (= HETTANGIA Terquem.)

TANCREDIA ? INORNATA.
Plate 6, figs. 9-13.
Astarte inornata M. & H., Proc. Acad. Nat. Sci. Phil., May, 1860, p. 183.
Astarte inornata M. & H., Pal. Up. Missouri, p. 94, Pl. iii, fig. 12, a. b.

Shell transversely subelliptical, or transversely broad-triangular; ex-
tremities narrowly rounded and the basal border forming a broad, nearly
regular semi-elliptical curve. Valves convex, most ventricose along the
posterior umbonal portions. Beaks large, prominent, nearly subcentral and
incurved, usually a little nearer the anterior end; cardinal line strongly

JURASSIC FOSSILS. 369

arcuate, convex behind the beaks, and slightly contracted and a little con-
cave just in front; anterior end much narrower than the posterior, and the
longest point below the middle of the height. Lunule, as seen on the
separated valves, very narrow-lanceolate. Surface of the shell smooth, or
with obsolete lines of growth forming obscure concentric indulations. Fre-
quently a very faint depression, or sulcus, passes from in front of the beaks
to the antero-basal margin. The hinge line is marked by a rather strong,
curved cardinal tooth in each valve, with corresponding cavity or pit situ-
ated beneath the beaks; the left valve having the tooth anterior to the pit,
and reversed in the right valve; a small posterior lateral tooth appears to
exist in the left valve, and may, possibly, in the right, but it has not been
noticed. Muscular impressions small; pallial line with a broad, shallow
sinus; interior margin of the shell smooth and thickened.

We have supposed this to be the shell described under the above name
by Messrs. Meek and Hayden, as it agrees with their description and figure
in its external characters. It appears, however, that they had not seen the
internal features. In quite a number of specimens in the collection before
us the internal features, as given above, are more or less clearly seen,
mostly by the removal of the external shell, leaving the impression of parts
of the hinge, and on some of the casts the pallial sinus is clearly marked.
This latter feature is one that does not belong to the genus Tancredia, and
it is with considerable hesitation that we have left it under that name; still,
as we know of no other established genus to which it can be properly
referred, we have preferred this rather than to propose a new division on
insufficient grounds. ‘The following species appears to have all the charac-
ters of Tancredia, except, perhaps, the pallial sinus, which has not been
detected on any but the present form. They are, therefore, more nearly
true Tancredia.

Formation and locality—In shaly, arenaceous limestone of Jurassic age,
at an elevation of 350 feet above the red beds referred to the Triassic, east
of the Belle Fourche River, near Bear Lodge Butte, Black Hills.

24 BH

370 GEOLOGY OF THE BLACK HILLS.

TANCREDIA CORBULIFORMIS.
Plate 6, figs. 5-8.
Tancredia corbuliformis Whitt., Prelim. Rept. Pal. Black Hills, 1877, p. 21.

Shell small, seldom measuring more than half an inch in length, very
broadly ovate in outline and largest on the posterior side of the beaks, the
length being a little more than once and a half the height; beaks large and
full, slightly enrolled, almost central and strongly inclined toward the ante-
rior part of the shell. Anterior end narrowed, strongly constricted in front
of the beaks, giving a somewhat concave antero-cardinal line, the extremity
acutely rounded; posterior end broadly rounded and, the postero-cardinal
line convex to near the beaks; basal line regularly curved, except at the
posterior part, where it becomes a little more abrupt. Body of the valve
strongly convex, almost inflated on the umbo.

Surface of the shell apparently smooth, but under a magnifier showing
faint, scarcely defined, lines of growth. ,

The species differs from T. inornata M. & H., in its smaller size; more
inflated valves; proportionally larger and more prominent beaks, and
greater inequality in size of the anterior and posterior parts of the sheil.

Formation and locality—In sandy and somewhat shaly limestone of
Jurassic age, 350 feet above the red beds of the Triassic, east of the Belle
Fourche River, near Bear Lodge Butte, Black Hills.

TANCREDIA BULBOSA.
Plate 6, figs. 1-3.
Tancredia bulbosa Whitf., Prelim. Rept. Pal. Black Hills, 1877, p. 22.

Shell very small, the larger individuals not measuring more than three-
eighths of an inch in length by a height of one-fourth of an inch; very
broadly ovate in outline, being inflated and globuliform in the middle and
posteriorly, and attenuate, narrowed and compressed toward the anterior
extremity. Beaks strong, inflated, curving anteriorly and situated a little
to the anterior of the middle of the shell; anterior end acutely rounded,
the sides of the shell abruptly compressed by a broad, undefined, constrict-
ing sulcus, or depression, which passes obliquely across the valve from in
front of the beaks to the basal border, in which it forms a distinct emargi-

JURASSIC FOSSILS. 3 371

nation; posterior end broadly rounded and the postero-cardinal line strongly
convex; antero-cardinal line constricted in front of the beaks and concave
between them and the anterior extremity; basal line very convex for a little
more than two-thirds of the length from the posterior end, where it becomes
emarginate at the base of the oblique sulcus or depression which crosses
the anterior part of the valve. Surface semi-polished, and under a magni-
fier showing fine lines of growth.

The species resembles T. corbuliformis herein described, but is a smaller
shell, seldom occurring of more than half the usual length of that one,
and is much more extreme in the unequal size of the anterior and posterior
parts of the valve, besides being much more globose in form and having
the anterior oblique sulcus of the valve much more strongly marked.

Formation and locality——In rock of Jurassic age, associated with T. cor-
buliformis and T. inornata, at the same locality.

TANCREDIA POSTICA.

Plate 6, fig. 14.
Tancredia postica Whitf., Prelim. Rept. Pal. Black Hills, 1877, p. 22.

Shell small, transversely ovate, the height and length being about as
three to five. Valves very ventricose, becoming tumid near the beaks and on
the postero-cardinal part. Beaks large and but little elevated above the cardi-
nal line, slightly enrolled and directed forward, situated at about one-third
ot the length from the anterior extremity; antero-cardinal line abruptly
declining in front of the beaks to the middle of the height of the valve;
anterior end narrow and sharply rounded; posterior end very broadly
rounded and the postero-cardinal and basal margins subparallel behind the
beaks, the extreme height of the shell continuing to the posterior end;
antero-basal line strongly curving upward to the anterior end of the shell.
Surface of the valves apparently smooth.

The shell differs from any of the preceding species in the greater
length and proportionate size of the posterior portions of the shell, in the
situation of the beaks, and in their strong anterior inclination, the others
being much more erect than those of this species. It will be readily recog-

372 GEOLOGY OF THE BLACK HILLS.

nized by the inflated valve, subparallel cardinal and basal margins, and short
anterior end.

Formation and locality—In shaly limestones of the Jurassic formation,
east of the Belle Fourche River, Black Hills, associated with the preceding

species.
TANCREDIA WARRENANA.
Plate 6, fig. 4.
Tancredia warrenana M. & H., Proc. Acad. Nat. Sci. Phil., May, 1860, 183; ibid., Oct.
1860, p. 418.

Tancredia warrenana M. & H., Pal. Up. Missouri, p. 96, Pl. 3, fig. 7.

Shell small, subtriangular in outline, or triangularly ovate, moderately
convex, and nearly two-thirds as high as long. Beaks proportionally large,
projecting above the cardinal line, erect, pointed, and subangular; situated
rather more than one-third of the entire length from the posterior end of
the shell. Hinge line contracted in front of the beaks, and somewhat regu-
larly sloping anteriorly. Anterior end of the shell much the longest,
narrowed and compressed, rounded at the extremity, and, judging from the
form of the shell as seen in separated valves, has been distinctly gaping;
posterior end short, obliquely truncate and abrupt; basal line gently and
regularly arcuate throughout; posterior umbonal ridge sharply angular,
the posterior cardinal slope narrow and abruptly declining. Surface un-
known.

The specimens of this species present in the collection are casts of the
interior on layers of fine white sandstone, and do not preserve the surface
features or any of the internal features of the shell.

Messrs. Meek and Hayden refer this species provisionally to the genus
Trancredia, remarking that its form leaves little doubt of its relations to that
genus. Our specimens are not in a condition to give any additional light
on its generic relations, and we are therefore obliged to leave it as originally
placed by its authors.

Formation and locality —In soft white sandstone of Jurassic age, asso-
ciated with Pseudomonotis curta Hall and other Jurassic forms, at a horizon
of 135 feet above the red beds of the Triassic, at Redwater Valley, south-
east of Warren Peaks, Black Hills.

JURASSIC FOSSILS. 373

VENERIDA.

Genus DOSINIA Scopoli.
DOSINIA JURASSICA.
Plate 5, figs. 21-24.

Dosinia jurassica Whitf., Prelim. Rept. Pal. Black Hills, 1877, p. 23.

Shell of moderate size, subcircular or very slightly transverse in form,
and for the genus quite ventricose, with rather large, prominent beaks.
Cardinal line arcuate, but less curved than the general circle of the shell,
while the anterior end is more sharply curved and slightly angular and the
posterior portion from the extremity of the hinge to the basal border very
slightly flattened or truncate. Beaks anterior to the middle of the valve
directed forward and approximate at their apices; lunule small and very
slightly impressed; ligament proportionally long, but narrow, the shell at
its margins slightly incurved. Body of the valve ventricose, most gibbous
on the umbones and below, while anteriorly and posteriorly the shell is
more compressed; umbonal ridges not defined.

Surface of the shell smooth with a few obsolete or faintly marked con-
centric irregularities, but no defined varices; fine concentric lines of growth
are seen on the perfect shelis under an ordinary magnifier. Inner margins
of the valves smooth; muscular impressions, large but faintly marked, sub-
marginal. Pallial line deeply sinuate, the apex of the sinus being directed
toward the beak of the shell.

The shell is a well-marked species of Dosinia, so far as the characters
have been ascertained, but the hinge structure has not been seen, none of
the casts being in a condition to show the teeth. The casts are quite abun-
dant on weathered specimens, where they have apparently been subject to
the percolating action of mineral waters, which has partially destroyed
them.

Formation and locality—tIn Jurassic rocks at the top or the highest hills,
two miles south of the Belle Fourche, and at a horizon 350 feet above the
Triassic red beds, east of the Belle Fourche, and also on the east side of
Spearfish Creek, near junetion with the Redwater, Black Hills.

374 GEOLOGY OF THE BLACK HILLS.

PSAMMOBIID AL.

Genus PSAMMOBIA Lam.
PSAMMOBIA ? PREMATURA.

Plate 5, fig. 31.

Psammobia ? prematura Whitf., Prelim. Rept. Pal. Black Hills, 1877, p. 24.

Shell small, transversely elongated, with parallel dorsal and_ basal
margins, the length equaling a little more than twice the height. Valves
very depressed-convex and distinctly gaping at each end. Beaks small
and inconspicuous, compressed, situated a trifle nearest the anterior end;
the antero-cardinal line gradually declining with a very slight convexity to
the narrowly-rounded anterior end; basal margin straight for more than
half the length of the shell, rounding upward anteriorly and posteriorly ;
postero-cardinal line a very little lower than the apex of the beak, behind
which it is straight to near the extremity of the shell; posterior extremity
reaching its greatest length considerably above the middle of the valve, the
margin being directed obliquely forward below to the end of the basal line.
Surface of the valve regularly curved from beak to base and from the
posterior umbonal ridge forward to the anterior extremity of the shell,
forming nearly a level line; posterior to the umbonal ridge the shell is
depressed, forming a broad oblique sulcus extending from behind the beaks
to the posterior margin of the shell. Muscular markings faint. Pallial
line not profoundly sinuate, but distinctly emarginate behind. Hinge and
teeth unknown.

The species is only recognized by single valves, but the form is so
precisely like that of some of the recent Psammobias that it seems unnat-
ural to refer it to any other genus. The parallel dorsal and basal margins
and the form of the posterior slope will readily distinguish it from any
other shell in the rocks from this region. |

Formation and locality —In the sandy limestones of the Jurassic beds,
east of the Belle Fourche River, near Bear Lodge Butte, Black Hills.

JURASSIC FOSSILS. at

ANATINIDA.
Genus THRACEA Leach.

THRACEKA ? SUBLEVIS.
Plate 5, fig. 34.

Thracea ? sublevis M. & H., Proc. Acad. Nat. Sci. Phil., May, 1860, p. 182; ibid., Oct.
1860, p. 418.

Shell rather below the medium size, transversely elongate with mod-
erately convex valve, which appear to have been somewhat gaping at the
posterior end. Beak large and wide, projecting somewhat above the hinge
line, and situated a little in advance of the middle of the length; anterior
end more broadly rounded than the opposite; basal line nearly straight or
very slightly sinuate near the middle, and rounded upward at each extrem-
ity; posterior extremity more narrowly rounded than the anterior, and
slightly oblique on the truncation; cardinal line sloping very moderately
from the beaks posteriorly, and rounding more abruptly in front; surface
of the valves very slightly impressed across the middle from the beaks to
the base by a very broad, undefined depression; posterior umbonal ridge
faintly marked, and the postero-cardinal slope rounded; anterior slope
more abrupt

Surface marked only by a few irregular concentric undulations of
growth parallel to the margin of the valve.

The specimens examined are single valves and imperfect, so that the
relative convexity cannot well be determined There can be no doubt of
their identity with those figured by Meek and Hayden as above cited; the
specimens are all of smaller size, however, but agree in all other respects.
They are preserved as casts in a white friable sandstone, and are associated
with Pseudomonotis curta, Tancredia warrenana, and other Jurassic fossils.

Formation and locality—tIn rocks of Jurassic age, at Redwater Valley,
Black Hills.

316 GEOLOGY OF THE BLACK HILLS.

Genus NEAZRA Gray.
NEARA LONGIROSTRA.
Plate 5, fig. 35.
Neera longirostra Whitf., Prelim. Rept. Pal. Black Hills, 1877, p. 24.

Shell very small, scarcely exceeding one-fourth of an inch in length;
transversely elongate-ovate or clavate, widest anterior to the middle and
narrowed behind, a little more than twice as long as high. Valves very
convex, becoming inflated near the middle and on the umbones. Beaks
proportionally large, erect, strongly projecting above the hinge line and
situated in front of the middle of the length; anterior end large and
broadly rounded, somewhat excavated beneath the beaks; posterior end
narrowed, elongate, and very slightly recurved, and obliquely truncate
above the umbonal angle; basal line strongly convex, more distinctly so
just in front of the middle opposite the beaks, and broadly constricted
behind; posterior umbonal ridge very faintly angular, and the cardinal
slope rather abrupt. .

Surface of the shell marked by a few concentric lines of growth, and
crossed on the anterior and middle parts of the shell by a few proportion-
ally strong elevated radiating ridges, to the number of eight or nine, with
wider flattened interspaces.

The species is small, and being preserved in a friable sandstone the
surface characters are not clearly defined, nor can any of the hinge or
other internal features be seen. ,

Formation and locality—In white sandstones of Jurassic age in Red-
water Valiey, Black Hills, associated with Pseudomonotis curta, Tancredia
warrenana, and other Jurassic fossils.

GASTROCHANIDA.

Genus SAXICAVA Bellerue.
SAXICAVA JURASSICA.
Plate 5, figs. 25-30.
Saxicava jurassica Whitf., Prelim. Rept. Pal. Black Hills, 1877, p. 25.
Shell small, elongate-subcylindrical, with subparallel dorsal and basal
margins; beaks approximate, distinct, situated near the anterior end, and

JURASSIC FOSSILS. 377

flattened on the exterior surface; umbonal ridge strongly marked and sub-
angular, placed behind the middle of the valve. Anterior end narrowed
and very slightly excavated below the beaks; postcrior extremity wider,
and rounded on the margin, the sides being laterally compressed; basal
margin very gently concave in the middle of its length. Body of the valves
very broadly sulcated between the anterior end and the umbonal ridge,
and somewhat inflated along the latter feature posterior to the middle of
the length. Surface of the shell rather distinctly marked by concentric
lines parallel to the margin, which are elevated and irregular, but not
lamellose; also by a few strong undulations of growth. Just below the
hinge line, on the postero-cardinal border, the surface strize are slightly bent,
and the surface of the shell very slightly angular. Internally, as seen on
casts, the anterior muscular impression is narrow, and situated along the
antero-basal margin. The pallial line appears to be strongly sinuate, and |
the dorsal margin shows evidence of a rather strong ligament. The casts
of the burrows as seen in the rock are almond-shaped or very elongate-
ovate.

A small fragment of argillaceous rock in the collection was found to
contain quite a number of the burrows, and on being broken a few were
found with the shells in position; but in an effort to develop them from the
matrix the shell is usually removed from the casts, although some of it
is at times retained, and it is from this rather imperfect material that the
description has been drawn. The general form of the shell and also the
external texture would seem to ally them with the angular group of the
genus Lithodomus characterized by L. gruneri Phillippi, but the sinus of the
pallial line would seem to forbid this reference.

Formation and locality —In rocks of Jurassic age, at a horizon of 350
feet above the red beds of the Triassic, at Redwater Valley, Black Hills.

378 GEOLOGY OF THE BLACK HILLS.

CEPHALOPODA.

TETRABRANCHIATA.
AMMONITID#.

Genus AMMONITES Bruguiere.
AMMONITES CORDIFORMIS.

Plate 6, figs. 20-24.

Ammonites cordiformis M. & H., Proc. Acad. Nat. Sci. Phil., March, 1858, p. 57.
Ammonites cordiformis M. & H., Pal. Up. Missouri, p. 122, Pl. v, fig. 2.

Shell attaining a large size, lenticular in a transverse section; young
individuals depressed-bi-convex, or slightly flattened for a short distance
on the side bordering the umbilical area, but becoming much more ventri-
cose in older individuals from the greater projection of the ventral or um-
bilical margin of the volution, the section of the volution in large specimens
being nearly an equilateral triangle. Umbilicus of moderate size, the
diameter equaling, or nearly equaling one-third the width of the outer volu-
tion ; its sides vertical on specimens of a little more than two inches in
diameter and larger, but on small individuals it is rounded, the parts of
each volution exposed within the umbilicus not increasing in width equal
to the increased size of the shell. Volutions sharply keeled on the back,
and the edge finely denticulated or transversely ridged. Side of the volu-
tions marked by transverse flexuose costa of very variable strength, which
have a sigmoidal curvature in passing from the margin of the umbilicus to
the dorsal carina, being strongly curved forward for the outer third of the
distance, and are increased by bifurcation and intercalation, so as to number
from three to six times as many on the dorsal margin as at the border of
the umbilicus. On some of the larger specimens the ridges become obso-
lete, the surface beg only marked by irregular strie, having the same
general direction in their passage across the shell as do the costae where
they exist.

The septa are moderately crowded, being placed so as to have the
lobes of one pass within the area of that in advance, but not so as to inter-

JURASSIC FOSSILS. 379

fere with the lines. The form of the different lobes and saddles cannot be
obtained from any of the specimens of moderate size in the collection, they
being too much mutilated, so we have copied the following description of
these parts from the authors as above cited :

“The dorsal lobe is a little wider than long, and has two principal
branches on either side, the two terminal of which are slightly larger than
the others, and each provided with seven or eight unequal digitations. The
dorsal saddle is about the size of the superior lateral lobe, contracted in the
middle, and divided at the extremity into some four or five short, unequal,
sinuous, and digitate branches. The superior lateral lobe is as long as the
dorsal lobe, but narrower, conical in form, and ornamented with three or
four lateral branches on the dorsal side, and two or three smaller ones on
the ventral side; while its terminal branch is bipartite, and its margins, as
well as those of all the other principal divisions, are more or less sinuous
and digitate. The lateral saddle is smaller than the superior lateral lobe,
and has on each side three or four short, obtuse subdivisions, with sinuous
margins. The inferior lateral lobe is smaller than the lateral saddle, and
divided at the extremity into two nearly equal, rather short branches, each
of which is sinuous, and shows a disposition to give off short subdivisions
on the outer side. The remaining lobes are very small, and obtusely digi-
tate, the inner one showing a tendency to bifurcate.”

The species is exceedingly variable in its surface markings, and also
somewhat so in the degree of convexity, the latter feature depending mostly
on the age of the specimens ; but the former variations are individual char-
acters only, and are almost limitless among the individuals even from the
same locality. The smaller specimen figured on Plate 6 has the primary
costa numerous and crowded, and seldom dividing or increasing to more
than twice the original number on approaching the dorsal margin; while
the next larger individual figured has them more distant at the umbilicus,
and dividing or increasing to the number of six to one in some parts, while
on still other specimens many or most of the costa are obsolete.

Messrs. Meek and Hayden compare this species with A. cordatus
Sowerby, and appear to be somewhat in doubt if it should not be referred
to that very variable form. There are, however, differences in the form of

380 GEOLOGY OF THE BLACK HILLS.

the septa and in the character of the umbilicus when compared with
specimens of the same size that would seem to distinguish them. A. cor-
datus does not appear to become so ventricose, nor are the volutions so
nearly triangular in the larger individuals as in the western shells.
Formation and locality—In rocks of Jurassic age, associated with other
Jurassic forms, at a horizon 350 feet above the red beds referred to the
Triassic, at Redwater Valley; also on the tops of the highest hills two miles
south of the Belle Fourche River, near Bear Lodge Butte, Black Hills.

AMMONITES CORDIFORMIS var. DISTANS.
Plate 6, fig. 25,

Shell of moderate size, slightly cordiform in a transverse section of the
volution, or approaching subquadrate, and distinctly keeled on the back.
Volutions few in number, largely embracing, leaving a broad, open umbili-
cus equal to nearly one-third of the diameter of the entire shell, and in
which is exposed less than one-third of the breadth of each volution. Um-
bilical margin of the volution abruptly rounded, sides depressed convex,
somewhat flattened in the middle, slightly decreasing in convexity and
thickness outward to about the outer fourth of the width, beyond which
point the surface abruptly declines to the thickened, rounded, and promi-
nent dorsal keel.

Surface marked by strong, distant, and abruptly elevated flexuous ribs
or ridges, with concave interspaces; originating a little outside of the umbil-
ical margin, they are directed, with a slight sigmoidal curvature, nearly
across the volution, and are then directed abruptly forward along the dorsal
slope for a distance nearly equal to one-half the width of the volution at the
point of their occurrence, and form strong, wave-like ridges in crossing the
dorsal carina. On the dorsal slopes there are also one and sometimes two
additional ridges between the primary ones, but usually of a little less
strength. The primary ridges sometimes form pointed spine-like nodes at
their intersection with the intermediate or secondary ones; but this is not
a constant feature, even on the same shell, and only occurs when the pri-
mary ridge dies out or bifurcates, forming two secondaries on the slope,

JURASSIC FOSSILS. 381

which is an exceptional feature. Lines of growth apparently coincident
with the ridges or nearly so.

We at first supposed this to be only a strong variety of A. cordiformis
M. & H., but on further examination are strongly inclined to the belief that
it is a distinct species; but not having sufficient material to satisfactorily
determine the question, we have left it under a varietal name for the pres-
ent. Should, however, our suspicions prove correct, on the examination of
additional material, it may need a distinct specific designation.

Formation and locality—F¥ound associated in the same shaly limestones
of Jurassic age, with A. cordiformis, and other Jurassic forms, on the tops of

the highest hills, two miles south of the Belle Fourche River, near Bear
Lodge Butte, Black Hills.

DIBRANCHIATA.
BELEMNITID&.

Genus BELEMNITES Agricola.
BELEMNITES DENSUS.
Plate 6, figs. 15-19.

Belemnites densus M. & H., Proc. Acad. Nat. Sci, Phil. March, 1853, p. 58; ibid. Oct. 1860,
Pilnctes a M. & H., Pal. Up. Missouri, p. 126, Pl. iv, fig. 10, and PI. v, fig. 1.
Calcified guard or shell attaining a large size, frequently nearly four
inches long below the phragmacone, and often but little less than an inch
in diameter at the thickest part; subcylindrical, ovate, or oval in section,
and in the larger individuals sometimes obscurely subquadrangular; often
somewhat laterally compressed; upper parts straight or sometimes slightly
constricted, and more or less rapidly tapering below to an obtuse point,
with a narrow, obscure, or faintly-marked groove along one side for some
distance above the point, and in some cases extending almost to the lower
end of the cavity occupied by the phragmacone. Phragmacone short (?),
somewhat rapidly expanding from below upward, the sides diverging at an -
angle of a little more than 20° and slightly curved, the convex side being

389 GEOLOGY OF THE BLACK HILLS.

opposite to the groove or cicatrix of the lower end of the guard. The cone
is divided transversely by thin, very closely arranged septa, gradually
increasing in distance with the increased growth of the cone. The lower
half inch of a specimen containing about thirty-four septa, and the upper
half of this space having only about ten or eleven. The septa are very
gently and regularly concave throughout Apex of the cone subcentrally
situated in the guard, the point being directed toward the side marked
by the impressed groove or cicatrix, but above it is sometimes reversely
excentric.

Substance of the guard thick and dense, with a very distinct prismatic
structure radiating from the line of the constantly receding apex of the
phragmacone, and in a transverse section often shows the successive con-
centric layers of which it is composed. Surface smooth.

The species is quite common in some of the Jurassic beds of the Black
Hills region, and appears to be very variable in the proportional thickness
of the guard, which is the only part found. In the smaller individuals it is
usually much more slender than in the older ones, but as the increase in
this direction is by concentric additions to the exterior surface, they may
continue to grow in this direction long after they have attained their maxi-
mum-length. In the younger individuals the alveolar cavity is also more
nearly central, and the eccentricity is added afterward, as may be seen by
the weathered transverse sections showing the greater thickness of the con-
centric rings on one side of the cavity.

Formation and locality.—In Jurassic rocks on Beaver Creek, and at the
top of the gray shales of the same formation, resting on the red marls of the
‘Trias, east of the Belle Fourche, near Bear Lodge Butte, Black Hills.

CRETACEOUS FOSSILS. 383

SECTION IV.
FOSSILS FROM THE CRETACEOUS ROCKS.

LAMELLIBRANCHIATA.
MONOMYARIA.

PECTINID A.

Genus SYNCYCLONEMA Meek.
SYNCYCLONEMA RIGIDA.
Plate 7, fig. 1.

Pecten rigida H. & M., Mem. Am. Ac. Sci. and Arts, vol. v, new ser., Pl. 2, fig. 4.
Pecten hallii Gabb., Cat. Cret. Foss., 158.
Syncyclonema rigida (H. & M.) Meek, Smithsonian Check List Invert. Foss., p. 7.
Syncyclonema rigida (H. & M.) Meek, Pal. U. S. Geol. Surv. Terr., p. 27, Pl. 16, fig. 5.
Shell small, depressed-convex, erect or nearly so, truncate-ovate in
outline, widest below the middle, and the height slightly exceeding the
width ; hinge line straight, nearly as long or about half as long as the
greatest width of the shell below; auriculations distinct, the anterior one
largest, broadly rounded on the lateral margin, and separated from the
body of the shell by a very shallow notch only on the margin of the shell;
posterior wing, small, obtusely angular, and not at all distinct from the
body ; sides of the right valve straight above the point of greatest width,
and forming an angle of nearly 90° with each other; base regularly
rounded from the points of greatest width, where the margin is subangular.
Surface concentrically striate, with distinct even strie, as preserved
on the cast; hinge with a very distinct, triangular, concave cartilage pit in
the center of the right valve; muscular impression, if the markings which
we see are rightly interpreted, situated on the posterior side of the middle,
and nearly apical, and extending along the posterior side just within the
thickened border of the valve to near the middle of the height. Surface
and substance of the shell unknown.

384 GEOLOGY OF THE BLACK HILLS.

Mr. Meek, in his description of the genus SyncycLonema, which is
founded upon this species, does not mention the existence of a cartilage pit,
nor give the form of muscular imprints. The specimen in hand, which is
an internal cast in blackish limestone, shows the cartilage pit very dis-
tinctly and the muscular imprint quite plain. It is possible, however, that
we may have mistaken the nature of the latter, being misled by the ‘small
size of the shell, but the structure is exactly like that of a muscular scar,
although its position may be quite unusual. From the form of the external
border of the anterior ear we should suppose the notch was intended for the
passage of a byssus.

Formation and locality—In limestone of the Cretaceous, at the forks of
the Cheyenne River, Black Hills.

HETEROMYARIA.

AVICULIDA.
Genus PTERIA Scopoli.

PTERIA LINGUIFORMIS.
Plate 7, fig. 2, 3.

Avicula linguiformis Evans & Shumard, Proc. Acad. Nat. Sci. Phil., vol. 7, p. 163.
Avicula linguiformis (KE. & 8.) M. & H., Proc. Acad. Nat. Sci. Phil. Nov. 1856, p. 21.
Pteria linguiformis (EK. & 8.) Meek, Smithsonian Check List Inv. Foss., p. 9.
Pteria linguiformis (K. & 8. sp.) M., Pal. U. 8. Geol. Surv. Terr., p. 32, Pl. 16, fig. 1.
The examples of this species in the collection are all more or less
exfoliated and imperfect, und therefore do not present the natural surface
of the shell, so that we obtain but little else than the general form. The
shells are obliquely subovate or obscurely rhomboid in outline, very ine-
quilateral and inequivalve; hinge line straight, nearly or quite as long as
the body of the shell below, but projecting anteriorly and short behind.
Anterior wing of the left valve of moderate size, acutely triangular, and
pointed at the extremity ; posterior wing long, the posterior margin nearly
at right angles to the hinge line for a short distance below, and then

directed obliquely backwards to the extremity of the shell; beak large and

CRETACEOUS FOSSILS. 385

ventricose, projecting considerably above the cardinal border, slightly
incurved and directed obliquely forward; body of the valve highly con-
vex and very oblique; anterior and basal margins sloping backwards, with
a shallow sinuosity below the anterior wing; posterior extremity obliquely
rounded; ligamental area proportionally large and slightly concave. Right
valve smaller and much less convex than the left; beak small, pointed,
directed obliquely forward and not extending above the cardinal line;
anterior wing apparently larger than on the left valve, much more convex
and pointed; posterior wing of the same form as that of the left valve, but
concave toward the upper edge. Muscular imprint large, subcentral, a
little nearer the posterior margin and distinctly subreniform ; pallial line
composed of elongated pustules. Substance of the inner layers of the
shell nacreous ; outer layers, as far as ascertained, very finely prismatic.

This species appears to have been a common form in the seas of this
region during the deposition of the rocks of the Fort Pierré Group, as the
broken and comminuted shells are quite numerous in the dark concre-
tionary layers of this formation at most of the localities from which col-
lections have been made, though but few individuals are obtained in a good
state of preservation. It is an easily recognized form.

Formation and locality—tIn limestones of the Fort Pierré Group, on
the South Fork of the Cheyenne River, near French Creek, and on Old
Woman Fork, Black Hills.

PTERIA (OXYTOMA) NEBRASCANA.
Plate 7, fig. 4.

Avicula nebrascana EK. & Shumard, Trans. St. Louis Acad. Sci., vol. i, p. 38.

Pteria nebrascana (EK. & 8S.) Meek, Smithsonian Inst. Check List Inv. Foss., p. 9.

Pteria (Oxytoma) nebrascana (BK. &. 8.) Meek, Pal. U. S. Geol. Surv. Terr., p. 34, Pl. 16,
fig. 3, and pl. 28, fig. 11.

Shell of moderate size and smaller, obliquely rhombic-ovate in form,
very inequilateral. Left valve depressed-convex, with a small, pointed, and
suberect beak, slightly extending above the cardinal line and situated
about one-fourth of the entire length from the anterior end; hinge line two-
thirds as long as the shell below; anterior wing very small, obtusely -
rounded; anterior margin gradually rounding below and forming a con-

25 BH

386 GEOLOGY OF THE BLACK HILLS.

tinuous curve with the antero-basal and basal margins; posterior basal
margin more sharply rounded, and extended obliquely backward; posterior
wing large, scarcely pointed at the extremity, and separated from the body
of the shell below by a very broad shallow sinus.

Surface marked by closely arranged, rounded, radiating ribs, separated
by flattened interspaces of twice their width, and increased in number by
interstitial addition ; about six or seven of the ribs occupy a space of a fifth
of an inch at the margin of the largest valve seen, which is about one inch
in its extreme height. The radii are crossed by very fine concentric lines
of growth, but so fine as to scarcely form a feature of the shell except
when viewed by the aid of a lens. Right valve of the shell only recog-
nized by a few fragments associated with a large number of left valves, on
the same block, and is apparently nearly or quite smooth.

Formation and locality—tIn hard concretionary limestone of the Fort
Pierré Group, on Sage Creek, Black Hills.

PTERIA (PSEUDOPTERIA) FIBROSA.
Plate 7, fig. 5.

Avicula ? fibrosa M. & H. (1856), Proc. Acad. Nat. Sci. Phil., p. 86.

Pholadomya fibrosa M. & H., ibid, p. 286.

Pinna fibrosa Meek, Smithsonian Check List Invert. Foss., p. 9.

Avicula (Pseudopteria) fibrosa M. & H., Sixth An. Rept. U.S. Geol. Surv. Terr., p. 489,
Pteria (Pseudopteria) fibrosa Meek, Pal. U.S. Geol. Surv. Terr., p. 36, Pl. 17, fig. 17.

A single very imperfect example of a left valve of this species has
been observed among the collections from the top of the gray shales of
No. 4, on the Cheyenne River, near Rapid Creek. The surface is much
exfoliated and the nacreous character of the shell destroyed. The shell is
very oblique, the axis of the body forming with the hinge line an angle of
about forty-five degrees. The valve is quite ventricose toward the beak,
but becomes compressed and flattened below. Anterior wing small and
obtusely pointed; surface of the shell marked by rather strong concentric
undulations, and also by coarse, irregular, and unequal radiating folds of
the substance, which are not true radii, but simply foldings of the shell. It
may be readily distinguished from P. (P.) sublevis herein described by
its larger size, greater obliquity, and by the surface folds.

CRETACEOUS FOSSILS. 387

PTERIA (PSEUDOPTERIA) SUBLEVIS.
Plate 7, fig. 6.

Pteria (Pseudopteria) sublevis, Whitf., Prelim. Rept. Pal. Black Hills, 1877, p. 29.

Shell small, erect, subrhomboid or subovate in outline, left valve de-
pressed-convex, most ventricose on the umbo and toward the beak, near
which it becomes subangular. Hinge line shorter than the length of the
shell below, and about two-fifths as long as the height; anterior wing
minute, obtusely pointed, posterior wing moderate in size and convex,
scarcely separated from the body of the shell by a slight, almost impercepti-
bly depressed line; anterior side of the shell gradually receding from
below the anterior wing to the basal border, which is rather sharply rounded,
and the postero-basal margin a little more sharply rounded than the basal.

The surface of the valve, in all the specimens seen, is much exfoliated,
so that the surface features are not positively known, but it has, appar-
ently, been quite smooth; the substance of the shell remaining on the speci-
mens is highly nacreous.

Several individuals of the left valve have been noticed in the collection,
but none of the mght have been recognized. Those seen all have the same
character, and are of about the same size, being a little less than three-
fourths of an inch in length by about half an inchin width. It most nearly
resembles in form P. (Pseudopteria) fibrosa M. & H., Paleontology of the
United States Geological Survey of Territories, p. 36, Plate 17, Fig. 17),
but differs entirely in the surface features, being entirely destitute of the
faint plications of that species.

Formation and locality—tIn limestones of Cretaceous age, No. 4, Old
Woman Fork, Black Hills.

Among the collections from the Fort Pierré Group there are large num-
bers of Inocerami, representing several of the species and varieties recog-
nized by Mr. F. B. Meek, in his excellent work on the Upper Missouri
Cretaceous formations, just issued by the Department of the Interior. But
notwithstanding the careful manner in which these forms have been de-
scribed and figured by that author, we find great difficulty in arriving at
any very satisfactory conclusions as to the limits of species when so large

388 GEOLOGY OF THE BLACK HILLS.

a collection is examined. The species, as figured in the above-mentioned
work, appear distinct enough and the lines of demarkation well drawn
when a few individuals only are before one; but among the collections in
hand we find the boundries crossed in every direction, so that we are at a
loss in many cases for characters by which to separate the different forms
there indicated; while there are still others among them so entirely differ-
ent from any of those described and figured, that we are very reluctantly
compelled to consider them as entirely distinct.

Among the forms representing those given under the names I. vanuxemi,
I. proximus, and I. proxunus var. subcircularis and also as I. converus and
I. sagensis vay. nebrascensis and I. balchii we find such gradually connecting
links as to make it extremely difficult, if not impossible, to draw lines of
distinction between them. Again, those resembling the forms given under
the names I. cripsii var. barabini and I. tenwilineatus, are similarly united.

The forms which we had referred to I. sagensis and I. nebrascensis of
Owen vary so greatly in the posterior prolongation of the shell, and also
in the direction of the basal margin, as to defy all attempts to classify them
by their form; and in the relative degree of convexity and the comparative
distance of the surface undulations they are equally variable and unsatis-
factory. We find also that the relative projection of the beaks and the
width of the cartilage area, as well as the distance of the beaks from the
anterior end, is subject to great variation. Although in the collections
before us there are but few individuals which retain the right and left valves
in contact, still of many of them we have both valves of similar size and
form from the same locality and we find that the difference in convexity
between the two valves is not in any case very great, and often scarcely
perceptible. The beak of the left valve is usually larger, and projects more
bevond the line of the hinge than that of the right, and the cartilage area
is also a little wider. Perhaps if the real surface features of the shells were
preserved on the specimens, more reliable characters for specific distinction
might be presented, but the fibrous coating is almost always absent, being
generally left in the matrix, and not collected; or perhaps in many cases
removed by some action of decay before the shells are finally imbedded in
the rocky sediment, so that in collections it is seldom that any part of this

CRETACEOUS FOSSILS. , 389

layer is retained on the specimens, except a little around the beaks or along
the hinge margins.

Owing to these difficulties, the same that Mr. Meek has found to exist
among his specimens, and also to the impossibility of giving a sufficient
number of figures to show fully and clearly the variations which we have
found among the examples in hand, we shall be obliged to follow very
nearly the same specific limits which that author has found desirable; though
we must confess that in some cases we should prefer rather to consider
some of the forms found associated together in the same localities, and
presenting only slight differences, as one and the same species, than to
identify these far western forms with species described from Europe, as has
been done by so many authors. We do not dispute their great resem-
blances, but believe them to be rather representative species than equivalent
forms.

Genus INOCERAMUS Sowerby.

INOCERAMUS PROBLEMATICUS ?
Plate 7, fig. 11.

Mytilites problematicus Schlot., Petrafact., p. 312.
Inoceramus problematicus of authors.

The examples which we have doubtfully referred to this species, one
of which is figured on Plate 7, Fig. 11, are all very imperfect, and, as in the
case of that one, are mostly destitute of shell, being merely casts of the
interior surface in a yellowish sandstone; consequently the characters
retained are not sufficient to fully determine their specific relations. They
are generally more or less obliquely-quadrangular or obliquely-subovate
in outline, with flattened valves and rather sharp, pointed, almost terminal
beaks, which project but little beyond the cardinal line; the hinge line is
shorter than the shell below and nearly or quite at right angles to the
anterior or buccal border; height of the shell usually greater than the
length and widest below the middle of the height, the posterior border
gradually receding from the extremity of the cardinal line, with a slight
curvature, to the postero-basal angle; umbonal ridge subangular; anterior.
slope abrupt and rather narrow.

390 GEOLOGY OF THE BLACK HILLS.

- Surface of the casts marked by strong, irregular, concentric undula-
tions parallel to the margin of the shell and generally increasing in size
and strength with the increased growth of the shell.

Formation and locality—In ferruginous sandstone of Cretaceous age,
on the east fork of Beaver Creek, Black Hills. Probably of the Fort
Benton or Niobrara Group.

INOCERAMUS FRAGILIS.
Plate 9, fig. 10.
Inoceramus fragilis H. & M., Mem. Am. Acad. Arts and Sci., new ser., vol. viii, p. 388,
Pl. 2, £. 6. |
Inoceramus fragilis (A. & M.) Meek, Pal. U.S. Geol. Surv. Terr., p. 42, figs. 1 and 2,
Pl. 5, fig. 5.

Shell rather below the medium size, obliquely rhomboid-ovate in out-
line, with moderately convex valves and small, somewhat pointed and
nearly terminal beaks, which scarcely project beyond the cardinal line;
hinge line straight, shorter, and sometimes not more than two-thirds as long
as the shell below; anterior border straight for some distance below the
beaks, and at right angles with the cardinal line; posterior end obliquely
rounded and prolonged in the direction of the postero-basal angle; basal
line rounding at its junction with the anterior border and below, sub-
parallel with or slightly diverging from the line of the hinge to near the
postero-basal extremity, where it is somewhat sharply rounded. Body of
the valve irregularly convex, most prominent on the umbonal ridge, which
is often subangular and the surface somewhat flattened on each side, espe-
cially along the postero-cardinal slope ; anterior margin nearly vertical.

Surface marked by fine, even, concentric lines and sometimes by con-
centric undulations, the latter, however, are not always fully developed and
are frequently entirely obsolete.

There is considerable variation in the form of the outline of this shell
among the different specimens, many of them being less oblique and
rounded on the basal margin, the posterior extremity being less prolonged.
They also differ greatly in the strength of the surface markings, some of
them having the surface linings developed into irregular concentric folds of
greater or less strength. The right valve is, so far as can be ascertained

CRETACEOUS FOSSILS. 391

from the separated valves in the collection, usually more evenly convex
than the left, being destitute of the slight angularity along the umbonal
ridge.

Formation and locality.—In Cretaceous strata referred to the Fort Benton
Group, on Beaver Creek, and on the eastern fork of the same, Black Hills.
INOCERAMUS ALTUS.

Plate 9, fig. 11.
Inoceramus altus Meek, Geol. Rept. U. S. Surv. Terr. 1871, p. 302.
Inoceramus altus Meek, Pal. U. 8S. Geol. Surv. Terr. 1876, p. 43, Pl. 14, fig. 1.

The specimens of this species present in the collection are all more or
less imperfect and fragmentary ; they are so strongly marked, however, that
they are very readily distinguished from any other form yet observed. The
shells are obliquely ovate exclusive of the alation of the hinge, which is
usually absent, and strongly convex, especially on the umbones and along
the umbonal ridge ; the beaks are only of moderate size, strongly incurved,
with a forward inclination, are pointed and terminal, and project somewhat
beyond the cardinal line; anterior border short and nearly vertically
rounded to the umbones, extending along the valve to a little below the
middle, where it rounds into the basal margin; base prolonged obliquely
backward in the direction of the umbonal ridge.

Surface marked by small, but very distinct, concentric undulations,
which are remarkably uniform in size, being generally about an eighth of
an inch in width or a little more, and not sensibly increasing with the
increased growth of the shell. Substance of the shell, as preserved on the
specimens, highly nacreous.

The example figured by the author, Joc. cit., is of very much larger size
than is indicated by any of ours, and the undulations somewhat more dis-
tant, increasing in size toward the margin, which is not the case with those
under consideration. He also mentions radiating lines on the surface of
what he speaks of as a cast. Our specimens all preserve more or less of
the nacreous layers, and do not show radiating lines.

Formation and locality.—In limestones of Lower Cretaceous, probably
of No. 2, as they are associated with I. perplexus and Scaphites wyomingensis:
M. & H., on the Belle Fourche, ten miles west of Crow Peak, Black Hills,

392 GEOLOGY OF THE BLACK HILLS.

INOCERAMUS PERPLEXUS.
Plate 8, fig. 3, and Pl. 10, figs. 4, 5.

Inoceramus perplexus Whitf., Prelim. Rept. Pal. Black Hills, 1877, p. 31.

Shell rather below the medium size, erect, truncate subovate in outline,
shortest at the hinge line and gradually expanding to below the middle of
the height; valves convex; beaks terminal, slightly inclined forward,
pointed and incurved ; hinge line short and straight, not exceeding two-
thirds of the length below in any of the examples seen; anterior border
straight or very slightly concave for more than half the height of the shell,
when it unites with the deeply rounded basal border; posterior margin of
the shell gradually widening from the extremity of the hinge line to the
point of greatest width in an antero-posterior direction, which is rather
below the middle of the height where it unites in a regular curve with the
basal margin. Valves most strongly convex along the umbonal ridge,
which is situated nearest to the anterior side of the shell and slopes gradu-
ally to the postero-cardinal portion, where it becomes almost flattened ;
while the anterior border is vertical, or sometimes slightly concave, for
more than half the depth of the valve.

Surface of the shell marked by strong, irregular concentric folds or
undulations parallel to the margin, and passing off on the vertical anterior
border. Substance of the inner layers highly nacreous. Fibrous coating,
when preserved, apparently thin.

This species is somewhat remarkable for its erect form and strong con-
centric undulations. In form it resembles the specimens of J. fragilis H.
& M., given by the latter author (Paleontology of the United States
Geological Survey of the Territory, p. 42, Figs. 1 and 2), but in the surface
characters it is entirely distinct from that species, and when compared with
examples of that species having the characters of the original specimen is
very readily distinguished. It also somewhat resembles I. ellioti Gabb.,
from the Cretaceous sandstones of San Francisco Harbor, California.

Formation and locality—In concretionary limestone at the top of shales
of Cretaceous No. 2, on the Belle Fourche, about ten miles west of Crow
Peak, Black Hills.

CRETACEOUS FOSSILS. 393

INOCERAMUS SUBLA‘VIS.
Plate 10, figs. 1-3.
Inoceramuss sublevis H. & M., Mem. Am. Acad. Arts and Sci., new ser., vol. v., p. 386,
Vee rier 1
Inoceramus sublevis (H. & M.) Meek, Pal. U. S. Geol. Surv. Terr., p. 58, Pl. 12, fig. 1.

Shell below medium size, suboval in outline, moderately gibbous, with
almost evenly convex valves, which are slightly more ventricose on the
umbones; beaks small, inconspicuous, incurved, and situated near the ante-
rior end; hinge line straight, two-thirds as long as the whole length ot the
shell; anterior end rounded, projecting but little beyond the line of the
beaks, the greatest projection at about one-third the height of the valve,
below which the border, including the base and posterior end, forms a nearly
regular section of an oval curve.

Surface of the specimens, where a portion of the nacreous layers are
preserved, presenting distinct, somewhat interrupted radiating lines, or lines
of pustules, with a few very faint indications of concentric undulations.

A number of individuals among the collection, presenting similar feat-
ures, we have referred to this species. Their regularly symmetrical form
and smooth surfaces, marked by faint to distinct radiating lines, are features
that at once attract attention and render them easily distinguishable among
the other species of the genus. The radiating lines, as indicated on the
exfoliated shells, are still more conspicuous on the complete casts of the
interior, one of which is figured on the plate, and presents lines of elon-
gated pustules, making a conspicuous feature.

Formation and locality—kIn Cretaceous, No. 4, at the Forks of the
Cheyenne; and about three miles east of Camp Jenney, Red-Water Valley,

Black Hills.
INOCERAMUS SAGENSIS.

Plate 7, fig. 12; Pl. 8, fig. 2.

Inoceramus sagensis Owen, Geol. Rept. Wis., Iowa, and Minn., p. 582, Pl. vii, fig. 3, 1852.

? Inoceramus nebracensis Owen, tb., p. 582, Pl. viii, fig 1.

Inoceramus sagensis var. Nebracensis (Owen) Meek, Pal. U.S. Geol. Surv. Terr., p. 52,
Pl. 13, fig. 2.

Compare Inoceramus convexus H. & M., Mem. Am. Acad. Arts and Sci., new ser., vol. v,
p. 386, Pl.2; Pal. U. S. Geol. Surv. Terr., Pl. 12, fig. 5.

Compare Inoceramus balchii M. & H., Proc. Acad. Nat. Sci. Phil., vol. xii, p. 180; Pal. U.
S. Geol. Surv. Terr., 56, Pl. 15, fig. 1.

394 GEOLOGY OF THE BLACK HILLS.

Shell large, the general form being oblate or more or less transversely
broad-oval, with moderately convex valves, and large, somewhat tumid, and
slightly incurved beaks, situated but a short distance from the anterior end
and projecting above the line of the hinge. Hinge line straight, equal to
about half or a little more than half the length of the shell below; anterior
and posterior ends rounded, the former longest above the middle and the
latter below the middle of the valve; basal line obliquely rounded, more
or less prolonged behind in the direction of the umbonal ridge; extremity
of the hinge line rounding to the posterior margin, with a long and gradu-
ally increasing slope. Valves most ventricose along the umbonal ridge and
on the umbones, retaining considerable ventricosity toward the anterior
margin, which is often quite abrupt, but sloping more gradually posteri-
orly, and becoming much compressed and flattened on the postero-cardinal
extension.

Surface of the valves marked by strong concentric undulations of very
varying size and distance, and often by finer concentric lining in the depres-
sions between. Faint indications of radiating lines are also frequently seen
on the exfoliated surfaces.

The specimens of this species are subject to very great variation; in
fact, there is scarcely a single feature,that is in any degree constant in its
character through many individuals. In convexity they vary from depressed
convex to highly gibbous. They also differ exceedingly in the strength
and number of the concentric undulations, some having been noticed where
the undulations become obsolete and the shell suddenly geniculated, giving
a strongly deformed character to the valves The extreme variation of the
species has been noticed by others; and Mr. Meek remarks, under his
description of the form on page 53, Paleontology of the United States
Geological Survey of the Territories, when speaking of Dr. Owen’s species,
that ‘‘a careful study of our specimens, in connection with Dr. Owen’s
figures and description of his J. sagensis and I. nebrascensis, has led to
the conclusion that the forms for which these names were proposed are
not specifically distinct”; and in the following paragraph he further says,
in speaking of the variation of the outline between his and Dr. Owen’s
figures of I. nebrascensis: ‘There appears, however, to be so many gra-

CRETACEOUS FOSSILS. 395

dations in character of this kind, that to separate the form we have figured
as a variety or species would require that we should, in the same way,
separate almost every individual specimen under a different name.” Taking
into consideration these extensive variations, we are inclined to consider the
different forms of this type as only varieties of the one species. Mr. Meek
appears, from his description and remarks, to have considered his J. balchii
as allied to I. vanuxemi, and consequently as allied to I. proximus Toumey ;
but from the character of the beak and that of the concentric undulations
we should think it more nearly related to this form.

Formation and locality—In Cretaceous beds of the Fort Pierré Group,
on the Cheyenne River, near Rapid Creek; also at the top of the gray
shales at the mouth of Rapid Creek, Black Hills.

INOCERAMUS SIMPSONI.
Plate 8, fig. 1.
Tnoceramus simpsoni Meek, Proce. Acad. Nat. Sci. Phil. 1860, vol. 12, p. 312.
Inoceramus simpsoni Meek, Rept. of Expl. across the Great Basin of Utah, p. 360, Pl.
4, fig. 4.

Shell very large, transversely and obliquely-ovate, with strongly con-
vex and slightly unequal valves, which are the most ventricose along the
antero-basal third of the shell, and gradually compressed toward the pos-
tero-cardinal margin. Right valve apparently the most convex on all the
specimens examined, and the greatest convexity a little more forward than
that of the left valve. Hinge line long and straight, extending from the
beaks to about the posterior third of the valve, where it gradually slopes to
the posterior extremity. Beaks of moderate size, not very prominent, and
but slightly projecting beyond the line of the hinge in comparison with
the size of the shell, situated near the anterior end of the shell, but not ter-
minal; anterior end round and full, much narrower than the posterior end
and gradually rounding into the basal line, which is broadly curved and
prolonged in the direction of the umbonal slope; posterior extremity
obliquely rounded from the end of the cardinal line to the postero-basal
margin .

Surface of the shell marked by numerous concentric undulations;
which gradually increase in width from the beaks as the shell increases in

396 GEOLOGY OF THE BLACK HILLS.

size. Surface of the cast marked by oblique curving lines, or lines of pus-
tules, which incline slightly forward as they approach the basal margin.

This species may be distinguished from any other form described by
the great postero-basal extension of the valves, coupled with their mod-
erate gibbosity. In its younger stages of growth, when within two inches in
length, it has resembled the forms referred to J. vanuxemi by My. Meek, but
that it would have been much longer in proportion to its height. The finer
and more equal undulations and smaller beaks will readily distinguish it
from I. sagensis Owen, or any of the forms referred to that group. The
cartilage area appears to have been very narrow and linear; but the
most noticeable feature, and one that will easily distinguish it, we think,
when the valves are found in contact, is the greater convexity of the right
valve, and apparent greater prominency of the beak of this valve, whereas
the opposite is usually the case with all species of this genus. The beaks
of the right valves are all broken, and we judge only of their size by the
parts remaining. The specimen figured by Mr. Meek, loc. cit., differs from
our figured specimen in being narrower posteriorly and in the slight con-
striction or sinuosity of the basal margin, but we do not deem these features
of specific importance. The type of the species was from a lower horizon
than most of those in this collection.

Formation and locality—In Cretaceous rocks of the Fort Pierré Group,
on Old Woman Fork ; one specimen is marked as coming from the east fork
of Beaver Creek, three miles west of Camp Jenney, Black Hills, at a prob-
ably somewhat lower horizon.

INOCERAMUS VANUXEMILI.
Plate 7, figs. 8,9; Plate 8, figs. 4, 5.

Inoceramus vanucemi M. & H., May, 1860, Proc. Acad. Nat. Sci. Phil., p. 180.

Inoceramus mortoni M. & H., Oct. 1860, Proc. Acad. Nat. Sci. Phil., p. 428.

Inoceramus proximus M., Pal. U. 8S. Geol. Surv. Terr., p. 53, Pl. 12, fig. 7; and var.
subcircularis M., ib., p. 55, Pl. 12, fig. 2.

Compare Inoceramus proximus Toumey, Proc. Acad. Nat. Sci. Phil. 1854, p. 428.

Compare Inoceramus confertim-annulatus Roemer, Kreid. von Texas, PI. 7, fig. 4.

Shell of moderate or large size, with depressed convex to subdiscoid

valves, subcircular to subovate in outline, with short, compressed, often

CRETACEOUS FOSSILS. 397

inconspicuous beaks, which project but little, and often not at all, beyond the
line of the hinge, and are situated near the anterior end, but not terminal ;
height and length of the valves subequal or longer than high; anterior end
very short and rounded below the beaks, uniting in a more or less regular
curve, according to the form of the shell, with the basal margin ; base gener-
ally somewhat regularly rounded, but often a little prolonged obliquely in
the direction of the umbonal ridge ; posterior end rounded, and the upper
margin gracefully curving forward to the extremity of the cardinal line;
hinge line straight, usually half as long or more than half as long as the shell
below. Surface of the valves most convex on the umbones and along the
umbonal ridge, which is low, rounded, and not distinctly defined; anterior
slope usually more or less abrupt, and posterior slope and cardinal portion
of the valve flattened or but slightiy convex.

Surface of the shell marked by strong, rather closely arranged, sub- .
angular concentric ridges, with regular concave interspaces. The ridges
are variable on different individuals, but on the same specimen usually
increase gradually and regularly from the beak outward with the increased
erowth of the shell, and on some specimens which we have referred to the
species have finer concentric linings in the depressions.

The specimens of this shell before us, to the number of more than a
dozen, varying from less than an inch to over four inches in height, are quite
variable in the degree of convexity and outline as well as in the propor-
tional strength and distance of the undulations, no two agreeing exactly
in any of these particulars. For this reason we have considered the forms
previously given as species and varieties cited above, which were obtained
from the same region of country as our specimens, as probably belonging
to one species. It is quite likely that those described by Dr. Roemer and
Professor Toumey, loc. cit., are also identical forms, and that they should be
all referred to I. proximus Toumey ; but not having access to specimens of
these we do not feel certain. Besides, those coming from distant parts of
the country are more likely to prove distinct. We notice among the speci-
mens of this type, as in those of J. sagensis, a tendency often to abrupt or
sudden geniculation of the valves after attaining a certain size, and in such,
cases the concentric undulations are usually very faint or obsolete beyond

398 GEOLOGY OF THE BLACK HILLS.

such point. The most marked and striking difference between this form
and J. sagensis is in the size and form of the beak of the shell, these being
small and compressed, those large and prominent. Several specimens of
each valve are present in the collection before us.

Formation and locality—In Cretaceous beds of the Fort Pierré Group,
on the Cheyenne River, near Rapid Creek ; on Old Woman Fork, and at
top of gray shales near mouth of Rapid Creek, Black Hills.

INOCERAMUS VANUXEMI, var. ?

Plate 7, fig. 10.

The single individual represented by Fig. 10, Plate 7, presents such a
marked departure from the characters of the other specimens in the collection,
that we do not feel certain that it belongs to the same species, although of
the same type. The form is erect, the height considerably exceeding the
length of the valve, giving a broad ovate form, slightly truncate above by
the hinge line, which is quite short, and the beaks compressed and entirely
within the limits of the outline. The concentric undulations are very simi-
lar to the more closely arranged ones on the forms which we have referred
to I. vanuxeni, and also to the form figured by Mr. Meek as I. proximus
Toumey. The specimen isa left valve and quite depressed convex, although
it has suffered accidental compression. A part of the right valve is also
preserved, but in a much more mutilated condition and more compressed,
so that we cannot judge of the convexity with certainty. Owing to the
above-mentioned differences we have hesitated to include it under the same
specific designation until further collections shall demonstrate the fact.

Formation and locality—Near the top of the gray shales of the Fort
Pierré Group, on the Cheyenne River, near Rapid Creek, Black Hills,
Dakota.

INOCERAMUS BARABINI.

Plate 7, fig. 7; Plate 9, fig. 8.

Inoceramus barabini Morton, Synop. Org. Rem. Cret. N. A. 1834, p. 62, Pl. 17, fig. 3.

Inoceramus cripsti var. Barabini (Morton) Meek, Pal. U. 8. Geol. Surv. Terr., p. 49, Pl.
ib}, soyee ILS. VEAL, WA alee, ois

Inoceramus gibbus Toumey, Proc. Acad. Nat. Sci. Phil. 1854, vol. vii, p. 170.

Inoceramus cuneatus M. & H., Proc. Acad. Nat. Sci. Phil. 1860, p. 181.

CRETACEOUS FOSSILS. 399

Shell varying from medium to large size, transversely-ovate or sub-
elliptical in outline, usually a little larger behind than in front of the
middle of the length. Valves very convex, especially in the anterior half
and along the umbonal slope, becoming more compressed and cuneate pos-
teriorly, slightly unequal, the left being the largest; beaks proportionally
large and slightly tumid on the umbones, but smaller and pointed toward
their apices, slightly incurved, and nearly terminal, somewhat elevated above
the hinge line, but not prominent; hinge line long, usually nearly or quite
three-fourths as long as the shell below, and rounded at the extremity;
anterior end very short, almost on a line with the beaks and rapidly sloping
backwards from just below them to the basal line, giving a somewhat sub-
cuneate character to the anterior extremity of the shell; posterior extremity
rounded; basal line broadly rounded or forming a semi-elliptical curve,
being more abruptly rounded at each end than in the middle, but generally
slightly diverging from the cardinal line to behind the middle of the valve.

Surface of the shell marked by numerous irregular, concentric undula-
tions of unequal size and strength, parallel to the margin.

Upon one of the smaller specimens of this species (see Plate 9, Fig. 8),
we have been able to detect the outline of muscular scars. Those near the
apex of the valve are quite distinct and easily recognized, but the larger or
posterior scar is much more faintly marked, and we were under some doubt
at first if it were rightly considered as a point for muscular attachment, but,
after careful examination of this and a large number of individuals of dif-
ferent species, we think we are able to see faint traces of this larger scar, in
a similar position, on several of them. The anterior scar is situated quite
near the anterior end, and does not exceed a tenth of an inch in its greatest
diameter. There are five small dot-like scars between this and the apex of
the valve, some of them over the turn of the beak. No remains of the,
pallial line could be satisfactorily detected. It is probable that, like the
pallial line of other shells of the Aviculidee, it was composed of isolated
points of attachment, and in this case would be difficuit to trace, as the
surface of many of the casts is covered with similar points.

In deference to the opinion of Mr. F. B. Meek, who has examined the.
original specimens of I. barabini, we have referred these western forms to

400 GEOLOGY OF THE BLACK HILLS.

that species, although from the figures and description given in the Synop-
sis of the Organic Remains we certainly should not have done so. We had
previously tried to see Dr. Morton’s types in the collections at Philadelphia,
but did not succeed, owing to the absence of persons having charge; con-
sequently we were compelled to depend upon the figures and descriptions
above referred to until we received a copy of Mr. Meek’s excellent work, in
which he describes these forms and figures, the types above referred to.
But we are not prepared to identify them with J. cripsti Mantell, nor with
any shell conforming to Mantell’s description ; and the forms referred by
authors to that species are so variable, that we can rely only upon the orig-
inal type specimens.

Formation and locality.—In limestone of the Fort Pierré Group, Chey-
enne River, near Box Elder Creek, and on Beaver Creek, two to three miles
west of the Black Hills.

INOCERAMUS TENUILINEATUS.
Plate 9, figs. 12, 13.

Inoceramus tenuilineatus H. & M., Mem. Acad. Arts and Sci., vol. viii, p. 387, Pl. 2, fi
Inoceramus tenuilineatus (H. & M.) Meek, Pal. U.S. Geol. Surv. Terr., p. 57, PL. 12, fig.

Shell of rather large size, transverse, subovate or rhomboid-ovate in
outline, with very ventricose, almost inflated valves, and large, inflated,
slightly prominent, incurved, and nearly terminal beaks; hinge line shorter
than the length of the shell below and rounded at the posterior extremity ;
cardinal and basal margins subparallel; the latter gently rounded in the
middle and a little more abruptly so toward the ends; anterior end broad,
obliquely truncate in a side view, projecting a little in the lower part
beyond the line of the beaks, forming with the cardinal line an angle of
from 95° to 120° in different individuals, but generally not more than 100°;
posterior margin rounded, most strongly from below ; anterior slope of the
valves very abrupt and on some specimens nearly vertical for one-half the
depth of the valves; posterior slope more gradually declining from the
prominent umbonal portion of the valve, giving a somewhat cuneate form
to the posterior half of the shell when viewed in a cardinal profile.

Surface of the shell marked by, sometimes indistinct, but often very

CRETACEOUS FOSSILS. 401

strong, irregular concentric undulations; with finer ones in the broader
interspaces, and crossed by indistinct radiating lines on internal casts.
The fibrous coating, where preserved, appears to have been very thin on
the younger portions of the shell, but toward the outer margin, in larger
individuals, it attains a thickness of a sixteenth of an inch or more. None
of our specimens are in a condition to show the surface of the fibrous coat-
ing, consequently we have not seen on them the fine concentric linings
characteristic of the species.

There is, perhaps, no better marked, or more distinct, species than this
among the Inocerami of the Black Hills region. It is most nearly related
to the forms referred to I. barabini, but is easily distinguished by the
larger and more prominent beaks, the inflated valves, and broad, abrupt
anterior end, and the abrupt, concave posterior cardinal slopes, as well as
the more nearly parallel basal and cardinal margins.

Formation and locality—At the top of the gray shales of the Fort Pierré
Group, on the Cheyenne River, near Rapid Creek, Black Hills, Dakota

Among the Inoceramus-like shells in the collection are two species,
which are characterized by a strong and broad internal rib on each valve,
extending obliquely backward from behind the beaks along the posterior
umbonal slope to near the postero-basal angle of the shell, leaving upon the
internal casts a concave depression or sulcus of greater or less depth, and
increasing in width and depth from the beaks outward. This rib does not
affect the outer surface, nor produce any external feature on the shell, being
exclusively confined to the inner nacreous layers, and formed by the addi-
tion of successive coatings on the inner surface only and within the margin
of the valve, so that it is seen only on the interior of separated valves, on
internal casts, or on exfoliated specimens. From the interior of valves it is
readily removed, even from the outer nacreous layers, as the feature is sel-
dom developed at the edge of the shell during growth, but at a point some
distance within the margin. It can sometimes also be detected on examples
where the pearly layers are nearly all preserved, showing the margins of
the depression faintly defined through the partially transparent substance.
In such cases, however, it is only detected upon close observation.

All individuals of species possessing this feature do not have it devel-
26 BH

402 GEOLOGY OF THE BLACK HILLS.

oped to the same degree, and often it may not be developed until an
advanced stage of growth, as in the case with the ridges bordering the mus-
cular impressions of Cucullea and allied forms; but this is no reason for con-
sidering it as an abnormal or accidental feature where it does exist, for in
many cases its absence may have resulted from partial decay before final
imbedding.

This feature has long been known to exist in shells of this group, but
has generally been considered as of accidental occurrence and of no specific
value. Dr. F. Roemer, in his work on the Cretaceous formation of Texas,
figures a form possessing it, which he regards as belonging to I. cripsi
Mantell, and also refers others to the same, apparently regarding it as only
an abnormal feature and not of specific value. Still in his description of
the figure on Plate VII, he applies to the shell the varietal name sulcatus,*
descriptive of this very feature. Mr. Meek also mentions its existence on
specimens which he refers to I. cripsi var. barabini, but which are probably
distinct from that form and identical with one of those above referred to
Some authors, however, have considered it of more importance. Mons.
D’Orbigny founded his I. impressus t on the existence of this feature in his
types, and Dr. Morton’s I. alveatus is another example.

Considering the development of this feature to so great an extent, and
in several species, not only in America but also in Europe and elsewhere,
we deem it other than an abnormal or accidental one, and not only of
specific importance, but as marking a distinct generic group, and propose
for it the generic name ENpocostEa, under the impression and belief that
it marks the line of recession of the larger or posterior muscular scar, as in
the forms of Inoceramus on which this scar has been detected it occupies
the same relative position.

Genus ENDOCOSTEA Whitt.
Genus ENDOCOSTEA Whitf., Prelim. Rept. Pal. Black Hills, 1877, p. 31.

Shell resembling InocerRAmus, being bivalve, with both sides convex,
but more or less unequal, and composed of two layers, an outer vertically

* Not J. sulcatus Parkinson, from the Gault of England.
+This species is referred to the genus Thetis by Woodward, See Woodward’s Manual of recent
and fossil shells.

CRETACEOUS FOSSILS. 403

fibrous coating and an inner nacreous or pearly lining; hinge line straight,
edentulous, with a narrow linear external cartilage area on each valve.
Valves provided with an oblique internal rib passing from behind the
beaks, along the postero-cardinal slope, toward the postero-basal margin,
marking the position of the posterior muscular imprint; other muscular
markings unknown. Type, H. typica Whitf.

We have not been able to detect the anterior muscular scar or pallial
line, except the latter as an irregular transverse line of small tubercles
across the beak of internal casts in several cases, and a slight curving
ridge, faintly marked on a smaller number of examples, passing from the
apex along the anterior side for a short distance. The genus differs from
Inoceramus so far as yet known only in the existence of the internal rib.
The species now known are L. alveatus = Inoceramus alveatus Morton; E.
impressus = I. impressus D’Orb.; EF. sulcatus = I. cripsii var. sulcatus Roemer,
and EH. typica Whitf., herein described.

ENDOCOSTEA TYPICA.
Plate 9, figs. 1-7.
Endocostea typica Whitt., Prelim. Rept. Pal. Black Hills, 1877, p. 32.

Shell of medium size, transversely-subovate, oblique and slightly in-
equivalve, the right side being the largest in the only example where they
are preserved in contact. Valves strongly ventricose at the anterior end
and on the anterior part of the umbonal region, becoming more compressed
and attenuate behind and along the posterior cardinal portion, sometimes
strongly depressed and concave between the cardinal line and dorsal slope.
Hinge line straight, often two-thirds as long as the shell below and slightly
rounded at the extremity; beaks small, incurved, projecting but little above
the cardinal line and situated near the anterior end, but not quite terminal;
anterior end short, sharply rounded at the antero-cardinal angle, and
extending a little forward below for about half the height of the valve,
when it rounds backward to the basal line, the upper part forming, with
the cardinal line, an angle of about 95° to 100°; posterior end nearly
equal to or narrower than the anterior, and more sharply rounded, most-

strongly from below; basal line forming nearly half of an ellipse or semi-

404 GEOLOGY OF THE BLACK HILLS:

ovate figure, the widest part varying from in front of, to behind the middle
of the length in different individuals.

Surface of the valves usually marked by very distinct concentric
undulations, though sometimes they are only moderately developed;
oblique internal rib strongly marked, narrow and pointed near the beak,
and gradually widening and deepening posteriorly, the concentric furrows
distinctly crossing, and leaving, on the deeply concave channel of the casts,
corresponding depressions. Inner layers of the shell highly nacreous;
outer prismatic layer very thin.

This species resembles Inoceramus barabini, as it is recognized in the
same region, in the general form and in the subcuneate anterior end of the
shell; but the transverse furrows are generally more distinctly marked and
regular. It is readily distinguished by the oblique sulcus and by the
opposite valve being largest, if the example above referred to, and figured
on the plate, is rightly interpreted.

We have great doubts of the identity of the western forms with I.
barabini Morton, from Alabama, and are inclined to believe they would be
more naturally classed under a distinct name, as formerly done by Messrs.
Meek and Hayden.

Formation and locality—In limestone of the Fort Pierré Group, at Old
Woman Fork of the Cheyenne River, Black Hills, where they occur very
abundantly, densely packed together in the rock, and possessing the specific
characters and the oblique sulcus in a remarkable constant degree.

ENDOCOSTEA SULCATA.
Plate 10, fig. 6.

? Inoceramus cripsii var. sulcatus Roemer, Kreid. von ‘Texas, p. 56, Pl. vii, fig. 2.
? Inoceramus cripsii Roemer, Texas, p. 100.
Not Inoceramus sulcatus Parkinson.
Compare Inoceramus conveca H. & M., Mem. Am. Acad. Sci. and Arts, vol. 5, p. 386,
Ved Ab vies 2h

Shell moderately large, transversely-ovate, with ventricose valves,
most gibbous on the anterior central region, becoming more compressed
behind and toward the posterior dorsal angle; beaks strong, tumid, situated

near the anterior end, slightly enrolled and moderately projecting above

CRETACEOUS FOSSILS. . 405

the hinge line. Hinge long and straight; anterior end short and obliquely
rounded; posterior end longer and rounded; base rounded or forming a
short semi-elliptical curve. Surface marked by concentric undulations.
Oblique sulcus well marked and broad.

A single individual, which we have referred to the above-named
species, occurs in the collection. It is an internal cast of both valves, much
weathered and somewhat displaced, as well as a little imperfect posteriorly,
but still a well-marked species and entirely distinct from any other form.
It is more ventricose than we should suppose Dr. Rcemer’s specimen had
been and the concentric furrows are less strongly marked, but otherwise
very similar.

Formation and locality—tLoose, on the East Fork of Beaver Creek,
Black Hills, probably from the Fort Pierré Group.

INTEGROPALLIA.
ARCIDA.

Suscenus IDONEARCA Conrad.

IDONEARCA SHUMARDI.
Plate 11, figs. 8-11.

Area (Cucullea) shumardi M. & H., Proc. Acad. Nat. Sci. Phil., vol. 8, p. 86.

Cucullea shumardi (M. & H.), Proc. Acad. Nat. Sci. Phil., vol. 8, p. 285.

Cucullea fibrosa (M. & H.), Proc. Acad. Nat. Sci. Phil., vol. 12, p. 428.

Cucullea (Idonearca) shumardi Meek, Pal. U. 8. Geol. Surv. Terr., p. 86, Pl. 28, fig.
15; Pl. 29, fig. 4.

Shell obscurely trapezoidal or rhombic-ovate, usually a little longer
than high, with strongly ventricose valves, which become almost inflated
on the umbones and along the rounded umbonal ridge. Beaks large,
inflated, moderately elevated, approximate, and slightly incurved, situated
a little in advance of the middle of the length; hinge line straight, from
half to two-thirds as long as the shell below; hinge-plate narrow and marked
by three or four very oblique, neariy parallel, linear teeth on the posterior
end, the sides of which are finely striated vertically, and by one or two -
similar ones on the anterior end. (The authors of the species state that

406 GEOLOGY OF THE BLACK HILLS.

there are small, irregular, intermediate transverse teeth in the center. These
we have not seen, our specimens not showing this part of the hinge plate.)
Hinge area of moderate height, marked by distinct, oblique, ligamental
grooves, widely diverging from the center of the area; anterior end of the
shell broadly and regularly rounded, and imperceptibly passing into the
basal line; posterior end obliquely truncate, and directed backward to the
posterior extremity, below the middle of the height of the valve; basal
border more broadly rounded.

Surface of the valves marked by fine concentric lines of growth and
by very fine indistinct radiating lines, which form pits at the concentric
furrows, seen only by the aid of a lens. Anterior muscular imprint large
and subcireular, situated close within the margin and near the extremity of
the hinge line; posterior impression obliquely elongated, gradually increas-
ing in width from above, and distinctly bordered on the inside by a thin
elevated ridge, as in Cuculleea.

Formation and locality—In beds of the Fox Hill Group of the Cre-
taceous, on the Cheyenne River, near Old Woman Fork, Black Hills.

Genus NUCULA Lam.

NUCULA PLANIMARGINATA.
Plate 11, figs. 5, 6.

Nucula planimarginata M. & H., Proce. Acad. Nat. Sci. Phil., vol. 8, p. 85, ib., Nov.
1856, p. 21.

Nucula planimarginata (M. & H.) Meek, Smithsonian Check List Invert. Foss., p. 8.

Nucula planimarginata (M.& H.) Meek, Pal. U. S. Geol. Surv. Terr., p. 101, Pl. 15, fig. 8,
and Pl. 28, fig. 16.

Shell rather above the medium size, transversely-ovate, about two-
thirds as high as long, with convex valves and somewhat prominent beaks,
which are slightly incurved, and piaced within the anterior third of the
length of the valve; anterior end short, obliquely truncate, the longest
point rather below the middle of the height, and rather sharply rounded ;
posterior end long and more broadly rounded than the anterior, basal
margin strongly curved, having a semi-oval outline; cardinal line behind
the beaks gently arcuate.

Surface of the shell not clearly determined, but, as far as can be ascer-

a

CRETACEOUS FOSSILS. 407

tained, has been faintly concentrically striate, and there is also evidence on
the exfoliated surface of fine obscure radiating lines.

On the internal casts the muscular imprints are distinctly marked, and
of rather large size, the posterior scars oval and placed close to the cardinal
line, and the anterior imprints of nearly the same size and form, but sub-
marginal; pedal scars elongate oval, very much smaller than the posterior
adductors, and placed a little in advance of them, and close beneath the
hinge plate. Teeth numerous; evidence of about twenty-four can be seen
on the posterior side of the beaks, and of about ten or eleven on the ante-
rior side.

The specimens in hand are imperfect and much exfoliated, so that the
entire features cannot be determined. They do not agree in all respects with
the species to which we have referred them, being a little broader posteriorly
and rather more excavated in front of the beaks anteriorly; still it is too
nearly related to be considered distinct.

Formation and locality—tIn limestones of the Fort Pierré Group, on the

Cheyenne River, ten or fifteen miles west of the mouth of Beaver Creek,

Black Hills.
Genus NUCULANA Link.

NUCULANA BISULCATA.

Plate 11, fig. 7.

Leda bisuleata M. & H., Proc. Acad. Nat. Sci. Phil., 1861, p. 440.
Nuculana bisuleata Meek, Smithsonian Check List Invert. Cretaceous Foss., p. 8.
Nuculana bisulcata Meek, U. S. Geol. Surv. Terr., p. 104, Pl. 15, fig. 4.

Shell quite small, not exceeding three-eighths of an inch in length, the
extreme height rather less than half the length, subovate or subelliptical in
outline; anterior end largest and broadly rounded; posterior end narrower
and compressed, subangular below; basal line broadly curved and slightly
constricted behind the middle; beaks full and strong, rather more than one-
third of the length from the anterior end; cardinal margins sloping gradu-
ally from the beaks, the posterior side sometimes very slightly concave.

Surface of the valves convex, and marked by fine, even, concentric lines.

The specimens of this species are quite similar to N. subequilatera herein

described, but are not more than one-third as long, and the cardinal line is

408 GEOLOGY OF THE BLACK HILLS.

much less concave behind the beaks, and the beaks nearer the anterior end
of the shell and less prominent.

Formation and locality—In limestone of Cretaceous age, on the Chey-
enne River, near Box Elder Creek, and on the east fork of Beaver Creek,
Black Hills.

NUCULANA SUBEQUILATERA.

Plate 11, figs. 3, 4.

Nuculana subequilatera Whitf., Prelim. Rept. Pal. Black Hills, 1877, p. 32.

Shell of small size, transversely elongate-subovate, with large, promi-

nent, suberect beaks, which are placed a little in advance of the middle of
the length, and are slightly incurved, but comparatively distant; valves
convex, as seen on the casts, ventricose in the middle and below the beaks,
and compressed toward the extremities, more particularly so posteriorly ;
hinge line abruptly bent between the beaks, the opposite sides forming an
angle of about 140°, the posterior side slightly recurving in the outer part;
anterior end of the shell sharply rounded; posterior extremity acutely

rounded near the extremity of the cardinal line, and rapidly sloping for- _

ward below to the basal margin, which is broadly curved and almost
straightened in the middle.

Surface of the shell unknown, hinge plate marked by a large number
of comparatively long, slender teeth, minute in the middle and gradually
increasing in size and length outwardly; about twenty may, with difficulty,
be counted on the posterior side of the beaks and about eighteen on the
shorter side. Cartilage pit small; muscular imprints faintly marked. No
sinus can de detected in the pallial line.

The species seems to be nearly related to Nucula (Nuculana ?) equilater-
alis M. & H., but the beaks are not central as in that species, but are situ-
ated at about two-fifths of the length from the anterior end, and the teeth
are decidediy not obtuse, but on the contrary are very slender, as seen on
the casts.

Formation and locality—In Cretaceous rocks on the Cheyenne River,
near French Creek, Black Hills; supposed to be very near the top of the
Fort Pierré Group.

CRETACEOUS FOSSILS. 409

Genus YOLDIA Moller. .
YOLDIA EVANSL.

Plate 11, fig. 1, 2.

Nucula evansi M. & H., Proc. Acad. Nat. Sci. Phil., 1866, vol. 8, p. 84, and ext. p. 21.
Leda evansi M. & H., Proc. Acad. Nat. Sci. Phil., 1860, May, p. 185.

Leda (Yoldia) evansi M. & H., ib., 1860, p. 429.

Yoldia evansi Meek, Smithsonian Check List Invert. Foss., p. 7.

Yoldia evansi (M. & H.) Meek, Pal. U. S. Geol. Surv. Terr., p. 111, Pl. 28, fig. 10.

Shell small, transversely elongate-elliptical, as long again as high.
Valves depressed-convex, most ventricose on the umbones and becoming
somewhat flattened posteriorly ; beaks small and inconspicuous, located at
about one-third of the length from the anterior end; hinge line straight
and distinctly marked by a depressed longitudinal groove on each valve ;
seen only in a cardinal view; anterior end rounded; posterior end trun-
cate; longest near the cardinal line and receding below; basal line very
broadly curved.

Surface polished and marked by very fine lines of growth. Hinge
line occupied by a large number of small, angular teeth, about twice as
many on the posterior as on the anterior side of the beak; muscular im-
pression and pallial line faintly marked, the latter rather deeply sinuate.

- The species may be easily recognized by the peculiar longitudinal
groove along the hinge line when the shell is preserved.

Formation and locality.—In limestone of the Fort Pierré Group, on Old
Woman Fork of the Cheyenne River, and near Rapid Creek, Black Hills.

LUCINIDA.

Genus LUCINA Bruguiers.
LUCINA OCCIDENTALIS.

Plate 11, fig. 19-21.

Tellina occidentalis Morton, Jour. Acad. Nat. Sci. Phil., vol. 8, Pl. xi, fig. 3.

Incina occidentalis (Morton) M.& H., Proc. Acad. Nat. Sci. Phil., Nov. 1856; Ext. p. 20.
Inecina occidentalis (Morton) M. & H., Smithsonian Check List. Invert. Foss., p. 12.

Mold of Lucina ? Owen, Geol. Rept. Iowa, Wis. and Minn., Tab. vii, fig. 8.

Lucina occidentalis (Morton) Meek, Pal. U. 8. Geol. Surv. Terr., p. 134, PI. 17, fig. 4.

410 GEOLOGY OF THE BLACK HILLS.

Shell of medium size or smaller, transversely-ovate, largest on the
anterior side of the middle and opposite the beaks. Valves depressed-con-
vex, being strongly lenticular in a transverse section when united. Beaks
small, appressed, and inconspicuous, situated considerably anterior to the
middle of the length; cardinal line slightly inclined from the beaks to the
extremities, the two sides forming with each other an angle of about 140°;
anterior end of the shell broadly rounded below the extremity of the cardi-
nal line; posterior extremity more narrowly rounded and prolonged; basal
line irregularly arcuate, being somewhat straightened behind the middle;
posterior umbonal ridge distinct, the cardinal slope narrow and flattened or
slightly impressed ; escutcheon large, distinct, and rather deeply impressed;
ligament of moderate size. Surface strongly marked by concentric lines
of growth. ;

In the interior, the muscular impressions, as seen on an internal cast
of small size, are well marked, the anterior one large and semi-lunate, the
posterior one only about two-thirds as large and subcircular in form.

Formation and locality—In Cretaceous strata, No. 4, on Cheyenne
River, near Rapid Creek, Black Hills.

LUCINA VENTRICOSA.

Plate 11, figs. 14-16.

Lucina ventricosa H. & M., Mem. Acad. Arts and Sci., vol. viii, p. 427.
Lucina occidentalis var. ventricosa (H. & M.) Meek, Pal. U. S. Geol. Sury. Terr., p.
135, Pl. 17, fig. 3.

Shell of medium size, subquadrangularly-ovate, longer than high, a
little widest anteriorly, narrower and truncate behind. Valves convex,
lenticular in a transverse section when united; beaks small, appressed and
inconspicuous, but little projecting above the general contour of the shell;
anterior end rounded; basal line forming a broader curve; posterior truncate;
umbonal ridge indistinct and the cardinal slope distinctly flattened, escutch-
eon deep, the margin sharply angular, the ligament occupying about two-
thirds of its length; lunular area slightly elevated. Surface marked by
fine, irregular, concentric lines of growth; muscular imprints large and

deeply marked.

CRETACEOUS FOSSILS. 411

This species differs from L. occidentalis, with which it is associated, in
being more nearly circular and more nearly equilateral, that one being
much longer behind than before, while this one is nearly equal. It also
differs in being wider posteriorly with a wider postero-cardinal slope, and
also in having the beaks a little more inclined forward We have noticed
specimens in several collections labeled Z occidentalis Morton, both separ-
ately and mingled with that species, hut on comparing it with Dr. Morton’s
figures we find them to be of the more elongate form, and this one is certain-
ly very distinct from those having that character before us. We noticed
also that Mr. Meek, in the Paleontology of the United States Geological
Survey of the Territories, just published, has placed it as a variety of L. occi-
dentalis, expressing doubt, however, of the correctness of this view. They
are certainly much more distinct than many of the recent forms of the genus
considered as good species. Our specimens, which we have referred to the
L occidentalis, ave, however, proportionally longer, posteriorly, than those
he figures, and also much more like Dr. Morton’s figures.

Formation and locality—In beds of the Fort Pierré Group, near the
top of the gray shales on the Cheyenne River near Rapid Creek, and at
the same horizon at other localities near by. A few specimens undistin-
guishable from the above are marked “11 M. 8. of Belle Fourche,” Black
Hills, Dakota.

LUCINA (DIPLODONTA ?) SUBUNDATA.

Plate 11, fig. 17, 18.

Lucina subundata H. & M., Mem. Am. Acad. Arts and Sci., vol. viii, new ser., Pl. 1,
fig. 6.
Tucina subundata (H. & M.) Meek, Pal. U.S. Geol. Sur. Terr., p. 133, Pl. 17, fig. 2.
Shell small, orbicular in outline, with depressed convex valves; beaks
small, rounded, distinctly projecting above the general contour of the shell
and inclined forward; posterior side of the shell very slightly truncate, the
cardinal slope narrow and distinctly arched in its course between the beaks
and the posterior margin; basal line rounded, more sharply so at a point
opposite the beaks; anterior to the beaks the cardinal surface of the shell’

412 GEOLOGY OF THE BLACK HILLS.

is constricted, forming a slight fold within the margin. Surface of the shell
marked by fine concentric striz ; ligament of moderate size, deeply seated
within the borders of the valves, which are not inflected for its reception,
but are distinctly so to form the short, deep lunule on the anterior side of
the beaks.

The species is associated with the two preceding ones, but differs very
materially in the details of structure, although closely resembling them in
general form. The sulcus of the shell on the anterior border would place
it ina different section of the genus from either of those; and the orbicular
outline, narrow cardinal slope, deeply seated lunule, and more prominent
beaks will also serve to readily distinguish them.

Formation and locality —At the top of the gray shales of the Fort
Pierré Group, on the Cheyenne River, near Rapid Creek, Black Hills,
Dakota.

CRASSATELLIDA.

Genus CRASSATELLA Lam.

CRASSATELLA SUBQUADRATA.

Plate 11, fig. 12.

Crassatella subquadrata Whitf., Prelim. Rept. Pal. Black Hills, 1877, p. 34.

Shell small, subquadrangular in outline, with thin compressed valves
and not prominent beaks, which are situated within the anterior third of the
length; length of the shell exceeding the height; basal margin broadly
rounded; anterior end short and narrowly rounded; posterior end broad
and rounded truncate; posterior hinge line straight and subparallel to the
basal margin Surface of shell unknown. Muscular impression small; the
posterior one situated close beneath the extremity of the hinge margin, and
the anterior scar submarginal. Pallial line not distinctly marked; margin
of the valve crenulate.

The only specimen of this genus recognized among the collections
from the Black Hills, is a small internal cast, answering to the above
description, and -apparently a true Crassatella. Although the hinge plate

CRETACEOUS FOSSILS. . 413

has not been seen, the cast has all the features usually possessed by casts of
the typical forms of the genus.

Formation and locality—In Cretaceous beds on the Cheyenne River.
Probably from the Fort Pierré Group.

Genus ASTARTE Sowerby.
ASTARTE EVANSI.

Plate 11, fig. 13.

Crassatella evansi H. & M., Mem. Am. Acad. Sci. and Arts, new ser., vol. 5, p. 383,
Pl. 2, fig. 9. )

Crassatella evansi (H. & M.) M. & H., Proc. Acad. Nat. Sci. Hist. Nov. 1853, p. 2 a.

Crassatella evansi (H. & M.) Meek, Smithsonian Check List Invert. Foss., p. 11.

Crassatella (Pachytherus) evansi Meek, Pal. U. 8. Geol. Surv. Terr., p. 117, Pl. 17, fig. 6.

Shell of moderate size, triangularly-ovate in outline, with very ventri-
cose valves and strong projecting incurved beaks, which are situated ante-
rior to the middle of the valve; anterior and posterior cardinal margins
rapidly sloping from the beaks, and forming with each other a little more
than an angle of 90°, the anterior side being much shorter than the poste-
rior. Anterior and posterior extremities rounded; basal line less strongly
arcuate. Surface marked by concentric lines.

On the internal casts the muscular imprints are of moderate size, ovate
and deeply marked, the pallial line simple and distinct, margin of the valves
crenulate.

The species was originally referred to the genus Crassatella by the
authors, and we have seen specimens labeled by one of them as C. (Pachy-
therus) evansi. We are not familiar with the characters of the genus
Pachytherus, but can see no reason why this species should be classed else-
where than under Astarte, as it seems to have all the features of that genus,
and to be destitute of the internal cartilage pit of Crassatella. The exam-
ples in the collection before us are internal casts, and therefore we cannot
be entirely positive of all the external features

Formation and locality—tIn limestone at the top of the gray shales of
Cretaceous, No. 4, on the Cheyenne River, near Rapid Creek, Black Hills.

414 GEOLOGY OF THE BLACK HILLS.

VENIELLIIDA.

Genus VENIELLA Stoliczka.
VENIELLA HUMILIS.
Plate 10, figs. 7-13.

Cyprina humilis M. & H., Proc. Acad. Nat. Sci. Phil. May, 1860, p. 179.
Venilia humilis (M. & H.) Meek, Smithsonian Check List, Invert. Foss., p. 13.
Veniella humilis (M. & H.) Meek, Pal. U.S. Geol. Surv. Terr., p. 155, Pl. 30, fig. 5.

Shell of moderate size; transversely oblong or trapezoidal, or trans-
versely-oval; the length considerably exceeding the height and often, in
casts, the condition in which they are usually obtained, much less than
two-thirds as high as long; the thickness through the united valves but
little less than the height, which is greatest at about the anterior third of
the length. Beaks large, tumid, inflated on the umbones, slightly angular,
strongly incurved and approximate, directed forward, and situated nearly
vertically above the anterior end of the shell; hinge line arcuate, much
shorter than the length of the shell and gradually declining toward the
posterior extremity, which is obliquely truncate and longest below; basal
line somewhat regularly curved; anterior end rounded. Umbonal ridge
angular or more or less rounded angular, and strongly arcuate in its direction
from the beaks to the postero-basal angle of the valve. Ligament external
and of moderate size. Surface covered by strongly marked lines of growth.
Internally, the muscular impressions are distinctly marked, the anterior
very deep. Cardinal teeth strong, lateral tooth having the form of an
elevated angular ridge fully one-third as long as the valve.

The species is a strongly marked and rather abundant one, but is quite
variable in its proportions in different individuals; the length and height,
as seen on casts, varying from once and a half to nearly twice the height.
The substance of the shell is thick and massive, especially along the car-
dinal border, and when entirely removed the casts appear much more elon-
gated in proportion than when the shell is preserved.

Formation and locality—In ferruginous sandstone of Cretaceous No.
5, on the Cheyenne River, near Old Woman Fork, Wyoming.

CRETACEOUS FOSSILS. 419

Genus SPHARIOLA.
SPHARIOLA TRANSVERSA,
Plate 10, figs. 14-16.
Spheriola transversa Whitf., Prelim. Rept. Pal. Black Hills, 1877, p. 34.

Shell of rather large size, subspheroidal, a little transverse, or, longer
than high exclusive of the projection of the beaks, the outline of the
margin of the valve being slightly oblate or transversely broad-oval, and
nearly symmetrical. Valves highly inflated on the central area and um-
bones, with strong, highly elevated, strongly incurved, subcentral beaks,
which are slightly curved forward and subangular on the umbonal ridges.

Surface of the shell marked by sublamellose concentric lines of growth,
which form strong distant undulations in some cases toward the extremities
of the shell.

Internally the muscular impressions are large and subcircular, and
the pallial line simple and entire. The cardinal teeth, as obtained by a
gutta-percha mold from a natural cast, consist of two tuberculiform teeth
beneath the beak, and the laterals are represented by a strong oblique fold
or ridge, passing from near the beak to within a short distance of the pos-
terior border of the hinge plate, where it is marked, or divided, by an
impressed pit, which may be accidental.

Compared with S. obliquata Meck, this shell is more equilateral, the
beaks more nearly central, and the shell less oblique. It differs from S.
moreauensis of the same author in having much larger beaks, which are
more strongly enrolled and the shell is also more transverse.

Formation and locality.—In ferruginous sandstone of Cretaceous No.
5, on the Cheyenne River, near Old Woman Fork, Wyoming.

416 GEOLOGY OF THE BLACK HILLS.

SINUOPALLIA.
VENERIDZ.

Genus DOSINIA Scopoli.

DOSINIA MISSOURIANA ?
Plate 11, figs. 25, 26.

? Cytherea missouriana Morton, Jour. Acad. Nat. Sci. Phil., vol. 8, Pl. x1, fig. 2.

? Cytherea missouriana (Morton) M. & H., Proc. Acad. Nat. Sci. Phil. Nov. 1856, p. 20.
? Dione missouriana (Morton) Meek, Check List Invert. Foss. Smithsonian Inst., p.. 13.
Cytherea deweyi M. & H., Proc. Acad. Nat. Sci. Phil., vol. 8, p. 83.

Merctrix deweyi M. & H., Proc. Acad. Nat. Sci. Phil., vol. 12, p. 185.

Callista deweyi M. & H., Proc. Acad. Nat. Sci. Phil., vol. 15, p. 143.

Dione deweyi Meek, Smithsonian Check List Invert. Foss., p. 13.

Callista (Dosciniapsis ?) deweyi M., Pal. U. S. Geol. Sur. Terr., p. 182, Pl. 17, fig. 15.

Shell rather below a medium size, transversely subtriangular in outline,
with ventricose valves, which are most elevated on the umbones and grad-
ually declining toward the basal line; being cuneately cordate in a section
from the beaks to the basal line where the valves are united. Beaks of
moderate size, or for the size of the shell somewhat large, pointed, incurved,
and directed forward, situated much nearer the anterior end; posterior
cardinal line arcuate; posterior and anterior extremities of the shell rather
sharply rounded, the anterior most distinctly so, and the cardinal line on
this side slightly contracted below the beaks; basal line broadly curved,
more abruptly rounded toward the extremities.

Surface marked by fine, irregular lines of growth; muscular impres-
sions large and submarginal. Pallial line deeply sinuate, the sinus acutely
angular, and directed obliquely forward and upward, reaching to a little
behind the middle of the valve.

The specimens of this species in the collection are in rather poor con-
dition, having the shell considerably exfoliated and broken, but they reveal
the form of the muscular imprints and pallial line very satisfactorily. The
structure of the hinge plate, however, cannot be made out. The subtri-

CRETACEOUS FOSSILS. 417

angular form of the shell and gibbous umbones will serve as distinguishing
marks. We have some hesitation in referring this form to Dr. Morton’s
Cytherea missouriana simply from the fact that his figure above cited is
somewhat more distinctly triangular than any of the specimens we have
seen, and their outline would correspond rather better with that of Astarte
evansi = Crassatella evansi H. & M, but the valves are not represented
quite as ventricose as is the case with that shell, and it is scarcely possible
that Dr. Morton would have referred a shell of that character, as perfectly
preserved as his figure would indicate, to the genus Cytherea.

Formation and locality—In limestone of the Fort Pierré Group, on the
Cheyenne River, ten or fifteen miles west of the mouth of Beaver Creek,

Black Hills.
Genus THETIS Linn.

THETIS CIRCULARIS.
Plate 11, figs. 22 to 24.

Venus ? circularis M. & H., Proc. Acad. Nat. Sci. Phil., Nov. 1856, p. 8.
Cyclina ? circularis Meek, Smithsonian Check List Invert. Foss., p. 13.
Thetis ? circularis (M. & H.) Meek, Pal. U. 8S. Geol. Surv. Terr., p. 190, Pl. 17, fig. 8.

Shell small and very thin, subcircular and subglobose, with propor-
tionally large, elevated, pointed, and incurved beaks, which are directed
obliquely forward, and situated a little in advance of the middle of the
valve; border of the valve circular, except at the postero-basal margin,
which is slightly extended and obtuse; hinge line very arcuate; ligaments
small and rather deeply seated, owing to the prominence of the back of
the umbones of the valves Surface marked only by fine concentzic lines
of growth, and when entire and in good condition appears to have been
quite smooth. Muscular imprints faintly marked, the anterior most distinct
and submarginal; pallial line deeply sinuate, the sinus narrow, angular,
and directed obliquely upward toward the apex of the valve; lobes of the
pallial line digitate.

The small size of the shell and its rotund and gibbous form will readily
distinguish it from any other species.

Formation and locality—kIn beds of the Fort Pierré Group, near the
forks of the Cheyenne River, and near the mouth of Rapid Creek, Black
Hills, Dakota.

27 BH

418 GEOLOGY OF THE BLACK HILLS.

FAMILY 2?
Genus LEIOPISTHA Meek.
Suscenus CYMELLA Meek.

LEIOPISTHA (CYMELLA) MEEKI.
Plate 11, figs. 27, 28.

Leiopistha (Cymella) Meeki Whitf., Prelim. Rept. Pal. Black Hills, 1877, p. 35. _

Shell of moderately large size, transversely-oval in outline, about once
and a half as long as high. Valves very convex, with large, tumid, incurved
beaks, which are located a little more than one-third of the entire length
from the anterior end of the shell, and are considerably elevated above the
cardinal line ; anterior and posterior ends of the valve broadly and nearly
equally rounded, and the basal line between the longest points of the shell
forming a very regular and nearly symmetrical semi-oval curve; cardinal
line sloping gradually on both sides of the beak, the anterior side marked
by a narrow, lanceolate, lunule-like depression; and the posterior side by
a larger, broader area, bordered by an elevated ridge. Concentric undu-
lations of the surface, strong and distinct, continuing their sharpness to the
margins of the cardinal depressions, and gradually increasing in strength
with the increased size of the shell to below the middle, beyond which point
they become flattened and fainter; about twenty-seven may be counted on
the entire surface. The concentric undulations are crossed by comparatively
strong, radiating coste, which do not mark the depressions between the
undulations, but exist only on their flattened surfaces. The radii are
strongest on the central parts of the shell, and become gradually finer and
closer toward the lateral extremities, and are visible on the anterior end to
the margin of the cardinal depression, but on the posterior end are not
seen to exist quite so far. The crests of the radii appear to have been
marked by a row of minute puncta, seen only under a magnifier, three and
four existing to each undulation. The surface of the shell is also marked
by fine, somewhat wrinkled, concentric lines of growth, especially on the
larger parts of the valve, but apparently confined to the outer coating of

CRETACEOUS FOSSILS. A419

the shell, which has the appearance of a thick epidermis, and in some places
is excorticated.

We were at first inclined to consider this as C. undulata M. & H., but
on strict comparison with Mr. Meek’s description in the Paleontology of the
United States Geological Survey of the Territories, which we have just
received, have concluded it to be a different species. It differs in the
greater size and more robust habit, also in the comparatively stronger
undulations, and in having the radiating coste continuing to the anterior
end, if not to the posterior also. The outline of the shell also differs some-
what. ;

Formation and locality—In Cretaceous strata at Deadman’s Rapids
Upper Missouri. Probably of No. 5.

ANATINIDA.
Genus THRACIA Leach.

THRACIA SUBGRACILIS.
Plate 11, figs. 29, 30.
Thracia subgracilis Whitf., Prelim. Rept. Pal. Black Hills, 1877, p. 36.

Shell small, transversely ovate, and slightly inequivalve. Valves con-
vex, ventricose in the middle, but becoming quite compressed and almost
constricted behind ; anterior part large, forming nearly or quite four-fifth,
of the entire bulk of the shell, the extremity rounded; basal line full in front
of the beaks and constricted or sinuate behind; posterior end narrow and
subtruneate; anterior cardinal line long, nearly on a line with the beaks,
and very slightly convex ; posterior to the beaks the cardinal line is con-
stricted and narrowed ; beaks small and compressed, appearing as if directed
backward.

The surface of the only specimen is imperfect, the shell being in great
part removed, but where preserved is marked by concentric lines of consid-
erable strength, approaching in character to undulations rather than striz.
The beaks are small and marked along their apices, and fora short distance
below, by a slight notch or slit from the removal of a narrow ridge which .
has marked the interior of the shell, as in Anatina, and supporting the car-

420 GEOLOGY OF THE BLACK HILLS.

tilage pit. The shell, in its external form, has all the features of THractra,
being slightly inequivalve and twisted when viewed in profile, and also
in the character of the surface markings. The muscular impressions and
pallial line cannot be distinguished through the remaining shell and
we are therefore in doubt concerning these features. It bears consid-
erable resemblance to Thracia gracilis M. & H. (see Paleontology of the
United States Geological Survey of the Territories), but is proportionally
shorter and somewhat more contracted in height posteriorly.

Formation and locality.—In Cretaceous rocks, probably near the top of
No. 4; near French Creek, on the Cheyenne River, Black Hills, Dakota.

Genus NEZERA Gray.

NEARA MOREAUENSIS
Plate 11, fig. 31.

Corbula moreauensis M. & H., Proc. Acad. Nat. Sci. Phil., vol. 8, p. 83.
Neera moreauensis M. & H., ibid., vol. 12, p. 185.

Newra moreauensis Meek, Pal. U.S. Geol. Surv. Terr., p. 239, Pl. 17, fig. 11.
Compare Necra ventricosa M. & H., ibid., p. 238, Pl. 30, fig. 3.

Shell minute, semi-globular, as seen in separated valves, with a small,
narrow, projecting posterior end, or if the valves are united would be
globular, with the extended posterior surface marked with concentric strize
or undulations, which, in proportion to the size of the shell, are quite strong.
The posterior extension of the valves is not more than one-fourth, or per-
haps one-fifth the height of the anterior part, and the surface depressed to
a corresponding degree.

We are at a loss to which of Messrs. Meek and Hayden’s species. to
refer our shell, as they are so nearly alike, except in the character of the
surface, and occur in the same formation. More especially is this trouble
evident from the fact that the greater portion of the shell of our particularly
minute specimen has been removed, only a little remaining on the anterior
margin.

Tormation and locality—In limestone of the Cretaceous, at the forks of
the Cheyenne River, Black Hills.

CRETACEOUS FOSSILS. . 421

GASTEROPODA.

SIPHONOSTOMATA.
FASCIOLARIIDA.
Genus FASCIOLARIA Lam

FASCIOLARIA (CRYPTORHYTIS) FUSIFORMIS.
Plate 12, fig. 12.

Rostellaria fusiformis H & M.., Mem. Am. Acad. Arts and Sci., vol. v, 2d ser., p. 333,
Pl. iii, fig. 10.

Gladius ? cheyennensis M. & H., Proc. Acad. Nat. Sci. Phil., vol. 12, p. 422.

Gladius cheyennensis (M. & H.) Meek, Smithsonian Check list Invert. Foss., p. 20.

Fasciolaria (Cryptorhytis) cheyennensis Meek, Pal. U. 8S. Geol. Surv. Terr., p. 365, Pl.
19, fig. 13.

Shell of moderate or large size, fusiform, spire elevated, composed of
six or more somewhat rounded or slightly ventricose volutions, gradually
increasing in size to the last, which is rather more gibbous above the middle,
very rapidly contracted below, and extended to form a slightly twisted
anterior beak of moderate length, which, with the aperture, forms rather
more than one-half the entire length of the shell. Aperture obliquely-ovate,
obtusely pointed above, prolonged and extended into the canal below ; outer
lip thin and sharp; inner lip thin and slightly coated ; volutions marked by
strong, flexuous, vertical plications or folds, and by finer intermediate strize
of growth; suture deep and distinct The vertical folds terminate abruptly
just below the suture line, leaving a narrow, smooth, and slightly concave
space bordering the suture. Columellar fold not seen on our specimens.

This is a distinct and well-marked species, and will not be readily con-
founded with any other described from American rocks. It is most nearly
related to Fusus martinez Gabb (Geological Survey California, Paleontology,
vol. 1, p. 83, Pl. 18, fig. 3), but will be readily distinguished by the absence
of the revolving lines of that species. Mr. Meek compares it with Voluta
monodonta Binkorst, a European species, and with Voluta rigida Baily, as -
identified from India under the name Fasciolaria rigida by Stoliczka; but

422 GEOLOGY OF THE BLACK HILLS.

remarks that it differs from the former in the flexuous character of the
vertical folds, and from the latter by the possession of only one, instead of
several, plaits on the columella.

This species was originally described by Messrs. Hall and Meek under
the name Fostellaria fusiformis, and subsequently placed with doubt under
the genus Gladius by Meek and Hayden, with the new specific name Chey-
ennensis, as the name fusiformis had been previously used by Mons. Pictet
and Roux for a species of Rostellaria, and by Valenciennes for a species of
Fasciolaria. But as Mr. Meek has subsequently proposed a new subgeneric
name, with this species as the type, it will necessarily revert back to the
original specific name fusiformis if the new subgeneric name Cryptorhytis
is to be adopted. We have, therefore, thus referred it.

Formation and locality—In limestone of the Fort Pierré Group, on the
Cheyenne River, near Rapid Creek, Black Hills.

FASCIOLARIA (CRYPTORHYTIS) CONTORTA.
Plate 12, fig. 10.

Fusus contortus M. & H., Proc. Acad. Nat. Sci. Phil., vol. 8, p. 65.

Pleurotomaria contorta M. & H., Proc. Acad. Nat. Sci. Phil., vol. 12, p. 185.

Turris contorta M. & H., ibid., 422 ; and Meek, Smithsonian Check List Invert. Foss., p. 22.

Turris (Surcula?) contorta (M. & H.) Meek, Pal. U.S. Geol. Surv. Terr., p. 385, Pl. 31,
fig. 7.

Shell fusiform, spire elevated, number of volutions not determined
(53-6 Meek), but rapidly increasing in size with the increased growth of
the shell, ventricose and obtusely angulated in the middle, the outer one
more rapidly increasing on the aperture side. Volutions marked on the
angulation by strong, distinct, vertical costa or folds, which do not quite
reach the suture above or below; about twelve of them have occupied the
outer volution on the largest specimen. Aperture long-pyriform, narrowed
below and extended into the moderately long, slightly twisted canal.
Columellar lip twisted, and marked by a single distinct, very oblique fold,
which is situated above the middle of the length. Surface unknown.

The examples of this species in our possession are internal cast, with
portions of the shell remaining only as a white calcareous powder, easily

removed; and by breaking the larger figured example and brushing away

CRETACEOUS FOSSILS. ; 433

the powdery portion, the impression of a distinct fold, very oblique in its
direction, was revealed, the existence of which removes the species from
the genus to which it has been referred, and proves its close Jurassic rela-
tions to F. (C.) fusiformis H. & M. The specimens under consideration
appear a little more slender than the figures given by Mr. Meek, loc cit,
but the presence of the shell on his specimens will readily account for this
seeming difference.

Formation and locality—In limestones containing a mingling of the
fossils of Nos. 4 and 5 of the Cretaceous formations of this region, on Old
Woman Fork of the Cheyenne River, Wyoming. ,

FASCIOLARIA (PIESTOCHEILUS) CULBERTSONI.
Plate 12, fig. 11.

Fusus culbertsoni M. & H., Proc. Acad. Nat. Sci. Phil., vol. viii, p. 66.

Fusus culbertsoni (M. & H.) Meek, Smithsonian Check List Invert. Foss., p. 22.

Fusus haydeni (Evans & Shum.) Meek, Pal. U.S. Geol. Surv. Terr., p. 360.

Fasciolaria (Piestochilus) culbertsoni (M. & H.) Meek, Pal. U. S. Geol. Surv. Terr., p,
360, Pl. 32, 1.

Shell attaining rather more than a medium size, elongate-fusiforme ;
spire produced and slender; aperture elongate, much lengthened below;
volutions moderately convex below the middle and appressed in the upper
part and below the suture; columella straight, slightly thickened. Surface
marked by numerous elevated revolving striz, generally, but not always,
with flattened interspaces, and crossed by strong transverse striee of growth,
which have a broad ventral curvature in crossing the appressed upper part of
the volution, and are then directed forward, with a broad curve, across the
swell of the volution; below this they are directed parallel to, and along
the anterior rostration.

The specimens of this species in the collection are imperfect, and do
not afford material for a full description. The number of volutions cannot
be made out, nor can the entire features of the columella be seen. Mr. F.
B. Meek states that the columella has an obscure fold in the upper part,
which our specimens, although much larger than any figured by that author, _
show no evidence of.

494 GEOLOGY OF THE BLACK HILLS.

Formation and locality—In Cretaceous beds near French Creek, Black
Hills; thought by the collectors to have come from the upper part of the
Fort Pierré Group, but the species is given by Mr. Meek only as from the
Fox Hill’s beds, No. 5.

Genus FUSUS Lam.
FUSUS SHUMARDI.
Plate 12, figs. 7,8.
Fusus Shumardii H. & M., Mem. Am. Acad. Arts and Sci., vol. v, 2d ser., No. 391, Pl.
3, fig. 6.

Shell small, with a moderately elevated spire and rather short rostral
beak; volutions about six, strongly ventricose, and marked by compara-
tively strong, slightly oblique, vertical costze or folds, which are directed
forward on the lower part of the upper volutions and again recurved below,
as seen on the body whorl, and also by finer strize of growth between the
folds. The folds are crossed by numerous elevated revolving lines, with
wider interspaces; suture well marked and distinct; aperture obliquely
ovate, obtusely pointed above, and continued below into the short, narrow,
rostral canal; columellar lip slightly thickened, but without visible folds
or plaits.

The specimen used is imperfect at both extremities and much of the
surface shell removed; enough remains, however, to furnish the specific
characters. The species may possibly belong to Mr. Meek’s genus Tvachy-
triton; but although the vertical folds are distinctly marked where the shell
is entirely removed, there is no evidence of revolving lines on the spaces
between them, as required in the diagnosis of that genus.

Formation and locality.—In a ferruginous sandy limestone on the east
fork of Beaver Creek, Black Hills, associated with fossils referred to the

fort Benton Group.
FUSUS CHEYENNENSIS.

Plate 12, fig. 9.
Fusus cheyennensis Whitf., Prelim. Rept. Pal. Black Hills, 1877, p. 37.
Shell small, spire slender and elevated; the number of volutions un-

known, but probably six or more, strongly rounded, the last one somewhat
ventricose above the middle, but attenuate below; aperture semi-ovate, being

CRETACEOUS FOSSILS. 495

rather straightened on the inner side and slightly produced below ; volu-
tions crossed by numerous vertical folds or plicee, which are very slightly
bent backwards in their course across the volution. Surface of the shell
unknown.

The specimen from which the description is drawn is an internal cast,
and therefore the external characters cannot be given in detail. The species
is, however, so entirely distinct from any of the forms known from this
region, that there is no fear of its being confounded with any of them.

Formation and locality—In gray shales near the upper part of the Fort
Pierré Group, on the Cheyenne River near Rapid Creek, Black Hills.

APORRHAID A.

Genus APORRHAIS Dillwyn.
APORRHAIS NEWBERRYI.
Plate 12, fig. 4.
Anchura ? newberryi Meek, Rept. on Capt. Macomb’s Exp., p. 129, Pl. 11, fig. 5.

Shell small or of moderate size; spire elevated, composed of about four
subangular volutions, exclusive of the body whorl, as seen on the back of
the shell; apical angle about 40°. Volutions marked by a distinct angula-
tion about one-third of their height above the suture line, and the body vol-
ution by a second smaller carination a short distance below the first; also
by fine revolving lines, which alternate in their degree of strength; three of
the stronger ones may be counted above the carination on the back of the
outer volution, with a narrow smooth space above the carina, one strong and
two smaller lines between the carinations, and five strong ones with finer
ones between on the lower side of the volution. Outer lip expanded and
extended in two long, slender, diverging digitations, corresponding to the
carination on the outer volution, the lower one directed slightly forward in
the direction of the coil of the shell; margin of the lip bordered by a thick-
ened rounded rim; anterior prolongation or canal not observed ; posterior
canal extended along the spire to the summit, where it is deflected and
extended beyond to an unknown length; callus of lip coating the entire
spire and upper part of body volution, obscuring or concealing the revoly-

496 GEOLOGY OF THE BLACK HILLS.

ing lines of the surface; callosity thin and smooth, without tubercles. No
vertical folds exist. .

The species is so entirely distinct from any of the described forms of
this group of shells from our American rocks, that an elaborate comparison
seems unnecessary.

Formation and locality—In limestones of the Fox Hills Group, on the
Rio de la Plata. Collection of Dr. J. S. Newberry.

APORRHAIS MEEKI.
Plate 12, fig. 5.
Aporrhais meeki Whitf., Prelim. Rept. Pal. Black Hills, 1877, p. 37.

Shell of moderate size, with a low, very obtusely-pointed spire, which
is composed of only three ventricose or rounded volutions, exclusive of the
apertural expansion, and which rapidly increase in size; apical angle nearly
80° Volutions marked by numerous sharply-elevated, revolving lines,
with concave interspaces both above and below the middle. Outer lip
expanded and extended into two diverging carinated digitations of an unde-
termined length, which are deeply grooved on the inner face, the upper one
being directed slightly backward toward the spire, and the other one
slightly downward and more strongly forward in the direction of the coil of
the shell; anterior beak, judging from the part remaining, moderately long
and stout; posterior canal extending along the spire to the summit, where
it appears to have become free and deflected; callous slight (?), coating the
upper volutions over a part of their extent.

This species differs from any previously-described form of this group in
the short obtuse spire, combined with the two digitations of the outer lip,
and the posterior canal, which extends to the summit of the spire.

Formation and locality.—In limestone of the Fort Pierré Group, at the

top of the gray shales of this formation, on the Cheyenne River near Rapid
Creek, Black Hills.

CRETACEOUS FOSSILS. — 427

APORRHAIS (GONIOCHEILA) CASTORENSIS.
Plate 12, fig. 1. i
Aporrhais (Goniocheila) castorensis Whitf., Prelim. Rept. Pal. Black Hills, 1877, p. 38.

Shell small, with a moderately-elevated spire, composed of about four
flattened or very slightly ventricose volutions, which are crossed by fine,
flexuous, vertical folds, strongly directed forward in their course across the
whorl, and also marked by fine, thread-like, revolving lines; suture dis-
tinct; apical angle about 40°, but slighty variable on different individuals.
Body volution proportionally large and very strongly angular, or even car-
inate, along the middle, flattened or slightly concave on the upper surface,
and rapidly contracted below to the short, pointed, rostral beak. A second
rather indistinct carination marks the surface a little below the first, but
seldom or never extends to the margin of the lip. Outer lip expanded,
strongly carinate on the back, and projecting in the middle to form a short,
obtuse, slightly recurved digitation, and posteriorly extending along the
spire to the base of the second volution above.

This species somewhat resembles A. biangulata M. & H. (Paleontology
of the United States Geological Survey of the Territories, p. 322, Pl. 19,
Fig. 6), but differs in the subdued character of the lower carination and in
the strongly uniangular form of the body volution. Among a number of
specimens none show the posterior canal extending above the point de-
scribed, nor any evidence of a second digitation to the lip. The surface
markings are quite superficial, but few specimens showing them, appearing
quite smooth from slight exfoliation.

We are extremely averse to describing new species of this group of
shells, as from their extreme liability to variation with different degrees of
development they are easily mistaken, and we have feared that this might
prove, on the examination of a larger and better collection of specimens, to
be only a form of A. biangulata M. & H., above referred to, but the single
strong carination and the fact that it comes from a lower geological horizon
and distant locality has induced us to separate it under a new name.

Formation and locality—In ferruginous sandy limestone on the east
fork of Beaver Creek, Black Hills. Associated with fossils of the Fort
Benton Group.

428 GEOLOGY OF THE BLACK HILLS.

Genus ANCHURA Conrad.

ANCHURA ? SUBLEVIS.

Plate 12, fig. 6.

Aporrhais sublevis M. & H., Proc. Acad. Nat. Sci. Phil., vol. 12, p. 178.

Aporrhais sublevata (misprint) M. & H., ibid., 1860, p. 428.

Anchura ? sublevis Meek, Smithsonian Check List Invert. Foss., p. 19.

Anchura ? sublevis (M. & H.) Meek, Pal. U.S. Geol. Surv. Terr., p. 327, Pl. 19, fig. 3.

Shell small, with an elevated, slender spire; volutions about seven in
number, distinctly convex, with well-marked suture lines; body yolution a
little more ventricose than the preceding, very slightly angular, and ex-
tended below into a slender, pointed, rostral beak; lip not expanded, but
the margin making a strongly sigmoidal curve, being broadly sinuate above
and extended forward below the middle, again receding to the beak. Volu-
tions marked by numerous fine, sigmoidally-curved, vertical folds, having
the same direction as the margin of the aperture, and also by fine, closely-
arranged, thread-like, and elevated revolving lines. Aperture obliquely
ovate, pointed above and below.

On some specimens we notice a tendency in the vertical folds to form
varices on opposite sides of the shell, similar to those of Triton and Ranella ;
mostly confined to the two larger volutions, and we strongly suspect that
the true generic relations of the shell have not been properly ascertained ;
also that the specimen in hand, although quite numerous, as also those used
and figured by Mr. Meek, are all young shells, with the adult features of
the aperture yet undeveloped.

Formation and locality—In limestone of the Fort Pierré Group, near
Box Elder Creek, Black Hills, Dakota

CRETACEOUS FOSSILS. 429

ANCHURA (DREPANOCHEILUS) NEBRASCENSIS.
Plate 12, figs. 2, 3.

Rostellaria nebrascensis B. & S., Proc. Acad. Nat. Sci. Phil., vol. vi, 164.

Aporrhais nebrascensis (E. & 8.) M. & H., ibid vol. 12, p.423; Gabb, Synop. Cret. Foss.,

Anchura oe ean nebrascensis (i. & 8S.) Meek, Smithsonian Check List Invert.
Foss., p. 19.

Anchura (Drepanocheilus) nebrascensis (HB. & 8.) Meek, Pal. U. S. Geol. Rept. Terr., p.
326, Pl. 19, tig. 5.

Shell small, to moderate size; fusiform, exclusive of the outer lip;
spire elevated but moderately robust, about equal in height to the body
volution; composed of five or six moderately ventricose whorls, which
gradually increase in size; suture line distinct. Outer volution proportion-
ally large and bicarinate in the middle; outer lip expanded, and the margin
extended in the form of a short, falciform, recurved digitation which is |
strongly angulated on the back, corresponding to the upper carination of
the body volution. The lip is also slightly curved backward and upward
near its junction with the spire, forming a deep sinuosity on the inner face.
The lower extremity of the body volution is extended in form of a short
pointed beak, channeled on the inner face.

Surface of the shell marked by fine revolving lines and by small ver-
tical folds, which are flexuous, and directed forward ou the lower part of the
volution

The specimens which we have referred to this species vary consider-
ably among themselves, and all seem to be more robust than those figured
by Mr. Meek, loc cit.; still, from their variability, we conclude they are all of
the one species. Indeed the species of this entire group are extremely
variable, according to the degree of development, especially in the charac-
ters pertaining to the aperture and the strength of surface markings, and
we are inclined to believe that the same species may often pass beyond the
limits of genera, as now recognized.

Formation and locality.—In Cretaceous limestone on the east fork of
Beaver Creek, three miles west of Camp Jenney, Black Hills.

430 GEOLOGY OF THE BLACK HILLS.

HOLOSTOMATA.
NATICIDA.

Genus LUNATIA Gray.
LUNATIA CONCINNA.

Plate 12, fig. 13.
Natica concinna H. & M., Mem. Am. Acad. Sci. and Arts, vol. v, p. 384, Pl. iii, fig. 2.
Natica moreauensis M. & ., Proc. Acad. Nat. Sci. Phil., vol. 8, p. 64, and 282.
Natica (Lunatia) moreauensis M. & H., Proc. Acad. Nat. Sci. Phil., vol. 12, p. 422.
Iunatia moreauensis (M. & H.) Gab. Syn. Cret. Moll., p. 58.
TInnatia moreauensis (M. & H.) Meek, Smithsonian Check List Invert. Foss., p. 20.

Shell of medium size, subglobose or very broadly rhombic-ovate;
erect, with strongly ventricose volutions, of which four may be counted on
the example figured, the last one forming the great bulk of the shell. Spire
low; sutures very distinct, deep, but not channeled; aperture obliquely ovate,
nearly once and.a half as high as wide, obtusely pointed above and rounded
below; inner lip straightened, slightly callous and spreading upon the body
of the shell; umbilicus moderate; outer lip thin and comparatively sharp.
Surface marked by fine transverse lines of growth and by faint revolving
lines, seen only by the aid of a lens, except on the larger part of the body
volution, where a few may be detected with the naked eye.

Formation and locality—At the top of the gray shales of the Fort
Pierré Group, on the Cheyenne River, near Rapid Creek, and a specimen
undistinguishable from it, in its condition as an internal cast, from a much
lower position on the east fork of Beaver Creek, Black Hills.

Genus VANIKORA Quoy & Gaimard.

VANIKORA AMBIGUA.

Plate 12, fig. 14.

Natica ? ambigua M. & H., Proc. Acad. Nat. Sci. Phil., vol. v, p. 64.
Fosar ? nebracensis M. & H., Proce. Acad. Nat. Sci. Phil., vol. 12, p. 423
Vanikora ambigua (M. & H.) Meek, Smithsonian Check List Invert. Foss., p. 18.

Shell small, naticoid, subglobose or obliquely subglobose, spire mode-
rately elevated, volutions ventricose and separated by rather distinct suture

CRETACEOUS FOSSILS. 431

lines. ‘Aperture ovate, very oblique, obtusely angular above, and rounded
below; outer lip sharp, joining the whorl above nearly at right angles, slightly
reflexed at its junction with the columella below; axis apparently perfor-
ated by a very small umbilical opening which is not covered by the lip.”

Surface of the shell marked by very distinct, impressed, revolving
lines, with wider, flattened interspaces; the lines most strongly marked
below the middle of the outer volution, and crossed by irregular concentric
lines of growth, which have a decided tendency to form fascicles or transverse
folds on the body volution.

Our specimen of the species is imbedded in hard limestone, so as to
entirely conceal the aperture side of the shell; we have therefore quoted
Mr. Meek’s description of these parts from the Paleontology of the United
States Geological Survey of the Territories, p. 330.

Formation and locality.—In limestone of the Fort Pierré Group, on the
Cheyenne River, Black Hills.

Genus AMAUROPSIS Morch.

AMAUROPSIS PALUDINAFORMIS.
Plate 12, fig. 16.

Natica paludineformis H. & M., Mem. Am. Acad. Sci. and Arts, vol. v, p. 389, PI. iii,
Amauropsis paludineformis ae M. & H., Proc. Acad. Nat. Sci. Phil., vol. 12,
Amauropsis paludineformis H. ag Meek, Smithsonian Check List Invert. Foss.,
2
Amauropsis paludineformis H. “ M.) Meek, Pal. U.S. Geol. Surv. Terr., p. 318, Pl.
HOF fies

Shell subovate or elongate-ovate, spire moderately elevated, forming
a little more than one-half the entire height above the aperture; volutions
four and a half to five, convex, the last one ventricose and somewhat pro-
duced below, but not rostrate; suture very distinct and channeled; aper-
ture oblique, semi-ovate, or nearly semi-circular, the inner side being nearly
straight; upper angle acutely rounded, more broadly rounded below, the
columellar side of the base almost subrimate; outer lip thin and sharp;
columellar lip scarcely thickened ; umbilicus scarcely perceptible or closed.

432 GEOLOGY OF THE BLACK HILLS.

Substance of the shell thin; surface marked by fine closely-arranged revolv-
ing striz and by transverse lines of growth, which give an undulating
character to the revolving lines.

Formation and locality—In limestones of the Fort Pierré Group, on the
Cheyenne River, near Box Elder Creek, Black Hills.

TROCHID Ai.
Genus MARGARITA Leach.

MARGARITA NEBRACENSIS.
Plate 12, fig. 15.

Turbo nebracensis M. & H., Proc. Acad. Nat. Sci. Phil., vol. 8, p. 64.
Margarita nebracensis M. & H., Proc. Acad. Nat. Sci. Phil., vol. 12, p. 185.
Margarita nebracensis M. & H., Pal. U.S. Geol. Surv. Terr., p. 298, Pl. 19, figs. 8 and 9.
Shell small, turbinate, height and width nearly equal; spire regularly
conical, composed of from four to five rounded, ventricose volutions, which
increase gradually in size with the increased growth of the shell, the last
one appearing very slightly subangular just below the middle; suture line
deep and well marked; umbilicus apparently of moderate size (somewhat
obscured in the specimen used), and rather angular at the margin. Surface
marked by very fine, even, and quite regular revolving lines, and by a
narrow, very obscurely depressed space just above the angularity of the
outer whorl; also by fine, transverse striz, which are gathered into small
folds just below the suture and near the margin of the umbilicus, and have
a strongly oblique backward direction above the periphery, and cross more
directly below.
Formation and locality.—In limestone of the upper part of the Fort
Pierré Group, on the Yellowstone River, 150 miles above its mouth.

CRETACEOUS FOSSILS. ; 433

PULMONIFERA. ?
SIPHONARIID AL. ?
Genus ANISOMYON, M. and H.

A few examples only of this genus are found in the collections from
the Black Hills. These few represent four of the species previously
described from this region. The generic characters of the group are well
marked on all the species we have examined, but there appears to be some
doubt as to its family relations. Mr. Meek’s latest expressed opinion seems
to be that they are most nearly allied to the Siphonariide, and therefore that
they are pulmoniferous in their structure. To this conclusion the break in
the right side of the muscular imprint would naturally lead, for although
the interruption is not large, and often quite slight, still it is an interruption,
and would only oceur through some organic feature of the animal; the
natural inference would therefore be that it was for the protrusion of an
air-conducting siphon, or at least that it indicated a step in that direction.
Still, so far as our examinations extend, there. has been no depression of
the interior surface of the shell, as is usually the case in most if not all the
species of Siphonaria.

ANISOMYON ALVEOLUS.
Plate 12, fig. 20.

Helcion alveolus M. & H., Proc. Acad. Nat. Sci. Phil., vol. 8, p. 68.
Anisomyon alveolus M. & H., Amer. Jour. Sci. and Arts, vol. 28, 2d ser., p. 35.
Anisomyon alveolus (M. & H.) Meek, Pal. U.S. Geol. Surv. Terr., p. 292, Pl. 18, fig. 4.
Shell small, elongate-oval or narrowly elliptical in outline, the length
about once and a half the width, with rounded anterior and _ posterior
extremities; apex a little in advance of the middle, minute and apparently
recurved; elevation of the shell, in our specimen, about half or a little
more than half as great as the greatest width, the surface of the sides and
ends very gently convex. The surface, judging from the extoliated speci-
men, has been slightly marked by concentric undulations ; anterior muscu-

lar imprint on the right side long and narrow and a little obliquely placed:
23 BH

434 GEOLOGY OF THE BLACK HILLS.

Mr. Meek appears to think there may be some doubt of the true specific
relations of this form; that it may possibly be only a young, ora variety of
A. subovatus. The resemblance is indeed quite striking, differmg in our
specimens only a little in the degree of elevation, slightly in the relative
position of the apex, and somewhat in its greater length.

Formation and locality—tIn limestones of the Fort Pierré Group, on
Old Woman Fork of the Cheyenne River, Black Hills.

ANISOMYON SUBOVATUS.

Plate 12, fig. 19.

Helcion subovatus M. & H., Proc. Acad. Nat. Sci. Phil., vol. 8, p. 68.

Anisomyon subovatus M. & H., Am. Jour. Sci. and Arts 2d ser., vol. 28, p. 35.

Anisomyon subovatus (M. & M.) Meek, Pal. U. S. Geol. Surv. Terr., p. 291, PI. 18, figs.
5d, and 6.

Shell of moderate size, oval, slightly ovate or broadly elliptical in out-
line, the length and width as seven to five, or nearly so; ends somewhat
regularly rounded ; sides nearly straight in the middle or only very slightly
convex; height of the shell equal to a little more than half the width;
apex small, recurved even on the internal cast, situated a little less than
one-third of the entire length from the anterior end; anterior slope of the
shell forming nearly a straight line from the apex to the front margin;
posterior slope quite convex; sides slightly convex. Surface of the shell
apparently marked by moderately strong concentric undulations, as indi-
cated on the internal casts.

Muscular imprints quite distinct, the anterior ends large, situated
directly on a line with the apex of the shell, the left side rapidly narrowing
posteriorly to near the middle of the posterior slope, where it is perceptibly
widened again on the right side, the anterior portion is oval and a little
oblique, the interruption is quite slight, and the posterior continuation
linear, with a second faint interruption farther back. Anterior line con-
necting the opposite sides narrow, crossing the apex of the shell. There is
some variation among the individuals of this species, as is indicated by Mr.
Meek’s figures, given in the Paleontology of the United States Geological
Survey of the Territories, and of course the description given above will

CRETACEOUS FOSSILS. 435

not agree in its details with all specimens that may properly be referred to
the species.

Formation and locality—In limestones of the Fort Pierré Group on Old
Woman Fork; associated with A. alveolus and Endocostea typica.

ANISOMYON PATELLIFORMIS.
Plate 12, figs. 17, 18.

Helcion patelliformis M. & H., Proc. Acad. Nat. Sci. Phil., vol. 8, p. 68.

Anisomyon patelliformis M. & H., Am. Jour. Sci. and Arts, vol. 28, p. 35, Pl. 1.

Anisomyon patelliformis (M. & H.) Meek, Pal. U. 8. Geol. Surv. Terr., p. 290, PI. 18,
figs. 5a, b, c, and f.

Shell of medium size, slightly ovate or very broad-oval in outline, the
width equaling about four-fifths of the length. Surface of the shell ele-
vated, the extreme height about equaling one-half of the greatest width;
apex obtuse and apparently very little incurved, situated nearly over the
anterior end or but little within a vertical line above the margin; anterior
margin of the shell rounded; posterior end a little more broadly rounded
and the sides forming regular elliptical curves. Anterior slope abrupt and
slightly concave; posterior slope highly convex; lateral slopes concave in
front of the middle and convex behind. Surface of the shell unknown;
that of the cast marked by nearly obsolete undulations; muscular impres-
sions very distinct, the anterior portions large and subcircular, posterior
parts narrower, except at the right posterior angle, where it again widens,
interruption distinct ; anterior connecting band linear, crossing the summit
of the shell at a distance posterior to the apex, equal to about one-fifth of
the length of the shell.

Ovr specimens of this shell differ somewhat from those figured by Mr.
Meek, but not sufficiently so to be considered of much importance. The
apex is more obtuse and slightly inclined downwards, and is also situated
nearer the anterior margin, while the elevation of the shell and also its
relative convexity are greater.

Formation and locality.—In limestone of the Fort Pierré Group, on Old
Woman Fork, Black Hills; associated with A. alveolus and A. subovatus.

436 GEOLOGY OF THE BLACK HILLS.

ANISOMYON BOREALIS.
Plate 12, figs. 21-23.
Hipponyx borealis Mort., Jour. Acad. Nat. Sci. Phil., vol. 8, 1842, p. 210, Pl. xi, fig. 6.
Helcion carinatus M. & H., Proc. Acad. Nat. Sci. Phil., vol. viii, p. 68.
Anisomyon borealis M. & H., Am. Jour. Sci. and Arts, vol. 28, 2d ser., p. 35.
Anisomyon borealis (M. & H.) Meek, Pal. U. 8S. Geol. Surv. Terr., p. 288, Pl. 18, fig. 9.

Shell of large size, subcircular or very short ovate in outline, widest
behind the middle. Summit elevated; apex pointed or slightly recurved,
laterally compressed, and in the specimens in hand almost overhanging the
anterior margin of the shell; anterior slope short, abrupt, and concave;
posterior slope long and convex, the greatest elevation of the shell being a
little behind the apex; lateral slopes concave in front of the middle and
convex behind ; surface of the shell angulated along the middle of the
posterior dorsal region, and also between this and the sides, the median
angulation the most extreme. Also by indistinct, irregular, flexuous, radiat-
ing lines of varying strength, and by stronger concentric lines of growth.
There are also six distinct hair-like radiating grooves passing from the apex
toward the margin at subequal distances from each other, which appear to
be mostly superficial, although sometimes visible on partially exfoliated
specimens. Muscular impressions not observed.

On one of the specimens referred to this species, and which is a partial
cast of the interior, there are three radiating ridges passing from the apex
to a considerable distance along the surface; one of them being situated
near the median angulation, the others, rising from below and in front of
the apex, pass along the sides of the cast for more than half an inch. The
former of these ridges we judge to be only a line indicating a fracture of
the shell; the others are evidently a part of the muscular markings, and
most probably represent the anterior connecting muscular band seen on
other species. Here, however, it crosses in front and just below the apex
of the shell.

Judging from the figures given by Mr. Meek, the species is a very
variable one; our specimens are of the form represented by his profile
figure 9b, but less elevated.

Formation and locality—In limestone of the Fort Pierré Group, Chey-
enne River, Black Hills.

CRETACEOUS FOSSILS. 437

TECTIBRANCHIATA.
BULLIDA.

Genus HAMINEA Leach.
HAMINEA SUBCYLINDRICA.
Plate 12, fig. 24.
Bulla subcylindrica M. & H., Proce. Acad. Nat. Sci. Phil., vol. 8, p.270 (not of D’Orb., 1847).
Bulla speciosa (M. & H.) Meek, Smithsonian Check List Inve:t. Foss., p. 16, Proc. Acad.
Nat. Sci. Phil., vol. 12, p. 185.
Haminea subcylindrica (M. & H.) Meek, U. S. Geol. Surv. Terr., p. 272, Pl. 18, fig. 10.

Shell of moderate size, elongate-oval or slightly ovate in form, with
rather sharply rounded extremities; upper end marked with a small central
umbilical pit or depression indicating the position of the sunken spire, and
the outer volution elevated but little above the preceding one; lower
extremity somewhat extended and narrowly rounded from the short, slightly
curved, columellar-like inner lip around the base of the aperture; aperture
very narrow above but gradually widening below, and strongly arcuate
throughout; outer lip thin and sharp, lower umbilical slit minute. Surface
of the shell marked by fine impressed revolving lines, many of which have
a somewhat alternating character, and are crossed by finer concentric lines
of growth.

The shells of this species which we have in hand are none of them entire
cr full grown, but their specific features are well marked. It is the only one
of the group we have noticed in the collection, although several others
have been described from the Cretaceous formations of this region. It is
readily distinguished from the others by the form of the shell.

Formation and locality—tIn limestones of the Fort Pierré Group, on
Old Woman Fork of the Cheyenne River, Black Hills.

Genus AKERA O. F. Muller.
AKERA GLANS-ORYZA.
Plate 12, fig. 25.
Akera glans-oryza Whitf., Prelim. Rept. Pal. Black Hills, 1877, p. 38.
Shell minute, not exceeding one-fifth of an inch in length, and the

diameter being about twice and a half less than the length; cylindrical in

438 GEOLOGY OF THE BLACK HILLS.

form, with a very low, truncated spire, which consists of about three or
three and a half volutions, the outer margins of which are bordered by an
elevated knife-edge carina, giving a deeply channeled convolute character
to the spire, the center scarcely rising above the level of the outer carina-
tion. Body of the outer volution very slightly rounded near the margin of
the flattened spire and distinctly so to the base below. Aperture as long
as the shell, narrow above and gradually widening and rounded at the base.
Columella curved and apparently reflected upon the preceding volution.
Axis imperforate.

Surface of the shell marked by very fine, revolving, impressed lines,
strongest near the top of the volution and on the lower third; also by finer
transverse strie of growth parallel to the margin of the aperture, and indi-
cating by their direction that the central portion of the outer tip is a little
in advance of the top and base.

Formation and locality—In limestone near the top of the Fort Pierré
Group, on the Chyenne River, near French Creek, Black Hills, Dakota.

PROSOPOCEPHALA.
SOLENOCONCH AL.

DENTALIIDA.

Genus DENTALIUM Linn.
DENTALIUM GRACILE.

Plate 12, fig. 26.
Dentatium gracile H. & M., Mem. Am. Acad. Arts and Sci., vol. v., new ser., p. 303, Pl. 3,
fig. 11.
Dentalium fragile M. & H., Proc. Acad. Nat. Sci. Phil., vol. 8, p. 69.
Dentalium gracile (H. & M.), Pal. U.S. Geol. Surv. Terr., p. 266, Pl. 18, fig. 13.

Shell slender, tubular, very gradually and regularly tapering through-
out, circular in a transverse section and moderately thick; very generally
arcuate from end to end, the degree of flexure in the length of one inch,
measured on the concave side, being less than a sixteenth of an inch.

CRETACEOUS FOSSILS. 439

Surface of the shell marked by fine, rather deep, longitudinal flutings
of varying width, with the ridges between very slightly flattened on the
surfaces; the whole crossed by extremly fine transverse striae of growth;
indicating the inner side of the apertural margin as the longest. Inner
surface of the tube smooth.

Formation and locality—In limestone concretions at the top of the gray
shales of the Fort Pierré Group, on the Cheyenne River, near Rapid Creek,
Black Hills.

CEPHALOPODA.

TETRABRANCHIATA.

NAUTILIDA.

Genus NAUTILUS Breynius.
NAUTILUS DEKAYI var. MONTAN ANSIS.

Plate 16, figs. 10-11.
Nautilus dekayt var. montanensis Meek, Pal. U.S. Geol. Surv. Terr., p. 498, Pl. 27, fig. 2.

Shell attaining a large size, subglobose in form, the length somewhat
greater than the width. Volutions rapidly increasing in size, rather sharply
rounded on the periphery, very slightly flattened on the sides, and again
more rapidly expanding near the umbilical region. Umbilicus closed,
though in exfoliated individuals appearing as if open by the removal of the
shell. Aperture deeply reniform, a little more than twice as wide as long
and sharply rounded at the sides Septa distant, deeply concave, their lines
of junction with the outer shell passing across the volution without curva-
ture. Siphuncle small; in some parts situated exactly central, and in others
nearly central between the dorsal and ventral borders of the septa. Outer
surface of the shell not observed, but on the slightly exfoliated outer
chamber seems to have been marked by concentric lines of growth directed
strongly forward on the sides, and on the dorsal region to have had a broad,
deep, retral curvature, indicating a deeply bilobed margin.

The specimens of this variety are very closely related to N. dekay
Morton, the differences not being sufficiently marked to be noted except on

440 GEOLOGY OF THE BLACK HILLS.

critical examination. The principal variation consists in the more nearly
central position of the siphuncle and slightly more distant septa. These
features, however, are not more marked than may often be noticed among
different individuals of a species when obtained from one locality, and we
are therefore strongly inclined to doubt the propriety of separating it, even
as a variety, from those referred by its author to N. dekayi. We are the
more strongly confirmed in this opinion from the fact that in the specimen
we have figured the siphuncle is so nearly central in its position in the
fourth septum from the outer chamber as not to be readily detected by
measurement, while on the opposite side of the shell, in the smaller part of
the same volution, its position is much nearer the ventral border, showing
in the same individual as great a variation as between those referred to the
two forms.

Formation and locality —In limestone of the Fort Pierré Group of the
Cretaceous, on the Cheyenne River, near Rapid Creek, Black Hills, Dakota.

AMMONITID A.

Genus PRIONOCYCLUS Meek.

PRIONOCYCLUS WYOMINGENSIS.
Plate 14, figs. 1-3.
Ammonites (Prionocyclus) serrato-carinatus Meek, Geol. Sury. Terr., 1870, p. 298 (Hayden).
Ammonites serrato-carinatus Meek, ibid.
Not Ammonites serrato-carinatus Stoliezka.
Prionocyclus wyomingensis Meek, Pal. U.S. Geol. Surv. Terr., p. 452, note.

Shell attaining a medium or large size, subdiscoid and laterally com-
pressed. Volutions flattened on the sides in the younger stages and
strongly keeled on the dorsum, becoming proportionally wider and more
convex with increased age, and the keel strongly developed, rounded, and
serrated. The lateral diameter of the yvolution of a specimen which meas-
ures about 15 inches across is about two-thirds the dorso-ventral diameter,
but considerably more when they attain a diameter of three inches. Umbili-
cus large and open, exposing four-fifths to five-sixths of the diameter of the

inner volutions, the margin of the volutions being abruptly rounded.

3 CRETACEOUS FOSSILS. 44]

Surface of the shell marked by transverse ridges, which are extremely
variable in strength and in the manner of their grouping on different indi-
viduals and at different stages of growth, there being generally a stronger
ridge developing nodes at each extremity, with from two to five smaller
ones between. The inner nodes are often formed by the coalescing of
two or three of the ridges, though sometimes single; the outer nodes are
obliquely longitudinal and flattened on the back, formed by the thickening
of the principal rib or by the union of two or more. On the dorsum the
ribs continue, but are much subdued and subequal, and directed strongly
forward, forming crenulations in crossing the keel.

Septa rather simple and closely arranged; the lobes and saddles of the
adjacent ones passing within each other, as shown on small individuals.
Those of larger individuals not observed.

This species was first indicated by Mr. F. B. Meek in Dr. Hayden’s
report of 1870, as Ammonites serrato-carinatus; but, on learning that this name
had been previously used for a similar species, he subsequently proposed
the specific name Wyomingensis to be used, providing the two should be
found to belong to the same section; and as we found it so labeled in the
collection at the Smithsonian Institution, we infer that he intended to adopt
the name, and we have therefore so used it.

Formation and locality—In silico-caleareous layers of Division No. 2,
Cretaceous, on the east fork of Beaver Creek, near Camp Jenney, Black
Hills.

SCAPHITID A.

Genus SCAPHITES Parkinson.
SCAPHITES NODOSUS.

Plate 13, fig. 12.

Scaphites nodosus Owen, Rept. Geol. Surv. Iowa, Wis. and Minn., 1852, p. 580, tab. 8,
fig. 4.

Scaphites nodosus (Owen) M. & H., Proc. Acad. Nat. Sci. Phil., vol. 12, p. 420.

Scaphites nodosus (Owen) Gabb., Synop. Moll. Cret. Formation, p. 32.

Scaphites nodosus (Owen) Meek, Smithsonian Check List Cret. Foss., p. 24.

The examples of this species in the collection are so exactly similar to
the figure given by Dr. Owen (Report on the Geological Survey of Iowa,

442 GEOLOGY OF THE BLACK HILLS.

Wisconsin, and Minnesota, Pl. 8, Fig. 4) that there can be no reasonable
doubt as to their being the same variety of this very variable species, to
which the name S. nodosus was originally applied. None of the varieties
figured by Mr. Meek in the Paleontology of the United States Geological
Survey of the Territories approach the features presented by this form very
closely or sufficiently near to be considered typical, but this we have
deemed best to retain under the original name of the species. It appears
io be intermediate between Mr. Meek’s varieties brevis and plenus. The
general form of the shell is ovate, considerably longer than high, and very
ventricose; the inner volutions forming only about half of the length of the
shell, and much less than half the bulk. The volutions are closely coiled,
leaving but a very slight umbilical opening; the body volution is some-
what regularly arcuate on the periphery and straight on the ventral or
umbilical margin of the deflected portion; the aperture recurving and its
margin forming an angle of nearly a hundred degrees with the straight
ventral border of the deflected portion, the whole shell sensibly contract-
ing above the line of the deflected part to near the aperture, and still more
abruptly so just at its border.

The surface of the shell is marked by rather distinct, subangular, sinu-
ous costee, which bifurcate so as to form three, four, or five times as many
on the broadly-rounded dorsum, which they cross with a slight forward
curvature, and also by two rows of rather strong, distinctly elevated nodes
or tubercles on each side, situated, one about one-third or nearly one-
third of the width of the volution from the margin of the umbilical line,
and the other near the border of the rounded dorsum, the latter range
beimg longitudinally compressed, so as to form thin angular nodes. Both
ranges of nodes are traceable nearly as far as the volutions are seen.

The septa are rather complicated and somewhat variable in the differ-
ent forms and varieties of the species; they, however, all have a general
resemblance to each other, presenting nearly the same elements in each,
and having similar characteristics, which mark them as belonging to the
same group or type. ‘These features are shown in the diagram illustrating
S. nodosus on Plate 13, Fig. 9.

CRETACEOUS FOSSILS. 443

Formation and locality —In limestone at the top of the gray shales of
the Fort Pierré Group, on the Cheyenne River, near Rapid Creek, Black
Hills, Dakota.

SCAPHITES NODOSUS var. BREVIS.
Plate 13, fig. 8, 9.

Scaphites nodosus var. brevis Meek, Pal. U.S. Geol. Surv. Terr., p. 426, Pl. 25, fig. 1.

This variety differs from the typical form of S. nodosus Owen, in being
less ovate, the deflected portion being rather shorter, and in the more com-
pressed form of the shell as seen in profile, and also in the narrowly
rounded dorsum. ‘The costze are somewhat finer on all of the examples we
have seen, and the nodes smaller, and not commencing at so early a stage
of growth; while the inner range of nodes is usually obscure or only seen
on the deflected part of the body volution. The most conspicuous differ-
ences are the compressed form of the shell and the more narrowly rounded
dorsum.

Formation and locality.—The examples of this variety are found asso-
ciated with the typical form at the top of the gray shales of the Fort Pierré
Group, Cheyenne River, near Rapid Creek, Black Hills, Dakota.

SCAPHITES NODOSUS var. QUADRANGULARIS.
Plate 13, figs. 10, 11.

Scaphites nodosus var. quadrangularis Meek, Pal. U. 8S. Geol. Surv. Terr., p. 428, Pl. 25,
figs. 2-4.

Shell discoidal, with latterally compressed volutions, and the dorsum of
the deflected part of the outer volution somewhat flattened. General out-
line of the shell slightly ovate, the outer coil being somewhat deflected from
the general curvature of the involute parts, and the extremity again recurved,
so as to bring the ventral margin nearly or quite to the dorsal limit of the
preceding volution, and the margin of the aperture nearly at right angles
to the ventral line of the deflected portion.

Surface of the shell ornamented by fine, somewhat sinuous, transverse,
bifurcating costee with narrow concave interspaces, and also by two ranges

of nodes on a part of the last volution. The outer ranges of nodes are situ-

444 GEROLOGY OF THE BLACK HILLS.

ated on the angles of the flattened dorsum, but become obsolete on the
outer third of the volution, where the dorsum is also sharply rounded. The
inner ranges consist of smaller nodes, and are situated near the border of
the umbilicus. The septa closely resemble those of the typical form of S.
nodosus Owen, but are arranged so closely as to interfere or interlock with
each other.

This variety differs from the typical form of S. nodosus in the same
direction, but still more widely than the variety brevis Meek, being more
compressed laterally, more distinctly flattened on the back of the body
whorl, and the costz are still finer than in that variety, while the deflec-
tion is less extreme and the ventral border of that part more curved.

Fsrmation and locality—This variety has been obtained from beds of
the Fort Pierré Group, at the top of the gray shales of that formation on
the Cheyenne River, near Rapid and French Creeks, and also from beds
which contain a mingling of the fossils of this and the succeeding group on
Old Woman Fork, Black Hills.

Scaphites nodosus var. plenus, M.& H., Proc. Acad. Nat. Sci. Phil., 1860, p. 420; and Pal.
U.S. Geol. Surv. Terr., p. 429, Pl. 26, fig. 1.

This form differs from the typical S. xodosus in being much more ven-
tricose as well as larger, while in the strength of the costz it corresponds
closely to that one. The nodes are represented in the figures given as
being round and somewhat tumid. We have not recognized this form among
the collections brought from the Black Hills by Professor Jenney’s party.
Mr. Meek cites the Yellowstone River, one hundred and fifty miles from
its mouth, as the locality of the specimens referred to this variety.

SCAPHITES WARRENI.

Plate 13, figs. 1-4.

Scaphites warrent M. & H., Proc. Acad. Nat. Sci. Phil., vol. 12, pp. 177, 420.

Scaphites warrent M. & H., Smithsonian Check List Invert. Foss., p. 24.

Scaphites warrent (M. & M.) Meek, Pal. U. 8. Geol. Surv. Terr., p. 420, Pl. 6, fig. 5.
Shell of moderate size, transversely subovate in general form; regu-

larly coiled in the earlier stages of growth; the volutions rounded and

CRETACEOUS FOSSILS. 445

strongly involute, the outer embracing the inner so as to leave only a min-
ute umbilical opening, and in some cases the umbilicus is entirely closed,
concealing the inner coils. Outer volution large and deflected in nearly a
straight line for some distance, then recurved and extending nearly to the
center of the straightened portion. Aperture considerably contracted and
hood-shaped. Lateral diameter of the outer volution and of the deflected
portion somewhat exceeding the dorso-ventral diameter; the form of a
transverse section being equal to the larger two-thirds of a broad ovate
figure. The chamber of habitation in the large individual figured on Plate
13, Figs. 2 and 3, extends to about the middle of the straight portion of the
outer volution.

Surface of the shell marked by closely arranged, subangular costz,
which are even and of uniform size on the back and to near the middle of
the sides, where from four to seven of them unite in forming broad, rounded |
folds, which contract in width on approaching the umbilicus and become
prominent and angular. On the involute parts of the shell the coste are
directed nearly straight across the volution, but on the deflected portion
they have a slightly forward curvature in passing from the ventral to the
dorsal portion, and the costal folds are stronger and more distant.

Septa rather simple in their structure and closely arranged. The
siphonal lobe is about as wide as long, and provided with two bifurcating
branches on each side, the inner fork of each being longer than the outer,
and both minute. First lateral lobe much smaller than the siphonal lobe,
and divided into two principal branches, with a broad, rounded sinus
between, the dorsal side provided with three nearly equal spurs, one above
the other, and the ventral side with two larger spurs, each of which is min-
utely bifurcate at its extremity. Second lateral lobe long and narrow,
with a club-shaped extremity, marked by three minute points on the dorsal
and two on the ventral side. Third lateral lobe minute, narrowly linear,
and perfectly simple. Fourth lobe barely perceptible as a slight indenta-
tion. First sinus consisting of three nearly equal, cordiform divisions,
separated by secondary lobes, the first long, narrow, and simple; the second
larger, narrow, and clavate, with four minute terminal teeth. Second sinus

446 GEOLOGY OF THE BLACK HILLS.

consisting of two divisions, the first cordiform and the second simple and
rounded. Third sinus composed of two parts, both slightly flattened on
their upper surface. Fourth sinus simple, with a slight indentation at the
middle. The sinuses are all broad and the lobes very narrow. Siphuncle
not observed.

This species is a well marked and easily distinguished form among the
fossils of this region, and appears to be quite abundant at some localities.
It is very closely related to S. equalis Sow., and not readily distinguishable
from it, except in the form of the aperture, which in that one seems to be
bordered by a thickened margin, while in this one it is contracted to about
two-thirds the size of the shell, with the edge rather thin, or thickened very
slightly only on the inner surface. The shell is quite variable in size at
different localities, but appears to retain the full, ventricose form of the
volutions and other specific features to quite a remarkable degree.

Formation and locality—In Lower Cretaceous shales at the outer edge
of Camp Jenney, east fork of Beaver Creek, Black Hills, Wyoming.

SCAPHITES WYOMINGENSIS.
Plate 13, figs. 5-7.

Scaphites warreni var. wyomingensis M. & H., Pal. U.S. Geol. Surv. Terr., p. 421, figs.
61, 62.

The shells of this species closely resemble those of S. warrent M. &
H. in many of their features, but differ very materially in the general
form and proportion, as seen in the specimens from the Black Hills locali-
ties. They are always much smaller, and the volutions are laterally com-
pressed, so that their relative diameters are scarcely more than as two to
three, as seen on the involute parts, but widen rapidly on the deflected and
recurved parts, so that near the aperture the lateral diameter is greater
than the dorso-ventral. The deflected portion is also always proportion-
ally longer than in that one, the surface marking very much finer, and
those on the straight portions have a more strongly forward curvature.
The septa have the same general character as in 8. warreni, but the digita-
tions of the lobes are smaller and less distinct, presenting about the same
features in the extreme adult shell as is possessed by the septa of the rep-

CRETACEOUS FOSSILS. 447

ceding volution of that species; giving to these a very immature aspect
The finer character of the costa of this species depends in a great degree
upon the smaller size of the shell, as there are about the same number of
small costae between each of the stronger ones; but there are also one or
two more of the stronger folds on this species, on the deflected portion of
the shell, than in that one.

The principal differences, therefore, between the two shells, and those
which we deem to be of specific importanice, are, the greater length of the
deflected part, the laterally compressed form of the volution, and the dif-
ferent direction of the coste on the straight part of the shell. The two
forms are associated at the same localities, and even occur in the same hand
specimen of rock; but we think there is no difficulty in distinguishing
them. The examples before us present strong variations and points of dif-
ference, when compared with the figures of the variety given by Mr. Meek
(Paleontology of the United States Geological Survey of the Territories,
page 421, Figs. 61, 62), especially in the straightness of the deflected por-
tion and in the more compressed form of the volution; in fact these varia-
tions from his figures are so great, that we were in doubt of the correctness
of the identification, until we submitted an example to the author's inspec-
ion, by whom they were pronounced positively identical. We are of the
opinion, however, that they are specifically distinct from S. warreni, and
have so classified them. ;

Formation and locality.—In shales and limestones of the Cretaceous, on
the Belle Fourche, and on the east fork of Beaver Creek, Black Hills.
Probably of the Fort Benton Group.

Genus HELICOCERAS D’Orb.
HELICOCERAS STEVENSONI.*
Plate 14, figs. 5-8.
Helicoceras Stevensont Whitf., Prelim. Rept. Pal. Black Hills, 1877, p. 39.

Shell large and robust, with an elevated, moderately tapering spire,
which is composed of strong, cylindrical, disconnected, dextrally-coiled

*Named in honor of Prof. John J. Stevenson, of New York City, the eminent geologist, who has:
done so much good work among the Cretaceous rocks of the West.

448 GEOLOGY OF THE BLACK HILLS.

volutions, sharply enrolled and leaving an umbilical opening equal to or a
little greater than one-half the diameter of the volution encircling it. The
volutions are at first widely disconnected and rapidly descending, but
become more closely coiled below, and in the lower part of the example
figured are but slightly disconnected.

Surface of the shell marked by strong, rounded, annulating cost, pass-
ing entirely around the shell, and separated by wider concave interspaces.
On the upper surface of the volution the coste are strongly directed back-
ward, but are recurved, and on the outer face are directed gently forward
below and within the umbilicus. The costze are further ornamented by two
irregular rows of strong, obliquely-rounded, tuberculose nodes; the upper
range being situated along the middle of the volution, and the other half
way between it and the center of the basal surface. ‘The nodes of the two
ranges, although usually placed on the same costa, are not constantly so,
but frequently alternate, and in very many cases two of the coste unite at
the lower node, continuing only as one on the lower side of the volution.

Septa rather distantly arranged, leaving considerable space between
them, the convolutions of a single septum occupying a space on the periph-
ery of the shell equal to from two-thirds to three-fourths of the diameter
of the volution at the point examined. Siphonal lobe longer than wide, and
deeply divided at the extremity into two principal branches, each of which
is again deeply divided, and the divisions furnished with numerous ser-
rated digitations. First lateral lobe very large and unequally divided into
two principal branches, the outer one of which is the largest, and each is
again divided and furnished with numerous compound digitations. The
second lateral lobe is much smaller than the first and similarly divided, but
the divisions are smaller and less complicated (the inner half of this lobe
has not been distinctly traced). First lateral sinus rather large and deeply
cleft in the middle by an auxiliary lobe, the lower end of which is divided
into several digitations. Second lateral sinus shorter and comparatively
more spreading than the first, and also deeply divided in the middle by a
simple auxiliary lobe, having four spurs on each side. Other lobes and
sinuses not observed. Siphuncle rather small, marginal, and passing along
the middle of the volution.

CRETACEOUS FOSSILS. 449

This species would appear, without critical examination, to be some-
what closely related to Heteroceras ? angulatum M. & H. (Palentology of the
United States Geological Survey of the Territories, p 484, Pl. 21, Fig 3),
more especially as their species is stated to be ‘“ dextral (?)”, and their fig-
ures, being placed base upward—which may be seen by the position of the
nodes—are liable to mislead; but if critically examined will be found, from
the direction of the costae, to belong to a sinistral shell, as they incline in
an opposite direction to those of a dextral shell. Myr. Meek states, loc. cit.,
that the fragment figured is supposed to be from the deflected part of the
shell, and for this reason is placed provisionally, with doubt, under the
genus Heteroceras. It is, perhaps, impossible for one to feel positive that a
shell of this group has not been or would not be deflected at some period of
growth, unless a perfect adult individual is obtained. Our shell figured
shows no evidence whatever of any tendency to become deflected ; still it
is known to be imperfect, as it is septate to within an inch of the outer
extremity, and we cannot, therefore, feel positive of its true generic rela-
tions. The upper part of the spire has, however, been very loosely coiled,
or widely disconnected, becoming more compact with increased growth; in
this respect being the reverse of shells belonging to the genus Heteroceras.
Owing to this feature, and the absence of any evidence of the generically
required deflection in the adult stages, we have considered it most natural
to refer it to Helicoceras.

Formation and locality.—In limestone of the Fort Pierré Group, on the
west side of Beaver Creek, Black Hills.

Genus HETHEROCERAS D’Orb.
HETEROCERAS NEWTONI.

Plate 15, figs. 1-4.
Heteroceras Newtoni Whit#f., Prelim. Rept. Pal. Black Hills, 1877, p. 40.

Shell dextral, of moderate size, composed of from two and a half to
three loosely coiled, disconnected, and rather rapidly-increasing volutions,
forming the rather low but somewhat rapidly-spreading spire, below which
point the shell is deflected to an unknown extent; transverse section of the

shell circular, or nearly so; umbilicus very wide in the upper part of the
29 BH

450 GEOLOGY OF THE BLACK HILLS.

spire, but scarcely increasing in diameter with the increased growth of the
shell above the deflected portion, the increased diameter of the tube about
equaling the increased diameter of the whorl.

Surface of the shell ornamented by low, subangular, transverse ridges
or coste, which pass entirely around the shell, and are separated by wider
concave interspaces; also by two longitudinal rows of obliquely rounded
nodes, the upper one of which is placed at or just below the periphery, and the
other at about one-eighth of the circumference of the tube below the first,
and on the line of the same ridge with it. Transverse costa arranged in
sets of three, two of each set coalescing to form the oblique nodes, the third
one passing around the tube, without interruption, midway between the
two adjacent pairs of nodes. The direction of the coste is strongly back-
ward on the upper inner surface of the volution, then recurving and passing
obliquely forward in crossing the outer face of the shell from above to the
base, and also within the umbilicus; siphuncle small, marginal, situated
as far above the upper line of nodes as the distance between the two lines.

Septa approximate, the extremities of the lobes of one slightly inter-
fering with those of the saddles of the next adjacent, but not interlocking ;
the space occupied by the convolutions of the lobes and sinuses of a septum
is equal to three-fifths of the diameter of the tube at the position of the sep-
tum measured; the ramifications of the lobes are sharply angular and
pointed. The siphonal lobe is longer than wide, deeply divided at the
extremity into two rather long, compound, digitate processes, and a short,
bifid, median process. First lateral lobe very deeply and unequally divided,
and the branches widely spreading, and deeply serrate-digitate ; second
lateral lobe very much smaller than the first, and less spreading ; antisipho-
nal lobe single, longer than wide, deeply digitate on the side, and divided
into four small, unequal digitations at the extremity ; sinuses large, spread-
ing, and deeply cleft by auxiliary or secondary lobes.

The type specimen of the species is imperfect, but preserves one and
one-third volutions; the volutions are entirely disconnected, and increase
rapidly in size, while the umbilicus retains the same diameter, the upper
volutions appearing to have been not more closely coiled than those pre-

CRETACEOUS FOSSILS. 451

served. The outer extremity of the specimen retains a part of the deflected
portion, which is bent downward as well as outward, and is septate nearly to
the end. The species appears to be related to H. ? nebracensis M. & H.
(Paleontology of the United States Geological Survey of the Territories,
p- 480, Pl. 22, Fig. 1, a, b, ©), but differs, however, in the more rapidly-
increasing volutions, in the disconnected whorls, simple coste (i. e., not
bifurcating), in the position of the siphuncle, and in the details of the lobes
and sinuses.

Formation and locality.—In limestones of the Fort Pierré Group, on the
west side of Beaver Creek, Black Hills.

HETEROCERAS ? NEBRASCENSE.

Plate 15, fig. 6, and Plate 14, fig. 9.

Ancyloceras ? nebrascense M. & H., Proc. Acad. Nat. Sci. Phil., vol. viii, p. 71.
Turrilites nebrascense M. & H., ibid., p. 280.
Helicoceras ? nebrascense Meek, Smithsonian Check Llist Invert. Foss., p. 25.
Heteroceras ? nebrascense Meek, Pal. U.S. Geol. Surv. Terr., p. 480, Pl. 22, fig. 4.
Shell moderately large and robust, with a low, rapidly-contracting,
dextrally-coiled spire, having an apicial angle of about 50°, and com-
posed of a small number of rapidly-increasing volutions, which are in close
contact with each other, as far as observed in the example figured, and
coiled so as to leave an umbilical opening of large size in the upper
portion of the spire, which apparently increases but little in diameter with
the increased growth of the shell. Transverse section of the volutions cir-
cular or nearly so. Surface of the shell ornamented by strong, subangu-
lar, transverse ridges or costee, which pass entirely around the shell and are
divided by concave interspaces. The coste on the smaller volution of the
specimen are often duplicate, and cross the face of the volution with a strong
forward direction in passing from above to the lower side, but are directed
strongly backward from within the umbilicus on the upper surface. On
the larger volution the costze are usually simple, but sometimes bifurcate,
and pass more directly across the shell. The coste are ornamented by two
irregular rows of strong, rounded nodes on the older parts, situated one near
the periphery and the other just above the base of the volution.

452 GEOLOGY OF THE BLACK HILLS.

The septa are arranged at considerable distance from each other, leav-
ing an open space between. The convolutions of the lobes and sinuses are
very complicated, and are divided and branched much as in other species
of the group from the same locality. The details of their structure may be
seen by reference to the diagram on the plate. Siphuncle of moderate size
and situated just above the middle of the volution

The species differs from either of the related forms here described in the
proportional elevation of the spire and the compactly-coiled volutions, being
much less elevated than Helicoceras stevensoni, and more elevated than Hete-
roceras newton. ‘The tube also increases more gradually than that of the
latter species, and forms a smaller umbilical opening. They also differ
materially in the details of the septa. The specimen figured, as far as pre-
served, shows no evidence of the deflection of the outer volution; but the
compact volutions would seem to indicate relations with Heteroceras rather
than with Helicoceras.

Formation and locality—lIn limestone on the west side of the east fork
of Beaver Creek, Black Hills; supposed to belong to the Fort Pierré Group
of the Cretaceous section, but which also contains a mingling of forms of
No. 5 of the same section.

Genus ANCYLOCERAS D’Orb.

ANCYLOCERAS JENNEYI.
Plate 16, figs. 7-9.
Ancylocerus Jenneyi Whitf., Prelim. Rept. Pal. Black Hills, 1877, p. 42.

Shell of moderate size, composed of two or more (?) rapidly-increasing
volutions, enrolled on the same plane, and entirely disconnected, the inner
ones apparently leaving a broad, open, umbilical space. Shell rather rap-
idly increasing in size with increased age. Volutions slightly flattened on
the back, vertically compressed, and transversely oval in section; the ver-
tical diameter being only about two-thirds as great as the dorso-ventral in
the larger parts of the shell, the greatest height being nearest to the ventral
margin.

CRETACEOUS FOSSILS. ! 453

Surface of the shell marked by strong, distant, transverse, encircling
ridges, which are directed slightly forward in passing from the dorsal to
the ventral margin, and in crossing the latter they become nearly obsolete.
Occasional intercalated ridges occur at irregular distances on the dorsal
side. Intercostal spaces concave. The shell is further ornamented by two
lines of obtusely-rounded nodes, which are situated on the ribs at the
angles of the flattened dorsum.

Septa somewhat complicated and closely arranged, so that the inner
lobes interfere with the extremities of the sinuses of the preceding ones, but
on the dorsal portion they are more distant. Siphonal lobe longer than wide,
deeply divided at the extremity, and terminating in two large, strongly-ser-
rated digitations, having one or two lateral spurs on their outer sides. First
lateral lobe large, deeply bipartite, each branch terminating in two or three
unequal digitations, and with several smaller spurs on the sides above.
Second lateral lobe much smaller than the first, deeply bipartite, with
numerous strong spurs irregularly arranged along the margins. Anti-
siphonal lobe long, narrow, and simple, but with long lateral serrated spurs
and a slightly tripartite extremity. First and second sinuosities rather
large, deeply divided by large auxiliary lobes into two principal branches,
which are again deeply divided. Third sinus smaller than the others, and
divided into two principal branches. The margins of all lobes and sinuses
deeply serrated.

The species is described from an imperfect individual and a second
smaller fragment of a larger specimen. ‘They consist only of the convolute
parts, and show no evidence of the deflection of the tube. It is possible
they are not rightly referred to the genus Ancyloceras, but are more nearly
related to the genus Anisoceras of Pectet, which differs from the former
genus in being irregularly helicoid. The example figured of Plate 16,
Figs. 7-9, would seem to have been somewhat irregularly coiled, but this
may possibly be the effect of distortion, as the smaller coils of the shell
are considerably displaced. It differs from Ancyloceras also, as defined by
Mr. F’. B. Meek (Paleontology of the United States Geological Survey of the
Territories, p. 409), in having the terminations of the lobes bipartite instead

454 GEOLOGY OF THE BLACK HILLS.

of tripartite; but this character does not appear to hold good among many
of those referred to the genus; and, as we have not seen the septa of the
type species, we are uncertain if it is an original feature of the genus or
only an erroneously added one.

Formation and locality—tIn limestone referred to the Fort Pierré Group
of the Upper Missouri Cretaceous, on the east fork of Beaver Creek, three
miles west of Camp Jenney, Black Hills.

ANCYLOCERAS TRICOSTATUS.
Plate 15, figs. 7, 8.
Ancyloceras tricostatus Whitf., Prelim. Rept. Pal. Black Hills, 1877, p. 43.

A single fragment of a sinistrally helicoid shell, the volutions of which
have been entirely separate and coiled upon the same plane, with a rapidly-
increasing curvature, appears to possess features entirely distinct from those
of any described species. The form of the volution has been quadrangu-
larly ovate in section, vertically compressed, with the greatest vertical thick-
ness at about the inner third of the width, and slightly flattened on the
dorsum. The shell is marked by a line of strong angular nodes on each
dorsal angle, and by closely-arranged subangular encircling ridges or
costa, which are directed slightly forward in crossing from the ventral to
the dorsal margin on the upper side of the volution, and much more
strongly so in crossing from the upper to the lower side of the dorsal flat-
tening, and are recurved below and on the umbilical surface. The costze
are arranged in sets of three, the two adjacent ones of which unite in the
nodes on the upper and lower dorsal angles, while the third ridge of each
set encircles the shell between the nodes of two adjacent sets. Intercostal
spaces concave.

Septa very complicated and distant, the spaces between two adjacent
ones equal to about one-third of the space occupied by the convolutions of
a single septum at the point indicated. The dorsal lobe is almost twice as
long as wide, deeply divided at the lower extremity by a broad, tridentate

sinus, each division being again divided into two widely-divergent dentate

CRETACEOUS FOSSILS. - 455

branches. There are also two lateral dentate spurs above on each side of
the lobe. First lateral lobe large but slender, divided into two principal
widely-divergent branches, each of which is again divided, and furnished
with several strong dentate spurs on their margins; two other spurs of
similar character exist on each side of the lobe, one just below the bifurca-
tion and the other some distance above. Second lateral lobe smaller than
the first, deeply divided, with the branches less divergent, but again
divided, and the inner branches trifurcate, the outer branches short and
strongly dentate. Antisiphonal lobe small and simple, marked by one
small spur on each side above and two larger curved and dentate ones
below; the central termination being minutely tridendate at its extremity.
First lateral sinus large, very deeply divided into two principal branches,
each of which is deeply divided above and strongly lobed on the sides.
Second sinus smaller, less deeply and unequally divided, the outer half
smallest and deeply lobed, the other less deeply so. Antisiphonal sinus
very large (considering the parts separated by the antisiphonal lobe as one
sinus), the antisiphonal lobe dividing it nearly to the base, and the divisions
again very deeply divided and deeply lobed on the sides. Siphuncle small,
situated between the lines of nodes and marginal.

This species differs from Ancyloceras Jennyi, in being sinistrally coiled,
and in the character of the ridges of the surface and angular nodes. We
know of no other species described with which it is enough related to
require a comparison.

Formation and locality—In limestone at the top of the Fort Pierré
Group, on the Cheyenne, near French Creek, Black Hills.

Genus PTYCHOCERAS D’Orb.

In his remarks on the genus Ptychoceras (Paleontology of the United
States Geological Survey of the Territories, p. 410), Mr. F. B. Meek has
advanced the opinion that these shells have possibly been folded upon
themselves a second time in their more advanced stages of growth, as in
the case of Diprycuocrras Gabb; or that they may have even been bent
backward again, as is supposed to have been the case in the genus SOLENO-

456 GEOLOGY OF THE BLACK HILLS.

ceras Conrad (Hamulus annilifer Mort.). We have in this collection quite
a number of individuals of the species herein described under the name P.
meekanum, several of which show the prolonged curved portion of the
smaller limb, and two individvals of P. crassum; but all the evidence fur-
nished by these specimens is of a character opposed to either of these
suppositions. The peculiar bending of the smaller limb of the first of these
species would seem to preclude the probability of the larger part of the
shell following the curvature of the earlier and returning over its extremity
so as to infold it; while the assumption of old age characters in the contrac-
tion of the distance between the rings, as seen on several of them near
the end of the tube, would seem to indicate that neither of these theories
is correct; but that the shell is essentially complete at about this stage of
growth. Beyond this, among all the individuals of these two species
observed, none of them are septate beyond the commencement of the
fold, and at this point the septa are more crowded than below. We are
also much inclined to believe that the folding of the siphonal surface of a
cephalopod upon itself, after having coiled in the opposite direction, is a
feature seldom observed.

Although several of the examples of P. meekanwm, before us, show
the bending of the smaller limb, as seen in the. example figured, none of
them are perfect at the smaller extremity; so we are still uncertain as to
its character or form during the earlier stages of its existence. In the rock,
forming the matrix of some of these specimens, we have noticed fragments
of a smell Ammonite-like shell, having the same form of section and sur-
face markings with the smaller parts of these, and we have been induced
to infer that possibly they may be the earlier portions of the same shell,
and that possibly, in its younger stages, it may have been minutely pla-
norbitorm; but the fragments are two imperfect to determine the question.

We have also noticed another feature on the larger individual of P.
crassum (Plate 16, Fig. 3), which we had at first supposed to be the result
of accident; but which on further examination we find to be a thickening
of the external surface of the shell, and which does not in any way inter-
fere with or affect the septa or the internal portion of the shell. It com-

CRETACEOUS FOSSILS. 457

mences at the suture between the two limbs, and continues over the outer
surface of both, retaining the form of the shell, surface characters, and lines
of nodes throughout its entire substance. On the side of the specimen seen
in the figure the shell is mostly removed by exfoliation, but on the oppo-
site surface it is retained in great part, and shows a thickness of about a
twelfth of an inch at the smaller end, and less than a sixteenth of an inch ~
at the larger extremity of the specimen. If the thickening had been from
the inside, it would have affected the inside of the tube and the parts along
the junction of the two limbs; but this is seen not to be the case when the
shell is broken. From this feature of the external thickening of the shell
we have thought it possible that it was an internal appendage of the animal,
like that of Spiruua, and that it probably became enveloped within the sub-
stance of the mantle at the period at which the bending or folding of the
shell took place, even though it may have been external during the earlier
stages of growth.

PTYCHOCERAS MEEKANUM.
Plate 16, figs. 1, 2.

Ptychoceras Meekanum Whitf., Prelim. Rept. Pal. Black Hills, 1877, p. 44.

Shell of small size, subcylindrical or vertically compressed, giving a
somewhat oblate-transverse section, very gradually increasing in diameter
with the increased length; smaller limb slender, gently curved or bent in
the middle of its length, so as to give the earlier and middle portions of the
shell an angle of about 135° to each other. Larger limb, or outer chamber,
closely appressed and slightly embracing the smaller, and extending to near
the middle of the curvature.

Surface of the entire shell marked by strong, simple, sharply angular,
oblique, encircling ridges, with wider, deeply-concave interspaces, very
regularly increasing in distance from the apex outward; and on the dorsal
region by two longitudinal rows of spines or spiniform tubercles, situated
at about or nearly one-sixth of the circumference of the tube from each
other, and on the crests of the ridges. The encircling ridges are directed
obliquely forward in passing from the ventral to the dorsal surface in the

458 GEOLOGY OF THE BLACK HILLS.

smaller limb, but have the opposite direction on the larger limb; space
between the lines of nodes very gently concave.

Septa approximate, but more distant than the surface ridges of the shell,
deeply lobed and the lobes and sinuses somewhat complicated. The dorsal
or siphonal lobes are nearly as wide as long, broadly forked at the extremity,
and the outer side of the forks marked by several short, rounded digita-
tions. First lateral lobe divided into two diverging branches, with lobed
margins. Second lateral lobe narrower and more slender than the first, and
more deeply forked; the divisions being marked by short, rounded digita-
tions. Ventral, or antisiphonal lobe small, but deeply forked, and the
margins sinuous. Sinuses nearly equal in size, each of them deeply divided
in the middle by an auxiliary lobe; slightly bifid in the first and second
sinus, but simple in the third; division of the sinuses, marked by short,
rounded digitations. Siphon of moderate size, marginal and placed between
the lines of nodes.

Before entering upon a critical study of the specimens before us, we
had supposed them to be identical with Ptychoceras mortoni M. & H, and
hesitated to consider them as distinct; but there are so many points of dif-
ference, and the variations are so great, that it appears impossible to avoid
this conclusion, and equally difficult to unite the two forms here mentioned.
More especially is this the case if any reliance is to be placed on the struc-
ture and lobation of the septa. We are quite well aware that this latter
feature is one liable to great variation, dependent upon the growth of the
individual; but the lobations in the septa at the smaller extremity of the
specimen figured is much more complicated than that shown by Mr. Meek
to exist in the type specimen of P. mortoni. Besides the difference in the
septa, the form of the tube varies in being wider than high, the reverse of
that species, and the antisiphonal surface of the tube is always flattened,
and the costa always simple.

Formation and locality.—In limestone of the Fort Pierré Group, on
Beaver Creek, Biack Hills.

CRETACEOUS FOSSILS. : 459

PTYCHOCERAS CRASSUM.
) Plate 16, figs. 3-5.
Ptychoceras crassum Whitf., Prelim. Rept, Pal. Black Hills, 1877, p. 45.

Entire form of shell unknown. The portion preserved is rather robust
in habit and the shell much thickened, except on the ventral surfaces.
Transverse section subcylindrical or slightly compressed in a dorso-ventral
direction, the larger limb being concave on the ventral side and slightly
embracing the smaller part. Tube regularly increasing in diameter with
increased growth. Shell ornamented by strong, sharply angular, encircling
ridges, which are directed forward in passing from the ventral to the dorsal
sides of the smaller limb, but have the opposite direction on the larger
part; also by two longitudinal lines of pointed nodes, or spines, on the
dorsum, which are separated by a moderately wide, slightly concave space.

Septa distant, one septum nearly equaling two of the transverse ridges,
except near the bending of the tube, where there are two of the septa placed
nearer to each other, beyond which the shell is not septate. Lobes and
sinuses of the septa somewhat complicated; the siphonal lobe longer than
wide, and broadly forked at the extremity First lateral lobe large, divided
into two principal branches, the outer one being again deeply divided and
the margins of the branches serrato-digitate. Second lateral lobe smaller
than the first, divided into three short serrate digitations. Antisiphonal
lobe small and simple, marked only by two short digitations on each side.
First and second sinuses much larger and broader than the lobes, deeply
divided in the middle by a small serrated auxiliary lobe, and the divisions
each again divided and serrate. Antisiphonal sinus a little smaller than
the others, but more deeply divided by the antisiphonal lobe, and the
branches again deeply divided. All the margins of the lobes and sinuses
are characterized by small rounded serrations. Siphuncle of moderate size,
marginal, and situated between the lines of nodes.

The distinction between this and the preceding species, consists in its
large size, more robust habit, and thicker shell, and in the more distant and
much more complicated septa. It is still further removed by these charac-
ters from P. mortoni M & HL, as well as by the simple ridges.

Formation and locality. on limestone of the Fort Pierré Group, on Old
Woman Fork, Black Hills,

460 GEOLOGY OF THE BLACK HILLS.

SECTION V.

SYNOPSIS OF SPECIES FROM THE BLACK HILLS, NOTICED
IN OTHER WORKS, NOT DESCRIBED IN THIS REPORT.

POTSDAM SPECIES.
Lingulepis prima (Conrad) Meek.

Mr. Meek recognizes a form under this name from the central parts of
the Black Hills, in the Paleontology of the Upper Missouri (Smithsonian
contribution), p. 3, Pl. 1, Fig. 2.

Hyolithes gregaria = Theca gregaria M. & H.

Mr. Meek gives this species as from the Big Horn Mountains (Pale-
ontology of the Upper Missouri, p. 5), and we remember having seen
remains of a similar or identical form in the collection of Colonel Ludlow’s
expedition of 1874.

Agranlos ?

sp. ?, in Pal. Up. Missouri, p. 10.

Mr. Meek cites a species as above from the sandstones of the central

Black Hills.
JURASSIC SPECIES.

Ostrea englemanni Meek, Pal. Up. Missouri, p. 73.

A single imperfect valve of this species too poor for use occurs among
the fossils from southeast of Warren Peak, in the Redwater Valley.

Trigonia conradi M. & H., Pal. Up. Missouri, p. 83, Pl. 3, fig. 11.
Southwest base of Black Hills, in Lower Jurassic.

Unio nucalis M. & H., Pal. Up. Missouri, p. 92, P1.3, fig. 13.
In Jurassic rocks, southwest base of Black Hills.

Astarte inornata M. & H., Pal. Up. Missouri, p. 94, Pl. 3, fig. 12.
Southwest base of Black Hills, in Jurassic rocks.

Tancredia ? wquilateralis M. & H., Pal. Up. Missouri, p. 96, Pl. 3, fig. 8.

In Jurassic beds, southwest base of Black Hills.

SYNOPSIS OF SPECIES FROM OTHER REPORTS. 461

Protocardium shumardi, M. & H., Pal. Up. Missouri, p. 98, figs. a and b.
Southwest base of Black Hills, in Jurassic rocks.
Myacites (Pleuromya) nebrascensis and M. (P.) subellipticus M. & H.

Are both cited as occurring at the southwest base of the Black Hills
(Paleontology of the Upper Missouri, pp. 100-101), but we have not been
able to identify either of them among the collections.

Thracia ? arcuata M. & H., Pal. Up. Missouri, p. 102, Pl. 4, fig. 8.

From near the middle of the Jurassic, at the southwest base of the
Black Hills.

Pholadomya humilis M. & H., Pal. Up. Missouri, p. 104, Pl. 4, fig. 3.
Lower part of Jurassic, southwest base of Black Hills.

Planorbis veturnus M. & H., Pal. Up. Missouri, p. 107, Pl. 4, fig. 1.
Southwest base of Black Hills.

Valvata ? scabrida M. & H., Pal. Up. Missouri, p. 113, Pl. 4, fig. 2.
Southwest base of Black Hills, in Jurassic rocks.

Vwiparus gilli Meek, Pal. Up. Missouri, p. 115, Pl. 4, fig. 3.
Southwest base of Black Hills.

TInoplacodus veternus M. &. H., Pal. Up. Missouri, p. 116, with figs.
Southwest base of Black Hills and head of Wind River.

Ammonites henryi M. & H., Pal. Up. Missouri, p. 123, Pl. 4, fig. 9.
Southwest base of Black Hills.

Serpula

sp. ?, Pal. Up. Missouri, p. 128.
Southwest base of Black Hills, lower part of Jurassic.
CRETACEOUS SPECIES.
Websteria cretacea Meek, Pal. U. S. Geol. Surv. Terr., p. 3, Pl. 28, fig. 3.

A small coralline-like body from the Fox Hills Group of the south fork
of the Cheyenne River.

462 GEOLOGY OF THE BLACK HILLS.
Terebratula helena Whitf., Rept. of a Reconnaissance of the Black Hills of Dakota, by
Lieut. Col. Ludlow, p. 103, Pl. —, figs. 5-10.
A large species, related to T. harlani Mort. From No. 4, northeast

Black Hills, north of Belle Fourche.

Ostrea congesta Conrad.

Abundant on the Cheyenne River, near the Black Hills, Niobrara
Group.
Gryphwa vesicularis Lam.

Mr. F. B. Meek cites this species with doubt as from the Fort Pierré
Group, on the Cheyenne River, near the Black Hills.

Nucula subnasuta H. & M., Mem. Bost. .\cad. Arts and Sci., 1856, Yoldia subnasuta
Meek, Check List Smith. Inst., p. 8.

Sage Creek, upper part of No. 4.

Yoldia ventricosa = Nucula ventricosa H. & M., Mem. Acad. Arts and Sci., new ser., vol.
v, p. 385, PI. 1, fig. 11

Sage Creek, Fort Pierré Group.

Caprinella coraloidea H. & M., Mem. Bost. Acad. Arts and Sci., 1856, p. 380, Pl. i, fig. 3,
—= Icthyosarcolithus coraloidea (Gabb.) Meek, in Check List Smith. Inst. Cret.
Foss., p. 5.

In upper part of No. 4, Sage Creek.
Spheriola ? warrenana Meek, Pal. U. S. Geol. Surv. Terr., p. 138.

A species nearly related to S. transversa, herein described. From the
Fox Hills Group, near the eastern base of the Black Hills.

Callista (Dosiniopsis) nebrascensis M. & H.= Callista nebrascensis M. & H.= C. deweyt
var. robusta M. & H., and Dione nebrascensis Meek. See Pal. U.S. Geol. Surv.
Terr., p. 184, figs. 15-17.

A species closely related to C. deweyi Fort Pierré Group, Cheyenne
River, Black Hills.

Callista (Aphiodina ?) tenwis (H. & M.) Meek, Pal. U.S. Geol. Surv. Terr., p. 188, = Oy-
therea tenuis H. & M.= Meretrix tenuis M. & H., also Dione ? tenuis Meek.

South fork, Cheyenne River, Black Hills, Fort Union Group.

SYNOPSIS OF SPECIES FROM OTHER REPORTS. 463

Tellina (Peronea ?) scitula M. & H. (= Tellina scitula M. & H.), Pal. U. S. Geol. Surv.
Were plot el dO, tek.

South branch of the Cheyenne River, Fox Hills beds.

Acteon subellipticus M. & H., Pal. U.S. Geol. Surv. Terr., p. 280, Pl. 19, fig. 16, = Soli-
dula (Acteonina ?) subelliptica M. & H.

Crow Creek, near Black Hills, in the Fort Pierré Group.

Cinulia (Oligoptychia) concinna (H. & M., sp.) Meek, Pal. U. 8S. Geol. Surv. Terr., p.
284, —= Acteon concinnus H. & M.; Avellana concinna Meek; Avellana subglobosa
M. & H.

Sage Creek, Black Hills, Fort Pierré Group.

Acmeea occidentalis (H. & M., sp.) Meek, Pal. U. S. Geol. Surv. Terr., p. 295, = Capulus
occidentalis H. & M.; Tectura ? occidentalis M. & H.

Sage Creek, Black Hills, Fort Pierré Group.

Margaritella flexistriata (EK. & 8., sp.) Meek, Pal. U.S. Geol. Surv. Terr., p. 302, Pl. 19,
fig. H, = Solarium flexistriatum BE. & 8.; Margaritella flexistriata M. & H.

Sage Creek, Black Hills, Fort Pierré Group.

Closteriscus tenuilineatus (H. & M., sp.) Meek, Pal. U.S. Geol. Surv. Terr., p. 308, PI.
19, fig. 10, = Pusus ? tenwilineatus H. & M. and Tritonifusus ? tenuilineatus
Meek.

Sage Creek, Black Hills, Fort Pierré Group.

Gyrodes conradi Meek, Pal. U. 8. Geol. Surv. Terr., p. 310, figs. 33-36.
Cheyenne River, Fort Pierré Group.

Odontobasis constricta (H. & M., sp.) Meek, Pal. U. 8S. Geol. Surv. Terr., pp. 352, 353,
figs. 41, 42, — Fusus constrictus H. & M. and Buceinum ? constrictum M. & H.

Sage Creek, Black Hills, Fort Pierré Group.

Odontobasis ventriosa Meek, Pal. U. S. Geol. Surv. Terr., p. 354, fig. 43, Pl. 19, fig. 1.
Near mouth of Sage Creek, Black Hills, Fort Pierré Group.

Baculites compressus Say, Am. Jour. Sci. and Arts, vol. ii, p. 41, 1821.

Abundant at Sage Creek and Great Bend of the Missouri.

464 GEOLOGY OF THE BLACK HILLS.

Baculites ovatus Say, Am. Jour. Sci. and Arts, vol. ii, p. 41, 1821.

Sage Creek and other places in the Black Hills, Fort Pierré Group.
This and the above species are represented by numerous fragments in the
collection, but it has been thought not desirable to illustrate either of the
species, as they have been so frequently given by others.

Baculites grandis H. & M., Mem. Am. Acad. Arts and Sci., vol. v, n. ser., p. 402, Pl. 7,
figo

Cheyenne River, Black Hills, Fort Pierré Group.
Baculites aspera Morton, Synop. Org. Rem. Cret. Group U.5., p. 43, PL. 1, figs. 12, 13.

A few fragments are present in the collection from the Fox Hills beds
at the eastern base of the Black Hills.

Ancyloceras uncum (M. & H.) Meek, Pal. U. 8. Geol. Surv. Terr., p. 409, Pl. 21, fig. 1,
= Ancyloceras (Hamites) uncum M. & H.

South fork Cheyenne River, Black Hills, Fort Pierré Group.

Scaphites larveformis M. & H., Proc. Acad. Nat. Sci. Phil., viii, 58; Meek, Pal. U.S.
Geol. Surv. Terr., p. 418, Pl. 6, fig. 6.

Kastern base of Black Hills, Fort Benton Group.

Scaphites conradi (Morton) Meek, Pal. U. 8S. Geol. Surv. Terr., p. 430, Pl. 36, fig. 2, —
Ammonites conradi Morton; ? Scaphites pulcherrimus Roemer; Ammonites danw
D’Orb.; and Ammonites nebracensis Owen.

Eastern base of Black Hills, Fox Hills Group.

Placenticeras placenta (= Ammonites placenta De Kay and others), see Pal. U. S. Geol.
Surv. Terr., p. 465, Pl. 24, fig. 2.

This species is well represented in the collection by some large indi-
viduals from the Black Hills, in bed No. 4.
Heteroceras ? angulatum (M. & H.) Meek, Pal. U.S. Geol. Surv. Terr., p. 484, PI. 21, fig.
3, = Helicoceras angulatum M. & H.

Head of south branch of the Cheyenne River, Black Hills, Fort Pierré
Group.

LIST OF SPECIES DESCRIBED.

SECTION VI.
LIST OF FOSSILS DESCRIBED IN THIS REPORT.

465

POTSDAM GROUP.
Name. Locality. Page.
PLANT.

iealeochordayprimaruaSpeeseseoeseee seca eee eee Head of Redwater Valley...-.....-.. .--- Sal
Paleophycus occidentalis, n. sp-..---.-.-----------|------ GW concocd seaese seeds cocoUoaueseses 332
ef Sp undetermine dias ee see emen eee es lesa ee- Gl) Seeeoccasasaconccos « A 333

INCERTECEDES.
JNO MES. Soy cocecedasoognuadecedccene saouee Near Warren Peaks.......-.--..-------- 333

BRACHIOPODA.
Lingulepis pinnaformis Owen-..---.-...---.-------- Red: Canon) Creeks =se--e see = hese ee 335
CuMeOlISH MNS Diets enisec ee see soc allemaal (0) epee SPB ee Bee CEE MEE Ee caa laa aio
DOMENIC MERI, 15 SOs -Scocoee5s ones caellosooce LO Herero he aca AN ici ay ate 337
daikotensisi Mii bl tee aes eeee eee ere Castle @reelke aac eee eee eae 337
Obolus)? pectenoids Wihitfese-- nessa e son seen oe eee Cotes esaee eas ccs conse eieaee: 338
Obolellaspolitapttiall lense meee eee sere eee asses Redwater Cafion.-.--.---..-- Eeocc es 339
UIGRTE YE Disgaea Sea An ee cee nace Sacre eeaCe sa acer GOR ceieeecierice seeseiee science 340

CRUSTACEA.
Crepicephalus (Loganellus) centralis, n.sp ---.---- iInCastletCreeke 25 2 ioe cb heaee coms a Gee 341
ERIE AD soocco eso s|loonese OO scosesssoccen cosebe cade coscHe cues 343
JURASSIC.
RADIATA.

ASterias @ubimm Maspeeeeees cscs coeeceae ae ese Spearfish Creeks see cseee see se ete eases 344
Pentacrinus asteriscus M. & H.......--.---------- Big Horm Mountains ceeee. seman see ae 345

BRACHIOPODA.
iiinoulaybrevirostris Mi. & Heese esses se else ea Speantisht Creokeereereses eee naeese eee 346
Rhnynchonelilay miysina Ey & Me oe cine see otnaie Redi@anonji@reelkgeerses ae ere ee a = 347

LAMELLIBRANCHIATA.
Ostreastrigilecula; Whites 222-5 <2. se -eene lee Belle Fourche River, Sun Dance Hills,and | 348
near Beaver Creek.

Gryphea calceola var. nebrascensis M. & H..-.--.| Big Horn Mountains ....--...----.------- 349
iRecteninew bertyion Spiaesaneeeeaeen eee aaa eee West of the Black Hills...--....--.-.----- 350
Camptonectes bellistriata Meek......--.----.---.-. (September 12 and 20) .........----.----- 301
Grameen wh Cy 18l seacsdeeanoasee East of the Belle Fourche....-..--------- 353

300 BH

466

GEOLOGY OF THE BLACK HILLS.

J URASSIC—Continued.
!
Name. Locality. Page.
LAMELLIBRANCHIATA—Continued.
Pseudomonotis (Eumicrotis) curta Hall -.......--. Two miles south of the Belle Fourche, &c..| 354
orbiculata, n. sp ------ (eptembersl9) seeesse eee eee eee eee 356
Avicula (Oxytoma) mucronata M. & H ......----. Two miles south of the Belle Fourche -.-.| 357
Genyailliaimecta Meeks invM Simeeeeeeeseeeeee ate ee Sun Dancesbilll seeereeseeeeeer ee eea eee eee oS
Grammatodon inornatus M. & H.......-...------- Locality label not legible ........-...-... 359
Mytilus whiteijm.(spescseeerecen se seacercce cesar OUneD) an cereal Strncmsmerseteee sass lee eee 360
Volsella (Modiola) formosa M. & H.........-.-.-. BigwetormyMountainseeeneees ete ere ee ee eon
pertenuis) Min Schl seee ese eee (Septemberi20) ese suet eeesic seme cones 362
Astarte fragilis) MiGente aceite aeeeeeeeeeer iRedwateriValleye-sast- nen says eee eere 363
Trapezium bellefourchensis, n.sp ..---.--..------- Bast of the Belle Fourche ..--........-..-. 364
subequallis; ms SPa-ss te nee cee ee ni Red Canon; Creek 2... soc. sb osce Seas Sees 365
Pleuromya newtoni, n. sp ------------------------- Two miles south of the Belle Fourche ....| 367
Tancredia (?) inornata M. & H ....--..-.....-------| East of the Belle Fourche .............-..- 368
Corbuliformissnsspeer eee ease eee | eeere GO ee ieee Lote ee tame arene Oo ieee 370
bulbosa; ny spiceet eee ec ac sen seein eee On hives Saeed Gat er Peel nas ceeies mes 370
postica, nap epee see maree eect este meee Oech de sare ae tus Cas va a were 371
Tyemoremenne WL, CY 18 oooscoaccasea nen Redwateravicllevmereeeere: aes cee nCree 372
Dosiniayjurassica, Msp aeeeeeee eee eee eee East of the Belle Fourche, &¢..---..--.-- 373
Psammobiay?) prematura wn spieete sae seeseaen ee cl seeee Coe SAE neh has Ney cen area ear 374
Mhraciasublevis Ms, hve ecrlescl ect stec see a= RedwatersVallevanceeeneceneatee es seaeeee 375
Newerayloncirostra sp ecene ates tesa ee ciaes eter seein COnacis ice eet ee teeta man Od)
Saxicajvajurassicams prema secs eeiiss aeeleseieaiaal eeeeee Oe ee A Se ce oar tet te ma 376
CEPHALOPODA.
Ammonites cordiformis M. & H .............-----. RedwaterValleyseesesseee ere eee eee ode
Vat. GIShANS sessed seer Two miles south of the Belle Fourche ..-.| 380
Belemnites densus M. & H......--..----------.--- East of the Belle Fourche...-...----.---- | 381
CRETACEOUS.
Systematic name. Division. Locality. Page.
LAMELLIBRANCHIATA.
No.
Cyncyclonema rigida M. & H...-........... 4 Forks of the Cheyenne River-......-- 383
Pteria; lingurformisih. e182. --2..--2 = sso. 4 Cheyenne River, near French Creek, 384
&e.
(Oxytoma) nebrascana E. & §..-.-.... 4 Sage Creek......-.-.--------e-0s ---- 385
(Pseudopteria) fibrosa M. & H ..--.-. 4 Cheyenne River, near Rapid Creek-...| 386
sublevis, n. sp .-..-.-| 4 Olds Wioman Shorea ee eeere seer eee 387
Inoceramus problematicus Schlot ..---..--- 2 and 3| East fork of Beaver Creek.......----. 389
frapilishit@ Mee: ee 2 and 3| Beaver Creek......-c0e-seeeeeeseeeee 390 |

* Only indication of locality given.

LIST OF SPECIES DESCRIBED.

CRETACEOUS—Continued.

Systematic name. Division.
LAMELLIBRANCHIATA—Continued. i
Inoceramus altus Meek..-.-....---.---..--- 2 4
perplexus, n. sp ....... ---..-.. 2
sublpvis Hed Mees 2 cee. ce | 4
sagensis Owen -.---.-.---.-..- 4
Simpson Meekees senna ase 4
VanuxeminMs hoebs ese. eos 4
VEN UDI WF ode sac caaeee cane 4
barabini Morton.......-...-...- 4
tenuilineatus M. & H...-.-.....- 4
Endocostea typica, n. sp -.-----------.----- 4and 5
Sul capa ROeMen= es vo. sees eee 4 and 5
Idonearea shumardi M. & H..----..--....-- 5
Nucula planimarginata M. & H...-........| 4
Nuculana bisulcata M. & H.---..-.....---- 4and 5
subequilatera, n. sp ..-.....-.---- 4
Woldiarevansi Ma Giese enema cece eee. 4 or 5
Lucina occidentalis Morton ....-...---..-.. 4and 5
VONELICOSA El. Go) Mien cones == cers 4
(Diplodonta) subundata, H. & M...| 4
Crassatella subquadrata, n. sp ...--.--.---- 4?
Astarteevansisie ae M 22s seoraiioc cee cies 4
iMenieliashumilig Me coehivesee erie sae neers 5
Spheriola transversa, n. sp ...--.-----.----| 5
Dosinia missouriana Morton ?........-..... 4
Thetis circularis M. & Hi ...-....---.-.----- 4
Leiopistha (Cymella) meeki, n. sp .----.--.. 5
‘Rhracia subpracilis, nm. sp)ssasceca-2----25: 4
Newra moreauensis M. & H ...... ....-.-.-- 4
GASTEROPODA.
Fasciolaria(Cryptorhytis) fusiformis H. &M.| 4
contorta M...---. 4 or 5
(Piestocheilus) culbertsoniM.&H| 4 or 5
ususshumardt He Go Mieee ss eee anc nee 2
CHEYENNENSISWnISPa--a- see eee acer 4
Aporrhais newberryi Meek.----.-.......-.. 5
TCO KIN SD ses crear ee as eee 4
(Goniocheilus) castorensis, n. sp--| 4 or 5
Anchura ? sublevis M. & H............-.-. 4

Locality.

Page.

Belle Fourche River, ten miles west
of Crow Creek.

Forks of the Cheyenne River-........

Sage Creek and Old Woman Fork ...-

OldGWomanphlor kets ss eee seers

Old Woman Fork, &c-.....---...--..

Belle Fourche River, ten miles west of
Crow Creek.

Cheyenne River, near Box Elder Creek.

(October 2)

OldiWromantHorkees ase eee e eee

Cheyenne River, near Old Woman Fork
Cheyennerhiven se sss peeces see eee
Cheyenne River, near Box Elder Creek-
Cheyenne River, near French Creek..
OldiwomantHork ik cose eae eee
Cheyenne River, near Rapid Creek -..

Cheyenne River
Cheyenne River, near Rapid Creek. -.

Cheyenne River, near Old Woman Fork

Cheyenne River

Cheyenne River, near Rapid Creek --.-|

Dead Man’s Rapids, Upper Missouri - -
Cheyenne River, near Rapid Creek-..
Forks of the Cheyenne River

Cheyenne River, near Rapid Creek -..
Old Woman Fork

Cheyenne River, near Rapid Creek -.-
Rio de la Plata
Cheyenne River, near Rapid Creek- --
East fork of Beaver Creek-....--.--.-
Near Box Elder Creek.....---...-----

eee eee wees eee eee re eee

391

392
393
393
395
396
398

398
400
403
404
405
406
AG7
408
409
409
410
411
412
413
414
415
416
417
418
419
420

421
422
423
424
424
425
426
427 .
428

468

GEOLOGY OF THE BLACK HILLS.

CRETACEOUS—Continued.

Systematic name. Division. Locality.
GASTEROPODA—Continued. x
Anchura (Drepanocheilus) nebracensis E. | 4 a 5 | East fork of Beaver Creek ......-.---
& &.

Lunatia concinna H. & M..........-------. 4 Cheyenne River, near Rapid Creek.. -

Vanikora ambigua M. & H.......---..----- 4 CheyenneyRiveraccer ssa eee eee eee

Amauropsis paludineformis H. & M ..-..--. 4 Cheyenne River, near Box Elder Creek -

Margarita nebrascensis M. & H.......-.---- 4 One hundred and fifty miles above

mouth of Yellowstone.

Anisomyon alveolus M. & H..-.--...---..-... 4 OldaWomanshorkeee ese ee eee eee
subovatus M. & H..-.-..---..... fe aaa 25 es OO 2 ey hace eset oie) Gineretetacien eye
patelliformis M. & H-........---. Aneto eee Owe tein se nectinesee steamer Bese
borealis Morton ........-.. -.---- 4 CheyennesRiveree eerste eee

Akera glansoryza, 1. Sp..----------+-2-. ---- 4 Cheyenne River, near French Creek. .
| Haminea subcylindrica M. & H..-....-...--. 4 Old Woman's! Horks9-4-eeee ee eeaae eee
| Dentalium gracile H.& M.............-.... 4 Cheyenne River, near Rapid Creek.. -

CEPHALOPODA.

Nautilus dakayi var. montanensis Meek.-..- Ae tear ial ane. Olesen paboootecenos eeandesHaue
| Prionocyclus wyomingensis Meek...-..-..-- 2 East fork of Beaver Creek .......----
| Scaphites nodosus Owen...--..-----.- ----. 4 Cheyenne River, near Rapid Creek.. -

var. brevis Meek....-..-... A ecard eae (Cte ates aoe ecca BOnMA a aeRO Baeocs
quadrangularisMeek.| 4 = |_.... COE Se eves tee ea toatciane

plenus M. & H....-.. Ae ee Be Netenciart ae rere eee mena Stee tare ara cee Microcar

WwarrentMy dceE ie sem nat ate eielell= = 2 East fork of Beaver Creek ......-----
wyomingensis M. & H............ PAM Ae) Al etied CO Re Ne erat Soke Or ea ae

Helicoceras stevensoni, n. sp----.----.-----| 4 West of Beaver Creek...-:....-.-.----|

Heteroceras newtoni, D.sp ----.-----..----- 4 See HOO FetGs Sestes cate ayer eis ee es

? nebracensis M. & H........-.- 4 or 5 | East fork of Beaver Creek.-.--.....---

Ancyloceras)jenneyi,n.speeccsstoec see iee Axe Arc) Nba ote Ose Sao toc lon seniee eee eeies eae

tricostatum, n. sp.--.-.-.-----. 4 Cheyenne River, near French Creek..|

Ptychoceras meekanum, n.sp--.-..----.---- 4 Beaver Creekysnesee veiser cejosa see oe

Crassus SPoseecaeeeee merece 4 Oldi Woman orkte ewe sesiesc econ

Page.

429

430
430
431
432

433
434
435
436
437
437
438

439
440
441
443
443
444
444
446
447
449
451
452
454
457
459

ee

Ee? yO eee

en

PALEONTOLOGY.

PLAS ke

Page.
PALAOPHY CUS #84? <2(s oe ere ein teae eter ee eyareleieisiapesisisiare) ane Pasa aes eee See Ree ese ee ee eee 333
Fig. 1. View of a fragment of sandstone having its surface covered with the disjointed
stems.
LEN by: NOVO KON MOY. GID MIN CC ore eE co asop.caaacaodnene. Hose becnah peo obe eadKen UaobUsnEsaceaouSSS.consae 331
Fig. 2. View representing the surface of a fragment of sandy shale, with several specimens
of the species.
PALAOPHY CUS?0 CCIDENTALIG! 328.00 5s eae Ue rcier er Saisie seleiategs eve iays ra) fohen a hare tera save eaaeel eres eerste 332

Fig. 3. View of a slab of sandstone, which is covered with stems of the ordinary form
and size, some of which show the mode of bifurcation.

Exploration of the Black Hills,

( Plantae)

PLATE |

H.M. Martin. del. . T. Sinclair & San, lith. Phila.

PASE ONT Ol7OG, Ye
PLATE II.

ILINGULEPIS PINNATORMIS 2 scemiee sae ee atelsicleteleletenalojere tare aie iete (eel eietato el eaietee telat ae ae eee tees

Ties. 1, 2. Views of the dorsal and ventral valves of the ordinary form from the greenish
purple sandstone at the headwaters of Red Cafion Creek, southwest of the
Black Hills.

Fras. 3, 4. Views of two specimens, dorsal valves, from the friable sandstones of Castle
Creek, west of the Black Hills.

LINGULEPIS!CUNEOLUS <i pucecet cae seen eee ane ale ne Meee ere <tee een ee een ee eee
Fias. 5, 6. Enlarged views of what are supposed to be the dorsal and ventral valves.

LINGULEPIS PERATTENUADUS S sare sei asec om at ciate soles ores ie tate epelaele ne creeiater stale evel eae ale eee ee eee

Fies. 7, 8. Views of two dorsal valves, showing a slight variation in form. Enlarged.
Fig. 9. Enlarged view of a ventral valve.

Ii ga(eh opti obs) Gin SyWICOuNOSicNiss Ganaoo gaabee esnoanoaeaco-6sos cde Hob asda duasob ease buaKon Sauabacooe dues
Frias. 10, 11. Copies of Mr. Meek’s figures, showing ventral valves of this species.

OBOLBELAPOLIM AL os, coed ob eee ojaratojcisleysse cae wie FO See eae Diese Se rete e te Ce nee ERE eat eerie

Fic. 12. Enlarged view of a dorsal (?) valve.
Fie. 13. Enlarged view of a ventral valve, showing the prolonged beak.

OBOLELLA NANA ha.cc hs See pee Seen ve SS Ble Gian s See ie See ce See olen sicice eae Ree Se eee

Fie. 14. Enlarged view of a specimen of the broad oblate form.

Fig. 15. Enlargement of a more circular specimen.

Fira. 16. Enlargement of an elongated specimen. -This and the specimen Fig. 14 show the
extremes of variation among the specimens on one block of sandstone.

Tic. 17. View of the interior, enlarged. The figure is a copy of that given by M. & H.,
Pal. Upp. Missouri, Plate 1, Fig. 3.

OBOLUS'? -PRECTUENOLDBS) 2 oe Le sce Pee Se ee ee ae oN en rte

Fires. 18, 19. Enlarged views of two valves, one of which retains the shell almost entire
and the other exfoliated, showing the radiating lines.

CREPICEPHALUS PLANUS 227562 teen sistas ces ele eule aatis eyslae eho ease ne nanan s ois ne ee\eicle ioe erseeee
Fira. 20. View of the specimen described, showing the characters as given.

CREPICEPHALUS CENTRALIS' 73. “2k e cineca ee a fae eae

Fic. 21. View of the glabella and fixed cheeks of a large individual, showing the broadly
conical form.

Fig. 22. View of another individual, showing the narrow form of glabella.

Fiq. 23. Profile view of the last specimen, showing the elevation and curvature of parts.

Fig. 24. View of an imperfect cheek referred to this species, being associated with it on the
same block.

ARENICOLITES sp. ?

Fic. 25. View of the specimen from Warren Peak, showing the form, relative size, and
direction of the tubes.

336

337

337

339

340

338

343

341

333

Exuloration ofthe Black Hills,
‘Ww }

IPA 100,

i)

POTSDAM » . Articulata.)

Dr,
6 f%

H.M. Martin. del. T. Sinclair & Son, lith. Phila.

=

2.

a he : :
pam - tk ‘ 5
é
a f a
ae 1, i > i i in
; ie “hia a Came a cel Pes ‘ :
7 , tue’ i ‘ , te. 0 ,
: : f i H i R ein
rs x i 4
= a : 3 7 ‘
i . ate \ : LW
is a) fi
4 is
y xe ‘ cs
t - i te = Ssh
{ : — ao
i . 3 a ie
a
= i =
) ' a = pee 7 =
i. = =a wo fi Me
= x i 2 ;
\ i = ‘ e
- , i : . ,
ss . ¥ - 4
a =) . 2 E
a ‘ 7 iF c
F ‘ : ! te 7
i = f : ; ; CF ; ar = {ae
- 1
pei f ~ 7 : 5

PALEON EOLOG Y.

PLATE. LET.

PENTAGCRINITES: ASTERISCUS:, -cioeieeeictee elec ece oe See rears ete ae atone eerie eee tetera ee ee re GaSe

Fias. 1,2. Enlarged views of two of the disks, showing the extremes of variation of acute
ness in the angles of the star-like points.

ASTERIAS ? DUBIUMss-c2s0 soc suoteceece eeeo see eee mnciee team Sue cere ae deine MeSeheaiee ee ceeceeres

Fie. 3. View of a fragment from a larger block, showing three individuals, as obtained by
gutta-percha from the natural impression.

LINGULA. BREVIROSTR A: 5 << scien ae a Te me oases ae aa elese Se aetein oe is eee ea aioe mee elaine las Oe eisiae

Fias. 4,5. Views of what appears to be a dorsal and a ventral valve, natural size.

RHYNCHONELLA MYRINA..-----.- YOO0 OO0860 SUS SOS SOD e Ss CObE S500 cSdh cous S dbo SESeeS coOSeSR oS Sness

Fics. 6,7. Views of two ventral valves, showing the extremes of variation in the number
of plications.

OSTRBIA: GSTRIGIUE CUA = 2 5 cca erers re ei aerator ere creme nee eee ote ere re ep eee at eeretctt cen ceerayeteere

Fria. 8. View of the interior of an upper valve of the ordinary form at the localities men-
tioned under the description.

Fic. 9. Interior of a small lower valve of the thin, flat variety.

Fig. 10. A profile of the same individual, showing the slight elevation of the margin.

Fie. 11. External or basal view of a larger deep valve, showing the scar of attachment.

Fig. 12. Side view of another similar specimen, showing the great elevation of the margin
at the anterior border and below the cicatrix of attachment.

GRYPH4A CALCEOLA Var. NEBRASCENSIS-...--- ----.c2.2. .2-- bosthe ced6bss aoseS4sces Guooos eto

Fic. 13. View of the interior of a specimen from the Big Horn Mountains, restored in front.
Introduced for comparison.

Fic. 14. External view of the same specimen.

Fic. 15. Profile view of the same.

Fic. 16. Profile of another imperfect specimen, showing the strize of the surface.

PSEUDOMONOTMS (HUMICROLIS) ORBICUDAMAG 2 soe. esse essen eee See eee eee eee eee

Fig. 17. View of the convex valve of the ordinary size.
Fig. 18. View of a right valve, twice enlarged, showing the very small ear.
Fig. 19. Enlargement of the surface striz from the specimen Fig. 19.

PSEUDOMONOTIS; (HUMICROTIS)) CURTA. 2 jose ~ moire - i= aie nee eee 5s Soho eee Secs e eee

Fic. 20. View of a left valve of the ordinary form and size, enlarged to two diameters.

Fic. 21. Enlarged view of the right side of a specimen, showing the characters of the
hinge Three diameters.

Fig. 22. A still further enlargement of the upper part of the shell, showing the generic fea-
tures of the shell.

Tie. 23. Profile of the specimen, Fig. 21, enlarged to correspond.

Fic. 24. Enlargement of the interior of a left valve.

Fic, 25. Enlargement of the interior of a right valve, showing the character and construc-
tion of the ear-like fold in the shell,

344

346

347

348

349

356

304

~

Crploration ofthe Black Hills,

JUIRAS SIC. , wees ae
ESTE (Radiata and Mollusca.) PLATE UI,

._ H.M. Martin. del. _
T Sinclair & San, Lith. Pia,

va

Pe

Ce

PALEONTOLOGY.

Pl Aet Ey live

AVICULA (OXYTOMA)"MUCRONATA S005. ie necisecece eee ao cee eee EERE ee ericerere ecm eee eee

Fic. 1. View of a left valve partly restored, showing the usual form of the specimens.
Tia. 2. View of the right valve enlarged to twice the natural size, posterior margin re-
stored to correspond with the lines of growth.

GERVILLIA, RECTA\ i 2 Flies nes onsen ae epee ea vo alain)(atalabeyeratatone allt e rayake olay ay cts eee) pet atere acetone ee ere pa
Fig. 3. View of a left valve, natural size.

CAMPTONE COTES: BYTE NWALUS se iielsreierncs cee ee oe eee ele ae ore ee ee Oe eee eter eee ee

Fia. 4. View of a very large left valve of the species from a locality east of Belle Fourche.
Fie. 5. View of smaller specimen, from the same lcoality, from which the surface shell has
been removed, the condition in which they are usually found.

CAMPTONECTES. BELLISTRIATA. sie2 2b Same cece Sa cleos ie Sic ears alba ttietanepiaye lors cibyelsjeyeie les 6istere le ners ee raeyeereen

Fic. 6. View of aright valve, the surface partially exfoliated. From Belle Fourche.

Fig. 7. View of a left valve, imperfect on one side, showing the surface striz. From Belle
Fourche.

Fic. 8. View of the interior of a large right valve from Big Horn Mountains, showing
the features of the type form of the species.

Fic. 9. Exterior of a left valve, showing the surface strie.

Fig. 10. Exterior of a right valve; no strie are visible on the specimen, whether from exfo-
liation or naturally so is not readily determined. All right valves seen have
the surface smooth.

Fie. 11. Enlargement of the surface as seen on specimens Figs. 6, 9.

IPA OSUOING INTO BED a (oe Som poboro doSobe CoSEed obuabD doud6 Gooo uodabe SHad OUCH SoU ooddcued obadgn0bes
Fic. 12. View of a left valve, imperfect on the anterior side of the cardinal line.
Fig. 13. View of another individual, showing the entire form.
Fic. 14. Enlargement of the surface, showing the elevated concentric striz.
Fic. 15. View of aright valve associated with the preceding, and supposed to be of the
same species.

308

303

3

3

1

0

Exploration of the Black Hills. .

PILE IY.

JURASSIC. 2
( Lamellibranchiata.)

—s

3
MAL

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T. Sinclair & Son, lith-Phitla.

H.M. Martin. del

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: : 1

PALEONTOLOGY.

PLATES:

TRAPEZIUM, BELLEKOURCHENSIS = cs5sss seen ccc aan see sees] iecenen casera eae
l1G. 1. View of the left side of a specimen enlarged, showing the usual form.
Fig. 2. Outline cardinal view of the same, slightly restored at the anterior extremity.
Fig. 3. View of aright valve, imperfect, of a broader form, and showing the cast of the
anterior muscular imprint.
Fic. 4. View of the left side of a broad form, showing the outline entire, but imperfect over
the body of the shell.

TPRAPEZIUM SUBEQUAMLIS, 25-f dc) nus seele ae eee cate seis eerie ee eel erence eee oe eee ere
Ira. 5. View of a large left valve, natural size.
lia. 6. A right valve of slightly different form.
Vic. 7. Enlargement of a similar right valve, but more constricted on the basal margin.
Fic. 8. Outline cardinal view, restored from the last specimen.

MYcRILUS WHEDEL «222 saison alee eee ete ere Oe eee ee Ce Eee eee eer SGbbOGeSnD cBaoae
Fic. 9. View of a left valve of the ordinary size.
Fia. 10. Profile view of the same, looking upon the buccal side.
Fic. 11. View of a right valve, which is slightly more arcuate than Fig. 9.
Fig. 12. View of another left valve, which is even straighter than Fig. 9, and has a less
oblique hinge.

ViQUSIELILAs PICK TIENT ES ree oo ote sere aisha ees ce hs oe as ERS Te eee Fe ade

Fic. 13. View of a left valve, natural size.
Tia. 14. Profile view, constructed from separated valves.

VOESHLUAN (MODIOLA))) HORMOS Were = selena) arses sieeiete celeste bo oodd abo5 DebadSeDca5 cocSoNSéS :
Fig. 15. View of a left valve of small size.

(CARA ROVONAROOYONS TOKOLUNPAGNOS Coe b do uooddd sooo dobSss Scdco odasce noUSat Gosescobno nde Stn sobossucona
Fic. 16. View of a right valve, natural size, showing the prevailing form and size, also
showing radiating strie.
Fig. 17. An enlarged view of a cast of a left valve, showing the hinge features as seen on
the cast.
Fic. 18. Outline cardinal view as constructed from separated valves.

PETER OMSYAGNE W LOND oc aie atcccicjoiey a oe eee errr eee ere aes ese ee wees cacceaee

Fig. 19. View of a left valve of the prevailing form.
Fia. 20. View of a larger right valve.

DOSINTANTIURASSIOAG Tee meena wasps sieve cielo ioeeattats pddddocsoubcodse SE DOS0 saesod beego”
Fras. 21,22. Views of left valves of the usual form and size.
Tig. 23. Cardinal view of the specimen Fig. 22.
Fig. 24. View of the cast of a right valve, showing the pallial line and sinus.

SAXICAVA, JURASSIC: [i082 5. o's ol Se maaeiee sei ajsin ce melee te = Seen ae eeT= ice eer eee ree

Fig. 25. View of an internal cast, natural size.

Fic. 25. View, enlarged, of the left side of a specimen retaining a portion of the shell, and
showing the pallial sinus on the cast.

Fic. 27. Enlarged cardinal view of the specimen, Fig. 25, showing the angularity of the
umbonal ridge.

Ties. 28,29. Enlarged cardinal and right views of a large individual, retaining a large

part of the shell.

Fie. 30. View of one of the casts of the burrows as separated from the surrounding clayey

matrix.

2

IPSA MM OBTAN PRE MAT UIRAG seeps (cisieselosie somes ates ope ee ee eee EAE nese sr

Fic. 31. View of the specimen described, which is an internal cast, showing the muscular
imprints and pallial line.

ASTARTE) (2) RA GEIS coco cee yay eas ee mesos os ee em ay See RS a anaes ti ae

Fries, 32,33. Right and cardinal views, enlarged, of a specimen which we have supposed to
belong to this species.

ERA CIA." SUBLE VAS rs. Soe ste e etme Caetano clere acon ten ein ee ae lereisiats Sep Ieee eis eee me

Hig. 34, View of a right valve referred to this species, by error on plate, made Fig. 24.

NEZGRA{ LONGIROSTRA oh ales Se Ree eee TE ee eo le a re ren, ne Sr

Fic. 35. View of a left valve enlarged, showing the characters of the species. .

365

360

362

361

309

367

373

374

363

375

376

ton ofthe Black

MURBAS SIUC, PLATE V,

(Lamellibranchiala.)

1

Sinclair &San, lth. Phila

PALEONTOLOGY:
PLATE VI.

AVX COR ODDION TOS HOV Gee eoccecodgeaboKe 656600 Cosco 9ecdeDS DodScomOGs GbO00D 6556 be 5ee s5oe00 sB6600 370
Fic. 1. View of a right valve enlarged, showing the prevailing form.
Fic. 2. A left valve slightly more extended at the posterior end.
Fic. 3. Outline cardinal view, showing the convexity of the valves.

LUGO SIDI UN WP NMI SINPNINI C3 oe 65 coco dosede 680595.0060 5000 code Géc0 GUDG 4005 soeS56 ao0a DHaT SH DODO OACS 372
Fig. 4. Enlarged view of a right valve, showing the features of the prevailing form.

TANCREDIA CORBULIFORMIS © ee - = -isyerse eine =i a oe a neeelelalal= Boo UNge o2d0 cosa dosaaad Goon oné0 370
Tia. 5. Enlarged view of aright valve.
Fig. 6. Enlarged view of a left valve.
Fic. 7. Enlarged view of the right side of an internal cast, showing the muscular imprints.
Frag. 8. Cardinal view of the same specimen.

MAN GREDIA (2) INORNADAl note a syesete nse ore as oa eV tee ere a le op rene a NB eee 368

Fig. 9. A right valve, natural size, showing the general features of the species.

Fig. 10. View of an internal cast of a left valve, showing the form of the muscular imprints

and a pallial sinus.

Fic. 11. View of a larger and proportionally longer left valve showing a slight differ-
ence in the pallal sinus, and may, with the change in form, indicate a distinct
species.

Fic, 12. Enlarged cardinal view of an internal cast, showing the impression of the cardinal
and a lateral tooth, and the muscular scars.

Fic. 13. Enlarged view of another specimen preserving the shell along the hinge, and show-
ing the projecting cardinal tooth.

MAN GREDIA: POSTICAM = Se)c-baanishecie 5 sales je CO Oee oe nie Sie tans SS EE EU ee cies tee eee ee eee eens 371

Fic, 14. View of a right valve, enlarged, showing the great breadth of the posterior part of
the shell.

IBELEMNITES DENS US ost ote teeta | ee SP Tis a Pe Pog ce gs 381

Fie. 15. View of a young individual.

Fic. 16. View of a large specimen broken off near the base of the alveolar cavity.

Fic. 17, Section of the upper end of the specimen, Fig. 16, showing the excentricity of the
alveolar cavity.

Fig. 18. Longitudinal section of a specimen, showing the concentric layers.

Fic. 19. Longitudinal section of another individual, showing the phragmacone in place,
with some of the septa preserved.

AMMONITES CORDINORMIS: emcciise ee ceeats seals occ cep ee sa ee Sep eee tere see Eee eae aieeriace 378
Ties. 20, 21. Side and profile views of a moderately sized individual, showing the prevailing
form.

Fic. 22. View of a small specimen from the Big Horn Mountains, in the collection of the
Smithsonian Institution.

Fic. 28. View of another individual, showing a different arrangement of the costa.

Fig. 24. Diagram of a septum, copied from the Pal. Upp. Missouri, Plate v, Fig. 2 ¢.

AMMONITES CORDIFORMIS VAR. DISTANS......-.---.--- ERS HEFO OES BOC Sc GSR Srne Bae OSU OcEA 380
Tic, 25, Lateral view natural size of the specimen used in description,

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Lamellibranchi

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PALEONTOLOGY.

PLATE VII.
Page.

SYNCYCLONEMA. RIGID A | Hi & Miyata ae foe elcctosleicieielcle scl sraia is te 7ore ats alallata tate’ sateen ese tne eer mS

Fig. 1. Enlarged view of an interior cast of a right valve, showing the filling of the carti-
lage pit and what appears to be the muscular impression.

PTERIA LINGUIFORMIS “B82 'S 223s ce mee oer eee sere leaisleciolsiee Sanne bce ee oo ante Re ee EEO.

Fia. 2. View of the left valve of an imperfect specimen.
Fic. 3. View of the right side of the same, showing the muscular marking and pallial line.

PTERTA)(OXYTOMA)) NEBRASCAN AG Bi Oc) Sisee ne eerste leeeieee seat ieee tee ice ee eer eee ee eee CD
Fic. 4. View of a large left vaive, natural size.

PTERIA (RSEUDOPTERTA) | EIBROSAN Meier Ele a cenion sseiie eee eisai ea eee eee ee Oe
Fig. 5. Restored view of a left valve.

= PTERIA (PSEUDOPTERIA)|SUBLEWISs Wihitfieraemeer aereal-ctsi ei oeieeie cise nie enim cet) eee eee ee
Fic. 6. View of left valve of the ordinary size and form, preserving the small anterior wing.

TNOCERAMUS: BARABINT | Mortons acc. ccic. torsion otee oe ens Ses See ole ene See ee Be EC Boe eee 398
Fig. 7. View of an imperfect right valve of this form.

INOCERAMUS VANUXEMI (M. & He 2 32253 -os-eeccrae ste. scl eee fee See ene meee ee eee 396, 398

Fic. &. View of a small individual representing the var. subcircularis M.

Fia. 9. View of a left valve representing the form referred by Mr. Meek to I. proximus
Toumey.

Fie. 10. View of a left valve of the variety described in this vol. p. 398.

INOCERAMUSSPROBLEMATICUS) SChlot wissen nese secret eer eeeteeieeteaiciseehiecerses eee eee eee 389
Fig. 11. View of an imperfect specimen of a right valve referred with doubt to this species.

JNO CERAMUS/SAGENSIS (OiGuccias Fes Soe om bo ceee renee ee OE EEGs See eR eee ee eee 393

Fig. 12. View of a right valve of rather large size, presenting the ordinary features of the
species.

Cxwl

CIO LACE OUS (Lamellibranchiata. )

loration ofthe Blick 2

a)

H.M. Martin. del. T. Sinclair & Son, lith. Phila.

PALEONTOLOGY.

PA ih yer:

INOCERAMUS | SIMBSONT -Meéeks S35 csioe Soee oe eee eee Ora ae ee eric oe ree ee

Fie. 1. View of the right side of a specimen, showing the form, size, surface marking, and
radiating lines of pustules, and also an area representing the muscular impression
near the postero-basal margin.

TINOCERAMUSISNGENSIS RO msc tiie seiner ee cieiemisienea = ieee eeeln ear neee arse role) aise rere erteter
Fic. 2. Cardinal profile view of the specimen, Fig. 12, Plate 7.

TNOCERAMUS:PERPEB RUS) Wihithie seserc -e ocnins Se neniens ce eee ee eee ele Ses rer oe en Cee eee
Fic. 3. Anterior profile of the specimen, Fig. 5, Plate 10.

LBXCOLel WAN TOFS Vuelo GON OC NG GO 18S o5565 sas5os ceed S600 coe B60 cbao0n caos oseodeEeay Sa00 aausceReDsCO
Fia. 4. Cardinal profile of the specimen, Fig. 8, Plate 7, var. subcircularis M.
Fic. 5. Cardinal profile of the specimen, Fig. 9, Plate 7, representing the form referred by
Mr. Meek to I. prorimus Toumey. (In a letter to the author, Mr. Meek stated that
he is very doubtful of the correctness of this reference, not having seen Professor
Toumey’s specimens, which were never figured. )

393

392

396

Se [op UyaAeW WH

ey 6 . (Pyepurrgypour
WAL eld alt SANO ALVA ed

Yon] Up wl 0! Ut oR Vi)

PALEONTOLOGY.

fA exe

Page.
HINDOCOSTHA TYPICAY \VV Mit fee ar =e sers eee alo ate meee ele eee eat aia see ae 403
Fig. 1. View of a cast of a left valve of medium size, with the ridge extending to the edge
of the cast.
Fic. 2. View of a partially exfoliated right valve, showing the impression of the ridge in
the upper part and the substance remaining below, but easily traceable.
Fig. 3. View of a larger right valve, retaining about one-half of the substance of the ridge,
the margin of the remaining portion being very perceptible.
Fic. 4. View of the left side of a still larger specimen, partially exfoliated, showing the ridge
less developed. A part of the shell here remains, which, if removed, would
make the impression still deeper.
Fig. 5. Cardinal view of the specimen, Fig. 4, showing the right valve the largest.
Fie. 6. Outline cardinal view of the hinge of a small individual, showing the area after
the fibrous coating has been removed.
Fic. 7. View of the interior of the left side as obtained by a gutta-percha impression from
the natural cast.
TNOCERAMUS BARA BING or seco reece oes cinta rein) = alctntnl sas eRe atone ne erect se eee reise 398 |
Fia. 8. View of a specimen of the form usually referred to this species, from this locality,
showing the muscular impressions, anterior and posterior.
INOCERAMUS SIMPSONI? Meek... ---. --------2- -- 2-2-2220 22 22 ons oe eee oo ne ee ee ee eee ee =- BD
Fie. 9. View of a young, slightly distorted specimen, referred with doubt to this species.
[NOCERAMUS!PRAGIUIS Ei idcaMl 5 22 oo0 2 cniseeee on cnisivicieis sos CREE eee elsibine shame steeeeie ee eee eee 390
Fic 10. View of a large left valve, having the characters of the type of this species.
LOCI PANTO NEMO Wh OS Isles os se6ese nbosds o5e6 Goaces desoso code 506 socOUd cabs poooodoosososeos 391
Fic. 11. View of an imperfect left valve of this species.
INOCERAMUS TENUILINEATUS JH. (Ge Mio 22 so jens esice einiciclowice osfeeceleneeie cielsise eae ee eee eee 400

Fic. 12. View of the right side of a large, well formed specimen of this species, preserving
a rim of the outer fibrous coating around the margin of the valve.
Fig. 13. Anterior profile view of the same, showing the great rotundity of the shell.

PY

y

ploration ofthe Black Hills. .

(Lamellibranchiata.)

—
T. Sinclair & Son, th. Phila.

ok

PALEONTOLOGY.

PLATE X.

INOCERAMUS|SUBLE VIS) Ha Ge Mire co = erence ep es eee ae ie eee ere on(ae elaine eee eee eee ee

Fic. 1. View of the right side of a specimen retaining both valves, and most of the nacre-
ous layers of the shell.

Fic. 2. View of the left side of an internal cast of both valves, showing the pustulose mark-
ings of the surface and near the postero-basal margin, what is evidently the
muscular impression.

Fic. 3. Cardinal view of the same cast, showing the convexity of the valves.

INOCERAMUS PERPLEXUSWIW Hith iesels ee nag oa ce Sere ere eee eae

Fic. 4. View of an imperfect left valve, showing the general form of the shell and the
undulations of the surface.

Fia. 5. View of a very perfect right valve, retaining all the features of the nacreous shell.
The profile, Fig. 3, Plate 8, is of this specimen.

ENDOCOSTEA SULCATA Reemer= i)... [50s Sea oe imintere te eer oe tec alee a eee ee eee

Fic. 6. View of the left side of an internal cast of both valves, showing the right valve
projecting above the left, and also the sulcus of the left valve.

VENTEGEA HUMILIS! Mu 0H #2. o-oo cece 3 core ee ee eee one ees os See Se eee

Fic. 7. View of the exterior of a right valve as obtained by a gutta-percha impression
in the natural mold.

Fig. 8. View of a specimen retaining a part of the natural shell.

Fic. 9. View of a cast of the right valve, showing an elongate form.

Fie. 10. The left side of a specimen of the ordinary form.

Fie. 11. The right side of a more quadrate form.

Fic. 12. Anterior profile of a cast showing the muscular impressions and marks of teeth.

Fie. 13. The interior of a left valve as obtained from a gutta-percha impression in the
natural mold, showing the teeth, muscular impressions, and pallial line.

SPH@RIOLA TRANSVERSA With geese os oee- seeeeric sete eee ose e nl cece ceee eae ees eee
Fie. 14. Anterior profile view of an imperfect individual retaining both valves, showing
the convexity of the shell.
Fig. 15. Lateral view of the left side of the same specimen, with the beak of the right
valve in outline.
Fig. 16. View of the interior of a left valve as obtained from a gutta-percha cast in the
natural mold, showing the hinge and the muscular impressions,

Page.
393

392 |

404

414

415

ls,

oy
U

if

|

la

(Lamellibranchiata.)

B

ed

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ith

Exploration o

ala.

th. P.

PLATE X.
ii

T. Sinclair & Son,

.Martin, del.

rc

CRETACEOUS

H.M

Pe
= Vet giee

PAE ONE Oa O1G Ne
PLATE XI.

YOLDIA BVANSI M.. & H-.----..-- So adoocs0 ss gc5e Sage BESS De SsS os Stes cacsas shes cadonddoos soba 409
Fig. 1. Enlarged view of a cast of a left valve, showing the teeth, muscular imprints, and
pallial line.
Frc. 2. Enlarged outline cardinal view of a specimen retaining the shell, showing the
groove extending along the hinge.

NUCULANA SUBEQUIDATERA, Whitt sii ono ctasjonc ieee eee e teclale aeieiee ne eiete ao ere eine te eerstaee 408

Fic. 3. Enlarged view of the left side of an internal cast, showing the form and muscular
imprints.
Fic. 4. Eniarged cardinal view of the same, showing the impression of the teeth.

NUCULAVPLANIMARGINATA Mis cE 3s esc a sonic oer see eae reeks eae oe See eee ee eee nee 406

Fra. 5. View of the left side of a partially exfoliated specimen, showing the general form.
Fria. 6. Enlarged cardinal view of the same, showing the impression of the hinge, along
which the shell is more completely removed.

INMOKOLOT UNA IST ISTOR ELON Is (8 JEL como bas eoo cadoor soe5 soosee Bees soba Done Sonn bods ocoees BSE 5086 gone = ENDL
Fic. 7. Enlarged view of a specimen, showing the form and surface markings.

IDONEARGASHUMARDI Miu Geiss 2he ee ees ee Bae aes eta iste es oe ea esey SL apa Gone 405,

Fic. 8. View of the right side of a specimen of'medium size, showing the form and general
character. >

Fic. 9. Cardinal view of the same, showing the cartilage area.

Fic. 10. Posterior view of an internal cast, showing the impressions of the ridges bordering
the muscular imprints.

Fic. 11. View of a large individual having the valves a little displaced and showing the
posterior hinge-teeth.

CRASSATELTA SUBQUAD RAMDAC Wihiliis = 9455 eee Mer ac ee ern aaa e eee eae See eee ae eee 412

Fic. 12. View of the right side of the cast, natural size.

ASTARTIS TWANG IY Ed Me seeing ecole rotor etc iininia ce See eee it aechon Sea eee ee ieeree eee 413
Fie. 13. View of the right side of an internal cast, showing muscular scars, pallial line, and
crenulated margin.

TU CINABVAENTRICOS Amel aocy Vleees ernie ter eee ease eeieceeaare Soko CobebS DUGEES Sae5 sangea Seno bac 410
Fig. 14. View of the right side of a well-formed specimen of medium size, showing the
general character of the species.
Fig. 15. Cardinal view of the same, showing the cardinal depressions and ligament.
Fie. 16. View of an internal cast of a large individual.

LWCINA (DIRLODONDA) SUB UNDAUIDAT Endzg Meter meses aaa eae eeem alae eae ee eeeeetseree ences 411
Fic. 17. View of the right side of one of the larger individuals, showing the narrow, curved
posterior slope and anterior furrow.
Fig. 18. Cardinal view of the same, showing the ligament and depressions.
WUCINAsOCCIDENTALIS Mort) 2.25. o/c Sac 22 seo eee eae eee oe eran gacose Kab6DS 409
Fie. 19. View of a well-formed specimen of typical form.
Fic. 20. Cardinal view of the same, showing the almost obsolete lunule.
Fig. 21. Internal cast of a small individual.

THETIS:CIRCULARIG: Mi & Hisee= Sete ac) See ee Seen oc eee ey net ios ioeen oc eeeeriet eee = ANE
Fic. 22. View of the right side of a specimen of ordinary form.
Ira. 23. Cardinal view of a similar specimen, showing the incurved beaks and the convexity
of the valves.
Fia. 24. View of a partial cast, showing the character of the pallial line and sinus.

DOSINTIASMISSOURIANA (Morty? 2 ry Se anata are Coaepeyotep erm, ale heel 2 apy ogee re ee ore arene ne aisiec eieeeee = 416
Fie. 25. View of the left side of a specimen referred to this species.
Fig, 26. View of the opposite side showing the pallial sinus.
LEIOPISTEVAs(C Sane A) Mion ian Wh ities Se ecce salar aoe sais oe eee Cee REE Co eer ere 418
Fic. 27. View of aright valve of the species, natural size.
Fic. 28. Cardinal view in outline, showing the areas bordering the hinge, over which the
rays and concentric folds do not extend.

THRACTIA SUBGRACIEIS W Litt... -c Sank. cei citee ie eet = rs eee IO eee sae eee eee eee eae 419
Tia. 29. View of the right side of the specimen, showing the form, and the slit in the beak.

Tig. 30. Cardinal view of the same, showing a slight twisting of the valves in the crooked
hinge line.

INH WON NICO IOV MODS Hf Wilh wy IBY See Bao Goace ao accede caoaceeseq cbbab sHsesa000 Sacdse0 o305. 50506 420
1G. 31, Enlarged view of a left valve, showing the features as described.

Cxuloration ofthe Black Hills.

CRIBLACKHOUS. (Lamellibranchiata. )

PILLAI XC.

H.M. Martin. del T. Sinclair & Son, lith. Phila.

iy
MA $i

Cae ee

Weare tsar yan a:

PALE, ONE OmMOG Ne
PDA Xr

APORRHATS! (GONLOCGHEIUA)ICASTORENSIS i WiDItiaseeee ieee Seer eee ete eee eee ree
Fig. 1. Enlarged view of a specimen, showing the extent of the posterior canal along the
spire. The expansion of the lip is seen a little more extreme on one other indi-
vidual. §
AN CHURAG(DREPANO CHETEUS) ENEIBRASCENS IG i ie Qc Se eee ee eee tere ae
Fig. 2. View of a small individual, the labial spine strongly directed backward.
Ia. 3. A larger individual, varying somewhat in the form of the labial projection.

APORRHAIS NEWBERRYD Meeks 22/5 2275 )o cee atte tees a raee oe ae ar ee Sr eee ge
Fic. 4. View of a specimen imperfect at the anterior end, but showing the labial spines for
some extent, though broken, and the posterior canal extending beyond the top

of the spire.

APORRHAIS MEEKTWihib R= (22 meeemmecs eter sce =o eie eae ese eee eee eee ee eee eee eee

Fic. 5. View of the imperfect specimen, which, however, shows the characters of the
species.

AANCHURA: ? SUBIE VIS! Mii& Hitceeoece reer sce eee eee ea eerie rere piemierae Sze Winget lecelnee Se oee

Fig. 6. Enlarged view, showing the features of the species generally observed and the
stronger varices on the right side of the second and third volutions.

FUSUS SHUMARDIOH:, & Mion 5.52 Bees cis ey eae nso aad eae aie ae ee eel ae ete heise eee ee ees

Fic. 7. View of an imperfect individual, preserving the strie in part.
Fic. 8. Enlargement of the surface.

FUSUS CHEYENNENSIS W bitfiiaasee cs ccin cece ce wate os ol sts Se oe See eer ee seu oinie seis sieneeyserereee re eeeeee
Fic. 9. View of the specimen described, which is an internal cast.

PASCIOLARYAN(CRYTORHYATS) ICONTORTAUMeels is Paceencee seen eee eee ee eee ene ase eeeeee

Fic. 10. View of an imperfect individual, preserving the two lower volutions, and showing
their form and surface characters.

BASCIOLARIA: (PIESTOCHELEUS) (CULBERTSOND Mondor bliss soe eerie ere semis isis iaee ales ee seine

Fic. 11. View of a specimen, preserving the two lower volutions, showing the surface char-
acters and form of the aperture.

HAS CIOLARIA (CRYTOREVLIS) USTRORMIS Elec) Misses ere seel ses ee tenes ee sae eee eee eee

Fic. 12. View of a fragment from the collection of Dr. Newberry, showing the lower volu-
tions with their characteristic markings.

IOAN GN Ofor(C1osiRO, aly es Wisp cose Sa05 sous soND ODED onoo edad sade coouGoEaaS mcSCD Saco o4o0 se tose
Fic. 13. View of a specimen of the species, showing the form of shell and aperture.
VANIKOIUA AMBIGUAN NIA Gusta, sere ene aise ee eiselse ciieeienicc mekcinieistaieie a ecae te see eae eee nineeere ees

Fic. 14. View of a specimen, enlarged, showing the character of surface and form of shell.

MUNNECNOIGY Nipor CORN ATC WI5 Gz 1als ce ea es cesd Sosa oseGds SHUb C4de Sec Se sHonDE coEg.GusS coup dbEgéoos
Fic. 15. Enlarged view of a specimen, showing the general features of the species.

AMAUROPSIS LALUDINASRORMIS Eladc Mie see eee eee cos coatesce eee nie eceree ne eee eee eee eer

Fic. 16. View of the back of a specimen, natural size.

ANUS OMY ON PARE DEMO RNS) Min ac Else ase eee SAG poR 6 dob aaaepanceocseberaasaon
Fic. 17. Vertical view of an internal cast of this species, showing the muscular impression.
Fic. 1. Profile view of the same, showing the elevation of the beak and its anterior posi-
tion.
IANTS @MGY.O.NISUIB OWWASUS Milo Ge Mle aeons ete ee alee re eee he ee leet eee
Fic. 19. View of a cast, showing the form of the shell and muscular imprint.

ANTSOMVON- AT: VBOLUS EM Gombe a cerses steers. senate ee eee ie ieee sae ee eee ee
Fic. 20. Vertical view of a partially exfoliated specimen, showing the muscular imprint
in part.
ANISOMYON BOREALIS Mort... -..----<- <0 -- 02 5-2- ccs ene = ono = oe eee we oe oe ne oan nie alenlmnnl=~ =
Fic. 21. Vertical view of a specimen preserving a part of the shell.
Fre. 22. Profile view of an imperfect specimen. retaining the shell.
Fig. 23

WwW W 2

3. View of a fragment, showing the radiating lines.

EDAMINIDA: SUBGYLINDRIGA Min So lisse ectecre 3 nce win foe wees eae tea ere le ml miele alata ole ial amin mle le
Fic. 24. Enlarged view of a specimen, showing the surface features and form of aperture.

AKERA GLANS-ORYZA Whitf...-- Fe oen SHE RBE HIE Be CGE DOU 5 ca eaO CHURN 2O0SbS atuede SBUEEaDSECOD C056
Fic. 25. View of a specimen, greatly enlarged, showing its form and characters.

DENTALIUM GRACILE H. & M..---- -2---- -- 2-2 2 oo = eo eee noe oe ne oe nn nn nn nee rece ne teen ee
Fig. 26. View of an imperfect specimen, preserving the features of the species.

SS ee alae te ea RT. SS ae

429

426

428

424

424

422

423

421

430

430

432

431

435

434

433

436

437
437

438

Crploration ofthe Black Hills.
ORBLACHOUS ( Gasteropoda 5) PY. MOE ACC,

ee
a
s

Mariin. del.

™ Sinclair & Son, lith. Phila.

PALEONTOLOGY.

PEATE. XL:

SCAPHITES: WARRENT MGC] 2.2 cis tee Shes eee re er es aa Sag eT ene

Fig. 1. Side view of a small, entire specimen, showing the costie of the deflected portion
directed forward more than is usual in this species.

Fia. 2. Lateral view of a large individual, with coarser cost than the last.

Fic. 3. Profile view of the same, showing the ventricose form of the volutions.

Fia. 4. Diagram of the second septum from the outer chamber of another large, imperfect
individual. Enlarged to two diameters.

SCAPHITES WY OMINGENSISUMeek 22052 oat Sateen See calutaes oes ys tieleisins See ei oeree eo eet See
Fie. 5. Lateral view of a specimen of the usual form and character of the variety as
obtained from the Black Hills.
Fic. 6. Lateral view of a larger individual, slightly imperfect at the aperture.
Fie. 7. Vertical profile view of the last specimen, showing the narrow inner volution.

SCAPHITES NODOSUS VAT B REVS) Me kee aee en rsiees ese eee eet ole aera ee
Fic. 8. Dorsal profile of an imperfect, septate portion of a large individual, showing the
markings and the relative thickness of the volution.
Fie. 9. Diagram of one of the outer septa enlarged to one anda half diameters, showing
the general features of those of the group.

SCAPHITES NODOSUS Vials QUADRANGULARIS Ma Goll oeeen eeeecetoene ne seeeaee eee eee eee

Fig. 10. Lateral view of a very perfect specimen, showing the features of the variety as
obtained at this locality.

Fig. 11. Profile view of the same, showing the flattened dorsum.

Fig. 12. Lateral view of a large individual, imperfect at the aperture, but presenting the
characters of Dr, Owen’s typical form.

446

443

443

441

Exploration ofthe Black Bills.

CRETACHOUS (Gepharoncda) PLATE XMM.

H.M.M.& RP.W.del. 'P. Sinclair & Son, lith. Phila.

Sst ean

PALH ONTOLOGY:

PLATE. XV:

PRIONOCXCLUSEWiY.OMINGENSISUM ee keane tote Sen pees Ee ne er tener sete siece = acess ce eeee 440
Fic. 1. View of a small specimen of the species.

Tig. 2. Back view of the same, showing the carina and continuation of the ridges.

Fig. 3. Lateral view of a larger individual, showing the arrangement of the coste.

* HELICOCERAS (HETEROCERAS ?) SIMPLICOSTATUM Whitf.-..-...-...-.-------------=-- (See foot-note.)
Fic. 4. View of the fragment, showing the features described.

HERICOCERASISTRVENS O NTMI beer a> seeens ee sere ei aan eee mee eae eee eee nariteer ies 447
Tic. 5. Lateral view of a large specimen, showing the features of the shell.
Fic. 6. View of the opposite side of the same specimen.
Fic. 7. Basal view of the same, showing the size of the umbilicus.
Tic. 8. Diagram of the dorsal and first lateral lobes of a septum, together with a part of
the second lateral lobe, as far as could be obtained without endangering the
specimen. Enlarged to two diameters. Obtained from the middle volution of
the specimen figured.

HETEROCERAS 2) NEBRASCENSIO Mtr Gz, icles fase eet eee ete a eeeetatete alateataiarsaisie eles tela ar 451
Fic. 9. Diagram of a septum from the lower volution of the specimen figured. Enlarged
to two diameters. See also Pl. 15, Fig. 6.

* The fragment figured is the non-septate portion of a dextrally-coiled shell of large size, marked
by simple, angular, revolving cost, which are nearly vertical on the dorsal side of the shell, and distant
about an eighth of an inch between crests. Intercostal spaces concave. At somewhat regular distances,
of about one-fourth of the revolution, there is a distinctly stronger costa, which is irregularly nodose
on the dorsum. Septa unknown. It is a distinct and strongly marked species.

Formation and locality.x—In ferruginous sandstone, East fork of Bever Creek, Black Hills. Fort
Benton Group.

i AY.

my

LX

ID

ovUs,

a
4

ACH

CRE.

Cephalopoda.)

PALEONTOLOGY.

PLATE XV.

HETEROCERASENEWLONT VOC eeeae eee teeseneeterssiae see Serer eeeecese rent eee nee eae
Fias. 1, 2. Views of the opposite sides of the type specimen, showing the rapidly expand-
ing tube, and preserving the surface characters.
Tia. 3. Vertical view of the same individual, showing the broad umbilical opening and the
commencement of the deflection of the outer end.
Fia. 4. Diagram of a septum from near the larger extremity of the specimen. Enlarged
to two diameters.

ANCYLOCERASHJENNE VA: Wihitb oes ees onto niece eh ee ales Clie horete ne Neste rate ee eerermie che nei te otesanetere eee

Fie. 5. Enlargement, to one and a half diameters, of a septum from a small fragment of a
specimen, showing some variations as compared with tliat shown on Plate 16,
Fig.9. See also Pl. 16, Figs. 7-9.

HETEROCERASE A NIEBRAS CONS Te Msn hemlet ieee were te rele rc oe ater ore ee ee ee eee eee

lig. 6. Lateral view of a specimen referred to this species, showing two volutions of the
septate shell. See also Pl. 14, Fig. 9.

ANCYLOCERASETRICOSTATUS: Wihlbte meee eis =tekene nitsee te oelnen ee ere ee etree beer ere einatse errr
Iie. 7. Lateral view of the fragment, showing the triplicate character of the costs, and
the obtusely triangular nodes on the dorsum.
Fic. 8. Enlarged diagram of a septum from near the commencement of the outer third of
the fragment. Two diameters.

452

451

454

lbs,

Qe
ne

e
Bi
I

lack

=
i
Als

4

Wot the

rp laratio

x

€

wa
2

XY

v
ut)

PLAT:

Cephalopoda. ).

ovs

1
1

ROB UACH

Cc

Sinclair & Son, lith. Phila.

a

del.

HM.M.& RPW.

Renn

PALEONTOLOGY.

PLATE XVI.

PTY. CHOCERAS-MEEKANUM > Willits 22. osreb eres ates ce ere ae ee ee ice aia ee ere eee EE eee

Fie. 1. Lateral view of a specimen preserving the curved extension of the smaller limb, and
also showing the commencement of old age characters, in the closely arranged
rings near the outer end of the larger limb.

Fig. 2. Diagram of a septum from just within the bend of a similar specimen. Enlarged
to two diameters.

PTVYCHOCERASICRASSUMOWibitis. i cae cats sctecse mec neeiae wise ce wise in ei Cie ic Sie ees ela ina elves eee

Fic. 3. Lateral view of the specimen described, natural size.

Fic. 4. Dorsal view of the same, showing the features of this part of a shell.

Fie. 5. Diagram of a septum from another individual, enlarged to the same extent as Fig. 2.
Fic. 6. Sectional diagram of the specimen, showing the thickness of the shell.

ANCYLOCERAS JENNEYI Whitf.-....- SES OS Ae ee eee ee ets etn 5 cog menbos SamoEe dooE Saco
Fic. 7. Lateral view of a specimen of the species, preserving an outer volution, and parts
of the inner smaller coil.
Ira. 8. Dorsal view of the outer part of the same, showing the ranges of nodes, not exactly
the same on the opposite sides.
Fig. 9. Diagram of a septum from near the middle of the larger coil. Two diameters.
See also Pl. 15, Fig. 5.

INAULILUS iD ERA Sal aM ON DAINIADNGTS o IM CC avaps oeterepe ai mae ecie) tree att aT pe at

Fie. 10. View of the inner side of a specimen, showing the breadth of the shell and the
distance of the septa.

Fic. 11. Lateral view of the same specimen, showing the rate of increase in the coils. The
apparent umbilical perforation arises from the exfoliation of the shell.

Page. —
457

459

452

439

hax

J

he

i
1,

Exploration of

( Cephalopoda.)

CRETACEOUS

U. 8. GEOGRAPHICAL AND GEOLOGICAL SURVEY OF THE ROCKY MOUNTAIN REGION.
J. W. POWELL, IN CHARGE.

MICROSCOPIC PETROGRAPHY

OF THE

BLACK HILLS OF DAKOTA.

By J. H. CASWELL.

469

CHA PER V Pl.

MECC O SCOR TC PE ERO G RAP HY:

By JouN H. CASWELL.
SECTION I.
QUARTZITES.

Quartzite is a granular to compact mass of quartz, having in general a
splintery fracture and a white or gray color.

Granular quartzite is made up of small to minute grains of quartz,
always possessing, however, a crystalline structure. It is difficult to dis-
tinguish it in certain phases from a crystalline sandstone; and in some cases
the quartzites resemble the sandstones, although the cementing material is
always wanting in the former. Again, some quartzites undoubtedly contain
rounded grains or pebbles of quartz.

Schistose quartzite consists of a compact mass of quartz, which splits
with more or less ease into plates, having also a somewhat stratified struc-
ture. This is occasioned by the presence of crystals of white or brown
mica arranged in parallel layers. These rocks belong really to the schists,
and pass into mica-schist by preponderance of the mica. In the other
extreme they are pure quartzite, when the mica is present in such small
quantities that it may be considered a secondary ingredient. The mica
crystals are often very distinctly grouped in parallel rows.* This structure
was observed in the quartzite from Rapid Creek [73], which has also an
indistinct schistose cleavage, although there is no stratification visible to
the naked eye. The granular variety of quartzite is represented by the
rocks from Hall’s Cut-off [38] and from Hall’s Water [209], which are highly

* Zirkel, Lehrb. d, Petrographie, I, p. 277.

471

472 GEOLOGY OF THE BLACK HILLS.

crystalline and have rather a splintery fracture. There is some mica pres-
ent in equally distributed crystals, but not at all grouped in layers or rows.

The quartzite from French Creek [208] possesses the rounded grains,
but without cementing material, while in those from Amphibious Creek
[205], Terry Peak [206], Red Canon Creek [207], Box Elder Creek
[200] and [201], the rounded grains are cemented together by some material
which has the appearance of having once been in solution. It is sometimes
silica, and at other times of an argillaceous nature. In the latter case the
rocks are sandstones rather than quartzites

The secondary minerals often occurring in quartzite are, besides the
mica already mentioned, principally orthoclase, hornblende, magnetite,
cyanite and garnet. With the exception of cyanite, all were observed to be
present in these rocks.

The quartzite from the Stockade, French Creek [17] is a grayish, fine-
grained rock of quite dark color, containing numerous small, dark, long-
shaped crystals having a high luster. An examination of the thin section
under the microscope shows that it is composed of crystalline quartz in
small grains full of cavities, black particles of magnetite and microlites,
the latter probably hornblende. Scattered through the mass are also
larger, irregular, broken crystals of hornblende, strongly dichroitic, and in
some cases still showing the characteristic cleavage lines of the angle of
124°. With crossed nicols they are of a fine dark-green color, changing,
upon turning the polarizer, to a lighter yellowish-green Some rather
opaque, non-polarizing masses are probably decomposed feldspar. ‘The
magnet readily attracts particles of magnetite from the pulverized. rock.

The quartzite from Hall’s Cut-off [38] is quite different from the above.
It is of a lighter color and contains mica in small spangles, abundantly
scattered through the mass. The microscope shows the quartz to be very
clear, containing some cavities, highly crystalline and giving beautiful
colors with the polariscope. The mica seems to be somewhat decomposed,
although it occasionally shows the laminations peculiar to its structure.
Large, isotropic crystals of garnet are present and are easily recognized.
There are also black, opaque masses of magnetite, submetallic in reflected

light.

PETROGRAPHY—QUARTZITES. 473

The quartzite from Rapid Creek [73] is gray in color and very uni-
form and compact in structure. Under the microscope, the quartz is
crystalline and pure, containing microlites which have the sharp edges of
crystals, and also small greenish leaves of mica arranged in parallel rows
and pointing in one direction. This structure gives a little schistose charac-
ter to the rock. Magnetite, as usual, is present in sharp angular grains, and
also some mica.

No. [75], from the same locality, is more pinkish in color, and in the
section shows crystalline quartz with cavities and microlites, the latter
being faintly dichroitic. There is much more mica than in [73], which
fact brings it nearer to mica-schist in character.

Jasper [92], from Jasper Hill, Box Elder Creek, is of a red color, with
- veins of white quartz through it. Under the microscope, the quartz is seen to
be very fine granular, with a reddish-brown pulverulent pigment, which is
no doubt oxide of iron. There are also some opaque, dark, cubical and
triangular crystals with hollow centers, the remains of decomposed pyrite.

In the quartzite from Box Elder Creek [200], which is from light-gray
to flesh color, the quartz grains are somewhat rounded, and in the interstices,
often surrounding the quartz particles, is seen a cementing material which
has the appearance of having flowed in streams through the crevices when
_ in solution, so as to fill up all to a solid mass. This allies the rock
more to the sandstones than to crystalline quartzites like the former ones.
There is some mica and a little orthoclase present, and in the quartz are
cavities and long, exceedingly slender microlites, similar to those in speci-
men [169]. :

The color, structure, and appearance under the microscope of [201],
also from Box Elder Creek, are the same as the above, except that there is
less mica.

The quartzite, however, from Amphibious Creek [204] is crystalline,
the quartz being sharp and angular in outline, and full of very large cavi-
ties and microlites. There are also masses of fibrous, dichroitic horn-
blende in great abundance, and some mica. The mineral observed as horn-
blende does not show any lines of cleavage, but it has not the appearance
of mica, and in the weathered parts of the rock these masses have become

474 GEOLOGY OF THE BLACK HILLS.

decomposed, leaving small empty holes in the rock, which appearance is not
often found with mica. There is no cementing material present.

The next rock [205], also from Amphibious Creek, is much darker
than the preceding, being of a brown color. In the section, it is seen that
the quartz is in rounded grains, cemented together by a material showing
the wave-like lines and traces of a former fluidity, as mentioned before.
In some parts of the slide this is very dark and almost opaque from oxide
of iron, the edges of the quartz grains also being colored very dark brown
by the same pigment. Quite striking is the appearance of the brightly
polarizing cementing mass, which is penetrating silica, between the dark-
bordered quartz grains. This rock is again rather a sandstone than a
quartzite.

The specimen from the locality southeast of Terry Peak [206] has a
decomposed, earthy luster of reddish-brown color, plainly showing the
presence of much oxide of iron. Under the microscope, it was observed
that the quartz grains were rounded, but with very little cementing mate-
rial between them, although large masses of opaque oxide of iron were
scattered abundantly through the rock. Needle-like microlites were seen
in the quartz, and in the rock some brown mica and occasionally a little
hornblende.

The rock from Red Cation Creek [207] consists also of rounded grains
of quartz, held together by a very dark or black cement. Nothing else of
note was observed, except some magnetite.

In [208], from the mouth of French Creek, the quartz is in grains a
little rounded, but pure and clear, with very little or no cementing mass.
There is some mica, opaque and probably weathered. The rock is of a
light-reddish color.

The quartz in [209], from Hall’s Water, is very pure and crystalline,
containing microlites and cavities, the former being in the shape of short,
stout crystals. The white mica is very clear and transparent, polarizing
finely, and showing lines of lamination. There is also some brown mica
present, and a few garnets are easily recognized by their isotropic behavior
with crossed nicols. The rock is very light colored, with glistening spangles

PETROGRAPHY—QUARTZITES. A475

of mica scattered through it, and is similar to [38]. It is a characteristic
crystalline quartzite.

That from Warren Peaks [210] is similar in color and fuster to the
above, though a little more reddish. In the section, the quartz is observed
to be sharp and crystalline, with a few crystals of transparent mica through
it and occasionally some brown mica.

In [211], from the mouth of French Creek, the quartz is again crys-
talline and clear, containing very large cavities and good sized microlites,
strongly dichroitic, changing from yellowish-green to red with the analyzer
alone. They may be hornblende, as there are some larger crystals having
the same peculiarity. The brown mica present is much less dichroitic.
The color of the rock is light-gray.

The rock from Amphibious Creek [212] is made up of rounded grains
of quartz, which are full of particles of a black mineral, probably mag-
netite, and exceedingly minute microlites. The section is so opaque from
the presence of large quantities of oxide of iron that it is difficult to render
it sufficiently transparent for observation.

In [215], from French Creek, the quartz is very pure and crystalline,
with numerous cavities and microlites. There are also transparent mica
and some opaque masses, probably a darker and weathered mica.

The rock from Rapid Creek [202] is a glauconitic limestone. Under
the microscope, the mass of rock consists of a whitish crystalline mineral,
which polarizes feebly, changing only from light to dark, while the lines of
cleavage are very distinct. This mineral has in every way the appearance
of calcite. Sparingly scattered through the limestone are pellucid and
brilliantly polarizing grains of quartz. There are also some brown masses
and occasionally a rounded, green body of finely granular texture. These
are the glauconite grains, the brown ones being the same almost entirely
decomposed. In some cases merely a thin, brown crust remains lining the
inside of the cavity. The hand specimen was not at hand to examine and
compare with the observations in the section.

The glauconitic sandstone [203] from Rapid Creek shows under the
microscope that it consists of quartz and glauconite in about equal propor-
tions, held together by a dark-brown cement. The quartz grains are mostly

476 GEOLOGY OF THE BLACK HILLS.

rounded, a few only being sharp and angular, and in some are cavities and
microlites. The glauconite bodies have a bright grass-green color, their
texture bemg tolerably uniform, with the exception of a few dark spots
and cracks in the larger ones. The grains vary in size from quite small to
very large oval, while the forms and shapes are also different, depending
upon the plane of section. Some are long and narrow and others round
or oval; the large ones are bean-shaped and quite symmetrical, a few being
broken and of angular outlines. They do not change color in polarized
light. A few columnar and banded bodies in the cementing mass are frag-
ments of shells curved in form. The cement is quite abundant and is
colored very dark-brown by oxide of iron, which is in numerous small,
round grains, seldom having a square outline.

SECTION II.
MICA-SCHISTS AND SLATES.

The rocks described in this section belong chiefly to the two classes of
schists and slates. Mica-schist is a crystalline mixture of mica and quartz,
both minerals being present generally in good sized crystals; and, even
when of minute size, their crystalline character can be distinctly seen under
the microscope. Examples of the above cases are the rocks [1], from
French Creek, which is a very fine-grained mica-schist, and [13] and [27],
which have a coarser structure, while [69], from Rapid Creek, is almost a
compact rock, showing, however, the crystaliine mica and quartz under the
microscope. ;

Mica-schist has the schistose structure more or less marked, accordingly
as the mica or quartz predominates. When the rock becomes more homo-
geneous in character and of a darker color, being micro-crystalline in struc-
ture, with a slaty cleavage and appearance, it is called mica-slate, the
‘“Thonglimmerschiefer” of Cotta and Zirkel. This is an intermediate rock
between mica-schist and clay-slate, differing from the former in closely
resembling a clay-slate, and from the latter in being distinctly made up of
erystalline quartz and mica, which can easily be observed under the micro-
scope in a thin section of the rock. The specimens from Rapid Creek
[64], [65], [67] and [71] are mica-slates answering to this description.

PETROGRAPHY—MICA-SCHISTS AND SLATES. 477

The true clay-slate consists also of quartz and mica, but never crystalline,
being so homogeneous and amorphous in structure that Zirkel defines it as
made up of ‘‘microscopic mica scales and dust-like quartz grains.” This
distinction is quite apparent under the microscope, when none can be made
between the two hand specimens. Note the resemblance between [64],
[65] and [74]; while the two former are quite micaceous, the latter [74] is
nearly a true clay-slate, showing scarcely a trace of crystalline structure.
By the dwindling in size, then, of its constituent minerals, mica-schist
graduates into mica-slate and argillaceous mica-slate as it comes nearer to
clay-slate in character.

I would also note that the variation in these rocks from French Creek
and Rapid Creek may be due to metamorphic influences of different degrees.

The mica-schist from the Stockade, French Creek [1], has a gray
color, inclining to greenish, and is evidently very rich in mica. Under
the microscope, quartz in abundance was observed containing numerous
cavities, some quite large, and also microlites. Occasionally, there are
large, pellucid masses of this crystalline quartz. The mica is of two
kinds, one greenish-brown and dichroitic, the other being in the form
of long white crystals, sharply defined and clear, but not possessing any
dichroism. These crystals generally point in the same direction, and are
sometimes bent and curved around a quartz grain and also imbedded in
the leaves of brown mica. They show longitudinal lines of lamination,
polarize brightly, giving red and green colors, and are undoubtedly white,
transparent muscovite. The brown, dichroitic biotite is quite irregular in
shape, and in large plates and leaves, and changes in polarized light only
to a darker greenish-brown. An abundant black mineral, sometimes having
a hexagonal section, although of minute size, and a submetallic luster, is
considered to be in part magnetite and in part small crystals of mica. The
structure of the rock is crystalline.

Mica-schist from the same locality [13] is quite different from the pre-
ceding, it being much coarser in structure and colored reddish by oxide of
iron. In the section, the quartz is seen to be predominant and in large
clear masses, containing cavities and small, well defined, dichroitic horn-
blende crystals. The latter are sometimes of large size and so strongly

478 GEOLOGY OF THE BLACK HILLS. |

dichroitic that they change from brown to green and red with the analyzer
alone. ‘They are also abundant in the rock. The brown mica occurs in
large masses, irregular in shape and sometimes striated very distinctly. It
polarizes only from brown to very dark-brown, being also dichroitic. Some
long, transparent crystals of white mica, similar to those in [1], are not at
all dichroitic, and show very little change of color even with crossed nicols.
There are also a few crystals of orthoclase present, quite large and toler-
ably well defined inform. A large, banded crystal may be cyanite. This
rock is a mica-schist, but approaching gneiss in character.

The rock [24] from the Stockade, French Creek, has a general greenish
color, caused by large crystals of hornblende imbedded in a whitish felds-
pathic mass. Under the microscope, large, green, strongly dichroitic
crystals of hornblende are at once remarked. ‘The lines of cleavage are
very distinct, and the sections showing these lines give the most marked
change of color with the analyzer alone from yellowish-brown to dark-
green. Quartz is also quite abundantly present in grains, having cavities
and microlites. Orthoclase makes up with the quartz the groundmass of the
rock. It is partially decomposed, so that it is somewhat cloudy and opaque,
but it occasionally shows colors in polarized light and also cleavage lines.
There is a little magnetite present. This rock is a hornblende-gneiss,
although it scarcely shows any lines or marks of the stratification peculiar
to gneiss, owing to its very crystalline structure.

The mica-schist [27] from Amphibious Creek is gray in color, with red
spots in it of oxide of iron, and has a crumbling, weathered appearance.
In the section, the rock appears to be made up of quartz, transparent, crys-
talline and in large masses, and mica. The former contains unusually
large and fine cavities, microlites, and also some short, stout, dichroitic
hornblende crystals. The mica is quite dark and nearly opaque, but still
changes to a darker brown when observed with the analyzer alone. It is
scattered through the rock in large, irregular masses. A small piece of a
granular and polarizing mineral noted is no doubt a fragment of orthoclase,
not being nearly as transparent as the quartz.

The rock from French Creek [40] has a crystalline luster, but a
very slight schistose character. It is very dark-green, the macroscopical

PETROGRAPHY—MICA-SCHISTS AND SLATES: 479

hornblende crystals being predominant and easily recognized, with white
spots or faint layers of feldspar or quartz and some pyrrhotite through it.
Under the microscope, beautiful crystals of hornblende were seen, varying
in color from pale yellowish-brown to dark-green and red. The pale crys-
tals, being sections across the vertical axis, show the characteristic cleavage
lines and a strong dichroism very finely. This hornblende, which is
greatly in preponderance over the other constituents, is very crystalline,
although the masses are irregular in outline. Next in importance is the
orthoclase, distinguished from the quartz by a little less transparency and
more fissures and cleavage lines; it is quite abundant in crystalline grains
The quartz is present in grains and masses of tolerably good size, which
polarize in very brilliant colors. It contains cavities and microlites, and is
of about the same quantity as the orthoclase. Quite remarkable is the
comparatively large amount of plagioclase present. This occurs in large
crystals, with very delicate but well defined twin lamellations or banding,
some of the crystals being very beautiful. Some garnet crystals, as hexa-
gonal sections imbedded in the hornblende, were noted, as they are isotropic
in behavior. There is also some magnetite. The structure of the rock is
coarsely crystalline, and much fresher than [24], with more hornblende,
some plagioclase, and titanite. It is a hornblende-gneiss, and the section
observed in polarized light presents a beautiful appearance, owing to the
great variety of brilliant colors.

The rock [64] from Rapid Creek is very dark indeed and fine-grained
and slaty in character, so that it can be cleaved into flat, tolerably smooth
pieces. Thin veins of white quartz traverse it at right angles to the strati-
fication, and are occasionally of considerable thickness. In the section, it
was observed that the rock consists largely of quartz in rounded grains,
large and small, and dark colored nearly opaque mica, and has a distinet
schistose structure. Sometimes a large mass of mica is seen, but most of
it is in very small particles, fibrous in character. The veins of quartz are of
course conspicuous, polarizing as well as the grains with bright colors. A
little triclinic feldspar and one small hornblende crystal were noted in the
slide.

The fibrous character of the groundmass, so plainly of a schistose

480 GEOLOGY OF THE BLACK HILLS.

structure, with the larger masses of mica and quartz, place the rock as mid-
way between mica-schist and clay-slate, but it belongs more to the schists
than the slates. It is therefore a mica-slate.

The slate [65] from Rapid Creek is similar in appearance to the pre-
ceding, but much more homogeneous and slaty, cleaving easily into very
thin pieces. Under the microscope, was observed, as before, quartz grains
and dark mica in a very fine groundmass of a schistose structure. There
are fewer lerge masses of mica than in [64], the rock approaching more
nearly the clay-slates. <A little plagioclase was also noted. This is again
a mica-slate.

The specimen [67], from the same locality, shows a precisely similar
character to [64] and [65], even to the presence of a small piece of
plagioclase.

The rock from Rapid Creek [69] resembles the preceding ones, but is
much more compact and has a greenish color, differing also in the absence
of any macroscopical mica. Under the microscope, the difference is remark-
able; quartz in pure, clear grains predominates, between which are small
long-shaped crystals of white mica arranged in the same parallel direction,
so as to occasion the slightly schistose character of the rock. These mica
crystals are almost exactly like those in [1] from French Creek, but much
smaller. The large, brown masses are wanting, however, there being only
one such piece in the slide. Remarkable is the abundance of magnetite in
good sized grains, which have a beautiful submetallic luster. The magne-
tite seems to follow in part the lines of direction of the mica crystals. The
quartz contains microlites, but they were too minute for determination.
From the above observations, this rock is an exceedingly compact and fine-
grained mica-schist, as it does not have the fibrous groundmass of the slates
[64], [65] and [67].

The next, however, from lower Rapid Creek [71], is very much the
same as [64] and [65], except that the color is quite reddish and the
appearance weathered. In the section, it was noted that the groundmass
is quite fibrous in structure and that there is less quartz scattered through
it. The mica appears quite black, opaque, and negative in behavior in
polarized light. There is also a reddish-brown mineral in considerable

PETROGRAPHY—MICA-SCHISTS AND SLATES. 48]

abundance, probably hematite as a resultant of decomposition, or it may
be only weathered mica. The fibrous structure mentioned before arises in
all likelihood from the interlacing of very small mica crystals This rock
is a mica-slate.

The slate from Rapid Creek [74] is almost black in color, and of a
uniform, homogeneous structure, cleaving easily into long columnar frag-
ments. It resembles much more a true slate than any of the preceding, a
fact which the microscopical examination undoubtedly proves. The struc-
ture of the rock was observed to be very fine-grained indeed, apparently
consisting of minute crystals arranged in parallel rows, with an occasional
dark line between them ‘There is but little quartz present, and that in very
small grains; also in lines parallel to the stratification. ‘The small crystals
are a little dichroitic, this being observed in some of larger size, which
might determine them to be mica. Magnetite is present, particularly in one
large mass surrounded by quartz. ‘The homogeneous character of the rock
macroscopically and also as seen under the microscope, together with the
absence of much quartz, decides this rock to be a clay-slate, although it
is not quite as uniform as true roofing slate.

The schist from Box Elder Creek [81] is of a dark-green color, with
veins of white quartz running through it, the mica being greatly in excess.
Under the microscope, the mica was observed to make up most of the rock
and to have a fine brownish-green color. It is but slightly dichroitic when
cut parallel to the lamination, but in the cross sections of prismatic shape
it is strongly so. ‘The fine green color in polarized light at first indicated
hornblende, but there was no satisfactory evidence found of the character-
istic cleavage lines, which could hardly fail to be present in such a ecrystal-
line rock had the mineral been hornblende. It was determined, conse-
quently, to be magnesia-mica, of which the dark-green color and strong
dichroism are usual peculiarities. There is considerable quartz present,
quite crystalline, and having interspersed through it small, transparent,
green crystals of mica. This rock is a mica-schist, the mica predominat-
ing, but of a different character from any of the preceding, being perfectly
fresh and crystalline, without any traces of weathering or decomposition.

The rock from Iron Ledge, Box Elder Creek [85], is lighter in color
31 BH

482 GEOLOGY OF THE BLACK HILLS.

and quite soft. In the section under the microscope, there appears to be
principally quartz, with irregularly shaped particles of a brown, partially
altered mica arranged in rows as if stratified. This mica is not generally
dichroitic, but an occasional long prismatic section is quite strongly so.
Between the quartz grains microlitic, needle-like crystals, pointing in one
direction, probably occasion the schistose character of the rock, and are mica
crystals. It is a mica-schist of similar character to the former ones [69].

No. [86], from the same locality as the preceding, is much lighter in
color, being brownish-white and quite hard. On the cross fracture it shows
very plainly a schistose structure. An examination of the section under the
microscope showed considerable white, but rather opaque, mica, and par-
tially decomposed orthoclase in a fibrous groundmass, strongly recalling a
similar appearance of the mica-slates previously described. There is also
a little quartz in small transparent grains, but subordinate in quantity.
Some plagioclase was also noted; it is weathered, but still shows the colored
banding of the twinned crystals quite plainly. The orthoclase is rather
muddy, giving, however, considerable color in the fresher portions, where
traces of the cleavage were also quite well marked. These minerals are
confused and ragged in outline, so as to render the examination somewhat
unsatisfactory. The fibrous groundmass and preponderance of the ortho-
clase over the quartz makes the rock a feldspathic mica-slate, or a clay-
slate partially metamorphosed and intermediate between that rock and
eneiss.

The dark-green rock [97] from Box Elder Creek has a slightly
greasy feel, and is weathered on the surface to a light-yellowish crust.
Under the microscope, it shows in polarized light with crossed nicols a dark
ground, with evenly distributed white spots of irregular shape, and occa-
sionally some yellowish crystals almost entirely altered to an opaque, black
mineral or magnetite. This mineral is also present in great abundance,
sometimes having an indistinct crystalline form. The section in ordinary
transmitted light has a pale-green color. The whitish particles have a
needle-like, crystalline form, with a fibrous structure, while the yellowish
erystals, being much broken, resemble olivine in process of alteration into
magnetite and opaque, black serpentine-mass. The fibrous, feathery and

PETROGRAPHY—RHYOLITE, TRACHYTE, AND PHONOLITE. 483

thread-like appearance of the general mass of the rock determines it to be
serpentine, which a blowpipe test confirmed. It has probably been formed
by an alteration of the slates, which theory an exact observation of its
occurrence would perhaps support.

SECTION IIt.
RHYOLITE, TRACHYTE, AND PHONOLITE.

The recent eruptive rocks, formerly known under the name of the
trachyte group, have of late been divided into several classes, depending
upon their structure and the presence or absence of the minerals, quartz,
and oligoclase, or other triclinic feldspars.

The quartz-bearing trachytes are called rhyolite and quartz-trachyte,
while those free from quartz are subdivided into sanidin-trachyte and
sanidin-oligoclase-trachyte, accordingly as the sanidin occurs in them alone
or accompanied by oligoclase. In close relationship and analogy to these
rocks are andesite, consisting generally of oligoclase and hornblende or
augite, and phonolite, which latter has sanidin for its chief constituent, with
nephelite, nosite, and various decomposable zeolites. While sanidin-oligo-
clase-trachyte, by the addition of quartz, falls into the class of the acid
trachytes or rhyolite, so on the other hand, by the gradual diminution of
the sanidin, it becomes andesite. In this rock the oligoclase occurs in com-
bination with hornblende as well as augite, and andesite is accordingly
divided into hornblende-andesite and augite-andesite. As with trachyte,
quartz is sometimes an ingredient, and causes a subdivision of both kinds
of andesite into quartz-bearing hornblende or augite-andesite, the former
being called dacite, and those free from quartz.

The glassy forms of trachyte vary greatly in appearances and struc-
ture, and are known as obsidian, trachytic-pitchstone, pearlite, spherulite,
&c. They may be regarded as masses of the same composition as the
varieties of trachyte already mentioned, but solidified under circumstances
preventing a crystallization of their constituent minerals. As may be
inferred, they vary in every respect similarly to the crystalline member of

484 GEOLOGY OF THE BLACK HILLS.

the class to which they belong, as is shown by a chemical determination of
the silica and composition.

Of the varieties of rocks mentioned above, there are represented in the ©
specimens from the Black Hills thus far examined rhyolite, sanidin-trachyte,
sanidin-oligoclase-trachyte, and phonolite; no andesite was observed.

Ruyoute.—Rhyolite is quite different in general appearance from
sanidin-trachyte, in that it is much more compact and fine-grained or fel-
sitic in structure. It consists of a groundmass, in which are visible in most
cases crystals of sanidin and biotite or hornblende, with small grains of
quartz. Its most predominant colors are white, yellowish and greenish-
white, light-gray, pearl-gray, greenish-gray, and sometimes pale-red. In
many cases the quartz can only be detected in the thin section with the aid
of the microscope. The groundmass varies greatly in structure and appear-
ance from a crystalline, or micro-granitic, and micro-felsitic to a felsitic,
spherulitic, half-glassy and glassy character *

The first or coarsely crystalline structure is somewhat granitic in
appearance, so much so that the geological occurrence must be relied upon
to a great extent to distinguish the rhyolite from granite-porphyry or feld-
spar-porphyry. This form of the groundmass does not occur very fre-
quently, but there is an example of it in the rocks [101] and [103] from
Terry Peak, which, according to the occurrence given, pass gradually into
well defined rhyolite or trachytic rock

A characteristic peculiarity of the compact groundmass of rhyolite is
a banded appearance, caused macroscopically by an alternation of two-
colors, generally dark-gray and pinkish-violet, im parallel, narrow bands.
These colors, in a great number of shades, are often in layers as thin as mere
lines, so that the rock has somewhat the appearance of banded agate, the
most delicate markings being scarcely visible to the naked eye. From
examination under the microscope by Zirkel, these bandings and also the
wavy, fluidal appearance are produced ‘“‘by a different amount of coloring
particles (needles and grains of ferrite and opacite) alternating in layers,
and by a band-like alternation of different varieties of structure, generally

*Vor a minute and detailed classification of the various microscopical types of the groundmass
see Zirkel’s Microscopical Petrography of the Survey of the Fortieth Parallel, p. 203.

PETROGRAPHY—RHYOLITES AND TRACHYTES. 485

with a gradual passage between one another.” Occasionally, the rock splits
easily into flat slate-like plates. ‘These appearances were observed in the
Black Hills rocks as [127], [135], &c. This groundmass has again a.
resemblance to burnt clay, with broad, reddish bands in a light-yellowish
mass of a porous and rough texture. The groundmass has also a half-
glassy or glassy structure, with the character of obsidian, pearlite, &c,
with but few imbedded crystals. This form of rhyolite is called half-glassy
or hyaline-rhyolite by Zirkel, and includes obsidian, pumice-stone, pearlite,
&e. which belong geologically to the rhyolites.

A determination of the percentage of silica is necessary, when the
rhyolite is of a very compact, felsitic texture with but few crystallized
minerals, such as quartz and sanidin, to explain its nature. In such a case,
the amount of silica, the microscopic behavior of the thin section, and the
geological association must all be called into requisition.

A rough, decomposed, porous structure with numerous holes and
cavities is frequently the character of the groundmass. The most usual,
however, is a fine-grained or micro-crystalline texture, generally of a light-
gray color, appearing almost compact; a close examination being required
to see the minute crystalline points. The microscope shows the mass to
consist of small sanidin crystals, quite rough or ragged in form, and closely
interlaced. Of this kind are the Black Hills rhyolites [135], [147] and
[152]. The imbedded crystals are not very abundant, sometimes entirely
wanting, and are sanidin and occasionally biotite.

Spherulites, often present in the felsitic groundmass, are small, round,
fibrous masses of a distinctly radiated structure. They vary greatly in
size, from very minute to quite large, and are not very sharply separated
from the groundmass. When the fibers are arranged on a line instead of
around a center, the structure thus produced is very peculiar and interest-
ing; it is called axiolite by Zirkel, and is stated to belong chiefly to
rhyolites.

As rhyolite is the acid variety of trachyte, owing to the presence of
quartz, the silica percentage of the groundmass is always much higher
than that of sanidin-trachyte. In the Black Hills trachytes it varies from
67 to nearly 80 per cent., while Zirkel gives the analysis of a rhyolite -

486 GEOLOGY OF THE BLACK HILLS.

having silica as high as 82 per cent. The percentage of silica in these
rocks was determined, as well as the amount dissolved in hydrochloric acid.
The loss in acid, however, cannot be considered of very much value, owing
to the change in the constituents of the rocks from weathering, which
materially increases the proportion of the soluble part and causes it to
appear as if there were decomposable minerals present. Notwithstanding
this uncertainty, the results of both determinations are given further on in
the table on page 526.

From the characteristics mentioned, the varieties of rhyolite are dis-
tinguished by Zirkel as follows:

Crystalline-granular— of a granitic character.

Felsitice— a felsitic groundmass, without separated crystals.

Porphyritic— a felsitic or crystalline groundmass, with imbedded crystals.

Half-glassy or glassy— consisting entirely, or in very large part, of glass, obsidian,
pearlite, &e.

Almost all of the Black Hills rhyolites belong to the porphyritic
variety, as they generally have large sanidin, biotite, and other crystals
porphyritic in a fine-grained groundmass. Other varieties occur in a few
instances, which will be mentioned in the detailed description of the thin sec-
tions under the microscope.

Quartz is the most important of the crystalline minerals separated
from the eroundmass. It occurs in grayish and transparent, round grains
or crystals, which have a distinct line of demarkation between them and
the groundmass. Macroscopically, they can be distinguished from the sani-
din crystals, which are in most cases also brilliant and glassy, by their
different luster and conchoidal fracture, while sanidin has a good cleavage
The hardness of the quartz assists m the distinction. It is sometimes crys-
tallized in the form of doubly terminated crystals, with prismatic faces. In
the thin section under the microscope, the quartz appears either in rounded
grains or crystals. It can be distinguished from sanidin microscopically by
its greater pellucidity, polarizing in brilliant colors, and its lack of cleavage
lines. The crystalline form is also of great assistance, when the resemblance
between the two minerals makes the distinction doubtful. It often contains
microlites and brownish glass bodies, which latter inclusions are sometimes
hexagonal in shape. Characteristic for the quartz in trachytic rocks, as

PETROGRAPHY—RHYOLITES AND TRACHYTES. 487

differing from that of granite and gneiss, &c., is the absence of any fluid
inclusions,* so usual in the latter rocks. Instead of these are particles
of volcanic glass, called glass inclusions, which are never found in granitic
rocks. The crystals of quartz are generally of sharply defined outline
and often twinned, which latter occurrence is most clearly seen in polar-
ized light, as shown in [127], Plate I, Fig. 1.

Sanidin, the chiet constituent of trachytic rocks, occurs in transparent
erystals, full of fissures, cracks and cleavage lines. The crystals in rhyo-
lite, however, are not so large as those usually in sanidin-trachyte. The
form and the crystals as seen in the thin section varies ereatly, from large,
rectangular sections to long, columnar crystals, the latter being often very
small. The sections are also six and eight-sided. Carlsbad twin crystals
are of frequent occurrence, the two parts giving different colors in polarized
light, according to the position of their optic axes. The crystals polarize in
quite brilliant colors, often much resembling quartz in transparency and
appearance, the distinction, however, being made by the general rectangular
form and the fissures and cleavage lines of the sanidin. In very small
and irregularly shaped, often ragged, crystals, sanidin makes up almost
entirely the groundmass of many of the rhyolites. These small crystals
are only visible in polarized light, being seen with tolerable distinctness
when the nicols are crossed.

Plagioclase, or oligoclase, occurs quite frequently, but always subordi-
nate to the sanidin. It can be easily recognized under the microscope by
its characteristic colored banding in polarized light, caused by the twin
lamellation of the triclinic crystals. In some cases when this is not so
distinct, dependence must be placed upon the more weathered or decom-
posed condition of the smaller, needle-shaped crystals. Plagioclase crystals
often interpenetrate those of sanidin, the two forming together a symmettri-
cal crystal, one end being sanidin and the other plagioclase. It is also seen
as minute crystals, inclosed in large sanidins. Inclusions are less frequent

than in sanidin.

* Zirkel, in the Microscopical Petrography of the Survey of the Fortieth Parallel, p. 197, mentions
the occurrence of a fluid inclusion in rhyolitic quartz, but concludes that the quartz itself is a foreign
inclusion in the rhyolite.

A488 GEOLOGY OF THE BLACK HILLS.

Biotite occurs in many of the rhyolites and is characterized by its
brown color and distinctly marked lines of lamination. It is strongly
dichroitic when the sections are rectangular, or cut about parallel to the
prismatic faces, and not at all so when the sections are hexagonal in outline,
or parallel to the basal pinacoid. Biotite crystals often have a border of
magnetite grains, which is quite characteristic, as in the section figured in
Plate I, Fig. 2.

Magnetite, in small black grains generally quite uniformly distributed
through the groundmass, with an occasional larger mass, is of frequent
occurrence and is recognized by its submetallic luster in reflected light.

The groundmass, even when macroscopically compact and of uniform
texture, in the thin section under the microscope, is seen to consist of small
feldspar microlites or crystals, interwoven and interlaced so as to form a
solid mass. In some cases, these crystals are of larger size, but they
always have ragged or forked terminations. This formation of the ground-
mass can be best seen with crossed nicols, when a portion of the small
crystals are light, the others being dark. By then turning the slide on its
center the dark crystals become light and those previously light, dark, thus
proving that the entire groundmass is an aggregation of microlitic feldspar
crystals. In a few cases, a more uniform or glassy groundmass and on the
other hand a more crystalline appearance were observed and are mentioned
in the detailed description of the thin sections. The majority of the Black
Hills rhyolites have a erypto-erystalline or felsitic groundmass, uniform in
texture and often colorless; but no truly glassy groundmass occurs, the
crystalline prevailing.

Tracuyte.—The trachytes proper are distinguished from the rhyolites
and quartz-trachytes by the absence of quartz, having consequently a much
smaller percentage of silica, and by the preponderance of crystallized
sanidin, either alone or with oligoclase.

These minerals are imbedded in a rough, porous groundmass, which is
more or less crystalline. It generally has a dull luster and light, white, or
light-gray colors, though dark varieties sometimes occur. The variation in
the color of trachyte is due to the groundmass, the petrographic compo-
sition being always identical. Hornblende, magnetite, and biotite are the

PETROGRAPHY—RHYOLITES AND TRACHYTES. 489

most frequent accessory minerals, and Zirkel has recently proved the pres-
ence of augite.

Trachyte has been divided, according to the character of its feldspars,
into sanidin-trachyte and sanidin-oligoclase-trachyte; but, as the triclinic
feldspar or plagioclase has been shown by the microscope to be almost
always present with the sanidin, this distinction cannot be considered very
exact, nor can the line be sharply drawn been the two varieties. It being
the same with the Black Hills trachytes, these names are only used as con-
venient to indicate the predominant composition of the various rocks. The
silica percentage in these sanidin-trachytes varies from about 56 to 65 per
cent.

Owing to the occurrence of augite mentioned above, a new variety,
augite-trachyte, has been introduced by Zirkel.

The sanidin occurs generally in tabular or columnar crystals, varying
greatly in size, but having a bright luster and the characteristic structure,
being traversed by numerous fissures. The crystals are very frequently
composed of colorless zones, one completely surrounding the other in the
form of the crystal, but each varying a little in such a way that the external
shape is different from the interior commencement. This formation is easily
observed in the thin sections under the microscope, when the zones, often
of extreme delicacy, are distinctly seen by reason of their different colors
in polarized light. This structure of sanidin is much oftener met with in
trachyte than in rhyolite. For examples see Plate II, Fig. 1, and also the
section of the rock [141-2].

As inclusions, sanidin contains in great abundance particles of color-
less or brownish glass, hornblende microlites, grains of magnetite, &c., with
which the larger crystals are often crowded. Occasionally, these interposi-
tions are arranged in zones as the crystal has increased in size, and particles
which appear to be only fragments of sanidin are seen from this grouping
of the inclusions to be crystals having an irregular coutour, the interior
zones showing the sharper form. Again, there is sometimes an opaque
kernel of these inclusions, around which a more transparent rim of feld-
spar has been deposited. Portions of the groundmass are also found as
inclusions in the sanidin crystals. Fluid inclusions were formerly consid-

49() GEOLOGY OF THE BLACK HILLS.

ered as always absent from the feldspars of trachytic rocks, but Zirkel men-
tions several cases as occurring in the sanidin both of rhyolite and trachyte
in the rocks of the ‘“Fortieth Parallel” Twin crystals according to the
Carlsbad law are very frequent, even the minute crystals often showing
this peculiarity in polarized light. Broken crystals are also observed, which
give rise to the explanation that the magma while soft had moved after
the crystals were formed or separated from the groundmass. The fragments
lie near each other and have the same rough, jagged line of fracture, while
the intervening space has been filled up again by the groundmass This is
well exemplified in one instance in the Black Hills trachytes, there being a
large sanidin crystal broken in two parts and the fragments displaced by
another sanidin mass (Plate II, Fig. 2).

Plagioclase is very often present with the sanidin, sometimes in large
crystals, finely banded, and when subordinate in quite small crystals the
bands are distinct enough for recognition under the microscope.

Hornblende occurs in trachyte quite frequently as large crystals, which
are green or brown in color. They often have inclusions of magnetite and
a border or rim of magnetite grains similar to that of biotite. Glass par-
ticles are also often included by the large crystals. The lines of cleavage
and the dichroism can be observed in most cases, which serve to distinguish
it from augite. Its sections are distinguished from biotite under the micro-
scope by the cleavage lines, as well as by the different position of the optic
axes. With hornblende the sections parallel to the base are the most
strongly dichroitic, while those parallel to the prism are not at all or very
slightly so. . The contrary is the case with biotite. ‘The hornblende prisms,
columnar crystals, and microlites, often abundant in the groundmass, are
generally green and yary greatly in size in the same rock from crystals to
very minute needles, as in [123]. The terminations are also different in
character, some being sharp with distinct crystal faces, while other crystals
have rough, ragged, or forked extremities. In some trachytes, there is but
little hornblende present.

The brown crystals of biotite are often met with, and are easily recog-
nized by being strongly dichroitic in the prismatic sections. The hexag-

onal, basal sections have under the microscope an oliye-brown color, are

PETROGRAPHY—RHYOLITES AND TRACHYTES. 491

not very transparent and not at all dichroitic (Plate H, Fig. 4). The pris-
matic sections are deeply striated, quite transparent, and have a light yellow-
ish-brown color. The crystals are often partially decomposed, becoming
quite ragged, broken and opaque and full of magnetite crystals and grains,
which latter form a border completely around the edge of the crystal (Plate
I, Fig. 2). This, when carried further, changes the biotite crystal into an
aggregation of magnetite grains in the form of biotite, of which only an
occasional transparent particle remains to show the origin of the mass.
Biotite generally occurs in trachyte in large crystals and not in small scales
or leaves.

Magnetite occurs in great abundance as grains, large masses and sharp
crystals.

Minute, colorless needles of apatite have been noticed in all trachytes,
almost without exception, being most readily found when included in the
large crystals of sanidin or hornblende. It may therefore be regarded as
a constituent of the rock, although in minute quantities, and only discover-
able in the thin section under the microscope. In the Black Hills rocks, it
is of frequent occurrence.

Zirkel reports tridymite to be a distinct ingredient of some trachytes,
in the form of small six-sided scales or leaves, arranged in groups some-
what as tiles or slates on a roof, but none was satisfactorily determined to
be present in these rocks.

Titanite and augite are occasionally noticed, but were not found in
the rocks under examination.

The groundmass, as seen under the microscope, is generally quite
erystalline, being usually made up of thickly crowded feldspar microlites,
with needles and grains of green hornblende, and magnetite grains. A
fluid-like structure is often recognized from the position of the hornblende
crystals, which appear as if imbedded in a mass flowing in streams around
a large sanidin crystal or grain of magnetite. There are several fine
examples of this structure among the trachytes [123] and [159-162] (Plate
IJ, Fig. 3). The number of the feldspar microlites can only be truly appre-
ciated by turning the slide on its center between crossed nicols, in order to
cause all the crystals successively to become bright by changing the'r

492 GEOLOGY OF THE BLACK HILLS.

optical position. Sometimes a little glass mass is seen between the micro-
lites, but very sparing in quantity.

Sanidin-oligoclase-trachyte, also characterized by its lack of quartz,
consists of crystallized sanidin and oligoclase, with biotite and hornblende
as accessory minerals. ‘The entirely feldspathic groundmass is composed
of a fine-grained or crystalline aggregation of these minerals, in which
crystals of the same minerals are imbedded. The oligoclase can be dis-
tinguished from the sanidin by its twin lamellations, and is often present in
ereater abundance than the sanidin.

The Drachenfels trachyte is a rock of this class, and some from the
Black Hills [144], [149], [151], and [157] (Plate II, Fig. 2), are of a simi-
lar character and may be regarded as the most typical of those thus far
examined.

Prono.tite.—Phonolite is a compact, dense rock, standing in appear-
ance between trachyte and basalt, from which latter it differs in its lighter
color, lower specific gravity, schistose structure, lack of olivine and the
constant presence of sanidin, all of which characteristics place it nearer
trachyte than basalt. Phonolite has a more compact groundmass than
trachyte, and is also free from quartz.

The microscope has proved what the chemical analyses have always
indicated, namely, the presence of nephelite as an essential constituent of
all phonolites, and of nosite in nearly all. This occurrence of nephelite
satisfactorily explains the large percentage of soda in the portion of rock
soluble in hydrochloric acid, as well as the frequent presence of zeolites as
products of decomposition in the cavities and cracks.

Phonolite consists, then, of sanidin, hornblende, and nephelite, some-
times nosite, in a compact or crystalline groundmass. The sanidin crystals
are generally sharp in outline, except when the rock is partially decom-
posed, in which case the formation of zeolitic minerals affects them also, so
that they lose their form and become filled with a fine fibrous mass. They
include minute, pellucid crystals of nephelite, generally in a row near the
edge of the crystal, and also exceedingly small, almost colorless horn-
blende microlites.

Nephelite is found in all true phonolites in great abundance in the

PETROGRAPHY—PHONOLITE. 493

eroundmass in crystals having the general form of hexagonal prism and
base. In the thin section under the microscope, it is seen in its peculiar
hexagons and rectangles, the former being sections parallel to the base and
the latter parallel to the vertical axis. Consequently, the hexagons become
simply light and dark with parallel and crossed nicols, the polarized light
passing through the optic axes, while the rectangles polarize quite brilliantly,
being most distinctly seen when the nicols are crossed about 45°. When
the crystals are cut obliquely, the section will have an irregular shape, the
sides of the hexagon not being equal. This is not caused by any irregu-
larity in the crystal, but by the position of the plane of section. Square
forms occur, which polarize brightly and therefore are sections cut parallel
to the vertical axis from prismatic crystals as thick as they are long. There
are generally more hexagons than rectangles, which arises from the fact
that the nephelite crystals are arranged with their basal faces parallel to the
schistose structure of the rock, while the fragments used for thin sections are
most conveniently obtained and ground parallel to the same schistose forma-
tion. The nephelite crystals in phonolite frequently have inclusions of
microlites, the presence of which in the hexagons as well as in the rect-
angles proves the two sections to be from the same mineral. Apatite in
section also gives hexagons, but the sections in the other plane are those
of long slender needles, while the crystals of nephelite are short and stout.
Again, nephelite often make up a large part of the groundmass of phonolite,
while apatite occurs in most every case only sparingly in needles.

Hornblende in small, green columns or microlites is present in almost
every phonolite, and these crystals often have forked or split terminations.
Besides these, there are also grains, minute in size and larger crystals and
masses.

Nosite has peculiar forms, consisting of a nearly transparent central
part, which is often covered with a striation of black lines at right angles
to each other like a net-work, and a dark, opaque border, quite irregular in
shape. It is isotrope, changing simply from light to dark, but its peculiar
and striking appearance causes it to be easily recognized. It is also dusty
or filled with a great number of dark dots, as if shaded by points. This is

494 GEOLOGY OF THE BLACK HILLS.

the beginning of decomposition, which, when further advanced, causes a
slight polarization of a newly formed mineral.

Magnetite also occurs in phonolite quite frequently.

The groundmass is usually crystalline and, for the trachytic phonolites
or those containing considerable feldspar, a fluid-like structure is very char-
acteristic. Of the Black Hills rocks, the specimen [139] from Black Butte
is a phonolite, being made up of sanidin and hornblende, with nephelite in
great abundance.

EXAMINATION OF THE THIN secTIONS.—The rock [101] from the top of
Terry Peak has a light-gray to pinkish color, large crystals of feldspar,
with small ones, being thickly crowded together in a feldspathic ground-
mass, in which quite small, black needles and crystals are occasionally visi-
ble. It has a somewhat porphyritic structure, except that there is very
little groundmass to be distinguished macroscopically from the crystals.
In the section under the microscope, the rock appears to consist of large
and weathered or dusty crystals of orthoclase or sanidin, with numerous
large and small, columnar hornblendes imbedded in a partially crystalline,
quartzose groundmass, made up of feldspar and quartz granules and some
large quartz masses. No mica was observed, except a few opaque, white,
and decomposed masses, which may have been muscovite when fresh. The
sanidin is quite dusty, but the interior of some of the crystals is still clear
enough to give color with polarized light, a few of the small ones being
quite transparent. Their outlines and crystalline form are very distinctly
defined against the brightly colored groundmass, very interesting being the
appearance of a bright line around the cloudy central portion, having the
usual termination of base and hemi-orthodome, while outside of this line
the crystal is finished flat and quite opaque and the terminal faces replaced
by one plane, making the exterior form rectangular. This is the very char-
acteristic, zonal formation of sanidin, which is not so often observed in the
orthoclases of granite. There are some twin crystals; and the interior of
some of the large crystals is filled up with the groundmass, leaving only a
dark rim of the feldspar. <A very little plagioclase was noted, distinguished
by its twin lamellations.

Quartz is in small grains, evenly distributed through the groundmass,

PETROGRAPHY—RHYOLITE. 495

there being an occasional large piece. It contains microlitic needles ot
hornblende and but few cavities.

Hornblende is quite plentiful in long, prismatic crystals and also as
minute needle-like microlites in great abundance. The crystals are of a
fine green color and dichroitic, but generally with ragged terminations, a
few of them only being sharply defined in form.

The groundmass is crystalline, and consists of feldspar, associated with
quartz and hornblende needles, the latter being thickly crowded togetiier.
The percentage of silica was determined to be 72.35, this large amount
being due to the quartz in the groundmass. ~

The general behavior of the feldspar is much like that of granitic or
felsitic porphyry, particularly the impellucid border and the fibrous radiat-
ing ageregation of the large crystals, while again some appearances of the
groundmass are rhyolitic. Were it not for the geological occurrence given
as passing gradually into a trachytic rock, it would have been classed as
granite-porphyry. Unfortunately, no more exact observations could be
made as were intended, so that the rock must be provisionally named a
erystalline rhyolite of granitic character, until some future examination
shall confirm or change this determination. The rock [103], from the same
locality, presents no essentially different appearance from the preceding,
though it is somewhat fresher and the feldspar crystals more transparent.
Silica is 71.13 per cent.

The rhyolite [109] from southeast of Terry Peak is of a light greenish-
gray color, with lustrous transparent crystals of sanidin plentifully scattered
through it. The rock is quite compact in texture, being hard and tough.
With the microscope, were observed sanidin, plagioclase, quartz and some
hornblende in a groundmass, which is an aggregation of very small needle-
like microlites. The large amount of silica present (75.09 per cent.) con-
firms the determination of the quartz in the thin section.

The sanidin is abundant in fine, clear crystals, both large and small
polarizing brilliantly. Some are twinned according to the Carlsbad law, one
part of the twin with crossed nicols being blue and the other colorless. They
also contain inclusions of glass, magnetite and small rectangular plagioclase

crystals, the latter showing very plainly, owing to their different color from

496 GEOLOGY OF THE BLACK HILLS.

the sanidin. The plagioclase is quite fresh and has distinct lines of twin
lamellation, its crystals being both prismatic and rectangular in shape. It
is also occasionally grown upon the extremity of a sanidin in such a manner
as to form one large crystal together; an occurrence noted by Zirkel as
quite frequent. Some of the sanidin, but oftener the plagioclase crystals,
have a dark border or rim entirely around the edge, as if from decomposi-
tion.

The quartz is not as distinct and easy to determine as the feldspars,
but is present in comparatively large, roughly shaped hexagonal crystals,
quite transparent and containing an abundance of microlites sharply
defined in the clear mass. These masses do not polarize very brilliantly
between crossed nicols, except upon turning the slide. It is aiso in irregular
masses and small grains, all having the microlites, the smaller grains giving
brighter colors in polarized light.

Hornblende is very sparingly present in small bright-green crystals.
Some brown films of oxide of iron were also noted.

The groundmass consists of an aggregation of fine microlites, interlaced
and piercing the innumerable small grains of sanidin and quartz, so that
with a high power the needles may almost be separately distinguished.

The sanidin-trachyte [113] from the ridge east of Terry Peak is quite
different from the preceding. It is of a decided greenish color, with yellow-
ish-brown ferruginous veins through it. In the section, the sanidin is in
long, columnar and almost needle-shaped crystals, which make up the
greater part of the rock, but which are not very pellucid. Some are rectangu-
lar and twinned, but all are quite dusty in appearance. The brown masses
may be remains of a mica, as they polarize somewhat and are quite trans-
parent The crystalline form of the sanidin is quite distinct in a few of the
larger crystals, and around the only large group of sanidins a fluid-like
structure in the arrangement of the needle-shaped crystals and microlites
is very apparent, being also seen in other parts of the section. The silica
is lower than in [109], being 58.33 per cent. The groundmass is composed
of grayish, minute microlites, in which are imbedded the slender feldspar
crystals mentioned above.

The rhyolite [120] from the hill southeast of Terry Peak has a flesh-

PETROGRAPHY—SANIDIN-TRACHYTE. 497

colored appearance as to the groundmass, with numerous, very lustrous and
glassy sanidin crystals and a few large grains of quartz, the two being
macroscopically distinguished by the latter not showing any cleavage.
There is also some pinkish feldspar in the groundmass. In the section, were
observed large, clear sanidin crystals, some being cloudy and rather opaque,
and a few large and very clear, rounded quartz masses, all in a finely erys-
talline, feldspathic groundmass containing also numerous small quartz grains.
The large sanidins are very pellucid and generally show numerous fissures
and cleavage lines. They have also a dark border of alteration and fre-
quent cases of intrusion of the groundmass into the center of the crystal
In the last respect they are similar to those of [101] and [103]. The
other crystals are entirely cloudy or altered to almost opaque masses,
which, however, still preserve their outline distinct from the groundmass.
The quartz present, both large and small grains, polarizes in a brilliant blue
color. Some dark-brown particles are probably remains of decomposed
biotite. The groundmass is crystalline, being made up chiefly of small,
ragged feldspar crystals and opaque ones, so that with crossed nicols the
erystals are white on a dark ground and quite conspicuous, as are also the
blue quartz grains. The silica percentage is 72.27. There is some simi-
larity between this rock and [101], [103], [124] and [140].

The sanidin-trachyte [123] is from the same locality as the preceding,
but differs widely in appearance. It is bluish-green in color, somewhat
glassy and quite compact. White feldspar crystals are visible, and small
green needles in the groundmass can be seen with the loupe. In the sec-
tion, there are large and somewhat cloudy sanidin crystals, around which,
with a remarkable and beautiful fluid-like structure as if hardened at the
time of flowing, is a brightly polarizing groundmass, full of green horn-
blende crystals from large size to microlitic needles, the majority being of
medium size. The sanidin is generally in rather prismatic and rectangular
crystals, quite dusty and opaque, or having occasionally a clear and polar-
izing central mass. There is a large crystal, which polarizes in very irregu-
lar blotches of color, with a very pellucid interior. In this point it bears
some resemblance to the large feldspars of [101] and [103], as also in the

abundance of hornblende prisms, At the angles and edges it appears
o2 BH

498 GEOLOGY OF THE BLACK HILLS.

almost as if small portions of the crystal had been broken off by the action
of the once fluid groundmass, which completely envelopes these fragments
while carrying them away.

The hornblende crystals are very conspicuous as small yellowish-green
blades; they are sharply terminated and outlined, the sections in the differ-
ent planes affording long, slender, and small rhombic forms, respectively.
It is, of course, rather rare that any of these crystals, which lie in every
possible position, are cut so nearly at right angles to the vertical axis as to
afford a perfect rhombic section and to show the lines of cleavage, but it
was observed in a few cases with the careful use of an objective of very
high power. The crystals are also plainly dichroitic, changing with one
nicol from yellowish-green toa deep-green. A few large hornblendes show
this characteristic more plainly, but they are not so sharply terminated.
On the other hand, some are so minute as to be just discernible in great
quantities in the mass, sometimes heaped up or collected in bunches in a
re-entrant angle of a sanidin crystal, and filling also the interstices between
the larger prisms. The groundmass is colorless, but polarizes in tolerably
bright colors—red, blue and yellow—as if it were feldspathic In its ap-
pearance, it shows distinct signs of a former fluidity so marked and general
in all parts of the section that the wave-like structure is a striking feature.
These waves, so to speak, sometimes meet the opposing extremity of a
crystal and divide into two streams, one on each side, leaving at the point
of division quite a number of the hornblende crystals crowded together
and heaped up like logs in a river when an island has interrupted their
motion down the stream. Again, the once fluid mass fills all the fissures,
cavities and cracks in the feldspar crystals, the very small fissures contain-
ing only the microlites of hornblende, as if the larger blades had been pre-
vented from entering. The whole phenomenon is quite interesting. A
little magnetite is present, but in small quantities only. The rock contains
63.56 per cent. of silica, and 8.58 per cent. is soluble in hydrochloric acid.

The sanidin-trachyte [124] from southeast of Terry Peak is of a gray
color, containing large crystals of sanidin and numerous small, dark horn-
blende crystals. It is also quite porous in structure, the holes resembling
cavities which have been once filled by some crystallized mineral. Under

PETROGRAPHY—RHYOLITE. 499

the microscope, the sanidin appears to constitute the greater mass of the
rock, being in some places quite clear and pure. The crystals, however,
are very indistinct in outline, and are apparently aggregated to one mass.
There is hornblende in abundance in large, fine, green crystals, somewhat
decomposed and including grains of magnetite of good size, although they
are but slightly dichroitic. Nearly every crystal has magnetite either in it
or adhering to it. Occasionally, several hornblende crystals are grouped
about a large grain of magnetite. This is quite a usual characteristic of
trachyte. The hornblendes vary in size from quite large and clear, green
erystuls to small blade-shaped or prismatic crystals with ragged termina-
tions. There is a little biotite present, and an occasional apatite crystal.
Magnetite, besides that mentioned as inclusions, is scattered abundantly
through the rock in large to very small grains, approaching a little to a
crystalline form The groundmass is feldspathic, and has a fine-grained
structure resembling a fibrous microlitic aggregation.

The rock contains 57.75 per cent. of silica, and the soluble portion in
hydrochloric acid amounts to 13.48 per cent.

The rhyolite [125] from near Deer Mountains has a porous appear-
ance, caused by numerous empty cavities, the mass of the rock itself being
quite compact. Its color is pale-brownish to pink, having an indistinct
banding of two colors, light and darker brown. Upon close examination,
quite a number of quartz grains of good size can be seen, while many of
the empty cavities have a very plain imprint of the quartz crystals that
formerly filled them. With the loupe, a granular structure is recognized,
but no crystals of any mineral except the quartz already mentioned. In
the section under the microscope, it consists apparently of whitish, opaque,
rounded bodies, with large and very clear quartz masses in a partly granu-
lar and isotropic groundmass, in which are also numerous small quartz
grains. The rounded bodies are somewhat fibrous in structure, and gen-
erally have a narrow, transparent rim, and are probably imperfectly formed
spherulites. They are aggregated in large masses, leaving only small
interstices of the groundmass between them, so that the greater part of the
rock is made up of these masses. They resemble spherulites a little, and
a faintly hexagonal shape is also noticeable. The large quartzes polarize

500 GEOLOGY OF THE BLACK HILLS.

very brilliantly, but are irregular in form and have inclusions and irruptions
of the groundmass, as well as black specks and some rectangular crystals
of an undetermined mineral. Magnetite occurs in small grains, but very
sparingly, and mica and hornblende are present only in a very few crystals.
The groundmass is colorless and quite transparent, polarizing with crossed
nicols in white irregularly shaped grains in a dark ground, this latter being
the isotropic portion. There are also some needle-shaped, white microlites.
The absence of any defined crystalline structure, and the partially glassy
character of the groundmass is remarkable and different from the other rocks.

The rock [127] from the same locality has more the characteristic
appearance of rhyolite. It is very compact indeed and slightly banded in
color, which is a light-gray, inclining to greenish. The banding resembles
faint traces of a fluid-like structure, although this was not observed in the
section. Scattered through the rock are macroscopical crystals, colorless,
but very brilliant; part of these are sanidin and some are quartz, the dis-
tinction being made by the presence or lack of cleavage, sometimes, how-
ever, difficult to observe. A few dark crystals of mica are also to be seen.

In the section, it consists of large, clear quartzes, with numerous small,
rectangular sanidin crystals in a fine-grained groundmass, with biotite and
some hydrated oxide of iron films. The silica present is 73.22 per cent.,
this large amount being due to the quartz.

The sanidin occurs occasionally in large rectangular crystals, but it is
mostly in small ones, quite uniformly scattered through the groundmass.
They do not polarize very brilliantly, and in some cases contain microlites
and glass inclusions. They may be distinguished from quartz by being
less transparent and more uniform in shape. The quartz is exceptionally
fine in this section, some of the crystals being twinned so that one crystal
with crossed nicols will be brilliant, while the other remains dark, making
the line of twinning very marked. There are two such examples in the
slide, one of which is shown in Plate I, Fig. 1. It contains a few cavities
and microlites, but not to any marked extent. There are also small grains
and erystals through the groundmass.

The biotite is in its characteristic, yellowish-brown prismatic crystals,

showing very plainly the lines of lamination. They are strongly dichroitic,

PETROGRAPHY—RHYOLITE. 5Ol

turning from quite pale-brown to dark greenish-brown, almost black, upon
revolution of the analyzer alone. When cut parallel to OP it is more olive-
brown and is not dichroitic.

The groundmass is pale-brown in color, half-glassy in character and
inclines a little to a microlitic texture, with traces of a fluid-like structure.
In it are numerous small, black specks, but no magnetite was observed.

The rhyolite [131] from southeast of Terry Peak has a light yellowish-
brown color, with broad reddish, parallel bands across it. It is quite com-
pact and fine-grained, and of a peculiar appearance like burnt clay. The
outside surface is weathered to a very dark-brown, the light shade showing
on a fresh fracture.

In the section, the groundmass appears quite finely crystalline, being
made up of small, rather dusty crystals of sanidin, with some magnetite
and an abundance of quartz in small rounded grains. The silica in the
rock is 72.22 per cent.

The sanidin through the groundmass is easily seen with crossed nicols,
as the indistinctly rectangular crystals are then light on a dark ground.
They are, however, quite cloudy and the outlines are not at all sharp. The
quartz polarizes brilliantly in colors, blue and yellow, and is present mostly
in irregularly shaped grains of small size, many of which have inclusions
of the groundmass with microlites and magnetite. They seldom have any
crystalline form, and are in considerable abundance. Magnetite is in small
submetallic grains; also a little biotite, none of which, however, is dichroitic.
Nothing very peculiar was noted in the groundmass, except that the reddish
bands, colored by iron, were plainly seen in the section.

The rhyolite [134] from the top of Custer Peak is very homogenous
in appearance and structure. It has a light-gray color and a fine-grained
texture, with an occasional small, black needle of biotite visible. In the
section, is seen a colorless groundmass, in which are numerous quartz grains,
abundant magnetite, a little biotite and sanidin as in the preceding rock,
seen as faintly defined crystals on a dark ground. The silica present
amounts to 68.62 per cent.

The sanidin apparently constitutes the greater part of the groundmass,
but the outlines of the crystals are very irregular and in general scarcely

502 GEOLOGY OF THE BLACK HILLS.

separated from the surrounding mass When the nicols are crossed it
polarizes faintly, so that the feldspathic portions of the rock appear toler-
ably bright and white, while the groundmass remains dark; the distinction,
however, being made with some difficulty. On the other hand, the quartz
strikes the eye at once with its brilliantly colored and sharply defined grains.
It is scattered quite abundantly through the rock, but rather in groups and
irregular streaks or veins, the larger particles seldom being seen isolated.
It contains as inclusions some microlites and small cavities. The biotite
occurs quite abundantly in very ragged and irregular crystals of a green-
ish color; the prismatic sections are dichroitic, while the basal ones are
browner in color. It is too much decomposed to show any laminations
and it is difficult to distinguish from hornblende, except by reason of the
different position of the optic axes of the two minerals. Magnetite in
small granules is quite uniformly distributed through the rock, and by its
appearance on the light groundmass aids in giving the rock the character-
istic rhyolitic appearance. There are also some brown films of hydrated
oxide of iron. The groundmass is crypto-crystalline, but does not possess
any microlitic structure.

The rhyolite [135] from the same locality has a similar appearance
to the preceding, being of a compact, uniform texture, very fine-grained,
and of a light-gray color with a few macroscopical black crystals of biotite
and quartz masses. The slide under the microscope also resembles that of
[134], but is a little finer grained in structure and has a few large and
unmistakable biotite sections.

As before, the sanidin crystals appear as faintly outlined light spots
on a dark ground, but there is one crystal quite transparent and sharply
defined. 'The quartz grains are abundant and give bright colors—blue, red,
and yellow—with polarized light, containing also microlites and black parti-
cles. Most of the biotite is present in the ragged, decomposed crystals as
in [134]; one crystal, however, of a light-brown color is still quite trans-
parent and fresh. It is very strongly dichroitic, changing with one nicol
to a very dark-brown, almost black. It has also a border of magnetite
grains of good size completely around it, which makes it a very conspicu-
ous object in the almost colorless groundmass. A similar one is shown in

PETROGRAPHY—PHONOLITE. 503

Plate I, Fig. 2. A second crystal, of the hexagonal basal section, has
magnetite grains, not only as a border, but also filling up the central part
and leaving only a small amount of brown mica. ‘This residue is not at
all dichroitic, thus agreeing with the plane of section determined from its
erystallographic outline. In both cases, the magnetite grains are much
larger than those scattered through the groundmass, the latter particles
being very numerous and quite small. The groundmass is crypto-crystalline
as before. The amount of silica is 72.33 per cent.

The rock [137], also from the top of Custer Peak, is again a rhyolite,
and very similar to [134] and [135], the sanidin in the colorless ground-
mass, together with the quartz and magnetite, presenting no essential differ-
ences. The example of biotite, with its border of magnetite grains, is much
finer than in [135] and is figured in Plate I, Fig. 2. The groundmass is a
little more microlitic in structure. In the rhyolites thus far examined, there
was found in the sections but little, if any, fluid-like structure, the ground-
mass being more granular and crystalline in character.

The rock [139] from Black Butte is a phonolite, and very different in
appearance and behavior from the trachytes and rhyolites. The ground-
mass has a grayish-brown color and a greasy or waxy luster, with dark-
green, irregularly shaped streaks and masses through it. It is quite
compact or crypto-crystalline, and weathers to a white mass. An occasional
whitish crystal can be distinguished with the aid of the loupe.

In the thin section under the microscope, it is seen to consist of a
groundmass composed mostly of nephelite, with sanidin, nosite and green
hornblende, in which latter mineral are imbedded transparent hexagons and
rectangles of nephelite (Plate I, Fig. 3). The rock gelatinizes very strongly
in hydrochloric acid, the soluble portion being 24.08 per cent. Boiled in
nitric acid and tested with ammonic molybdate, it gives but a very faint
reaction for phosphoric acid. The silica is quite low, only 56.32 per cent.

The crystals of nephelite, very conspicuous and abundant, are quite
uniformly distributed through the rock, the characteristic sections being
very distinct. The hexagons vary somewhat in size, a few quite large ones
being present, and all have similar inclusions, probably glass particles as
they are brownish in color. No needle-like microlites were found in any

504 GEOLOGY OF THE BLACK HILLS.

of the small crystals, but one large mass had a green, columnar microlite
and a few acicular ones. Some of the nephelite has become cloudy and
thick, probably from decomposition. In the rectangles are seen the same
kind of inclusions as in the hexagons, near the center in both cases, which
proves quite conclusively that the two forms of sections belong to the same
mineral, the crystals of which are short, stout, hexagonal prisms with the
basal pinacoid. The hexagons are sections cut parallel to the base; and,
the optic axis being coincident with the vertical axis, they are consequently
simply refracting and dark between crossed nicols. On the other hand, the
rectangular sections are of a bluish-white color when the nicols are crossed,
so that in the dark field they are quite conspicuous. In a mass of horn-
blende are several of the two forms of sections lying close together which
show this behavior perfectly, the hexagons remaining dark, while the rec-
tangles become bright in striking contrast. In the illustration (Plate I, Fig.
3) they are drawn when both are light, in order to show. the outlines dis-
tinctly. There are also a few square nephelite sections, which polarize
quite brilliantly.

The hornblende is in irregularly shaped green masses, crystalline and
dichroitic, but very thickly crowded with transparent nephelite crystals It
has the appearance of being large crystals much broken and separated, so
as to resemble broad bands through the rock. It is also quite abundant in
fine needles through the groundmass.

Although nosite is a frequent constituent of phonolite, it was only after
much consideration that it was determined to be present in this rock. The
two particularly large and distinct sections, one shown in Plate I, Fig. 4,
were at first named sanidin, but a closer examination revealed the fact that
the fresher parts of the crystals were simply refracting, remaining dark with
crossed nicols, which could not be possible if they were sanidin. Again,
the peculiar dusty appearance, parts of the crystal being lighter that others,
and a dark border around the edge are all characteristic of nosite. The
two sections mentioned are five-sided, different in this respect from the
usual forms of sanidin. They are not very transparent, except in places
which have been altered to a doubly refracting mineral, probably natrolite,
as is often the case. These altered parts are faintly bright with crossed

PETROGRAPHY—SANIDIN-TRACHYTE. =| 505

nicols. The deciding peculiarities, then, are the form, the dusty or dotted
structure, the simple refraction, the dark border and the behavior of the
decomposed portions of the crystals Besides these two large sections, there
are quite a number of smaller nosite crystals more irregular in shape, some
being hexagonal and others rectangular, more opaque and in varying stages
of alteration, though they are still partly isotrope.

The sanidin is in the form of indistinct, long, rather roughly shaped
masses and columnar microlites, lying between the nephelite crystals and
showing with the hornblende a distinct, curved and fluid-like structure in
places, and particularly around the two large nosite crystals mentioned
above (Plate I, Fig. 4). The columnar, somewhat fibrous-looking crystals
polarize with tolerable distinctness with crossed nicols. No magnetite nor
biotite were found. Besides the minerals already described, no other
groundmass is discoverable as the rock is made up of sanidin, nephelite,
and hornblende in intimate union, the structure being quite crystalline.

The strong gelatinization, large amount soluble in acid, and low silica
percentage of this phonolite all aid in confirming the above determinations,
and it is to be hoped that more observations of its geological occurrence
will be made at some future time.

The sanidin-trachyte [140] from Black Butte is light-gray, inclining a
little to yellow in color, but has not the uniform and fine-grained appear-
ance of the rhyolites. Scattered through it, small yellow spots and dark
needles of hornblende can be seen with the loupe. Under the microscope,
the section shows the rock to be mostly sanidin, in clear, roughly shaped
erystals and partly in masses, with abundant long, prismatic crystals or
blades of hornblende. It is quite similar to [124] and [171].

The sanidin, besides being the mass of the rock, is also seen in indis-
tinct crystals, which have many irregular lines of fissure and also contain
long, needle-like, colorless microlites, probably apatite, and hornblende
erystals and fragments. Most of it has a cloudy or dusty character, which
is seemingly caused by innumerable short, stout microlites of exceedingly
minute dimensions scattered in quantities through it.

The hornblende crystals are of a fine green color, and some have

506 GEOLOGY OF THE BLACK HILLS.

sharply defined terminations and angles. They are also dichroitic and scat-
tered plentifully through the rock.

As in [171] there seems to be some transparent glass mass, which is
perfectly isotrope and of a very different texture from the sanidin. The
yellowish spots in the hand specimen are seen in the section to be of very
irregular shape, but transparent. An occasional yellowish, opaque and
hexagonal crystal may be decomposed mica or feldspar, but its exact nature
could not be determined. Some magnetite in large masses is present, but
sparingly. The groundmass, as mentioned before, is entirely feldspathic,
clear and cloudy in irregular masses, and showing, perhaps, traces of a
slight fluid-like structure. The percentage of silica is 58.53, and the
amount dissolved in hydrochloric acid 18.59 per cent.

The rock [141, 142] from Crow Peak is a rhyolite containing plagio-
clase, and is much more crystalline than the preceding, having macroscop-
ical sanidin crystals plainly imbedded in a groundmass. ‘They are white
and very transparent. There are also some black crystals of hornblende
and empty cavities, which were formerly filled with the latter mineral. In
the section, the microscope shows the rock to consist of large, clear crystals
of sanidin and plagioclase in a crystalline groundmass, also containing
broken biotite crystals and some quartz in grains and crystals.

The sanidin in this rock is very beautiful, being unusually large and
transparent. The crystals are sharp in outline and sometimes terminated
on both ends, showing numerous faintly marked zones parallel to the edges.
Many of them are twinned, the different colors of the two parts being very
conspicuous. Numerous microlites are iucluded, some of them tolerably
large, columnar in form and quite long. Others again are in short, stout
crystals, distinctly showing prismatic and terminal faces. ‘The former may
be apatite and the latter hornblende. Magnetite and small biotite folia are
also among the inclusions of the sanidin. The colors in polarized light are
very brilliant, but are in irregular masses or blotches in the same crystal ;
near one edge a bright red predominating, then yellow, turning gradually
to a greenish-yellow, with spots of red and blue. All these colors are
interlaced, often penetrating from the edges in lines and points one into
the other.

PETROGRAPHY—SANIDIN-OLIGOCLASE-TRACHYTE. 507

The plagioclase is often crystallized inside of the sanidin and upon the
edges of the crystals. The banded appearance of the twin lamellations is so
broad and beautiful as to resemble greatly that of labradorite; a few of the
independent crystals are very large.

There are numerous quartz grains of irregular shape throughout the
groundmass and occasionally a large mass more regular in form. The bio-
tite is in very large, broken, and decomposed crystals, either long, prismatic
in shape or in hexagonal plates. Although both forms are much torn and
broken and but faintly dichroitic, the distinct laminations can be easily seen.
It is, moreover, quite dark and opaque in many places. Magnetite occurs
in small grains, abundantly scattered through the groundmass and also in
quite large masses, having the usual submetallic luster. The groundmass
is crystalline very distinctly indeed, being an aggregation mostly of rectan-
gular and ragged sanidin crystals, with some quartz, magnetite, and a little
biotite in small brown leaves. The silica was determined to be 67.36 per
cent.

The sanidin-oligoclase-trachyte [144] from between the forks of Bear
Butte Creek is brownish in color and of a very rough texture, with macro-
scopical crystals of feldspar, between which can be seen dark-green needles
and crystals of biotite. In the section, were observed large and tolerably
clear sanidin and plagioclase crystals in a fine-grained, light-brown ground-
mass with biotite and magnetite.

The large sanidin crystals are quite clear, and give fine colors in polar-
ized light, but there are still a great many fissures and cracks, along which
they are cloudy and altered. Microlites, as beautifully distinct long needles
and tolerably stout prisms and rounded glass masses, are among the many
inclusions of these sanidin crystals. The colorless needles are probably
apatite, with which are associated magnetite and biotite. Some of the
sanidins are twinned, the two parts polarizing differently. The plagioclase
is in large crystals and of distinct outline, although they are often formed
in conjunction with the orthoclase. The twin striations are in some cases
very broad and distinct, while in other crystals they are so fine and delicate
as to resemble the sanidin striations arising from structure. Generally they
are sharp and plain, The crystals have similar inclusions to those of the

508 GEOLOGY OF THE BLACK HILLS.

sanidin, but not quite so abundant. The biotite is very dark and much
decomposed, but still shows the characteristic, deep furrows and a strong
dichroism. The sections are very abundant and quite large. Magnetite is
thickly scattered through the groundmass in small grains and sometimes
in large masses, while there are also some very opaque and thick films of
oxide of iron of a dark reddish-brown color, in which the large magnetite
grains are imbedded

The groundmass is made up of small irregularly shaped feldspar
crystals, of very indistinct outlines, and but feebly polarizing, mixed with
minute grains of magnetite and brown biotite. It has the peculiar tra-
chytic appearance, which cannot easily be mistaken, and a partly fibrous-
microlitic structure. This rock borders closely upon the rhyolites, but its
macroscopical rough, ragged and porphyritic appearance and structure
differ so widely from the fine-grained and uniform light-gray characteristics
of the former as to place it among the trachytes proper. The silica amounts
to 65.46 per cent., and 10.09 per cent. is soluble in hydrochloric acid.

The rhyolite [147] from the north peak of Inyan Kara is a compact,
fine-grained and very light-gray rock, with only an occasional white sanidin
crystal and black biotite needle visible. Under the microscope, the section
appears to consist of a great quantity of small, bright sanidin crystals in a
groundmass, with biotite and magnetite. The silica present is 73.18 per
cent.

The similarity of the small sanidins to large ones is very easily seen
in their clearly defined outlines and numerous twinned crystals. They
have inclusions of microlites. There is one group of large and very trans-
parent crystals in the slide, which polarize in very beautiful and brilliant
colors showing some banding, all of which, however, is not that of plagio-
clase. The bands of color, except in one case, are not exactly parallel and
resemble more the varying colors of sanidin. Biotite is in brownish masses
and leaves of small size, and also in very minute black needles, which are
partly altered to magnetite, a few being still dichroitic. Magnetite grains,
as in almost every one of these rocks, are plentiful. Some quartz in rounded

grains and polarizing in bright colors is present.

PETROGRAPHY—SANIDIN-TRACHYTE. 509

The groundmass is mostly made up of the small sanidin crystals men-
tioned before, but between them appears to be a very fine partially micro-
litic mass, which remains dark with crossed nicols.

The. sanidin-trachyte [149] from the central peak of Inyan Kara is
dark in color, being gray, inclining to greenish. Macroscopical crystals of
sanidin are visible, as well as some black prismatic hornblendes. It is very
different from the preceding rhyolites, having much less luster and being
darker.

In the section, it is immediately seen that sanidin is in great preponder-
ance, the groundmass being composed of it and there being also a great
many large, fine crystals. Hornblende and biotite, with magnetite are
scattered through the groundmass in large and small crystals and grains.
There is also some plagioclase. The large sanidin crystals are very char-
acteristic, polarizing in fine colors and showing the different colored zones
of the formation of the crystals. Sometimes a well formed section with
perfect outline has a very different color from the more roughly shaped
mass forming the exterior coating, the interior for instance being light
brown and faintly zoned, while the other part is a brilliant purple. This
zonal structure is quite usual in this rock and is shown in Plate II, Fig. 1.
The inclusions are long and very delicate prismatic microlites, which may
be apatite.

The hornblende is present in large crystals, somewhat broken and full
of fissures, but still polarizing quite strongly from yellowish-green to dark-
green, although they are but faintly dichroitic Many of them have crys-
tals of sanidin and magnetite imbedded in the interior, the form of the
sanidin being quite perfect. Besides these large crystals, there are innum-
erable quite small and irregular ones, many of which in quite a striking
manner are tipped with magnetite on both ends, and nearly every one has
a large grain of magnetite in some part of it. Not to be confounded with
the hornblende is the biotite, which occurs in large crystals, very much
decomposed and broken to such a degree that their former outlines are
shown only by the rows of magnetite grains till remaining in their stead.
The biotite is ight-brown and strongly dichroitic, changing to very dark-
brown upon turning one nicol; it is also deeply striated and full of magnet-

510 GEOLOGY OF THE BLACK HILLS.

ite. In a few instances the plane of section is parallel to the base, when
it is not at all dichroitic. It is not so plentiful as the hornblende, which is
distinguished from it by its fine green color in almost every case. There
are a few large plagioclase crystals, which have quite sharp bands of color,
but they are so much grown together with the sanidin that it is difficult to
discern any dividing lines between the two. From the preceding descrip-
tion, it is readily understood how abundant the magnetite is through the
whole rock, giving at almost every point its bright luster. Long, colorless
apatite needles in considerable abundance can also be recognized without
difficulty in the groundmass.

The groundmass is coarsely crystalline and composed of irregularly
shaped sanidin crystals which polarize in bright colors, mixed with horn-
blende, biotite, and magnetite. There does not appear to be any isotropic
glass mass between the above ingredients. The percentage of silica was
found to be 60.51, which, with the observations already noted, determines
this rock to be undoubtedly a normal sanidin-trachyte.

The sanidin-trachyte [150] from a locality five miles northeast of
Inyan Kara has a much duller and more weathered look than [149], being
also less crystalline in its structure. The color is dark-gray, mottled with
greenish spots, which have disappeared on exposed surfaces, leaving empty
cavities.

In the section, it is observed to consist of sanidin and hornblende in a
somewhat fibrous groundmass with but very little magnetite. The sanidin
crystals are very much confused with the surrounding mass and ragged in
their outlines, but occasionally there are some twins. In the simple crys-
tals, cloudy streaks resemble the dusty-looking parts of the groundmass.
From the variation of color in the large masses of sanidin it is quite easy
to make out their polysynthetic nature, being built up of a number of small
crystals. ‘The hornblende is in fragments and small, sharply defined crys-
tals, quite dichroitic and sometimes showing the lines of cleavage.

The groundmass consists of cloudy or dusty masses and crystals of
sanidin, which only faintly betray their outlines with crossed nicols The
rock is similar to [124].

The sanidin-trachyte [151] from the north peak of Inyan Kara

PETROGRAPHY —RHYOULITE. 511

resembles both in color and luster [149], being dark-gray, with macro-
scopical sanidin crystals and black needles of hornblende. In the thin
section under the microscope, it is exactly the same, namely, a crystalline
mixture of sanidin, hornblende and magnetite. ‘The sanidins have the
same zonal structure as before, as well as the marked difference between
the interior and exterior parts of the crystal. The colorless, long, prismatic
microlites of apatite are also present and a few masses of plagioclase and
biotite. The large, green hornblende individuals are different from those
of the scarce, brown and dichroitic biotite, because the former are fresher
and much greener than is usual for biotite. Again, if they are biotite, it is
remarkable that more of them are not cut parallel to «oP, considering how
plentifully they occur in the slide; for all the green, non-dichroitic sections
in the above case would be sections parallel to OP, which theory their long,
prismatic shape hardly seems to warrant. ‘The biotite crystals also have
a border of magnetite grains, which appearance was not observed with
the green hornblende, although they include large grains of magnetite.
The cleavage lines are very indistinct and difficult to make out, but in a
few cases they seem to be decisive.

The groundmass is, as before, a coarsely crystalline mixture of feldspar,
magnetite and small crystals of hornblende.

The rhyolite [152] from Inyan Kara (?) has a light-gray color and
is quite homogeneous in structure, being fine-grained, with numerous
very small biotite needles imbedded in the mass, resembling [147] the
rhyolite from Inyan Kara. Under the microscope, it seems to be made up
of sanidin crystals, with biotite and magnetite in a partially crystalline
groundmass. The sanidin is in crystals of moderate size, quite transparent
and having the characteristic zone structure, and also twinned crystals.
The slender, biotite needles are abundant and generally dichroitic. The
difference in the plane of section is strikingly shown in this slide, there
being a large hexagonal form of a fine brown color, which shows no change
upon a revolution of the nicol, while the prismatic forms change from light
to dark-brown. The biotite has magnetite grains through it, as usual in
these rocks. Magnetite in small grains of uniform size is quite evenly dis-
tributed through the mass, though there is an occasional large piece. The

512 GEOLOGY OF THE BLACK HILLS.

groundmass exhibits the peculiar half-fibrous and half-crystalline appear-
ance of the rhyolites, as if it consisted of microlitic needles of sanidin
between the larger but still indistinct crystals, which only betray their
form by being of a faint whitish color with crossed nicols.

The sanidin-trachyte [157] from the hill west of Inyan Kara has the
most characteristic appearance of a normal trachyte of any of the rocks
examined. Its color is light grayish-white, with occasional reddish and
brownish spots and cavities, which have the shape of biotite crystals, the
latter having disappeared and left only a little magnetite. At first sight
these cavities seem to be black needles of mica, but a closer examination
shows that they are empty holes. An oceasional glassy sanidin may also
be seen. The microscopical examination of the thin section showed some
very beautiful and interesting sanidin crystals in a crystalline groundmass
of feldspar, with magnetite and a little biotite. It resembles [149], but
has no hornblende. The amount of silica is 61.88 per cent

The sanidin crystals are quite transparent, but are colored in irregular
blotches and spots in polarized light, owing to their composite character.
They include colorless needles of apatite, considerable magnetite and
biotite, the needles being sometimes grouped in a sort of star around a
grain of magnetite. The larger and more perfect crystals are quite rect-
angular in shape, and have the usual zonal structure of sanidin. The inte-
rior portion of the crystal has a very perfect form, being terminated with
the base and hemi-orthodome, while the exterior, rectangular form is made
by an additional growth of feldspar in a different optical position, or of a
different nature. The result is that the interior, well formed crystal polarizes
a violet color, while the exterior shell or coating is deep blue, making a
distinct contrast. In other cases it is yellow and blue. There were also
observed some very nice twin crystals, both from interpenetration and juxta-
position. The most interesting occurrence is that of a large sanidin crystal,
long and rectangular in shape, which has been broken by a fragment of
feldspar so as to cause the larger piece to be pushed out of place. The
former continuity of this crystal is shown by the fact that the two pieces
polurize a fine deep blue at the same time, while the irregular fragment is
yellow. By revolving the analyzer or slide the colors change—the crystal

PETROGRAPHY—SANIDIN-TRACHYTE. 513

to yellow and the fragment to blue. In either case the appearance is strik-
ing, and is not often met with in such a perfect condition. It is shown in
Plate II, Fig. 2.

Magnetite grains, large and small, are in abundance all through the rock,
the occasional large masses having a fine luster. Long, colorless needles
of apatite of quite good size are often noticed in the groundmass, and also
exceedingly minute dark colored needles, probably biotite. The larger
biotite crystals are very ragged and indistinct, being so much decomposed
as to scarcely show any traces of dichroism Some of the feldspar crystals
are faintly banded, but are not all plagioclase, the lines being too irregular.

The groundmass is crystalline and composed of sanidin masses, with
grains of magnetite and a little biotite. There are slight traces of a fluid-
like structure in parts of the groundmass.

The sanidin-trachyte [159-162] from Bear Lodge Butte has a greenish
color, with very glassy and transparent sanidin crystals porphyritic in the
groundmass, in which can also be seen large, green hornblende crystals.
Some of the sanidin has become opaque white, giving the rock a rough and
spotted look, which is added to by the small hornblende blades thickly
sprinkled between the white sanidin. The appearance of the rock in the
thin section immediately recalls that of [123], already described. It con-
sists of very large sanidins in a groundmass, full of small hornblende
microlites and blades and having a fluid-like structure, and also large,
fresh and green hornblende crystals with magnetite in large grains. See
Plate II, Fig. 3. The sanidin crystals are very large and quite clear,
but have cloudy or dusty streaks and spots through them, though with few
inclusions of any marked character, except occasionally a hornblende
crystal. The cloudy portions are sometimes almost entirely opaque These
are the result of alteration and are the macroscopical white spots. The
outlines of the crystals are quite sharp and distinct from the groundmass,
most of them being terminated by two planes. The hornblendes are very
conspicuous in the slide, their colors being from greenish-brown to a vivid
green and dark-green, and their outlines very clean and sharp. Most of
them have a hexagonal form, with two sides longer than the others, while

a few, especially one large crystal, have eight sides, six being predominant.
33 BH

514 GEOLOGY OF THE BLACK HILLS.

These crystals are strongly dichroitic, changing from greenish-brown to
green, and especially so when cut about parallel to the base, as is shown by
the more distinct cleavage lines. Ail of the large crystals have very marked
fissures and lines, some of which, however, arise from lamination, but in
some the cleavage lines at the angle of 124° can be seen, these being the
most strongly dichroitic. They have inclusions of small sanidin crystals,
large grains of magnetite and some glass masses. Hornblende is also
present in very abundant small, prismatic, or blade-shaped crystals, thickly
distributed through the groundmass. Their terminations are quite rough,
forked and ragged, and not nearly so sharp as the similar crystals in [123];
they are but faintly dichroitic. Grouped with two large hornblendes and
a mass of magnetite was observed a colorless mineral, irregular in shape,
and with quite a different structure from the sanidin. It polarizes faintly,
and is probably some zeolite or calcite, but its exact nature was not
determined.

The groundmass is feldspathic, polarizing white with crossed nicols,
and appears to be an aggregation of small, needle-like feldspar crystals, in
which are imbedded the small hornblende prisms. This whole mass shows
a very plain fluid-like structure, as if it had flowed around the large sani-
dins in streams and become suddenly congealed, thus preserving the unmis-
takable signs of the former fluidity of the rock. This appearance is not so
marked as in [123], but sufficiently plain to be easily noticed under the
microscope. The silica was determined to be 60.77 per cent., and the
amount dissolved in acid was 15.33. This large percentage of soluble min-
erals may be due to the abundant hornblende and partly also to the pres-
ence of some zeolite or calcite.

The rhyolite [166] from the north peak of Inyan Kara is of a gray
color, compact and homogeneous in structure, with a few lustrous sanidin
crystals visible to the naked eye. It resembles the rocks [147] and [152]
from the same locality. An examination of the thin section under the
microscope revealed its composition to be of small sanidin crystals, with
magnetite and dark-brown biotite needles, the latter being almost opaque.
Occasionally, a very large and clear sanidin is seen having the zonal struc-
ture mentioned before. The small crystals are of sharp outline and dis-

PETROGRAPHY—SANIDIN-TRACHYTE. 515

tinctly shaped forms, many being twinned. The biotite prismatic crystals
are very small indeed, but are thickly scattered through the rock. The
magnetite is generally in very small grains. The groundmass appears to
be of a fine fibrous or microlitic structure, filling the interstices between
the sanidin crystals. Itis feldspathic in nature and dusty, so that it polarizes
but feebly, and there is less quantity than at first sight appears. While one
set of the sanidin crystals are bright with crossed nicols, those in a different
position are dark and might be mistaken for the groundmass. Upon revoly-
ing the slide, however, the crystals respectively change their appearance,
the gereral aspect of the rock remaining the same, while there are some
crystals always bright and conspicuous.

The specimen [167, 168] from Little Missouri Buttes is a sanidin-tra-
chyte, but approaching phonolite in structure and in the presence of some
zeolitic minerals. Its color is a quite dark, dirty-green, with an abundance
of white, glassy sanidin crystals conspicuously scattered through the ground-
mass. <A few blac hornblendes can be also seen. The structure of the
groundmass is quite compact, with the sanidin from very small to large
crystals imbedded in it. On the surface of some of’ the large sanidins is a
yellowish-brown coating or crust of alteration. Under the microscope, the
rock appears made up of large sanidin crystals, some clear and some dusty
or decomposed, in a yellowish-green, fibrous groundmass, with a few green
hornblende and brown biotite crystals. The sanidins are quite well defined
in form, showing generally the six-sided sections corresponding to prism,
base, and hemi-dome. Some are very transparent and give a fine blue or
yellow color in polarized light, while others seem to be altered, having
become quite cloudy from numerous small acicular or fibrous microlites in
nature like the groundmass, so that only small portions of the crystals give
any color. This alteration commences in streaks across the clear crystal,
eventually affecting the whole mass; in a few cases a radiated zeolite has
been formed in the fissures and also in the interstices between two sanidin
crystals. The transparent crystals are characteristic and have cleavage
lines in two directions. The inclusions are portions of the groundmass and
small, pale-greenish columnar crystals and dark needles. Besides these are
numerous round and long cavities in rows and scattered through the crys-

516 GEOLOGY OF THE BLACK HILLS.

tals; their brownish color shows them to be probably glass inclusions.
There are a few dark-green hornblende crystals rather prismatic in shape, but
also tabular and irregular ones, which are strongly dichroitic. Some of them
are altered into a dark reddish-brown substance, notably two quite large
hexagonal sections. The brown, resultant mineral does not polarize nor is
it at all dichroitic. There are also a few plagioclases present, and the single
grain of magnetite discovered has an unusually brilliant luster. In some of
the sanidin crystals and also filling up fissures is a granular mineral, which
polarizes faintly like sanidin, but with a rougher surface. Its exact nature
could not be determined, but it is probably zeolitic. The radiated, trans-
parent mineral already mentioned is quite remarkable and conspicuous, as
it gives bright blue, yellow, and red colors in polarized light. It is a zeo-
lite, presumably natrolite, and gives a phonolitic character to the rock, shown
by the very large percentage of the soluble portion.

The groundmass is very fibrous in character, bemg composed of a
ereat quantity of long, capillary, yellowish-green needles closely interlaced
and grown together. They may be hornblendic. The silica present is
59.06, and 29.25 per cent. is soluble in hydrochloric acid, but no nephelite
could be found in the rock or thin section.

The rock [169] occurring at the contact between the trachyte and
sandstone at the base of Little Missouri Buttes has a very porous, spongy
structure, full of large, rounded cavities, so that it is much like pumice to
the touch. In the mass are seen quartz grains, white, decomposed crystals,
dark-colored spots, and some transparent sanidins. It has an earthy, dirty-
yellow color, but is hard and resonant. In the section, it was observed to
consist of large grains of quartz, sanidin erystals and a little plagioclase,
with fragments of another rock, a rhyolite, imbedded in a rather opaque
cementing mass of volcanic character.

Many of the sanidin crystals are so much decomposed as to be nearly
opaque and whitish in color, while others are very clear and transparent,
having inclusions of microlites. Some of the smaller feldspars are banded
like plagioclase. The quartz grains are rounded, polarizing, of course, in
brilliant colors, and are easily recognized. They contain long, hair-like

microlites, besides an abundance of cavities and some prismatic-shaped

PETROGRAPHY—SANIDIN-TRACHYTE. Sin

erystals that may be hornblende. Quite remarkable is the appearance of
fragments of rhyolite, similar to those already described [147], [152], [166],
in which all the constituents are plainly to be seen, small sanidins and bio-
tite in a fine-grained groundmass. The color of these fragments is quite
different from the surrounding rock mass. The groundmass of the rock
under examination is granular and has an earthy color, with darker spots
through it, bemg also full of small boles and sanidin crystals, so that is no
doubt trachytic. It is a rhyolitic breccia, which has inclosed fragments of
both the sandstone and the adjoining rhyolite.

The sanidin-trachyte [171] from Warren Peaks has a grayish color,
faintly mottled with white and red spots, there being, however, no feldspar
crystals visible to the naked eye. In the section, its composition appears
to be sanidin in large, indistinctly defined crystals in a fibrous groundmass,
with a great number of small, prismatic hornblende crystals.

The greater part of the rock is sanidin in a partly dusty and opaque
condition and almost in one mass; it is also in the form of some quite clear
crystals, confused in outline with the mass around them. These clear
crystals are sometimes twinned and have inclusions of hornblende, while
the cleavage lines and fissures are prominent and distinct. The opaque,
white crystals have a little more distinct outlines and are most easily seen
in reflected light. The hornblendes are very thickly scattered through the
rock, seemingly more’ plentiful between the clear sanidins. They have
generally a prismatic shape and ragged or forked terminations, with an
occasional large crystal of more distinct outline. They are slightly dichro-
itic from brownish-green to a fine deep-green, but the cleavage lines are
almost obliterated. The rich green color of the small crystals makes them
very conspicuous objects in the field of the microscope. Between some of
the opaque sanidins was noted a colorless, transparent, isotropic mineral
which could not be satisfactorily determined. It may be glass or calcite.
Very little magnetite was seen, but considerable brown oxide of iron in
spots. The groundmass is almost entirely sanidin aggregated to one mass,
with fibrous streaks traversing the rock in every direction. These streaks
contain most of the hornblende columns; and in parts of the slide may be
observed a slight fluid-like structure around the smaller sanidins. This

518 GEOLOGY OF THE BLACK HILLS.

rock is very similar to [124] from Terry Peak, although this has larger
hornblendes and an abundance of magnetite, which is lacking in the rock in
question. The resemblance between the two hand specimens is not so
marked, [124] having large porphyritic sanidin and hornblende crystals,
while [171] is more uniform and compact. There is a similarity in struc-
ture to [123] and [159], the small hornblende prisms in the two latter,
however, being much more numerous and the rocks in a fresher condition.

The sanidin-trachyte [173] from southwest of Warren Peaks is light-
gray in color, and quite compact and uniform in structure. It has an
occasional large, glassy sanidin, while the entire rock is thickly besprinkled
with tiny, green hornblende crystals, easily seen with a loupe. Under the
microscope, the section appears to consist entirely of sanidin, partly in
well defined, clear crystals and partly in a cloudy mass, scattered through
which are seen the green hornblendes.

The clear sanidins present a new feature as yet not observed in any of
these rocks, namely, inclusions of small, rounded, light-brown glass masses.
These particles do not polarize at all and are abundant in almost every
crystal, having sometimes hexagonal and rectangular forms. They are also
partially transparent. It is interesting to note that the single macroscopical
sanidin crystal in the hand specimen contains near its center a light yellow-
ish-brown, spherical inclusion about the size of a small mustard seed,
undoubtedly of the same character as the glass masses observed in the
slide, which unfortunately does not happen to have a large sanidin in it.
There are also a few transparent hornblende microlites in the sanidin. The
hornblende crystals are of a fine green color, slightly dichroitic and pris-
matic in shape, somewhat similar to those in the preceding rock, but broader
and more sharply terminated.

The groundmass, if any can be distinguished between the sanidin
crystals, is cloudy and thick, but more granular than microlitic and having
but very slight traces of any fluid-like structure. The rock is similar to
[171], but not so much weathered, both the hornblende and sanidin being
sharper and more crystalline in form.

The rock [174] from north of Warren Peaks is quite interesting and
different from any of the other specimens and rather difficult to determine,

PETROGRAPHY—SANIDIN-TRACHYTE. — 519

It has a grayish-green groundmass quite crystalline in structure, through
which in great abundance are large, black, lustrous biotite crystals and
smaller, green columns of hornblende. Besides these there are numerous
particles of a white mineral; some are small and hexagonal inshape and others
quite large and crystalline, one in particular having a crust on the surface
as if it had filled up a cavity in the rock. In this large mass lies a trans-
parent crystal of calcite, which, with many of the smaller masses, effer-
vesces in acid. The harder, white particles of more hexagonal form do not
effervesce and are probably apatite. The rock does not gelatinize in acid,
but, treated with nitric acid and ammonic molybdate, gives an abundant
yellow precipitate, thus proving the presence of apatite as described in the
examination of the thin section. It has 52.02 per cent. of silica, and 23.14
per cent. is soluble in hydrochloric acid. The rock is a trachyte, with the
accessory and accidental minerals apatite and calcite.

In the section under the microscope, is seen a feldspathic groundmass,
in which are very abundant biotite, hornblende and apatite crystals, with
magnetite grains and colorless masses of calcite. The sanidin is in indis-
tinct and not very transparent crystals in the groundmass, which seems to
consist of the same mineral. The crystals are bright with crossed nicols,
when their shape can be made out with tolerable ease, while an occasional
good rectangular section may be seen. The hornblende is very abundant
in large, pale-green, prismatic crystals, which give very beautiful bright
colors, green, red, blue, &¢., in polarized light. There are also numerous
small crystals, which are quite sharply and distinctly terminated, but they
show little dichroism, the majority being cut parallel to the vertical axis.
A few sections, however, parallel to the base. have the cleavage lines and
are dichroitic. The hornblende has inclusions of magnetite and sometimes
of calcite.

Much more conspicuous is the biotite in its very large and strongly
dichroitic, light-brown sections. It is very plentiful in the rock, from long,
slender crystals and small fragments to large, brown and almost opaque,
hexagonal basal sections. The lines of lamination are distinctly marked,
and inclusions of magnetite and calcite are very frequent. Remarkable is
a group of hexagonal sections, in which are white, calcite masses, including

520 GEOLOGY OF THE BLACK HILLS.

in their turn sharp, square crystals of magnetite, forming a double inclusion
not often met with (Plate II, Fig. 4). The partially altered biotites are very
dark, full of magnetite and nearly opaque, while the light-brown, transparent
prismatic sections often have apatite inclusions. The magnetite is very
abundant in large grains and masses. Apatite is present and is recognized
in the hexagonal white sections, which change only from light to dark with
the revolution of the nicols. The long, slender sections parallel to the
prism are seen to be doubly terminated by a pyramid, while they are of a
faint violet color with crossed nicols. The basal sections are quite sharp
and clear in outline, and of large and small size, the latter being most
brilliant That this mineral is apatite and not nephelite is confirmed by
the chemical reaction obtained for phosphoric acid as well as the form of
the long, acicular prismatic sections, which are more usual for apatite than
nephelite. The pyramidal terminations belong also to apatite, the crystals
of which in this rock are unusually large and fine. The calcite is in irreg-
ular, colorless masses, which appear to fill up cavities and also to be inclu-
sions in hornblende and biotite. It changes only from light to dark, and
does not have in the section any of the usual lines of twinning and cleavage.
A fragment broken from the large mass previously mentioned showed the
characteristic cleavage very distinctly under the microscope, while the
effervescence with acid also proves its character. It may be the result of
decomposition, or more probably it has been formed in the cavities of the
rock from extraneous sources as an infiltration.

The groundmass is made up of sanidin crystals, confusedly inter-
grown and interlaced, a few of which are still fresh enough to show their
forms as bright sections between crossed nicols, while the whole mass is also
sufficiently clear to make its structure apparent.

The sanidin-trachyte [175] from southwest of Warren Peaks has a
dark-green color and is very compact and solid, resembling [123] and
[167]. Scattered through it are whitish crystals of feldspar, quite conspicu-
ous in the green mass. The thin section is seen under the microscope to
consist of a remarkable mass of delicate, acicular microlités of hornblende,
in which are a few sanidin and large hornblende crystals, with magnetite.

The sanidin crystals having a distinct outline are rather scarce. They are

PETROGRAPHY—SANIDIN-TRACHYTE. 5? 1

quite transparent and include a great many microlites, and the needles of
the groundmass press into the crystal along the border in such quantities as
to explain perhaps the formation of the rock. The solid mass consists for the
most part of clear and transparent sanidin, which, however, has been pierced
through and through and filled up with vast numbers of yellowish-green
hornblende needles, leaving an occasional crystal free, which now behaves in
polarized light in a similar manner to the mass in the interstices between the
microlites. The green colorof the rock results from these microlites. A similar
structure, but with much larger hornblende crystals, can be observed in the
rocks [123] and [159-162], the fluid-like structure in the latter being also
much more marked. In the slide now under examination, this structure is
indistinct, being best seen around a sanidin crystal as if the force of the crys-
tallization had pushed the microlites closer together. ‘There are a few quite
large, yellowish-green hornblendes, which are dichroitic, although not very
strongly so, and show some traces of cleavage lines. They include grains
of magnetite and one in particular contains a piece of magnetite about one-
third of its size, which conforms to the shape of the hornblende as if it was
the result of a secondary formation. The section of [124] has a similar
occurrence of hornblende and magnetite. The hornblende has also brown
spots through it, the beginning of alteration. Magnetite in small grains is
present, but not very abundantly, and must not be confounded with very
minute black biotite needles.

The greenish color of the microlitic groundmass can be seen to the
best advantage with reflected light.

The sanidin-trachyte [178] from the top of Warren Peak is a charac-
teristic looking rock, with enormous sanidin crystals in a light-grayish
groundmass, with iron-brown spots in it. Some of the crystals are from
one to two inches in length. In the section, the rock appears to be very porous
‘and to consist of a fine groundmass, in which are the large crystals, with
some hydrated oxide of iron and nearly decomposed biotite The large
sanidins present no remarkable appearances, while the feathery or fibrous-
microlitic groundmass has been previously described as characteristic of
trachyte. The biotite has become so nearly opaque and brown as to lose
all of its peculiarities, except the rough, hexagonal outline. But little mag-

522 GEOLOGY OF THE BLACK HILLS.

netite can be seen, it having been altered to limonite. There are through
the slide a few veins of a partly fibrous mineral, having the appearace of
filling up a fissure; and in some parts of the section an indistinct fluid-like
structure was observed.

The rock [187] from Gold Ledge, Warren Peak, is felsitic, compact
and porcelain-like in structure and appearance. On a fresh fracture it is
light-gray in color, mottled with pale-yellow spots of a resinous luster, and
some black spots. It weathers to an iron-red or brown, so that large parts
of the rock have the various intermediate shades from white, through flesh-
color, to dark-red. A few large, opaque white sanidin crystals can be seen,
which are exceedingly hard, as if altered to some siliceous mineral. The
yellowish spots, and also some of a bluish-white, milky color, resemble
chalcedony or opal, which minerals occur in trachytic rocks. In the thin
section, the felsitic groundmass remains cloudy and not at all transparent
and in it are seen dusty and cloudy sanidins, partially altered to a radiated,
brightly polarizing chalcedony or quartz mass. Some of the smaller, rect-
angular shaped ones are entirely changed to this chalcedony, which affords
a dark or colored cross in polarized light. This cross revolves and
changes color, following the motion of the prisms, and is due to the radi-
ated or fibrous structure of the chalcedony. The sanidin crystals are
quite cloudy and have lost all their crystalline characteristics except the
external form, which can still be recognized against the dark groundmass
by reason of their slight transparency. They do not polarize at all, remain-
ing dark between crossed nicols. Twinned crystals can be seen occasion-
ally, and in one case the alteration to chalcedony has begun at the twin
line. A few reddish spots and blotches of oxide of iron are scattered through
the rock sometimes surrounding a sanidin crystal, but no other mineral
constituents were observed. The rock is evidently trachytic in nature and
might be called a felsitic rhyolite, with chalcedony or opal as a result of
infiltration or secretion. The silica was determined to be 79.89 per cent.,
much higher than any of the other Black Hills rhyolites. This rock, and
the following one [192], occurs, according to Mr. Jenney’s report, p. 47, in
a “ledge of irregular shape, without any well defined walls or boundaries,
and merging on all sides in the adjacent trachyte rocks.” From the fact of

PETROGRAPHY--RHYOLITE. 523

the evident chalcedony druses in [192], it may be inferred that the brightly
polarizing mineral in [187] is of the same nature.

The specimen [192], also from Gold Ledge, Warren Peaks, has an
exceedingly compact, jaspery or felsitic, reddish-brown groundmass, in
which are imbedded large, whitish sanidin crystals, quite lustrous on their
cleavage faces. There can also be seen small, dark colored druses, which
appear to be lined with a bluish-white mineral of botryoidal form like
chalcedony. The sanidin erystals have tolerably sharp outlines, being
quite conspicuous in the red mass, and, by the difference in luster between
two parts of the same crystal, it is noticed that some are twinned. The
groundmass resembles hornstone or jasper in its compactness, and has the
cavities of chalcedony very abundantly scattered through it.

In the section under the microscope, the sanidin is conspicuous by
reason of its translucency and behavior in polarized light. The cleavage
lines are very distinct, and the only noticeable inclusions are small, round
particles of red oxide of iron. The groundmass is of a whitish color, trans-
parent in places, but quite filled with small, red, ferruginous granules, which
occasion the color of ihe rock. The cavities mentioned are quite numerous
and are filled with chalcedony, its usual formation in layers conforming to
the shape of the cavity being plainly seen. In the interior of the druses,
between the layer of chalcedony, is some transparent, crystalline quartz, as
is often seen in geodes. The feldspar is more like sanidin than ordinary
orthoclase, having fissures and cracks and being also quite transparent,
while the groundmass has also a rhyolitie appearance the same as that of
[187], but with the addition of particles of oxide of iron. The rock isa
variety of rhyolite, in the cavities of which the quartz or chalcedony has
been secreted at the same time as the iron granules, greatly changing its
appearance.

The sanidin-trachyte [213] from Whitewood Creek, has a ground-
mass of a bluish-gray color, in which are numerous opaque, white feldspar
crystals. The rock is quite porous and full of holes, left empty by the
weathering of the sanidin crystals. Under the microscope, the section
shows a fine groundmass consisting chiefly of minute sanidins, in which are
a few quite large and well defined but cloudy sanidin crystals, with mag-

524 GEOLOGY OF THE BLACK HILLS.

netite, and some very sparing quartz grains. The sanidins still retain their
rectangular outline, although they have become quite dusty and even
opaque. With crossed nicols they polarize faintly white so as to be plainly
seen, a few giving pale blue and yellow colors. One crystal, broken and
twinned with a second so as to resemble a geniculation, is quite interesting.
The fissure lines in these crystals polarize in bright colors, thus being very
distinct in the cloudy mass. <A few brilliant grains were named quartz;
they are rounded and of irregular shape, containing some microlites and
round cavities, but may be sanidin, as some uncertainty as to their
nature still remains. The occurrence of biotite with a border of mag-
netite grains has been often mentioned, and in this section the border is seen,
but the interior is partly or entirely composed of transparent quartz. One
of these formations has an hexagonal shape, but they are generally pris-
matic. The biotite in only a few cases retains its greenish color in the
small fragments, around which the magnetite border is quite conspicuous.
Magnetite is scattered quite uniformly through the groundmass in minute
grains, with some large and sharply defined masses.

The groundmass is made up of minute and almost feathery sanidin
crystals, which, although. very indistinct, are faintly white with crossed
nicols, showing also very sparing traces of a fluid-like structure. The rather
low percentage of silica, 61.98, gave rise to the uncertainty as to the
quartz grains in the rock. Amount dissolved in acid is 9.93 per cent.

The rhyolite [214] from Terry Peak (?) is fine-grained, with small,
white feldspar crystals. The rock is quite full of pores, which contain
hydrated oxide of iron, but is otherwise tolerably homogeneous. In the
section under the microscope, it is seen to consist of large and cloudy
crystals of sanidin, with large grains and masses of magnetite, brown
biotite and abundant quartz grains in a groundmass of very small and
indistinct sanidin sections. 'The large crystals of sanidin are in every way
analogous to those in [213], being cloudy and opaque while still retaining
a distinct outline. Many of the erystals are banded. he quartz is in
clear grains, having brilliant colors and microlitic inclusions. The biotite
is mostly so decomposed that it is very brown and opaque, with, however,

a good crystalline form. It is very abundant through the rock, much more

PETROGRAPHY—ORTHOCLASE. 525

so than in [213], and is also in part altered to magnetite. The latter
occurs in large masses, mostly in former biotite crystals, but is very spar-
ing in the groundmass and not at all so uniformly distributed as noticed
before. Large, opaque, brown masses of hydrated oxide of iron are also
present.

The groundmass is very fine indeed, it being very difficult to trace any
outline of the small sanidin sections, which appear as mere whitish spots.
A few colorless, but sharp and clear apatite needles were recognized. One
of them of columnar form has a very distinct black center, with a light
exterior border. The whole appearance of the rock, both in hand specimen
and section, shows it to be considerably weathered.

The section of feldspar from the granites of the Black Hills is ortho-
clase very beautifully striated, so that it much resembles plagioclase. It
is similar to the striation of the amazon stone from Siberia, and differs from
the banding of plagioclase because the lines are not exactly parallel, but
rather pointed and sometimes at right angles to each other. It is a beauti-
ful example of this occurrence of banded orthoclase. Zirkel, in the N. Jb.
f, Min. 1872, p. 12, explains this banding of orthoclase in polarized light as
due to particles of some foreign substance, arranged in layers and strata,
so that between them is seen the pure and clear feldspar, which causes the
phenomenon by its bright colors. The dark bands are made up of long-
shaped cavities, varying somewhat in size, and yellowish needles and leaves.
When these bands are interrupted by a layer of clear orthoclase, the rows
of cavities become very thin and finally disappear in the feldspar with
delicate comb-like borders, very beautiful, but not to be confounded with
the striations arising from the twin lamellation of triclinic feldspar, the latter
being sharper, more exactly parallel to each other and more distinctly
defined. This feldspar has inclusions of long needles of apatite, horn-
blende and probably mica. Masses of uncrystallized orthoclase run through
it in irregular shapes, and some quartz and magnetite are also to be seen.

No.

101
103
109
113
120
123
124
127
131
134
135
139
140
141
144
147
149
157
161
167
174
187
213

GEOLOGY OF THE BLACK HILLS.

Silica determinations and amount soluble in hydrochloric acid.

Rock and location.

Rhyolite! (granitic) jtopror Merry beakteeas = asec arse eee eee
Rhyolite(eranitic) toprotmertyheakesereem- cece =r oaaeeisie ee seis
Rhy olite; southeastiof Mery heakemaseeeeeea eee eee isan einceiaei es rea
Sanidin-trachyte, ridge east of Terry Peak.......--..........-.+-----------
Rhyolitessoutheastiot Mery eakys-as ee eee eee sree ee a aaeaenstesieaes
Sanidin-trachyte, hill southeast of Terry Peak ...--...---. 5 9O5GG0 6660506 S606
Sanidin-trachyte, southeast of Terry Peak........-....--..-.-----------+---
Rhyolite near Deer Mountainsp-eis-eeesaeee eestor cteaeeteercmeecmerreeee
Rhyoliteysoutheastior Mertyskeakeee sere seeeer sets ete aches ain eeeiecistenee
Rhyolitembtop of! Custer cake secre ster etileecricscelecenene a eeiee cere nats
Rbyolitestopiot Custerbeakstacrseie see cscseecciecie meee cents ceieceieeecisenc
Phonolite;- Black Butbe sce s seein ae aarectahe oie ele yl we ate elo ete Veeeioneeias eerecile
Sanidin-trachyite, black Buttewacesseiem sciececeniesieste sate e essere eee reste
RhyolitesCroweheakeeyesscee eee eee ee cence Gene eee ence ene
Sanidin-oligoclase-trachyte, Bear Butte Creek ...........----.---- +--+. ----
Rh yolitewNorthyPealesinyantKara seeer ees aeree eee a ee eee eetse eee eeeee cee

| Sanidin-trachyte, Center Peak, Inyan Kara..............-..----------------

Sanidin-trachyte, hill west of Inyan Kara.........--.-.-- So0be0 as06 so 4sc6ee
Sanidin=trachy te; Bearod ge. mms. sacs nceneseeeeecrseceeacee cine stteses
Sanidin-trachyte (phonolitic), Little Missouri Buttes.........-..-...--.----
Sanidin-trachyte, north of Warren Peaks...-...---- <5. «-----------------
Rhyolite (quartzitic), Gold Ledge, Warren Peaks .......-....---.-.----- ----
Sanidin-trachytewWihitewoods@reekssesmse peice seteeee ee ceeereneeeeee eee

Silica.

72, 35
71.13
75. 09
58. 83
72.27
63. 56
57.75
73, 22

72,92 |

68. 62
72. 33
56. 32
58. 53
67. 36
695. 46
73.18
60, 51
61. 88
60.77
59. 06
52. 02
79. 89
61. 98

Sol. in
acid.

4,56
3. 12
2. 92
16.8
3.74
8. 58
13. 48
6. 67
5. 31
5. 62
5. 61
24. 08
18. 59
3. 54
10. 09
4,21
6. 32
6. 55
15. 33
29. 25
23. 14
6. 45
9. 93

[139] gelatinizes strongly in hydrochloric acid and does not give any

phosphoric acid reaction with ammonic molybdate.

[174] does not gelatinize, and gives an abundant yellow precipitate

with ammonic molybdate, which, after solution in ammonia, gives a crys-

talline precipitate with magnesia mixture, proving the microscopic determi-

nation of apatite.

PETROGRAPHY—RHYOLITES AND TRACHYTES. BAC

The various rhyolites and trachytes fall into three groups, according
to their similarity to each other, as follows:
RHYOLITES.

27|—Near Deer Mountains.
31|—Southeast of Terry Peak.
4|—Top of Custer Peak.
5|—Top of Custer Peak.
7|—Top of Custer Peak.
|j—Inyan Kara?
7|—North Peak, Inyan Kara.
166]—North Peak, Inyan Kara.
[141-142]—Crow eel

[1
[1
[13
[13
[13
[152
[14
[

SANIDIN-TRACHYTES
(normal).

[149]—Center Peak, Inyan Kara.
[151J]—North Peak, Inyan Kara.
[157|—Hill, west of Inyan Kara.
[178|—Top of Warren Peaks.
[144|—Between forks of Bear Butte Creek.

SANIDIN-TRACHYTES
(with hornblende, microlites, &c.).

[123|—Hill, southeast of Terry Peak.
[159-162|—Bear Lodge.
124|—Southeast of Terry Peak.
[140|—Black Butte.

150|—Northeast of Inyan Kara.
171|—Warren Peaks.
173|—Southwest of Warren Peaks.
175|—Southwest of Warren Peaks.

[
[
[
[
[

In some cases felsite-porphyry resembles trachytic rocks, especially
rhyolite, so closely as to make the distinction between them extremely
difficult, and the last group, which differs considerably from the normal
sanidin-trachytes, might have been named felsite-porphyry were it not for
their low silica percentage and occurrence with the trachytes.

In conclusion, the writer desires to express his obligations to Mr.
Arnold Hague, of the Survey of the Fortieth Parallel, Dr. Egleston, Mr.
Julien and Dr. Waller, of the School of Mines, New York, and other
friends, who have given him valuable suggestions and assistance in the
examination of these interesting rocks.

MICROSCOPIC PETROGRAPHY.
PLATE fe

DRAWN FROM NATURE BY JOHN H.. CASWELL.

Tic. 1. Rhyolite (}’ objective, x 88, polarized light) [127], near Deer Mountains, containing twin
erystal of quartz, the two parts not being distinguishable in ordinary light. Biotite in
prismatic and basal sections, and small, rectangular sanidin crystals in the groundmass.
(See p. 500.)

Fia. 2. Rhyolite (3 objective, x 88, polarized light) [137], top of Custer Peak. Biotite crystal with
border of magnetite grains and lines of lamination. Brilliantly polarizing quartz, abundant
magnetite and indistinct sanidin crystals in the crystalline groundmass. (See p. 503.)

Via. 3. Phonolite (4 objective, x 250) [139], Black Butte, showing the hexagons and rectangles of
nephelite in a large hornblende mass. Inclusions of the same nature in both sections.
Groundmass consists of sanidin. (See p. 503.)

Fie. 4. Phonolite (# objective, x 88, polarized light) [139], Black Butte, containing large, dusty
nosite crystals, with nephelite sections and small hornblendes in the feldspathic ground-
mass. Fluid-like structure around the nosite crystal. (See p. 504.)

ielatenls

Fig.l Fig 2

ZK I ISERE RS
gpes Oe =

"Ga

(ee ae
OO ERI ENS
US: Se) ras,
Dein

Fig.3 Fig 4

J Bien. lith

MICROSCOPIC PETROGRAPHY.
Po Ah ey:

DRAWN FROM NATURE BY JOHN H. CASWELL.

Fic. 1. Sanidin-trachyte (2 objective, x 25, polarized light) [149], Center Peak, Inyan Kara. Zona
structure of sanidin crystals; the purple zone is of the same color as the rest in plain light.
Hornblende crystal with inclusion of a small sanidin and magnetite; also small hornblende
fragments and needles with magnetite grains through the crystalline groundmass. Apatite
in hexagonal sections, and much decomposed biotite in largeforms. (Seep. 509.)

Fia. 2. Sanidin-trachyte (2 objective, x 25, polarized light) [157], hill west of Inyan Kara, showing
fine sanidin crystals, one of which is broken by an irregular mass. Near the edge is part
of a twinned crystal. Abundant magnetite as inclusions, as well as in the groundmass.
(See p. 512.)

Fic. 3. Sanidin-trachyte (2/’ objective, x 25, polarized light) [159-162], Bear Lodge, showing large
sanidin and hornblende crystals, with some magnetite in a groundmass full of hornblende
microlites and having a distinct fluid-like structure. (See p. 513.)

Fig. 4. Sanidin-trachyte (}’ objective, x 88, polarized light) [174], north of Warren Peaks, having
group of hexagonal biotite sections with double inclusions of calcite and magnetite. Pale-
green hornblendes with colorless apatite sections and magnetite in a groundmass composed
of indistinct sanidin crystals. Calcite mass near the edge. (See p. 518.)

Phectexil:

Fig. Fig.2

J Bien, hth

regi

ei

U. 8. GEOGRAPHICAL AND GEOLOGICAL SURVEY OF THE ROCKY MOUNTAIN REGION.
J. W. POWELL, IN CHARGE.

Bb Oy A N.Y

OF THE

BLACK HILLS OF DAKOTA.

By ASA GRAY.

529

»

* ‘
©
c

CHAPTER VILL.

BOUT AUN Ye:
By ASA GRAY.
LIST OF PLANTS COLLECTED BY THE BLACK HILLS SURVEY.
I. POLYPETALA.

CLEMATIS ALPINA Mill., var. occIDENTALIS, subvar. TENUILOBA.

Stems very short, hardly, if at all, climbing; divisions of the leaves
lanceolate or ovate-lanceolate and acute or acuminate, pinnately 3-7-cleft
or parted, the longer and narrower lobes commonly almost linear ; sepals
acuminate; staminodia all linear, hairy, and more or less antheriferous, not
half the length of the sepals, little exceeding the true stamens. All the
American forms, which are confined to the Rocky Mountains, from the
Black Hills of Dakota to New Mexico, agree in having only narrow and
antheriferous exterior stamens or staminodia, none of which are dilated
into petals, and the foliage is finer than in any of the ordinary forms of the
old world species, except Ledebour’s Atragene macropetala and Regel’s
A. alpina var. tenuisecta. In Pl. Fendleriane I had referred the American
form to A. Ochotensis ; but it is best to regard it as an independent variety
of that polymorphous species which takes the name of Clematis alpina. The
present form of it (tenwiloba) is so remarkable for the fine dissection of its
leaves that it would most naturally pass for a distinct new species. It
appears to be the analogue of Regel’s A. alpina var. tenuisecta.

CLEMATIS LIGUSTICIFOLIA Nutt.

ANEMONE PATENS var. NUTTALLIANA Gray.
531

532 GEOLOGY OF THE BLACK HILLS.

A. muuriripa DC.

A. CYLINDRICA Gray.

THALICTRUM DioIcuM Linn.
RANUNCULUS AQUATILIS Linn. var. TRICHOPHYLLUS Chaix.
R RHOMBOIDEUS Hook.

R. BREvicAULIS Hook, a variety of the next.
R. arrinis R. Brown var. CARDIOPHYLLUS, Gray.
DELPHINIUM BICOLOR Nutt. ex Watson.
ACONITUM FISCHERI Reichenb.
ARGEMONE MEXICANA Linn.

ARABIS DRUMMONDII Gray.

VESICARIA ALPINA Nutt.

ERySsIMUM ASPERUM DC.

SISYMBRIUM CANESCENS Nutt.

POLANISIA TRACHYSPERMA Torr. & Gray.
VIOLA CANINA var. SYLVESTRIS Regel.
VIOLA DELPHINIFOLIA Nutt.
HELIANTHEMUM CANADENSE Michx.
CERASTIUM ARVENSE Linn.

MALVASTRUM COCCINEUM Gray.

LINUM PERENNE Linn.

GERANIUM CAROLINIANUM Linn.

G. RIcHARDSONI Fischer & Meyer.

G. incisum Nutt.

PotyGaLa ALBA Nutt.

.THERMOPSIS RHOMBIFOLIA Nutt.

Lupinus ornatus Dougl var.

L.. ARGENTEUS Pursh var.
PETALOSTEMON VioLACEUS Michx.
PSoRALEA ESCULENTA Pursh.

P. aRGOPHYLLA Pursh.

GLYCYRRHIZA LEPIDOTA Nutt.
ASTRAGALUS CARYOCARPUS Ker

A. HypogLortis Linn.

LIST OF PLANTS. : 533

A. ADSURGENS Pallas.

A. gracitis Nutt.

A. aupinus Linn.

A, ABorIGINUM Richardson.

A. SIMPLICIFOLIUS Gray.

OxyYTROPIS LAMBERTI Pursh.

QO. CAMPESTRIS Linn. var.

Victa AMERICANA Muhl.

VY. AMERICANA var. LINEARIS Watson (Lathyrus linearis Nutt).
LATHYRUS ocHROLEUCUS Hook.

HEDYSARUM CANESCENS Nutt.

SoPHORA SERICEA Nutt

SPIRZA BETULIFOLIA Pallas.

GEUM RIVALE Linn.

G. TRIFLORUM Pursh.

PoTENTILLA NIVEA Linn. var. pissecTA Watson.
P. nipprana Lehmann.

P. arcuta Pursh. a dwarf form.

P. rissa Nutt.

RuBus NUTKANUS Mocino.

R. trrFLorus Richardson.

Rosa BLANDA Ait.

AMELANCHIER CANADENSIS var. ALNIFOLIA Torr. & Gray
LITHOPHRAGMA TENELLA Nutt.

EPILOBIUM ANGUSTIFOLIUM Linn.

Gaura coccinea Nutt.

GaAYOPHYTUM kAcEMoSUM Torr. & Gray.
CENOTHERA BIENNIS Linn.

Ci. cHrysantHa Michx.

CH. serRULATA Nutt. var. pepuMMonDu Torr. & Gray.
CH. PINNATIFIDA Nutt.

CH. czspitosa Nutt.

CaRUM (EDOSMIA) GAIRDNERI Gray.

‘THASPIUM TRIFOLIATUM Gray.

534 GEOLOGY OF THE BLACK HILLS.

CYMOPTERUS GLOMERATUS Nutt.
MUSENIUM DIVARICATUM Nutt.
CoRNUS CANADENSIS Linn.

Il. GAMOPETALAS.

VALERIANA SYLVATICA Richardson.

GALIUM BOREALE Linn.

Liatris scartosa Willd.

L. punctata Hook.

ASTER (MACHZRANTHERA) tanacetifolius H. B. K.
A. Lavis Linn.

A. MULTIFLoRUS Ait.

ASTER FALCATUS Linn.

A. SIMPLEX Willd.

A. PTARMICOIDES Torr. & Gray.

ERIGERON PUMILUM Nutt.

E. GLABELLUM Nutt.

E. MACRANTHUM Nutt.

E. strigosum Muhl. var.

GUTIERREZIA EUTHAMIA Torr. & Gray.
SoLipaGo NeMoRALIS Ait. and var. RaDULA Torr. & Gray,
S. speciosa Nutt. var. ancustatTa Torr. & Gray.
S. MISSOURIENSIS Nutt.

S. RIGIDA Linn.

CHRYSOPSIS VILLOSA Nutt.

ECHINACEA ANGUSTIFOLIA DC.

RupBeEckKIA HiRTA Linn.

HELIANTHUS RIGIDUS Desf.

H. strumosus Linn.

H. petionaris Nutt.

HELIANTHELLA UNIFLORA Torr & Gray,
GAILLARDIA ARISTATA Pursh.

ACTINELLA ACAULIS Nutt.

ACHILLEA MILLEFOLIUM Linn.

ARTEMISIA LuDovicIANA, Nutt.

LIST OF PLANTS. . 535

ANTENNARIA MARGARITACEA R. Brown.
SENECIO INTEGERRIMUS Nutt.
LyGopEsmia JuNcEA Don.
HIERACIUM CANADENSE Michx.
TROXIMON MARGINATUM Nutt

T. cusprpatum Nutt.

MULGEDIUM PULCHELLUM Nutt.
CAMPANULA ROTUNDIFOLIA Linn.
ARCTOSTAPHYLOS UVA-URSI Spreng.
DopECATHEON MEADIA Linn. var.
ANDROSACE SEPTENTRIONALIS Linn.
LysIMACHIA CILIATA Linn.
SoLANUM ROSTRATUM Dunal.
CoLLINSIA TENELLA Nutt.
PENTSTEMON GLABER Pursh.

. ACUMINATUS Dougl.

. GRANDIFLORUS Nutt.

. CRISTATUS Nutt.

. ALBIDUS Nutt.

. GRACILIS Nutt.

CASTILLEIA PALLIDA Kunth var. SEPTENTRIONALIS Lindl.

ne} Ago) Iga] te) tae)

VERBENA BIPINNATIFIDA, Nutt.

Monarpa FIsTuLosa Linn.

SALVIA LANCEOLATA Car.

LopHANTHUS ANISATUS Benth.
MERTENSIA OBLONGIFOLIA Nutt.

M. tancrouata DC.

ERITRICHIUM GLOMERATUM DC.
ECHINOSPERMUM REDOWSKII Lehm.

Gitia spicata Nutt. var. cAPITATA Gray.
PHLOX LONGIFOLIA vars. STANSBURYI, BREVIFOLIA Gray.
CoNVOLVULUS (CALYSTEGIA) SEPIUM Linn.
APOCYNUM ANDROSZMIFOLIUM Linn.

536 GEOLOGY OF THE BLACK HILLS.

TI. APETALA.
OXYBAPHUS NYCTAGINEUS Sweet.
TEXRIOGONUM MULTICEPS Nees.
Comanpra Potiipa A. DC.
EUPHORBIA MARGINATA Pursh.
I. nexacona Nutt.
Humutus Lupuuus Linn.
Axpigs ALBA Michx. ? Foliage only.
MONOCOTYLEDONES.
CALOCHORTUS NUTTALLU Torr. & Gray.

Specimens in flower and with mature fruit. This is noted as an insect-
capturing plant, flies having frequently been found fast among the bristles
that fringe the gland of the petals, where they had perished. Those who
have the advantage of seeing this and similar species alive, either in their
native haunts or in cultivation, should learn whether these bristles manifest
any irritability. The petals are evidently white or whitish, except the
claw and the purple blotch above it. The well-formed mature capsules are
2 or 3 inches long, triquetrous-lanceolate, four or five lines in diameter.
There is hardly any doubt that Nuttall’s Calochortus luteus was correctly
referred to this species. Although apparently Wyeth did not obtain mature
fruit, Nuttall’s description, ‘capsule linear-oblong, three-sided,” and “the
capsule much like that of a tulip,” suffice to show that his plant ought not to
have been referred by Mr. Baker to his section ‘‘Platycarpus.” ‘The only
species of that section likely to be found about the sources of the Columbia
is C. nitidus Dougl., to which belongs C. ewrycarpus of Watson, and both
its ovary and pod are broadly oval in outline. The C. nuttallii of Baker’s
Revision of Tulipeze is evidently made up of more than one species, viz, of
Hall and Harbour’s 549 (misprinted 529), which is C. gunnisoni, and for the
— rest probably of ©. nitidus. If the specimens cited from Nuttall, Burke,
and Bell really belong to C. nuttallii, they cannot have well-formed fruit.
The misunderstanding of this latter species accounts for the introduction of.
C. lechtlinti Hook. J., Bot. Mag. + 5862, which is plainly our C. nuttalli.
LILIUM PHILADELPHICUM Linn.

PROSARTES LANUGINOSA Don.

LIST OF PLANTS.

ZYGADENUS GLAUCUS Nutt.
AMIANTHIUM NUTTALLU Gray.
IRIs TOLMIEANA Herbert.
SISYRINCHIUM BERMUDIANA Linn.
TRADESCANTIA VIRGINICA Linn.
AGrRosTiIs scaBra Willd.
MUHLENBERGIA GLOMERATA Tin.
VILFA HETEROLEPIS Gray.

V. cusprpata Torr.
CALAMAGROSTIS CANADENSIS Beauv.
BouTELOUA CURTIPENDULA Gray.
B. orteostacHya Torr.
GLYCERIA AQUATICA Smnith.
Bromus KALMI Gray.

B. cruratus Linn.

TRITICUM VIOLACEUM Hornem.
ELYMUS CANADENSIS Linn.
PHALARIS ARUNDINACEA Linn.
ANDROPOGON FuRCATUS Muhl.

CRYPTOGAMIA.

CHEILANTHES LANUGINOSA Nutt.
PELLZA ATROPURPUREA Link.
ASPLENIUM FILIX-F@MINA Bernh.
ASPIDIUM FILIX-MAS Swartz.
STRUTHIOPTERIS GERMANICA Willd.
ONOCLEA SENSIBILIS Linn.
Woopsta scopuLina Eaton.
EQUuISETUM ARVENSE Linn

E. sytyvaticum Linn. ?

537

U. § GEOGRAPHICAL AND GEOLOGICAL SURVEY OF THE ROCKY MOUNTAIN REGION.
J. W. POWELL, IN CHARGE.

ASTRONOMY AND BAROMETRIC HYPSOMETRY

OF THE

BLACK HILLS OF DAKOTA.

By HORACE P. TUTTLE.

Wasuineton, D. C., July 1, 1876.
Sir: In obedience to your orders I have the honor to present herewith
my report of the astronomical and barometric work done in the Black
Hills of Dakota and Wyoming, during the summer of 1875, while attached
to the party under your direction
Very respectfully, your obedient servant,
HORACE P. TUTTLE,
Astronomer.
Wa ter P. Jenney, Geologist in charge.
541

CHASE hei, Xe

ASTRONOMY AND BAROMETRIC HYPSOMETRY.

By HoRAcE P. TUTTLE.
SECTION I.
THE ASTRONOMICAL WORK.

1. General remarks.

My appointment was dated April 13, 1875, and I was ordered to re-
port to you without delay, which I did on the 24th of the same month, at
Chicago, Ill., and with the other members of the party arrived at Cheyenne
on the 27th of April.

The funds at the disposal of the Department of the Interior, and which
could be used for the purpose of purchasing instruments for our outfit,
was very limited, but the Hon. E. P. Smith, Commissioner of Indian Affairs,
under whose immediate direction our party was, authorized the purchase
of one new marine chronometer, one sidereal pocket chronometer, and also
to hire one or more marine chronometers, as I might deem expedient.

Upon my arrival in New York, I proceeded to the store of Messrs. T.
S. & J. D. Negus, where I found that they had selected for the expedition
one of their new marine chronometers, No. 1572; they also showed me a
Parkinson & Frodsham marine chronometer, No. 3192, which had an
extremely small rate, and which they offered to loan to the expedition.
As this chronometer was considerably lighter than the usual marine chro-
nometers, I at once signed a contract for its loan to the expedition. Sidereal
pocket chronometer, No. 54004, Duval, was purchased at the same time,

and performed most admirably during the time we were in the field.
543

544. GEOLOGY OF THE BLACK HILLS.

Believing that after our arrival in the country to be surveyed, wagons
would have to be dispensed with, and that we should have to take to the
saddle, I did not think it advisable to take more than two large chronom-
eters; and my experience in the field during the past summer showed that
I was correct; for had I taken more, some of them would have had to be
turned into other hands and would have been of no use to me, and most
likely would have been ruined. As it was, the two chronometers received
from the Messrs. Negus did not pass out of my hands from the time of
leaving Cheyenne, in May, until our return there in October.

From Stackpole & Brother the department authorized the purchase of
one transit theodolite, one astronomical and one lunar sextant, and two
artificial horizons. ‘These instruments were all new and of the very best
workmanship, as are all instruments which come from the hands of these
celebrated makers. For the rough country in which we had to work, the
theodolite was not well suited from its great weight, but a lighter one could
not be procured.

2. Longitudes.

Upon my arrival at Cheyenne I learned something definite about the
character of the Black Hills country, and it at once became evident that
the only thing to be done, so far as longitudes were concerned, was to
measure ‘meridian distances” from point to point, obtaining the chronom-
eter errors and rates as often as our delays would permit, until we should
arrive at some prominent point in the Hills, where our theodolite could be
brought into use. From the nature of the country we were to visit, it was
simply out of the question to start from Cheyenne or Fort Laramie with
the errors and rates, and then trusting to chance of obtaining them again
on our return, and deducing therefrom the longitudes. This would have
been the proper method to have pursued had we been going to a country
easy of access and travel, but not in a rugged country like that which we
visited; and my only course was to follow the more complicated method
of ‘meridian distances.”

It was my intention to have combined my chronometric longitudes
with those deduced from occultations, or in case of accident to the chro-

ASTRONOMY AND BAROMETRIC HYPSOMETRY. 545

nometers, to have deduced the longitude of some elevated point from occul-
tations alone; but, unfortunately, the only two good occultations which
occurred during our presence in the Hills, viz, a Scorpii, on June 16, and
a Virginis, on August 6, were both lost. The first occurred while we were
at Camp Harney, a place almost exactly on the meridian of Harney Peak,
and after making very correct observations for the local sidereal time and
getting my telescope in position, I had the mortification to see the moon
sink behind the western slope of Lookout Mountain jive minutes before the
occultation took place. The second was lost by the failure of our ambu-
lance containing my telescope to meet us at our appointed rendezvous.
Both of these stars were of the first magnitude and disappeared behind the
dark limb of the moon. ‘The loss of these occultations was disheartening
to me in the extreme, as they would have enabled me to have fixed our
positions within a mile.

Observers in the field do not place that degree of confidence in longi-
tudes obtained from occultations, to which I think them entitled; and from
my long experience I am led to believe that the indifferent results generally
found from observations made in the field are greatly owing to the want of
experience in the observers themselves, and to errors in the exact local time.
With a 2-inch telescope, or that of a theodolite, stars as small as the third
magnitude will be easily seen close to the dark limb of the moon, when she
is not more than five days old. A single observation of an immersion by
a practiced observer, under the above conditions, will give the longitude to
within three seconds of time, and in this statement I have the concurrence
of some of the most eminent astronomers in the country.

The longitudes of the more prominent peaks in the Black Hills deduced
from my chain of ‘meridian distances” agree very nearly with those of
Captain (now General) G. K. Warren, who explored the western, southern,
and eastern portion of the hills in 1857. His longitudes were, I believe,
determined by moon culminations, which, next to occultations, is the safest
and surest way of determining absolute longitudes, when the base or prime
meridian is very far distant. From our triangulations the relative positions
of Bear Butte, Dodge Peak, Custer Peak, Crow Peak, Terry Peak,
Inyan Kara, Warren Peaks, and Bear Lodge are correctly located with

35 BH

546 GEOLOGY OF THE BLACK HILLS.

reference to Harney Peak and its longitude as given by the chronometers.
This triangulation was wholly performed by the topographer, Dr. McGilly-
cuddy, in addition to his duties as topographer, and the true azimuth of a
great many points in the Big Horn range ascertained; but unfortunately
our map will not be on a scale large enough to take in anything beyond the
Black Hills proper.

3. Latitudes.

Observations for latitude were made at every camp when the weather
was favorable, principally by double altitudes of Polaris; while at the most’
important camps, such as Harney Peak, Bear Lodge, and the junction of
the forks of the Cheyenne, by both north and south stars. During our
various trips up and down the numerous streams, circum-meridian observa-
tions of the sun were made daily, being rarely lost by cloudy weather.
So accurate were the courses run by the topographer that the differences
of latitude found by observation, and that platted from courses and dis-
tances, seldom varied more than a few hundred yards in a run of twenty-
five miles.

My observations for time and latitude were all made with a sextant
attached to a small tripod of my own invention, weighing less than two
pounds. So convenient is this arrangement that the contact of the direct
and reflected image of a heavenly body can be observed with the same
accuracy as the passage over the wire of a transit instrument.

An observer who is familiar with the use of a sextant can by this
method easily obtain the latitude of his station to within one second of are
in a single night, provided his instrumental errors have been carefully
ascertained, which unfortunately is seldom the case. Here the hands are
relieved from the weight of the sextant, which soon becomes tiresome,
especially with a heavy instrument. This contrivance permits the sextant
to move in azimuth without any sensible friction, while a delicate tangent
screw is used to bring the face of the instrument instantly into a vertical
plane. The sextant and clamp are instantly detached from the tripod and
readily replaced without aid of artificial light.

The computations have been performed by the usual methods and need
not be detailed. The determined positions will be found in the table at
the end of the report.

ASTRONOMY AND BAROMETRIC HYPSOMETRY. | 547

SECTION II.

MAGNETIC VARIATION.

The variation was frequently obtained by means of the needle of the
theodolite. Owing to the smallness of the circle surrounding the needle,
there was an error of reading of + 5’ in every reading, but the mean of
several readings was always taken. Great local disturbances were found at
one place on Box Elder Creek, and also on the summit of Inyan Kara. At
one spot on Box Elder the prismatic compass was entirely useless for some
miles, while at Inyan Kara so great a magnetic power did the rock possess
that a small fragment, when brought near the needle, would carry it com-
pletely round the circle. In preparing the table at the end of the report
all observations made in the vicinity of rock recognized as magnetic were
omitted. ‘Ten stations in the Black Hills show a range from 15° 16’ east to
15° 50’ east, and give a mean of 15° 33.3’ east.

SHCTION III.

BAROMETRIC WORK.

The meteorological instruments were furnished by Mr. James Green,
and were of the best quality. They consisted of two mountain barome-
ters (mercurial), five aneroid barometers, and a number of thermometers.

The mercurial barometers were read regularly in our camps, but the
smallness of our party rendered it ordinarily impracticable for us to carry
them when we ascended peaks ‘They were observed, however, on the
highest points of all, Harney and Terry Peaks.

The deduced altitudes will be found in the table. The base station
was in each case the signal office at Cheyenne, and the computations were
according to the method and with the tables given by Guyot. The observa-
tions and computations are omitted except in the case of the peaks.

HEIGHT OF HARNEY PEEK.

Our barometrical base at Cheyenne was about one hundred and eighty
miles distant, but a glance at the weather-map on the day on which observa-

548 GEOLOGY OF THE BLACK HILLS.

tions on Harney Peak were made shows that there was no local disturb-
ance east or west of a line joming Cheyenne and the center of the Black
Hills, and the deduced height of Harney can be considered as very near
the truth, not more than 50 feet in error, I think.

The height of Terry, as deduced from barometrical observations on
August 20, and from a zenith distance from Harney, agree within 12 feet.

The observations on Harney were all made on the highest point, which
gave us much trouble and risk of life and limb to reach. The mean of four
of Green’s compensated aneroid barometers gave as the height of Harney
7,440 teet.

As my altitude of Harney is so widely different from that found by
Colonel Ludlow, in 1874, I give both observations and computations here
complete.

The altitude of the railroad track at Cheyenne is, according to an
elaborate investigation by Mr. James T. Gardner, 6,075.28 feet, and by
measurements by Dr. McGillycuddy and myself, with a theodolite, the
cistern of the standard barometer in the signal office is 9.58 feet above the
rails. This gives for height of cistern above the sea-level 6,085.86 feet,
exactly one geographical mile.

Observations made on the summit of Harney Peak, July 25, 1875, lat. 439-52’ N.

Observer, H. P. TuTriz.

in. fe) °
Bar. 2123 10.00 a. m. 23.248 Att. th. = 63.6 Ex. th. = 59.5
10.30 23.238 = 64.9 = 60.5
10.45 23.242 — (L(G = 58.0
11.00 23.249 = 65.6 = 59.2
Means 23.244 63.9 D9}oi—au
Reduced to Cheyenne standard — .003
Reduced to 52° — .073

23.168 = h’

ASTRONOMY AND BAROMETRIC HYPSOMETRY. Ry)

Observations made at Signal Station, Cheyenne, July 25, 1875, lat. 41° 08’.

Observer, A. C. Doppins, U. S. A.

in. ie io)
Standard bar. 133. 7.00 a. m. 24.270 Att. th. = 61.0 Ex. th. 58.0
10.19 24,256 = 63.0 62.0
12.00 m. 24.260 = 69.0 65.0
Reduced to 32°. 24.262 =h
( 61.6 =¢

I 4 —
From Guyot’s tables wehave 4 DIE Hs
| 120.9 =t4 ¢
Table I for h 24.262 inches = 23,156.7
h’ 23.168 inches = 21,951.2

Difference = D= 1,205.5 = approx. diff. level.
Dx(é+t—64) _| a9

900 ~

Ds 1,281.7 = second approx. diff.

Table III fer D’ gives + alt
Table IV for D’ gives + 3.0
+

Table V for h = 24.26 wl

1,282.5 Harney Peak above Cheyenne.
6,085.9 Cheyenne above the level of the sea.

Feet 7,369.4 Harney Peak above the level of the sea.
HEIGHT OF TERRY PEAK.
Observations made on the summit of Terry Peak, lat. 44° 20’, August 20, 1875.

Observer, HENRY NEWTON.

in. ° fo)

Bar. 2120 9.30 a. m. 23.404. Att. th. = 58.5 Ex. th. = 56.0

10.00 23.408 Os 58.0

11.00 23.420 = 60.5 62.0

3.00 p. m. 23.448 = 67.5 61.0

Means 23.420 61.2 592
Corrected to standard + .006
Reduced to 32° — .068

lh! = 23.358

550

GEOLOGY OF THE BLACK HILLS.

Observations made at Signal Station, Cheyenne, August 20, 1875.

Bar. st’d 133

14
66

Reduced to 32°

Observer, A. C. DoBBINS, U. 8. A.

in.

10.19 a. m. 24.300
2.00 p. m. 24.310
2.44 24.373

h= 24.328

Table I gives for

Table I gives for
Approx. diff. level

D x (t+? — 64)

900

Second approx. diff.
Table III for D’ gives
Table IV for D/ gives
Table V for h 24.33 inches

Terry Peak above Cheyenne
Cheyenne above sea level

Terry above sea level
Harney above sea level

Terry below Harney

°

Att. th. = 63.5

h

= 69.0
= 68.0

23,093.4

h! 22,164.7

— i)

== 1) =

I

1,058.7
+ 66.9

Teel
TE e30
Lie Ji

1,129.4
6,085.9

7,215.3 feet.
7,368.4 feet.

153.1 feet.

fe)

Ex. th. 64.0
= 68.0

= 53.0

t =61.7
t= 59.2
t+¥ 120.9

ASTRONOMY AND BAROMETRIC HYPSOMETRY.

TABLE OF POSITIONS AND ALTITUDES OF CAMPS AND OTHER POINTS.

dd1

- Place of observation.

oOmonrtnn rk wwe

CO 2 ol ee
mp oOowomonrt onrh wwe ©

SSERSSNSERESLY

30
31
32
33
34

Fagan’s Ranch

Owen’s Ranch

Fort Laramie, flag-staff
IPOS ITN GS Ssach dace eneadees seeRaBar

------G0O ------ - 2-2 ee + eee ee eee 2 eee

Camp Jenney-..---. aeSoneseSses eee
East Fork Beaver (near its head)
Rona Vallee teense ssa ease

Camp Harney

Amphibious) Creeks =a. see ce se a2

Amphibious Creek (Buffalo Gap)

| Amphibious Creek and Cheyenne.-.....
jeBurniwood! Crecks=ens-peeseeaees see

French Creek
Pleasant Valley

RediCanon/ Creele eae eeen eee eee |

Red Cation and Cheyenne. ..---..------

Sweetwaber Creek. == :22- sssess e-55--
Cascade Creek, headwaters of_....-.-.
Falls of Cascade Creek........-...----
Junction with Cheyenne......--..--.-

Amphibious Creckses eee sees eee eee
French Creek

Magnetic Altitude
Longitude. | Latitude. Sane above

variation. ehonen:
[e) / ul fo) / i co) / Feet.
stosonenesee AW 2728) |e aan se a= =| NO 240
See seasco|| ZEA M8} pcos oeesee|| Sr
104 32 42 12 30 | 15 21 E. | 4,590
Waiwera uses leneee esas 15 24 E. | 4,570
suse tees aaa 42 24 4| 15 24E. | 4,380
BE fereieldae Sak eat oe eae [eames 5, 000
Seige iade ceue 42 46 0/| 15 20. | 5,080
Setar 42 56 15 | 15 30 E. | 5,160
iigiskeiste Noein 43 5 55] 15 33 E. | 4,785
Sapstisiater eee ASSN Si ee =e 45,000
Eeepyelsnehaeci< 43 26 57 | 15 25 E. | 4,400
soa Senseo 43 32 58 | 15 33 E. | 4,250
Soe caneEeee 43 32 58 |.-.-.-----| 4,300
103 59 48 43 48 46 | 15 16 E. | 4,700
S5k Gan Sheen Maceraeaeras| cameras 6, 000
103 55 5 44 811] 15 33 E. | 6,600
sesSeatess aus 44 210 |.......-.-| 6,400
103 39 59 44 1 2/ 15 50E. | 6,133
103 20 51 43 46 9 | 15 40 E. | 5,373
Jenceeesteee A339) AAs eee ccee =| eso
pacbensecees 43 36 3 |.---------| 4,626
Seats aye ae 43 31 2] 15 30E. | 3,634
102 59 46 183 5) 1K) Ne one oops 3. 127
103 6 51 ASCO EG, eee esas 4 350
103 9 8 ASW42 AG) | Beneen eee 4, 840
esoeacesaces 43 40 35.|..--..----| 5,152
103 34 8 43 33 8 | 15 45 E. | 4,582
103 34 24 LE ae ee eee 3, 850
Senosecesess 43 18 20 | 15 26 E. | 3,360
Sonstiges AB) Pil XD) |eeedoosean| eytelll)
Betemacomeee ASP 20106) |eaee eee 3, 900
Sees saci: 43 23 52 |.----.----| 3,230
saraaaeeest 18) OS}, Penne csccec|| eye)
pocSuR ek Sess boeeees acne eae 4, 900

siswese sees 43 43 19 |2.---.--.-| 4,700 |
stb scunOaeee 43 43 13 |.-..-.----| 4,300
3 Se ee ASPAT s Giltaeee Shee sle ACO
Sosa asceiscs 43, AG 52 |---- =2----| 5,200
See sesaa caeeleecececceces| seeiaceneee 6, 150

D2

GEOLOGY OF THE BLACK HILLS.

TABLE OF POSITIONS AND ALTITUDES OF CAMPS AND OTHER POINTS—Continued.

= 4. | WMaanetic Altitude
- 3 Date. Place of observation. Longitude. | Latitude. Say above

Zs S variation. inenent
1875. Lele pis yi Ore tats On Feet.

35 | July 24 Harn ey (Pealkeiasate.aah one omeeee re see 103 20 25 43 51 57 | 15 16 E. | 7,363.9
Bo | diwhy ch) Sinmun Oneele oc con cecboad scbece cocuce 103 16 37 ABS Bie)! eo oooaae 4,700
By || artes, IL) WeNwanOM IBA, 4855 acosoKs oonesasenace 103 23 46 43 57 4 | 15 39 E. | 5,050
38 | Aug. 3 Southwest Fork Castle Creek -.....-.- 103 30 8 AAS Ae OE ct tapos 5, 000

PSs) |eeNinieas (6h || Shortness Chelle be coo scosSosusocou tose ||ooodes sosde5 AZ (59UA4. | Nee |e
40 | Aug. 8 | CampiCro0 ke ee eee eee 103 18 23 MA BAD noe cose 4, 650
4Y | Aug... 10) Rapidi@reck..2a.e7ee - oe ne - eee hee eee HUN 8) SE) ona o scenes 4,550
AM) || AMES Wl ooose ClO ae SORES S LIA Sen Sarees Sem see lbemonenesogs AAS Si (Al ee ceeeee 3, 750
AB} | Ahnes, 1133 || Chinnewk@ Cirle oan checcesanccon usones 103 12 40 AAS 7 GOS eee eee 4,475
44 | Aug. 14 I Boxe ddan of cats eerere Rie Woon @ds3s-| 44 3 Gieecsec see 4,775
AY | UNS 6) |) Chri OOKAD seo Good 6ocuca sukcoda codous|lesseO céden AAS ied: | aaa 4,925
AY | nis, 1G kos OP Top IDVGVee coc soco osecocccose RS eOVOTN RE aalhe ue M Veil ieyeteyopulle Me ge 3 5, 225
ATs Anis 5165 NB oxeb ld er tees teeters Renan ley alles aa ee BAe (Sy Ady eee 5, 400
NS) | INI AVE | (Chigiaye PATS, 5 Sess Saseeecae see cacao 103 33 11 AAS TAGATE | seer .| 6, 967
AG) || Aus, Ike} | Opie Way s5c5 coAS coos adeucs cleo couclleatoeeas ones [AA SIGIR OM inane ly 5, 550
50 | Aug. 22 | Southwest Branch Elk Creek..-.......|------------| AAV AG. \o eo cates 5, 100
51-| Aug. 24 | sees GER eee ik eee een ll Noon obs VA Ai} A ns one 4, 045
|| Nive, DA) Rerw Bite Chedk. one occask Sauece ek Bladen LON 3, 750
RS) AN, 20 | IR IBWHIO occ nccsonceceonoces cososoe 103 14 11 MN FS} 8) | someo cane 4, 573
By | aNws, Bs) |) opie IBIIO Cie) 05 conn cooceconenace||cooces codec MA Be? OF Neaascaccac 4,000
Biss |) Ake, 2) || Sjoeaneiiigln Challe 35 sees ccna sooscs cosaljoooede scones IM) TVA Nee on ee 4, 450
RG || Anes,” Sul | TRechymiise Chale occ socccc ccncncusse|oooses benee AVN BP 13 lo o5 sconce 3, 900
57 | Sept. 1 | Sun Dance (CHITTY 2555 dooceanonnboo oeca|eseoso ddeces | AAS AGA Gin eee 4, 900
57 | Sept. 1 | Sun Dance Hill @vestern) seeeeee sree Noon obs AVA OY XD) Noo co co 6, 400
58 | Sept. ~ 2 | CamprBradleypeccsstec seo eee eee rene ace AM UN OS Wo os5 cabs a6 5, 200
58 | Sept. 3 Summit of Inyan Kara..-.-..-.--. ___.| Noon obs AGE127 29 8 eens 6, 563
BY || Semis 2) |) Chnrayy WMNSTSP oho bnsssen casscs cone||eseo cous 2a56) 44 711)! 15 45 E. | 6,100
2) || Sets 9) Chxonih Mesio-5 6 cccone sacceea coseesce Noon obs Ad TCA TAI a 5 et 7, 140
GO" Sept. 27. Groot oes ao ee ne nea ado: aoe OT) FB ome 7, 323
GO) | Soe 2 |p Moll Wallley7 sone concce sonSascccooas nal|eoeo 9656 eco: 7 Was rs Yi ese epere 6, 050
Gil || Sots Sell INeihenOe a5 45 ens coon ecoces ccecccce Noon obs ALS SA ol ee ees 5, 475
62a Sepia S |peseen ils a et WR nae oe Se Bo Cn aAcnlpopeGd aoriaesllaneonoSaue 4,140
G35 septs 95"Southwesh BranchvRed water: sesemeese| =e ee alse eee Pe eee 4,900
64 | Sept. 11 | South Fork Belle Fourche River ..-.-- Noon obs 44 20 47 |....------ 5, 600
a || Sey aul dots et ee ee | eee ANOS) Cg _...| 4, 600
G5aliSeptagiollpRenried scm eee. s,s eee A PL) | A SS | oe 5, 263
66 | Sept. 14 lpBelllesMourcheissec.\-0--o- jose ne eel eee reece ligt 2445 A5 Sh eee eae 3, 870
67 | Sept. 15 | Belle Fourche, great bend of -....-....|+----------- A4 56 56 |.--------- 3, 560
@3} | Seo IG || ahhh TaREND --caascone concen sana ecae|leoco onon tee 44 47 46 |......-.-- 3, 300

69 | Sept. 17 |---2=- do Befapeeieicteie e mye'<ialescimiarecois||aierever eletentere ABAD V7) i saee os eal Seeeiece

ASTRONOMY AND BAROMETRIC HYPSOMETRY. —

553

TABLE OF POSITIONS AND ALTITUDES OF CAMPS AND OTHER POINTS—Continued.

6g, Magnetic BORG
g &| Date. Place of observation. Longitude. | Latitude. alas above
& variation. nioneat
1875. oe ON aes Ont Feet.
TL || Seite 14) 4) stale Bored esas nscces cone coe ousa| sooo cooduene VATS AO Wo Bo ese 2,970
We | Sept 20N| pee OOWssoeettae Sess eee necsesabie ean leoe aime de chee AAG 2IUQO Gece seo 2, 870
73 | Sept. 24 |...--. dope se aa eee CNS ees ue eae AA, Oly S6a lass es 2, 480
AM Septeneon sss a =— GOs eae er ce ee eee ao eee alee eoniaeeatt AAS OA LOL EA St Se sale oe nels
Gon Septsncos|-se= = DON eereien ete apace eee nao tam eel oamici ami tee AAS DOU QAD Wendie sete erse eats
76 | Sept. 27 | Junction of North and South Forks of | 102 31 19* VND) 58) | Seaacestae 2,470
Cheyenne.
fale oepiecen| south Rorkof Cheyennes: <2. 5--1--el|eoss 5-45-45 - AAAS OIG Ree ee sae 2, 500
78 | Sept. 29 |.--.-. dO eee ne sete oe ee cnn See wae eee careers JV Ssh ses eee 2, 630
79 | Sept. 30 |.----. COE eee een ee cece es naan sat aces ASUS ARSON | peta sete 2, 680
SON hOct=® 422 22-55 O) Bae Se ORR C TRE Or Ae Ee EES es eee AS OOL en Pome ees eececk=
81 | Oct. 7 | Spotted Tail Agency, 1,200 feet south- |....-..----- AQT SOVADN Pana eae 3, 760
east of flag-staff.
82 | Oct. 9 | Red Cloud Agency, 2,000 feet south of |.--.-----.-- ADE SE) BS) enon asacca 4,290
flag-staff.
Som eOcvmmel ORV hiberkuveDs nse = a2 os eee wee moc Gece eonece ce AQUSO Muh etsenisterese 4, 600
SAR EO cimalite INiobrara IRiverisaccce ates set ee oe ose | awaesecccee WN axl AN) | scence 4,970
* Not reliable.
MISCELLANEOUS.
Longitudo.| Latitude. Mascon ee
| variation. | ihorau!
OP OH ie Oe Feet.
ImvyanyKearay as ssc se se a. ss ehsee cece eee cece aes 104 15 57 CY ea eee Se sie 6, 870
Crook mower sre ts Pee ce eee eee eae eee ee 103 43 50 MA OMS ON Merete Mee 7, 325
(ChIS oie] er eee Seat esas ees eadeens seaatoasemseetac cosas | 103 33 11 AA SAGAS |S So oe 6, 932
Mermypheghe. 51H. .cos tse sense sae ete see gan ces sae easts || ataeteees ABAD: 59) eases ose 7, 215
Crowehedleace sou sande cokes teeta teem ee ne seen se saline oat eme oe LUNAS WPS a es oleic | eae
BOAT ULLCL 5-6-0 ae vests selene see ea selaec eee ee eee 103 14 20 HAM ZS E507 eee = Alicea s er
Warren Peake 2. on. (ssc sec cc cose sisebebe/ seasons ose aece Saou doe seerelee AAS OWN A er Aertel = sic Sei
SuneDance Halll (western base) 22-2 =--)2- 42s se ete ee leece eee eees AAS ODEO) ee acer | aoe eee
Haine yah ea kas pe ocr tes eae sateen an aetna oe sa eee eee eteal| Sac nae ce Seca) secctens << 7, 368

5d4- GEOLOGY OF THE BLACK HILLS.

SECTION IV.
SUPPLEMENT.

In the summer of 1877 I was an assistant of R. J. Reeves, esq., United
States Astronomer and Surveyor, who had a contract for running so much
of the boundary line between Wyoming and Dakota as lies between the
parallels of 43°-45° of north latitude. The longitude of our starting-point
had been determined in 1874, and depended upon the longitude of Sid-
ney, Nebr., which had been established by telegraph. I think that our
starting-point can, therefore, be considered as very nearly correct. Our line
ran through the western portion of the Black Hills, and by estimate one
and one-quarter miles east of Camp Jennev, the longitude of which, as
given by my chronometers, is 103° 59’ 48’.0 yest of Greenwich. Assum-
ing the correct longitude of our line to be 1:14° 03’ 05.85, the correct
longitude of Camp Jenney is 104° 04’ 35”. This will make the longitude
of Camp Jenney, as given by my chronometers, 4’ 47” too far east; and as
the longitudes of all other places given in the table depend upon this
determination they will be in error to this amount. The meridians on our
large map of the Black Hills are made to conform to our boundary line
of 1877. |

Early in 1877 the telegraph line was extended to Deadwood, in the
northeast portion of the Black Hills, and later in the season Capt. W. 8.
Stanton, Corps of Engineers, determined, by telegraphic signals from
Detroit, the longitudes of a great many places not only in the Hills, but of
places south nearly to Cheyenne.

I quite agree with Capt. W. A. Jones, Corps of Engineers,* that the
use of box or marine chronometers for determining longitudes in a moun-
tainous country is most unsatisfactory. It makes no difference how carefully
they may be handled their rates cannot be depended upon.

One and perhaps the principal cause of the variations in the rates of
chronometers is the rapid changes in the height of the barometer in ascend-

* Report of a Military Reconnoisance to Northwestern Wyoming in 1873. Washington, 1874,

ASTRONOMY AND BAROMETRIC HYPSOMETRY. 555

ing and descending high mountains. Every large change in the height of
the mercury will have a corresponding effect on the rate of the chronometer.

From some experiments madé by Prof. W. C. Bond at the Cambridge
Observatory in 1856, it was found that when at a mean pressure of 29’.90
a chronometer which had a daily gaining rate of one second, when put
under the glass receiver of an air-pump and the pressure brought down to
20’.00, the daily rate increased to nine seconds.

It is yet to be determined whether or not the decrease in the force of
gravity from the sea level to the very high altitudes to which chronometers
have been carried may not have some sensible effect on the delicate moving
portions of a chronometer.

Page.

"Acme occidentalis-- ------ -- =~ 22 = =~ neem ona 463

Actxonina ? subelliptica 463

Actzon concinnus --- 463

Spel ph C OS ee ee 463

Age of the igneous rocks ....-.....-.----------------- 219

Agraulus —— sp.?.---------.------- -------------+---- 460

Ge oats = ose aoe eeerEc he Saseeseeenee=e 342

Agricultural lands 314

Agricultural resources of the Sioux Reservation. ----- 5

from Cheyenne to Fort Laramie 23

Akera glans-oryza..--.--.----------------------- ----- 437

PAdlenaWir AMES ClLCU tea ae aaa ea eee eee a = 252

Pale TONE Wry GILeU mms 2 ta te ee ee 252

Altitudes and positions ....-.-----.- 551
Amauropsis paludineformis 431 |

Ammonites conradi.-.-.. .-- neeoee 464

COVOADUS = 232 eos ae ee eae een 379

COLOTOLMIS =e eee eee 378

Var. distans --- --=---2=-------- 380

464

461

464

THER pane n woe seo sSohosece sos stesonsese . 464

Serrato-canmatus — == 2----—= --22— se === = 440

wyomingensis ..-..-.--.------------------ 440

Amphibious Creek, [27] 478

; [204] 473

(205) 472, 474

PAPA | oss ts ose cccodsssezesscese 475

MOGI soe. setes scessedacceoseea: 235

Anchura (Drepanocheilus) nebrascensis ---.---------- 429

SGU HS ken ne So ees Se sSoserecace dees 428

Ancyloceras jenneyi-----.------------- 452

nebrascense 451

tricostatum 454

SOANGUIMN a soe oe eie fe se eee oe se ee 464

EME ee se esossessece spcnsse stone stored seenoseae 483

RGD aio = = boa caeencecc ssoeessesoreanco0 483

NOEND en Gas sae a ee eee eee 483
Anisomyon alveolus -- 432 0

DORCAS ee aaa ease eae 436

patelliformis 435

SST OU ULS ee tore 433

Antecedent drainage----..-.---.--..--.----.----------- 216

FAP AbLLO Ml SANG asa soe an one ce owe en 507

SANIGIN- OPAC HY LO serene sneer see ee ele 512

Aphrodina ? tenuis..-..-.......---
Aporrhais biangulata .....-...-.--
MOOK: 52s sscett este
nebrascensis
MEW DEED Ure mene weasel eee ne a
Sublovataean-s os - ascent eee eee nae
Sublovis tease oa sso a sass ae ee ee eae ce
(Drepanocheilus) nebrascensis...-.... .--- 429
(Goniocheilus) castorensis .--..----..------ 427
ATCA MOMAtas sons ase soled coco s eo eeeese ee ass 359, 405
SWUMARd ihe ee me eee eee es qantas 405
Archzan formations, correlation of......- -....------- 63
gold from the. ------...-.-------- 50, 54
history, summary of -....-....-. 220
island 214
of Canada 45
Castle Creek district.-..-.-.--- 262
Rawhide Bnutte:-----ce-.---s=- 27
the Appalachian Mountains -. 47
Black Hills’. -5-s----ss- 48
headwatersof the Niobrara 28
Rocky Mountains -....-..-. 48
subdivisions of the, in the Black
HIS eee et ease ae 41, 50, 63
system; the.---=.----.-.--2..---- 45
thickness of the -.--.-..-.------ 61
time, history Of--------—-—--—--—- 62
topography of the......--.------ 48, 212
unconformity in the.........---- 62
PAT ENICONGES VSD Atte aoe o ese eee eae eee tieeee 333
PABSayS Ole Old QUuarig= —-=-5-ss- selena eae e ee sean 294
SABLATIO | OVANIAIA NS) eens sete rene Comme ationae 413, 417
(ig (rl 1S) 2 4 88 ee San eke peep bo aSe rr pEeaCS eee ae 363
ANOLNA LA gee eee ae ame ene aa oe 368, 460
PASLOTiaS t Cu DIUM esse cccas sooner asco se o naw el 344
AstronomicaliwoErkoss2 2s <2. c2=ce- so scene soc eeest 543
lPAvelana Concinnae e.ce ares cio ac capa eo o aes cccsee =e 463
subglobosa: aoa sc2nsc eee ssec-ceaesteeccce 463
PAI CHAI G HEL enn ane cise aero na soaaascc=s2ce-tue 354
linguiformis 384
RHIDTOSa yee 5 se atin oa ce 386
nebrascana 385
(Monotis) tenuicostata ......-----...-.------- 354
(Oxytoma) mucronata --=---------.----------- 357
| Audubon, exploration by-.-.---..--.------.------------ 7
JAG Pes ier Ph AS EE econo ect HORE oes 489
|: FASTA, Se Eo ea pee 485
Bach, Leopold yon, cited 7

p08 INDEX.
Page.
464 | Camptonectes platissiformis
463 Sty Glu Sees eee eee ee
464 | Caprinella coraloidea.-.-..-............-----.---------
464) |) 'Capulusioccidentalisee-nas-ee tetera reesen eee eere ee
Bad WandsjofWihitesRiversas-seeesseeseeen ese cesecese 8,36 | Carboniferous about Crow Peak .........------------- 128
Led mi hyp Ges ANG Non COMIC co ocqocascacessoc50 Jaeoscecee 97 Wiarrenvh ealss\ep see eeeierlae 129
Barometric) w OTe ee cee cee sere aise 547 and Potsdam, separation of.... .-...--- 109
1eierne IBAA Koo ocubciocoeds soqacopa pondbOsocéoSdseones0505 195 Red Beds, separation of....---.-- 110, 118, 131
Bear Butte Creek [144].-....--.------...--------..---- 507 exposures in detail ..................... 120
PLospectin Con ees eee eeaeeeasce 279, 282 formation, headwaters of the Niobrara. - 28
hopographiysOlemereeeeeseeesaeeteses 279 fossils\-= tre ser eeee eee eee eee eee 130
IB ARe ALIS SoS Godnb ea cabapoocecoodesesasobasdabosEne 191, 200 ideal restoration of .......-..-...--..--. 204
Bear Lodge Butte [159-162] .........-..--..-.--.------ 518 in Bear Lodge range.......-......------ 116
Bear Lodge district, prospecting in oftheyBlacksenlllseeeese eens eee nena 42
topography of......-.--.. JOR VIVCSW Sacesobsnceocs SoogooSSee 42
iBearsWodgemanle cman em srereer eee eee eee reer ees Rocky Mountains ...---..-..----- 108
iBelemnitesidensusie see eeseee eerie eee eee eeee eae on Amphibious Creek .........--..-.--- 121
Belle Fourche, valley of the ........-.-...--.---. Battle Creeks 2e-- eae see ee eee 123
Belle Fourche Valley, structure of.......-..--..-.-.-- Box Elder Creek ...... - J aidlatavaterst sree rare 126
Big Cafion of the Cheyenne ...............------------ Castle: Creékisssae cere eee eee 120
ISCO) a ooo oo cosonbocasegEbassBSaseocs0NssesEbC Wrench) @reekye-e ec s-eaer eee eee 123
in mica-schist.----.-----------------.-- Minne Katta Creek .........-.-..-. 121
PM NOUS acodaneodoouaDeee accuse s605 OldiWiomantorkseese see eee eee 29
WER E, osoodoondesocbonoscuspocosodaHmeacds Rapidi@reelgeeee erat eee ee eeee eee 124
maonetitehnee ssc assesses eee eee eee seers Spearfish Creek ........ ..-..:.-.--. 128
HOUT Seqo paSaSt aban ocosnooRseneso Plateat ies es ace ora ceecnee eee 115, 117, 204
ssh SeGh/@ VA fo 0005 250000 anqnon sone sseo0ne0 seasseSooE subdivisions of the ...-..--...--.--.---- 107
TV EAC ISM) ccoocnecoooecescansssoy ocesoDoonebouasace topography of the -.--...--------------- 114
(GRIT Secon onsdsHeconastochcosostereeessac 503 | Castle Creek mining district ........-..-..----------- 261
[240] iesescrs ieee crt 505 Potsdam sandstone on ..-..--.---.------ 262
ING Oo cccosgsones 281 PLOSpechiN\g One eee =e eeee eee rere 264
Black Hills, age of the 214 topography of ...-..-...----2...---.--. 261, 263
an epitome of the Rocky Mountains...... 3) 380 NCaswellydiohnbbes citediessaseseesse se neeere eee 190, 194, 203
defined acces. sane eee ee see teenie Seeinieee caer 1,39 | Cavities in quartzite ..........--.-.....-.-.-.-------- 473, 474
drainage system of the...---..-..-.. 212)1215, 218) | @ementiniquartzitesese sn eee se ese erasers eee 472, 473
form of displacement...--..-----.-------- 209 | Chalcedony in rhyolite. -.-...----.------------------- 522, 523
general structure of the.........-...----. Bi} CABS. || (ney @aN® <- 5466 sacs sucess socoossosocsbbesces05 S2 cron 22
summary of history of 220 | Cheyenne River of Post-Miocene origin...-...--.-.--- 217
Tek TERE, Wife Ohy CHT esag accede ooocanogenDanaease 555 | Chugwater River, the 23
paqonecenoe Ho dgnDooeEoonEDReS 531 | Cinulia (Oligoptychia) concinna..-.........-.--------- ~ 468
Sooropboseass Pi) I OER AEN GS ooo senmad ceeoucdouDaanensecesusunoosmace My Cell
Se aerate ee aera ate aloe nie eelnictetelelein\evein sais CHL |) (GbE) 2S ose soESoaoocesSccomaoteebsoosssecodeccsesos> «© SNL
soodnip 900000 onBooboosHeEDo5.oc00RE 482 | Closteriscus tenuilineatus........--.-.---------------- 468
sodeontinnodcnanevoSodbouesoocanade 473 | Color of Red Beds, origin of .........-----------.---- 188
S00 dda coabooubosSonSU sodOadcoeREs CUPLCWR) || (Coomera, 3ekeore, WN, 18) ses Spcnsbesccemeseeseasooccccess © GH
274, 275, 295 Cited? sense scone ere reece eect 24
PLOSPeCtiN GON ee e-em cee eee 276 exploration by ..-.---------.---- 14
topography of 272 | Conformity of Carboniferous and Red Beds ---....----- 130
Breccia Thy Oliticnsassee eee ase eee eee ee ee eeeceete 516 granite and schists...........--.-----.- 227
IBuccinums{sconstlictumies- sree ee eee eee eee ee reer 463 Jura and Cretaceous ..-...-.--.--.------ 167
iBuildingistoneee.seeee- se eeeete eee eee eee eae 2958 eC onrads nee eeee ree seer eee Buby ponmadosEDEebECooor 7
Bulla SPECiOSayace sec eee cee eee eee eee eee eee 437 | Consequent and inconsequent drainage ...--..--..--- 215, 218
subcylindrica 437 | Cora, Mr. George W., cited 279
OMG) s sotboscbedeok ooedanaseacespescouaES 475 | Corbula moreauensis............---..---.--.---.- -- 420
ADVTACH YO) sae aole telnet nelle cele ice eerie 5IOMeCrassatellateyans i aes eee eee eee sco) 2483
Callistaldeweydismrcsc\-eecccena-eaeteeieesscescemerre 416 SRC RCTEMIE) oon6 coassononsoSsoncoaessaoaece 412
VERS TOQU RES opoooecodoppoddsacoseesses 4624 KCreeksisinkingiofemeceen see eae ee eee cee eaeeee 123
(Dosiniopsis) nebrascensis..--..+-.----.------ 462 | Crepicephalus (Bathyurus ?) angulatus 342
(Aphrodina) tenuis 462 Centrale ye aos koe GARE beep ee ares 341
Camp /Jennoy? ss sessescicsc se neisis2ceceiscinwiceciecineleeeinec 140 planusiiss-cs.cssces se ceaenceasceine 343
MerYeTGE) OF conban desounconenagecend econ 554 quadrans 343
Camp Terry, prospecting near ..-----..--...-...---... 281 | Cretaceous and Tertiary, separation of.....--.- 185
Camptonectes bellistriatus....-..-.--..----....------- 351 clays; decoloration of.----2-----2---------- 189
GeQieNPENTNSS nopocp dosnooabaasoceseooane 353 exposurespn) de tadl meee see eseese eerie 178
OMENS Com ooboriessdaseoobdaddicnsaecce 353 | formerly continuous over Black Hills .--.. 186

INDEX. | 559

CWretaceousitossilseseaee cee sence ee esas es cineeeeer 185
in Belle Fourche Valley ---.-.------- eS
OftherBlacks Hall s==see = eee e rete ----48, 175

JOO WY CRiie Setmecetnoseconssescise a7 169

on) Beaver! Creekier ss sae 4esteeen ee eense tee. 33, 178
Mrenchi Cree kiss ee eae se eeeee meen ee 181
Minne Matta Creel: -s..-ee—= me = 181
OldhWromanshorke= senator eee Z 31
RapidiCreeky---es-sea- nase ao, _ flGal
Redi@anon @reek===-ses- sence ase 178, 182
South Fork of the Cheyenne...-..--.--. 33
TAGUCHI sacaqetenans atieeas socsesdseaseaace 177
section of Meek and Hayden.--..-.-......--. gal
Lopoeraphiy, Of Une ese ae ae sees eee see 176
WO WEIS OF Wie) cosoosdssceageseosccsosse 180

Crows Peale asec sen ooo etsnes Gasiaw sacle eonaienceceee 108, 128, 194
[TAT RTAO Sees eae 2 oa Mec aalar an Ura S 506

(Olean dock bee eb eqodsubEdcas SonesO ese Me rane sdgaaa 334

(CRYO EANNE necoo sos sonesusenoceecne deo sSaancoEoseSae 537

Cxyptorhybismusitonmisnea= sess 22. c osc semee emer cee 421

Crystalline quartz in mica-schist 47

quartzite...... So: 472

GURIIVAIE aeitand: choca cdesnessousesosesaos 474, 475

Oimauillesey TUE bes sseocansoesSenesenBeeeeocdoudesases 405
ANON Mae eee eemseeriaes wcle feces nace 359
shumanditeae seremoee ene oe eee em anne re cece 405
Culbertson, Dr. T. A., exploration by 9
@uster General (GaAS cited eee eee eee cae peel G)
_ exploration by 15

WustemGulehessetce eee season cace ecm cc eile ences 237
Custer Peak ........... Mefen inate sai Sea sees ams secee 192
(GUBY | BAe oie te Sats ie ate ee eR 501

(DEA atari tea eet eet caper aE RaeEes 503

Wnstersbeals Tock Of. --ecess amet sci sec cee ccteme cae 281

Cyanitenemica-Sehist: ae ees aee ee sea se ee eee aera 478
quartzite 472

Oyelinaticinenlanisess: cae sme o ec sees eee ee cer see 417

(ChmiGlb AN CG) cls eee eresinasardearoastesnensenasosoassee 418

Cy prinahumilispencseeeseeeeen ease eee eee eae 414

Gypricardiatesasse pen sac nenes sere ae een ares 364

Cytherea deweyi 416

missouriana 416
UGS aco osopcoosesones ue soderesesdsuacesor 462

ID ACIUC Raat eee ase cee oe esa oes Bae ESE eee 483

IDEN OU] MCLE AscmonpesccocusscoseoscstEescudaecared 4

Dakota sandstone, ideal restoration of............-.--- 205

Lopoprap hy Ofeese eee e ee see eee eaee 177

Dawsons MiriGaMe cited. ssssccccse seen cece cline 150, 191

Wri Wics ClLCU see ee meee emer neers eieee 98
DMeadwood\Creehk-ee. sae sea oe esos eee eee ae 280
OLOS NOC HINE Oo 355 ono hasosecosSese 282

Decoloration of dark clays ..........-...----..-------- 189
Deer Mountains. -------.-. ude Hehe Serena eee 194
[125] 499
Dentalumepfracil ere. cemes oe ss ee see ae ee ae eeeerce oes 438
Tailor: sesyse aes cies see a eee eee ale ate 438

Mion dEweyl e- nase soaeasss ee See ee ee ee ee eee eee 416
TVS BENIE) onc oe einonbadesssue cease erQuencues 416
MODTAS CENSIS: = 2h te aes eee eee ee 462
SGENnWIS 22 sees ee sane een ene cea ee tee cee see eae. 462

Devonian formation, absence of ..........-.....-.----- 42

LO Se mensreconce Ha bAS AA teme San Senn S cane sha we seen ale 301

Diplodonta subundata..-..........- Fae = See eee 411

Displacement pr>ducing the Black Hills, form of ... 204, 209
Dodge, Col. R. I

DodcoenColskhalejonuhimberee-- cee see esee ce eee ese e 324
Dosinia Jurassica 373
missouriana ? 416
MOSINIONSIS|d Cwieylee semen aera aki eee ame oe 416
MODLASCENSISe mem aeeeine seem eeen eee ee 462

Double inclusion of magnetite and calcite in bio-
LAU ai eet seeie se ale eis oiae soa e wise Sine ecco s/s seis 520
Drainaeeot the Black Hullses:2-2-s---e-esess----ee6-- 2
system of the Black Hills..-..-......-. 212, 215, 218
Drepanocheilus nebrascensis.-..--..-...-:------.----- 429
ihrenberoe Dre Citedyasccseeeeer cee ae mcisse ence sre 97
HikiCreek, wopograplysOte scree eee eee nieeee eee 272
i MMONs PE LOtessSOW aes sees ieee ieee eneen cee 86
Endocostea ..-...-. noo NadaoD Gs DCOsUoEeUD CESdenaSeaDE 4 402
AINGHIPY, sonaoscoqod bancboSSnSDoBAced 403
impressa 403
Sulcatateeeaseseacc ceaceee ces eee cee heen 403, 404
UI DCP acoso censescoser ap dscncooneesyensoano 403
Hozoonicanad ensues sesee cree saeeieeeeemiteceeeeeacs 46
HM pid ober sence seem cee ere menaioee se wine Meese eh emerne 54
Erosion, epochs of .-...--.---. 296

Eruptive (see Igneous)

Eumicrotis curta...........- 354
Onbiculavaere nena pacer eneeet en 356
Evans, Dr. John, exploration by 8,9
Examination of thin sections...........-..-- ---- 472, 477, 494
Manny :Pealct eee ieceaacsece ecco ecens see sees 111, 119, 140
Hl arniin o@lantd Seeememaer see sas sae eee ce eee ei areeeise 314
Fasciolaria (Cryptorhytis) contorta .........-.....-..- 422
USILOLIMI Sie ees ee eee eee es 421
(Piestocheilus) culbertsoni.--...........-. 423
Heldspansromioraniiespsss--eaeeseee eee eee eceee nes 70, 525
MV CRDUIGS. scosenosood0 osSsos badeneneaasooacce 491
DOM D Ny ARycoscocoosoooQcondoaRaneoseceenaoscée 484
Helsite-porphytyeeen=- assesses eee eee eee 527
MOEDiCe meh wa eeie wees eine oeeie sone Sees oa ne Benne 484
Flora of Black Hills, Jenney on 315, 320
Fluid inclusions in rhyolite ...-..- decedadcauecnasancsee 487
HMlordlikeistructurese sees eeese- eee eeeer nears 498, 513
OSPR Y TE DHE 4 soc oo ad eommoocmaseusaadcascesdeeae 430
HossilsplantsfromyAth) quis ase e eee ee eee ne 149
Mid dlevParks eaeseteen sen eee 150
near Moqui villages .----.:--..-.---..-. 149, 168
INOS wOOGL, OS) WEBNS oo pon oas aeeoseeacasdeaceosoe 149
Fossils, Carboniferous 110, 130
(Cretaccouseseeacecacme se eeeaeceeeee cece 185, 383
UTASSI Ceres see eee eee 162, 165, 166, 168, 344
of thesPotsdam' sac cee eeceeee eset aeons 87, 107
DUS AIEN YT: son canotoouanboe nasabcwsounacasocnce 7, 26
Primordial eeeesseasne saeco eee re eae ce 331
why not found in Red Beds .............-.-.- 138
Moothillskt)-e Saas aes asec cia eens aecaaeen 32, 177, 204
section at Camp Jenney..-..-............---- 34
TN EXOSIS Ot casos tdec ORB SCOROCE Ee cOgeOnEEAAeBe 289
(DLOSPEC LIN OyIMe sees se ena eee eee eee eae 291
Fort Union group on South Fork of Cheyenne..-..-.. 31
HirenchiCreeka (40) eeeememeiase eae cee ee aese se eceed aa 478
els cbeasocecocoteonr a aeecne eee aeeaana 472
(PUR case AUR Re een aoe 475
Mescribed wea vccren cei acces tele ae 229
district, topography of 226
prospecting in 230
mining district ..-....--...-..- 226
LAO MIN OH [PWS sae co mo adacons doe oeseecamee 474
DALE ree see enter ee eee 475
JOTATEHIS, Al pec neeeho ooocmonEecod Eegtnewsece seeeitaes 315
Hincoidesiduplexseecesee maaan eset emer saree aes ee 332

560

Page.
HUSUS|CheyeNNENSIS:ceecieee ae seeeses seer eee eee 424
constrictus 463
CONTOLEMS o-~ Sccicleciciswia re sie Socio aeieineenince snes 422
culbertsoni 423
haydente sce = sca clench aeiwce etc see ee ae 423
Shumardijeeeeeeseeeeee 424
tenuilineatus
Galena a2 22 sceneeacemeeacc ess
Gamopetaleze
Garnet in hornblende-gneiss
CW ENAWANIE) Goode sonic acon cocasosHacostence6e
Garmets* os << 2522: eee oes pose ee one eee eee ee aoe 52
Geological history of the Black Hills.............----- 296
Gervilliairecta we: ose scater eas Sees eee ree eee 358
Glacialiperiod¥oravelsiolees-eeeeseesesseeeaaeeeie ese 298
Gladiusicheyennensisiesscesseeeecee eas oaeeeneeee eee 421
Glasstinclusions;aS5-cmis-seeemea ace Seen 516
in'sanidin 3 2220=.-o2 5-5 seaeeee seers 495, 518
MASS! sjaics2e ae otioe ee inet cesar eRe SRE bree 506
Glauconite stern cies sescese cece se noe See: 95, 475, 476
analy Se@si0femecy eo eccce ctisce eee cenee eee 96
GlauconiticHimestonesses sense eee eee eee noes: S475
sandstone esa. cose- cere eeeeceeee ah 475
GrGiss issn SAAS Se eee ree cls censor ee ee a Bee 53
Gold} ageob 228 0h) ye ears niaisstynsise cae seat ete ee een 296
characteriolters sce ccee-eeeeeeraee 235, 237, 249, 254, 265 |
derived from the Potsdam conglomerate .....--. 299
trachytersseyee cere ee eee ree rer 282
Giscovery, Off 5-1-1- ie sterstere- os cease tetera 229, 264, 292
in the Bear Lodge range....-..--.-- 286
manner ofoccurcencelOfeae ee eee eee 225
(i End cosnemnaccud ma gnoncsnaausnconeaasscaabsane 236
SOuTCeOLet as rest cme sop eter eee 54, 61, 84, 103, 200 |
ledcemvjarrensrealks [1 87i|eeseeeer eee eteere cere 522
Goniocheilus castorensis. 2-22 222 co 2e- eee ee eee eee 427
Grammatodontinormatuss=---een cece eeer eee ee 359
Granite <2 5 esis sede see seis Ses esse ae eee Sess 41
blocksunchidedsinweres eee eee eeeeeee reer 72
charactenilolcesem ce ena eeics se eiceeeeceeeccies 69
CO NOGGIN OF socscessscasdsackocesnesoSeccean 228
distributioniofersseeee eee ree eee eee ete
intrusive character of. 9
lenticulariformiofsmassesie-eeeeeeereer ee eee eee 78
ofeRawhiderButtere = see reece cere creates 27
the Black Hulls) age of .-..-52.22---------- 77
INCrUSIVG Ne eee eee see eee 76
Oni ginyo fern eo eee ee eee eee ee Reece ee eeeeee 75
pebbles in base of Potsdam .-.........--.-.--- 79
White River conglomerate ----.-.-- 214
relation to schists .-...---. SS ACES UO AICHE DEO CS 72
relations of, compared with those of trachyte . 78
Slickensidesions so". = cee ne Ree ee CeCe Ee 228
SULUCtITOLOL ssa ane te ee eee ene eee val
HOOP TOIROR ooonngécaossanescnencodosnoaesee 65, 227
‘Granite-porphyry.sss--nes- eee eee eee eee eee 484, 495
Graphite rsccc-sccmce cele eo tainte cee sees toeeeese cee 54
Grassicharacter0 feseeeeseeceeee ee neers 317 |
Gravels¥place reeeerer ee eee eee caer cree eee ree ee ee 287, 242
QRNICIMEFAy scccosoSoces srooncceESsacconescade 298 |
(Che, AASB ocooepanbobesone nosatunct comddooomEscscocame 531
Grazing lands of the Sioux Reservation.---...--.----- 5
Greensands meerrese sae meron eee cease steisnc/-ttet=r=i=i= 95
Greenstoneie seer anes eae eee eee eee caer re cis 194
Grinnell, Mr. G. B., exploration by--------------------- 15
Groundmasssbandedseser een eer eee eeee ease ae 484

INDEX.

Groundmass, crypto-crystalline ...--.....--..+-.-----. 502
crystalline mee. oases ates seas 510, 513
IGA sous Resese sos bbuosdodascoco cree 523
fibrous wes ges stern\.) hese ee setsa ee see 516
fluid-like structure of .....-..---.------ 491, 513
ISOtLopiCan-celecise ae cce eects 499
MICTOLULC) joes eee eee eee ee 508, 515
Of phonolitereseee re ==e eee eee eee 494
Wan OIE) cocoo cosepescoseesaueods 484, 488, 491
trachyitemeetee sees see ee eer 491
Groups of rhyolites and trachytes ..........---------- 5a
Grypheza calceola var. nebracensis ...-.. ..--. ----. 348, 349
COMBE) saecocuons tose case sadcon isecsosanane 462
vesicularis ssi. 22h shite ease eee ae eee 462
(CNDSWUN scooncenoson saccmudecanacscdseQeosaas 134, 188, 146, 295
Gymodesiconra dite er merce ease sec aer teen eee etree 463
HallSProfidiames'ee se ssee ce cetera soeceeenne sess 9
Cited 22a 22 Meco aerate’ 97
HMallisih@ut-ofteseeeee asec eee eee eerie eee ene 471, 472
Hall's Water [209]. 222 o252 52-28 38s ease eee 471, 474
iHaminearsubeylindricage-se see eee eee eee eee 437
amitesiuncum@es. -cese er aa seer eee ner sees eee 464
Hamulustannuliterseseseeeeseen eee eee eee eee 456
Harris, Mr. Edward, exploration by ..----.-.-----.---- 7
Harney Peaks serine fee cui le cee sseer a eeee eee 15, 227
AS CON tOfi esas ci cece aa aae tee ete se Eee 67
barometric observations on ...-----..--- 547
INGEN Os Socseosesdodous Jose baboou seotes 548
ISENGNG Ny IREANS TEER ooo cnsesocos se cosesewocoobeesSopeE> 226
Hay deny Dir HaViereseaee eee eee ee eeee 6, 31, 81, 112, 151, 166
exploration by ---.---......!- 9) 10; 12) 13) 14
Cited ieee Sieteabsckeee 38, 74, 96, 113, 131
dlelciontalyeolust-sess- eck ee cee eee ee ee eee eR eeeee 433
CENDUEIRUS ooo secssosodd= cons esouebedoeeon=ndcod 436
patellitormiSseeeer eee eee tere rmer terete ates 435
SUDOVACUSE: =a: bre oem sen ee seria eeereet 434
Helicoceras angulatum .--.-..-- 464
c nebrascense..-...-- 451
stevensoni ..-..-- 447

Hematitosss yeas Goa oa yes Seb at ee ete oi ay cea ae
oneBoxeHldeni@reelkare-eeee eee seer ee eer 274, 295
Heterocerasjanyial at umes ete eee eee 449, 464
MOW-DONT SY oatsasacel seine se ele erecta 449
Yinebras Cen Serer see ee niece vitce me WADI
‘Hinman sRev.ShDi cae jesse ence ence erecseeeceecr. 230
Hipponyx borealis! 2222 ses 5. a5 yest cteihacs peices citer 436
Hornblendencleavart eloteseceertaesereeeeee sees eeae 472, 514
crystalseeceee-csee eee ere eee eter erence 498
Gichroiticie ses cama Seer eee eee 472, 514
| Hornblende-gneiss (/24]| [40]. ----.----...----------.- 478, 479
TAB NCTA) We, no5 dooce oocor aseoseas 479
PEWBNEH Wile no scgnsaescsocoseesoNee 479
| Hornblende-microlites - ar RS a EAN dS et ag 497, 513
NET) Gocens copsomenneaosaaannestosontac 521
anyphonolites=serer eee ereeee reer ater 493
DENCH) soos caobasseobsucsneococooasesss 490, 519
qQuanbzite ce 2a. 4 a easoecceneen cee tinseciae 472, 473
TOCK eee aia oA ee eee Nee eRe eee 54
47
analyses of glauconite...-....----.----- 96
(OI Wan ee eee aoa aeaeesoucoRteoacacedes 133
Hunonianeorm abioneh) ee meee ates sete esses eer 37
SG MOd WED 10) - ssn esscousmocapcsasotabanceossenosny 12
Eyaline-chyOlitemeereasseace eer sees eee eee eee eee 485
Hyolithes gregaria 460

By =

INDEX. 561
Page. | Page.
Icthyosarcolithus coraloida .--..---..-.---..-. =-.---- 462 | Jones, Capt. W. A., exploration by ----.-.-. ----.--. 14, 554
Ideal restoration of the Black Hills uplift ...-.-.----- Z0Ds Mera a DOWLED CAB UULeis eee erin cione ae ce es eeentee ee 196
Md onearcals RUMI aT Cee aaa eas eee eee 405 and Red Beds, separation of ....-..---..---..--. 131, 153
Igneous displacements, relation to main displacements discovery in the War West------..-.----.---..... 151
of the Black Halls 2-5. 22--- =.= 208 in Belle Fourche Valley ..------.---..--- Paseo oe 153, 164
masses of the Black Hills 44 OE TBM see tesaceaemebeanabcerAcEnceereneeD 151, 167
matter did not overflow ..----.-- .--..--.---- 197 THOVBIACsEGISeeescntcem mon sila ce si es 43, 152
TDCHUNS. co masmnoddate sosagne ssosvases Jaongacose 189 ohenNorthwestmer sereeesseen ei east scien oers 152
and the Red Bed limestone .--. ..----. 133, 191 @n Mim NOUS Chee Co docoos season neocencecscecs 158
relation of, to Potsdam-.--.-.---.2-..---_--. 103, 200 Boxpblderi Creeks ca oss eeeaes eee ese 159
TOCKS as Zoe ee ate Nee as orctoralees ete aistete alot eet 190, 281 Medi Canon Cree ksese ayeaias va ieilece as leele = cae 156
BIR) OF WG 2 socccos es ososemosssecouases - 219 IRetdl VV WEI (Onion sos oee nes oes po anomossesos 160
TCM SiONS ns SAT Oe ate ee = lela ao ee 489 variation in thickness of the------.-..---.-..--- 152, 166
Up GbEN SS JOERGES occ aemocco .sace soncosseesercadamsene 4) Pe UTASS! CH OSSILSs eee nese eae sae sera 162, 165, 166, 168, 344
ILEC RSENS Mins) soso scdosdeasecsescdacoeoondesscanes SUG pKonsleralvir who uissantseaee on ease eeee areca eee sae 292
Ab HTC aosdiscncodcdesmenosconecsosseace S027 maken oy Mine Clarence asbestos tinet-tsine cle jie aaron 150
ball Chie se see eee eee eee ee een eeee ee 393 Cle de eee ne eee Stier ieee enya 75
WERE A mond eccesenes cegaasos 398 lonherAmcheamesterr eee eaeaaeee 48
confertim-annulatus ........-------------- S13] Ilemdls, merrophimeM 56 cenanoossenemseocosecneoosenas 314
CONN GEWE): ost 2sce sc ossssoccsseacars ----893, 404 grazing 317
OH -esoasscos sAponotsceseeosensases 308 A0Ss ieleatitndesise sees aehce ccc Orece Atos See eum eaioot en: 546
Veit WERE 66 oases oHaneshos ose SOS eannen tian Onn abl ON eee ere eee Here e see 46
We SCAN TIS) Seb epee eee coseec sae S04 mledabisul catayese nesses ween eee eae tee cesses 407
UNGER) secon eesereeotagunesesnetenasace 398 OVANS ss oe ences ena sec eb masses ees sies 409
GUO econ scacesasaessaumonsesesceassoee 3928 beidys Dre dlosephiesaaeasee es seee ec saen saree 8, 9, 13, 37, 188
MEGUNS corcc sqnscsuesoorasoesme secnsosee 390'| Leiopistha (Cymella) meeki..--..-.-.---.-----.------- 418
BHD NOS 5 sore ccacine Spap25Se soseegasar scence 323i |Siesquereux x0 tlc oe eee een e eee near ereer eee ae 112
TNO ESSUS) oes poSesengsseccsnesoscogases 402 | Lewis and Clarke, exploration by ------ .-------------- 6
MAOH oe go sens ses seacuensuceconeoecoce SoGRieieimestonerc] anconitic ye ssss heer eser ease sees see 475
MEL TASCONSIS la ee as = ial inl = 393 | Limonite on Box Elder Creek ......-.-.--.--.--+.----- 275
B02 hiblhin oul alan ti quai seas tee oo cee eee Renee sem caecese rs 335
389 DLS VALOS bhai, Senos soe mace oes ooeneee eee 346
SAVIO cc ossoceseenscenadssessacaosess -- 395 spimnmatonmisy este cesar eee een bese ee cee een o80)
DUOMO). = scoseescesss esaeeocessose seer 395, 396 (Q)polita he secce dos Se eee oes ose eee ees 339
var, subcircularis .------------- 396 | Lingulepis cuncolis 336
SAL CNSIS 22 = oo eee = eee 393 dakotensis 336
var. nebrascensis ...---.--..----- 393 JOUER GANS) Gases ecaon seodsedeos 329, 335, 336, 337
sulcatus .-..--.-...-.-------------------- 403 perattenuatac Sesssekstecwe seen a: 337
RWS ce csedsete Heese qecusscecoseesee 393 DLL ay sectors Sek on eee eee toe 460
GEN UU N Ca GU See ee eee lee 2000 Mino placodusiveturnusmseeereae seer ese eee eee serene 461
VENUE soe hcisosoocesson- Heme aeevososne 3960) MiithlesMissourwisuttes) = ees -e-ees meeee se eecen ee <-e 202
WAS P ccascecostedenddcdcess Soe 398 Oe AGE) eens Sees concen 515
USCS) WODS OWE Socecsraasec ehosacooseocoasaecosonssce 320 [eS] Seer odansséasco BH
Imitenlamin ated avin Si-5 se = =f ae eae eee eee eee PPA} |) UO papi: She Wadler, oo ecceasesaapd sos cdedosessesnecesas 47
LaTMN INE) eee cogeapeonscorSpesbesemosspepedc so7dasee LOT uoranellusicentralishy =e -ecere ee eesen eee eee eee 341
Bef SoennnSretorese ss S084 ion citndest aoe cem arse subs enceeecmcset eee ene sles ale 544
[149] ccecssts ras sce aee wos aeee eee eee SOSH MOssimM acids 2554 eee cena cissse Serene eee ewceeseeie sees oe 486
DBP spaghecataeaeroess vec stderr ae pale eo cern OLS Zo wensaprdiCreels [Will |eeeeesementeasseeeem ere er erat. 480
MOGUHTEAS 1.0.65 [190] ee eee eee eer 510 | Ludlow, Col. William, exploration by .--.....---.------ 15
Norah pedo [Lol lesa se eee eee eee 510 oniclimatemesce ce seem arenes oss 307
[GG eee eee roe eee cece iA loucinaoccidentalisiess- asec eer tee emai cee a 409
west of [157i s> cme caceenncs stese sceeeetss 512 VOT avieN Uri COSA mee seieseisei-lsizreie = 410
Iron Ledge, Box Elder Creek [85] (Diplodonta?) subundata .........---------.--- 411
WORN ONG) sosecdsscttessssec sesece subundata - -- 411
on Beaver Creek ventricosa --- 410
Box hlder, Oreo kims-si seen oateraeeiceeeee Pfit ||. Ibi eriey COMOb NA. He oq oaopeeseasod bos seseboneee saaeeee 430
Isotropic behavior of garnets -...-.--..--.-..--.---. 422, 474 MMOLEAMENSISMee ere sees eesas ee aie ae eee ase 430
Mineral eacaeals = Wee see eee ee eee wee Dia eC Golly cud diya rsaViee ee atte se meee n=l“ 19
CERN co comacsegcesaeb Swen goss san asncoosh vase Eeese sa: 473 | Maenetic variations ..-......-...------4--------------- 547
Jasper, Hill [92] 473 | Magnetite border in biotite......--..---.-------------- 503
Tenney vine Watery bs eee ae ee eee eee ee eee 161, 163 iin [ONE Goode coesee SAAC saEemaeauneeesmRboD 502
GG ee cos Soacdodedoosacodesene 188 G@(TORHIZANS): so cage cendeonsesneanconccconos - 472
on climate 301 THOVOWWIE): sao co deepens cesses cconesSstedoce
225 submetallic luster of
VO) Heiss see se eeios oad coco sopsseotnendese ones 159 | Mallory, Mr. Thomas H., cited
Jones, Prof. P. B., cited SC Mammothvledeoressnesnsacceceeerice cesses mace cisetise

36 BH

562

Mammoth ledge, prospecting near......-.--..---.+----
iMammothiWiodexn saeco na -naces nae eae eee cee
Margarita nebrascensis-..--...-------
Margaritella flexistriata.-:.-....-.:.:--5.22.--5--<--=-
MarshyProf, Of Cimess ses scesseereeceee

Marvine Vir PAGUR.. (Citedissase ees aaecee eee eee eee
Maximilian, Prince, exploration by
Meek, :‘Prof.sh) Bicsececcascees eae eee

exploration byerese-seceae eases eee
Meek and Hayden’s Cretaceous section...-.-....--.--. 171
Meretrixideweyiisssee sas sae eet sae ee eee eee ane 416
ULM) oe Ses ance ene cont asceadnosooesosesse mass 462
Meridian distancesticer «= en-n- te mes near eee alee eee 544
Metamorphism of Potsdam sandstone -------.-.-.----- 280, 285
sedimentary rocks by contact with
igneous
Mica in granite. ---.-------+.----=----
QU ATUZIbO = = =a elise ee =e
IMU Ca-SCHISb Ms ses ommee nee tae eae
and slates 476
DiObibe AN s eases ese eae eee ene sere
PLOWMEM Canines eee eee eee
crystalline quartz in
CYyanilerineerersas- eens oa nee el eanecies
hornblend evine ee ecis= noes se eee eee
MAoNesiaMMiGANN soe. eee = ae ee eee eee
MUS COVI LO} Nee nesn eee eee eee APR
orthoclasein se so. ssee seen snes eee ae
AMIE NEE THY eo moan secagencescHe ane
IMica-slate tase ee accra eee eece csceeee 476, 480, 481
arcilaceous === =— eens sete = ee eEeeeereae =r 477
fibrous groundmass of .....:.--..--..------- 479
MiICcrOLtES ang UanbZtO seers eee eee ene eee a naae eee eas 473
SPM Gb NS. - cosa nocthnennoadatsocooseomseeeas 507
Microscopic petrosraphy ---..--.---..-2..--.---------- 471
Mineralicolorlessmeeer sar acesee eee enters 514
Mineralsniquaciziv@ memes -rea acess e eee es eae nese 472
Mineral!Resourcestesssoseeee see eeee sees eee teens 15, 225
Reportionitheesssas- eee 4,21
Mining district, Castle Creek......-..-...-...--.------ 261
Mrenchi@reekeeesneesese sete eee ene 226
Spring | Creckye ssa eee reer eee ae 238
Mioceneilake. soe. passes ose seine eee ee eeiseie 219
IMG HORN ocetsscosgovosacesee poSsed aech oocedeo ot toca GL
Missouri region, exploration of ..-..-...--..-----..---- 5
IModiolanformos geeeee eee eee eee eee 361
Monoclinal fiexures, duplication of ..--....------ 119, 139, 142
TIC COS eee eee ee ee ener eater 32, 175, 177
Monocotyledones .-.-.-.--- nS ore ore Seto oe eee eee 536
WOODS Quine scmcoosseoscostasoconodsecdosa6 sas0e6 354
ha Wiese noe eee eee Ome ere eerie etos 355
Spelun Carl deere nee ete eae ne eee eee ee eae 355
(LENUICOSUAbUS eae eae ee ee eee eee 354
EMOrLOn TNO Gis eee ee eer eeee cee eee eee eee 6,7
Cited assse 2: sce as 1
Myacites (Pleuromya) nebrascensis 461
subcompressus .-....---..------ 368
Subellipbicusie=s--eese a eeeeree 461
Mytilites problematicus ..... -..-....-..2-..-----.... 389
MB ECa CNR oo oécceposaneacecoc US LospoascEsses 362
WAH sosposeosescascosScadaed: sbossoossceusad 360
Natica ambigua 430
concinna 430
MOLERUCNS IS eeeee eee eee eee a eee eeiece ae 430

INDEX.

Page.
Naticaipaludinsformish--- << ---s-. sees eee e eae eee 431
INatrolitese-ese- eee ee eee ee eee eee eee ee 516
Nautilusid ekayieen seen eceen sehen eccrine ee eer 439
var. montanensis 439
NeerailongiTOSthiSeass ese ese n eee ee eee eee 376
moreauensis? -..---..----- bs Byeenaden es ne eee 420
VENELICOSA 2s secs oaise oe oe mea soe ene tee ee ese 420
Nephelite in phonolite- ------..-----.-- 8. te. 492, 503
Newberry, Dri Ci Gsietesescecseane nee cece eeteee seer 19
DriiS yes acco ae cece eee eee 106
Cited hea sess cece eee 131, 149, 168
Nicollet; J.C:, explorationiby--------2 = --se--2eeeeee 7
NoOsitehni phon oliteteeseeseere= eee eae eee eee 493, 504
Nuculaievansl 3 355.752ee nese eee ee ane eens 409
Planimarginatares- sess see. eee eases eee ee 406
Subequilateraisscs-eeecee reece sees eee sree eee 407
subnasuta.........--.---. Para G2,
VONUriC0S8) =. 28 e)- 22 joes See ese aseiveceseees - 462
INucmana) bisul cataeesse see eeeeee ae eee eee eee 5 CON
equilateralis-eeacsn-ser eee eeeee tessa eee 408
subequilateraiee- meses eae es eee eee 408
Obellanpolitayrey amceeeseectae- eerste eee eee 339
MAN Wee ele eae eteieeesieisioie sissies 340
Obolus appolinus ? ...-- eee seers = 8B
{ipectenoldeseaensas| eabescins sas etisaeass eee eee 338
OSGI 5 < Sane ccoonp emcanecososocessoocSsanES dsosben6 483
QOdontobasis)constrictass-2---=s=--2ess-2 eae 463
SONU COSA erate seis eta ete Eee 463
Old WomanWorky: 9-2 -ee2s ese e cee cere cee eee ees 29, 30
Oligoptychia concinna .......-.-.-...........--------- 463
(OUPEYONG) «os bscanstanomoss cee soopssdonoscocoSsasesenc6 484
@paltinirhyolitenssepeee aoe tee ee eeaereese secon eee 522
Organizationtormield works) s-seee< ess -=6 =e eee eee 19
Orthoclase in quartzite. ---.-.......--....-...---.---- 472, 473
Sechloniofsband ed s=-perer ee eee sae eeaae ee 525
@streaiCOn ges tare reas aoe seem eee eee eee eee 462
eng lem anes pear eee eee eee 460
Stnicilecn laisse eee ses eee a= eee eee eee 348
OwenyDreD iD alopesse=seee see nse ener eee eee 8
cited 97
Oxytoma mucronata 357
MUNSteELe sees ase eee eee 357
MODLASCAN Ae oe amoe = eee eeae ia resansds 385
Pachytherus evansi ----..--.--.--- 2+ -n noe n wenn nee 413
Raleochordaip lim geese ener ears eee eee eR eee 331
Palzophycus occidentalis ...........---.-----
tubularist-.----2---==
sp. undetermined . -
Paleozoic formations .......-----.--
Parks 4SCeneryiOlies-se eee ae eee eee eee eee eee een
TRAN ER ceases, Gsesapcoucusosots csacsesasseascons
Patricks VEremWiephyeseseceess see Semcinat cia soeeeeeseee 19
Cited soe acess ine ee eee 121, 162, 163
Pay, gravels characterOl esse. sa--e- eee sess see 287, 244, 265
POSibONIOfEe=n eee eee 236, 237, 242, 255
leer), 10nY AN OC). 3 SoSce cosbsoseacnasdesesscGnoosobssso¢ 96, 150
Cited See soos. ose sesee eee oeene eee 112
LYS epee cane sect Sake Seema Senseo cacoobsasesoccsbed 483, 485
Rectenibellistriatamers:.--=-sser~-e secre eee eee 351
WENT Ss cocnecceadconeseeno socesenosaosececeen 383
TG 70s) #80 oom oso aes Seeeeec cOsoe =aecoaueaead 350
INVACB< ssooseoscSoosspadouNs osdacdscescDsec ---- 383
Pentacrinites asteriscus...-...--..--------.----------- 345
PentacninusjasvelisCUse- eeeecs cee eeteeeeeee eee 151, 345

INDEX. 563
Page. Page.
PR O@RMAUAaN emcee ci ace oe wines soe a eves =a lalate 112,150 _|-Prionocyclus wyomingensis --.--......--.-----.--.--- 440
Perna OFM OSA saree a siarces sie aeaeie teine sens ee 361 | Prospecting at Mammoth ledge.-.-.-....---..-.--------- 242
Reroncea is citiulaeace «cme aeee aes eaa= Se eee eee ee 462 in the Bear lodge district....-....-:..--. 286, 287
Peholad omiya fib LOS Me see eee a sane ae eel 386 IDRC SBI, - 25 sedise gas Ses0eo: soos 17, 19
TNH Esmee eMC Aa REQ acRae ace mes osesHes 461 WOM AMG =o eke sot horo SaeeeSjoseoeed 291
Phonolite .22.--2<--5- 483, 503 French Creek district.... .--...--. 23
cCharacterideseribed =. .-<-- 2-2 -2sses= eee 492 Spring Creek district ..-...-.------ 240
gelatinization of. ----------..--.-.---------- 503 sae pHe (Chhenys) INRA oo. oSorsecooreccoseedaor 281
Hormmblende an: ..2ec= oe ase eee eee eee ee 493 on Bear Butte Creek) 22. -2-=--------=---- 272, 282
WO DANO Mb ae canes aecoessSoccoosased 492, 503 Box inlder\ Creeks teense. ewes nee 276
MOSUGO WI =/2/< 25 sissies sismaie spaniel Castlei@nreekeeeema= eae aaa eer 264
sanidin in MeadwoodiCreekses=.-a-as-e aes = 282
Piestocheilus culbertsoni ....-..-.---.-.<-.----.------ 423 Ima (Oraeelis Gaaseny cosocsesecee 267, 271, 291
MINN AM DTOSA Gaede seca 2 isn sai nope sees +) se etSsiniee nal 386 med Canon Creeks = eee. === === 236
Placenticeras placenta ......--.------2--c2-2--2 Breda ne 464 Speartish) Creelenece cece ssaeseeee ene 278
NRL Acerid EPOSitS eeu eee eels ease es as eee aN eeee 237, 242, 289 Whitewood Creek 282
‘Placers\obihe toothillsen-cs-=-ss 6 oases ee eens 289 | Protocardia shumardi.....-------- eAGnen qaneenbcoseaae 461
Plagioclase in mica-slate AG) | Teh, Whe, 1G AL ose aseesesoesocn cogs SooRseceodeennae 8
hornblende-gneiss .-...-..-------------- Cfo) || Teisphecteaorey ) jyderee hn oes Se nee kee eee sce seseseece 374
THY OMbG i a2 ssatee ese este telsctnacteials 487, 507 | Pseudomonotis (Eumicrotis) curta .-..-.- .----.------ 354
PACH Yt see ae ce sale sae ae einclnicisierei= a 490 orbiculataeess eee eae 356
PINS withenoTedbeeaer eee een asanes ceeem meee acios SP eleeseud op tear ROS ase eee later le 386
maantalli@ten- ane ssee eee eens e ai 309 RWI DNAS seacssassssoues osesse see SSecuan< 387
MoerbianylOts=.25se 2s esses ee eaecenee 24 | Pteria linguiformis : 384
Planorbis veturnus ... 461 (Oxytoma) mucronata .--......-.--------------- 357
Plants collected...-.-..--. 53L TPG ooo ssea sesso ceooceesaoss 357
IPenieehol, (bn yoy ems) CoC) ceoeey eaas Caan aosoresoersecacs 115, 117 M@DLASCAM Ale ss eis es eee eee a= 385
EJeuromyaenebrasCensiSe-2- 22 eee eae acess See 461 (Pseudopteria) fibrosa.-..--.--.-----.--.-----.- 386
ME WON Sas oe Meme asecessecee cat ca maesece 367 GMI NEWGS casscecsnonasossnennen 386, 387
SUNCOM PLessaie sete eae seer eee BGS) || IEANVENOEEHES = aon Sone sone oge econ ose soeseeoeeoedocs 455
Pleurotomaria contorta ......-.-.---.--------- =-- se) ADD Crass UM een eee ese oe eee ase 459
EROLY PGtal Ores anc sarees eeists oeetoa eee se ace tiem assesses 531 meekanum 457
osivions/andialtitudess=2=-sss= 0 -se5 soe sese eee = Bpal MOLUOM Tee seis Benes eee ee ccs nes 458
Potsdam and Carboniferous, separation of -....-..---. LOOM Pumice-stonessssese es ene e eee Ben ae ee rere 485
conglomerate a source of placer gold... ..--. 299 | Purple limestone, topography of ..--.----------------. 132
granite pebbles in .-...--.-. et TAD) |) TeX pul fey r00l (0 WENAIAUNG) = como aaseeasasccoseecEs Seeemnoneece 473
distribuuloniotee = eases Se Ses an iseeoae SBN eR yrltesse see: loc eda ocets sa ssiek eas nomisel cnici-leicie 61
formation, character of ..-.....-.--.--.---.-.- 84,86 | Pyrrhotite in hornblende-gneiss .--.-..-.. ------------ 479
LOSSIISIOFGUNOE= m2 soe =e ea ea eens eee eee 107 | Quartz, ferruginous
gold from the.--..------ eee cecee ceed ompeeten £4, 103 in rhyolite ....:--
history. SUMM al yO beer cr mere ae eee eee 221 Led oes ese Byam see bee ata wero eae tema es eee
metamorphism of ..-...---..--. 83, $5, 88, 103, 193, 200 OLS STANTON an = meen nea ease eee eisies as aeen er
Of Ne wi WoLkessi. nse. 2 22 esccegssssesee seeh 86 ihwannedlcrystal siofe sess ssee sees een nasa 500
the Black Hills, detailed description of. --. 98 AOS, <2 Se sae een See aera OL nat SES eee 53, 59
Rocky Mountains, quartzites of... .-.. SOR | eQuantz-trachytemeie= see qqcese eae cieaceen ese aasarer rose 483
Wind River Mountains ...... _.--..... SOR eQ@uaternanyadepositsipepee eset aa eeeease eaee ee ee erence 44
AVES COTS 110 ene eee eee 86 GIES): oacssanacsc0Sc0 sonSeascosescoesEeas 298
onvAmphibious) Creeks ae a- 7 eee eee LOOM RQ WantZtGren- = setae as- ace seace2eneeceatenceewcc 471
Bail ei Cree Wah aene eens <2 ease a eee ees ene 101 CamablessinyqUamt7O sere eeeee see eh eee =e 473
BUT WOOd! Oreck eer eee nee ee eater see ee 101 Gementinl soy as ceacm inci: eeciece seigesetiscewe se = 472
CastlesCrecker na ts oes eens eee 98, 262 crystallin ewer te sere eee ree cee Sao e es 478, 475
OGM One Ee oe case oeaasmosocecons Suskdar 101 cyanite in 472
iRedi Canon Creckeeassee eee =e eee aes 100 CAL Obes esa y= ee wives aais eee eee miscainisi='= 472, 474
Seni Crees oo2cee Sosansecenececossascass 99 granular egret See ors ane hee cescleseeee ewes 471
princi Creelee 2 = 2 aes eee Seer 102 hOLnplertd Grins sees eles sere ieee caer 472
Qiiambztesiofe ras 75720 ae seen e steers 88 TH AO SUL UCE MNO ere Op eo sete ieee 472
resting on uneven surface ..- .--...------.--- 102 TCA TI 6 BGR Ee RS Sees SEE Se ee emer: 471
sandstone, manner of formation .-.--..--..--- 104 MICTOLbES Dee Sea e see ee a tease eee 473, 475
metamorphism of.......- eerie 280, 285 OMWGNESChIStSh seat ee eee eae st eee eres 256
TOPOS AID bys Ofer == terse = eae ee ee ee tees 82 OLUNOC ASOhiNvs se me nes oe soca e me seine Saece 472, 473
the only representative of the Silurian uncon- DVLLU QUIN S Semester Sete a eens 473
formable on the Archean. -....-.-.--..--.-- 81 THOWRATEG! aE sb) Ga saseadenachesdessoenkees 472
Powell Maj adiaaWr, Clbeds-2 se.) s-eea-eeeeenecsmeres 28 secondary minerals in ---..-.-...---------. -- 472
Precipitation: See Rain-fall. : SC IISHOSOe ocr Eee ety Baa er ecre eae aaae 471

564 INDEX. .
Page. Page.
Quartzite, white mica in.---.--.-..-.--. .-.--s-------- 474 | Rhyolite; chalcedony im) ----5-0- 2-2 =n eee =e 522, 523
Quartzites, interbedded, origin of .........-----..----- 92 charactordescribedess=—ereesee ene aeeeesee 484
Offth es Dako baee= = sere eee eee er eee ee 176 PelSttiG ase cla sejeci-le oe ae sno eae eee 522
ofthesRotsd am lee eseeee een ee eee eer 89 Hnidsinclusionsin}t=see eee sere eee eee 487
Radi ated Zeolite yes eet err setae ae ee eter 515 STADLLICY. 22 2b See cee nee seer meee 494
Rain-fallyemounulO feee sere seer eee eee eee 308 groundmass (0 fsse. =e ees eeeeee eee eee 484, 488
distribwtion\0 fesse eee eee eer eee 305 PLOUpSOLi seo swee eee ae ee eee eee eee a 527
TORAH) Otsoso55- sosoaseegaadcessocIamssco9 306 homiblendenneeeee esterase seen eee ee 495, 496
of the northern plains -....--...----------=-=- 309 hyaline we ess 4. see oc see aoe eee eee 485
Rapidi@reeks[64]) tose eesees-cee eee r eee eee 479 MaAcnetivenines segs Ae eee See ee eee 488
(G5) a6] A[G9] e528 cer sees nek eee 480 Opal tase oes oe a a es ea 522
[73] 471, 473 plagioclaseyn@es-eree-n eck neee eee eee 487, 507
[74] 481 quartz ini... 28 sseacm es oee ose eee 486
202) j [208 inset Geen eae ean Bee 475 ganidindneee. Gen ackh eee Bae es ee 487, 506
prospecting on .-.--..--:.----.-.--- 267, 271, 291 silica, percentage Of,--- 2-252. c2=-222-4-=-ee" 485
WSHPKCES OM) 256552 ycbsnseasuen danesedeasse 291 trachyte and phonolite .-.. -. :.-.--.-..--.- 483
topography of ..-.......----- dasa Sasties 269 varieties of .....2.--.- SU tose nas SSS REE 486
WEA MVD Olen s 525 -s4eessqus s]sdeacyebaoss 268) Rhyolitie| breccias === sea =ee= nee alee 516
RawhidewButter ssa see se ee os eer eee eee 26 | Ricketts, Dr. P. de P., analysis of greensands -.---..--. 96
Raynolds, General W. F., exploration by .----.-------- 6, 12 Cited te tsace ce hee ee 133, 184, 275
RediBediclays sen aceenses= eee ese ean ane 133 oldtassays\pye-seeeeeeeeeeere 294
Red Beds, absence of fossils in the ---.-.-------------- 188 | Rocks of the Black Hills, tabulated ...........-..---- 40
EX) O)8 cs snob6 see ckac socoseosernenessseecsouE 150 || Rosevquarta --f5255 2 hbase se oee sec teeeeeameseaee 70
and Carboniferous, separation of - -...- 11ORS S13 WR ostellaniaitusitormis taper eee eee re eee eer ee eee eeeee 421
ipneous peaks) sees. a-- ee enn aaee 145, 197, 198 Nebrascensis 2.24224 she ste eee eres 429
Jura, separation of....--..------------ 131,153 | Routes to and from Black Hills, geology of ...--.-.--. — 22
COON OF WN) ssc scone sessosaqnodecopsosess 138.) ‘Sandstonevecieerciscec sc wasseine sacs ane Meme rere 472, 474
exposures in detail: -.2-- 22-22. --22=------5 189, 155 Cementaniss) 522,252 eae gn ee eae eee 474
in Belle Fourche Valley.------------------- 147 elauconiticeee sen sts-e see eee ese ne eeeeeee 475
mear Campin yeas eee ene ee eee ee eeaeees TOON Sanidinwapa ited nies seer esse eeee eee a eee ea aeee 512
ofthe Black Halls - 2222-2 eee 42 Ibroken\crystals!ofeess== sees asses eee eee 490, 512
Rocky Alountains: ---2--------------- 148 Characteristi¢ies-sessee on ee ane eee eeee 509
on Amphibious Creek .-.--.---------------- 141 glasstinclusion synWes ess se esas een nee 518
Beaver Creek 139 inclusionstine-cs ss: os= eee sen Ee eee eee Beers 489
Tem AGl CHEV 555 ced cope aaoseusasesss 143 insphonolitet=2. ese ce feos ate ea eee eee eee 492
Red Cation Creek...-- J sagcnreasosereenes 140 rhyolite 487, 506
Red! Wiater\Creeke: ie. oeeane aeeitee - 145 trachytolssscesencee ten ce cee eee eee ee 489
RediCanoniCreels\ [207 jee sees er eee eee 472, 474 MicroliteswD) += -o2 ese eee es see ee ees 507
prospectinpionle a= s2---—-- =e -- 236 wintery stalsioleere. eases eee eee tee eee 490
Redavolleyegecseees erm ese eee eee ee 32, 42, 135, 142, 204 ZONCISLLUCLUTEIO Le Eee eee eer ee ere eer 509, 511, 512
DROS, Usd! soodacndeseanancdaconooesoes cooocasceHaSsac 554 | Sanidin-oligoclase-trachyte.--....-.....----------- 483, 492, 507
Reporippreliminanyase-ee sees a-ha eee eee eee eee 4521: ||| Sanidin-trachyites senses seceeces see ee ee cscs ee eee 483
Reservation, Sioux 4 pb RoseesacanereccuesaaeaNarese Arc 496
tesources, mineral 225 PE) Renee tein ane Seueacisca atocob aos 497
other thansmineraluss. sso see -ee eee sear 311 | [E24 ic Sorte ee 8 ee A ese ete 498
Rhynchonella/enathophoraieqss92 42s eee eee eee 347 | [40] Se ee. Seis eet sae ees 505
HINT OUIG). Sesesa age ssneseassoncdossqdee ve 347 Ov) oeNeceretaaauaeseransnonscdusodes 509
(Rly oliteteescc Scene cree eee eae 192, 194, 195, 203 (fatal fa lish Hae Genrer e ea carodSaciae 510
(101 494 FAST ioc ees eee een ee aera ea 512
(109] 495 513
[120] 496 515
[125] 499 517
127] 500 518
[131 501 520
[135] 502 521
[137] 503 523
(141, 506 376
{147 508) | Scaphites|conradi\eesser see eeer eee ee eee eta 464
(WER |s-sscescesdesas spduccoonescoedsoacanasode 511 IPR EDR EINE) 64a osedeeooococsossestoscossoanE 464
[166] 514 TOGO WE ace scbosaesS seco soSsogasasde0s oosue= 441
(HGP) sanossdcoponSososcessese sseswacoosagasan 523 var. brevis 443
(PED) penoscecccccumnnpsdansesoccemsavccuedaag 524 plenus 444
banded groundmass of.....-...-------------- 484 quadrangularis -....-.--..----.---- 443
WOU IN cone sasocessesosceoccoscES soonegesse 488 pulcherrimus=-scee seo eee === ease 464

INDEX. 565
Page.
Scaphiteswarrent -- 2 -- 2-5. 2. sac oe ne ne oe AAAI SLALOS Sataaarrd Sak ace oe tea aed sation doeweeedeacteced
var. wyomingensis 446 the, of the Black Hills
WYODMNPENSIS so = 22-22 == - = emeiee = 446 strike and dip of -----..---.-----------.---.
Schist included in granite. --..---...--..------------- 72, 229 fopopraphiyiOtese ass sese ese <a =
Schists, composition and structure of.--.-.------------- 2723 |) SO REET GIES) ceo Ac coobesteoso scar cSere SEE eSeO Scleriaane
of the Black Hills ....--.-----.--.----------51, 56, 64 On RAT) 6 o-5-se Soc dsossocageesosseec5
Spring Creek district ----------- ---- 241 | Smet, Father de ree
strike and dip of the. ---.-------. ------------ Do) ||Snow-tall amount) Of sae. --ac= =e ae ==
topography of the .-...--.--- .-------------- TH) || SOS) srasctcssccoassonetdsessseccconsnacenesebaceasoaoS
Scolithus lineages sss ssassen reas oe ee oe 88, 104, 200, 334 | Solarium flexistrialum ........-.-.----.---- ----------
Section, descriptive, Carboniferous and Potsdam, on SO ETOCEHAS ~ - socreestcucdonosasace csopeshbosasessss056
Site Creel ate att te San aig Siac Solidula (Actzonina?) subelliptica.-.--..----..---.--- 463
in valley of Beaver Creek South Fork of the Cheyenne, cafion of -........-...--- 177
on Amphibious Creek. - ---.- Spearfish Creek, prospecting on 278
Box Elder Creek. ---..---- topography of 277
Castle Creek...-..---- ---- Spheriola moreauensis ....-..------------------------- 415
lower Rapid Creek..--.....--.--.---------------- OUNOPEUES 25. cc Sececesasccceccontecusce=ese0 415
Minne Katta Creel: ----..------------------.----- TRANS VOLSA isis -tao ears gcse aec ees 415
Speamtfishi@reekes esses = == ee ae eee WERERS IE MEY oc eneoeoccconenbaesacss eossbece 462
Cretaceous and Tertiary at mouth of Rapid Creek .. 185 | Spherulite .....-..-..-------------------------- 483
at forks of the Cheyenne ----.--.----.--- WBESESpherulites! seasons learn atiatnercie - 485, 499
near Bear Lodge ----..------------------ 180 | Spring Creek, volume of .... Sera faje Ss 254
oneHirenchueree kee ae eee 181 | Spring Creek district, prospecting in -.-...-- 240
north bend of Belle Fourche ... ---- 180, 183 topography Ofer eee ees 238
Red Cation Creek .------.-------- --- 182 | Spring Creek mining district --...........------------ 238
South Fork of Cheyenne -..- .--..--- SOME Spine sigmnin Crall ee eee ee lesan oe ee eee ee 295
general, of Black Hills -~--22--------2------=- ------ 40 temperature Of. 2<1.ce=2ee occ aes eee ene = se 303, 312
Carboniferous in Black Hills. -..-------- LOS me Standeofebar eee aaestes sae soa eee eee se 251
Cretaceous by Meek and Hayden -.------ TPAL Ey rit Raa (he aR Ree SAE Grier as Saat SBE SHE e PSA AIEe 54, 260
Red Beds in Black Hills .-.-------------- 131 | Stevenson, Dr. J. J., cited 75, 149
Tertiary by Meek and Hayden ------.--- SMES tockad ew theweys aa aco sear eee ene eae eeee 17
Jura about Bear Butte.----. -..-.------------------ 196 Hrench! Creel [lll =-2 sees eee neee 477
and Cretaceous on Amphibious Creek --..---- 158 [IS] cee eas, ede 477
in Redwater Valley: -.-.-../...--/2.-.--.- 161, 162, 163 [tence otee rer eae 3525 472
paGHRP TeYeONP IDO a oaneae Seeeeaoeenans seas oeeoe 165 | aE re ae oe ee 478
Camp Jenney -.---.-------------------- 155,156 Stock-raising, future importance of 317
Spearfish Creek ----- Faceneas sesocseeeae: GY, IL |! Stignmss, THEE ~~ 5 saoseneesoscencosscecnce 310
Sun Dance Hills--------.---.--------..--- 14 aleS treams snolumeyo fe se= tea ae eee eee 312
on Red Cafion Creek -..---...---.-.----------- 157 | Structure and age of the Black Hills ............... -- 203
Potsdam on Box Plder'Creek=--=----2-2- ---4---.2--- 91 AUS Kote Ment eee Oe ieee a ee ee a 513
lowerHrench\Creek:--- --2-= =2---.-=-- Sale SunkeDanceskillgrrere: ae - set Noe se ee kee 145, 197
Rapid Creek.-....-. --..--.----- 85,94 | Superimposed drainage 216
Spring Creek..--- wee e ec eee eres eee =--- | 98)! \Surenla contorta..--------:---«- poise.) COP)
Red Beds and Jura near Bear Lodge .----- --- 148) 5g RNGy Clon eniaini oid ssa ee nes pce ety
on Amphibious Creek ----....-- 142 | Synopsis of the rocks of the Black Hills......-...-..-- 40
Red Canon Creek TZ0R eiancrediaiequilateralisees sess = essa eee ae ee 460
near Rapid Creek _-------2-2.22-- Soc beane 142 | Dil pos ame eee ek oe eh enone ee Ue. 370
Tertiary and Cretaceous near Old Woman Butte.... 30 | Coubulitorunis 370
oni Oldy Woman vWorks sae epoe = esac ney 31 Qanormath wee ee es 368
SOL P OIG O re oe eens eeicise oe eae ne ee 482 DOSti came eaee 371
Serpula SD eee 461 warrenana 372
Sheridan, General P: H., cited ------.--: -J22---------- iMleMocturaoccidentalistete soe sy 463
Shumard; Dr on oe Been een anne OelteMellinaroccidentalise=se see... a2 seen a aeeeee ones 409
wideriteion Beaver Creeks: 2225 soe) eae sysesssecn = e255. 295 SCiCUl ae ee a ete nn et. |S 463
Silica determinations +2 se eee ee eee ae 526 (Beronweai?)scitula, 2-55-20. - 202-25 se cee cee 463
percentage of rhyolite .--..---.--.......-....... Seoul Terepratilaihelenasee.. oo eee ee 462
trachyte.......---.--.--------.--- 489 | Terraces on Rapid Creek 291
Silurian formation headwaters of Niobrara...-.....--- 285i Rornvee cd pes eer eet neice eee mL 103, 193
Silurian. See Potsdam. e TIO ere ee ers wen a ee UY 494
Simpson, Col. J. H., exploration by 13 (PUIG Scene chester ens. ae eee nae 472
DLIPSNOLES iN Oy PSWM ono ose Eee ae ee -- 146 (aU |e a re eee eget ee, ie, 524
Sinking of creeks. -..--..-.------ 1.2.22 +.---+-++-+---- 123 barometric observations on 549
PLO UKOR POCA OM ea set nya Hos ose ne as SAS 10 height of 540
BEB CEN U10 Thee ae 4 Eidgeeast of [i13]\c---.s25- eee ae 496

566 INDEX.
Page. Page.
Terry Peaks rock ofisasscae eens cose ae sees Peo lee Erapezinmisnibequalis= see es = =e a eee 365
southeast of [120] 496 (Rachymya)troncatas=s----s22--s2554---—- 365
ZB} | spsoccesouesusscossosasce 497 | Trias: See Red Beds.
MeN RoosescceRoscece tostecda 4985) Pridymitennitrachyteysss-s-- 2s ose aeeeeeee econ ere eee 491
[RSM ccoscasese ososstesso0cs 0015) |(eErigoniaicontadiee= sen eee eee ee Ree see eee eee 460
(PAD Besescstocsedan Saadeseseo £74") Eritonitusus)? tenuilineatuses ss) eee = aaa 463
MertianydossilSeeererer ees =e eee eee ee eee eee eee (GAD |) ANTOA NOC OSG S65 Adoosdedascngason Sa iconoscece 432
5) JOG WING 6 ese e one a so scenes oc sccsesuede Sly PturrlitesmebLascensisiies=— eee eee eee ee eee ee eee 451
history SUM any fesse e eee eee 2220) | MAL Tris(COntOrta seer eee ae eee eee Eee 422
of the Great Plains ....-. -..--.----------- 24,187 | Twin lamellations of plagioclase ---..--..--.---------- 479
, White River and Cretaceous, separation of-. 185 | Unconformity at base of White River group --.---.--- 24, 27
, conglomerate at base of. -..---- 188 | between slates and schists ..----------- 62, 263
of the Black Hills. --.-.-..-.--- 44 of Carboniferous on Mesozoic ---------- 130
on lower Rapid Creek --..--.--- 35 durajand Red'Beds = 222----2--22-5 149
White River ....----.-- 241, 36, 186 Potsdam and Archean. --...-.------ 81
, unconformity at base of...-.--- 35 Red Beds an | Carboniferous ---..--- 149
Theca gregaria ....--..-.- AGO) Unio muealise: sete oo acer neste aoe ne eee teary 460
Thetis circularis ANT) |) Uplift waretor the) s5- setae a nee see eee 214
Thin sections, examination of. 494 | Valvata ? scabrida ..........--.-- 461
Thonglimmerschiefer -.--.-----.----------------- ---- 476)" Vianikoraambigua o=s-224225e 4 430
Mhraciaiarcuatase ss sees sess eee ace eae eee eee 461 | Varieties of rhyolite 486
(AEVOUDS < ca os casesccdasaDoaacanasascqadbeccdacs COD |) NGOS, RGAE 25555 poaaconcansdecacdacseag sancHe 58, 59
subgracilis 419 interlaminateds! <2). cises-e-o Seeesia ee ase eeeeeee 228
Thunder StonMsS)sseeeee ee een eee eae ae 310 Quarta: eens. Aes rate ose eee 58, 59
Mim bereecr-nas Cee eee eee eee eee 321 | Veniella humilis 414
burning of..--...-.--------------------------- 322 | Venilia humilis 414
Titanite in hornblende-gneiss ---..--.----------------- ATOM Vents gi CIrCULAT So cate eee seen cere ee See Se 417
trachyte...------+-----.2------------------ 4915 iVeiviparus| eile eee eee ene Renee eae aeeeeeie 461
Topography of Box Elder and Elk Creeks. -.-----.----- 272 | Volcanic: See Igneous.
C@astle/@reeks-essaciss-- eee ee ees 261, 263 | Volsella (Modiola) formosa........ -.--.-------------- 361
French Creek district .---....-.------ 226 pertenuisy. soe ce ener Seen ee 362
Rapid Creek ...-.-.-----------------— 269 | Warren, General G. K., exploration by.-----.--.------ 10
Spearfish and Bear Butte Creeks. ----- Ziel aWiarrent beaks esse eenee eae eee eee eee
Spring Creek district .--. ---..------- 238 BUA eeseesieS Sacecenaseseacqeeaccbou:
the Bear Lodge country ......--------- 283 [210] eceeas eo veetace so soa- eke Se cee oe
Black Hills, origin of ..--...----- 210 Goldidedges|il87i esses esac meee
granite 227 [092] ease et eee eres
schists 55 Morbhvosy [74s se eeeaee eee eee eee
Whitewood Creek --- 280 southwest of [173], [175]
Tourmaline pees seen) eee eee eee eee eee ee Eee ee 70 Structure) Obese =a eae eae eee ae
AU EON) cosnaooes eaasoseeqeonegsess 196, 197, 199, 201, 203, 483 RIG ster sé aescnéacee 7 Sonzescuseksooas
GUS) SecocmcceseonScndretcsedascarccocastoscse 518 HON OF (DU) scons asec sco oaesconssosssac
ANSOULCOLOLHS Ol deere eects eee eee 282,289 | Water-shed of the Black Hills ......-...--------------
EW PUNKS) TN, joqasebnosocboesesossescoseasaos< 491,519 | Water supply----.------ 2... cee n-ne ne eae a=
BM Veate coos ssedoaseocoons cocucd cenacsSace sc A890) wWiebsteriaieretacemer eae ero r re aera enna renee
Dio titeuns sos eA oes ACER eee 490 | White River conglomerate, composition of. ----------- 290
Calcitetinem sr= 2c esse ose seen ee ner eee nee 519 mnica in quartzite 474
Character: describede oases e ee eeeeeee eee eeee 488 Whitewood Creek [213] ...---.---..------+------------ 523
date of eruption SARS Snes SE AOR OC eee Ics 281, 289 5 topography OF. 2 oon no 22a 280
Wihiskeyi@reekeer a= -eer een eee eer eee ee eae eee 259
groundmassOl seme -emc mee ieee eae 491 : / :
ip MER Pon a PaO RONS “ce 527 White River group: See Tertiary. :
La cee White River group from Cheyenne to Fort Laramie.- 24
hornblend chinese set ee sees = eee eee 490, 519 Somahide Button ele 27
manner of: occurrence.-:----.----------~---- 281 Gn OGL WONTEMA INGA oosccs soocooee 30
on Rapid Creek .....-.----------------+----- 268 0 owihitheld’ ProtsRob «ee ine erase one eas tee eee 3
pebbles in White River conglomerate. ...--- 220 Wiitney, Prof. D., cited 92. 5.202222 scesee se seese 86
plagioclase in ......-.-----+---+++++++++-+--- 490 | Winchell, Prof. N. H., cited.....-.-.----.----------- 114, 132
relations of, compared with those of granite. 28 exploration by.-------:-------- 15
Samidinwineeene see ree sce errs acer 489) Violdialevansiac costs Ne ce oe ce Ree eee ere 409
Silicaspercentage Ofsa-- 244-22 -n- << 2-=- 488 subnasuta 462
TLtANL LOH Dee eee eee eee aeenie ce sate tetera 491 7 ON tri COS Ae eee eRe eee aecieem 462
tridiyimitepin essere beer amnion OM Ah ieasaocbes Aes SeesepabcHarbecebooosacmpancosaosaee 514
Mrachy tic pitChs ton ewes eerie seer eee 483 TRY REP Be on ose eg SRRRbA sooaod beesareseboscseda 515
Trapezium bellefourchensis. -------------------------- 364 | Zone structure of sanidin ......------------------ 509, 511, 512
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