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LIBRARY

OF
JOSEPH PAXSON IDDINGS
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PRESENTED
TOTEE
NATIONAL MUSEUM
MCMXX

UNIVERSITY OF CALIFORNIA PUBLICATIONS

BULLETIN OF THE DEPARTMENT OF GEOLOGY

ANDREW C. LAWSON

EDITOR

VOLUME 4

WITH 51 PLATES

Jnsonian Instjz, *s

(2260 44%\

BERKELEY
THE UNIVERSITY PRESS

1904-1906

bo

- 10,

oj; dae,

. 13.

. 14.

15.

CONTENTS.

PAGE

The Geology of the Upper Region of the Main Walker River,
INievadarmibiye Wit) Wh Smith see cece re cee ccee oc sc- ce eeee cee eeeereeereeeee

. A Primitive Ichthyosaurian Limb from the Middle Triassic of

INIGNENCEI, Lowy) Iovate (Cry NU Keva wiehenl Seek ay yee ear eee

A Geological Section of the Coast Ranges North of the Bay of

man Hrancisco, by Vance ©: Osmomt .....2..2..2
Areas of the California Neocene, by Vance C. Osmont —..............

Contribution to the Palaeontology of the Martinez Group, by
Charles PW) W Cave re a. -5 cece eee iee eee Ae geen eee een ee ee

. New or Imperfectly Known Rodents and Ungulates from the

John Day Series, by William J. Sinclair —.........20..-200..2.22..------
New Mammalia from the Quaternary Caves of California, by
AWNGUU DE sat BAS Teel ei See ee ee ut Brn ror aan ese
Preptoceras, a New Ungulate from the Samwel Cave, California,
oy? Wustace. las WMurlon ey 2 se eet eee cescocs sree eee eee ene ene ees
A New Sabre-tooth from California, by John C. Merriam —..........
The Structure and Genesis of the Comstock Lode, by John A.
S96 ele a Pe eS ew RP ee ee OE

The Differential Thermal Conductivities of Certain Schists, by
Parl th elles -See ses eee cece, ovens carer SNe RENE, (2 be A cctces. yeeros

2. Sketch of the Geology of Mineral King, California, by A. Knopf
ours Fes el ena, a. cess ee cc vrcnge ste seve oss eee te Bioee 2

Cold Water Belt along the West Coast of the United States, by
SECU THPTS SS ss DELIV iyi ce create esos oe ee oc eee ne we gee ene cee

The Copper Deposits of the Robinson Mining District, Nevada,

Jepreewatanolntehyis MO TUE ISON ete reeene eeceereyee see ee Mr eee ry y

I. Contribution to the Classification of the Amphiboles. II. On
Some Glaucophane Schists, Syenites, etc., by G. Murgoci

39
89

PAGE
No. 16. The Geomorphic Features of the Middle Kern, by Andrew C.

UAWSOD (hz. 208. scecledy ests ee 39

No. 17. Notes on the Foothill Copper Belt of the Sierra Nevada, by A.

Kopf 48. ce deste ee 411
No. 18. An Alteration of Coast Range Serpentine, by A. Knopf .............. 425

No. 19. The Geomorphogeny of the Tehachapi Valley System, by An-
drew C.. iawson. <..22.:-.ie ioe 431
06 116 >. quan ee ERE oa nT eretemocte 463

MAPS.

Geological Map of the Upper Region of the Main Walker .......................- 4
Whirlwind. Mountain 2: -..c.-12--te--scte ee 8
Index Map of the Coast Ranges North of the Bay of San Francisco ........ 43
Geological Map of the Mineral King District -......0020-0........... Sc eeee ee Pl. 30

Geological Map of the Tehachapi Valley System ..............2..2...2-.22..2.22---- Pl. 42

UNIVERSITY OF CALIFORNIA PUBLICATIONS
BULLETIN OF THE DEPARTMENT OF

GEOLOGY

Vol. 4, No. t, pp. 1-32, Pls. 1-4 ANDREW C. LAWSON, Editor

THE GEOLOGY OF THE UPPER REGION

OF THE

MAIN WALKER RIVER, NEVADA.

BY

Dwicur T. SMrrH.

CONTENTS.

Page
HM raN CRs GLAAD OAM ease pece ler a Shes ebae uieastt tees age hob cor) cide ged cette ancy ae anailopiout re daytscawenes © 2
RhysicaluMeatures of theR@GiOM . c.g sce science os soa dine ap ees 3
Dishralyuatrvom) Ot WORMAGVONS 2. cae terse eee ee aieisserote sole este aise alee ae 4
MIMOMAL NS RECO C Reig en u cin «ile bass Gale aeciiele oi Gi wessgln ake ate Qeads ames 2
SUM OPAUS CG RUG O 5 41. cic cteacaas a's See assess Haven goes eaodin cae eins 4
WER bIT AMIRI SCS Sees ceecteson ce 2 degre dy tayo ules weaned ee teeta 7
AWalnsl cya Gl fer MOUNT ARI: Sos oeecues cesttsthcncte, cies ereisns, me talae eee aya ele eeeconone 8
he mVinid- valley UB Ubtes cies. nee ar eeuecon ke Oe eae ad bane maud die ale queleut te 9
Wan COmROMMUUT OS Bia ec. ast acct osc8 = ce 5, xP cetetiev ans Fars abe: ahh gue frat due opie seubiaais ough enaeh eens g
ithe BedrockiGomplex and the Dertiary 2.2.............-s-+-ee0e 9
hemherwany andethe Quaternary 2.2... ser aeee see ce aoa vee ceanes 11
Relative Age and Unconformity of Igneous Rocks ............... 12
SS RISETRNE AGC) UA em ae Nm eae 12
Meas edo cks' Complex: seus. ghcs ch aesse-e sete ays apette one aries ay aee cel augnpueineesgelaee il
AMO CGAY. Ges eredeigcehe sect ea 3g Mis ysuedeouer dns grees die esatoayie aleeeaecinds Gln eee ile)
Relief of pre-Tertiary and Tertiary Surfaces as compared with the
RPeSOMCeMVOlVO Re ipa sg. see ceaesetls ctsere ae ancachs se Shcueke Go taehy cl al aeegeee eee age nees 15
Explorations beyond the Region mapped .............. 0.000.000 00 16
Description ‘of the Doneous Rocks’ ..... 28... eee e eee een se see 17
MUS Gena Mb CAMVOCKS aPeegas jaupiere cssvsyikl Son: acres cytencte ea eat faye cowie cease meet seas NG
MH EeV ROTM Ya Chace sctesrycots ohones Gratye.setwly sare sadam ait cae Beier ees 23
Mhes Eiornblendem Amdesube! Geese cu. oles ese sueseaeets ete. se eee eee 23
Pe wWaten AmCeSibese rece acpes:, us margere-o ecescnets Shee hse Oke 2. Se (aed mae Ree 25
PIU yO tw Frcee cteuceageaccs eGsuc severe saunas eRS MUNA Sieue oeertiachsesc gate ae eeoee 25
peg Basalt, Ric .uttececatasaeq-er score ieleuty joes) acest AR eased ha as hire 26
MINOVISCHUSCS! aires Sh lae cleans cake tiene woh sede neers Reece Se. ey doaes ! nedeecne awe 28
Hequencerot Temeous: MOCKS! 22 oye cece eer ee re ones cee ee oe 28
OCPD STO SIL Sip cr satocssacgeecneyse selene fests eiepsaints oped Gia) susie mie gon codes eee etna 28
Greolo cyl DCW OSICS i aceees os rewatehs nade pus eet heist aunts sea suc.e sc -Moueee ees 28
(aves. 1DYeyoxofssSy Maly Jee nanKOMENE 66a Gea cae ec ceed oooh we Ree gan as day 29

Adin Oyooubinreinyees one INENnhYe: (Clyjleie Ae oo ag 5 unos eh eos h one cos] 32

2 University of California Publications. [ GEOLOGY

INTRODUCTION.

This region, which the writer has termed the Upper Region
of the Main Walker, is situated between Jatitudes 39° 10’ and
38° 58’ 48”7, and longitudes 119° and 119° 22’ W., in the western
part of the Great Basin. It is thirty miles due east of Lake
Tahoe, and twenty miles southeast in a direct ne from the
Comstock Lode of the famous Washoe District. It is seventy
miles northwest of the Esmeralda Formation. To reach it one
may go by railroad from Reno, Nevada, to Wabuska, a dinner
station on the C. C. railroad, the distance from Reno being
seventy-elght miles.

The earliest notice that this region received was by Fremont
while on one of his explorations in search of a route to the
Pacific Coast, and in later times it has been sought by the stock-
man, ruralist and miner. The river received its name from the
ereat explorer who gave it in honor of Joseph Walker, a noted
scout and guide; and while on the ridge through which the West
Walker flows for the purpose of joining its confluent, the East
Walker, he ventured an opinion concerning the character of
the rocks composing the ridge.

The region has not, however, received special attention at
the hands of any geologist. The mention it has received has been
mainly cursory or in a subsidiary connection; and recently’ as
incidental to a reconnaissance of Nevada and part of California
south of the fortieth parallel of latitude.

The region being somewhat removed from other fields that
have been studied, its investigation has been undertaken in the
hope of contributing some independent observations to the geo-
logical history of the Great Basin, of which it forms a small part.

The rock series of the Upper Main Walker fall naturally into
two major divisions corresponding to the Bedrock Complex and
Superjacent Series of the Sierra Nevada.

The Bedrock Series comprises shales and limestones in a
closely folded condition invaded by large intrusive masses of
granite and granite porphyry and by dykes of quartz-porphyry
and porphyrite. The Superjacent Series, reposing in uncon-

Spurr, U.S8.G.S. Bull. 208.

Vout. 4] Smith.—Upper Region of Main Walker River. 3

formity upon the worn surface of the Bedrock Complex, com-
prises Tertiary sandstones and conglomerates together with an
earlier and a later andesite, andesitie tuff and breecia, rhyolite
and basalt. These Tertiary rocks have a prevailingly westward
dip and are repeatedly monoclinal. Still later in age, lying hori-
zontally upon these are beds which are questionably Quaternary
or late Tertiary, and also formations of undoubtedly Quaternary
age. ‘The ridges bound areas that are rudely rectangular. Muin-

eral veins are numerous, and several of these possess value.

PIYSICAL FEATURES OF THE REGION.

The immediate area mapped is shown on the two aecompany-
ine plates, 1 and 2. The second is a continuation of the first
at the southeast corner. and contains one ridge, Whirlwind
Mountain. Pl. 1 contains three, two of. which entirely cross
the area; the other les along the western border part way. Their
trend is northerly and southerly, and between each are valleys
having long alluvial slopes to the west; much shorter slopes come
down to meet these slopes from the west, in which event they
meet along a line, but in some instances they meet on a margin
of a plain or playa. Where the meeting is along a line it may
be readily recognized as an axis of drainage. These two fea-
tures, the line and plain, may meet, and if the latter has a suffi-
ciently low outlet the drainage line is continued toward the out-
let. As the western slope of the alluvium is much the longer,
so also is the slope above the alluvium toward the crest of the
more or less bare rock. The eastern slope is much the steeper
as well as the shorter.

The westernmost or first ridge is separated from the second!
by a broad canon which is rather too wide to be termed a canon
and may be designated a canon-valley, and is known as Churchill
Canon. The northward extension of this valley is a cafon from
the west. his canon disconnects the first ridge at its northern
end from a plateau or ‘‘benchland,’’ a portion of which comes

*Mr. C. H. Asbury of the Carson Indian School was very kind in endeay-
oring to obtain the Indian name of this ridge. Through Mr. R. C. Dyer,
an interpreter, he ascertained that its name was Sing-ats’-e.

4 University of California Publications. [GroLocy

on the map Pl. 1 in the northeast corner. It also exposes
several of the formations.

The second and third ridges are separated by a broad valley
known as Mason Valley, of about ten miles width, and through
it the river finds its course. Two streams, the East and West
Walker, unite about two miles south of the country mapped in
Pl. 1 in this same valley, and form the main river.

DISTRIBUTION OF FORMATIONS.

The First Ridge.—The ‘‘ Benchland”’ in the northwest corner
of the map is made up for the most part of andesite tuff and
breecia, and is capped by a nearly level lying later andesite. The
thickness of the eap is not uniformly the same, but the sections
that were closely inspected were less than twenty feet. The
andesite breccia in the tuff underlying the cap is entirely dif-
ferent from the eap, hornblende being a striking constituent.
The tuff possesses occasionally some stratification. The erosion
of the canon has not eut entirely through the tuff, and an esti-
mate of its thickness was not made. A few occasional springs
make their appearance along a ‘‘wash’’ which is in the bottom
of the canon, and these are presumably where bedrock comes
near the surface. Near one of these a knob of granite may be
seen. At the northern end of this first ridge there are a few
small and irregular areas of shale and limestone. These oceur
in a mass which appears to be one of the earliest intrusives. It
is a porphyrite which will be deseribed later. Rhyolite presents
itself throughout the remainder of the ridge, with the hornblende
andesite protruding through it in a few places, and also one
small knob of granite near the southern end. The granite, shale,
limestone and porphyrite is a basement complex corresponding
to the Bedrock Series of the Sierra Nevada. The rhyolite, ande-
site and tuff may be regarded as members of a series that in a
similar manner correspond to the Superjacent Series of that
region. The remaining territory promises for the two major
divisions, the members already mentioned and others additional.
A couple of small exposures of iron-ore are at the base of the
ridge; one near the southern end and the other with one of the
limestone areas near the northern end.

ma
oy
:

{ik

ree
val

Rn

{

GEOLOGICAL M.
BULL. DEPT. GEOL. UNIV. CALIF. UPPER REGION OF THE

KY

AWKALI FLAT
A 4553

Vertical Scale of Secth|
Base-level of Sections 4

Portion of Wabuska and
Wellington Quadrangles
From Topography of U.S.G.S.

Hee RE
N WALKER

WALES in dmlenealé

the horlzontal
pbove mean tide

Geology by D. T. Smith

LEGEND

Alluvium

SUPERJACENT SERIES

Stb

Andesite Tuff
and Breccia

[si

la

Later Andesite

Sedimentaries

R yolite
and Rhyolite Tuff

Sea

Earlier Andesite

BEDROCK COMPLEX

a=

Porphyrite

Bop
Granite Porphyry
Bg

Granite

Schist

Shale

Limestone

Dike

Zz
Ze
Z

ome

Schisted Dike

lron Ore

NWS
Ore Deposits

ic}
Numbers de-
scribed in text

havnizsal

a1ozosay

Foc Mi

IF THE
patie a OF THIN WALKER VOL. 4, PL. 1.

Ca

EPT. GEOL. UNIV. CALIF.
Saye

BULL. D

LEGEND

SS
Alluvium

SUPERJACENT SERIES

Sto

Andesite Tuff
and Breccia

Sla

Later Andesite

=
Sedimentaries

: olite
and Rhyolite Tuff
Sea
Earlier Andesite

BEDROCK COMPLEX

Porphyrite

Bop
Granite Porphyry

Limestone

Dike
Schisted Dike

lron Ore

nw
Ore Deposits
(c}

Numbers de-
scribed in text

horizontal
Vertical Seale mean tide

Base-level of : am.

Geology by D. T. Smith

Portion of Wabuska and
Wellington Quadrangles
From Topography of U.S.G.S,

haviqsay

ajozosay

Vou. 4] Smith—Upper Region of Main Walker River. 5

Sing-ats’-e Ridge.—This ridge at the northern end, within
the limits of the map Pl. 1, is made up of andesite and andesite
tuff and breecia, similarly to the first ridge. The cap of later
andesite, however, in this case is broken up, and along with it
there is considerable of the breccia which is in the tuff; the
breecia, in fact, forms nearly half of the cap. This is undoubt-
edly due to the tuff being easily eroded and earried away from
around the blocks, thus leaving them residual. The only con-
tact between the rhyolite and the tuff was found here, and its
character is such that the relation of the rhyolite to the tuff
could not be made out satisfactorily. The tuff is fragile, and a
sharp contact was not to be expected. It shows no planes of
slipping, and no pieces of the rhyolite were found in the tuff to
indicate that there had been any faulting. The rhyolite appears
from beneath the tuff, and in this connection the composition of
the tuff is of some importance. The apparent absence of all
other rock fragments from the tuff except the hornblende ande-
site 1s worthy of note; and perhaps of equal importance is the
composition of the tuff aside from the hornblende andesite bree-
cia it contains. There was found in it no quartz, but feldspar
and a little dark-colored ferro-magnesian mineral were observed.
Some good cleavage flakes of the feldspar gave extinction angles
of andesite and labradorite, some flakes showing an optic axis
nearly normal. This indicates the tuff to be andesitic. The
material of the tuff is fine and splintery. The absence of all
other rocks just mentioned from the tuff will be considered in
another connection when the structure is discussed. The rhyo-
lite makes its appearance along this second ridge in considerable
foree, and two dykes of rhyolite about four miles apart are quite
marked; and along with one there occurs a dyke of the horn-
blende andesite. The two seem to mark the same line of frac-
ture. West of this dyke there is an area of andesite and tuff,
the latter showing some well stratified sandstone and some loose
blocks of conglomerate; and midway of the ridge along the
lowest canon cutting across it an earlier intrusive is uncovered,
as weil as some granite and hornblende andesite. The rhyolite
evidently formerly covered these areas. Near the south end of
the second dyke the hornblende andesite and the rhyolite reach

6 University of Califorma Publications. [ GEOLOGY

their highest altitude, and from this on the ridge, which is now
still higher, is continued by granite and metamorphies, the rhyo-
lite being relegated to the flanks of the ridge. The andesite is
rarely to be seen from this on southward, and only then as a few
loose blocks here and there, separated by dividing summits from
that which is in place. Part of the stock from which it may
have been derived may be covered by wolian sands or debris;
or else these erratics are the remnants of a once extensive flow.
The rhyolite near the southern dyke is frequently faulted, both
transversely and lengthwise of the ridge, so that it is much
broken. The contact which we now come to is that between the
rhyolite and the granite. It appears to be not a fault contact
from the evidence the writer was able to obtain. There was no
contact metamorphism noticed, nor was there found any inclu-
sion of the granite in the rhyolite. A small area of conglomerate
is revealed near the contact where erosion has carved away the
rhyolite. No bedding is shown, and every pebble, almost without
exception, is faulted. The formation is not shown on the map
Pl. 1, the area being too small. The rhyolite of this ridge appears
not to present the structure which, according to the terminology
of some writers, would be designated as sheeted. The andesite
near by possesses this structure in a marked degree. At this
contact the rhyolite ceases to be prominent in the ridge, and the
hornblende andesite does not continue farther southward. The
rocks that are now encountered are granite and granite-por-
phyry, schists, garnetiferous rocks, basalt and limestone. The
contact between the granite and granite-porphyry is more irreg-
ular than it was possible to show on the map. The contact
between the eranite and the schists and garnet rocks is also irreg-
ular. The strike of the granite-porphyry is east and west, and
it occurs as a very wide intrusive in the granite. The strike of
the belt of schists is somewhat north of east. The belt of schists
contains numerous segregations of copper ore, and a reef of
exceptional interest, containing disseminated sulphides of copper
and iron. It appears to be a metamophosed dyke. In places
it has ineluded in it a light colored rock, which may be pieces
of the granite that were caught up at the time the dyke was filled.
More will be said of this supposed dyke under the head of ore

Vou. 4] Smith—Upper Region of Main Walker River.

“|

deposits. It is in this ridge that the best exposures of the lime-
stone occur. There is presented in one place about eight hundred
feet of its thickness, and as to how much thicker it may be was
not ascertained. Capping all these rocks and debris is basalt.
The debris is very susceptible to erosion, and is readily carried
away, the basalt being thereby readily sapped. West of the
summit, at the Ludwig Mine, iron ore again occurs with lime-
stone, as it did in the first ridge, only in this case its strike is
continuous with that of the limestone. It is also continuous
with the limestone in depth, so far as could be ascertained from
the mine openings, which had a depth at the time the writer was
there of about four hundred feet. ‘The continuation of this ridge
south of the map consists of granite intrusives, some sedimen-
taries, quartz-porphyry and basalt. One of these intrusives was
found containing an inclusion of granite-porphyry. The investi-
gation of the ridge was not continued south of the Hutson Pass’,
which is about six miles south of the area covered by the map
Pl. 1. The Superjacent Series, in this ridge, is represented
by tuff, andesite, earlier and later, rhyolite, Tertiary beds and
basalt within the area of the map; but these rocks do not extend
the entire leneth of the crest line. From Mickey Pass south-
ward the latter is continued by several members of the Bedrock
Complex; as, for instance, several granites nearly alike, granite-
porphyry and some more basic intrusives. The lmestone, how-
ever, les a little lower. The two major divisions, the Bedrock
Complex and the Superjacent Series, are probably not better
represented within the region as to the number of formations
comprised, but the relative sequence of the rhyolite and the
basalt of the Superjacent Series is better seen in other parts of
the territory.

The Third Ridge.—The third or easternmost ridge is alone the
eastern margin of the map Pl. 1. Its northern end is merely a
chain of buttes which, it may be said, begin at the base of a very
considerable ridge which has a trend at right angles to those that
have been so far mentioned. Unfortunately, it was not possible
to make an excursion to this quarter, and their mapping is accord-
ingly hypothetical. Some schist, metamorphosed sandstone,

‘See U.S.G.8., Wellington Atlas sheet.

8 University of California Publications. [GEOLOGY

unaltered and metamorphosed intrusives of the Bedrock Com-
plex and rhyolite and hornblende andesite of the Superjacent
Series are represented. The bedrock is limestone and granite,
the latter being present in the lower half of the ridge and consti-
tuting the dominant rock.

A few gold and copper bearing veins occur in the southeast
corner of the area of the map PI. 1.

Tertiary beds which yielded fossils are exposed at the eastern
base. Their exposure is not within the map, but about two miles
east of it, and about two-thirds of the distance from the top.
Their base is fine white rather sharp sandstone, and their top is
conglomerate, with well rounded pebbles. The intermediate
sandstone contains some hornblende and the pebbles are abun-
dantly rhyolitic. There is also a yellowish and whitish stratum
of chalky appearance. No test was made upon it to ascertain
its composition, either chemically or mineralogically. The
thickness of these beds was estimated to be twelve hundred feet.

Figure 1.—Profile of a portion of Whirlwind Mountain along the line
h-F in Pl. 2. The prominence on the right is a basaltic cap on sandstone.
Along the broken line this sandstone rests on rhyolite, which rises to a pyra-
mid on the left.

Whirlwind Mountain.—This ridge is shown on Pl. 2. It is
made up of rhyolite, sandstone and a basalt cap, all being of the
Superjacent Series. The relations of the basalt, sandstone and

BULL. DEPT. GEOL. UNIV. CAL. VOENGuiren 2

fSbusl _—S
Basalt Tertiary —Rhyolite Alluvium
Sedimentaries

a

eS

=

Contour interval 50 feet

WHIRLWIND MOUNTAIN.

Vou. £]) Smith—Upper Region of Main Walker River. 9

rhyolite are here well revealed, as may be seen by consulting
Fig. 1. The basalt rests on the sandstone that overlies the rhyo-
lite.

The Mid-valley Buttes.—The broad valley below the second
or Sing-ats’-e Ridge is studded with four buttes which peer up
through the alluvium. The northern one, Mason Butte, is com-
posed of granite and dykes of hornblende andesite. There are
no less than seven or eight of these that cut through the butte
lengthwise. Another butte southeast of this one is made up of
granite and rhyolite, and across the river are two more buttes,
of which the more westerly is granite and granite-porphyry
similar to that already mentioned in Sing-ats’-e Ridge, and the
fourth butte is granite and earlier intrusives similar to that
mentioned in the first ridge.

UNCONFORMITIES.

The sedimentaries occupy about one-thirtieth of the entire
area. There is enough of them and a few fossils, however, to
give information as to their age and the structure of the region.
The range of the sedimentaries is from the end of the Palaeozoic
or early Mesozoic to the present, as the fossils show. The Creta-
ceous and the Eocene are not recorded by any accumulations, but
there are indications of considerable erosion which took place
within a time that may correspond to these two periods. There
was no section found where the entire column could be measured.

The Bedrock Complex and the Tertiary—The unconformity
between the shale and limestone of the Bedrock Complex. and
the beds of the Tertiary is usually very marked. The amount of
disturbance and deformation of the complex is considerable,
while that of the Tertiary is not so great. <A few fossils indi-
cate the limestone to be Triassic. In the Tertiary one pebble was
found containing a fossil, which was submitted to Dr. J. P.
Smith of Stanford University for determination of stratigraph-
ical position, and the following communication was received:
“The black silicious rock contains what appears to be Daonella,
a pelecypod characteristie of the Middle Trias. The Geological
Survey of California discovered some Triassic fossils! at Vol-

* Described in Amer. Jour. of Conchology, Vol. V, by W. M. Gabb,
““Description of some Mesozoic Fossils,’* ete.

10 University of California Publications. [GEOLOGY

ceano, an abandoned mining district, thirty miles southeast of
Walker Lake. Triassic fossils like those of the West Humboldt
Range (Nevada) were also found near Wabuska. I think I have
seen them in the Mining Bureau or in the Harvard collection. As
I remember them, Daonella dubia (Gabb) was the most charac-

1 The eurator of the museum at the Min-

teristic fossil—Lias.
ing bureau said that fossils from near Wabuska had _ been
received and they were now stored and not available, but he was
sure there were not many.

A section south of west in the Pine Nut Range might yield
further information of this character. So far as the writer is
aware, these represent all the rocks of marine origin within the
region.

The evidence for the Tertiary is perhaps a little more com-
plete. The Tertiary is supposed to be of lacustrine or conti-
nental origin. The evidence for the lacustrine origin of the
beds is perhaps not so complete as for their age. One portion of
the evidence is the remains of a land fauna which they have
yielded; and in this connection the following communication has
been received from Dr. W. J. Sinclair, to whom they. were sub-
mitted for determination: ‘‘The specimens submitted comprise
fragments of the astragulus, caleaneum, and metapodals of a
rhinoceros and the astragulus of a large camel. The presence
of a large camel indicates that the beds from which the speci-
mens were obtained are younger than the John Day. The John
Day camels, belonging to the genus Protomeryx, are all small
forms. The beds are probably late Miocene or Pliocene, corre-
sponding to the Maseall and Rattlesnake formations of Oregon,
but the material is not complete enough to determine these points

”?

with certainty. Of a date nearly twenty years earlier is the
following? by Professor Russell: ‘‘Mammalian bones were
obtained at a number of localities in the sides of the Humboldt
and Walker River canons, and, with the exception of a single
vertebrate found in the medial gravels, they were all derived
from the upper lacustral beds. These fossils were submitted to

‘Dr. Smith also kindly adds that he has reviewed the fossils from Vol-
cano in the Harvard collection, and found their determination correct.
*Mon. XI, U.S.G.8., p. 238.

BULL. DEPT. GEOL. UNIV. CAL. ViOlA ries

Showing the westward dip of the Tertiary Strata.

Vou. 4] Smith—Upper Region of Main Walker River. 11

Professor O. C. Marsh for determination, but only a partial
report of their character has been rendered. So far as deter-
mined, they inelude a proboscidian (elephant or mastodon), a
horse, an ox, anda camel. The fossils were usually detached and
seattered through the sediments, more than cne or two bones of
the same individual being seldom found at a single loeality.’’
This refers to the Quaternary, and the medial gravels referred
to are those of the Lahontan beds. The detached occurrence of
the fossils is the same as in the case of the Tertiary. The fossils
which the writer found were dug from strata tilted about 35°,
an amount which is greater than was at any place recognized
in the Quaternary. Pl. 3 shows the amount of tilting. Whether
the species are the same in the two instances it 1s impossible to
say, but apparently they are not; and there can be no doubt as
to the relative position of the two sets of beds. Professor Rus-
sell has mentioned the possibility of fossils being derived from
lower beds. However, the amount of their deformation appar-
ently is on the side of their being Tertiary. The beds show clearly
a gradation of material from fine to coarse.t The finer sand-
stone shows some sharp grains which may be of voleanic origin.
The apparent absence of fossils of an aqueous life might be
regarded as an indication of voleanic origin for the whole of
such strata, but this for the greater part is not true.

Specific correlation of the Tertiary beds throughout the Great
Basin continues to be on the whole not very satisfactory. Erosion
and alluvium isolate and cover them to such a degree that it is
impossible to trace them continuously. The value to be placed
on their fossil life seems to be somewhat uncertain, with the
conclusion of work in each separate region so far investigated.

The Tertiary and Quaternary.—The uneonformity between
these is quite sharp. The latter lies very level, and it is mostly
obliterated within the area shown on the maps, but in the north-
east and northwest corners of Mason Valley lacustrine beds and
terraces are preserved. Their thickness, measured in the Walker
River Canon is one hundred and sixty feet.*

West of the second, or Sing-ats’-e Ridge, and south of the
map PI. 1, in Smith Valley, are a few hundred feet of beds which

1 Bull. Dept. Geol., Univ. Calif., Vol. 2, No. 9.
* Mon. XI, U. 8. G. S., p. 141.

12 University of California Publications. [ GEOLOGY

are revealed as a result of the cahon cutting by the West Walker.
These beds appear to be horizontal, and it is difficult to say
whether they are Quaternary or Upper Tertiary. A few large
bones have been found on their surface, and, as a matter of
record, it may be here stated that a few large bones have been
reported as found in building a road grade in the Wassuck
Range, southeast of these beds, and also that fish impressions
occur at the mouth of the canon just mentioned as cut by the
West Walker.

Relative Age and Unconformity of the Igneous Rocks.—The
uneonformity between the Bedrock Complex and the Super-
jacent Series is also well brought out by the stratigraphic rela-
tions of the igneous rocks of the two groups. The granites and
eranite-porphyries of the Bedrock Complex appear to be intruded
into the Triassic, and cutting these are dykes of porphyrite,
which is perhaps also of the complex. The hornblende andesite
reposes in tilted attitudes upon the tilted abraded surface of the
Bedrock Complex. This was followed by the rhyolite, which is
found intrusive in the andesite in the form of tongues. Both
the hornblende andesite and the rhyolite yielded pebbles to the
shore drift of the Tertiary lakes which succeeded the extravasa-
tion of the rhyolite. But the andesite is not so abundantly rep-
resented as the rhyolite. The next lavas in order of occurrence
are the later andesite and the basalt. These two lavas appar-
ently succeeded the lacustral epoch, since they yielded no peb-
bles to the Tertiary Lake beds. The later andesite and the basalt
approximate horizontality. They both occupy eminences and may
be regarded as caps. The basalt occurs in many isolated and
detached areas, and these all, with the exception of that on the
Wassuck Range, are of the same altitude as the later andesite
cap.

STRUCTURE.

The Bedrock Complexr.—The Triassie limestones are much
crumpled, folded and broken, and the accompanying batholithic
intrusions of granite and porphyries are also much fractured
and broken. The bedding planes of the shale are not exposed.
The axis of folding is nearly north and south, and there are indi-
cations, at least, that this structure would not be apparent in

€

Vou. 4] Smith.—Upper Region of Main Walker River. 13

the present topography were it not that the direction of subse-
quent faulting coincided with it very closely ; thus, following the
establishment of the Bedrock Complex, there apparently inter-
vened a considerable period of erosion which wore it down to a
low relief.

The Tertiary—The dip of the Tertiary beds is about forty
degrees to the west, and they present a series of monoclines, and
the apparently plain-like surface on which the rhyolite rests is
also similarly inclined. The dip of it and that of the beds is
nearly the same. There are some bands of stratification in the
tuff lying under the later andesite cap, but their tilting is some-
what less. The altitudes are in striking contrast to the verticality
of the schists of the underlying Bedrock Complex. These schists,
moreover, strike northwest and southeast. The region is divided
by parallel ridges, which may be classed in two systems—those
trending northerly and somewhat westerly, and those approxi-
mately at right angles to these. The westward alluvium slopes
are many times longer than the eastward slopes, and the crest
of each system of ridges pitches toward the base of the other:
for example, the pitch of the third ridge shown along the east
margin of Pl. 1 pitches north to the base of Cleaver Mountain,
which is just north, off the map, and it trends nearly east and
west. By pitch is meant the slope of crest-line. The pitch of
that mountain is also westward toward the base of Sing-ats’-e
Ridge. The crest of this last ridge pitehes northward toward
the base of Cleaver Mountain, but the pitch is not as great as
in the ease of the other north-south ridge, which, as may be seen
on the map, is broken into several buttes at its northern end.
The degrees of these respective pitches seems to be nearly pro-
portional, for the highest point, Cleaver Peak, is in line with the
chain of buttes. Some notion of these relations may be obtained
by consulting the Wabuska sheet and Fig. 1; and, as to the
general block tilting of the Cleaver Range both parallel to its
trend and transversely, an idea may be had by consulting the
earlier topographical map! of that range. This range is capped
with basalt, and it has been seen from two sides, so there may
not be great doubt as to the accuracy of the observation. This

*Map No. 48, Wheeler Survey West of 100th Meridian.

14 University of California Publications. | GEOLOGY

mountain presents a bold face toward the south, overlooking the
alluvium plane below; and at the base, not near either of the
north-south ranges, there are hot springs. At the eastern base
of Sing-ats’-e Ridge and about nine miles south of the map PI. 1,
steam issues from the rocks. In Smith Valley at Wellington,
near the eastern base of the Pine Nut Range, is a well the water
of which is too warm for drinking purposes; and at the same
base, and about twelve miles north of this last place, at Hind’s
Hot Springs, there is one at scalding heat. Thus, at the base
of each of the systems there are hot springs. Wherever the trans-
verse system is not present the valleys are closed by an arrange-
ment of ridges en echlon.

There are several features that are conformable to the two
systems within the area mapped and near to it; as for instance,
to the transverse system there are the course of the cafons, strike
of the andesite and rhyolite dykes, strike of the schists, trend of
two of the mid-valley buttes and outcrop of several of the min-
eral veins. The third butte and the remainder of the mineral
veins are conformable to the other system, while the fourth butte
is circular, or conformable to both.

- N . :
\F \
\\ \ oS ome

| \ Pai

ADIL

\\ \
\ \

NIN co my) N coe _

icurg 2.—Ideal representation of the structure of Walker River region.

4

Fig. 2 shows somewhat ideally the type of structure that is
presented in the region; and it is believed that this region offers
fair opportunities for a quantitative study of the generally rec-

BULL, DEPT. GEOL. UNIV. CAL. VOR Plr4

Illustrating the geomorphy of the region where the rhyolite is a prominent feature. On the left is the
northern end of Mason Valley and on the right the Walker River Valley. In the distance is the Cleaver Mountain
Range. This range is capped with basalt the dip of which is indicated by the sky-line. The range is just north
of the map, Plate 1.

Vou. 4] Smith.—Upper Region of Main Walker River. 15

ognized Basin Range structure, since there appears to be a degree
of proportionality between the north-south system of faulting
and the east-west system.
RELIEF OF PRE-TERTIARY AND TERTIARY SURFACES AS COMPARED
WITIT PRESENT RELIEF.

That considerable time has elapsed since the faulting began,
and that it was apparently periodic in its progress, seems to be
evident. The absence of granite pebbles from the Tertiary and
the presence in it of the rhyolite, which the writer has shown
was subsequent to the earlier andesite, would indicate that the
surface of the region was reduced to one of low relief previous
to the efflux of the rhyolite and the appearance of the Tertiary
lake, the granite being reduced to a position below the erosion
zone. This is also rendered apparent by three other considera-
tions: the surface on which the rhyolite rests presents a plain-
like character; the several isolated and detached areas of the
rhyolite have the dip of this plain-like surface, and this is nearly
uniformly the same for each; and this dip is also practically the
same as that of the beds of the Tertiary. It may be possible,
from the relative proportion of the earlier andesite in the Ter-
tiary, to fix the date of the completion of this planation more
definitely ; that is, to place it after the effusion of the earlier
andesite. It is possible that the lower portion of the Tertiary
accumulations are in part granitic debris, but the upper portions
certainly are not. This would extend the period of planation
into the early Tertiary.

The consideration of the basaltic sheet is somewhat of a simi-
lar character. The isolation of the areas, their sheet-like char-
acter, and their similarity of elevation seems to indicate that
they once were all connected. The later andesite can be regarded
as an associate on the same elevation. If these areas were once
connected, it would seem to indicate that the surface had been
reduced to that of a peneplain, and that the ridges have been
subsequently lifted. The distance between these areas is hardly
less than ten miles in any instance; and supposing them to be on
the upturned edge of a block the width of which is that much,
the amount of rotation or tilting would be less than a degree
and a quarter to lift the edge above the floor of the valley a

16 University of California Publications. [ GEOLOGY

thousand feet. This is a surprisingly small amount of rotation,
and the attitude of the lava might easily be mistaken for hori-
zontal. However, it has been considered that the separated
basalt sheets of the Great Basin were never connected.t A few
basie dykes were found within and near the areas of Pls. 1 and
2, and it may be possible to trace the basalt to them. The char-
acter of the material is such that a very narrow fissure might
discharge considerable molten rock, since the basicity of the
rock indicates a great degree of fluidity at a comparatively low
temperature. While the latter hypothesis attempts to account
for their isolation, it remains to be seen how to account for their
attitude. This is one of the ‘questions that arose that was not
answered beyond the attempt indicated. The author’s opportu-
nity did not permit of his making any further investigation.

)XPLORATIONS BEYOND THE REGION MAPPED.

It was the writer’s opportunity to make an excursion to the
West Walker and through Carson Valley. This gave him an
oceasion to make some observations of a general character. The
structure of the first system was found to prevail, with now and
then suggestions of the transverse system. The West Walker
flows through two valleys before it reaches the Main Walker. In
flowing through the first of these (Antelope Valley) it bears
along near the eastern base of the mountains at the west for a
considerable distance, and at the northern end of the valley the
course is northeast, passing through the Pine Nut Range, which
is very low at that point, there being a considerable mass imme-
diately north. The river then turn sharply to the north and
swings eastward across the valley, being entrenched on a flood-
plain between two bluffs of sandstone. These bluffs are the beds
of sandstone that were referred to as of uncertain age when the
unconformity of the Tertiary and Quaternary was considered.
The bluffs converge toward the east, and the river is more and
more confined between them. The stream runs near the base of
the northern bluff, and is gradually invading it, thus gradually
taking a more and more northward direction, which seems to
indicate a tendency of the river to change its course and flow

* Mr. G. K. Gilbert, Surveys West of the Hundredth Meridian, Vol. ITI,
p- 125.

~l

Vou. 4] Smith—Upper Region of Main Walker River. 1

along the western margin of the valley near the steep eastern
face of the Pine Nut Range; but so long as the river is con-
strained to remain in the present canon of the Sing-ats’-e Ridge,
the tendency is somewhat offset, and the gradual invasion of
the northern bluff is probably only a manifestation of such
tendency. The river after emerging toward the open valley con-
tinues in the direction of the canon for a short distance, but it
soon turns quickly to the north, bearing a httle to the west;
this being the general direction of the base of the ridge. It is
joined by the East Walker at a point about two miles south of
the map Pl. 1. The East Walker flows in a canon-valley through-
out almost its entire length and, therefore, this valley does not
show the difference of the valley slopes that is shown in the
wider valleys. Walker Lake hes under the steep eastern slope
of the Wassuck Range, and from the eastern and southern shores
the ground rises gently. So much for the Walker River System.
As to the Carson River, which has its source near the West
Walker, it flows near the eastern base of the mountains just east
of Lake Tahoe, and Carson Valley has a more or less gentle
eastward rise to the summit of the Pine Nut Range.
DESCRIPTION OF THE IGNEOUS ROCKS.

The numbers on the maps indicate approximately the places
where the samples were taken. The hand-specimens and the
corresponding thin sections bear the same number as the place.
The region was not traversed consecutively, hence the reason for
the numbering being apparently at random.

The Granitic Rocks —Hand-specimen No. 123 is a fair repre-
sentative of the granitic rocks that occur in the southeastern
portions of the map Pl. 1. This rock has an even grained granitie
structure (allotriomorphie granular), and is made up of feld-
spar, quartz, biotite and a greenish ferro-magnesian mineral.
The color is grayish and the fracture is irregular. Microscopically
the structure is granitic; no mineral has idiomorphic outline.
The essential minerals are biotite, augite, plagioclase, orthoclase,
and quartz. Magnetite in somewhat irregular grains, 0.25 mm.
in size, is distributed throughout all the essential minerals. This
mineral is apparently original when possessing that size in this
rock. The biotite is brown and in irregular erystals, often with

18 ‘University of Califorma Publications. [GEOLOGY

dimensions normal and parallel to ¢ about equal. It shows a
leaching to a green variety, and a further change to chlorite and
black specks of iron oxide.

The ferro-magnesian mineral agrees very well with augite.
It is nearly colorless and practically free from pleochroism. A
section nearly normal to the prism, «# P (110), shows a cleavage
angle of about 90°, and the extinction bisects this angle. There
is an alteration of the mineral to a green pleochroie one, possess-
ing an absorption color of yellow-green which has some of the
properties of epidote; the alteration, however, is incipient.
Green hornblende is also present. It seems in some instances to
have been derived from augite. The plagioclase feldspar shows
no alteration to calcite, but contains kaolin. No properly ori-
entated sections were found in which to measure extinction
angles of the lamellar twinning. Orthoclase distinguishable by
lowest rehef and birefringence and freedom from lamellar twin-
ning is present. Quartz with irregular cracks, and possessing
eas and liquid inclusions, is of similar importance. Some apa-
tite, 0.8 mm long, is present. This rock may accordingly be
designated an augite granite. Another similar rock is 172,
which occurs east of it in the Blue Jay Butte. The similarity
of the two is marked. The biotite is less altered and the rock on
the whole is fresher. In the pyroxene, in sections showing a very
pronounced prismatic cleavage, there appears a fine lamellar
cleavage which is somewhat discontinuous yet pronounced, and
cutting across the coarser at a considerable angle. This lamellar
cleavage is basal, and indicates the species diopside. An extine-
tion with the coarse cleavage was obtained in one ease as large
as 52° on a section parallel to c. The prismatic cleavage is
straight and well defined. The alteration of the pyroxene is the
same as in slide 123. It shows apparent incipient change to a
green pleochroic hornblende. In one instance where the pyrox-
ene is surrounded by a considerable border of hornblende, iron
oxide is traced along their contact, the hornblende itself being
free from it. Biotite ineludes quartz and pyroxene. In regard
to the latter, it occurs both as inclusions and intergrowths, and
their relation is such in either case as to indicate that the period
of crystallization of the biotite continued beyond that of the
pyroxene. The feldspar is the same as is usually seen in granitic

Vou. 4] Smith —Upper Region of Main Walker River. 1B]

rocks. The extinetion of orthoclase was obtained in the section
of the eclinopinacoid, » P#, (010). It was further recognized
by a relief lower than quartz. The plagioclase is larger, having
dimensions of 0.5 mm. and 1.5 mm. It contains inclusions of
biotite, pyroxene partly altered to green hornblende, iron ore,
some of which shows erystal faces, and hexagonal and_ lath-
shaped sections of apatite. Some of the larger plagioclases
inelude smaller ones of a slightly different orientation. Mag-
netite occurs in all the essential minerals, and is mostly devoid
of crystal faces.

The occurrence of pyroxene in these two rocks indicates that
they belong to, perhaps, a less frequent class of rocks, namely,
the augite granites. It should be noted that these rocks show
effects of pressure, since many of the minerals show wavy extine-
tion and small erystals are faulted.

The next three rocks, Nos. 94, 95 and 157, show remarkable
similarity. They are all samples of the granite-porphyry dyke.
Nos. 94 and 95 were obtained west of the river, in Sing-ats’-e
Ridge, below the middle of the ridge, and No. 157 was obtained
in Cemetery Hill. The rock possesses porphyritic structure.
Carlsbad phenocrysts 1 em. in length, in granular groundmass
of about 2 mm., is characteristic. The groundmass is phanerie,
and its mineral content is readily recognizable in the hand-
specimen. There is some difference in the ferro-magnesian con-
tent. There is less of it in 157 than in 94, but No. 161, which
will not be deseribed, is from the same exposure as No. 94, and
it shows less biotite. The hornblende seems to be as abundant
in one ease as the other. In 95 the light and dark colored min-
erals are about equally abundant. In the microscopic slides of
all three the phenocrysts are microcline, which is recognized by
the combination of albite and pericline twins, which are very
fine and have an equal and simultaneous extinction. The ground-
mass is made up of microcline, plagioclase, quartz, biotite and
hornblende. The grain of the groundmass varies from 1.5 mm.
to 2 mm. The biotite is brown, with some leaching to a ereen
eolor. The hornblende is original, as it shows in sections normal
to ¢ the prism and clino-pinacoidal faces © P (110), and x P#
(010), and the prism faces are at an angele to one another of
125°. This also is the angle of the cleavages. The color is green.

20 University of California Publications. [ GEOLOGY

There is no chlorite or calcite, but in slide 95 there is some epi-
dote. The epidote has irregular outline, but its absorption tint
(pistachio green), high relief and strong double refraction in
nearly equally dimensional sections make its identification quite
certain. It has apparently replaced hornblende. <A consider-
able portion of the feldspar is somewhat elongated in the zone
«© P ©:OP(100:001). No section normal to © P ® (010), was
found in which to measure extinction angles of the albite twins.
Carlsbad twins are numerous. In sections nearly parallel to the
brachypinacoid the axial figure is only a little to one side, and
the axial plane makes an angle of a few degrees with the most
pronounced cleavage, which is the basal. Hence it is quite cer-
tain these feldspars are not very basic. Quartz often contains
plagioclase, as also does microcline. Apatite and sphene are
present, and the latter is frequently of irregular outline and of
good size. There is magnetite present, and in slide 95 a black
opaque mineral with narrow border of sphene may oceasionally
be seen, especially in the larger crystals of hornblende. It may
be ilmenite. In slide 94 the association of sphene, hornblende,
biotite and magnetite is marked. Strain effects are apparent, as
many minerals have a wavy extinction and show slight faulting.
Apatite needles are broken and slightly displaced. No indication
could be obtained that any movement had taken place during
the crystallization of the rock. The following analysis was made
of specimen 94:

Per Cent.
SSO tersrcsstcnsea eat tcevty Sronsasenne, oe ve ee cee 67.70
BAN Os Uectan-aterketoarionce-vesnscdsueeeeaer cerns Pare 15.95
PN C.O spawn siauatcicwke ae ese eee 1.53
MECN 2. sislsiscecse eons d Wepoeen cavers ences 1.14
MSOs ectsec ious ctandssbeceravesevee=cssaie iso enetees 1.23
CAO ere a arnsG mere hay kp eee er nee 2.70
PK OP beach asigieaceiaginvs accoeudena sis cee 3.74
PEN ASO) batehcy walere prone aba ce en oa ce eee Pee 4.83
ET O7@ MOS Oi Cia ecer rere siehe reset sestol snes 0.19
letKO)(@)soihnteyl Seen aoeoueccdasodns 0.36
AlilO Sees AAO OR OAR AN ara oA nae 0.23
MnO, present, not determined.
P.O;, present, not determined.
Mota ns Scat science ewe ageesitors 99.60

“These were duplicated, and were concordant within .06 per cent.

Vou. 4] Smith—Upper Region of Main Walker River. 21

Specimen 100 oceurs at the south margin of the map PI. 1, in
Sine-ats’-e Ridge. It is an even-grained rock, made up of about
equal amounts of light and dark colored minerals. The light
colored minerals are feldspar and quartz. Biotite and hornblende
are easily recognizable. The slide contains plagioclase feldspar,
whose extinction angle in the zone normal to the brachypinacoid
oP x (010) is symmetrically 14°, but the sign was not deter-
minable, and this one measured was not a Carlsbad twin, hence
the tables of Michel Lévy could not be used. Some of the plagio-
clase attains a leneth of 2 mm. Microcline and quartz of about
equal grain are present, but the plagioclase predominates. Green
hornblende of a length of 2 mm. is present and in size about
equal to the plagioclase. There is less of the biotite than horn-
blende, and there is less iron oxide in this slide than in the pre-
vious slides. Sphene in part idiomorphie toward microcline and
allotrimorphic toward plagioclase is a constituent. This rock
may be termed a biotite granite. No. 120 is a similar rock. It
occurs farther south, off the map Pl. 1, in the same ridge and
under the basalt cap west of Nordyke. In the hand-specimen
the feldspars are of two colors, brownish and white. These are
about of the same dimensions and about equally abundant. The
remainder of the rock, about one-third of it, is hornblende. The
average size of the first named minerals is a little less than 0.5
em., and that of the hornblende about 3 mm. The contrast of
colors readily characterizes the rock in the field. In the shde the
brownish colored feldspar is orthoclase. Its color is due to dust-
like impurities. The plagioclase is clear for the most part. Bio-
tite is absent and the hornblende is of a greenish color. No min-
eral is idiomorphic except some accessories. The iron ore has
irregular shape and shows a preference for the hornblende. The
slide as a whole shows considerable fracturing of the roek, and
thus indicates the disturbance to which it has been submitted, as
seen in the field. The disturbance evidently was not long con-
tinued, for no mineral indicating dynamie metamorphism is ree-
ognized, and this is equally true of all the slides thus far exam-
ined, unless epidote and microcline be so regarded. The neces-
sary water for hydration of the iron and lime to produce epidote
may be derived from the water found in the bubble inclusions

22 University of California Publications. [GEOLOGY

of the quartz. In the case of those rocks containing biotite it
may be due to decomposition of that mineral, but in the present
instance it is not clear from what source the water was derived,
for the bubble inclusions occur along the fractures of the quartz.
No. 89 is an even grained rock, composed of light green horn-
blende and feldspar, showing polysynthetic twinning as viewed
in the hand-specimen. The rock occurs at the east base of Sing-
ats’-e Ridge, and haif way from the top of the map Pl. 1. It
apparently is not of great extent. Hornblende appears to be
about one-third of the rock. The grain of the rock is about 2.5
mim. In the slide the last named mineral is pale green and some-
what pleochroic. No section normal to the prisms was obtained
in which to measure cleavage angles, but in some sections, show-
ing the cleavages parallel or very nearly so, the extinction was as
great as 15° or over. The cleavage is very fine and lamellar. Ortho-
clase and quartz have less prominence. The plagioclase differs
not essentially from that seen in previous sections. They show
zonal structure, and their decomposition has had zonal progress.
The quartz is fractured, and through its rifts are minute liquid
inclusions. The cracks are quite parallel throughout the slide.
No. 141 is the granite of Mason Butte. The leht and dark
minerals are about of equal proportions. The dark minerals are
hornblende, biotite and chlorite. Epidote is noticeable. Quartz
and feldspar comprise the light colored minerals. The average
erain of the rock is 4mm. In the slides the feldspar appears to
be mostly orthoclase, since it is free from lamellar twinning and
possesses low relief and birefringence. Quartz is next in import-
ance, and there are a few individuals of microcline. The horn-
lende is sparingly present, its cleavage and form normal to prism
zone indicating its presence beyond doubt. Brown biotite is
believed to have been once present in an abundance, for chlorite,
with a few remaining shreds of brown biotite, is very plentiful.
The chlorite shows the micaceous cleavage, and the extinction is
parallel to the cleavage. Its very low double refraction, ‘‘ultra
blue,’ between crossed nicols, makes it easily recognizable. Some
iron ore and perhaps secondary silica is in evidence. Enpidote is
easily recognizable by its relief and strong double refraction. It
is thought to be secondary because of its intimate association with

Vou. 4] Smith—Upper Region of Main Walker River. pas

chlorite, and it is idiomorphie toward the chlorite and thus ante-
dates it in formation. The necessary ingredients for these pro-
ducts doubtless were derived from the ferro-magnesian minerals
for the most part. Much of the quartz possesses inclusions along
eracks, and the latter preserve nearly a singleness of direction.
The feldspar also shows alteration to a fine fibrous or shredded
mineral giving interference colors of yellow and green of the
second order. It is thought to be sericite. The epidote shows
fracturing, so that it was formed previous to the general defor-
mation suffered by the rock. This rock evidently would be
termed a biotite granite.

No. 77 is a representative sample of the granite south of
Mickey Pass. It is a nearly white rock, being sprinkled through-
out with hornblende 4 mm. in average length, the quartz is pres-
ent, fairly idiomorphie, and of a width of 3mm. Feldspar forms
most of the rock, and twinning is apparent, though the rock is
somewhat altered. The rock is porphyritic. This roek is some-
what similar to Nos. 94, 95 and 157, and its only apparent dif-
ference is that it is more acidic. No. 109, which occurs near the
Ludwig Mine, differs only a little from it, and that in containing
a little epidote. The groundmass is very fine, and is resoluble
with difficulty.

The Porphyrite-—This roek was not studied microscopically.
It oceurs in the north end of the first ridge shown on Pl. 1, and
also in a few dykes in the third ridge and Blue Jay Butte. It is
a porphyritie rock, apparently free from quartz, and has a dark
colored aphanitic groundmass in which are phenocrysts of feld-
spar averaging from 3 mm. to 4 mm. in length.

The Hornblende Andesite-——No. 142 is from the dykes of
Mason Butte, and 146 is from near Mickey Pass. Phenoerysts of
dark hornblende are ineclosed in a light blue or lavender colored
groundmass. The hornblende is abundant and from 2 mm. to
3 mm. in length. Occasionally the feldspar assumes a leneth of
1.5 mm. The rock weathers to a dull red color, and may easily
be confounded at a distance with the later andesite and with the
rhyolite. The hornblende is occasionally twinned. The feldspar
shows a growth by zones which have not been equally spaced,
and sections approximating parallelism to # P # (010) have a

24 University of California Publications. [ GEOLOGY

variation of extinction of 16° from center to periphery. The
extinction of labradorite was obtained for the peripheral zones.
Squares of magnetite 0.12 mm. are frequent, and small and large
sized crystals of apatite are abundant. Some flow structure is
exhibited for the earlier products of crystallization. The ground-
mass remains equally luminous between crossed nicols when the
stage is rotated; and with a high power and intense light there
seems to be no glass present; and apparently it is wholly felds-
pathic. he larger phenocrysts of feldspar exhibit the phe-
nomena of resorption and subsequent growth, and their outline
is less regular than the smaller sized ones. Calcite, as an altera-
tion product, pervades both the groundmass and the phenocrysts,
and chlorite occurs only in 142. The hornblende of No. 146
shows a marginal lhghter color and a breaking down into a fibrous
or leafy aggregate which is notably free from chlorite. The horn-
blende is often fractured and disloeated. Apatite occurs in stout
prisms, and in some instances without idiomorphic outline. Mag-
netite, which is in grains rather too large to be considered sec-
ondary in this rock, takes form against the apatite irregularly,
with a tendeney to inclose it. This indicates that the magnetite
and apatite had erystallized contemporaneously, but that the
magnetite had continued longer to crystallize. Some of the apa-
tite shows embayments and inlets suggestive of corrosion, and
in these are calcite. It is also somewhat fractured, and it is per-
haps in the groundmass that the record comparable to that
already found in the granite, of the general dynamic effects
which are the result of the deformation of the region, are found.
The flowage of the molten rock, which more or less fractured the
phenocrysts, makes it evident that, in studying the dynamic
effects as revealed in the rock, any disturbance that affected the
eroundmass after it erystallized should be distinguished from
that which had affected the phenocrysts during their movement.
In the case of the phenocrysts the effects due to movement in the
magma are, in the present rock, greater than those due to defor-
mation after the rock had erystallized: hence-it is in the ground-
mass that the record is clear. The effect is apparent through
the groundmass, but it does not show any indications of dynamic

mineralization.

Vou. +]. Smith—Upper Region of Main Walker River. 25

The Later Andesite.—-This rock occurs as a cap in the north-
west corner of the map Pl. 1. Specimen No. 131 is representative.
The eolor of the rock is red, both on the weathered and fresh
fractured surfaces. There are numerous phenocrysts of feldspar,
2 mm. to 4 mm. long, inclosed in a groundmass. The specific
eravity of the feldspar was determined by a heavy solution to
be 2.685, thus indieatine it to be a basic andesine or acid labra-
dorite. The evidence obtainable in the slide was not sufficient
to be confirmatory. No quartz was detected, and a determination
of the silica gave 57 per cent., which clearly indicates the rock
to be an andesite. A few large phenocrysts of feldspar in the
slide are polysynthetically twinned, and they show zonal growth.
Oceasionally the centers of the phenocrysts contain numerous
inclusions, while the margins are free, and a few crystals of horn-
blende of lesser size are present. The groundmass contains innu-
merable lath-feldspars and an abundance of a translucent min-
eral of a reddish brown color and of rectangular cross-section.
It may be a pseudomorphie replacement of hornblende by lmon-
ite. There is no parallelism of structure in the groundmass. and
no glass.

The Rhyolite—This rock is well represented over the region.
It weathers to a reddish color, and on a fresh fracture it is some-
what lighter. It often contains foreign material, such as frag-
ments of the surface over which it flowed. Quartz, glassy feld-
spar and some biotite are noticeable in the specimens. Lying
usually under this rock is a white one which appears rather tufa-
ceous, and on the weathered surface of this latter may be found
dihexhedral quartz erystals 3 mm. to 4 mm. in length; also a
glassy, idiomorphic feldspar of similar size. These crystals of
feldspar and quartz are frequently corroded and often frac-
tured. The pyramidal faces of the quartz are well represented,
and there is usually a prism face in evidence. Faces correspond-
ing to the following are recognized on the feldspar: OP (001),
co P (110), 2P (201 and 201), P(101), P (111), P3, (130)
and (130), ©P* (010), and2P* (021 and 021). In the sections
only one of the phenocrysts could be measured for a positive
result. A section normal to the brachypinacoid,« P © (010) of
a erystal possessing lamellar twinning shows the two feldspar

26 University of California Publications. [GEOLOGY

cleavages, one parallel to the twinning and the other more pro-
nounced at approximately the feldspar angle. The extinction
is nearly symmetrically 20° to the twinning lines, and the biaxial
figure is nearly central. A section possessing such characters
incieates it beyond doubt to be albite. Another erystal has char-
acters which suggest in a rock like this one the soda-lime feld-
spar, oligoclase. Sections from different portions of the rhyo-
lite vary somewhat as to ferro-magnesian content. Some speci-
mens contain hornblende with biotite, while other specimens,
from other localities, contain either alone. The biotite is often
bent, and fluidal structure is exhibited. It and the hornblende
show alteration to magnetite and hematite. Many of the feld-
spar phenocrysts show a marginal growth and a concluding
corrosive action. The quartz and feldspar usually show embay-
ments and inlets of the groundmass, and rounded corners. Sub-
sequently there was a fracturing of the phenoerysts and migra-
tion of sharp, angular pieces. The groundmass is red and cloudy
from inclusions. Spherulitic structure is shown to some extent.
From the opacity of the groundimass it is difficult to ascertain
if it is wholly erystalline or not. The phenocrysts make up about
one-third of the rock. The following analysis was made of this

rock. Duplicate. Difference. Average.
: %o %o %o To
SLO) Se Res rzonsu chivas eyuct-laehsaeaevo es eee OO TSO) 69.46 0.03 69.47
AT Os ee fo ole sasschep teh oe oes eames 11.74 11.72 0.02 11.73
1H O a ney Seca terrae er cE reer ere 5.11 5.06 0.05 5.08
WOOD clits cse eeychan casts ersioleeretecas Antes 0.48 0.47 0.01 0.48
INT Oe reer citer ooeettert ers, Sooners 1.02 0.96 0.06 0.99
GENO) Bers Na AN ART a error re 2.60 2.66 0.06 2.63
IKE On, seieochertary crecoderayns shoes ests eleatnece 5.40 5.29 0.11 5.34
Nae ©) By bs .oarers ets eee tee ria ees ere 3.45 3.47 0.02 3.46
EO@ M05 SM Cae. serene sist 0.31 0.32 0.01 0.31
HOi@ ag ee Sees nt cen canes 1.28 1.28 0.00 1.28
En OR vietictravat cog cwacrcecuemeas eects eaten present present not determined
Een) piscetbosynssiensbaxensctshoctera nace auseyeeetens present present not determined
100.88 100.69 100.77

The Basalt.—This rock oceurs on the map Pl. 1 at the south
end of Sing-ats’-e Ridge and on Whirlwind Mountain, shown on
Pl. 2. Two thin sections were made of these rocks, but as they
are not distinguishable from one another only one, No. 121, will
be deseribed. This rock on the freshest fracture is black, but on

~

Vou. 4] Smith—Upper Region of Main Walker River. 2

a long exposed surface it turns slightly red. At a distance it
always appears black. Microseopically, feldspar and pyroxene
make up the bulk of the rock. Opaque iron ore is relatively abun-
dant and in irreewlar form. Translucent hematite of a reddish
brown color is also recognizable. No olivine was with certainty
recognized, and nearly half the rock is ferro-magnesian mineral,
which is an aluminous monoclinic pyroxene. It and the feld-
spar are apparently contemporaneous to some extent in erystalli-
zation; the pyroxene is often twinned, and has a nearly reetan-
eular cleavage in sections normal to an optic axis, and has
oblique extinction and irregular boundary. Its color is faint
yellow or greenish, and its double refraction is strong, being blue
and yellow of the second order, adjacent to quartz showing gray
or grayish blue of the first order. Within the augite are needles
of apatite and also iron oxide. The feldspars are of various sizes
The largest are about 1 mm. in leneth. Then there are sections
nearly squared 0.5 mm., and the smallest feldspars are lath-
shaped. The twinning of the larger phenocrysts exhibits rather
broad and irregular stripes, and zonal growths are also pro-
nounced. Oblique intergrowths are frequent, and many of the
larger feldspars show resorption near the margin, and subsequent
erowth. This growth is more acid, having a lower relef and
different extinetion. The margin occasionally contains granular
inclusions agreeing quite well with the augite, which would seem
to indicate that it continued to crystallize up to a late date, which
may be as late as, or subsequent to, the period of effusion. As
for the phenoerysts of feldspar, a last attack is also noticeable
on their margin; but not so on the small, lath-shaped ones, which
may have grown in part at the expense of the more acid exterior
of the larger ones. No glass was recognizable. Where alteration
has taken place the plagioclase shows no calcite. But it is thought
this agrees with what has usually been observed, that even should
the plagioclase contain more calcium, calcite does not séem to
form as readily as in the less basic members of the series. The
absence of isotropic glass and a fluidal arrangement of the lath
feldspars seem to indicate the ability to crystallize at a compara-
tively low temperature. It may be remembered in this connection
the apparent sheet like appearance of this lava.

28 University of California Publications. [GEOLOGY

The Schists—Nos. 168a and 168) are samples of the schists
shown on Sing-ats’-e Ridge near the southern end, as may be
seen on the map Pl. 1. The grain of the schist is variable and
the slides differ but a little. Biotite and quartz, and occasionally
some small areas of sericitized feldspar may be seen through
them. Shde 168c is from the schistoid dyke which is contained
within this area, and which was mentioned as containing disseimi-
nated sulphides of iron and copper. It differs not essentially
from the other two. In slide 1688 the biotite is somewhat decom-
posed to epidote and chlorite near the feldspathic areas within
the shde.

SEQUENCE OF THE IGNEOUS ROCKS.

The relative ages of the igneous rocks are granite, granite-
porphyry, porphyrite, hornblende andesite, rhyolite, later ande-
site, and basalt, the relation of the last two not being determined.

Of the lavas, two were traced to points of exit and two were
not. The hornblende andesite and the rhyolite were found in
dykes as well as distributed on the surface, but the basaltic and
later anedsitic rocks were not found in any sort of vent. This
does not signify, however, that their points of exit are greatly
distant, but perhaps that the writer’s acquaintance with them
is less.

THE ORE DEPOSITS.

The deposits of value carry copper and gold, but the two
metals are not associated with one another in pay values. The
richest copper deposits carry no gold, except perhaps as a trace,
though occasionally a gold bearing vein contains copper, but
not in values sufficient to warrant treating the ore for that metal
alone.

Geology of the Deposits—It has been stated in considering
the general geology of the region that the mineral veins are con-
formable to either one or the other of the main structural features
of the region, and such being the case, it would seem that they
were consequent upon the inauguration of these systems, but it is
not to be inferred that they were formed subsequently to all the
structural features. In fact, there seems to be very positive evi-
dence that they preceded the present topography, which stands as
a record of the later stages of deformation. In some instances

Vou. 4] Smith—Upper Region of Main Walker River. 29

there are a few veins that do not conform to either system.

That the mineral veins have preceded the present topography
seems quite clear, and this is thought to be so for two principal
reasons, which are, the absence of the veins from the rhyolite
and the fact that the veins often reach to the highest summits.
The latter condition would indicate that there is not now suffi-
cient hydrostatic head under present conditions of surface con-
figuration to brine the solutions from which the veins were
formed to their present height. It may be remembered in con-
nection with the first of these reasons that previous to the advent
of the rhyolite the region was reduced to one of tolerably low
relief. This evidently indieates that the vein formation was not
active at the surface, and it was not until the later Tertiary,
when the present ranges had been lifted and erosion had begun
its work of uncovering them, that they became exposed.

The period of formation of the veins closed with the making
of the present mountains in the Tertiary, but when it began is
not so clear. Most likely it was after the effusion of the early
andesite, for in one instance an andesite dyke forms one wall
of a vein. It appears that no andesite remains residual near
the metamorphies in which the strongest deposits of copper
oceur.

The Deposits in Particular—In a few instances the mining
has progressed beyond the prospect stage. At the Ludwig Cop-
per Mine a depth of about four hundred feet has been reached.
The ore occurs in chambers in limestone. These chambers when
taken together occur each more or less below the other, and when
considered as a whole the idea of an ore chute nearly expresses
their character. The chambers are along the contact between
the iron ore deposit and hmestone, which two occur as a simple
outcrop having considerable length and a width of less than a
hundred feet. They do not meet squarely in this outerop. but
somewhat diagonally, hence there is a longer contact zone for the
chutes. The rest of the country rock is granitic. The ores are
sulphide, oxide and carbonate. At the Douglas Mine the ore is
chaleopyrite and chaleocite; the gangue is garnetiferous. About
half of the ore is sulphide. It was apparently along the lines
of fracture that the ore solutions found their way. The country

30 University of California Publications. | GEOLOGY

rock is in part almost wholly garnet and in part granitic, with
small areas of limestone overlain. At the Blue Stone Mine the
country rock is an almost entirely altered limestone. It is perhaps
more than half epidote, and presents in the hand-specimen a pale
ereenish gray color. This mass has been more or less fractured
and refilled with calcite, in which the chalcopyrite is imbedded.
The chaleopyrite is usually idiomorphic, at least it usually has
one or two well formed faces. The rifts contaming the ore betray
some parallelism. The mine was named from a deposit of chal-
eanthite (blue-stone) which occurs near the surface. Farther
south on this same ridge is the MeConell Copper Mine, where ore
occurs mostly as an oxide. Oxidation has probably extended
deeper there than any of the places thus far mentioned. Near
this mine are several prospects, which usually are near a contact
of limestone and granite. The deposits so far mentioned are
all in or adjacent to the belt of schist. One reef of schist of a
dark color, which is thus in contrast to the rest of the surround-
ine schist, crosses the summit transversely. In it there was
found disseminated sulphides of copper and iron. The reef was
supposed, on account of its strike and width, to be a dyke which
had suffered alone with the rest of the rocks the dynamie action
which produced the schists. Sulphide was also found near the
erano-porphyry where it had been involved in the metamorphic
action, but the sulphide did not appear to be so much dissem1-
nated as in the case of the dark reef.

Farther south of the MeConell Mine, and off the map PI. 1,
gold oceurs, and it also occurs in the Mason Pass, to the north.
There is also mineralization to some extent northeast of the Blue
Stone Mine, in the low hills near the west side of the river. East
of the river, near the eastern border of the map PI. 1, are several
veins of copper. They have a very definite strike and dip. and
are transverse to the summit of the ridges, and they occur along
faults. There is not apparent the same amount of replacement
of the wall rock or corrosion of the included breccia as in the
case of the Ludwig and Douglas mines. Of these eastern ledges
the Blue Jay has been most prospected. The mineralization in
this case is confined to a belt about two hundred feet wide along
a fault. The ore, which at the surface is cuprite, occurs in cracks

Vou. 4] Smith—Upper Region of Main Walker River. 31

and fissures. The thin sections of the rock of this belt show
more or less alteration of the rock and substitution of quartz
which contains liquid inclusions. Sulphide ores make some
appearance farther down in the prospect, and there has been
considerable oxidation along the fault, and more particularly
because it is vertical and in the bottom of a canon. A hydrous
copper phosphate, which the miners termed malachite, occurs in
the mine, and from qualitative chemical tests made by the
writer it appears to be libethenite; and from some goniometrical
measurements made by W. T. Schaller of the United States Geo-
logical Survey it exhibits a few new forms. Also of some interest
is the formation of chaleanthite since the mining began. It
appears to have formed in consequence of the steam which was
introduced in diamond drilling. The remainder of the ledges
occur from two to six feet wide, and the ore is much oxidized
and leached. In some of the microscopic slides of the ores that
have not been mentioned a very intimate relation of epidote to
chalcopyrite is noticeable. The epidote occurs quite irregularly in
outline, and the chaleopyrite tends to inclose it. The latter
usually shows one or more quite distinct faces. This would seen:
to indicate that the chaleopyrite ceased to crystallize after the
epidote and before the calcite or the quartz. In this connection
it may be well to mention some of the considerations of a petro-
graphical character that guided the writer in the study of the
ores and their occurrence.

There appears as a corollary to many of the contributions to
the subject of the formation of mineral veins, with respect to
their structure, that relative idiomorphism and chemical phase
eannot be regarded as having exactly the same significance that
they have in the ease of the igneous rocks. Their significance
depends upon a different set of conditions. The banded strue-
ture frequently seen is due to a change in the solutions while
the fissure is being filled; and as the filling starts on the walls
and extends by successive layers or bands toward the middle,
each mineral composing the layers is formed against a previous
surface, and hence must have on one side the form of that sur-
face. The other sides may not be freely developed on account
of interference due to the minerals being contemporaneously

32 University of California Publications. [GEOLOGY

erown. This is comparable to the allotriomorphie structure in
eranitic rocks. The bands may not show successively any regu-
larity of chemical phase; one may be more acid than the next,
or may be capriciously either, thus not possessing the regularity
of the Rosenbusch order of crystallization. The writer was
enabled to exemplify these propositions at the Steamboat
Springs, which are near. This occurrence, as is well known, is
often cited as an instance of vein filling now in actual progress,
and consequently is one from which many of the ideas in regard
to vein filling, including those on the crystallization of vein min-
erals, were derived. Another very good instance also occurs at
Bridgeport, Mono County, California, near the source of the
Jast Walker. It appears to have passed so far unnoticed. In-
stead of quartz being the filling material, a variegated travertine
is filling the fissures. It is shown at this place, in addition to
what is shown at the Steamboat Springs, how a portion of a vein
may be formed without being directly attached to a previous
surface. Hence idiomorphism has been taken in the sense just
described in the study of the ores.

An Occurrence of Native Copper.—One occurrence of native
copper has been discovered. It is not extensive enough to have
sufficient economic value to make the mining of it profitable, but
a study of its origin was found to be of an economic worth.
While the ore bodies themselves have been produced by aqueous
solutions, this occurrence of native copper was produced by
reduction due to the heat generated by subsequent dynamic
action, and a close parallelism was thus found to smelting pro-
cesses, and by chemical and microscopical investigation of the
ore and rocks adjacent to the native metal many of the steps that
have been taken in the reduction are revealed, with the result that
several suggestions were obtained for the actual treatment of
the ores, and thus an opportunity was offered for an improve-
ment in the smelting formulas and some troublesome irregulari-
ties lessened.

University of California,
December, 1904.

UNIVERSITY OF CALIFORNIA PUBLICATIONS
BULLETIN OF THE DEPARTMENT OF

GEOLOGY

Vol. 4, No. 2, pp. 33-38, Pl. 5 ANDREW C. LAWSON, Editor

A PRIMITIVE ICHTHYOSAURIAN LIMB

FROM THE

MIDDLE TRIASSIC OF NEVADA.

BY

Joun C. MERRIAM.

During the last swmmer an expedition from the University
of California spent some weeks in searching for ichthyosaurian
remains in the Middle Triassic limestones of Nevada. Both Mr.
E. L. Furlong, who directed the work, and Mr. H. M. Evans, who
accompanied him, discovered unexpectedly good material, which
will make possible considerable advances in our knowledge of
these very early forms.

The oldest known Iechthyosaurians of which more than iso-
lated elements or very fragmentary material have been deseribed
are the Mixosaurs of the North Italian Triassic. They were
obtained from beds which have been held to represent the upper
portion of the Middle Triassic. The oldest American Ichthyo-
saurs of which more than the vertebrae have been described are
the Shastasaurs and the accompanying types from the Upper
Triassic of California. Up to this time the limbs and arches of
the North American Middle Triassic forms have been known only
from seattered bones, the description of which has been withheld
until more satisfactory material should be obtained.

Among the specimens discovered this year is one which shows
the anterior half of the vertebral column, one side of the pec-
toral arch complete, the first two segments of a pectoral limb,
~ and nearly the entire skull. It was found in the Middle Triassic
limestones of Cottonwood Canon by Mr. H. M. Evans. As

34 University of California Publications. [GEOLOGY

nearly as ean be determined, these beds seem to be somewhat
older than those from which the Mixosaurs of the Italian Trias
have been obtained. From the limestone horizon exposed in
Cottonwood Canon two saurian species have been described by
Leidy.* Both were founded upon portions of vertebrae neither
the generic nor specific characters of which have yet been satis-
factorily determined. The most common ichthyosaurian species
in these beds shows a strong similarity to the imperfect speci-
mens designated as Cymbospondylus petrinus by Leidy. The
specimen described here is tentatively referred to that species.

The greater number of the Ichthyosaurians showing primi-
tive limb strueture which have been described up to this time
have been very small forms, and a suggestion of doubt may rea-
sonably have been entertained concerning the probability of large
forms from the same beds showing these archaic characters to
the same degree. The earlier representatives of most groups are
small, and in such forms primitive characters appear frequently
when they would not be present in larger members of the same
croup. It is, therefore, a matter of some significance that the
specimen under consideration ranks among the larger Ichthyo-
saurs, the skull measuring’ at least a metre in length and the
humerus 280 mm. in length.

The elements of the pectoral arch and the limb were found
in nearly the position in which they are figured, Pl. 5, excepting
the scapula, which had been partly inverted.

The pectoral arch differs from that of all ichthyosaurian
genera heretofore described. The coracoid is sickle-shaped, with
a convex anterior border and an acute posterior angle. A fora-
men of considerable size is situated a little in front of the prox-
imal articulation. This element differs from the coracoid in
Mixrosaurus and in Shastasaurus in possessing a convex anterior
border, while in both of the other genera the proximal end is
narrowed or pedunculate and the anterior border concave in part.
Excepting the presence of a distinct perforation, the form is
much the same as in the coracoid of the recently described Delphi-
nosaurusy from the Upper Triassic of California.

*See Bull. Dept. Geol., Univ. Calif., Vol. 3, No. 4, p. 104.
yAm. Jour. Sci., Vol. 19, p. 24, Jan., 1905.

a

Vou. 1] = Merriam.—A Primitive Ichthyosaurian Limb. 35

The scapula is very stronely curved laterally to accommodate
itself to the curvature of the body. The anterior and posterior
borders are broken somewhat and may have extended out into a
hook on each side, as in most of the Triassic forms. The outer
border is practically entire and is nearly straight, giving the
element somewhat more of the form seen in the true Ichthyo-
Saurs.

The clavicle is very large and heavy ; much broader and more
robust than in Mirosawus. The median end appears to have a
large facet for the interclavicle, but, strangely enough, that ele-
ment has never yet been clearly seen in any of the numerous
Ichthyosaurians obtained from the West-American Triassic.

Taken as a whole, the pectoral arch resembles that of Delphi-
nosaurus more than it does that of any other form. As will
appear later, these forms also show evidences of affinity in the
structure of the extremities.

As much of the pectoral lunb as is known shows more resem-
blanee to the type seen in Mixosaurus than to any other form.
The Lumerus is of much the same type as in Mixosaurus, but 1s
if anything a little more slender. Of the two humeri figured by
Repossi* the principal illustration (fig. 2) represents an
extraordinarily long and narrow form. In the other speeimen
(fig. 1), as in still others, the humerus is almost as broad as it
is long.

The epipodial elements are relatively long, as in all of the ear-
her Ichthyosaurs, and the space between them is very broad. The
radius is, so far as the writer is aware, the narrowest specimen
known in the Ichthyosauria, and the constriction of the median
or shaft portion is pronounced. The ulna shows the most primi-
tive form known in this group, and at the same time presents
certain rather peculiar characters. In all other Ichthyosaurs.
excepting Delphinosaurus, the postericr border of the ulna is
expanded and usually convex. In these two forms it is concave
or notched, lke the outer or anterior border of the radius; and

*Atti Soc. Ital. Sc. Nat., Vol. 41, Pl. 9, figs. 1 and 2.

7It would appear to the writer that Repossi’s figure 4, Plate 9, loc. cit.
represents a femur rather than a humerus. It has the form of the femur

in other specimens and does not resemble any other deseribed mixosaurian
humerus.

36 University of Californa Publications. [GEOLOGY

the median portion of the ulna is drawn in from both sides,
showing a true constriction. In Delphinosaurus this constric-
tion appears somewhat stronger than in this specimen, but the
ulna is much shorter and broader, and the first two segments of
the limb are, in general, more specialized.

On both the proximal and distal ends of the ulna the thick,
cartilage covered portion of the margin extends far back toward
the middle of the posterior side. The thickened margins come
so near to each other that the posterior notch is made quite nar-
row. At the distal end this part reaches around quite to the
middle of the shaft, reminding one of the surface against which
the pisiform rests in Mixosaurus. At the proximal end the sur-
face makes a sharp turn, forming a face which looks as if it
might have supported a small supernumerary bone.

With another specimen of the same type as that described
above there is an element appearing to represent either a fibula
or an ulna showing a very primitive form. The shaft is nar-
rower and the articular surfaces of the two ends are not swung
back as far is in the specimen figured here. If this is really an
ulna, it represents a stage more primitive than that described
above.

Unfortunately, we have no very definite evidence concerning
the character of the phalanges in this species. With both this
specimen and the one from which the simpler form of ulna was
obtained, there are several rounded ossicles resembling carpals.
It may be that they are really reduced phalanges which rested
in cartilaginous pads as in Baptanodon. If this be true, the gen-
eral primitiveness of the limb would be reduced by some degrees;
even in that case, however, the fact that the propodial and epi-
podial segments of the limb had failed to adapt themselves per-
fectly, even when the manus had become specialized, would tend
only to show more distinctly the influence of an ancestry in which
locomotion by crawling or running was more common than by
swimming.

As far as we know it, the type of limb found in this specimen
is more primitive than any heretofore described. The humerus
is hardly more slender than that of certain other Triassic forms,
but is among the most slender known, and is not more abbrevi-

©

Von. 1] Merriam.—A Primitive Ichthyosaurian Limb. 37

ated than that of Mixosawrus. In the epipodial region, where
specialization of a high degree appears in the later members of
the order, we find a strueture which is somewhat more primitive
than any which has previously been observed in the Ichthyo-
sauria. This is a particularly significant fact, when it is noted
that the beds in which this specimen was found are probably a
httle older than those from which we have obtained the most

ancient known Kuropean specimens showine the limb structure.

University of California,
February, 1905.

EXPLANATION OF PLATE.

Figure one-siath natural size.

Cymbospondylus petrinus Leidy (?).

Pectoral arch, external side; anterior limb, inferior side. R, radius; U, ulna.
The constriction of the ulna is immediately above the letter U.
The broad, cartilage covered marginal faces of the ulna are
discontinued suddenly at the upper and lower ends of the pos-
terior emargination.

Vi© A ae ee)

BULLE, DEPT, GEOL, UNIV. CAL.

\ SS

2 AWW

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PE=_ ZB
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UNIVERSITY OF CALIFORNIA PUBLICATIONS
BULLETIN OF THE DEPARTMENT OF

GEOLOGY

Vol. 4, No. 3, pp. 39-87, Pls. 6-7 ANDREW C. LAWSON, Editor

A GEOLOGICAL SECTION

OF THE

COAST RANGES NORTH OF THE
BAY OF SAN FRANCISCO.

BY

VANCE C. OSMONT.

CONTENTS.

PAGE
MG ROGNIGELOMS areca cicucucseeenmersters cetvenseavee oe orisvaeeveweomm nits dunner ennere estat 41
eG C1S Cai amen eanae PnP MENESTSDE sh tie ental iter 5 nets rs ewate gc, Scie, 42
Sedum entaniGs mem en.. ca ne Mokena os Go ac eae ao eae etinte acme alone aden 2
BO CeO ae) FOMUCC renee orcne aey tener eee re ae cys seri remit airy ¢ Serienekel aabenieianaee 43
HVC UA ST CES gr aece ae veent seerctcsenswueraisys wo seainieienwes's Sen pera, acebape Brak acoee we 43
PELE Ovni TD I hy aera ieeree Mem evap ete eoetetiaeess Mevestett cc jcent fen eemrens castes eauaasyeteremcdeter 2 44
SBVOUUGEC AD LOTUUC! © eters carne, sustes fccie ceveee secs) eoegeueiehoue cewiaencvalans uecnlacs dels 44
QUsMuZBVOULte LOI Le Maer me eters acre terse ee teneiel © ues: cae loe cae 45
Olive saKer Hl WORD GES: oon co sens ola open eG nao otc © Gorman oo 46
Basic Secretions ...............0. ee CP gn a eee arr ee 47
PAN CUCMBIID) Va OS Mmre skews teeye ts ete lorh tue sreies cetsscats ers anes se gs loss Sab, Suasederoeas aa 47
(Come arora a0 Cl Ate aes oteeg acceso steven ster seees de ations aiere arenes = Suees aeheveas-enalss 48
AUN AT GUSCAN Emre. Corea ea tiaiee toe cute cat aida mb Gems den nein Sect we 48
Gonstibiwen tect Onin AtlONS eee ease acne sg as ase ipa aw eae snes leis ceo 48
PAT Cay PLD IS GTO TUGLO We eecece-meiteaa are rue oteee = fecceel ee cueee wie Muereneieye.n car foear ea case 49
Quivolesilhiere Jenn aoc anno bon hen oon v4 ooo mo pei oe oe 50
hats Ga Ohi Comers eace tweens. geste ee cus er auee.ss ins Sosneuny tee Mrassus, Stans elect emitinayts 2 co muetens 51
Tr tholo orally CHavace er, see geass sects us ae rereneter es chs epsuatese) shel oie sates 51
SS GREG MO Mel TO li vaaerewscens ney sesedeesc cercueas corsa MUevsde vende wunsnee unions gay ae RAzasae 51
FING OMe ete seets tec c re eee eM eet, pay ege Vey ses ere eye easement con koe yee Gia tee tae ys}
Yellow Sandstones on Carneros Creek...........0. 00. ce eee eee Be
EIQ TUL CTC Yammer ats Se oy We san sPs ns aucusnemeessene ame snitersie a. oe legates: 53
Point Reyes Peninsula 53
Soma LOW ast ceennis Sones, cute eieee es Oeecent Aue Acacia ais Heautie aueie KS a eesar 54
Blue Sandstone (tuff) of Carneros Creek....................25- 54

40 University of California Publications.

iM eee AON DADO Ooo oy oRa ors Con uOdtonOON Romo HOA
Sieuiles or Volkov Cr) ee rare en Ae OOO e bono ain Uda ne o-c
Pre-Volcanic Beds near Freestone ............2 2.0 eee eee
Pre-Voleanie Bedse at) Mremtome cya s+ ctenseeiees iene nel caste yer euevereuees
Pre-Voleanie Beds of Pleasant and Capay Valleys..........
INS Matin ean Oe ano oo hon poe one du ee mourn oo me.cl5t
Oram ane WGP es seiewnct cre cucre eee sence esotc eens omee gegeastaeererse ote stat) eb orer home
Red Gravels of Santa Rosa Valley................-.+-++2005
Sedimentaries Beneath Andesite on Petaluma Creek.........
iiomitic: Beds of Whawlon’s: Ramchi2 e220. cre oles oss ererestenst=
Lignitie Beds of Mark West Creek..................0.0005
PAIGE ahed ste, cbeaels hake ret darken iol cersecest asus tickets eae genees omer emeron eee Se men Rn aoueR
MLAter UBMO CEN ay ak.k tees chens cooraente cee one da eneru eaten cn een ia de eine gatee
Mark, Wiest Amde@Site: sani i acto ccetuse wel oo csneeaieeele cue aienasnens aavenws
Areal Distribution and Thickness ...............00 eee ee
StU Chur oo aece eset Ws tuetnleie es buen ayaa ayace dena aye eee: avenue biel meeendcateuseets
PAO OA coeices eich at eea cs tie legate covcdescsantyeten aietenet sve opsncber sk uebe east seat Mer ta Meas
IMamQyar yy Lasianen obo macmoedsoueheboudda dooomo ate
Sonoma, CLUE sec ceke ies coe corsesmsne-ececeneya cre ser sfeheier epeven saseene aya qieSoe auemeneee
Charactersot dhe: Mitt aise eea-ccstaysccl coeveretercisceasacre aceucmereueh spe nerees
Aveal Distributiom and! Whickwesss. 2 <ercuers ot -ceeten-te sha seep ees
Interbedded Sandstones and Conglomerates .............
Lava Flows Within the Sonoma Tuff..................0.
IEPA Oe Banner ceo ceed he otra bn as coob oh ome 060s
UCN een 8 armen ey Geko paca oaand ceil Oso tid PEO On Gon penton
Marine Beds of Wilson’s Ranch...........5...-2...050+--
Tntholo pica Charac ber ieaspe crane secnsenenciepenetete tyes atetaneee en sate e
Areal Distribution: acon csccctrostasuc ners cone seaet sie, -anemeneereneens
Morse chikoh (Opal Atop omhA o oonnn eo onndo odd amesone one os

Sti. Helena Rhyolite: 5 21sec acim enacts mite aps sey atene eae

Field Aspects, Areal Distribution and Thickness

Quarter ay ae. carenetatstenersnencestercle sei honsesttal Peatea eA teaser Weel Weee en eae tea
Tomales Bay Deposits sp. 65. cc oes ai eseei se aisiys aeeace scutes
Bodega Bay Deposits, Wat svsictenis syntocteter-scietensacne sus-suentenenseereeeees
Filood-Plain WDepositsi crs cterctar. suche cnstre. tere cvoneneae mauen seh aieeenanee ys

DEMUCHUREY sass sonarus Grace chelates oN) saat e eka ee Wane ee ae eae
Bolding=of the Werced Weep. siesta scene erence,
St: lelena “Walt... 28 Son awe orate oeares ea eee ney eenee eateries

NOC) 6 decane Saute) aputelra s eccneaktacacavcr cat ueews Oreietaeec ne es eis oR eect ee eae

Betro oraip hiya is vsentecs ters cociersa-enoa sete nte acon eF a eegee Eee esp te eicacm rece
Becket/s) SS: Asperite sarc yandetencesoncusvesieps oust sneuscouet paebeieneteps
Agecot the: Above :Seriesssilee ets ec vescpoeed ea eene a aiereie eG eetregs
EDT CKMESS cater cro toeerernetbe Fates etucpedoncPerepeaseetsn nea brace gene eaters

GO) i cere she eictecd scare 84. «, at aeueleye oud ove case Cer ciedeye aRoie Sieve os Soo

[ GEOLOGY

Bre hic 54

ee 59

Vout. 4] Osmont.—Geological Section of Coast Ranges. 41

PAGE

FEOMOLPNOLO PY. Oss sgen cle aeec. «cenecin selene sviaie oy erup ccelebanestetier et apatie “ete (eles reeis 80
The Elevated. Coastal Peneplain.............s0scenscenceteerere 80
Wide, Flat-Bottomed Valleys of Erosion ................+22005- 80
Synclinal Valleys and Subsequent Drainage..................... 80
IWiaminve mR CLTACCSW same rcarets aicstQeucncneronatadetsts sl Susts nach etal anetitoveys Gmc ienanaTt at 81
IPpnvihe Ohaverunl CE MVE this Melee a ae no 5 ocd eo omoo de ann onan 82
MRECentmS WOM STO CMCC Mec a axe clere tases el siete ere ete nie = (eeisiiesberens: © exe ste vere etenene 82
Geomorphi cay clemency. sae ops cuse ease eile tele ci mone elevate eleteheun auelerecn exe 83
FELL SCOTCH HRESWING ancy te te ee aye) sieves cs ore yehas ays ye Seatenaie Aieleee eno @usia eae seats 83

INTRODUCTION.

The work of which this paper is the outcome was undertaken
during the Fall of 1901, when the writer was a graduate student
in geology at the University of California. The subject was sug-
gested by Prof. Andrew C. Lawson, who rendered the writer
invaluable assistance by his advice and personal supervision of
the work, which has oceupied the latter’s spare time for the past
three years. Acknowledgments are also due Dr. J. C. Merriam,
Dr. Gidley, Dr. W. J. Sinelair, and C. E. Weaver for palaeon-
tologieal aid.

No topographical maps of most of the area being available,
county maps had to be used, and since these represent the topo-
eraphy poorly or not at all, it was not found feasible to map in
the areal geology.

Two continuous cross-sections were made. Section AB starts
at the south end of Bodega Peninsula, and runs in a northeast
direction across Bodega Bay, through the towns of Bodega and
Freestone, through the low hills east of Freestone, across the
Laguna de Santa Rosa, and enters the broad valley of Santa
Rosa a little north of Sebastopol; crosses the hills west of this
valley about midway between Windsor and Mark West Creek:
passes through Mark West Springs, crosses the watershed of that
ereek, passing about two miles north of the Petrified Forest ;
crosses Franz Valley and the high ridge east of it, and comes out
at the low divide on the southwest flank of Mt. St. Helena, which
separates Knights Valley from Napa Valley; thence it’ swings
somewhat more to the north through Mt. St. Helena, and thence
in an easterly direction across St. Helena Creek, passing a little
north of the Oat Hill Quicksilver Mine, following approximately

42 University of California Publications. [GEOLOGY

the boundary line between Napa and Lake Counties to Knox-
ville; continuing in this same general northeast direction, pass-
ing through the high ridge between Knoxville and the north end
of Capay Valley at Rumsey, and thence through the low rolling
foothills to the Sacramento Valley and Arbuckle, a distance in
all of about eighty miles.

Section CD starts at a point about midway along the west
shore of Point Reyes Peninsula, and runs northeast across To-
males Bay, continuing over the high ridge and rolling foothills
for about fifteen miles, to the valley at Petaluma, thence, swing-
ing a little more to the eastward, it passes through a low series
of hills and crosses Sonoma Valley, some three miles south of
the town of Sonoma; thence northeast to Napa City, continuing
across Napa Valley, through the high ridge to the east to Wooden
Valley and the upper end of Gordon Valley; through the promi-
nent ridge separating the latter from Pleasant Valley, and thence
through the rolling hills to the Sacramento Valley at Winters, a
distance in all of about sixty-five miles.

Together the sections enclose an area of about fifteen hun-
dred square miles, and since, as displayed in the graphical repre-
sentations of the sections, there appears to be a well marked con-
tinuity of formations, it is believed that the geology is fairly
typical of the Coast Ranges for a considerable distance north
and south of the lines chosen.

The geological formations encountered in these sections range
from pre-Francisean to Pleistocene. They will be described in
chronological order.

PRE-FRANCISCAN.
SEDIMENTARIES.

The oldest rocks known anywhere in the territory are a few
small remnants of limestone and crystalline schists deseribed by
Anderson™ in his paper on Point Reyes Peninsula. According to
him, they consist of a ‘‘ Marble similar to the white crystalline
limestone of Montara Mountain and the limestone of Santa Cruz
and the Santa Lucia Mountains.’’ Associated with these lime-
stones is quartzite, and at another place mica-schist and wollas-
tonite schists are found overlying the granite.

*Bull. Dept. Geol., Univ. Cal. Vol. 2, No. 5.

BUEN DERITS GEOL UNIVE CAL,

HILDERS P)

a
\f Ave
“yCOB8 MT 24a
x

fliddiaton
INE’ MT Me
GAN

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servile

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' t aJ\o
MT-ST.HELEN 7

pore west "Ke
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Pr. BONITA

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FARRALONES ISLANDS Pr.Losos
o

SAN FRANC/SCO

Index map

of the Coast Ranges north of the Bay of San Francisco,
showing the lines of Sections examined.

oo

«

Vou. 4] Osmont—Geological Section of Coast Ranges. 43

The age of this ancient series can only be guessed at from its
relation to the granite which is intruded in it, as no palaeon-
tological evidence is available. From considerations which will
be mentioned later this granite is believed to be of post-.Juras-
sic age. Hence the above mentioned strata cannot be later than
Jurassic.

BODEGA DIORITE.

Bodega Peninsula is made up almost wholly of a biotite-
diorite. Toward the north end of the peninsula this disappears
from sight under wolian sands, and the coast line to the north
of Salmon Creek is made up entirely of Franciscan sandstone.
The east shore of Bodega Bay is entirely Francisean.* To
the south, however, Point Reyes Peninsula is composed very
largely of this same diorite and granite, while a comparison with
the geology of the coast to the south shows that this is only a
northward extension of the plutonies occurring at Montara
Mountain,; on San Franciseo peninsula, and at Monterey, which
are intruded in the old erystalline schists and limestones above
mentioned.

FIELD ASPECTS.

The best exposures of the diorite occur on the ocean side of
the Bodega Peninsula at the south end. Here it stands up in
steep cliffs fifty to eighty feet high. It weathers deeply, and
this makes it extremely difficult to get fresh specimens for exam-
ination. On account of the large amount of coarse mica present,
it frequently shows a white honey-combed surface, resembling
coral. Basie secretions are very abundant. They vary in size
from a few inches up to six feet in length, and are usually lentic-
ular in shape, having their longer dimensions more or less par-
allel and pointed in a westerly direction, suggesting pressure at
right angles to their course. Dikes or veins of aplite, pegmatite
and quartz occur. A very prominent pegmatite dike seven feet
thick is exposed on the southeast side of the peninsula, while
numerous smaller ones may be seen on the west shore. There is
a general westerly trend also to these dikes. That a large amount

*Anderson, Bull. Dept. Geol., Univ. Cal., Vol. 2, No. 5.

7Sketch of the Geol. of San Francisco Penin. Lawson, U. 8S. G. S., 15th
Ann. Rpt.

44 University of California Publications. [GEOLOGY

of movement has taken place is abundantly shown by the sheared
and crushed appearance of the rock in many places and numer-
ous small faults displayed by the veins of quartz and aplite. So
much movement indeed has affected these rocks as to render them
utterly unfit for quarrying purposes. In this small area no rem-
nant remains of the schists and limestones into which the gran-
ites are intruded at Point Reyes and to the South.
PETROGRAPHY.

Two varieties of diorite occur on the peninsula—Biotite-dio-
rite and Quartz-diorite. The first variety 1s very abundant, the
second is searce and represented only by a few loose fragments
found near the north end of the bay.

Biotite-diorite.
crystalline rock, made up apparently of only two minerals in

Maecrosecopically it 1s a coarse grained holo-

about equal proportions: a sugar-white feldspar and a dark green
mica. The flakes of mica occur up to 6 mm. in length, and the
ordinary length of the feldspar is about 4 mm.

Microscopically this rock is seen to consist of the essential
minerals biotite and a soda-lime feldspar as determined below
in about equal proportions, together with the accessory minerals
apatite, magnetite and titanite, apatite being very abundant, and
a large amount of decomposition products in the shape of kaolin
and chlorite.

The twinning lamellae of the feldspars are very unequal in
size, very coarse lamellae alternating with very fine ones. Single
crystals, however, sometimes show fine, equal sized lamellae,
together with a system of alternating coarse and fine ones. Albite
twinning is the rule, though an additional pericline twinning
was observed in some eases. Carlsbad twinning also occurs.
Wavy extinction 1s very common and shows that the rock has
been subjected to great strain.

By Michel Levy’s statistical method a maximum angie of
20° was obtained on the albite twinning plane, corresponding to
a feldspar of the composition between Ab. An, and Ab, An,, or a
medium basic andesine.

One section was found which could be utilized for M. Fouque’s
method for determining the feldspars on sections eut perpen-
dicular to a bisectrix. This section gave an angle of 22° 16’

VoLt. 4] Osmont.—Geological Section of Coast Ranges. 45

between the trace of the plane of the optic axes and (010). This
value on the », curve corresponds to an acid labradorite.

Some of the rock was crushed and cleavage flakes of the feld-
spars selected. On examination under the microscope certain of
these sections parallel to P, and showing albite lamallae which

)

extinguish symmetrically, gave the extinction angle 5°. They
also showed the emergence of a biseetrix very inclined to the sec-
tion. If this angle is negative, it corresponds to a composition of
Ab, An,, according to Schuster. Sections showing no twinning
lamellae and rhombie in form gave the following angles, 10°,
10°, 914° and 6°, and extinguished in the acute angle of the
rhomb. Hence, the angle is negative. Ab, An, corresponds
to 5° 10’, while Ab, An, gives 17° 40’. Hence the determination
points to a composition between Ab, An, and Ab, An..

In order to determine the specifie gravity of the feldspars
the erushed rock was put through an 80-mesh sereen and caught
on a 100-mesh. Thoulet’s solution was used. At 2.652 about
two-thirds of the feldspars remained suspended, though they all
sank at 2.645. The temperature was 1514° C. On concentrating
the solution the heavier feldspars became suspended at 2.675.
The average specific gravity given by Rosenbusch-Iddings for
andesine is 2.65, and of labradorite 2.69, hence this checks very
well with the optical determinations. It also shows that quartz
and orthoclase are absent.

The biotite presents no novel features. It is strongly pleo-
chroie, the color for ¢ being dark reddish brown, b dark reddish
brown, and @ straw yellow to yellowish brown. The absorption
isC=b >a. The biotite occurs in irregular plates with frayed
edges, and the cleavage lamellae frequently are bent, due to
shearing in the rock. It is usually altered around the edges to
green chlorite. Magnetite occurs sparingly as inclusions, and
occasionally titanite. Apatite is abundant, both included in the
biotite and in the feldspar. A small amount of green hornblende
was observed in one slide.

Quartz-Biotite Diorite—Macrosecopieally this rock is seen to
be a coarse grained holocrystalline rock, made up principally of
white feldspar and a dark green mica, the feldspar forming about
two-thirds of the bulk of the rock. The ferro-magnesian minerals

46 University of California Publications. [| GEOLOGY

occur in smaller flakes than in the mica-diorite above described,
and the rock accordingly presents a harder surface to the weather.
Its specific gravity is 2.731.

Microseopically the essential minerals are seen to be a soda-
lime feldspar and biotite, a small amount of quartz and green
hornblende and a little orthoclase. The accessory minerals are
apatite and titanite, and the decomposition products kaolin para-
gonite and chlorite.

The feldspars are not very fresh, but are much clouded with
kaolin and paragonite. Favorable striated sections gave by M.
Levy’s statistical method a maximum angle of 19°, indicating a
medium basic andesine of a composition of about Ab, An,.

One section was found twinned on both the albite and the
Carlsbad laws upon which M. Levy’s method of concurrent angles
was used. It gave the extinction angles 8° and 18°, indicating
a section of andesine (Ab, An,).

Some of the feldspar sections are free from albite twinning,
and look like orthoclase. Some of these are rhombic in shape,
and three eave the angles — 12°, — 24°, and —15°. These see-
tions were probably eut parallel to (010). The negative sign
precludes the possibility of orthoelase, as also the large angle
24°, orthoclase’s maximum extinction angle being 21° against c.

Orthoclase is, however, probably present in small amount.
Certain sections show inclusions of plagioclase with poikilitie
structure, all the plagioclase inclusions extinguishing at the same
time.

The biotite is identical with that of the mica-diorite above
described. It contains little magnetite, its principal decompo-
sition product being chlorite.

A small amount of green hornblende is present, which seems
to have erystallized later than the biotite.

Chemical Analyses——Two analyses of these rocks were made
by the writer. No. I. is the biotite-diorite, and No. II is the
quartz-biotite-diorite.

Vow. 4] Osmont.—Geological Section of Coast Ranges. Aq

No. I No. [I

SiO. 58.44 63.12
ALO, 17.06 16.13
MeO, 1.36 ahaa}
FeO 5.06 3.65
MgO 2.96 1.86
CaO 5.82 5.04
Na.O 3.40 2.78
K.O 2.84 1.08
HO +- 2.12 .93
HO .38 97
Mi@s 15 trace
P20; 1.41 aS)
MnO 50 38
Sie eee .03
Motaliae. aes s 101.50 99.89

Basic Secretions.—Maeroseopically the basic secretions are fine
grained dark rocks, containing, apparently, a much larger pro-
portion of ferro-magnesian minerals, and being of greater spe-
cific gravity. They vary from medium to very fine grained.

Mieroseopieally this rock is seen to be holoerystalline and fine
grained, and made up of a plagioclase feldspar and green horn-
blende in about equal proportions.

The feldspar, though later than the hornblende, occurs in
fairly well shaped lathes, almost always showing albite, and fre-
quently also pericline and Carlsbad twinning. Several sections
showing both albite and Carlsbad twinning, and cut perpendic-
ular to (010), were reeognized, and these were utilized for M.
Levy’s determination by coneurrent angles. One section gave
the angles 2814° and 14°, corresponding to a section of labra-
dorite (Ab, An,) cut at an angle of 20° with (101). Another
gave — 25%2° and —1714°, showing labradorite (Ab, An,),
making an angle of 10° with (101).

Fouqué’s method for sections, cut perpendicular to a bisec-
trix, gave an angle of 23° 15’, which corresponds to a medium
basic labradorite on the ng curve.

Acid Dikes——Dikes of pegmatite, aplite and greisen are
abundant, but no microscopical study was made of them. In the
field the pegmatite was seen to be a very coarse grained rock made
up of large crystals, up to more than an inch in diameter, of
orthoclase quartz and muscovite. One section of the orthoclase
afforded a beautiful illustration of cataclastie structure.

48 University of California Publications. [ GEOLOGY

CORRELATION AND AGE.

The above described dioritie rocks of Bodega and Point
Reyes peninsulas occupy but an insignificant part of the surface
area of the territory under discussion, but from evidence at Point
Reyes Peninsula, and elsewhere, it is probable that, together
with what remains of the crystalline schists and limestones into
which they are intruded, they underlie a large portion of the
Coast Range. Their similarity, both chemically and mineralog-
ically, to the granites of the Sierras, points to their being an
outher of the latter.

The evidence as to age of these rocks is not conclusive. If
they are outliers of the Sierra granitics they are post-Jurassic,
since Lindgren* and others have shown the latter to be intrusive
in Jurassic strata. But we know that they le uneconformably
below the Franciscan, and the age of the latter is still a moot
question, some geologists not being prepared to admit so recent
an age for it as lower Cretaceous.

FRANCISCAN.

Constituent Formations—tThis series consists of the usual
elements so well described by Lawson in his Sketch of the Geology
of San Francisco Peninsula.t Briefly they consist of hard mas-
sive gray sandstone, weathering yellowish brown, known as ‘‘San
Francisco sandstone,’’? from its prevalence on that peninsula;
soft gray shale interbedded with sandstone and occasional fora-
miniferal limestone or with radiolarian chert; massive radio-
larian cherts in various colors from white to red; intrusive masses
of basalt, having peculiar spheroidal forms, and known as ‘‘spher-
oidal basalt’’: together with local variations in the forms of dia-
bases, and even of gabbros; also pyroxenites and peridotites as
intrusive dikes, sills and laccolites, usually almost entirely altered
to large masses of serpentine; and lastly metamorphic contact-
zones of glaucophane, actinolite, or mica-schists. It forms the
basement upon which the later rocks of the Coast Ranges rest,
and, wherever seen, shows evidence of having been repeatedly
sheared and contorted by the many movements which have
affected the latter.

“U.S. G. S. Geologic Atlas, folio 66, Colfax, Cal.
7U. S. G. S., 15th Ann. Rpt.

vot. 4] Osmont—Geological Section of Coast Ranges. 49

It was not found practicable to work out in detail the strue-
ture of this formation, though with good maps and careful work
it probably could be done. The whole series has been displayed
in the sections as a unit.

Areal Distribution—As regards its distribution within the
territory under discussion, it is found in one small and four
large areas. The most westerly of these forms a large part of
the high ridge, following the coast line from Mt. Tamalpais
northward through Marin County to the Russian River, and
northward, except that part occupied by the granitics previously
described. This Franciscan area varies in width from eight to
fifteen miles, and forms a high coastal ridge, with a very even
erest line, at an elevation of 1,000 to 1,200 feet above sea level.
Being for the most part composed of rather hard roeks which
resist erosion well, the canon topography is frequently rugged,
and the hillsides usually dotted with clumps of gray boulders
of hard sandstone or chert, while trees seem to grow better upon
the soil furnished by these rocks than upon that of the later
formations. A trained eye can easily distinguish at a distance
this formation from the smoother, more rounded contours and
treeless aspect of the overlying Tertiary sedimentaries.

The second Franciscan area 1s a narrow strip about two
miles wide, which forms the core of the range of hills between
Santa Rosa and Napa valleys. Its extension north of a point
about two miles north of the Petrified Forest, where section AB
crosses, 1s not known to the writer, but it is found in the hills
to the east of Rincon Valley, near Santa Rosa, but does not
appear at the surface in section CD between Petaluma and Napa,
it being covered over by Tertiary sediments and voleanies. At
the waterworks, two miles east of Napa, a well sunk through the
andesite encountered Franciscan chert at a depth of 1,500 feet.

The above mentioned area is worthy of note, since there is
evidence to show that in the vicinity of the Petrified Forest at
least, dry land existed during the period of voleanic disturbance,
which will be shown presently inaugurated the later Pliocene
Section AB passes through this area, crossing it at a point about
1,300 feet above sea-level. Large pieces of petrified wood lie
strewn along the flanks of this ridge where the pumicious tuff

50 University of California Publications. [ GEOLOGY

of the later Pliocene overlies the Franciscan, and on the same
ridge, two miles to the south, large petrified redwoods, ten feet
in diameter, and fully 500 years old, as shown by their rings,
are lying on a Franciscan surface covered with pumicious tuff.
Of some eight or ten trees observed, all lay with their roots
pointed toward the northeast, the natural inference being that
they were uprooted by a blast of air from some voleano to the
northeast, and subsequently buried in the pumicious ashes in
which they now lie. Another argument in favor of this ridge
having been an elevated portion of the land during Phocene
times is the absence of andesite on both of its flanks, when two
miles to the west, and five miles to the east, thick flows are found
beneath the tuff.

A third small area of Franciscan is exposed on the southwest
flank of Mt. St. Helena, low down on the divide between Knight’s
Valley and the upper end of Napa Valley. It is exposed here
by the faulting which has tilted the block forming Mt. St. Helena,
and is quite limited in extent. It is largely made up of serpen-
tine. .

A. fourth area lies on the northeast flank of St. Helena, along
St. Helena Creek at Mirabel and Middletown, extending north-
west toward Cobb Mountain.

A fifth large area is near the last mentioned one. It oceurs
at the Oat Hill Quicksilver Mine, and extends to Knoxville, and
occupies a large area west of Berryessa Valley.

Quicksilver Deposits.—The last two areas mentioned contain
important deposits of cinnabar. These deposits occupy the west-
ern part of the two areas last mentioned in a general northwest-:
erly and southeasterly direction along the eastern flank of Mt.
St. Helena and its outhers, Twin Peaks and Round Valley Peak.
The cimnabar deposits are invariably associated with serpentine,
and usually oceur at contacts between serpentine and sandstone,
or crushed shale (‘‘alta’’), or rarely radiolarian chert. The
veins are not true veins at all, but merely zones of silicified ser-
pentine. The silica is in the form of opal, and has largely
replaced the serpentine, the opal containing the cinnabar and
metacinnabarite. The opalized areas are from a few feet to
over two hundred feet in width, and very irregular in shape.

Vou. 4] Osmont.—Geological Section of Coast Ranges. 5]

While the richest ore is usually at the contact between the opal-
ized zones of serpentine and the sandstone or shale country rock,
there are sometimes large bodies of low grade ore directly within
the opalized area and many feet away from the contact. One
instanee* is known where the ore body consists of radiolarian
chert, along a contact with serpentine, which has been filled with
veinlets of opal carrying cinnabar.

Serpentine is very abundant throughout all the above men-
tioned areas, but it was not found practicable to map it. In some
cases, especially near Knoxville, the masses of serpentine are
more than a mile in width, their great size seeming to preclude
the idea of their being dikes and to suggest that they must repre-
sent intrusive sills or laccolites.

SHASTA-CHICO.

The eastern portion of both sections is largely made up of
Cretaceous shales and sandstones, most if not all of which prob-
ably belong to the lower Cretaceous or Knoxville series.+

Lithological Character.—This series consists of an enormous
thickness of rather hard tawny yellowish sandstone, interbedded
in monotonous succession with dark blue fissile shales, with oeea-
sional thin beds of dark blue limestone. The sandstone strata
are usually less than two feet thick, and almost never more than
ten, while their regular alternation with soft shale made the bed-
ding very distinct and characteristic.

Stratigraphy—While standing at high angles, these beds do
not show any important faulting alone either of the sections.
From near Knoxville, where they appear to overlie a large
laccohte of serpentine, they extend in unbroken suecession
with steep northeasterly dip, to the head of Capay Valley, at
Rumsey, where they are covered by ‘Tertiary gravels and sand-
stones. The average angle of dip from Knoxville to Rumsey
cannot be less than 45°, which would give the series a thiekness
of four miles, and this does not represent the whole of the accumu-
lation of sedimentary beds, since the upper limit is not exposed

*“Noted by Lawson at the Great Western Quicksilver Mine, Napa County,
and communicated verbally to the writer.

7Becker, Mon. XIII, U. 8. G. 8. Quicksilver Deposits of the Pacific
Slope.

52 University of California Publications. [ GEOLOGY

Eocene fossils are said to have been found near Arbuckle, but
the locality is not known to the writer. Eocene strata may under-
lie the San Pablo(?) gravels and sandstones east of Capay Valley
in the portion left blank on section AB.

As far as physical resemblances go, the Cretaceous exposed
at Rumsey is exactly similar to that near Knoxville, with the
possible difference that it may have a large proportion of sand-
stone and less shale. A magnificent section is exposed along
Cache Creek across the strike of the beds for several miles, and
the writer was not able to find any conglomerate beds or impor-
tant changes in sedimentation to suggest the presence of Chico.
From lack of palaeontological evidence, however, he has not ven-
tured to call all this enormous accumulation of sediments Knox-
ville.

In Section CD an even greater thickness of Cretaceous sedi-
ments is shown between Pleasant Valley and Wooden Valley.
This section represents certainly not less than five miles of strata,
as it dips steeply to the northeast the whole distance, and shows
no evidence of faulting. The Cretaceous of this section, as in
section AB, disappears to the east at Pleasant Valley under late
Tertiary gravels and sandstones, still with a northeasterly dip
and a Knoxville appearance, and for similar reasons the whole
series has been represented as Shasta-Chico. None of the mas-
sive, thick-bedded, cavernous sandstones so characteristic of the
Eocene was observed. Becker* believed these strata to be of the
same age as the Franciscan, considering the latter to be a meta-

‘

morphosed phase of the former, in which the ‘‘ prominent char-
acteristics are the predominance of recrystallization, serpentini-
zation and silicification.’’

Contacts between Knoxville and Franciscan at many places
are now known, which show an unconformity existing between
the two formations. No better illustration of this can be seen
than at Berkeley. Here unmistakable Knoxville shales and sand-
stones containing aucellae may be seen along the lower slopes of
the hills between East and North Berkeley, resting at moderate
angles across the steeply pitching eroded edges of the various
Franciscan members. In both the sections AB and CD the Knox-

*Mon. XIU, U.S. G. S.

Vout. 4] Osmont.—Geological Section of Coast Ranges. 53

ville rests on serpentine at Knoxville and at Wooden Valley.
Wooden Valley is probably near the base of the Knoxville series,
since at the lower end of Capell Valley, about three miles north of
section BB, a bed of heavy conglomerate at least 100 feet thick
oeeurs in the formation. This conglomerate seemed to be made up
practically of Franciscan chert and old eruptives, and of course
points to an erosion interval between the two formations.

TEJON.

Yellow Sandstones on Carneros Creek.—Just east of Carneros
Creek, about midway between Napa City and Sonoma, occurs
an exposure of yellow to buff colored, massive sandstone, ocea-
sionally interbedded with buff colored shales. Apparently it
dips beneath an exposure of blue San Pablo sandstone to the
west, but no good exposures were observed to show the exact
relation. The fossils found here were too imperfect for certain
identification, but at Thompson’s, two miles to the southeast,
directly on the line of strike, in sandstone of identical appear-
ance, C. EK. Weaver has collected and determined the following
Tejon species :

Leda gabbi Con.

Cardium brewert Gabb.

Meretrix wvasana Con.

Tapes conradiana Gabb.

Tellina hoffmani Gabb.

These strata extend only a mile or two north of this point,

and are, so far as the writer is aware, the only strata of Eocene
age represented in his territory.

MONTEREY.

Point Reyes Peninsula.—According to Anderson,* the sur-
face of the orographie granite block of Point Reyes Peninsula
is a Shallow basin or trough, upon which rests a broad syneline
made up of sandstone and the characteristic and well known bitu-
minous shales. This formation occupies large areas to the south
in Contra Costa County and southward, but has not been encoun-
‘tered by the writer in any other part of the area under discus-

*Bull. Dept. Geol., Univ. of Cal., Vol. 2, No. 5.

54 University of California Publications. [ GEOLOGY

sion. At least 500 feet of these shales are represented at Point
Reyes Peninsula.
SAN PABLO.

Blue Sandstone (Tuff) of Carneros Creek.—The only strata
of undoubted San Pablo age occur as the core of the low range
of hills between Sonoma and Petaluma. As illustrated in sec-
tion CD, blue San Pablo sandstone occurs on Carneros Creek. It
consists of the peculiar and very characteristic bluish to grayish,
rather soft sandstone, exactly similar to that deseribed* by Tur-
ner from Mt. Diablo and Corral Hollow, which is so common in
the Coast Ranges to the south. It is really an impure andesitic
tuff. It varies from a gray to deep blue in color, and from a
coarse, massive rock to thin bedded shales. At the point where
section CD crosses it, it dips at 50° to the southwest and is over-
lain uneonformably by the Mark West andesite.

Age.—This formation is unique in appearance, and of wide-
spread distribution throughout the Coast Ranges south of this
territory, it also occurring on the west flank of the Sierras, where
it is placed in the Ione formation. Even without the aid of fos-
sils it can be unhesitatingly referred to the San Pablo, but at
Carneros Creek a good bed of shells of this age exists. So far
as the writer is aware, this is the most northerly locality in the
Coast Ranges at which it has been encountered.

SAN PABLO (?).

In addition to the strata above described, there are certain
others which are tentatively referred to the San Pablo. They
certainly antedate the Phocene lava flows of the Coast Ranges,
which, it will be shown later probably belong to the later Phocene.
They consist of a variety of sandstones, shales and conglomerates,
free from pebbles of voleanie rocks.

Pre-Volcanic Beds near Freestone-—Between Freestone and
the mouth of Tomales bay and the town of Tomales these beds are
well exposed, being here some 400 feet thick, and made up about
as follows: At the base about 50 feet or more of a very coarse
hard sandstone, approaching a conglomerate in texture, most of
the grains being well water worn, and composed of chert or*

“Notes on some igneous, metamorphic and sedimentary rocks of the
Coast Ranges of California. Jour. Geol., Vol. 6, No. 5, 1898.

Vou. 4] Osmont.—Geological Section of Coast Ranges. 5!

~

quartz; some 200 feet of sandy shales, usually yellow to buff in
color, but sometimes variegated and interbedded with thin layers
of Franciscan pebbles; and about 150 feet of massive yellow sand-
stone, sometimes firm, though usually soft, and containing layers
and nodules of hard, dark gray limestone. These strata are lying
almost horizontal in this vicinity, but farther east they dip gently
to the northeast. At Freestone they are overlain conformably by
the Sonoma tuff, which will be shown below to belong to the later
Pliocene. Badly preserved marine shells. and two large indeter-
minate vertebrae were found in them.

Near the mouth of the Estero San Antonio, about three miles
west of Valley Ford, is a good cliff-section in these sandstones
which is fossiliferous. In this vicinity the writer found the fol-
lowing species:

Pecten caurinus Gould.
Natica sp.

Leda sp.

Machaera patula Dixon.

Solen sp.

Neptunea recurva Gate.
Crepidula grandis Midd.
Clementia subdiaphana Carpt.

Pre-Volcanic Beds at Trenton.—At Trenton a well sunk
through the Sonoma Tuff into the sandstones beneath encoun-
tered a shell bed, but the only specimens procurable by the writer
were casts, and indeterminable, though of a Merced appearance.

Pre-Volcanic Beds of Pleasant and Capay Valleys.—The
strata along the Sacramento Valley slope of the range overlying
the Cretaceous resemble very closely in character those above
deseribed. They consist of heavy bedded soft yellow to buff
colored sandstones, soft pinkish to white fissile shales, and non-
voleanie conglomerates made up of pebbles of Franciscan and
Knoxville rocks. The principal difference is the frequent coarse
character of the conglomerate, some of which is made up of peb-
bles six inches in diameter, and the inclusion of large angular
boulders of Cretaceous sandstone. At Pleasant Valley the So-
noma Tuff of the later Pliocene overlies these sandstones, being
conformable in dip, and in the same relation to them as at Free-
stone.

56 Vniversity of California Publications.. [GEOLOGY

Age.—The question of the age of these strata cannot at pres-
ent be conclusively settled. Gabb* referred the beds near Free-
stone doubtfully to the Miocene. Pecten caurinus is not sup-
posed to extend back of the Pliocene, while Clementia subdia-
phana is not known back of the Pliocene. These beds lie con-
formably beneath the Sonoma Tuff, which will be shown later is
probably of late Pliocene age. But on the eastern side of Santa
Rosa Valley a thick flow of andesite lies conformably beneath
the tuff, with no intervening sedimentaries, while beneath the an-
desite is a marked unconformity separating the latter from fresh-
water beds of probable Orindan age. Henee, since the marine
sedimentaries near Freestone beneath the tuff are non-voleanic
in their nature, they are tentatively referred by the writer to the
San Pablo.

The sedimentaries beneath the Sonoma Tuff in Pleasant and
Capayv Valleys, while conformable in dip with the latter, are
also non-voleanic in nature That they are marine in deposition
is shown by a bed of marine shells found in’ Pleasant Valley
earrying numerous species of poorly preserved shells of the San
Pablo appearance. These beds are also referred tentatively to

» San Pablo.
the San Pablo ORINDAN (2).

Red Gravels of Santa Rosa Valley—Certain strata of un-
known age are here inserted, since they are certainly older than
the Merced, and probably younger than the Cretaceous. They
occur on the west side of Santa Rosa Valley, between Trenton
and Healdsburg, where they form a low ridge of hills which, on
account of their very red color, form a striking feature of the
landscape. Where exposed in favorable places, as at landslides,
it is found that this peeuliar brick-red soil is derived from a
formation which is characterized by being made up almost en-
tirely of chert and sandstone of unmistakable Franciscan appear-
ance. Sandstone predominates, about 60% being sandstone,
10% radiolarian chert, 5% quartzite, and 25% red clay, which
holds it loosely together and gives it its striking color. There is
a notable absence of volcanics, only a few pebbles of quartz-
porphyry being seen. The gravel is of the average size of a
pigeon’s egg, with a small percentage of large pebbles up to

*Geol. Calif., pp. 83, 84.

Vou. 4] Osmont.—Geological Section of Coast Ranges. Dill

four or five inches in diameter. No stratification is discernable,
coarse and fine material being indiscriminately mixed. This
formation lies unconformably upon the Franeisean, and beneath
the Sonoma Tuff, seemingly unconformably. These gravels do
not oceur north of Healdsburg, so far as known, and have not
been looked for by the writer south of Trenton, though they
probably extend down to Forestville. On the east side of Santa
Rosa Valley they have not been encountered. No fossils having
been found in them, nothing definite can be said of their age, but
for certain reasons, which will be shown in the chapter on corre-
lation, they are supposed to correspond to the Orindan, Their
lack of bedding points to their being of fluviatile origin, and
they ure probably quite local in occurrence.

Sedimentaries beneath Andesite on Petaluma Creek.—On the
eastern side of Petaluma Valley, near Penn’s Grove, on the head-
waters of Petaluma Creek, are sandstones, shales and non-vol-
eanie conglomerates of very similar appearance to those beneath
the Sonoma Tuff at Freestone and Tomales. This formation is
dipping at rather steep angles, 20° to 50°, and is overlain uncon-
formably by Mark West Andesite. No Sonoma Tuff was observed.
A fine grained clay shale yielded numerous good specimens of the
rare fossil Cyrena Californica Gabb.

Lignitic Beds of Lawlor’s Ranch.—About six miles southeast
of the locality above described, and five miles east of Petaluma,
on Lawlor’s ranch, is a small bed of lignite in apparently these
same strata. The beds are folded at angles up to 45°, and lie
unconformably beneath the Mark West Andesite. A few inde-
terminable shells of fresh-water appearance, and several horse
teeth have been found. The teeth were submitted to Dr. J. W.
Gidley of the American Museum, who kindly furnishes the fol-
lowing information regarding them:

‘“ he last upper molar, specimen No. 2251, belongs to a spe-
cies of Neohipparion with a very progressive protocone. The
lower molar, with the same number, is a different individual.
This tooth has a peculiarly compressed appearance which does
not agree with the ordinary full proportions of the upper molar.
The little fold of enamel at the anterior external corner of the
protoconid proves lower tooth, No. 2251, to belong to a genus

58 University of California Publications. | GEOLOGY

more primitive than Hquus, but the small size of the fold indi-
cates a very advanced stage for a Miocene form.”’

Lignitic Beds of Mark West Creek—On Mark West Creek,
about half a mile above the point where it enters Santa Rosa
Valley, are lignitie beds which have been worked in a small way
for coal. The henite occurs in a diatomaceous shale which here
underlies the Mark West andesite. The henite deposit is small
and unimportant, but interesting geologically, since these beds
probably represent a fresh-water lake contemporaneous, if not
connected, with that at Lawlor’s Ranch.

Age.—Lignite is known to exist in these beds at two places,
and, at the lignite beds of Lawlor’s Ranch, horse teeth of late
Miocene or early Pliocene age have been found, and imperfect
casts of fresh-water shells. Cyrena Californica oeceurs abund-
antly on Petaluma Creek, and is known certainly from only one
other locality, viz: Kirker’s Pass, in the very uppermost part of
the San Pablo section.*

Andesite intervenes between these beds and the Sonoma Tuff,
and rests uneconformably across the eroded edges of their strata.
Ilence they are considerably older than the tuff, and, as will be
shown later, the latter is probably not later than early Merced.
These beds are, therefore, referred tentatively to the Orindan,
and will be discussed more fully later in the chapter on the cor-
relation of the Neocene.

LATER PLIOCENE.

The formations observed by the writer in the region under
discussion, and ascribed by him to the later Pliocene, make up
a series conformable in dip, but containing erosion intervals.
They consist of lava flows and sedimentaries; the former of two
well marked characters, the one of intermediate acidity, the other
acid; the latter partly of marine, and partly of lacustrine, fluvia-
tile and aeolian deposition, but made up largely of voleanie detri-
tus of intermediate acidity.

Starting at the base, the series consists of :

The Mark West Andesite, of varying thickness up to 1,500
feet.

*Palaeontology of Cal.. Gabb, Vol. II, p. 26, pl. 7, fig. 45.

Vou. 4] Osmont.—Geological Section of Coast Ranges. 59

The Sonoma Tuff, andesitie in character, and interbedded
with thin flows of basalt, to the west with sandstones and voleanie
conglomerates, and to the east with voleanic agglomerates and
breeeias. he maximum thickness of the tuff and agelomerate
observed at any one place is 1,700 feet.

The Marine Beds of Wilson’s Ranch, made up of soft, friable
yellow sandstone and fine voleanie conglomerates of a thickness
probably exceeding 2,000 feet, and carrying typical Merced
fossils.

The St. Helena Rhyolite, of varying thickness up to 2,000 feet.

The maximum thickness observed for the whole series at any
one place was about 4,000 feet, which does not take into account
that portion of the rhyolite removed by erosion.

This series mantles indifferently over the older formations
throughout the large portion of the area under discussion, and
engaged most of the writer’s attention. Hence it will be described

in considerable detail.

MARK WEST ANDESITE.

Areal Distribution and Thickness—The andesite flows in the
central and northern portion of the area under discussion agegre-
gate a great thickness, while to the south and west they thin out to
mere sheets. Where exposed by a fault on the southwest slope
of Mt. St. Helena they are over 1,500 feet thick, while the anti-
elinal fold just west of Mark West Sprines shows a thickness of
about 700 feet. At Napa City the waterworks well shows them
to have a thickness of nearly 1,500 feet. Near Petaluma they
thin down to about 100 feet, and somewhere under Santa Rosa
Valley they run out to a thin edge, since they do not appear at
all on its west side.

Structure.—They lie usually at small angles, mantling indif-
ferently over the various older formation beneath them.
Age.—tThese andesites seem to be conformable in dip with the
Sonoma Tuff above, but an erosion interval existed between the
two, as shown by the numerous andesite pebbles included in the
latter. The conformability of the dip with the Sonoma Tuff, the
age of which, as will be shown later, is pretty certainly late Plio-
cene, together with its uneonformable relation to the blue San

60 University of California Publications. [ GroLocy

Pablo sandstone and to the supposed Orindan beds below, points
to its being of late Pliocene age.

Petrography.—A specimen of this rock from beneath the
Sonoma Tuff near the contact on the west limb of the anticline
near Mark West Springs showed itself to be macroscopically a
dark, heavy rock, varying from dark greenish black to brown in
color, according to degree of weathering, and sufficiently coarse
erained to enable the lath-shaped feldspars of the ground mass
to be readily seen with the naked eye. Seattering phenocrysts of
feldspar and of olivine occur up to 4 mm. in length.

Microscopically this rock is coarse in texture, consisting of a
few large phenocrysts of labradorite and_ olivine seattered
throuzh a rather coarsely crystalline ground mass, made up
chiefly of labradorite feldspar in well shaped laths almost uni-
versally twinned on the albite law, and rounded grains of augite,
the strueture being the common one called by Rosenbusch ‘‘ Inter-
sertal.’’ The feldspar phenocrysts, measured by the common
methed of symmetrical extinctions on the albite twinning plane
(101), gave a maximum extinction angle of 37.5°. According
to Michel Levy, this angle corresponds to a labradorite of about
the composition Ab, An, One erystal, rhombic in section, with
good cleavages parallel to (001) and (100), and showing no
twinning lamellae, was evidently cut parallel to the albite twin-
ning plane (010). It gave an extinction angle measured against
the trace of (001), of 22°. The extinction fell in the acute angle
of the rhomb, making the sign negative. This corresponds to
labradorite of a composition between Ab, An, and Ab, An..

Small erystals and grains of magnetite occur in some cases
formed around the ends of the feldspar laths, never included in
them. Hematite in flakes and irregular patches, and as a mere
stain discoloring the feldspar, is very abundant. It seems to have
come from some exterior source as an infiltration. Flow struc-
ture is very noticeable, the feldspar laths of the ground mass
being drawn out in more or less parallel lines, and wrapped
around the ends of the phenocrysts. <A little glass is present.

A specimen from beneath the Sonoma Tuff on the east limb of
the anticline near the contact at Mark West Springs is very simi-
lar in appearance to the rock above deseribed from the west

vou. 4| Osmont.—Geological Section of Coast Ranges. 61

contact. It is dark greenish black, heavy rock, rather too coarsely
erystalline for a basalt, with scattering phenocrysts of feldspar.
Microscopically it is also similar. It is somewhat fresher,
and contains much less hematite. By Michel Levy’s statistical
method the feldspars gave a maximum angle of 43.5° This indi-
eates a basie labradorite of a composition somewhat more basic
than Ab, An, or nearly Ab, An,. Augite occurs sparingly as
phenocrysts up to .88 mm. in length. These crystals are rounded
and corroded as though acted upon by the magma prior to con-
solidation. The abundant augite in the ground mass occurs in
rounded grains lying between the laths of feldspar in the ‘‘ Inter-
sertal’’ structure of Rosenbusch. The feldspar lathes are short
and stout, and invariably twinned on the albite law. The augite
is of the usual lavendar gray color. It appears to be altering to
chlorite of a dark green shade, which stains the rock freely. No
olivine was observed in this slide. <A shght flow structure was
observed. No glass was recognized. A careful determination of
the silica contents of this rock gave 65.13%.
A specimen from below the Sonoma Tuff on the southwest
slope of Mt. St. Helena may be described as follows:
Macroseopieally it is a dark grayish black rock, containing
phenoerysts of lath-shaped feldspars and irregular greenish yel-
low decomposed augite crystals in a fine grained ground mass,
which does not appear erystalline to the naked eye.
Microscopically this rock is made up of numerous large and
small phenoerysts of feldspar and of augite embedded in a semi-
crystalline ground mass composed of numerous feldspar micro-
lites embedded in glass. The feldspar phenoerysts are frequently
well terminated, but the larger ones are usually broken and show
wavy extinction. The maximum angle observed in sections show-
ing symmetrical extinctions on (010) was 38°. This corresponds
to a labradorite of about the composition Ab, An.. The augite
phenocrysts are worn, broken and corroded, and usually altered
to chlorite and hematite. They were preceeded by the magnetite
which is found ineluded in them. The feldspar is moulded on
the angite. There is much magnetite dust in the glass of the
ground mass, and also much chlorite, which stains the rock green
in thin sections. This may have come from original augite grains

62 University of California Publications. [ GEOLOGY

in the ground mass. Flakes of hematite, and stains of the same,
are abundant. Two erystals of ilmenite, altering to leucoxene,
were observed. This rock contains 64.8% SiO,. <A finer grained
rock from the same locality yielded 65.5% 810,. Similar lava
extends from the hills on the east side of Santa Rosa Valley and
extends west of Penn’s Grove for about one mile. It rests uncon-
formably upon the yellow sandstone and gravel which, near the
headwaters of Petaluma Creek, some two miles northeast of
Penn’s Grove, contain the distinctive upper San Pablo fossil,
Cyrena Californica. These andesites are supposed by the writer
to be the same as those above described from Mark West. Springs
and Mt. St. Helena.

A specimen from one mile west of Penn’s Grove station
showed the following characteristics.

Macroscopieally it is a heavy dark greenish gray rock of suffi-
ciently coarse texture to enable the eye to recognize the erystal-
linity of the ground mass. Occasional small, well shaped pheno-
erysts of feldspar were observed, and small yellow spots, due
apparently to the decomposition of the pyroxene, are numerous.

Microscopically this rock is seen to be rather coarsely erystal-
line in texture. The phenocrysts are very abundant, consisting
of well shaped laths of feldspar and stocky prisms of augite,
embedded in a erystalline ground mass of small feldspar laths
and well shaped augite needles.

The feldspar gave a maximum extinction angle on a section
eut perpendicular to (010) of 41°. This would indicate a feld-
spar somewhat more basie than Ab, An,. The usual leneth of
the labradorite phenocrysts is about .38 mim.

Augite is plentiful. While the needle-like crystals of the
ground mass are well shaped, the large phenocrysts are usually
badly corroded by the magma. The maximum leneth of these
phenocrysts is about .5 mm. Much magnetite occurs as small
cubes and octahedra, included principally in the augite. No
olivine was observed, and no glass could be certainly determined
in the ground mass. There is a distinet similarity between this
rock and the ones described from the vicinity of Mark West
Springs.

Another specimen from the same locality showed the follow-
ing features:

Vou. 4] = Osmont.—Geological Section of Coast Ranges. 63

Maeroscopieally it is a heavy dark greenish black rock, very
similar in appearance to the last one described. It is evidently
erystalline in character but with few phenocrysts showing to
the naked eye.

Microscopieally it is seen to be made up of numerous, but
small, erystals of feldspar and pyroxene embedded in a ground
mass of feldspar microlites and augite grains in the ‘‘Inter-
sertal’’ strueture of Rosenbuseh. The maximum extinction angle
of the feldspar phenoerysts was 41°, hence it is a medium labra-
dorite. The largest erystals of feldspar observed measured
6 mm. in length, the largest of pyroxene 5 mm. These pyroxene
phenoerysts proved to be orthorhombic. They were distinguished
from the augite of the ground mass by their straight extinction,
lower double refraction, and pleochroism. The latter, however,
is very weak, and suggests enstatite. The color of the fresher
erystals in ordinary hght is a greenish lavender. The larger
ones, however, are badly altered along the cleavage planes to
hematite and a ereen mineral of weak double refraction, prob-
ably serpentine.

Augite is plentiful in the ground mass in small, short prisms
and rounded grains. The rest of the mass seems to be made up of
microlites of bytownite feldspar. No glass was certainly identified.
Maegnetite in cubes, and in grains seattered through the ground
mass, is abundant. Also much serpentine and chlorite is present
from the alteration of the pyroxenes.

The feldspars of the above described rocks vary from a
medium to an acid labradorite, and this fact, taken in connec-
tion with the abundance of augite and occasional presence of
olivine and enstatite, would lead one to eall them basalts. But
their silica contents is invariably high, averaging close to 65%,
Henee they must be classed as pyroxene-andesites. The elass in
the ground mass must evidently be very acid. Becker* probably
referred to these rocks when he spoke of the ‘‘older andesites.’’
He classed them as pyroxene-andesites. Similar rocks are de-
seribed by Palachey+ from the Berkeley Hills.

*Quicksilver Deposits of the Pacifie Coast. Mon. XIII, U. 8. G.S.

+The Berkeley Hills. Lawson and Palache. Bull. Dept. Geol., Univ. of
Cal., Vol. 2, No. 12, p. 412.

64 University of California Publications. [ GEOLOGY

SONOMA TUFF.

Following the andesite came enormous quantities of volcanic
ashes. These ashes covered a large area, part of them falling
upon dry land, part upon water, and part being washed down by
the streams to form tuffs in the seas and lakes.

Character of the Tuff —This tuff is a fragmental rock made
up wholly of the voleanie material, and characterized by con-
taining numerous fragments of pumice, in size from very small
grains up to an inch or more in length. ‘Two silica determina-
tions made on the pumice, from two localities in Santa Rosa Val-
ley, gave respectively 61% and 63% Si0O,. Hence it is ande-
sitic in character.

The rock is usually very hght in color and in weight, and,
where well exposed, forms a conspicuous feature of the land-
scape. Certain fine grained varieties of it are easily worked into
blocks, which make very good building stone where great strength
is not required.

Areal Distribution and Thickness.—It is widely distributed
in the Coast Ranges north of Mt. Diablo for at least 100 miles,
and, as it is easily recognized, it was the writer’s idea at one
time to use it as a datum plane in an attempt to trace out the
late Tertiary basin of the region. It was soon found, however,
that this would take more time than was available, and the orig-
inal plan of a continuous cross-section through a typical locality
was resumed.

Good exposures of this tuff may be seen from Freestone south-
east to Bloomfield, near Trenton and on the Russian River near
the mouth of the Mark West Creek, in the lower foothills north-
east of Windsor and near Mark West Springs as shown in Sec-
tion AB. From here east to Calistoga, and beyond to the high
ridge of Twin Peaks, there are large areas and immense thick-
nesses of it. As shown by Section CD, it is much thinner to the
south. In fact, it was necessary at many places to exaggerate its
thickness to show it at all on the section, since toward the south-
west part of the area it is sometimes not more than ten or fifteen
feet thick. From Mark West Creek to Franz Valley and at Twin
Peaks southwest to Oat Hill Quicksilver Mine it has its greatest
thickness, about 1,700 feet. Toward the west side of Santa Rosa

Vou. 4] Osmont.—Geological Section of Coast Ranges. 65

Valley it thins out very much. The great bodies above mentioned
at Franz Valley and near Twin Peaks seem to be of the nature
of agglomerate rather than tuff, containing an immense number
of aneular fragments of lava, mostly andesite. At the latter place
fragments are sometimes encountered many tons in weight.
The Interbedded Sandstones and Conglomerates.—Toward
the west, on both sides of Santa Rosa Valley, beds of the pumi-
cious tuff, ten or fifteen feet thick, are interbedded with sand-
stone and gravel. The sandstone is usually a rather coarse, yel-
low, loosely compacted rock. The conglomerate is very distine-
tive. It is made up almost entirely of voleanics. The pebbles
are mostly andesite, some appear to be basalt, and quite a large
proportion is a white rhyolite which the writer has never encoun-
tered in place. Rhyolitie breecias, and occasional pebbles of
Francisean chert, glassy obsidian and petrified wood, also occu.
Between Mark West Springs and the edge of the Santa Rosa
Valley, along the line of Section AB, these gravels are very
coarse, 75% being over two inches in diameter, and 10% over
six inches. At this loeality fully 1,900 feet of these buff colored
sandstones and heavy gravels rest on top of about 200 feet of the
punicious tuff, but on the east limb of the anticline, and in the
synclinal basin of Mark West Creek east of the springs, the same
character of gravel is seen to be interbedded with considerable
thicknesses of tuff, though at the base is nearly 600 feet of tuff
free from sandstone and gravel. Thus the lower portion of the
beds at this point are wholly tuffaceous, while the upper part
contains no tuff at all, though the gravel is the same. On the
east side of the anticline there is no line of demarcation between
the tuff and the sandstone. Tuff seems to be interbedded with
sandstone up to a considerable distance above the base, and then
sandstone continues to the top. On Section AB two beds have
been shown, one representing the tuff and the other the sand-
stone, but the line between the two is an arbitrary one, as the
writer could not find it in the field, and is of the opinion that
tuffs and sandstones belong to the same period of sedimentation.
Lava Flows within the Sonoma Tuff-—Intereallated with the
tuff, on the east side of the anticline at Mark West Springs, about
300 feet from the base, is a forty foot flow of basalt. At Gree-

66 University of California Publications. [ GEOLOGY

ley’s Ranch, three miles northeast of Windsor, this same flow
seems to occur, resting on the Sonoma Tuff. At Mt. St. Helena,
Sacro Canon near Napa, and at other places flows of lava inter-
callated with the tuff and agglomerate were observed.

Petrography.—A specimen from Mark West Springs showed
the following characteristics :

Macroscopically this is a dense dark greenish black rock, in
which a few large phenoerysts of feldspar and of olivine can be
seen with the naked eye. The ground mass does not appear to
be erystalline.

Microscopically it is a very porphyritic rock, consisting of
large phenocrysts of feldspar up to 2 mm. in length embedded in
a micro-erystalline ground mass of small, well shaped feldspar
microlites separated by augite prisms in the common intersertal
structure. The microlites appear to be universally twinned, and
a maximum angle was obtained on (010) of 83°. A large pheno-
eryst also gave 33°. This maximum angle corresponds to a labra-
dorite of a composition midway between Ab. An, and Ab, An,.
Olivine in prisms and rounded grains is rather abundant. The
largest phenoeryst observed was about 5 mm. in diameter. They
are usually rounded on the corners and altered along the cracks
to serpentine. The most characteristic feature of the structure
is the sharp distinction between the two periods of consolidation.
Large, well shaped erystals of labradorite enclosed in a micro-
crystalline ground mass of well formed feldspar laths in inter-
sertal structure with augite grains. Flow structure is beauti-
fully developed, as shown by the disposition of the microlites
around the phenocrysts. A little glass is present in the ground
mass. <A silica determination gave 43.06% SiO,. The rock is
a good example of an Olivine-Basalt.

Another specimen from Greeley’s Rranch, about three miles
northeast of Windsor, will be described. Here the hills have
a thin capping of basalt resting on Sonoma Tuff and gravels.
Structurally this basalt appears to the writer to correspond to
the flow above described at Mark West Springs.

Macroscopically it is grayish black rock, quite secoriaceous,
with many vesicles which have been subsequently filled with opal
and iron oxides. The phenocrysts are numerous and easily dis-

Vou. 4] Osmont.—Geological Section of Coast Ranges. 67

cernable to the naked eye, some of them being 2 mm. in length.
They appear to be wholly feldspar. he ground mass is unre-
soluble to the naked eye.

Microscopically it is strikingly similar to the rock described
from Mark West Springs. The two periods of consolidation are
even more sharply divided, and the movement of the magma be-
tween the two periods is still more clearly shown. The feldspars
eave 35° as their maximum extinction angle, indicating a labra-
dorite of composition near Ab, An,. Large lath shaped labra-
dorite phenocrysts were embedded in a microcrystalline ground
mass made up of a multitude of very minute mierolites of labra-
dorite and grains of augite in intersertal structure. No olivine
was observed. A small amount of brown glass is present, which
seems to have come from some exterior source. This rock would
be ealled ordinary basalt.

Age.—Near Freestone numerous easts of shells were found
in this tuff, but they were not determinable, though they were
certainly marine in character and resembled the shells of the
Merced above. Its conformable relation to the Wilson Ranch

beds suggests its being of lower Merced age.

MARINE BEDS OF WILSON’S RANCH.

Lithological Character—Near Wilson’s Ranch, on the Rus-
sian River, some two miles above the mouth of Mark West Creek
and lying conformably upon about 100 feet of Sonoma Tuff
interbedded with coarse voleanic conglomerate and yellow sand-
stone, is a formation of heavy-bedded, friable yellow to buff col-
ored sandstone, interbedded occasionally with fine voleanie econ-
glomerate and beds of shells. It dips gently toward the Santa
Rosa Valley, and is of unknown thickness, but is probably up-
ward of 2,000 feet. On account of their soft, friable nature these
beds weather in characteristic ‘‘ Bad Land’’ forms.

Areal Distribution—These beds extend alone the east bank
of the Russian River, apparently about half way to Healdsburg,
dipping to the east and disappearing under the valley alluvium.
On the eastern side of the Santa Rosa Valley, exposed along the
foothills north of Mark West Creek, are sandstones of very simi-
lar appearance and weathering, but interbedded with much

68 University of California Publications. [ GEOLOGY

coarser gravels. They show no fossil beds, and seem to be of the
nature of a river deposit. They he conformably above the Sono-
ma Tuff and are dipping toward to the valley to the west. At
Freestone, conformably above the Sonoma Tuff and lying almost
horizontally, is a yellow sandstone of almost identical character
to that at Wilson’s Ranch. It extends northward toward Tren-
ton and dips gently toward the northeast. No fossils were found
in it. In Petaluma is a small exposure which may be a remnant
of these beds.

Red gravels
Sonoma Tuff
Shell beds

Franciscan 3000 ft. 6000 ft

bre. di.

Section from the Russian River to Windsor, across the Santa
Rosa Valley, showing the stratigraphic relations of the Merced,
Sonoma Tuff, Red Gravels, and Franciscan, and the position
of the Merced shell beds at Wilson’s Ranch.

The only good shell beds observed in this formation are
located at Wilson’s Ranch, on the east bank of Russian River
some three miles southwest of Windsor and one mile north of
Trenton. They oceur about 1,000 feet above the Sonoma Tuff.
The writer made several trips to this locality and collected a
number of fossils, which he was enabled to identify as follows:

Tapes staleyi Gabb.

Macoma nasuta Con.
Standella nasuta (2?) Gld.
Schizothoerus Nuttali Con.
Natica clausa Brod. and Sby.
Natica lewis Gld.

Olivella biplicata Sby.
Chrysodomus tabulatus Baird.
Arca trilineata Con.

Nassa near californiana Con.
Cardium corbis Martyn.
Crepidula grandis (?) Midd.
Purpura saxicola Val.

Vou. 4] = Osmont.—Geological Section of Coast Ranges. 69

Solen sp.
Pleurotoma sp.

Age and Correlation.—The similarity of the above lst with
the species which occur in the Seven Mile Beach section and
those of Capitola, Half Moon Bay and the Scotia section of Tum-
boldt County is at onee apparent and fixes the age of these beds
as Mereed. The abundance of arca trilineata points to their be-
ing of about the horizon represented at Capitola.

The physical appearance of these sandstones also strongly
suggests the Mereed and Wild Cat series. They are soft and
friable and easily weather in the characteristic *‘Bad Land’’

forms so commonly seen in the above mentioned formations.

ST. HELENA RHYOLITE.

Field Aspects, Areal Distribution and Thickness —lLying
eonformably above the tuff are thick flows of lava of a very
much more acid composition than that below. The section at
Mt. St. Helena shows a thickness of fully 2,000 feet, not taking
erosion into account, all of which is of the same general char-
acter, being a very lght colored trachytic looking roek which
readily weathers and is conspicuous by reason of its lack of ferro-
magnesian phenocrysts. Lava of the same character forms the
erest of the high ridge east of Napa City, occurring in great
thickness and dipping toward the valley, so that a thin layer of it
still remains in the valley itself, just east of the town, capping
the tuff and andesite. It also forms the highest member in the
country between Napa and Sonoma, and between Sonoma and
Petaluma, the latter place being the farthest west it has been
found.

Petrography.—A specimen from the top of Mt. St. Helena
showed the following characteristics.

Macroscopically it is a very ight colored, almost white, rock,
occasionally shghtly reddish from iron stains, notably lacking in
ferromagnesian minerals. It has a rough, trachytie-like surface.
Numerous large, glassy feldspar phenocrysts can be seen, but no
quartz. The ground mass appears to be nonerystalline.

Microscopically this rock is seen to consist of numerous rather
poorly formed phenocrysts of potash and soda-lime feldspars

70 University of California Publications. [ GEOLOGY

enclosed in.a fine grained ground mass composed mostly of glass.
No ferromagnesian mineral is present, the only iron bearing min-
eral being occasional cubes of magnetite and flakes of hematite,
the feldspars frequently being stained with the latter. The most
abundant phenoeryst is sanidine. Its frequent straight extine-
tion and absence of repeated twinning served to distinguish it
from the plagioclase present. It is very abundant, and some-
times oceurs in well terminated crystals, but usually in broken
fragments, frequently badly kaolinized. <A relatively small
amount of plagioclase occurs, of which the highest extinction
angle observed on (010) was 10.5°. This would indicate either
albite or oligoelase. The ground mass is very fine grained, and
under the high power is seen to be composed of minute frae-
ments of feldspar, apparently sanidine, intimately mixed with
unindividualized glass.

Determined solely by its optical properties, this rock would
be called a trachyte, since no quartz phenocrysts were observed.
A silicia determination, however, showed it to contain 72.13 SiO,.
Henee it is classed as a Rhyolite. A similar rock from above the
Sonoma Tuff on the west side of Wooden Valley, Napa County,
yielded 72.36% SiO,

A specimen from a quarry in Sareo canon, east of Napa City,
shows the following features:

Macroscopieally it is a nearly pure white rock, with a rough,
sugary fracture and conspicuous absence of ferromagnesian min-
erals. The only colored constituents are small specks of hematite.
Large phenocrysts of feldspar are visible to the eye, but no
quartz. It has a roughly laminated appearance.

Microscopically it shows large phenocrysts of sanidine em-
bedded in a micro-crystalline ground mass of a very acid plagio-
clase in well shaped microlites in simple twins. These laths have
a well defined parallel arrangement, due to flowage of the magma.
Scattered octahedra of magnetite are present, and a large amount
of hematite dust, which by its arrangement serves to bring out
the flow structure more clearly. No primary quartz was observed,
but a small amount of secondary quartz was seen. This rock
is very similar to that at Mt. St. Helena, and the writer has
classed it as rhyolite.

Vou. 4] Osmont.—Geological Section of Coast Ranges. 71

The area east of Petaluma is largely composed of St. Helena
rhyolite, and at certain places very laminated phases of it occur.
Near Kelly’s Ranch, six miles southeast of Petaluma, a beautiful
laminated variety occurs.

Maerosecopieally this is a lght colored, almost white rock,
marked with numerous parallel reddish lines giving it a beauti-
ful laminated appearance.

Mieroseopieally it is seen to be composed of sanidine and
quartz phenoerysts with no definite erystal boundaries, which
have been drawn out into parallel lines by the movement of the
molten magma. They were rolled over and over, and fractured
and rounded before the magma finally solidified as a glass around
them. The ground mass now folds around the phenocrysts and
broken fragments in eye-shaped form, the flow structure being
beautifully brought out by numerous wavy parallel lines of
hematite dust. It contains 72.24% SiO,. This rock is an excel-
lent example of a banded rhyolite.

Similar banded rhyolites have recently been observed by Ch.
E. Weaver farther to the south, on the ridee between Petaluma
and Napa, and at Glen Ellen. In both eases they he above the
tuff.

Becker’s ‘*‘ Asperite.’’—Becker*™ refers to these rocks as fol-
lows: ‘‘Extensive areas of andesite occur to the southward of
Clear Lake. Mt. Cobb and Mt. St. Helena and, indeed, a great
part of the range of which the latter forms the culminating
peak, known as the Mayacmas Mountains, are andesitic. The
andesites extend down almost continuously to within a few miles
of Vallejo, at the head of the Bay of San Francisco.

Both dense andesites of the earlier type and the asperites are
represented. . . . The andesite is for the most part glassy
when fresh, though asperites are also found. This rock consti-
tuted the greater part of the mass of St. Helena, and covers large
areas to the north, east and southeast of that mountain. The
summit of Mt. Cobb is also andesitic. Tuffaceous forms of ande-
site, usually much decomposed, are also abundant, especially to

the south.”’

*Quicksilver Deposits of the Pacific Coast, Mon. XIII, U.S. G.S.

=~
bo

University of California Publications. [ GEOLOGY

From the above statement, and his petrographical descrip-
tions, it appears that his asperites correspond to the St. Helena
rhyolite, and his older andesites to the Mark West andesite of
the present writer, while his andesitic tuff is the Sonoma Tuff,
which is extensively developed just southwest of the Oat Hill
Quicksilver Mine.

AGE OF THE ABOVE SERIES.

In the excellent section near Freestone the Sonoma Tuff,
containing marine shells, is resting horizontally, and strictly con-
formably, upon marine sandstones and conglomerates non-vol-
cani¢ in their nature and containing shells referred doubtfully
by Gabb to the late Miocene. On the eastern side of Santa Rosa
Valley, however, near Mark West Creek, some 700 feet of Mark
West andesite occurs, directly underneath and conformable with
the tuff, while to the south, on the head-waters of Petaluma Creek.
this andesite may be seen resting unconformably across the eroded
edges of nonvoleanic sandstones and conglomerates very similar
in appearance to that near Freestone, but of fresh-water origin
and containing a typical upper San Pablo fossil, Cyrena Cali-
fornica. In these latter strata also, at Lawlor’s Ranch, horse-
teeth very similar to those of the Orindan have been found,
which Dr. Merriam refers tentatively to late Miocene. The Mark
West andesite appears therefore to certainly be post-San Pablo,
and probably post-Orindan in age.

At Rodeo, on San Pablo Bay, occurs an exposure of pumi-
ceous tuff indistinguishable in appearance from that described
above in the writer’s territory. It rests conformably upon the
typical San Pablo, but recently Dr. J. C. Merriam found horse-
teeth and other vertebrate remains in it, showing it to be not
older than Pliocene. Dr. J. W. Gidley kindly examined these
horse-teeth, and reports as follows:

‘*Number 2142 is an upper molar of Protohippus.’’

On the west side of Santa Rosa Valley, alone the Russian
River, the Sonoma Tuff les conformably beneath the Wilson
Ranch Beds, which are certainly of Merced age, probably about
the horizon represented by the Capitola section and the base of
Seven Mile Beach section. The Sonoma Tuff is, therefore, pretty
certainly of lower Merced age.

Vou. 4] Osmont.—Geological Section of Coast Ranges. 73

Beyond the fact that the St. Helena Rhyolite followed the
Sonoma Tuff, the age of which is pretty well established, the
writer has not been able to gain much evidence as to its age. It
has not been observed in contact with the Wilson Ranch Beds,
but is probably later in age, as the latter do not seem to carry
any pebbles of this rock.

Becker* determined the lower limit of the age of this rhyo-
lite, which he ealled ‘‘asperite,’’ by the facet that it overhes fresh-
water beds near Clear Lake, called by him the Cache Lake Beds,
and referred doubtfully by Marsh, on the evidence of very frag-
mental vertebrate remains, to the late Phocene. At every place
where seen in contact with the tuff, with the possible exception
of one locality in the edge of the foothills east of Sonoma, where
the rhyolite may be lying across the eroded edges of the tuff,
it appears to be strictly conformable in dip with the underlying
tuff. These dips are frequently steep, and this fact, taken in
connection with the topographical consideration that deep, wide
valleys such as those of Santa Rosa, Sonoma and Napa have been
formed subsequent to the folding of the rhyolite, and have cut
through thousands of feet of it’ and deep into the underlying
formations, makes it seem unlikely that the St. Helena rhyolite
ean be much later than the end of the Phocene or, at most, the
very early Quaternary.

THICKNESS.

The later Phocene voleanie and sedimentary formations
form a series, conformable in dip, of varying thickness, which
is shown in the section at St. Helena to be at least 4,000 feet
thick, leaving out of account the rhyolite removed by erosion.
In Santa Rosa Valley, to the west, the marine sediments and
fluviatile deposits are certainly not less than 2,000 feet thick,
and the synelinal structure shown in Section AB at Santa Rosa
Valley points to their being fully 3,000 feet. In most places the
series is gently folded, mantling indifferently over the older
formations, but in a few places near the axis of the range, notably
near Iranz Valley, the axes are steep and the folds numerous.

*Mon. XIII, U. 8. G. S.

74 University of California Publications. [ GEOLOGY

CORRELATION OF THE NEOCENE STRATA.

It has been thought advisable to discuss in some detail the
correlation of the various strata included in this paper between
Monterey and Pleistocene.

Stated in tabular form and in descending order, the writer
believes the Neocene of this territory to be made up as follows:

/
Str. HELENA RHYOLITE.

East of Santa RosaValley:
Sandstones, shales and a
large proportion of coarse
volcanic conglomerate. No
fossils. Coarseness of
gravel and close bedding
indicating fluviatile
origin.

West of Santa Rosa
Valley :Sandstones and
ye eer ort etid a small proportion of
MEIGS N RANCH ( shales and fine volcanic

BEDS ) ‘
(Fain Mir marine

7

fauna, Arca trilineata,
ete.

East side Santa Rosa
Valley: Interbedded with
heavy volcanic gravel and
fluviatile in origin.

East of Mark West Creek
Basin: Interbedded with
heavy volcanic agglomer-
ates and largely of aeolian

West of Santa Rosa

Valley: Interbedded

ee a with rather coarse vol-
Sonoma TUFE |] canic conglomerate and

LATER PLIOCENE.

carrying casts of ma-
rine shells.

deposition.
\ MarK West ANDESITE.
UNCONFORMITY.

Sedimentaries of Peta- Sandstones, shales and
Juma Creek and Lig- non-volecanic conglomer-
ORINDAN (?) nitie Beds of Lawlor’s ates. Fresh-water fauna.
Raneh and Mark West Neohipparion, ete., and

Creek, Cyrena californica.

non-voleanic conglomer-
ates. Marine fauna;
Clementia subdiaphana.
Pecten caurinus, ete.

( Pre-Voleanic Beds of
Freestone, Trenton,
Pleasant and Capay
Valleys.

{ ronsrotean shales, and

San Pasvo (?)

f Blue Sandstone (tuff)

SAN PABLO ;
' : L of Carneros Creek,

When we try to correlate the different members above tabu-
lated with well known formations in cther localities we can at
once refer the blue sandstone of Carneros Creek to the typical
San Pablo of Kirker’s Pass and the San Pablo Bay sections.

Vou. 4] Osmont.—Geological Section of Coast Ranges. 75

Also, we ean safely correlate the Wilson Ranch beds with the
typieal Mereed, with a strong probability, from the abundance
of arca trilineata, that it belones to about the horizon repre-
sented at Capitola. Beeker’s Cache Lake beds may be their
fresh-water equivalent.

Now, it was thought in the beginning of this work, that the
very characteristic pumiceous tuff called in this paper the So-
noma Tuff would serve as a datum-plane to connect the forma-
tions encountered with those of Contra Costa County, for pumi-
ceous tuff is extensively developed throughout the Mt. Diablo
region. Unfortunately, a difficulty has arisen, which wil! now
be discussed. In the Contra Costa distriet a pumiceous tuff
identical in appearance to that found in the writer’s territory
exists at the base, or interbedded near the base, of an extensive
fresh-water deposit, called by Lawson the Orindan, and described
as being a ‘‘Thick formation of pebbly conglomerate, feebly co-
herent sandstones, thin beds of voleanie tuff generally decom-
posed and of a dark brownish color, beds of blue and slate col-
ored clay containing fresh-water ostracods, sandstones contain-
ing ostracods and molluses, and occasional patches of lava of
quite limited extent intereallated (?) with sedimentary beds.
No marine organisms have been found in any part of the beds.’’

This Orindan formation mantles indifferently over the blue
San Pablo, the Monterey and the older rocks, but, save for the
pumiceous tuff near its base, it is nonvolcanic in its nature, and
precedes all the lava flows of the Berkeley Hills. In its gravels
certain vertebrate remains have been found by Lawson, Merriam
and Sinelair, the most important of which are horse-teeth. These
were referred to Dr. Gidley, who reports upon them as follows:

‘Number 1324 is a very interesting tooth as it is indistin-
euishable from Hipparion richthofeni, a species from Eastern
China. It is possible it may represent a species of true Hippa-
rion. Number 1323 is an upper molar of a smaller species, prob-
ably Neohipparion.’’. Hipparion richthofeni is reported from
the lower Pliocene.

The above evidence points to these eravels being of late Mio-
eene or early Pliocene age. Certainly they are later than the
marine blue San Pablo, and older than the Mereed. At Rodeo,

76 University of California Publications. [ GEOLOGY

however, is a syneline of pumiceous tuff resting conformably on
typical San Pablo strata, and of identical appearance to that
beneath the Orindan gravels at Pinole and southward, and in
this tuff Dr. Merriam recently found horse-teeth of more recent
type than those from the Orindan gravels. He thinks that they
cannot be older than Phoecene. No gravels oceur with the tuff
at Rodeo.

Proceeding on this assumption, therefore, the writer corre-
lates the fresh-water deposits beneath the Mark West Andesite
on the eastern side of Santa Rosa Valley with the Orindan.

If the above correlation is correct, it is evident that the gap
between San Pablo and Merced is somewhat bridged over, but
the writer thinks it premature to attempt at this time any cor-
relation of his intervening formations with those of the Berkeley
Thills, such as the Berkeleyan.

QUATERNARY.

It was not found possible with the scale used to adequately
represent the Quaternary deposits. All of the streams of the
territory under discussion show terraces, usually covered with
flood-plain deposits, while the shores of the bays and estuaries
frequently show wave-cut terraces covered with gravels and
ssands.

Tomales Bay Deposits —According to Anderson, the Pleisto-
cene deposits in the vicinity of Tomales Bay consist of ‘‘ Coarse
arkose detritus with an indistinet horizontal stratification. They
are found generally in the larger depressions of the peninsula,
and range in elevation from 500 feet downward. They form a
series of low, broad hills, extending along the middle of the
valley near Olema, and occur at intervals upon both shores of
Tomales Bay, forming there a system of low, bench-like terraces
below 200 feet in height. West of the main ridge they are found
in occasional patches around the flanks of the hills at the head
of Drake’s Estero and north of Abbott’s Lagoon.’’

Bodega Bay Deposits——At Bodega Bay similar deposits to
those mentioned by Anderson occur on both sides of the bay, but
only in small patches, most of them having been removed by
erosion. Near Bodega Point on the bay side is a remnant resting

an ®

Vor. +] ~Osmont.—Geological Section of Coast Ranges. 7

upon a wave-cut shelf just about at high-water mark and extend-
ing up to 113 feet above the same, consisting principally of dio-
rite sands, and occasional pebbles showing very indistinet hori-
zontal stratification and eross-beddine. On the ocean side of
the peninsula oceasional still smaller patehes, some twenty to
thirty feet thick, may be seen resting upon a very evenly worn
diorite surface, which at a point about three miles south of the
mouth of Salmon Creek dips gently toward the north and passes
under the beach and aeolian sands. On the eastern side of the
bay is a broad, flat terrace, about one-quarter of a mile in width
and some seventy-five to ninety feet above sea level at its back.
In most places only a thin veneer of gravel covers this terrace,
but at one point on shore, at the north end of the bay, a remnant
of gravel some fifty feet thick is resting upon the worn Fran-
cisean surface, which is here only some twenty feet above sea
level. It is made up chiefly of Franciscan pebbles, and loosely
coherent sands showing ecross-bedding. It has been somewhat
distorted, dipping shghtly to the north.

Flood Plain Deposits—AII the larger valleys of this portion
of the Coast Ranges, such as Santa Rosa, Sonoma and Napa Val-
ley, and the great Sacramento Valley itself, show extensive flood-
plain deposits extending up to an elevation many feet above the
present level of the streams. These terraces are usually covered
with, or largely made up of, ill-assorted heterogeneous material,
representing all the rocks of the immediate neighborhood. In
the case of the large streams like the Russian River, nearly all
the rocks of the whole area described in this paper are repre-
sented. Usually the stratification is very irregular and indis-
tinet, cross-bedding being common. Good exposures may be seen
along the railroad cuttings at many places in Santa Rosa Valley.
Here the material is usually made up of a very leght colored,
almost white, incoherent, silt-like sand, with much moderately
fine gravel containing a great variety of well worn pebbles, econ-
sisting of Franciscan cherts, quartz, sandstones and intrusives,
Knoxville sandstone, and a large proportion of Tertiary volean-
ics, conspicuous among which is a white rhyolite.

78 University of California Publications. [ GEOLOGY

STRUCTURE.
FOLDING OF THE MERCED.

It may be concluded that the folding of this series iInaugu-
rated the present Coast Ranges, and probably took place not
earlier than the very end of the Pliocene. Lawson’s work on the
Peninsula of San Francisco shows that the Merced beds to the
very top at Seven Mile Beach are sharply tilted, while resting
uneonformably upon these are strata of undoubted Pleistocene
age. This would seem to fix the uplift that disturbed the Merced
at the very close of Pliocene times. Recent work by Arnold*
points to the possibility of the upper portion of the Merced beds
at Seven Mile Beach being Pleistocene in age. If this is true,
the uphft did not take place until the Quaternary was some-
what advanced. In the present writer’s field the St. Helena Rhy-
olite is folded with the sedimentaries and voleanics beneath it,
and the upper portion of these sediments contains shells of
Mereed age. Furthermore, these rhyolites (‘‘asperites’’) overlie
the Cache Lake beds of Becker, which Marsh called late Pho-
cene. This, again, puts the date of the uplift not earlier than
the end of the Pliocene.

THE ST. HELENA FAULT.

Northwest of Calistoga, on the western flank of Mt. St.
Helena is an important fault. The shape of the mountain when
viewed from the south suggests a fault block. The straight line
of the top sloping gently to the eastward, and the precipitous
descent to the west, have all the appearance of a tilted block
with a fault escarpment. A trip on foot from the summit down
the southwest side of the mountain, along the divide between
Knight’s Valley and the head of Napa Valley, demonstrated to
the writer a condition of things as illustrated in Section AB.
The throw of this fault must be at least 2,500 feet.

Age.—This fault probably took place at the time of the uplift
which folded the Merced, since it appears to have been respon-
sible for the high ridge of which St. Helena and Cobb Mountain
are the culminating peaks, and to have preceded the great period

*The Palaeontology and Stratigraphy of the Marine Pliocene and Pleis-
tocene of San Pedro, Cal., Memoir Cal. Acad. of Sciences, Vol. ITI, p. 13.

Franz Valley

Sonoma Tuff

VY XXX
OR
0, XX)
x

KX) )
OOS
OX
i000, gilda
i ¢ OX XO nell RAK
CONAN MOL EONN LE SC OONeS,
SSI

x
ranuian

Franciscan

a Mark West
Andesite
A St. Helena
Rhyolite

~

S
® 3 s
= BS )
<< w
3 8 ‘S)
a E =
= ~ S
3 Ss 3
Y oy a

A
i
a
[|

[]
1]

= $ oer = > 23 Mt St. Helena
ES A: ri ‘anta Rosa 3 & 3 =3 fev. 4300 Mt.
é 3 2 E z ? : Vattey S% 2 x : es &
A Pacific Ocean e 3 g = e & MNaeWetl xo 5 3 Pe St. Helena =
f 3 s = Bois 5 Jark West = 3 2 Sonoma Tuff é
& San Pablo? é in Pablo? 3 Plain = é a é Rhyolite a Sonoma Tuff

Sea Level

a Franciscan Franciscan
Ss
Sr 5
2 ze == 3 : g ¥ -
= St. Helena 3B =i 5 6 mG s =
=: 2 $ = =
=§ Rhyolite __— 3= = s 5 2 m Ss 2
3 E é 2: g is San Pabio? z
~ fr = Sacramento =
2 =
as

Quaternary

Sea Level

Franciscan ‘Svasta-Chico

s S E
Point Reyes fad = =
© Pui eon Peninsula 3S 5
Monterey ea Tonister Bay) a a Quaternary
rl (ALA v x as =
Ce Peper er pre rete rye © = Siait
SAAAHA i Y EE Ee eT ht
‘Bodega Diorite Franciscan ‘Orindan?
aS s = ier ers = oe Sule
ZS Hi 6 es : = s 3 :
= 3 S23 (ss Se BS 2 < 3 e §
2 Sonoma Valley 223) ss se 6 é St. Helena § s Sus "
2 22) 2 He = Napa Valley Rhyolite 3 é eyes z
Soa § $= a= Hae © 5B = 5 Bs =
é laaternary es ; Cy 2 2 : a a @ Quaternary =
Sea Level a
ue ‘
ff HEE RE ss
‘San Pablo Tejon iFpanciacan
o
—
D = .
fee FE a fr
ig ed (| i iil — ei ee
M iy =
Quaternary Sp,Heien? Merced Basar Sonoma Tutt Mark West Gringan2 San Pablo? San Pablo Monterey ‘Tejon _—Shasta-Chico Franciscan Bodega Diorite

Vou. 4] Osmont.—Geological Section of Coast Ranges. 79

of erosion which resulted in the formation of Napa Valley, and
the other large valleys, of a similar stage of topographical matur-
ity, Sonoma and Santa Rosa. Napa Valley seems to have had its
inception along the line of weakness due to the St. Helena fault.
At Calistoga numerous hot springs oeeur. The writer does not.
know how far southward this fault extends. No evidence of it
was found in Section CD.
SAN BRUNO FAULT.

At Bodega and Point Reyes Peninsula the pre-Francisean
eranities (diorite) have probably been brought to leht by a
ereat fault along the line of Bodega and Tomales Bay, seem-
inely the northwest extension of the San Bruno fault dis-
eussed by Lawson* in deseribing the geology of San Francisco
Peninsula. Anderson suggests that this granite block during
Tertiary times may have been independent in its oscillations
from the mainland. Certainly Point Reyes Peninsula was be-
neath the waves during Monterey times, having been previously
relieved by erosion of nearly all the pre-granitic sedimentaries
and Franciscan which may have covered it, since Monterey
shales are found resting on the worn surface of the granite. On
the mainland, however, no Monterey is found nearer than the
east shore of San Pablo Bay. The Monterey is greatly folded,
occupying a synclinal basin in the granite, and the latter is con-
sequently sheared and faulted.

Evidence of Faulting at Bodega Bay—The only evidence of
faulting the writer obtained at Bodega Bay was:

1. The direction and shape of the bay, apparently merely a
northerly extension of the peculiarly long and narrow Tomales
Bay.

2. The very general crushed and sheared appearance of the
Bodega diorite, and numerous minor faults shown in it by the
pegmatite dykes.

3. The entire absence of Franciscan on Bodega Peninsula,
and of diorite on the east side of the bay.

4. The general westward trend of the Franciscan strata along
the east shore, pointing across the bay more or less toward the
diorite, as if abutting upon it.

*U. 8. G. 8, 15th Ann. Rpt.

80 University of California Publications. [ GEOLOGY

Age.—It seems likely that this fault is the northward exten-
sion of the San Bruno fault, which Lawson thinks was formed
about the time of the tilting of the Merced.

GEOMORPHOLOGY.

From the summit of Mt. St. Helena a magnificent view is
obtained of most of the area embraced in this paper. On clear
days the Sierras may be seen in the hazy distance beyond the
ereat Sacramento Valley, while to the west steamers may be
sighted on the waters of the Pacific. To the North Cobb Moun-
tain shuts off the view, but southward is the beautiful Napa
Valley stretching away toward San Francisco Bay, with Mt.
Diablo plainly discernible in the distance.

The Elevated Coastal Peneplain.—An interesting feature is
the very even, almost horizontal crest line of many of these
ridges. The one immediately adjacent to the coast appears
to have a very uniform elevation in the neighborhood of
800 feet for many miles south of the Russian River. The
break where the latter cuts through searcely makes any vis-
ible impression on this coast line. The ridge is composed entirely
of Franciscan strata, and has resisted erosion sufficiently to
retain a suggestion of its old topographic form. It is evidently
an old elevated and dissected peneplain.

Wide, Flat-bottomed Valleys of Erosion.—One of the most
striking peculiarities of the topography is the succession of par-
allel ridges extending in a roughly northwest and southeast direc-
tion, and separated by wide, flat-bottomed valleys.

Synclinal Valleys and Subsequent Drainage.—Between this
coastal ridge and Mt. St. Helena the hills are lower and not so
even in crest-line, being composed of hard lavas alternating with
soft tuffs and sandstones. This very fact has contributed to
the rapid maturing of the topography, causing the streams to
become largely subsequent in their nature, and to seek out the
synelinal and widen them as they approached base level, into
large, flat-bottomed valleys, such as Santa Rosa and Sonoma,
with well defined terraces up to 350 feet above the present flood
plain.

Vou. 4] Osmont.—Geological Section of Coast Ranges. 81

To the east is the wide, flat-bottomed Berryessa Valley, which
is also of the nature of a subsequent valley. It is not located in
a syneline, however, being along a contact between Knoxville
shales and sandstones dipping to the northeast, and large masses
of serpentine and Francisean rocks.

The Tertiary voleanics onee arched over this district, as
shown by the sections, and the valley may have started in a syn-
cline of Tertiary rocks which have now all been removed by
erosion. Immediately east of this valley is a very high ridge,
the crest of which is a very level sharp line about 2,600 feet above
sea-level for many miles north and south. This ridge owes its
even crest line to differential erosion, the alternation of hard
sandstone and limestone with soft shale in the Knoxville series
being peculiarly adapted to such weathering. *

East*of the above mentioned high ridge, but not visible from
Mt. St. Helena, are the subsequent valleys of Capay and Pleas-
ant. Here again the streams flow along a contaet between com-
paratively hard rocks and later softer ones, the Tertiary gravels
and soft sandstones overlying the Knoxville along this line.

Marine Terraces.—Anderson states that at Point Reyes Penin-
sula well defined wave-cut terraces occur up to 300 feet above
sea-level. In the portion of the coast with which the writer is
most familiar, namely, the vicinity of Bodega Bay, the only well
defined shelf is lower than this. On the eastern side of the bay
and northward toward the Russian River is a wide wave-cut
shelf of an average width of about one-quarter of a mile and an
elevation at its front edge of from twenty-five to thirty-five
feet above sea-level. This slopes gently upward toward the hills,
and at its back are frequently seen residual stacks and talus
from the old sea-cliff. A thin veneer of gravel oceurs in places
up to eighty or a hundred feet above sea-level. On the west
shore of Bodega Bay, as already mentioned under Pleistocene
deposits, is a distinet shelf cut in the diorite just about at high-
water mark. It is about 300 yards wide, and covered with gravel
and sand to a depth of 113 feet. The difference in the height of
this terrace on the two sides of the bay may perhaps be due to
comparatively recent movement along the Tomales Fault.

No well defined terraces were observed at Bodega Bay above

82 University of California Publications. [ GEOLOGY

the ones described. But the crest-line of the coastal ridge for a
considerable distance north and south is very nearly horizontal,
and at an elevation of about 750 to 800 feet above sea-level.
From a point on the upper road from Bodega Bay to the town of
Bodega, where it passes over the summit, the writer found nu-
merous pholas-borings in large Franciscan boulders which may
be residual stacks. At another place, about midway on the road
between Freestone and Occidental, and at nearly the same eleva-
tion, as determined roughly by aneroid, pholas-borings were
also observed.

Fault Origin of Mt. St. Helena.—Mt. St. Helena owes its
height mainly to a great fault, previously described, which has

elevated it at least 2,500 feet higher than the corresponding flows
of lava on the west side of Napa Valley. There is no evidence
of its ever having been a voleano. No erater, or residual neck, or
heterogeneity of materials is present. On the contrary, it is made
up of even, well defined flows of lava, which frequently show
evidence in columnar structure of having cooled as surface flows.
Mt. Cobb appears to be simply another point on this high ridge,
though the writer has no personal knowledge of it.

A nearly straight line through Cobb Mountain and St. Helena
southward would follow the high ridge east of Napa Valley,
crossing the bay near the Straits of Carquines, passing south
through Mt. Diablo, and, if continued farther south, would pass
through Mt. Hamilton. This line is evidently the axis of the
Range. Napa Valley has been determined partly by the St.
Helena Fault, and partly by its synelinal nature toward the
south.

Recent Submergence—The recent subsidence which has
affected this region is well illustrated at the mouths of all of the
streams flowing into the ocean and the bay. Russian River,
Salmon Creek, the Esteros Americano and San Antonio, and
Drake’s Bay at their mouths are wide, fiord-like bodies of water
with very precipitous shores, while the streams such as Petaluma
Creek and Napa Creek are mere sloughs in their lower limits,
meandering through broad, flat tule land bordered by steep hill-
sides. That they represent a submerged area is apparent to the
casual glance. Certain evidence exists to show that the sub-

a

Vor. 4] Osmont.—Geological Section of Coast Ranges. 83

mergence is going on at the present time in the vicinity of San
Francisco Bay. In recent excavations made at Shell Mound
Park, between Berkeley and Oakland, it was found that the base
of the shell beds are now four feet below the ordinary high-tide
mark. Since it is evident that the mound is a ‘*kitehen-midden,’’
and therefore built on the land, this fact proves that there has
been in very recent times a subsidence of at least four feet.
Geomorplhic Cycle—The topography of this section then may
be placed at a somewhat advanced stage in the geomorphie eyele,
and, sinee this eyele must have been inaugurated not earlier than
the beginning of the Pleistocene, the observer is immediately
impressed with the enormous amount of erosion which has taken
place, and the vast space of time represented by this the most

recent period of geological history.

HISTORICAL RESUME.

After the intrusion of the pre-Franciscan strata by the
eranities, a great period of erosion occurred, as shown by the
great unconformity existing between Franciscan and the older
rocks.

Upon this old, well worn surface the Franciscan series was
laid down, the variety of the sediments giving evidence of fre-
quent oscillations during their deposition, while the sharp fold-
ing and faulting that has taken place, and the voleanie intrusions,
attest the immense amount of movement subsequent to their
deposition.

During Shasta-Chico times probably the whole of this area
was deep under the sea and the Sierras were undergoing erosion,
for lying uneconformably upon the Franciscan, as well shown
in many places outside of this field, and suggested by the heavy
chert conglomerate of Capay Valley, is a vast accumulation of
thin-bedded shales and sandstones in monotonous rhymiecal sue-
cession, indicating deep-water deposition under certain peculiar,
and as yet unexplained, conditions. At the most conservative
estimate the Shasta-Chico strata in this territory have a thick-
ness of five miles, and they are probably considerably thicker
than this. The writer has no palaeontologieal evidence as to
whether or not they inelude the Chico. Certainly no heavy beds

84 Oniversity of California Publications. | GEOLOGY

of conglomerate were observed between the two, as seen on Yulen
Creek in Shasta County, and at Berkeley.

Very little Eocene strata were recognized in this field,
although they may exist in the lower foothills along the west
side of the Sacramento Valley beneath the late Tertiary sedi-
mentaries. The greater part of the territory to the west was
probably underoing erosion during this period.

The present almost entire absence of Monterey in this large
field, when it is known to be developed so extensively farther
south, does not necessarily mean that the Monterey sea was con-
fined to Point Reyes Peninsula, but the oceurrence of San Pablo
strata so near by, resting upon a very uneven Franciscan sur-
face free from Monterey, points to the region having been dry
land durine Monterey times.

In spite of the enormous length of this erosion interval, from
Zoeene to the end of the San Pablo, the Franciscan does not ap-
pear to have reached the stage of a peneplain, and it is not until
the end of the Pliocene that we find it reduced to that form.

The San Pablo strata are nowhere tn contact with the known
Monterey, so that the relations between the two are not clear
in this field, it being impossible to tell whether there was an ele-
vation of the region during the time between their depositon
and that of the Monterey, or whether continuous sedimentation
went on.

The blue San Pablo sandstone (tuff) at Carneros Creek indi-
cates that the andesitie detritus reached at least as far north
as the southern portion of this area. The sandstones and gravels
of supposed Orindan age in Petaluma Valley, containing lignite
beds and horse-teeth, indicate that lakes existed here during late
Miocene or early Pliocene times.

Between the supposed Orindan and the Mark West Andesite
there is a glaring unconformity. Hence it is probable that be-
tween the Orindan and the Merced there was an erosion interval
followed by a gradual subsidence of the land, the sea enecroach-
ing from the west toward the east on the area now roughly repre-
sented by Santa Rosa and Petaluma Valleys. Seemingly part
of the San Pablo beds to the west remained under water during
the elevation of those farther east, for along the Estero San Anto-

Vor. 4] Osmont.—Geological Section of Coast Ranges. 85

nio and at Freestone they lie nearly horizontal and conform in
dip with the Sonoma Tuff. Just prior to the Merced period
extensive voleanie disturbances took place, probably having their
center somewhere northeast of Santa Rosa Valley. Among the
reasons for this belief as to the locality of the center of disturb-
ance are the position of the overturned redwoods of the Petrified
Forest, with their roots pointed to the northeast, and the great
thickness of the tuffs and lava flows in their vicinity.

The voleanie disturbance was very great, and continued
throughout the whole of the Merced. The first outflows con-
sisted of pyroxene-andesite, which in the neighborhood of Mt.
St. Helena aggregates a thickness of about 1,500 feet. Follow-
ing this came a great outthrow of andesitic pumice and lapill,
with occasional thin flows of basalt, which spread over the
country to a maximum depth of nearly 2,000 feet, and were car-
ried down the streams into the lakes and seas, forming beds of
tuff and conglomerate from ten to two hundred feet thick.

While the voleanoes were throwing out this vast amount of
ashes and fragmental material, deposits, other than the tuff, were
forming in the seas and lakes, particularly in the region to the
west. Buff colored sandstone, and fine conglomerate with
numerous voleanie pebbles similar to those of the tuff, were
deposited in the region of Santa Rosa Valley to the depth of
between 2,000 and 3,000 feet. In the upper part of these beds
(Wilson Ranch Beds) fossils of Merced age were preserved.
Lakes of great size probably existed, since the relation of the
upper lava flows, the St. Helena Rhyolite, to Becker’s Cache
Lake Beds, and the correlation of the latter by Marsh with the
late Pliocene, point to a large Merced take in that neighborhood.

While the sediments were depositing in the seas and lakes,
large rivers were forming deltas with coarse gravels to great
depths, thus showing that a gradual subsidence was taking place.
A good illustration of this may be seen between Mark West
Springs and Santa Rosa Valley, where at least 2,000 feet of
coarse gravel has accumulated. The history of this old delta
bears a striking similarity to that of the Santa Clara-San Benito
Valley.*

*The Post-Pliocene Diastrophism of the Coast of Southern California.
Lawson. Bull. Dep. Geol., Univ. of Cal., Vol. 1, No. 4, p. 151.

86 University of California Publications. [GEOLOGY

During the gradual subsidence thus indicated, the sea prob-
ably encroached on the land from the west at Santa Rosa Valley
to form marine deposits.

So far as the writer’s personal observation goes, the last flow
of lava in this area was the St. Helena Rhyolite, which in the
vicinity of Mt. St. Helena has a thickness of at least 2,000 feet.
This How seems to have occurred at the end of the Merced, since
it everywhere overlies the Sonoma Tuff and the Cache Lake Beds,
and no pebbles of it are found in the Wilson Ranch Beds. Since
it is folded econformably with the Sonoma Tuff, and hence pre-
ceded the uphft and the great period of erosion which followed,
it is probably not later than the very latest Merced. Becker*
states that a later flow of basalt took place to the north, in the
Clear Lake region.

The great uplift which raised and folded all the Merced
strata is supposed by Lawsony to have taken place just at the
beginning of the Pleistocene. More recent work by Arnoldt on
the upper portion of the Merced, at Seven Mile Beach, points to
its somewhat later age. The fact that the St. Helena Rhyolite,
fully 2,000 feet thick in places, rests conformably upon the Mer-
ced sedimentaries, and is folded with them, would seem to sug-
gest this view, if we could be sure that the Wilson Ranch Beds
represent the whole of the Merced, but at present the palaeon-
tological evidence is not strong enough to settle this point.

At Wilson’s Ranch arca trilineata is very common, and Ash-
ley states that these large areas are common toward the base of
the Merced, but disappear before the top is reached. Hence the
Wilson Ranch Beds may represent only the lower part of the
Seven Mile Beach Beds.

Probaby during the time of this folding the St. Helena fault
occurred, by which the strata were displaced nearly 3,000 feet,
and the high ridge formed of which Mt. St. Helena and Cobb
Mountain are the culminating points. Probably about the same
time the San Bruno Fault on San Francisco Peninsula, and
its northern extension, the Tomales Fault, occurred, although,

*Mon. XIII, U. 8. G.S., pp. 157 and 223.

+Post Pliocene Diastrophism of the Coast of Southern California. Bull.

Dept. Geol., Univ. Cal., Vol. I, No. 4, p. 157.
¢Memoirs Acad. of Sciences, Vol. III, p. 13.

Vou. +] Osmont—Geological Section of Coast Ranges. 87

as suggested by Anderson, there may have been oscillations alone
this line in early Tertiary times.

After the folding an uphft occurred whieh was not contin-
uous, but was marked by periods of rest, and possibly of reversal
of motion, since along the coast these stoppages are recorded by
wide, wave-ceut terraces. The coast line of this section is made
up almost entirely of Franciscan rocks, which do not resist ero-
sion well enough to preserve the terraces higher than about 300
feet, the elevation of those at Point Reyes. The coastal ridge
between the writer’s two sections has a very even erest-line at
about 800 feet above sea-level, and on this he has found pholas-
borings at two places. To the north, however, Lawson” states that
a well defined wave-cut shelf exists at 1,520 feet. with many
others at lower elevations.

While this gradual elevation was takine place the streams
were dissecting and wearing down the rising land, and the im-
mense amount of erosion which has taken place since the inaugu-
ration of the post-Pliocene uplift is a measure of the vast length
of time represented by the Pleistocene. The geomorphic cycle
which had its beginning in the post-Phocene times has already
reached a stage of early maturity.

Following this elevation, and possibly only one of the retro-
grade steps in the general elevation of the coast, came the most
recent submergence of the region, as evidenced by the flooding
of the lower valleys of the streams and the formation of fiord-
hke estuaries at Russian River, Drake’s Bay, Estero Americano,
and San Antonio, Tomales Bay, and the great San Francisco
Bay itself, with its estuaries such as Petaluma Slough and Napa
River.

Evidence exists in submereed ‘‘kitechen-middens’’ to show
that this submergence is still going on at a rate which may be
measured in terms of inches and hundreds of years.

*“Geomorphogeny of the Coast of Northern California. Bull. Dept. Geol.,
Univ. of Cal., Vol. I, No. 5.

Berkeley, California,
December 1, 1904.

UNIVERSITY OF CALIFORNIA PUBLICATIONS
BULLETIN OF THE DEPARTMENT OF

GEOLOGY

Vol. 4, No. 4, pp. 89-100, Pls. 8-11 ANDREW C. LAWSON, Editor

ARCAS OF THE CALIFORNIA NEOCENE.

BY

VANCE C. OSMONT.

CONTENTS.

PAGE

lon trio cdhuiction tet eiais< Adil es Sa Gee weiss ely onto e wieaee gta needa oe 89
ATC AnNICLO CLO Mba O OMMEUG Me ceersudecrsyatava) erste tsratedel eats ais secre ete alee ete erie orice 90)
DOSGVIDGLONS seccnkencteat ayek-weie Shaan at es cere ate end ou etes saires SiG) cho epee eral auatle: Hes 90
Occurrence: and Associated Mauna 2.5.2 2s06 05252065 ene e ees . 91
FAM COMmmULMIIM Ceubeym COMMA A tay eset yesrevetenedecet sce ecs-aitereliettc atencpeteeleyie ists eqeiy eke et air 91
ID,esoath aRMlOysl, Rape aden Lede Oty cone iG Sam Odom Ua od Coo onto 9]
Occurrence and Associated Fauna .............:...-...--.--0-- : 92
AT CAM MODLETE YAN awe ILC W SPECIES cess teieyssseye qs ciate) alee cuseuens ete steeds 96
ESCLUP ELON core cucaenenes os aperenekeeNuedrey recat) gles er i ckenegetn sha eso a sonemeyon bicuscapertane,s2/ aie 96
Occurrence and: Associated Mauna 3.2.5.0... . 2222 -se se 96
No (aheaalkofertstesy, alan, Spores A Wa Ho ae es ey Bee od oon OS oe ce ac 98
IDEAYTOO Mss op oo eu Oo ono oeoG cd aaoe oe eco ome cote 98
Occurrence and Associated Fauna ...................0 0000 eae . 98
PATCH CANAIMS) COUNLAC Ns lecite clenes gis: teks sail ere usigre) sve) cis siuelisvers surveys ayiessl eteners 99
IDESCTIPLION™ 4 eioe acy wed wae shite oe eG ees. Sle cna sles See gts to eae 99
Occurrence and Associated Wauna Geese. oases eens te ; 99
GONCIUISIONS? 4.2) me tae. cute sie Simeone Giornaay soe ee eke leranine e santa miaee a oe 99

INTRODUCTION,

Among the most charaeteristic fossils of the California Neo-
cene the areas have an important place. They are widely dis-
tributed, both horizontally and vertically, in the geological sec-
tion. They seem to have been present in all parts of the region
and at all depths in the water. The species, being generally
short lived, are especially useful for age determinations. Unfor-
tunately the species have not been well defined or figured, and
some of the most characteristic ones have not been described. In
the following paper the writer has presented a comparison of

90 University of California Publications. [GEOLOGY

the described species, and a description of the forms recognized
by him, together with memoranda of their occurrence and the
associated fauna.

In this work the writer has had access to the collections of
the University of California, Stanford University, the California
Academy of Seiences, and the California State Mining Bureau.

ARCA MICRODONTA, Conrad.
Plate 8.
Arca microdonta. Conrad, 1853-4. Pac. R. R. Reps., Vol. V, p. 323,
Pl. II, fig. 29.

Description.—This species was originally described by Conrad
as follows: ‘‘Rhomboidal, ventricose, thick in substance, anterior
side very short, umbonal slope rounded. Ribs 25, prominent,
narrow, wider posteriorly except on posterior slope, where they
are small, and not prominent, about five in number. Cardinal
teeth small, numerous, closely arranged, margin profoundly
dentate, dorsal area rather wide and marked with about six im-
pressed lines, beaks distant.’’

The variations in this form, as shown in figs. la to 30, is con-
siderable, and was at first thought to be of specific value. The
specimen shown in figs. 2, 2a, and 2b was, however, found to
bridge over the differences and le near Conrad’s type. It was ac-
cordingly figured as the best representative of the type, along with
outline representations of other forms in figs. la, 1b, 3a, and 3b
for comparison. The specimen shown in figs. 3a and 36 is rather
small, measuring 45x33 mm. It is more ventricose and more ine-
quilateral than A. trilineata. It has 27 somewhat beveled ribs,
showing no sign of a median groove. The shell is wide and heavy,
with high beaks separated by a profound ligament area. The
posterior end is noticeably concave as far forward as the fifth or
sixth rib, as shown in Conrad’s figure.

The individual represented in figs. la and 16 is very inequilat-
eral, extremely ventricose, with beaks very heavy and high, and
the ligament area flaring end enormously developed, making the
thickness of the closed shell fully as great as its height. The
hinge line is relatively short, the beaks strongly incurved,
though very distant, and placed so close to the anterior end as

7

Vou. +] Osmont.—Arcas of California Neocene. 9]

to make this portion of the shell appear almost flat. The poste-
rior end is pointed, and that portion near the hinge coneave.
The basal margin is nearly straight, and parallel to the hinge
line. The ribs number 25 or 26, and are narrow and without
grooves. The growth lines tend to produce a beaded effect.

The specimen displayed in figs. 2, 24 and 2b appears to
bridge over the differences between those of figs. 1 and 3. It has
26 ribs.

Occurrence and Associated Fauna.—TVhe specimen shown in
fies. 8a and 30 is labelled Santa Moniea. In the Geology of Cali-
fornia Whitney states that the fossiliferous sandstones of Santa
Moniea have yielded the following fauna :

Neverita recluziana Desh. Cerithidea sacrata Cpr.
Twrritella ocoyana Cony. Cardita subtenta Cony.
Trochita costellata Cony. Mytilus edulis Winn.

Trurritella ocoyana alone shows this horizon to be lower Mio-
cene.

The specimen shown in figs. la and 16 was colleeted by Eld-
ridge from a limestone series below the silicious shales of the Dev-
i1’s Den region, in Kern County. Here were also found:

Astrodapsis tumidus Rém. or possi- Peclen sp., very large.
bly Clypeaster brewerianus Rém. Ostrea sp.
Pecten pabloensis Cony,

The form shown in fies. 2, 2a and 26 is from an unknown
locality.

A. microdonta seems to be a very variable, and is, so far as

known, confined to the Miocene.

ARCA TRILINEATA Conrad.
Plate 9, Figs. 4—4e.
Area trilineata Conrad. Pac. R. R. Reps., 1854-5, Vol. VI, p. 70,
VEIL, 1s cakes, GY
Area sulcicosta Gabb. Palacontology Cal. Vol., IL, p. 31, Pl. 9, fig. 53.
Arca schizotoma Dall. Trans. Wag. Ir. Inst., Vol. 3, Pt. 4, p. 659.

Description —Conrad’s description is as follows: **'Trape-
zoidal, somewhat produced, inequilateral, ventricose, ribs 22-24,
scarcely prominent, square, wider than the intervening spaces,
ornamented with three impressed or four raised lines; disk con-
centrically wrinkled; summits prominent; beaks approximate.
Leneth 3 inches.”’

92 University of Californa Publications. [GEOLOGY

Gabb gave the following description: ‘‘Shell thin, broad;
beaks prominent, ineurved, approximate, slightly twisted ante-
riorly ; hinge line short; ends and base pretty regularly rounded,
posterior basal portion a little the most prominent; area very
narrow, shehtly sunken. Surface marked by about 25 prominent
square ribs, with flat, equal interspaces; these ribs are each
marked by a more or less distinct median groove, and crossed by
pretty strong concentric lines of growth, breaking up the surface
into a beautiful beading. Hinge straight, composed of numerous
fine teeth, very small and irregular in the middle, longer and
shehtly oblique toward the ends.’’

This shell is ordinarily elliptical to quadrate in form and
inequilateral. The ratio of length to height is about 114 to 1.
The size of average adults is about 77x63 mm. The beaks are
prominent, close together, wide, centrally located, and strongly
ineurved over a ligament area which though wide is not flaring.
The elevation of the ligament area and width of the beaks makes
the upper margin appear strongly rounded.

There are 25-27 ribs. These are flattened, considerably wider
than the interspaces and marked by a very distinct median
eroove, to which are added toward the margin in old individuals,
two subsiduary grooves, and later in the largest specimens an
additional pair. In these latter the ribs toward the margin are
often several times as wide as the intervening spaces. Crossing
the ribs are numerous closely arranged lines, giving the shell a
beautiful beaded effect, especially well shown in younger indi-
viduals.

This species becomes very large, some individuals being
observed 114x76 mm. The smaller individuals showine the
heavily beaded ribs have generally been considered as Gabb’s A.
sulcicosta, the larger being referred to Conrad’s A. trilineata.
A number of fine specimens from Capitola, and also a good suite
from Russian River, show the apparent specific differences to he
merely those of age.

Occurrence and Associated Fauna.—Conrad gives Santa Bar-
bara as the type locality for A. trilineata, and lists the following
fauna from that place:

Vou. 4] Osmont.—Arcas of California Neocene. 93

Pandora bilirata Cony.

Mulinia densata Conv.

Arca trilineata Cony. Cardita occidentalis Cony.

trea canalis Cony. Diodora crucibuleformis Cony.
Janirva bella Cony.
is found at Santa Barbara,

Gabb states that A. suletcosta

Santa Rosa, Valley of Russian River, Half Moon Bay, Capitola,
Foxins (Griswold’s ?), San Fernando. He ealls the above forma-

tion Pliocene and lists the following fauna:

SANTA BARBAR

Neptunea tabulata Baird.
Lunatia lewesti Gld.

Crepidula grandis Midd.
Schizothaerus nuttalli Cony.

Lutricola alta Cpr.

SANTA ROSA
Nassa fossata Glad.
Crepidula princeps Cony.
Modiola recta Cony.
Machaera potula Cpr.
Cryptomya californica Cour,
Macoma nasuta Cony.

A (Gabb).

Macoma edulis Nuttl.
Caryatis barbarensis Gabb.
Tapes tenerrima Cpr.
Saridomus gracilis Glad.

Cardita ventricosa Glad.

(Gabb).
Val.

Tapes staminea Cony.

Chione succinta

Lucina borealis Linn.
Solen rosaceus Cpr.
Axinea patula Cony.

Area sulcicosta Gabb.

SAN FERNANDO (Gabb).

Lucina richthofent Gabb.
Lucini borealis Linn.
Neptunea tabulata Baird.
Neptunea humerosa Gabb.
Nassa fossata Gld.
Nassa perpenguis Has.
Purpwa saxicola Val.
Lunatia vichthofent.
Lunatia lewisii Gld.
Neverita recluziana Desh.
Sinum planicostum Gabb.

Conus californicus Hinds.
Cancellaria altispira Gabb.
Tritomium cooperi.
Crepidula grandis Midd.
Crepidula dorsata Brod.
Calliostoma costata Mark.
Acmaea rudis Gabb.
Bulla Glad.

Solen rvosaceus Cpr.

nebulosa

Siliqua edulata Gabb.

At Wilson’s Ranch, Russian River, near Mark West Creek,

the writer has collected the following:

Tapes staleyi Gabb.
Macoma nasuta Cony.
Standella sp.

Schizothaerus nuttalli Cony.
Natica clausa Brod. and Sby.
Natica lewisii Gld.

Olivella biplicata Sby.
Neptunea tabulata Baird.

Area trilineata Cony.

Nassa perpengus Hads.
Cardium corbis Martyn.
Crepidula grandis (2?) Midd.
Purpura saxicola Val.

Solen sp.

Pleurotoma sp.

94 University of California Publications. [| GEOLOGY

In Ashley’s paper on the ‘‘Neocene of the Santa Cruz Moun-
tains,’ he gives the following fauna for presumably the same
beds as those Gabb refers to at San Fernando, though he men-
tions no areas. He calls it Merced, transitional in the lower part:

Amusium caurinwm Glad. Nassa californiana Cony.
Cancellaria ef. vetusta Gabb. Ostrea veatchtii Gabb.
Calyptraea filosa Gabb. Neptunea humerosa Gabb.
Cardium meekianum Gabb. Pachypoma gibberosum Chem.
Chione simillima Sby. Livopecten estrellanus Cony.
Crepidula rogosa Nutt). Pisania fortis Carpt.
Dentalium hexagonum Sby. Saxridomus gibbosus Gabb.
Dosinia ponderosa Gray. Solen sicarius Gld.
Drillia torosa Carpt. Turritella cooper Carpt.
Lunatia lewesii Gld. Turritella jewettt Carpt.
Macoma nasuta Cour. Venericardia ventricosa Gld.

Myurella simplex Carpt.

For the section from Montara to Capitola, Ashley gives a
fauna of fifty-two species, which includes three areas. There is
little doubt that his 4A. microdonta is really A. trilineata. Since he
states that ‘‘In these strata we find great numbers of several spe-
cies of areca, some of which are over four inches broad.’’ And
after examining a large number of specimens from Capitola I
find all these large areas to be A. trilineata. The young individ-
uals are identical with A. sulcicosta. Conrad deseribed A. canalis
from the same bed with A. trilineata, and the writer has seen
specimens from Ilalf Moon Bay. Ashley calls the main bulk of
these beds Merced; the lower part, or pecten beds, where Pecten
cauriius is very abundant, he calls transition beds, considering

them to be in part Miocene.

MONTARA 0 CAPITOLA. (Ashley).

Astyris gausapata Gld. Purpura saxicola Val.

Calyptraca inornata Gabb. Surcula carpenteriana Gabb.
Cancellaria tritonidea Gabb. Volutilithes indurata Cony.
Chorus belcheri Winds. Acila castrensis Hinds.
Crepidula grandis Midd. Arca canalis Cony.
Cryptichiton ef. stelleri Midd.

Lunatia lewisti Gld.

Arca microdonta Conr.
Arca sulcicosta Gabb.
Nassa californiana Cony. Cardium corbis Martyn.

Nassa perpenguis Hds. Cardium mechianum Gabb.

Natica clausa Brod. and Sby.
Chrysodomus humerosus Gabb.
Chrysodomus tabulatus Baird.

Purpwa crispata Chem,

Chione similima Sby.
Cryptomya californica Cony.
Cyrena californica Gabb.
Glycimeris generosa Gld.

VoL. 4]

Lucina borealis Linn.
Macoma nasuta Cony.
Macoma edulis Nuttl.
Meretria traskii Cony.
Modiola flabellata Glad.
Mya truneata (7?)
Pachydesma imezana Cony.
Pecten caurinus Glad.
Pecten pabloensis Cony.
Pecten propatulus Cony.

Psammnobia rubroradiata Cony.

Sanguinolaria nuttalliana Cony.
Saxridomus gibbosus Gabb.

Osmont.—Arcas of California Neocene. 95

Schizothoerus nuttalli Conr.
Siliqua patula Dixon.
Solen sicarius Gld.
Standella californica Conr.
Standella falcata Glad.
Standella nasuta Gld.
Tapes staminea Cony.
Tapes tenerrima Carpt.
Mectra pajaroensis Cony.
Yoldia cooperi: Gabb.
Zirphoea crispata Linn.
Scutella gibbsi Rem.
Scutella interlineata Stimp.

The Wild Cat series of Lawson has yielded the following

fauna, principally from the Seotia, Humboldt County, seetion :

Cardium meekianum Gabb.
Pecten cawrinus Glad.
Tapes staleyi Gabb.
Schizothoerus nuttalli Cony.
Machaera patula Dixon.
Macoma edulis Nuttl.
Macoma expansa Carpt.
Macoma nasuta Cony.
Solen rosaceus Carpt.
Standella falcata Gld.
Thracia trapezoides Cony.
Modiola multiradiata Gabb.
Mytilus californianus Cony.
Saxidomus gibbosus Gabb.
Yoldia impressa Cony.
Balanus sp.

Neptunea altispira Gabb.
Neptuna tabulata Baird.

Drillia voyi Gabb.

Olivella boetica Carpt.
Lunatia pallida Brod. and Sby.
Purpura canaliculata Duel.
Columbella richthofen Gabb.
Scutella interlineata Stimp.
Cancer breweri (2?) Gabb.
Nassa fossata Glad.

Cardium blandum Glad.
Psephis lordi (2?) Baird.
Standella planulata Conr.
Natica clausa Brod. and Sby.
Fusus, a. sp.

Mactra sp.

Arca sulcicosta Gabb.
Priscofusus oregonensis Cony.
Priscofusus devinctus Conr.
Priene oregonensis Redf.

This formation has been correlated with the Merced of Seven

Mile Beach.

Mr. F. M. Anderson of the California Academy of Science

kindly showed the writer specimens of this species from the San

Pablo, associated with the following fauna:

KETTLEMAN HILLS, FRESNO COUNTY, CALIFORNIA.

Pseudocardium gabbi Rém.
Cardium meekianum Gabb.
Scutella gibbsi Rém.

Ostrea bourgeoisi: Rém.
Balanus sp.

Pecten sp.

96 University of California Publications. | GROLOGY

ZAPATO CHINO CREEK, FRESNO COUNTY, CALIFORNIA.

Saxvidomus aratus Gld. Seutella gibbsi Rém.
Clypeaster (Scutella) brewerianus Neverita recluziana Petit.

Rém. Nassa californiana Cony.
_istrodapsis tumidus Rém. Pecten sp.

TAR RANCH.

Chione sp. Neverita recluziana Petit.
Scutella gibbsi Rém. Zirphaea dentata Gabb.
Tapes staminea Cony.

Arca trilineata appears first in the San Pablo, though how
far down in this formation is not yet certain, and extends
through the lower and middle Merced, disappearing somewhere
between the Middle Mereed and the Upper Gastropod Bed of the
Seven Mile Beach section. It is most abundant in the Lower and
Middle Mereed.

ARCA MONTEREYANA, New species.

Plate 9, Figs. 5, 5a and 5b.

Description.—Rhomboidal, inequilateral, nearly two-thirds
of the leneth being behind the beak, posterior margin making a
very obtuse angle with hinge-line. Ratio of length to height
about 1144 to 1. Average size of adult about 51x33 mm. Beaks
not prominent, turned rather sharply forward, narrow and close
together, ligament area narrow. Hinge line long and straight.
Basal margin nearly parallel to hinge line. Ribs 26-32, usually
27, prominent, square, flattened, a little wider than the inter-
spaces and marked with a median groove. Occasionally, in the
older specimens, two subsidiary grooves inay appear toward the
Inarein, as In A trilineata. More or less distinct lines of growth
often roughen the shell, especially in the larger individuals, and
when these are fine and numerous they approach closely the
beaded effect of A. trilineata.

This shell is distinguished from A. trilineata and A. canalis
by its more inequilateral form, low, narrow beak, greater pro-
portional leneth, long straight hinge-line and generally less in-
flated shell. The latter characteristic, together with the median
erooves on the ribs, distinguishes it from A. microdonta.

Occurrence and Associated Fauna.—This species occurs most
abundantly in the sandy phases of the Monterey Miocene asso-

Vou. +] Osmont.—Arcas of California Neocene. 97
elated with the shale, and sometimes in the shale itself. In the

latter case it is usually small. It rarely occurs in the typical

shale. At Selbys, near Vallejo Junction, it is found in a calea-
reous iayer in the shale with the same fauna as that in the sandy
layers below.

It is
It probably oceurs in the typical

It is common in the Monterey of the Pinole section.
also found at Walnut Creek.
shale at Carmelo Bay, and is also found at Barker’s Ranch, near
Bakersfield.
it is associated with the following fauna:

It is most abundant in the middle Monterey, where

Crepidula grandis Midd. Tellina bodegensis Hinds.

Glycimeris generosa Glad. Nassd, n.

Pandora scapha Gabb.

sp.

Siliqua patula Cony,
Yoldia cooperi Gabb. Lucina borealis Linn.
Leda taphria Dall. .

Solen sp.

Chione succincta Val.
Callista, n. sp.
lewesii Gld. Mactra

Lunatia sp.

At Barker’s Ranch it is found with a fauna of lower Monte-
rey age, as follows:
Agasoma barkerianum Cpr.
Agasoma kernanum Cpr.
Agasoma, nN. sp.
Turritella ocoyana Cony.

Neptunea, n. sp.

Leda taphria Dall.
Yoldia coopert Gabb.
Lucina richthofeni Gabb.
Conus, n. sp. near californicus Hds. Neverita recluziana Cony.
Surcula carpenteriana Gabb.
Pleurotoma sp.

Trochita sp. like filosa Gabb.
Myurella sp. like simplex Carpt.
Cancellaria sp (a) new.
Cancellaria sp. (b) new.
Dosinia sp.

Natica ocoyana Cony.
Voluta, n. sp.
Standella indet.
Crucibulum sp.
Dentalium sp.

Solen sp.

Pecten sp.

Nassa sp. near perpenguis Hds.
Nassa sp.

Tellina sp.

The writer has seen specimens of this species collected by
Anderson and associated with the following lower San Pablo
fauna:

Pecten pabloensis Gabb.
Pecten estrellanus Cony.
Dosinia ponderosa Gabb.
Lucina borealis Linn.

Tapes tenerrima Gabb.

Mytilus californianus Gabb.
Mactra (Spisula) faleata Gla.
Macoma inquinata Desh.

Mactra (Pseudocardium ) sp.
Hemifusus sp.

Trophon(aff. T. ponderosum )Gabhb.
Neverita recluziana Desh.

Trochita sp.

Astrodapsis twmidus Rém.

Sharks’ teeth.

98 University of California Publications. [ GEOLOGY

This seems to be a characteristic Monterey Miocene species,
most abundant in the middle portion of that formation, but also
found in the lower and upper part, and in the lowermost San
Pablo.

ARCA CAMULOENSIS, new species.

Plate 10, Figs. 6 and 6a; Pl. 11, Figs. 6b and Ge.

Description.—Shell quadrate to circular, height only shehtly
less than leneth, (adult 90x 98 mm.), almost equilateral, thick-
ness through closed shell nearly equal to height. Beaks not
widely separated, very shehtly turned forward, and greatly
incurved over a wide and flaring heament area. Ribs about 32
in ntunber, rounded and without grooves, considerably wider
than the interspaces, and crossed by regular ridges, which eive
them a beaded structure. At about the ninth rib from the pos-
terior end is a very distinct shoulder, from which there is a steep
concave slope to the posterior margin.

Occurrence and Associated Fauna—A. camuloensis oceurs
near Camulos, Ventura County, in the Puente Hills, Los Angeles
County, and in the foothills of the Santa Ana Mountains.

Associated fauna five miles northeast of Camulos:

Cancellaria, a. sp. Clementia subdiaphana Carpt.
Cardium, indet. Fusus ambustus Gld.
Chrysodomus, i. Sp. Lutricola alta Cony.

Conus californicus Has. Natica (Lunatia) lewisii Gld.
Nassa californiana Cony. Nucula, n. sp.

Natica, sp. indet. Ostrea veatchiu Gabb.
Pachypoma, n. sp. Pecten cerrosensis Gabb.
Turritella, n. sp. Priene oregonensis Redt. sp.

Acila castrensis Hds.

It is reported from the Puente Hills* associated with a fauna
determined as of Pliocene age. This form is not distantly removed
from A. grandis, but can be distinguished from it by both the
form of the shell and the character of the ornamentation.

*Bull. No. 19, Calif. State Mining Bureau, pp. 220-222.

Von. +] Osmont.—Arcas of California Neocene. 99

ARCA CANALIS Conrad.
Plate 11, Figs. 7, 7a and 7b.
Areca Canalis Conrad. Pae. R. R. Reps., 1854-5, Vol. 6, p. 70, Pl. 2,
fig. 8.

Description.—This species was deseribed by Conrad as fol-
lows: ‘‘Subtrapezoidal, ventricose, ribs 24-26, flattened, scarcely
prominent, divided by a longitudinal furrow, disk concentrically
wrinkled, wmbo ventricose, sumanits prominent, remote from the
center.’

There seems to be little difference between this form and
A. trilineata, the prineipal difference being that the beaks are
more distant and less ineurved and the ligament area in cl. ca-
nalis more flaring. The additional erooves, and also the beaded
effect of A. trilineata, seem to appear occasionally on A. canalis
also. The flare of the ligament area does not appear to be an
absolutely constant factor, and its importance as a speeifie char-
acter is somewhat doubtful.

Occurrence and Associated Fauna—Vhis species oceurs at
Santa Barbara, as noted by Conrad, and is called Phocene by
him. Specimens are also known from the MeKittrick Oil Dis-
trict, from a horizon very doubtfully referred to the San Pablo.
It is cited by Ashley as occurring in the Ifalf Moon Bay and the
Capitola sections. The writer has seen specimens from Half
Moon Bay. It seems therefore to be a form closely related to,
if not identical with, A. frilineata Conr., and to have the same
range as that species. It also occurs in the San Pablo of Zapato
Chino Creek, Fresno County, the fauna of which is listed under
A. trilineata.

CONCLUSIONS.

The above species comprise all the Neocene areas of Cali-
fornia, so far as the writer has been able to determine. Other
species are mentioned by Conrad, viz.: A. congesta and A. obis-
poana. The figure of the latter is very poor. It may represent
A. montereyana, but is not perfect enough for identification
More investigation may, however, show it to be a valid species.
The former might be the young of any one of several species.

As to vertical range, we may, from our present knowledge,
fairly assume that :

100 University of California Publications. [GEOLOGY

Arca microdonta belongs to the Monterey Miocene.

A. montereyana ranges from the lower Monterey Miocene
through the middle and upper divisions, and into the lower San
Pablo. It is very much more abundant in the middle Monterey
than elsewhere.

A. canalis seems to extend from the middle San Pablo to the
middle Mereed.

A. trilineata is known in the San Pablo, though not certainly
in the lowest member, and seems to extend to a. point somewhat
above the middle Merced. It is most abundant in the lower and
middle Merced.

A. camuloensis is so far known from only a few localities,
occurring in strata probably referable to the Pliocene.

Berkeley, California.
November 30, 1904.

EXPLANATION OF PLATE 8.

Arca microdonta Conv.
Figures natural size.

Figs. la, 2a and 3a,—Outline views of three individuals, seen from above.

Figs. 2 and 2b.—Lateral and anterior view of specimen, also shown in out-
line in fig. 2a.

Figs. 1b, 2b and 3b.—Outline views of three individuals, seen from ante-
- vior side. The individuals are the same as those shown in figs.
la, 2a and 3a, and are arranged in the same order.

CAL.

UNIV,

BUDE DEPIn GEOL.

2a

Ta

\

HXPLANATION OF PLATE 9.

4.—Arca trilineata Cony. Lateral view. Natural size.
da.— Arca trilineata Cony. Anterior view. Natural size.

4b.— Arca trilineata Conr. Hinge. Natural size.

. 4e.—Arca trilineata Cony. Detail of beading on the ribs. 2.

5.—Area montereyana, vn. sp. Lateral view. Natural size.

5a.—Arca montereyana, n. sp. Hinge and inner side of left valve.
Natural size.
5b.— Arca montereyana, n. sp. Lateral view of valve shown in fig. 5a,

Natural size.

WIV, CAL,

i.
|

U

BULE DERI. GEOL

‘

.

EXPLANATION OF PLATE 10.

Arca Camuloensis, u. sp.
Figures natural size.

Fig. 6.—Side view of a somewhat weathered specimen from which the sur-
face sculpture has largely disappeared.

Fig. 6a.—Anterior view of specimen shown in fig. 6.

4, Pl 10

VOI

CALE

UNIV,

BULL, DEPT. GEOL.

EXPLANATION OF PLATE 11.

g. 6b.—Area camuloensis, n. sp. Outline view of upper side of specimen

shown on Plate 10. Natural size.

hig. 6e.— Area camuloensis, n. sp. Detail of rib ornamentation. 2.

Fig. 7.—Arca canalis Conr, Side view. Natural size.

Mig Ta.—Area canalis Conr. End view of specimen shown in fig. 7,
Natural size.

hig. 7b.—Area canalis Cony. Hinge. Natural size.

BULL. DEPT, GEOL. UNIV. CAL.

VOL, 4, PL

UNIVERSITY OF CALIFORNIA PUBLICATIONS
BULLETIN OF THE DEPARTMENT OF

GEOLOGY

Vol. 4, No. 5, pp. 101-123, Pls. 12-13. ANDREW C. LAWSON, Editor

CONTRIBUTION TO THE PALAEONTOLOGY
OF THE MARTINEZ GROUP.

BY

CHARLES EK. WEAVER.

CONTENTS.

PAGE

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102 University of California Publications. [GEOLOGY

INTRODUCTION.

In the following paper an attempt has been made to bring
together the already ascertained facts concerning the Palaeon-
tology of the Martinez Group, and to add to them a considerable
body of new evidence. The present investigation was begun by
Professor J. C. Merriam, who made an extensive collection of
Chico, Martinez and Tejon fossils from several localities in
Contra Costa County, to the south and west of the town of Mar-
tinez. These formations were mapped by Professor Merriam in
detail, the stratigraphic relationships were determined, and many
new clements were recognized in the faunas. The completion of
this work was suggested to the writer by Professor Merriam. The
continuation of the investigation has consisted in an examination
of all the known Martinez outerops in the State, in the collection
of additional fossils, in the study of the fauna with special con-
sideration of correlation, and in the description of a number of
new and characteristic forms.

During the early months of 1904, about four weeks of field
work were devoted to a study of the geologic and stratigraphic
relations of these formations in the vicinity of Benicia, Arms
Point and Martinez. Later in the year two trips were made to
Lake County, where fossils of Martinez age were reported to
occur. During the summer of 1904 about nine weeks were spent
in mapping the Napa quadrangle, upon which are located the
regions about Martinez and Benicia. In connection with this
work an attempt was made to discover any stratigraphic relation-
ships which might exist between the Martinez beds of Lake
County and those in the vicinity of Karquines Strait. The
study of the fauna has resulted in the description of twenty-one
new species.

HISTORICAL REVIEW.

The Martinez formation was first recognized in 1869 by Wil-
liam M. Gabb* in volume two of his work on the Palaeontology
of Catifornia. In the earher volumey on the Palaeontology of
California Gabb divided his Cretaceous into an upper and lower

“Rep. Geol. Surv. of Calif. Palaeontology, Vol. II, p. 13 op. preface.

7yRep. Geol. Surv. of Calif. Palaeontology, Vol. I, 1864.

Vou. 4] Weaver—Palacontology of the Martinez Group. 103

division, designating them as A and B and ineludine in the
former all the beds now known as Chico, Horsetown and Knox-
ville. His upper division, Cretaceous B, comprised the upper
division of the Eoeene as known to-day. Later, in 1869, when the
second volume of the Palaeontology appeared, this classification
was more clearly defined. Cretaceous A was subdivided into the
Shasta and Chico groups, and division B was named Tejon.
Between the Chico and Tejon he provisionally placed the Mar-
tinez Group, which he considered to be of small geographical
extent, and suggested that it might be a subdivision of the Chico.

The list of fossils collected from the Martinez beds by Gabb
appeared to indicate a possible transition from the Chico to
Tejon, and when later the Tejon came to be regarded as Eocene,

‘

still more significanee was attached to these ‘‘ Intermediate beds.’’

The classification as set forth in the Palaeontology of the Cah-
fornia Survey conflicted with later views, and hence led to
confusion. This confusion was largely cleared up in a paper

6

on the ‘‘Cretaceous and Eocene of the Pacifie Coast’? by Dr.
T. W. Stanton,* in which he reorganized the earlier classification,
basing it upon the results of more detailed investigations. In
this new arrangement he divided the Martinez Group of Gabb
into two parts and, on the basis of its faunal and stratigraphie
relations, placed one part in the Chico and the other in the
Eocene, designating the latter as lower Tejon.

In the following year a discussion of the question was
published by Professor J. ©. Merriam.; This investigation
was based on a study of the geological relations of the Martinez
Group at the typical locality. An extensive collection of fossils
was made, extending into both the Chico below and the Tejon
above. From the data obtained he was able to show that the
Martinez fauna, consisting of over sixty species, was a unit quite
distinct from the @hieco and Tejon. Only a very few species
were found in common with them. On a lithological basis he
distinguished the Martinez from the adjoining formations, in
that it showed the presence of considerable quantities of gelau-

*The Faunal Relations of the Kocene and Upper Cretaceous on the Pa-
cific Coast. 17th Ann. Rep. U. 8. Geol. Surv., pp. 1011-1060, 1895-96.

*The Geologic Relations of the Martinez Group of California at the
Typical Locality. Jour. of Geol., Vol. 5, pp. 767-775, 1897.

104 University of California Publications. | GEOLOGY

conite and possessed a peculiar gray color, in contrast with the
yellowish or bluish rocks of the Chico and the more massive white
to dull red Tejon sandstones. The thickness of the Martinez was
estimated to be somewhere between one and two thousand feet.
The results arrived at by Professor Merriam agree with those of
Dr. Stanton, and the position of the Martinez beds was deter-
mined as in the lower Eocene. The Martinez was, however, recog-
nized as a geological formation distinct from the Tejon.

Dr. W. H. Dall,* in an article entitled ‘‘ A Table of the North
American Tertiary Horizons, Correlated with One Another and
with those of Western Europe,’’ correlates the Martinez and
Tejon with the Midwayan stage of the southeastern United States
and with the Cernaysian of Europe. In other words, he considers
it to represent the extreme lower portion of the Eocene.

In an article written by Professor Andrew C. Lawsony in
1902 on ‘‘A Geological Section of the Middle Coast Ranges of
California,’’ the Martinez and Tejon are jointly termed the Kar-
quines series. ‘he combined thickness of the two is placed at
4,300 feet.

GEOGRAPHIC DISTRIBUTION,

The Martinez formation as at present known does not have
an extensive geographic range. The best studied locality, and
the one from which the formation takes it name, occurs in Contra
Costa County, to the south and west of the town of Martinez.
These beds run south from Martinez and disappear under the
alluvium of Walnut Creek valley. A portion of it extends up
Del Hambre Canon to the northwest. To the east of Martinez
and south of Bull’s Head Point, another outcrop occurs, having
a general northwest-southeast trend. On the opposite side of
Karquines Strait, at the Benicia arsenal grounds, a continuation
of these beds appears. They may be traced for a distance of
three miles to the north of Benicia. Farther north, in southern
Lake County, this same formation is again found. It first out-
crops just east of the town of Lower Lake, and may be traced
to the southeast for several miles. No connection of these beds
with those farther south could be found, and from the structural

*18th Ann. Rept. U. 8. Geol. Surv., Pt. II, 1898, pp. 327-348.
Science. N.S., Vol. 15, p. 416, 1902.

Vou. 4] Weaver.—Palaeontology of the Martinez Group. 105

relations between the two localities it does not seem probable that
it ever existed. At the present time these are the only localities
where beds of distinct Martinez age are recognized.

STRATIGRAPHIC RELATIONS.

The stratigraphic relations existing between the Martinez and
either the Chico below or the Tejon above throw httle light upon
its separation as a distinet formation. As yet no contact has been
observed where the exact relations between them can satisfac-
torily be determined, and at no loeality in this region has a dis-
tinct angular unconformity been noticed.

In the vicinity of the Strait of Karquines the Chico, Mar-
tinez, Tejon and Monterey have all participated in the folding of
the strata, which has resulted in the formation of a synelinal
trough the axis of which has a northwest to southeast trend. The
apex is situated about four miles to the north of Benicia. The
maximum width of this synecline, extending from a short distance
west of Pacheco on the east to Del Hambre Canon on the west,
is about four miles. In this cross-section the Chico, Martinez,
Tejon and Monterey are found in succession toward the center
of the syneline. The same holds true on the northern side
of the straits, except that the Monterey is not represented.

To the south and west of Martinez, on the western limb of the
syneline, all of these beds dip at high angles to the northeast.
West of the syneline the Martinez becomes thinner, and is repre-
sented by a narrow strip extending up nearly to the head of Del
Hambre Canon. At this locality the Martinez, together with the
Chico, dip to the southwest.

On the eastern flank of the syneline, beds of Martinez age
are represented immediately west of Bull’s Head Point, and
south of this point they appear east of the road leading from
Pacheco to Martinez. These, together with the Chico and Tejon,
dip steeply to the southwest. The strike of these beds carries
them across the Strait of Karquines, where they again outcrop
just north of Army Point Station. At this point the formation
was so thickly bedded that it was difficult to obtain accurate
observations of the dip. Apparently, however, they dip at high
angles to the southwest. In this locality the outcrops are sepa-

106 University of California Publications. . [GroLocy

rated from both Chico and Tejon by low marshes, so that no
aetual contact could be observed. However, no marked irregu-
larity in the dip was seen. The strike of these beds was traced
to a point about three miles northwest of Benicia. Farther
than this no outerops were seen which could definitely be called
Martinez. To the west of Benicia thick bedded sandstones closely
resembling those at Army Point were observed dipping steeply
to the northeast. Farther west the Chico again occurs, dipping
at the same angle as the thick bedded sandstones, but near the
shore it is folded and again dips to the southwest. The strike
and dip of these beds where carried across the straits are almost
identical with those south and west of Martinez. The most rea-
sonable conelusion would seem to be that there exists here a
closely folded syneline.

Farther north, in Lake County, a similar structure seems to
exist, viz: a closely folded syncline having a. general northwest-
southeast strike, with its apex about three miles northwest of the
town of Lower Lake. The width of the syneline below Lower Lake
is about three miles. The strata on both flanks dip at extremely
high angles toward the axis. The formations represented are,
Chico, Martinez and Tejon. The areal extent of the Martinez
outcrops was not determined, but they appear to be consider-
ably greater than those about the Strait of Karquines. Beds
of Martinez age may possibly be represented in northern Lake
County, near the town of Upper Lake. Dr. H. W. Fairbanks,*
who has examined that region, states that ‘‘a ridge of soft sand-
stone begins a mile northwest of Upper Lake and extends north-
westerly for about ten miles between Middle Creek and Bachelor
Valley. It rises perhaps one thousand feet above Clear Lake.
The strata are thick bedded and almost level, and are underlain
by the argillites of the older series which replace the sandstone
on the northwest. It contains no fossils, but from its resemblance
to the fossiliferous Chico-Tejon sandstones near Lower Lake, it
is Judged to be of that period.’’ When more detailed field map-
ping is carried out the Lake County beds will probably be found
to extend much farther to the southwest.

*Geology of Tehama, Colusa, Lake and Napa Counties, Cal. State Min.
3urean, 11th Ann. Rept., p. 62, 1891-92.

Vou. 4] Weaver—Palacontology of the Martinez Group. 107

The average thickness of the Martinez formation is about two
thousand feet. On the north side of the straits it is much less.
The section representing Martinez beds at Army Point railroad
station has a thickness of about eighteen hundred feet. The
Tejon above is nearly twelve hundred feet in thickness. In
southern Lake County the Hocene is much thicker than at Mar-
tinez. The Martinez appears to be represented by at least
twenty-five hundred feet of strata, and the Tejon by a volume
nearly as great.

The Martinez beds are for the most part composed of thick
bedded sandstones containing large quantities of glauconite, and
alternating with these are considerable beds of shale. The shales
are, however, not often seen, as they break down and do not
show on the surface. In general the sandstones prevail. They
vary somewhat in texture, and are sometimes cross-bedded. They
generally have a grayish color, in contrast to the red Tejon.
They are soft and break down easily. The variations in character
are such as to distinguish upper and lower sections of the forma-
tion.

In the section at Army Point the lower two-thirds of the
series is composed entirely of soft, thick bedded, light colored
sandstones, while the upper third is made up of alternating beds
of sandstone, varying in thickness from a few inches to several
feet. They are more compact and more resistant to erosion than
the lower portion of the series. The upper third of this series is
fossiliferous. In the region about Lower Lake the same eondi-
tions prevail, except that the lower portion of the series is not
entirely composed of thick bedded sandstones, but contains alter-
nating layers of conglomerate, sandstone and shale, with a few
beds of clay. Glauconite is very abundant. The facet that the
deposits are so largely glauconitic is evidence that they were
slowly deposited, and that the depth at which sedimentation took
place was moderate.

Although there is no angular unconformity between the Chico
and Martinez or the Martinez and Tejon, yet there exists a wel!
marked faunal distinction. The fauna occurring in the Martinez
beds is distinct, both from that above and below. Only four
species range down into the Chico, and seven into the Tejon

108 University of California Publications. [GEoLocy

above, and these are in most cases species having an unusually
long geologieal range. Altogether sixty-one species are entirely
confined to the Martinez. In the hills south of Martinez a section
was made across the western limb of the syneline. At various
loealities along this section collections of fossils were made from
the Chico, Martinez and Tejon. In the lower beds a typical
Chico fauna was represented, while above that several successive
collections yielded an entirely distinct group of species. The
upper portion of the series represents a fauna which is clearly
Tejon.

The several successive collections made across the strike of
the Martinez show a distinction between the faunas of the upper
and lower portions. The following lists represent those forms
occurring in the upper and lower portions in the vicinity of

Martinez.
LOWER MARTINEZ.
Foraminifera, indet. Tellina martinezensis, LD. sp.
Fabelium remondianum Gabb. Actaeon lawsoni, 1. sp.
Trochocyanthus zitteli Vaughn. Cylichna costata Gabb.
Schizaster lecontei Merriam. Dentalium cooperi Gabb.
Arca biloba, n. sp. Discohelia californicus, n. sp.
Cardium cooperi Gabb. Fusus aequilateralis, n. sp.
Cucullaea mathewsoni Gabb. Neptunea mucronata Gabb.
Leda gabbi Conrad. Perissolax tricarnatus, n. sp.
Lima multiradiata Gabb. Siphonalia lineata Stanton.
Meretria, sp. Urosyca caudata Gabb.
Modiola merriam, n. sp. Urosyca robusta, n. sp.
Nucula truncata Gabb. Xenophora zitteli, n. sp.
Pholadomya nasuta Gabb. Teredo, sp.
Tapes (aff.) quadrata Gabb. Turbinella crassatesta Gabb.
UPPER MARTINEZ.
Foraminifera nummuloid. Nucula truncata Gabb.
Schizaster lecontei Merriam. Pholadomya nasuta Gabb.
Cancer, sp. Solen stantoni, n. sp.
Arca biloba, n. sp. Tellina martinezensis, i. sp.
Cardita hornii Gabb. Tellina hornii Gabb.
Cardium cooperi Gabb. Tellina undulifera Gabb.
Cucullaea mathewsoni Gabb. Thracia karquinesensis, n. sp.
Leda gabbi Conrad, Ampullina (cont.) striata Gabb.
Modiola merriami, n. sp. Brachysphingus liratus Gabb.

Modiola ornata Gabb. Bullinula subglobosa, n. sp.

Vou. +]

Dentalium coopert Gabb.
Dentalium stramineum Gabb.
Ficopsis angulatus, n. sp.
Heteroterma gabbi Stanton.

Heteroterma trochoidea Gabb.

HHeteroterma, indet.
Megistostoma striata Gabb.
Morio tuberculatus Gabb.
Natica, sp.

Perissolax tricarnatus, 1. sp.
Perissolaa blakei Gabb.

Weaver.—Palaeontology of the Martinez Group.

Siphonalia lineata Stanton.

Architectonica tuberculata, n. sp.
Slrepsidura pacheoensis Stanton.

Tritonium impressum, ne sp.
Tritonium eocenicum, in. sp.
Tritontwm pulehrum, a. sp.
Turritella infragranulata Gabb.
Turritella pachecoensis Stanton.
Turritella conica, n. sp.

Turris, sp. indet.

Urosyca caudata Gabb.

109

In the outcroppings just north of Army Point railroad station
numerous fossils were obtained. A list of the known species
from this locality is given in the table below.

These species are nearly all fairly abundant at this locality,
and the majority of them occur in both the lower and upper
portions of the series in the vicinity of Martinez. Since only the
upper portion of the series is fossiliferous, the locality just north
of Army Point station may be correlated with the Middle Mar-
tinez beds in Contra Costa County.

In southern Lake County fossils have been found at several
localities on Herndon Creek, about one mile southeast of the town
of Lower Lake.
of the town, on the road to Knoxville, a large number of species

At a point about one-fourth of a mile southeast

have been found. Many of these are not represented in the vicin-
ity of the Strait of Karquines. The lower five hundred feet of
strata are non-fossiliferous, and resemble very closely the non-
fossiliferous beds at Army Point. The majority of the fossils
were collected about six hundred feet from the base of the series.
The larger proportion of forms resemble those belonging to the
upper beds at Martinez and not occurring in the lower. From
the stratigraphie position of the beds and the nature of the
included faunas it seems best to correlate the Martinez beds at
both Benicia and Lake County with the middle and upper at
Martinez.

The following table represents all the forms occurring in the
Martinez group at Martinez, Benicia and southern Lake County.
The oceurrence of these species in the type section at Martinez,
whether lower or upper beds, or both, is also indicated.

110

> 1 Homo s

=)

co “I

a ww ww Ww w ow OO
rs

University of California Publications.

Foraminifera nummuloid ............
Foraminifera, 3 sp. indet. ............
Flabellum remondianum Gabb .........
Trochocyanthus gitte Vaughn........
Schizaster lecontei Merriam ..........
Terebratullina tejonensis Stanton

ACG ;OULODO. NewSP wees oe sete seeres cre
Cardita horntt Gabb .........05 00 eae
Cardiwm cooperi Gabb..............--
Crassatella wnioides Stanton ..........
Cucullaea mathewsoni Gabb

eda alaeforms Gabo... 62. ca.c0. eee:
Leda gabbt Conrad 2.2... ene tu
Lima multiradiata Gabb............6.
Lucina turnert Stanton ..............
MCR ELMIG ES ss Menccsney assholes sont lateanaceemeveneuers
Modiola merriamt, N. Sp. .......+250.-
Modiola ornata Gabb > .2..-.......6-
Naucula truncata Gabb = 2.2.2... se 208s

Pholadomya nasuta Gabb
Pectunculus veatchi, var. major. Stanton

Plicatula ostreiformis Stanton ........
SOLE MSLOMLOTII. Mer SP arerires en ekersets ss
Tapes (aff.) quadrata Gabb ..........

Tellina martinezensis, n. sp...........
Melina horny Gabi otss sues ceeises ae
Tellina undulifera Gabb..............
USCT CLO RAST Mae sesenstt-ceuncs ttn see ge doe eee teens aye
Thracia karquinesensis, Nn. Sp. ....-.-4
Actacon lawson, MD. Sp. 22. esses s.2 ene
Ampullina (cont.) striata Gabb.......
Brachysphingus lvatus Gabb..........
Bullinula subglobosa, n. sp. .......005-
Cylichna costata Gabb ....2.+...:....
Dentalium cooperi Gabb

Dentalium stramineum Gabb .........
Discohelix californicus, 0. sp.

Ficopsis angulatus, n. sp.

Husus aequilaterats, nN. Spi... 3.2% «++
Heteroterma gabbi Stanton ..........
Heteroterma striata Stanton ..........
Heteroterma trochoidea Gabb.........
Heteroterma, indet. .................
Lunatia hornit Gabb .......2.-..4-..-
Megistostoma striata Gabb ...........

- Lower beds
XXXX: at Martinez

oe:

Upper beds
at Martinez.

x

x

xx XX:

[ GEOLOGY
d S
2
9 Ho
x x
x x
a Xx
x x
x x
x
x

Se x

x

obs x

x

x Be
x
x

x

ote x

x

x ae

x x

x x
x
x
x
x
x

Vou. 4] Weaver.—Palaeontology of the Martinez Group. 111

n 3 n 3
Be OBE
ee ee 8 is
ics ae y a
be ee ee SE
He PR ee HO
46 Morio tuberculatus Gabb ............. a x
AT ANGULO, (SPs Ww ancagcrcs.dees es ste evened weave toate a hioraien ee x
48 Neptunea mucronata Gabb ........... x
49 Perissolaa tricarnatus, 0. Sp........04- x x
50 Perissolax blaket Gabb a
51 Siphonalia lineata Stanton ........... x x sia x
52. Architectonica tuberculata, n. sp. ..... we <
53 Strepsidura pachecoensis Stanton ..... ae x
54 Tritoniwm impressum, 0. Sp. .... eee ee Le x
55 Tritonium eocenicum, un. sp. x
56 Lritonium pulchrum, n, Spe... se... cee ae x
57 Turbinella crassitesta Gabb .......... x
58 Turritella infragranulata Gabb ....... ff ys
59 Turritella pachecoensis Stanton ....... an x
60 Turritella conica, n. Sp...........2.005 eh x
]
GI urriss (SP a WMGCt. eva ancrapspar sons austen ne x
» SJ
G2 Usosyca caudata Gabb ..........0.65: x x x
63 Urosyca robusta, n. sp. .........--++- x
64 Xenophora zttiteli, n. sp. ..........-.. x
Game Cancer C2): Spy sac fens ene we ee sk x
66 Crustacean remains, macruran ........ Sia x

IS CUDULG wa. oteeGeelaih alee Mee ae. deeper a

CORRELATION.

Beeause of the somewhat divergent views held by various
writers in regard to the correlation of the different divisions of
the Eocene in other parts of the world, and owing to the fact that
a large majority of the species occurring in the Pacific Coast
Eocene are not represented elsewhere, it becomes extremely diffi-
eult to make a correlation of the Eocene of the West Coast with
other sections. In 1898 Dr. W. H. Dall* drew up a correlation
table of the American and European Eocene. In this paper he
represents the combined Eocene of the Pacific Coast as the
equivalent of the Midway stage of the Atlantic and Gulf States,
and of the Cernaysian of Europe. Thus, according to his views.
the Martinez and Tejon groups, taken together, form the lower

Eocene. Since in this case no use can be made of species, as

*18th Ann. Rept. U. 8. Geol. Survey, Pt. 2, pp. 327-348, 1898.

112 Tniversity of California Publications. | GEOLOGY

there are none common to other regions, it is necessary to base
correlation on the maxima of genera. For comparison with the
Martinez fauna the following important localities have been
selected: the Gulf states, the Atlantic states, the London and
Paris Basins and the Sind district of Western India.

Compared with these, the fauna of the Martinez Group is
seen to be a distinet unit. Of the forty-nine genera listed, only
twenty-two could be found in the literature on the Eocene of the
Gulf and Atlantic states. No species were found in common, yet
several were somewhat similar. This fauna has its closest affini-
ties with that represented in the Midway of the Gulf states and
the Aquia stage of Maryland and Virginia. The correspondence
to the Aquia is, however, less marked than to the Midway. Pro-
fessor Clark* considers the Aquia and Nanjemoy together to rep-
resent both the upper and lower substages of the Chickasawan of
the Gulf states, and also he considers it questionable whether the
Eocene is represented by any beds in the Middle Atlantic slope
older than the Chickasawan. The fauna of the Tejon group
bear a closer similarity to both the Aquia and Chickasawan than
does the Martinez. Since the Tejon overlies the Martinez, it
would seem very probable that if any correlation of the latter
can be made at all, it would best be made with a portion of the
Midway as represented in the Gulf states, and with that portion
of the lower Eocene which is not represented in the Maryland
and Virginia regions. Hence, the Martinez may represent some
portion or all of the lower quarter of the Eocene.

The similarity of the Martinez fauna to that of the London
and Paris Basins is less marked. Sixteen out of the forty-nine
genera are common to the Eocene of the London Basin, and the
fauna corresponds more closely to that of the Thanet Sands or
lower Eocene. Fifteen genera were found corresponding to those
in the Eocene of the Paris Basin, and bore the closest resemblance
to the Bracheux beds, which are considered to be lower Eocene.

In the Eocene fauna lsted by Mr. W. T. Blanfordy in his
memoir on the Geology of the Western Sind, nine genera, but
no species, were found which occur also in the Martinez group.

*Rept. Maryland Geol. Sur. Eocene. W. B. Clark, p. 84, 1901.
yMemoirs of the Geological Survey of India, Vol. XVII, pp. 1-200, 1880.

Vou. 4] Weaver.—Palacontology of the Martinez Group. 113

The genera represented in both resembled most closely the fauna
of the Ranikot group. This group is supposed to belong to the
lower Eocene. The small number of common forms indicates
that there was probably no direct faunal connection between
India and the Western Coast of North America in Martinez
times. The same view is arrived at by Professor J. P. Smith*, in
which he states ‘‘in the upper Chico horizon of California and
Oregon the connection with India appears to cease,’’ and ‘‘dur-
ing the early Tertiary or Tejon epoch in California we have no
evidence of any migration from <Asia.’’ The evidence seems
also to point to the fact that during this period the Martinez seas
were isolated from the regions of the southeastern United States.
Later, during the Tejon, a passage was possibly opened.

Although these localities are widely separated, and only a
small proportion of the genera is common, yet there seem to be
sufficient distinctive forms not only to place the Martinez Group
in the Eocene, but also to show that it represents a portion or all
of the lower quarter of the Kocene.

SUMMARY.

From the foregoing discussion it is evident that the Martinez
represents a distinct division of time in the geological history of
Calfornia. It contaims a fauna distinet from both the Chico
and the Tejon. On the average it is composed of about two thou-
sand feet of thieck-bedded sandstones, together with some shales.
thin-bedded sandstones and conglomerates. Its geographical
extent as at present known is confined to southern Lake County
and a belt extending north and south across the Strait of Kar-
quines. Its position in the geological scale seems to correspond
most closely to a portion or all of the lower quarter of the Eocene.

“Periodic Migrations between the Asiatic and the American Coasts of the
Pacific Ocean, by J. P. Smith. Am. Jour. Sci., Vol. XVII, p. 224, 1904.

114 University of California Publications. [GEOLOGY

DESCRIPTION OF SPECIES.
PELECYPODA.

Lima multiradiata Gaps.

Lima multiradiata Gabb, 1869, Palaeontology of California, Vol. II, p.
201, Pl. 33, fig. 101.

This shell is large, moderately convex and only shghtly
oblique. The posterior side forms an irregular curve from the
ear to the base. The anterior margin is concave from the ear to
a point midway to the base, and is regularly convex below thai
point. The surface is covered with numerous radiating ribs,
each of which in the vicinity of the margin is narrower than the
interspaces. These ribs have a somewhat wavy appearance. The
surface is also marked by several large and numerous smaller
well defined lines of growth.

Dimensions :—The measurements of two specimens are given.
The maximum height of a cast of the first is 92 mm. Its greatest
width is 88 mm. The second specimen, also a cast, has a maxi-
mum leneth of 106 mm. and a width of 96 mm. The margins
of both these specimens are more or less broken away. When
restored the maximum width of the casts would about equal the
distance from beak to base. These shells closely resemble Lima
multiradiata Gabb as deseribed by Stanton from Lower Lake.
They differ in that they are less oblique and much wider. The
width is one-third greater in proportion to the distance from
beak to base than in the ease of Lima multiradiata as deseribed
by Stanton. Although somewhat different in form, it seems best
to consider these specimens as multiradiata.

Occurrence:—This form occurs about three miles to the
southwest of Martinez, in the hills to the west of Del Hambre
Canon. <As yet it has been found only in the lower half of the
Martinez Group.

Modiola merriami, n. sp.
Pir. 12) Kies 2;

The shell is thin, elongated and moderately convex. The
beaks are broad and not very prominent. The umbonal ridge is
prominent, rounded, and curved only slightly downward. The
surface is marked by several rather prominent concentric
wrinkles. There is no radial ornamentation.

Vou. 4] Weaver.—Palacontology of the Martinez Group. 115

Dimensions :—The maximum length is 30 mm. and the great-
est width 15 mim.

Occurrence :—This form has been found about three miles
southwest of the town of Martinez, associated with Lima multi-
radiata. It also oceurs about three miles south of Martinez, on
the east side of the road leadine to Walnut Creek. It is charae-
teristic of both the upper and the lower Martinez beds.

Arca biloba, n. sp.
PL. 12, Fia. 4.

The shell is strongly arehed, moderately inflated and ine-
quilateral. The beaks are small, ineurved and grooved. From
the interspace between the two heads of the beak there runs a
moderately deep groove over the surface of the shell toward the
base. The beak is located about one-third the distance from the
anterior end. The anterior end is somewhat narrow. The pos-
terior end is obliquely truncated. The base is broadly rounded.
Behind the umbonal ridge the surface is nearly flat. The sur-
face is marked by numerous ribs, and these are crossed by many
regular lines of growth.

Dimensions :—The maximum length of the specimen described
is 9.5 mm., and the greatest width 3.5 mm.

Occurrence :—This shell has been found about three miles

southwest of Martinez, in association with Lima multiradiata,
and also about five miles southwest, near the head of Vaca Canon.
It occurs in both the upper and lower beds.

Tellina martinezensis, n. sp.
PL. 12, Fie. 3.

The shell is small, thin, compressed, and about twice as long
as the distance from the beak to the base. The anterior end is
rather broad. The posterior end is considerably narrower and
truneated obliquely. The beaks are small and nearly central.
The basal margin is convex. A ridge, especially wel! marked
near the beak but gradually becoming fainter toward the base,
passes from the beak to the posterior basal angle. The surface
is ornamented by numerous small, regular, concentric lines.

116 University of California Publications. [GEOLOGY

Dimensions :—The maximum length is 21 mm., and the great-
est breadth is 14 mm.

Occurrence :—This specimen was found about two miles south

of Martinez, on the east side of the road reading to Walnut Creek.
It ocewrs in both the upper and lower beds.

Solen stantoni, n. sp.
Pu. 12, Fic. 1.

The shell is thin, elongated and moderately convex. The
cardinal and basal margins are nearly parallel. The beaks are
anterior. The base is straight and the ends somewhat
rounded. The posterior end is more abruptly truncated than
the anterior. The surface is marked by faint concentric lines of
erowth. Passine down from the beak to the base of the anterior
margin there is on each side a deep, sharp constriction which is
nearly at right angles to the hinge line.

Dimensions :—The maximum leneth of the type specimen was
found to be 50 mm. The greatest widthis 7 mm.

Occurrence :—This form has been found at several localities
in Contra Costa County. It is most common about four miles
south of Martinez, on the west side of the road to Walnut Creek
and near the mouth of Vaca canon. As yet it has been found
only in the upper beds.

Pholadomya nasuta Gasp.
Pu. 12, Fic. ‘6.

The specimen which was described in Volume I, Palaeon-
tology of the California State Geological Survey, is distorted,
and hence the drawing does not represent the normal form. In
the distorted specimen the beak is too high and narrow and the
lip slants inward from beak to base. Such is not the case in
normal forms which are now known from perfect specimens.

This shell is considerably inflated, beaks moderately high,
broad and prominent. Anterior ends incurved and approximated.
The posterior end is produced and rounded. The anterior end
is inflated and sharply truneated. The surface is marked by
about fourteen strong radiating ribs, which are present only on
the middle of the shell. Numerous prominent concentric ribs

Vor. +] Weaver.—Palacontology of the Martinez Group. ay

extend to the shell margin. The base and the anterior end are
closed and the posterior end gapes considerably. The lip extends
shehtly outward in the upper half and then is obliquely trun-
eated inward toward the base.

Dimensions :—The leneth of the specimen deseribed is 69 mm.
The maximum thiekness is 37 mm., and the distance from beak
to base 46 mm.

Occurrence :—This species is found at numerous localities
south of Martinez; also on the arsenal grounds at Benicia. It
is characteristic of both upper and lower beds.

Thracia karquinesensis, n. sp.
Pu. 12; Fre. 5.

The shell is thin, moderately convex and marked with con-
centric stria. The beaks are prominent and located about one-
third the distance from the anterior end. The base is nearly
straight. The upper margin of the wing is nearly parallel to the
base. The anterior end is rounded and the posterior somewhat
produced, the body of it where it joins on to the wing sloping
downward toward the base and making an angle of about forty-
five degrees.

Dimensions :—The maximum leneth of this specimen is 29
mm., and the distance from beak to base 15 mm. Only one speci-
men has been found.

Occurrence :—This form was found about two and one-half
miles south of Martinez, on the west side of the road to Walnut
Creek. It occurred in the upper beds of the Martinez.

GASTEROPODA.

Architectonica tuberculata, n. sp.
Pr. 125) PGS 7 %& fa:

The shell is small, the spire low, and the number of slightly
convex whorls present is six. The surface is marked by a number
of small tubercular ribs. There are eight ribs to each whorl.
This description is taken from a east.

Dimensions :—The diameter was found to be 9 mm., and the
distance from base to apex 2 mm.

118 University of California Publications. [ GEOLOGY

Occurrence :—The locality is about two and one-half miles
south of Martinez, on the west side of the road to Walnut Creek.
It ocewrs only in the upper Martinez beds.

Discohelix Californicus, n. sp.
Pu. 12, Fie. 9.

The shell is of the typical discohelix form. The number of
whorls is five. The characteristic angles are sharp, especially on
the outer whorl. The first whorl is more prominent on the upper
than on the lower side. The upper side of the shell is flat to
slightly coneave. The surface is smooth and the aperture nearly
square.

Dimensions :—The specimens are not perfectly circular, due
to distortion. The maximum diameter is 21 mm. and the mini-
mum diameter of the same specimen 1914 mm. The width of the
outer whorl is 4.5 mm.

Occurrence :—It is most common about four miles to the
southwest of Martinez, on the west side of the Del Hambre Cafion

road. It occurs in the lower beds only.

Turitella conica, n. sp.
PL. 13, Fic. 2.

The shell is moderate in size and rather robust. The number
of whorls present is nine. They increase rapidly in size and are
flat to shehtly convex on the outer face. The suture is impressed.
Each whorl is marked by five distinet, equidistant, revolving
ribs, the lower three of which are very prominent. Between these
are several fine striw. The aperture is subquadrate.

Dimensions :—The maximum length of the specimen deseribed
is 18mm. The maximum diameter is 7.5 mm.

Occurrence :—It is common on the west side of the road be-
tween Martinez and Wanut Creek, about three miles south of
Martinez.

Xenaphora zitteli, n. sp.
Pu. 12, Fic. 8.

Three specimens have been found. The largest of these has
seven nearly flat whorls. The spire is low. The base is nearly
flat. The aperture is obliquely quadrilateral. A line joining the

Vou. 4] Weaver.—Palacontology of the Martinez Group. 119

outer edge of the last whorl with the apex makes an angle of
about forty-five degrees with the base. The whorls are covered
with extraneous objects, which appear to be pebbles of quartz
ranging up to 15 mm. or more in diameter.

Dimensions :—The diameter of the type specimen is 87 mm
Height from apex to base, 57 mm.

Occurrence :—Found southwest. of Martinez, on the west side

of the Del Hambre Canon road. This species occurs only in the
lower beds of the Martinez group.

Ficopsis angulatus, n. sp.
Pre lo) Ries 5:

Spire low, with four or five angular whorls. The body whorl
is marked by three prominent equidistant angles which distin-
euish it from Ficopsis remondi. The surface between the angles
is coneave. The surface of all the whorls is marked by numerous
sharply defined fine revolving lines and linear ribs which eut it
into minute squares. The space between these ribs is concave to
flat.

Dimensions :—Maximum leneth from base to apex is 6 mm.
The greatest width is 4 mm.

Oceurrence :—About three miles south of Martinez, on the
east side of the road to Walnut Creek. It oeeurs only in the
upper beds.

Urosyca robusta, nu. sp.
Pu. 13, Fra. 1.

The spire is very low. The whorls number six. On the body
whorl there are four very prominent and nearly equidistant
nodose revolving ribs. On the lower part of the body whorl there
are numerous fine revolving striae. The aperture is broad. The
canal is long and from the impression in the matrix appears to
be shehtly twisted. This species differs from Urosyca caudata in

the constant presence of a fourth revolving nodose rib.

Occurrence :—This species occurs near the base of the beds.
Urosyca caudata has been found in both divisions of the Martinez.
Found southwest of Martinez, on the west side of the road

through Del Hambre Canton.

120 University of California Publications. [GEOLOGY

Tritonium impressum, n. sp.
deny aly Sires, By

The shell is moderately long. The spire is elevated. The
number of whorls is five. The second whorl is about one-third
the height of the body whorl. The surface of the whorls is mod-
erately convex. The mouth is broad. The suture is deep. The
surface is marked by numerous small longitudinal ribs. The
varices are moderately large but few.

Dimensions :—T'he distance from base to apex is 28 mm.. and
the maximum width of the body whorl 14 mm.

Occurrence :—Three miles southwest of Martinez and west of
the Del Hambre Canon road. It occurs in the upper beds only.

Tritonium eocenicum, n. sp.
Pu. 13, Fic. 4.

The spire is moderately elevated. The whorls are five in
number, possibly six. They support broad, prominent transverse
ribs, of which there are about twelve on the body whorl. These
ribs are shehtly oblique and may be almost sinuous. They are
about one-half as broad as the interspaces. These ribs are crossed
by numerous well marked revolving striae. The few varices are
well marked. Only one specimen was found.

Dimensions :—The distance, measured from apex to base, is
10mm. The maximum width is 6.5 mm.

Occurrence :—About two and one-half miles south of Mar-

tinez, on the east side of the road to Walnut Creek. It has been
found in the upper beds only.

Tritonium pulchrum, n. sp.
Pi. 3 iG. 6:

This shell is fusiform and turreted. The spire is high and the
number of whorls is eight. They are sharply angulated and the
slope nearly straight above. The body whorl is convex below.
The surface is marked by numerous longitudinal and revolving
ribs. Upon the body whorl are twenty-six revolving ribs. Nine
of these were above and seventeen below the angle. The varices
are very prominent, about ten in number on each whorl, and
support prominent nodes on the angles of the whorls.

Vou. 4] Weaver.—Palacontology of the Martinez Group. ile Al

Dimensions :—Distance, measured from apex to base, is 34

mm. The maximum width of the body whorl is 16 mm.

Occurrence :—About two and one-half miles south of Mar-
tinez and on the west side of the road to Walnut Creek. Its geo-

logical range is confined to the upper Martinez beds.

Fusus aequilateralis, n. sp.
Pr. 13) biGs (

The shell is small and elongated. The whorls number six.
They are very convex and prominently angulated. The upper
and lower faces are equal and slightly convex. The suture is
distinct. The spire is high. The canal is long and straight. The
surface of each whorl is marked by nine or ten quite large nodes
on the angles. This form resembles Fusus martinezensis very
closely, but differs in the greater length of the spire, in the
prominence of the angles upon the whorls, and in the nodes upon
the angles.

Dimensions :—The distance, measured from apex to base, is
21mm. The maximum width of the body whorl is 8 mm.

Occurrence :—The type specimen was obtained about. five
miles south of Martinez and one and one-half miles north of
Grayson Creek. It occurs only in the lower beds.

Perissolax tricarnatus, n. sp.
PL. 13, Fic. 9.

Shell elongated, spire moderately elevated. Whor!s six in
number. The body whorl is ornamented by three prominent
revolving carinae. The upper two form prominent nodose angles
on the whorl and separate a slightly concave middle portion from
the sharply sloping upper and lower areas. A short distance
below the lower of these two angles is the third carina, which is
less prominent and is searcely nodose. The remaining whorls
show only the upper carina. The aperture is elongated and
narrow. The presence of the three revolving ridges on the body
whorl seems to be a constant character for all specimens collected
in this region, and, as no intermediate forms appear, it seems
best to regard this as a new species, distinct from Per/ssolax
blaket Gabb of the Tejon.

PAP University of California Publications. [ GEOLOGY

Dimensions :—The leneth from the broken end of the canal
to the apex is 27 mm. The maximum width of the body whorl
is 19 mm.

Oceurrence :—Southwest of Martinez and west of the Del
Hambre Canon road. It has also been found at Benicia, on the
U. S. arsenal grounds, about two hundred yards northwest of
Army Point railroad station, and in southern Lake County,
about one mile southeast of the town of Lower Lake. It oceurs

in both the upper and lower beds.

Bullinula subglobosa, n. sp.
Pu. 13, Fic. 8.

The shell is small and sub-globose. The spire is low but acute.
The whorls number five. The aperture is broad. The surface
is marked by regular lines of growth and by numerous very fine
impressed revolving striae.

Dimensions :—The height is 8 mm. and the width 5 mm.

Occurrence :—About three and one-half miles south of Mar-
tinez and west of the road to Walnut Creek. It occurs only in

the upper beds.

Actaeon lawsoni, n. sp.
Pir. 3; Wiese TO}

The shell is subovoid and elongated. The number of whorls
is five. They are very regularly rounded. The suture is chan-
neled. The entire surface of all the whorls is marked by numer-
ous narrow revolving ribs. There are thirty-two ribs on the body
whorl, and these are connected by numerous very minute lines.
The aperture is narrow. The extremity of the columella shows
distinet plications.

Dimensions :—The leneth from base to apex is 9.5 mm., and
the maximum width of the body whorl is 6 mm. The specimens
appear to be shghtly compressed.

Occurrence :—Three miles southwest of Martinez and west of

the Del Hambre Canon road. It oceurs only in the lower beds,
but near the top of that division.

Vou. 4] Weaver—Palacontology of the Martinez Group. 23
CRUSTACEA.

CANCER (Lin.) Leach.

Cancer? sp.
Pu 13; Pre) di.

All that remains of the specimen is a portion of the carapace,
and from this it is at present impossible to determine the genus
and species more accurately than to show that it closely resem-
bles the genus Cancer.

Dimensions :—The maximum breadth is 29 mm., and the
leneth is 21 mm.

Occurrence :—About four miles south of Martinez and east

of the road to Walnut Creek. It ocemrs in the upper beds.

University of California.
Pebruary, 1905.

. 6.—Phaladomya nasuta Gabb. Nat. size.
7
s
7

EXPLANATION OF PLATE 12.

. 1.—Solen stanton, nu. sp. Nat. size.

2.—Modiola merriami, vn. sp. Nat. size.
3.—Tellina martinezensis, nv sp. 1M.

ig. 4.—Arca biloba, n. sp. Nat. size.

5.—Thracia karquinesensis, n. sp. Nat. size.

-—Arechitectonica tuberculata, n.

a.—Upper side of body whorl of specimen shown in fig. 7.

Fig. 8.—Xenophora zitteli, n. sp. X%.
Fig. 9.—Discohelia californicus, u. sp. Nat. size.

x5.

BULL. DEPT. GEOL. UNIV. CAL. V.@ ae ee

se

"

\

nine

LITH. BRITTON &REYB.E

Pe

EXPLANATION OF PLATE

ig. 1.—Urosyca robusta, n. sp. Nat. size.

bo

_—Turritella conica, n. sp. *1%.

‘No, 3.—Tritonium impressum, n. sp. Nat. size.

)

4.—Tritonium eocenicum, 1. sp. X22.
5.—Ficopsis angulatus, i. sp. X2.

‘jo, 6.—Tritonium pulchrum. Nat. size.

o, 7.—Fusus aequilateralis, n. sp. * 1.

. §.—Bullinula subglobosa, n. sp. 2.

‘ig. 9.—Perissolax tricarnatus, n. sp. Nat. size.

g. 10.—Actaeon lawsoni, n. sp. 3.

Figo. 11.—Cancer (2), sp. Nat. size.
D> ’

13.

VOEr 4; PEfd3

BULL. DEPT. GEOL. UNIV. CAL.

&REY, SF

LITH. BRITTON

UNIVERSITY OF CALIFORNIA PUBLICATIONS
BULLETIN OF THE DEPARTMENT OF

GEOLOGY

Vol. 4, No. 6, pp. 125-143, Pls. 14-18. ANDREW C. LAWSON, Editor

NEW OR IMPERFECTLY KNOWN
RODENTS AND UNGULATES

JOHN DAY SERIES

WILLIAM J. SINCLAIR.

CONTENTS.

PAGE
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MTOM bY CHUSMEOSLEAUUS Mam S Pinna care ciayecensce sete auerslicuer aterye teleieyey ay eqersserer aie 128
TEINS eA AS eo Goren conclave oo eet nec eo ae ao ceerareo retina coe clot 128
AulomenyxeplaniGepsss Me SeMe NC SP ee cesta ete eee gale secrete tele ties eterenen 129
Wiloperatein eMail we Gj) ae eos meee aoe ea aes oe ors Soe are oc 132
Mhinohyus (Bothrolabis) decedens Cope ..2..5....0 002.00. e es ees 134
Thimohyus (Bothrolabis) osmontl, M. Spi...) . 42.62. see ene et 138
IMIESO Hipp USMAG UNCON Sy Met SI) cists sdecci ere eve anenereccueaned ecu sues ieteversneueeseatey orient: 141

INTRODUCTION.

In the mammalian collections obtained in the John Day
region by the University of California parties of 1899 and 1900
there are a number of forms which are new to science, and others
which have been only imperfectly deseribed. Of these collections
Professor Merriam has turned over to the writer the ungulate
and rodent material for study and description.

In the following paper no attempt is made to discuss the rela-
tions of the faunas with which the described species are associ-
ated. In a later article by Professor Merriam and the writer,
there will be presented a general discussion of the relations of the

series of mammalian faunas known in this region.

126 University of California Publications. [GEOLOGY

PEROMYSCUS PARVUS, N. sp.
Pl. 14, Figs. 4 and 5.

Type.— Portions of maxillary and mandible, No. 84, Univ. of Cal. Palae-

ont. Coll.

Locality.—Upper Diceratherium beds, Middle John Day. Turtle Cove,

Grant Co., Oregon.

Smaller than P. nematodon. Upper molars with two princi-
pal and two subsidiary enamel inflections on the outer side of the
tooth crown.

The first two molars of the superior series are pre-
served in a fragment of the left maxillary. They are low
erowned and tubereulate. The subsidiary enamel inflections are
situated respectively anterior and posterior to the two principal
external enamel! loops, and would disappear were the teeth
slightly more worn. In M, there is one wide external and two
narrower internal enamel invaginations. The second and third
lower molars are represented by the roots only. The lower in-

cisor is delicately grooved on the outer face.

MEASUREMENTS.

Then phy ME to Maem GSview. senteserccstecnetcayec-iaionersieues-peneneie serene 3.9 mm
Length M, to M, inclusive, on alveolar border ............... 4

Then oti Wee aMcenro=p.OStery Only r mpcrwat ete stem -h= cee Mnteliseeseeetteve ne eaesasre tet 1.5
IDYouda one hee! lhe MS GAs Bote sunmd oomne a cae oodueG ones 3.3

ENTOPTYCHUS SPERRYI, Nl. sp.
Pl. 14, Figs. 6 and 7.
Type.—Cranium and mandible, No. 649, Univ. of Cal. Palaeont. Coll.
Locality.—Promerycochoerus beds, Upper John Day. Haystack Valley,
Wheeler Co., Oregon.

Rostrum long and broad. Interorbital region concave. Super-
ciliary ridges strongly developed, with abrupt posterior termina-
tion. Temporal ridges low, converging from the posterior ex-
tremities of the superciliary borders to form a prominent sagittal
erest. Mandibular symphysis with long straight superior border
separated from P, by a short concavity. Size large.

E. sperryi may be distinguished from EF. planifrons by the
flat forehead and absence of temporal ridges in the latter species.
In E. lambdoideus ‘‘there is no ridge-like thickening of the

Vou.4] — Sinclair—John Day Rodents and Ungulates. 127

supraorbital border. It presents, on the contrary, a subacute
superior edge, flush with the inferior part of the same border.
These edges leave the orbital border posteriorly, and converge in
straight lines to an acute angle, forming two temporal ridges.’’
* EH. minor is much smaller than EH. sperryt and the other species

‘

of the genus and like FE. planifrons is ‘‘ characterized by the per-

feetly flat interorbital region and the absence of temporal

(a3

ridges.”’ + In E. cavifrons, the supereiliary margins ‘‘do not
meet nor converge to form a sagittal erest. They are thickened,
forming two subparallel ridges which are separated by a shallow

“‘

coneavity of the frontal bone.’’ + In E. crassiramis the ‘‘inter-
nal orbital walls are rolled inward at the supraorbital region so
as to meet at a point opposite the posterior border of the orbital
space. Opposite the anterior part of the orbit, the ridges are more
widely separated, so that the interspace is a narrow wedge-

”

shaped fossa, opening forwards.’’ § Temporal ridges are wanting
and the sagittal crest is weak. The mandible differs from £.
sperryt in the absence of the long horizontal symphysial border
characteristic of that species. In E. crassiramus the superior
mandibular border between the base of the incisor and the alve-
olus of P, is broadly concave.

The new species is named in honor of its discoverer, Mr. J. C.

Sperry.
MEASUREMENTS.
Length of skull, supraoccipital to premaxillae inclusive......... 50 mm
Him Geroulouballe wrens ser ssetece ease ereveiereneee era eehewste cence iseaepeeeers ete we ots 6.5
‘Width across zygomatic arches ................4 Pears tnau reas 30
Wadthvot medians pOrclOm OL OSURUMO ayeteerenome sie csia/aelts tema leeetelne es val
Depth of rostrum at incisive foramina .....................-; 9.9

Length of rostrum from base of P, to anterior end of premaxillae..24.5

Wen othe OLenasals, sap prox Mate arms stedehesustercitetis selscfeete eisai e030
Length P* to M® inclusive, on alveolar border.................. ala
Length P, to M, inclusive, on alveolar border ................. 8.5
PS, antero-posterior diameter a... wee eee see secre ns eee 2
IPS tLANSVOLSO eC(LAMOCLETs a eve mierenea2e stsnaeiarane sven s eutateee: ete @ctuacs eels 2.5
MEF VAMbeNOsDOSLEION, Cla MO Lei we versed wersien. fetal) ot elveuete eieearena Galen)? 2
Ma eiransVvetse. Cameten! ads cclhsaceie cuseusaets sascavnus seo anauees ee aticneees 3

*H. D. Cope. Tertiary Vertebrata, p. 861.

7 Tbid.

t E. D. Cope, ibid., p. 862.

§E. D. Cope, ibid., p. 864. Pl. LXIV, Fig. 5a.

128 University of California Publications. [ GEOLOGY

Me anvero-posterzor diameter 2a. os sstess stele s esecreieie sean oie 1.5mm
Me transverse, diameter icici ieiteche stele cet ciemie cele a teein ae 2

Pgs antero-posterior .diameter oe .ciieicleeisne ie iste enn iel rien eee 2.5
PZ, tramsverse, diameter qa. cere seucresmerer ec) iereicteei tiene enste ioral ionennen ee 2

Mi, antero-posterior diameter Wa. selec iene cte acre ete) selene 1.75
M, transverse diameter) 2.2 cvustescc + sate Mites ss 1s hae eee eeeD
M,, antero-posterior diameter .............000 ccc edevuceeeeee 2

Mi,, stramsverse ‘diameter 222.22. sss) fe eeesietsie ste cre ee eee chee ee 2

ENTOPTYCHUS ROSTRATUS, Nn. sp.
PL 14, Figs. 8 and 9.

Type.—Cranium, No. 1651, Univ. of Cal. Palaeont, Coll.
Locality.— Promerycochoerus beds, Upper John Day. Haystack Valley,
Wheeler Co., Oregon.

Skull and rostrum longer than in any other described species
of Entoptychus.

Compared with E. sperryi, the rostrum is not only longer but
deeper, although the width is the same. The nasals are narrow
posteriorly and are not separated by a frontal process. Anter-
iorly they are as wide as in E. sperryi. The interorbital region
is imperfectly preserved and it is not possible to determine its
character. The upper teeth are badly worn. P* is apparently
the largest tooth in the superior series, the molars decreasing in
size posteriorly.

The specific name refers to the great length of the rostrum.

MEASUREMENTS.

Length of skull, supraoccipital to premaxillae in¢lusive......55.5mm
Interonbutaletwadith; sano pO xm ahem rar. ene eerste se ctereieretterenel “yore sneer cees 7
Width) at middie of rostrumas 2.222... seats eee oe tee 11
Depth of rostrum at incisive foramen....................00. 11
Length of rostrum from base of P* to anterior end of premaxillae..27.5
Irapeadie os ULI! eh Gs AAGh SoS GA GbannoA DoDatooooMm cdoePoono eT 27.5
Length P* to M® inclusive, on alveolar border.................. 9)
(Re RANLELO-POSveTIOI s CUAMeLCT wepetsrnsteee tetera ett. erste eeyentaietelag eee teeter Bee
Pe Transverse lameter eace sos aici sachets achs ei caskeaei snes eens
MER ohekneorioosinsmore (henntRe 5 Senn ano eden suns soos neo onGo or 1.9
Me. ‘transverse diameter’ a..co2cea- oe te clemson a eerie ree 2

HYPERTRAGULUS, sp.
Pl. 14, Fig. 3.
All doubt regarding the inferior dental formula of Hypertra-
gulus is removed by the specimen illustrated on Plate 14, Fig. 3,
(No. 1343, Univ. of Cal. Palaeont. Coll.) from the Promery-

Vou.4] — Sinclair—John Day Rodents and Ungulates. 129

cochoerus beds on Rudio Creek, Grant Co., Oregon. Three small
incisors and an incisiform canine are represented by roots. The
erowns and a portion of the adjacent alveolar border have not
been preserved. P, was functional as a canine. Its crown is unfor-
tunately missing. P, is also broken off, but the roots remain and
are separated by long diastemata from P, and P,. Small ledge-
hke cuspules are present on the sides of the outer molar eresents
and in the intervening valleys, except in M, where they are
developed only on the antero-external crescent and in the valley
behind it. There is but one mental foramen, situated anterior
to P,. In the specimen figured by Seott*, there is an additional
mental foramen below P,, and the mandible is somewhat deeper
than in No. 1343. The posterior portion of the ramus is not
preserved and has been restored in outline, together with the
crown of the canine, to correspond with Scott’s figure.

MEASUREMENTS.

eno theese CLUSLVGw accra es eeersrtcie sists ere aie Scns casters eiera eyes ene ens 61 mm

eenort hp Vise OM Cl SIV Gis eareatgaciasisemierevous aetss a vig cuecaueve.e Siemens inte 35
Wiens theyotedastemsas bend ebe ew cte erie sitciste wie sieve .)eie evicey ayes ay)
Wenmchwoteramusray mmc dUenod bes eer-cene terest eres state erenetntroe cys tepetetes )

ALLOMERYX PLANICEPS, n. gen. and sp.
Pl. 14, Figs. 1 and 2.

Type.—Cranium, No. T04, Univ. of Cal. Palaeont. Coll. The cranium
lacks the portion anterior to P* and is without mandible.
Locality.—Diceratherium beds, Middle John Day. Turtle Cove on the
South Fork of the John Day, Grant Co., Oregon.
Distinctive Characters.—Dentition ?,?,2’,3. P*® three rooted.
P* with inner and outer crescents. Molars without mesostyle, ex-
ternal ribs prominent and about equally developed. Metastyle
on M* much produced. Forehead flat. Sagittal crest low and
not elevated above interorbital plane, terminating posteriorly in
a prominent triangular knob. Brain case well rounded at sides,
somewhat flattened above. Orbits prominent and completely
inclosed with strongly developed frontal and jugal processes. A
prelachrymal vacuity present. Bullae small, with outgrowth of
petrosal between bulla and basioccipital.

* W.B. Scott. Trans. Wagner Free Inst. Sci., Vol. VI, Pl. 1, Fig. 3.

130 University of California Publications. [ GEOLOGY

Crantum.—The cranium had = suffered considerably from
weathering previous to the discovery of the specimen, and lacks
all of the region anterior to P? and parts of both jugal arches.
Superiorly the forehead is broad and flat, slightly domed post-
eriorly along the line of the median suture. The temporal ridges
unite at about the anterior third of the length of the brain ease to
form a sagittal erest, which does not rise above the frontal plane
and terminates posteriorly in a prominent triangular knob. The
brain case is somewhat flattened above and moderately con-
stricted back of the orbits. The lateral walls are well rounded.
Above each orbit is a small supraorbital foramen from which a
shallow groove extends anteriorly.

The back of the skull is narrow above, where the supraoccipi-
tal forms the posterior border of the knob-like occipital crest. A
narrow median keel is present but fades out toward the upper
border of the foramen magnum.

In the lower view (PI. 14, fig. 2) the bullae are seen to be
small, resembling those of Leptomeryx. They are separated
from the basioccipital by a prominent outgrowth of the petrosal.
Anterior to the bullae, a large foramen appears to represent the
conjoined foramen rotundum and foramen ovale, but as the
skull is somewhat fractured in this region the confluence of the
two foramina can not be fully verified. A foramen of consider-
able size occupies the interval between the inner end of the post-
elenoid process and the bulla. The posterior palatine border has
been somewhat crushed and the outlines are slightly restored in
the figure.

In the lateral aspect of the cranium (PI. 14, fig. 1) the orbits
are seen to be large and entirely enclosed. The frontal and jugal
processes overlap, but are not completely fused. The jugal bor-
der is more prominent than the frontal, indicating that the eye
faced upward. The lachrymal and anterior frontal borders of
the orbit are mammilated. A prelachrymal vacuity is present.
This portion of the skull has suffered from weathering and the
exact border of the vacuity is not well shown in the figure, but
the rounding of the unfractured free edges of the maxillary
and lachrymal may be seen with the aid of a lens.

Vou. 4] Sinclair—John Day Rodents and Ungulates. 131

Dentition—The teeth are short hypsodont and are well worn,
indicating the fully adult and somewhat aged condition of the
animal. Only the posterior root of P? is represented. P®* is sup-
ported by three roots, but the crown is too poorly preserved to
permit description. P* is composed of two erescents, an outer
and an inner. The molars are without mesostyle, with the ex-
ternal ribs prominent and about equally developed. In M®* the
metastyle has considerable posterior prolongation extending
above the alveolar border as a lamina of the postero-external root.

Affinities —The new genus finds its closest affinities among
the Hypertragulidae, in which family it may be placed. The
skull is larger than in Hypisodus and of a different shape. The
bullae are much smaller, approximating in size those of Lep-
tomeryx. It may be distinguished from Leptomeryx by the ecom-
plete closure of the orbit, the flatness of the top of the skull
and the projecton of the petrosal between the bullae and the

ee

basioecipital. In Leptomeryx, the bulla is ‘‘separated, as in the
deer, from the basioecipital by a large reniform foramen within
which a portion of the petrosal is visible.’’ *A mesostyle is pres-
ent on the molars of Leptomeryx, and there is no posterior ex-
tension of the metastyle on M* comparable to the structure devel-
oped in Allomeryz.

Hypertragulus agrees with the new genus in the absence of
mesostyle, but the orbit 1s incompletely closed and jugal pro-
cesses are wanting. + The brain ease is not as long as in Allo-
meryx,t and there is no extension of the petrosal on the inner
side of the bulla. In Allomeryax the interorbital tract and the
superior border of the sagittal crest he in the same plane. This
is not true for the other members of the Hypertragulidae. The
palatine region also differs from both Leptomeryx and Hyper-
tragulus. In neither of these genera does the palatal border of
the nares extend anteriorly between the posterior molars as in
Allomeryx.

* J. Leidy, Ext. Mamm. Fauna of Dakota and Nebraska, p. 168 and PI.
XIV, fig. 4.

7+ W. B. Scott, Trans. Wagner Free Inst. Sci., Vol. VI, p. 18, 1899.

t+ Compare Pl. 14, fig. 2, with Scott, op. cit., Pl. 1, fig. 4.

32 University of California Publications. [GEOLOGY

MEASUREMENTS.

Basilar length of cranium from the anterior border of the al-

veolus of P* to condyle inclusive asic sae scien cree eltaiene 79.5 mm
Width between superior orbital rims.................-.-0008- 42
Length of sagittal crest from point of confluence of temporal

PUD SES wide aud te eevee. Geto eenars egy are ceneseretincmy io ecunecd wie teh ewey eoeme ace che Bee 29
Depth of skull to alveolar border through middle of orbit...... 33
Length from point of union of temporal ridges to fronto-parietal

SUCUME: verde tasncereia eects vaoueaner eee coe eeensyctey eee meray suer renee 11
Antero-posterior diameter of orbit .......6 00.0 eee eee ee ee 26.5
Mransverse diameter On jority... evap: ctetvcyene t-te set eeeee nese yeleneece 21
Width of brain case at postorbital constriction ............... 30
Greatest width tote foram CASO! sa lseceensercesineesrcuete ye cesses eres ey neneuen 35.9
Wactthe:of palate cats Ne is ctstsiene cole tepech-eemete teusiene ener estan ats =t ses ap eee 22.
henoth) (PMS samclusive™ ts 92 0 acaecd soe tes screenees tac pe nue eenees 31
Theme thes MEMS san Clive e esusisue eat stests eieleests te ttasle evarsieusccee ere sieaeieiete 22
M', greatest antero-posterior diameter..................+..- 6.5
M’, transverse ciameter on triturating face through anterior

CLESCONIUS so cos crc ehedina io isis.s. = wom isle siayets eile cueisie eh aiein nis ere eee xa 7
M’, greatest antero-posterior diameter ....:..........-+++--0% tf

M*, transverse diameter on triturating face through anterior

CKESCONUS pcssssshers aa cleas te tcrce enaene henna eepenere Re yer sms ito gs eae ae 8
M*, greatest antero-posterior diameter...............+--+0-- 9

M*, transverse diameter on triturating face through anterior

CTCSCEN LS Wie vt Bree er te eee ees Ee eT Reo erent Eno Ree 9

ELOTHERIUM CALKINSI, nN. sp.
Pl. 15.

Type.—Cranium and mandible, several cervical vertebrae and portions of
fore and hind limbs, No. 953, Univ. of Cal. Palaeont. Coll.

Locality.—Upper part of the Promerycochoerus beds, Bridge Creek,
Wheeler County, Oregon.

Chin rounded, without knob-like bosses. Posterior mandi-
bular protuberances small and hollow. Jugal processes plate-
like, with thickened rib, directed posteriorly, not extending be-
low inferior mandibular border. Size large.

The teeth are greatly worn and partially shed, with closure of
the alveoli, indicating the extreme senility of the individual. P* to
P* are double-fanged, with simple, laterally compressed crowns.
P* is separated from the canine by a short diastema (9.5 mm).
Between P! and the alveolus of P? there is a considerably greater
interval (27 mm). In the figure (Pl. 15) P? is not shown, as this
tooth has been shed from the left maxillary. P* is in practically
continuous series with P* and the molars. P* is supported by

Vou.4] — Sinclair.—John Day Rodents and Ungulates. 133
three roots. The crown has two cusps, a protocone and a deutero-
cone and there is a strong external cingulum. The pattern of
of the anterior molars is entirely obscured by wear. Anterior
and posterior cingula are rather prominently developed. M* was
found separate in the matrix. In this tooth the broad dome-
shaped hypocone is unworn, while the remaining cusps are
much reduced. There is a broad anterior cingulum, but no
posterior cingulum is observable.

In the mandible, P, has been shed on either side and the
alveolus closed. P., preserved only on the right ramus, resembles
the smaller premolars of the upper series. P., has been shed, the
alveolus on the right side only remaining open. Anterior and
posterior cingula are well developed on the lower molars. In M,
the hypoconulid is not differentiated from the posterior cingu-
lum, which projects slightly forming a very small heel.

The right side of the cranium has been badly crushed. The
left side is less distorted. The chief point of specific value at-
taching to the cranium is in the shape and direction of the jugal
processes. These processes are plate-like with a thickened me-
dian rib. The free edges, especially the anterior, are thin and
sharp. The processes are short, not extending below the lower
mandibular border. The orbits are posterior in position, their
anterior borders lying above the posterior edge of M?’.

The mandible is peculiar in the absence of the knob-like
bosses on the chin, which are so prominently developed in FL.
mgens and EH. imperator.* The protuberances beneath P, are
small and deeply cupped. The dependent angle slopes gradually
baekward without the abrupt downward curvature characteriz-
ing EF. ingens.

With the skull were preserved the atlas, axis and three an-
terior cervicals, all considerably crushed, fragments of a radius,
an imperfectly preserved tibia, an astragalus, the right and left
unciform and navicular, the left pyramidal, the fused ecto-meso-
cuneiform, a seaphoid, a third metatarsal and a phalanx. These
do not differ sufficiently from EF. ingenus as described by Scott to
warrant separate description here.

* W. B. Scott, The Osteology of Elotherium., Trans. Am, Phil. Soc., Vol.
XIX, p. 285.

134 University of California Publications. [ GEOLOGY

The species is named in honor of its discoverer, Mr. Frank C.
Calkins.

But one other complete skull of Hlotherium has been obtained
from the John Day. A number of years ago Messrs. Leander S.
Davis and William Day, while collecting for Professor Marsh,
discovered a perfect cranium in the lower Diceratherium beds in
the Blue Basin, Turtle Cove. This specimen, now in the Marsh
collection at Yale University, is a distinct species.

MEASUREMENTS.

Motal: Leng bh: Of (Ska Seepee sks chsheecereuse aver Sere ease) ereretacees ocho eeeemes 616 mm
Wen othe on wman dy lemse re... esc wtever tener Oo om Bee oy Ao oe)
Length P?-M® inclusive, on alveolar border...............+....280
Ierieqdd NEC! sbINe! ween noo aoe on mene enone Ae eon og ooc 97
bene thi SME anclusiviencstytqe 1 a)-sctemenerteer valet cteteeeter secret enemeene 105
IDYeyoyeles ToRe aaukznaKehiloliey exon Jet oe un con enon ache cannecouodnocer 78
IDYeyondat Cone asokehakobd ites loieNone Wis GRA Seo one ons BHA SoS beh eoh odes 109
Jee hihweimoryXosinemlope heheh oo anon nn pAe oo enbo noe eb Gos ace 37.5
PS santero postemomr GUAM CLE I nr tenes usrerotepeienste(aencnepen eter ene rene 25.5
ME antero-posterior Giamever! ie. cc. cere crete ete ie steer ater eke 31.5
Me transverse (diameter eivacars spore ote eel tenant speneie olcpeae reins 33
INE Chale emo oxy fevakore GWEN Wao none BOWen eae be eno oo ae ci 33
IME tCrATISVELSe FET AMeL CI west ious c tone ekehcaeseie cia sicue + cleneusienstenete ale evene 33.5
IMLS Ebahtenteovofqtereoe beh ee Saa ena onodwanas owe cone anne 31
Me tRansV.erses (lame ue tamer er yetetetetsiar <n. teers ferns ne teenie 28
Mp, SANTETO-POSteriOT CUAMVCLON Fores ete tene etete af tensors tonop steno 35
Mi; bransvierse ‘Glametver oye ric.< oss icreioncie se stele ele lois ei cleus een 29
M,,. antero-posterior Giameter seer. seine sacs sc ets cisiere sats 34
MM, transverse diameter rec, -ccts cielo sete sacs oieshseensiereiae 26
Wenoth on birder etrartan Seller cesta i edeu-tonstel suet smetereraler-eu-uetea payee 168
Meno thitote astra cal se sarc crite: teehee ta ietele nye ues nan ten 76
Width across proximal end of astragalus.................... 2

THINOHYUS (BOTHROLABIS) DECEDENS Cope.
Pl. 16.

Chaenohyus decedens Cope. Pr. Am. Phil. Soe., Vol. XVIII,
p. 373, 1879, Vol. XXV, p. 63, 1888.

Type.—Cranium in the Condon collection, Eugene, Oregon. Mandible,
No. T989, Univ. of Cal. Palaeont. Coll. The mandible is associated
with part of a cranium in which I’, part of the canine, P* and Ms!-%
are preserved.

Locality.—Diceratherium beds, Middle John Day. Near McAllister’s
ranch, below Twickenham, Wheeler Co., Oregon. The specimen was
recovered from a horizon situated about fifty feet above the top of
the Lower John Day.

Vou. 4] Sinclair—John Day Rodents and Ungulates. BS

Specific characters.—Facial region shortened, profile concave.
Forehead convex. Molars rapidly increasing in diameter pos-
teriorly, with strongly mamimilated enamel. M’ with large
antero-internal style and prominent postero-internal heel. In-
ferior dental series interrupted by a diastema on either side of P.,.

Two speciemens have been referred to this species. In addi-
tion to the imperfect cranium associated with the mandible which
has been taken as the type of the inferior dentition, there is in
the University collection a much more perfectly preserved cran-
ium (No. 556) collected by Mr. L. S. Davis from the middle
of the Diceratherium beds below Sheep Rock, in Butler Basin,
Grant Co., Oregon. This specimen, combined with mandible No.
T989 is figured on Plate 16.

Generic position.—Thinohyus decedens was placed by Cope
in a distinct genus, Chacnohyus, which he distinguished from his
Bothrolabis by the presence of three superior premolars in the
former and four in the latter. The type of Chaenohyus has been
examined by Professor Merriam, to whose notes the writer is in-
debted for the following particulars. The first superior pre-
molar is a double-rooted tooth situated inside the base of the
canine at a distance about equal to its own diameter, and reach-
ing about as far forward as the posterior margin of that tooth.
Posterior to P*, of which the base is preserved, the alveolar bor-
der is somewhat broken, but there is a small alveolus close to that
for the anterior root of P*. The dental formula is therefore the
same as in Bothrolabis, and the two genera must be regarded as
identical.

The writer has examined the type of Marsh’s Thinohyus,
which was proposed* for the reception of two porcine species from
the John Day,7. lentus and T. socalis, and is unable to distin-
euish Bothrolabis from it. Bothrolabis is therefore bracketed as
a probable synonym. An imperfectly preserved mandible (No.
1990) from the the Diceratherium beds near Price, in the
Crooked River Basin, Crook Co., Oregon, corresponds fairly well
in the spacing of the lower premolars and in size with 7. lentus
and has been referred to that species in our list of the fauna
from the Diceratherium beds.

*O, C. Marsh, Am. J. Sci., 3d Ser., Vol. IX, pp. 248-249, 1875.

136 University of California Publications. [ GEOLOGY

Cranium.—Anterior to the orbit the facial region is abruptly
contracted both laterally and vertically. This feature is peculiar
to T. decedens. In the remaining species the facial region is of
the elongated type of 7. osmonti (Pl. 17). Between the orbits,
the forehead is convex, without elevated superciliary borders. A
pair of broad grooves diverging anteriorly extend forward from
the supraorbital foramina. They are separated by a low
ridge. The median ridge and the grooves are minor features
and do not materially affect the general convexity of the fore-
head. The palate is flat. There is but little downward curvature
of the premaxillae, in striking contrast with 7. osmonti and Dico-
tyles. The premaxillary border of the anterior nares has been
fractured on either side and is restored in the figure.

Mandible—Portions of both rami are preserved with era-
nium No. 7989, The left ramus represented in Plate 16 is the
better preserved. It increases in depth posteriorly. There are
four mental formina observable, one slightly posterior to P.,
two beneath P, and one beneath the anterior half of M,.

Dentition.—The crowns of the first pair of superior incisors
are not preserved in either specimen. The second pair resemble
the corresponding teeth in Dicotyles. The third pair, preserved
in cranium No. 1989, are long and pointed and considerably
recurved. The eanines are broad blades, triangular in eross-
section with the apex of the triangle directed posteriorly. The
outer face is marked by two ridges, the posterior much stronger
than the interior. P! is double rooted and is situated on the
inner side of the base of the canine. In the figure, it is repre-
sented as having slipped from the alveolus. As preserved, the
extension of this tooth below the alveolar border does not exceed
the length of P*. P? is like the first, but larger. P* carries a
large postero-internal basin-shaped heel. In addition to proto-
cone and deuterocone, the tritocone is more or less developed in
Pt. There are short diastemata anterior and posterior to P',
but the rest of the superior dentition is in close series. The
molars increase rapidly in diameter posteriorly. The enamel of
the crowns is mammilated especially in M*. A large antero-
internal style is present on this tooth and also a prominent pos-
tero-internal heel, the surface of which supports a number of

Vou. 4] — Sinclair.—John Day Rodents and Ungulates. 137

lesser tubercles. Mammilated external einegula appear on P*
and the molars. Anterior and posterior cingula appear on P*
and the molars... An internal cingulum is developed on P* and on
Ms **. On the latter teeth it is mammilated like the external
eineulum.

The lower incisors have not been preserved. The canine is
triangular in cross-section with a prominent median ridge on the
outer side. P, is represented by a single large alveolus close to
the canine. P, is double rooted with a simple laterally com-
pressed crown. P., supports a small anterior basal eusp and a
moderately broad heel. On P, the protoeconid and deuteroconid
are equally developed and separated by a deep notch. There
is a broad heel with an antero-posterior ridge formed by the
confluence of two small conules. The diastema between P, and
P, is 6mm. in length. A somewhat shorter interval (5mm.) sep-
arates P, and P,. Like those of the superior series, the lower
molars inerease rapidly in size posteriorly. The heel on M.,, is
large, supporting a number of small cuspules, which vary in po-
sition in the same individual. External and internal cineula are
developed on the heel of P, and at the mouths of the transverse
valleys in the molars. Anterior and posterior cingula are pres-
ent on P, and the molars. In M, the greatly developed heel re-
places the posterior cingulum.

The only other part of the skeleton known is the ealeaneum,
a part of which was preserved in the matrix investing each of the
two erania. It is similar to the caleaneum of Dicotyles, but is
considerably larger.

MEASUREMENTS.

Length of cranium from anterior extremity of pre- No.556 No.1989

masa layetoy condyles Inclusive‘, . scene) scene eer 204 mm
IbanoMoMol Wyalbil aoe on es cena eb aoe oe ao 84
Depth of skull to alveolar border at front of orbit. 80 73.5 mm
Width of palate<at, Pts... sct ces eevee tes ce eee 27
Width of palate at middle of M’................. 25.5
ILyWatedaly [EAVES ahh eve ec cae o aa Oo commana ooode 79.5 81.5
Ie lekeINLs mR Sane e ne sneao beeen eo oe 96
Gen oye MSIE UCU SIC aaoteenyceseaeccten ere) welajanseeesnets he 46 48
seme there Niee un CMUSIy Cl creas cesta -eteke pete elena erereavat: 5]
P2, antero-posterior diameter ........02.5....55.- 8.5 9
Pee UNANS VOLSe mOLAINC UC Tas eiep-c ue sate oe aiere ini orane ene stan 9 12

?

138 Umversity of Californa Publications. [GEOLOGY

No.556 No.1989

M’, antero-posterior diameter ..............-...-6+ 12mm 13 mm
Me, tramsverse diameter “25... «see see os ele errs 12 12.5
M®, antero-posterior diameter .........-.5..:0-:-- 19 19
Me transverse sdtameter yg ey see sr eiyeuteiens sis nee-cenee reese 16 15
12h, Phaederdorjosinentore (Cuil He eae kaon on Ana sconcoabmooadans 12
Pz, transverse \dVamMeter’ ceegyecce 2 «ee credence cone ch cuatcih coca sarvatteuenee ences 7
Mi aDILErO-POSbCTLOM MCMaMet ere at teteccteherascls letete iste euetener sensei onetets 13
MM... transverse! diameter <o.5 co cnce-ecre ances, ersienenene/ oteverers srieuemeeeeere 9
M,, antero-posterior ‘diameter 223.2. 56-6 os «cies se eee sole ie esis 22
Mies LrANSVETSe «C1AMeter m staccdeceustse tetas susie ere eneroncncs toons wen erenenemenen sete 12
Approximate length of caleaneum, combined from dimensions of

WORE SPCCLIMCDS!, £5.-Ph-re-tack.rotogelelecenchohoge ots Sense eMenerepseenisuet ss, sla; soos 61
Width of tuber calcis (dorso-plantar).....................4. 18

THINOHYUS (BOTHROLABIS) OSMONTI, n. sp.
leak. aff

Type.—Cranium and mandible, No. 393, Univ. of Cal. Palaeont. Coll.

Locality.—Diceratherium beds, Middle John Day. West side of the
John Day Valley, about six miles north of Clarno’s Ferry, Gilliam
Co., Oregon,

Specific characters —Facial region elongate, in profile an
even slope from frontals to tips of nasals. Forehead flat between
orbits, becoming slightly convex toward median line. Upper
molars inereasine little in size posteriorly. M* without promi-
nent antero-internal style, with narrow heel extending as a shelf
across the entire posterior border. Inferior dentition in close
series. separated by a long interval from the canine.

The species is named in honor of its discoverer, Mr. V. C.
Osmont.

A second specimen referable to this species was collected by
Messrs. Osmont and Davis from the upper part of the Dicera-
therium beds on the north side of the John Day Valley at Mc-
Allister’s ranch, Wheeler County, about 150 feet above the top
of the Lower John Day. This specimen, a cranium without man-
dible (No. 1988), has those parts of the skull anterior to P+ and
posterior to the opening of the inferior nares broken away. The
crowns of the upper teeth are much less worn than in the type
specimen.

Cranium.—The facial region is greatly elongated, forming in
profile an even slope from the forehead to the tips of the nasals.
Between the orbits the forehead is flat, becoming slightly convex

Vou.4] — Sinclair—John Day Rodents and Ungulates. 139

toward the frontal suture. Anteriorly there is a strongly convex
swelling on either side of the median line, inclosing a deep de-
pression which extends forward from the supraorbital foramina.
The sagittal crest is thin and rises in a gentle convexity above
the interorbital plane. ‘The superciliary borders are moderately
elevated. 'The premaxillaries are decurved to about the same ex-
tent as in Dicotyles. In the type specimen the maxillary is
strongly rugose anterior to the base of the jugal arch. This is
hardly noticeable in No. 1988.

Mandible—Vhe rami have about the same depth from P, to
M.,, tapering anteriorly. The long and narrow symphisial region
is inchned about thirty degrees to the axis of the jaw. The
mental foramina are the same in number and relative position
as in 7’, decedens.

Dentition.—The first superior incisor has a much broader
crown than the second and third. The principal wear is on the
tip and outer side of the crown. I?’ is broken, but the eross-
section of its roots shows that it is a small tooth. I* is long and
pointed and considerably compressed laterally. The upper ea-
nines are oval in cross-section at the base, but become triangular
where the anterior edge is exposed to the wear of the lower ca-
nine. P? is a simple crowned, double-rooted tooth separated
from the eanine and P? by diastemata. Unlike 7. decedens, Pt
is in this species situated entirely posterior to the canine, and is
not overlapped by the posterior border of that tooth. It has
been broken off on the side seen in the figure. The remaining su-
perior premolars are unspaced and resemble the corresponding
teeth in T. decedens. The upper molars increase very slightly
in size posteriorly. On M* the heel is narrow and equally promi-
nent on the outer and inner sides of the crown, giving to the pos-
terior border of the tooth an even convexity. External, anterior
and posterior cingula are present on P* and the molars. Internal
cingula are feebly developed or wanting.

In the inferior series, the incisors are inclined forward in
conformity with the slope of the symphysis and are worn prinei-
pally on their posterior faces, although the tips of the first pair
are abruptly truneated. The lower canines are triangular in
cross-section, somewhat recurved, and have a strongly marked

140 University of California Publications. [GEOLOGY

median ridge on their external faces. The lower premolars are
unspaced and are separated by a long interval from the canine.
All the anterior premolars are double-rooted. Unlike the su-
perior series, the molars increase in length posteriorly. There
was at least one prominent cusp on the heel of M,. External, an-
terior and posterior cingula are developed on the molars.
Affinitics—Thinohyus osmonti may be readily distinguished
from 7. subacquans by the absence of spacing between the lower
premolars and the presence of a long diastema in front of P,. In
7. subacquans the inferior diastemata are short and are anterior
and posterior to P,. The length of M'-M®* is also considerably
ereater in that species and the molars increase somewhat in di-
ameter posteriorly. 7. pristinus is characterized by a large heel
on M®* separated from the posterior cones by a valley. In the
mandible of this species, P, is separated from P, and the canine
by short diastemata. In 7. trichaenus the first lower premolar
is close to the canine and there are short intervals immediately
anterior and posterior to P,. In both 7. pristinus and T. tri-
chacnus the superior dental series is considerably longer than in
T. osmonti. T. vostratus ditfers not only in the greater length of
the superior dental series, but in having a longer M*, on which the
heel is extended particularly along the inner side, being nearly
in a straight line with the inner border of the protocone and
hypocone. It differs also in the spacing of P? and P* which are in
close series in 7. osmouti. These species are all of the type with
elongated facial region. The short-faced 7. decedens differs
from 7. osmonti in the coneavity of the facial profile, the con-
vexity of the forehead, the increase in size of the superior molars
posteriorly, the rugosity of the enamel on the molars, the charac-
ter of M*, and the spacing of the lower anterior premolars. In
the mandible of the more imperfectly known 7. lentus, P, 1s
separated from the canine and P, by diastemata of respectively

Smm. and 10mm.
MEASUREMENTS.
‘Length of skull from premaxillae to foramen mag- No,.393
MURA We MEMO oth cenle. ce Beare! hao Bante Apeme-6i0 & 225) mm
Length of mandible from anterior extremity to con-
Gyle- INCIUSIVEes Sika ars etencrstecshere wear euster spades tote vante vers 186
Length P'-M* inclusive ........ en Rar Cee er 79.5

Vou. 4] Sinclair.—John Day Rodents and Ungulates. 141

No.393 No. 1988

Length M'-M® inclusive ........... 0. ccc eee eee 39 mm 42 mm
Meno thm. Mein Glisuveneedet aera eerie ree 81
Length M,-M, inclusive .............:..0-20000. 45
Width of skull at postorbital processes ........... 83
Depth of alveolar border at front of orbit........ 78 72
Length of diastema between lower canine and P,

(average: of bothwisicdes).... 2....-.s.4.55--s-0 16
Depth of mandible below P, .................0.. 33.5
Depth of mandible below M, ................... aa 5)
p*, antero-posterior diameter .................-. 10 9
Re suransversemtlam clei eur mee sane cine tie 10.5 a
M’, antero-posterior diameter .............2.. 000. 12.5 125
IME AULaNSyerse diameter ae erase ine cents iat 11
M*, antero-posterior diameter ................... 13.5 14
Me, transverse dianteter” 5... 20...0s0... 0206205 11.5 11
P,, antero-posterior diameter ..................;; 12
P,, tramsverse diameter ...........0.eee0eeesseee 7
M,, antero-posterior diameter.................... 12
M,, transverse diameter ..............200ee0cees 8
M,, antero-posterior diameter ................... 18.5
Viera DRAM SVCTSemOLaIMeler immer taeeekereteneaie le eerie te 9

MESOHIPPUS ACUTIDENS, Nn. sp.
PIE 18:

Type.—Cranium, portion of the left fore limb, and a few vertebral

fragments; No. 376, Univ. of Cal. Palaeont. Coll.

Locality.—Promerycochoerus beds (?), Upper John Day. Powell’s

ranch on the Middle Fork of the John Day River about five miles
above Ritter, Grant Co., Oregon.

Superior canines lone and pointed, with acute anterior and
posterior edges. Metaloph hardly interrupted by metaconule,
sharply separated by a deep notch from the ectoloph. Protoloph
with well marked protoconule, united with ectoloph by a narrow
shape-edged ridge which widens in moderately worn teeth.
Parastyle broadly rounded except in M* where it is compressed
antero-posteriorly. M*® with metaloph storter than protoloph
(4.e., a8 8.5 mm. :12.3 mm.), producing almost a triangular out-
line for the tooth crown. Mesostyle sharply defined and ribs
broadly rounded and prominent. The measurements seem also
to be characteristic.

The moderately worn teeth indicate the fully adult condition
of the animal. The incisors show incipient cupping and are
marked by a slight depression in the center of the external face.

142 University of California Publications. [ GEOLOGY

The long, dagger-shaped canines resemble those of a carnivore,
and are quite unhke the corresponding teeth in any other known
species of Mesohippus. The edges developed anteriorly and pos-
teriorly are sharply set off from the rest of the tooth crown.
The tips are unworn. A large hypostyle is present on all the
molars and molariform premolars. On all except M® it gives off
a narrow spur-like cmegulum which borders the hypoecone pos-
teriorly. On most of the molars and premolars there are one
or more small tubercles at the mouth of the transverse valley.
No other traces of an internal cingulum are seen. The external
cingulum is not continued across the bases of the styles.

The cranium lacks the bones investing the posterior portion
of the brain case and has been somewhat crushed, accentuating
the flatness of the forehead. The orbit is almost completely closed
by the strongly developed postorbital process of the frontal. The
supraorbital notch is entirely encireled by bone, forming a large
foramen. There is a well marked preorbital fossa.

With the cranium were preserved portions of the left scap-
ula, humerus and radius. Only the glenoid portion of the seap-
ula is represented. It agrees with M. bairdi as described by
Scott,* except that the free border of the coracoid process is bent
inward, forming a rather open hook. The humerus is without a
supratrochlear foramen. In this respect it differs from M. bairdi
in which the anconeal fossa is perforate. The radius, of which
the proximal portion is preserved, is very much like that of WM.
bairdi.

The specific name refers to the sharp pointed canine teeth.

The new species may be readily distinguished from the horses
of the Middle and Upper White River by the dental measure-
ments, the great length of the canine and the character of the
orbital region. It approximates in dimensions WM. brachystylus
Osborn? from the Leptauchenia beds, but differs from that
species in the shape of M°’, the form of the postorbital process
and the closure of the supraorbital notch.+

* Osteology of Mesohippus and Leptomeryx. Jour. of Morphology,
Vol. V, No. 3, p. 319.

+ New Oligocene Horses. Bull. Am. Mus. Nat. Hist., Vol. XX, pp.
167-179, 1904.

¢ Compare Pl. 18 with Osborn, op. cit. Pl. V, E.

Vou. 4] — Sinclair.—John Day Rodents and Ungulates. 143

In size M. acutidens oceupies a position intermediate between
the John Day species M. equiceps and M. praestans. So far as
it is possible to. compare the dental measurements with those
given by Marsh ¢ for MW. anceps there is close agreement, but the
skull of M. acutidens is not depressed between the orbits nor do
the molars extend further behind the orbit than in MW. bairdi, as
is said to be true for JI. anceps.

MEASUREMENTS.

Length of cranium trom premaxillae to condyles inclusive. ..... 238mm
Mben othe des=MErInGlusiviess ss jaee.ten ochre serena evelepteneneys borates citere ne ae 85
Ibength: .. Me=Me inclusive: aa wesc dene o cele ed wuieea ise sie acs ais ses 38.5
length of diastema anterior to canine ....:...5...-.:-+..-25+- 10.5
ihength of diastema posterior to Canine o.0 65.2. 0.. e eee = 23
Length of canine from margin of alveolus to tip, measured on
lingual’ ASPCGbeiinu aa cue a gale payers ance lene ou Amuse eisie Clara 17.5
MES, Chanenitob Loess aloes (une ea a nonon oon urs aa no hones acu oe 13
IME transverse dlameter® sca ese ees sos ee pees eee eee ese ss ees 16
IVE WeATILEHO-) OSLELION (lA M Cet Meter ust verstessisea of eevoen ete ei tenseyercnsiees 13
Mes transverse: ‘diameter ® ss 15 .ec.cvevare cs ecere Ghawe metal .2 aucveyer sees 16.3
MS; antero-posterior diameter ..% 2. aee.sde eee cseuus seusee ses 12.5
MSA tRaMS Verse: CUAMELCK! 9 siere e e oa alot wise eater oes eee ae 16

Umversity of Califorma,
March, 1905.

¢{ Marsh. Am. Jour. Sci., 3d Ser., Vol. VII, p. 250.

* Measured through the anterior cones at the widest part of the tooth
crown.

All

EXPLANATION OF PLATE 14.

figures three-fourths natural size, excepting Figs. 4 and 5, which are
three times natural size.

. L.—Allomerya planiceps, n. gen. and sp. Cranium from the left side.

, 2.—Allomeryx planiceps, n. gen. and sp. Cranium from below.

g. 3.—Hypertragulus, sp. Right mandibular ramus. The dotted outlines

are restored after Scott.

. 4.—Peromyscus parvus, n. sp. Portion of maxillary containing’ first

and second left superior molars. Occlusal view. 3.

. 5.—Peromyscus parvus, n. sp. Right mandibular ramus from above.

x3.

. 6.—LHntoptychus sperryi, n. sp. Cranium from above.

7.—Entoptychus sperryi, nu. sp. Cranium and mandible from the left
side.

. §.—Lutoptychus rostratus, nu. sp. Cranium from below.

g. 9.—Entoptychus rostratus, n. sp. Cranium from the right side.

BUEE. DEPT. GEOL, UNIV, CAL VOTE apie |4

EXPLANATION OF PLATE 15.

Blotherium calkinsi, n. sp. Cranium and mandible from the left side. The
extremity of the premaxillary supporting the upper incisors
is restored in plaster. Figure about one-fourth natural
size. X.24.

“WO 'AINN 1039 ‘1d30 ‘Ng

GI “Td ‘b “IOA

EXPLANATION OF PLATE 16.

Lhinohyus (Bothrolabis) decedens Cope. Cranium and mandible from the
left side. *%. Two specimens are combined in the drawing
(Cranium No. 556 and mandible No. 7989). P* should not
extend beneath the level of P*. The anterior nasal region
has been restored in the figure.

BULL, DEPT. GEOL. UNIV: CAly WAOIES IEG Me

ie)

EXPLANATION OF PLATE 17.

Thinohyus (Bothrolabis) osmonti, n. sp. Cranium and mandible from the
right side. Figure somewhat less than one-half natural size.
x .469.

“T1NG

Jel @

)4

‘AINA “IC

)

Wo

“OA

Z|

EXPLANATION OF PLATE 18.

Mesohippus acutidens, n. sp. Cranium from the left side. 4.

BULLS DEPT GEOL UNIV CAL VOEr4 ris l8

UNIVERSITY OF CALIFORNIA PUBLICATIONS
BULLETIN OF THE DEPARTMENT OF

GEOLOGY

Vol. 4, No. 7, pp. 145-161, Pls. 19-23 ANDREW C. LAWSON, Editor

NEW MAMMALIA

QUATERNARY CAVES OF CALIFORNIA

WILLIAM J. SINCLAIR.

CONTENTS. eee
mGro duct Ok | Svetefatgarser sy aueus sue oes ecenaus ols ine sac ei sitara. s.checuenes Saeee ais ats Seeders 145
MhomomyswmieToOdOn, Ne Spies aunts ae saciae ce iais cone Hees ac nee ayers eee as 146
PASO domittal ma, ORLOSSUTS ss Men SUS player sue er seteuereeucreesls arch y ererecesew ee cvenmens 147
Meonomay Spelaca. Ns Spice sia see e-< ge vsusnesoa.e oe eoseleus aiaversig Ausnseyekere: ees 148
Platyeonus( 2) Spice as sucec ce os 0 mbagsvianseien snail vee arch Rear msi seme a Re Renee 149
(GATE LE VET 21M Se enscuee sweted-qoust snc beranakat thnein a: clsuenene tay eet encacti ess sieueronshcceoee aueneeee 150
Hucerathermim collinum Bk& Sioscs... 2.6 otaas once eseee cee os dees s 150
ENV) LOCGGUS HIN OL Uhm Use) MCU cpaganopN/aister suetattch< vane te cate stavre,aqs(iycttey see veneer ler torsi ane 152
Nothrotherinmi(?)) Shastense, Di Spis..ec esq seees a a aa seas cau 4 ee 153
Megalonyx (SleITEnSIS; Is Spi ie emcees ce oie ots ests asia Gas Sle enact oe wee puslils 155
Wie all omsysxg (U2) OmmS |) steneteas sey stots eteustepevets te Merete <te,ecat arog a ccrec ee etensriaucte ahates aretnre tere 160
Meoalonyxswheatleya Cope (Ct). .-cciecle sss. esaes see esem ose eas coc se 161
Meoalonyx jefferson Werdy CP)ieiesaacs ae ou ce ciacniascs oes acca 161

INTRODUCTION.

The eave explorations conducted by the Department of
Anthropology of the University of California have opened to
the palaeontologist a new source of information regarding the
Quaternary vertebrate fauna of this state. Occasional scattered
teeth and bones from valley alluvium, clay beds, stream gravels
and asphaltum deposits of Quaternary age occurring in various
parts of California, have shown the presence of a considerable
variety of mammalian species, but it has been impossible to
eroup them into a fauna which might be regarded as a chrono-
logic unit, owing to more or less variation in the age of these
beds. The agencies involved in the accumulation of most of

146 Unversity of California Publications. [ GEOLOGY

the bone-bearing deposits have proved destructive to all but
the larger forms. On the contrary, the caves, having acted to
a greater or less extent as receptacles for the accumulation
of surface material, might be expected to afford a more complete
faunal record, as the conditions governing preservation are
usually quite favorable. This expectation has been fully
realized.

A large number of the species of Quaternary mammals col-
lected from the caves are new. The greater number of the new
species were obtained from the Potter Creek Cave, the explora-
tion of which has already been described.* New material was
also secured from the well known Mercer’s Cave situated near
the town of Murphys in Calaveras County. In the description
of the following species the writer is particularly indebted to
Dr. C. H. Merriam for information concerning the relationships
of the rodents.

THOMOMYS MICRODON, Nn. sp.
Pl. 19, Figs. 1-3.
Type.— No. 5738, Univ. of Cal. Palae. Coll. The anterior portion of a

skull without the mandible.

Locality.— Potter Creek Cave, Shasta Co., California.

This species closely resembles Thomomys mazama Merriam
C. H.. from which it differs in having a very prominent ridge
on the side of the rostrum, marking externally the position of
the alveolus of the superior incisor. The fossa above the ridge
is deep. Thomomys niger Merriam C. H. has the fossa behind
the incisor ridge almost as deep as in the fossil form, but differs
in having the rostrum heavier and the molars much larger. In
the fossil form, the rostrum is rather shorter and broader than
in Thomomys mazama, and the premaxillae are less pointed.

The new species belongs to the yellow toothed division of the
genus. The incisors are flattened on the anterior side, the
anterior outer corner is angular and the teeth are sharply
decurved.

*Science, N. 8., Vol. XVII, No. 435, pp. 708-712, May 1, 1903; Univ.
of Cal. Publ., Am. Arch. and Eth., Vol. 2, No. 1, 1904.

VoL.4] Sinclair —Mammalia from Quaternary Caves. 147

MEASUREMENTS.

Length of rostrum from base of P* to anterior surface of
UMGESONN chs. tension agrees copehsus yong aiwtaneneupushwaninnnces seats oes ctuane 1

3.5mm

Length of rostrum from postero-inferior extremity of pre-

maxillae to anterior surface of incisor ................ 10.5
Greatest width of rostrum) 25.2 -0.ssersucleecs + we cce sss sss Gee (6783)
Depth of rostrum from posterior extremity of nasals to margin

OTe AVE OLUST OL es aes, Sitiececcyehecs ereuohetslopiens Meremeus Siatsveneesasie afcusite 11
Depth of rostrum from posterior extremity of nasals to postero-

inferior extremity of premaxillae ...................-. 9
Width across frontal between orbits ...............2.20200- 6.5
Re antero-posterior (iameter | s.ayae ws os css aeierere ery ce ie 126
pe transverse diameter at Widest Pattee ec cies eters eecccre ere eel « 1.5
ME antero-posterior diameter 2. se asa. scectes ec se ee ess 1
Wi Anshalchwcwisiey tebe waKkey) Cane ore aa odo dana oeomen dade e 2
Witdthrsof AMCISOT) seal cc. cee sic tye Se snd oe es ae es tigle els eae 2

APLODONTIA MAJOR FOSSILIS, nN. sub-sp.
Pl. 19, Figs. 8 and 9.
Type.—No. 4160, Univ. of Cal. Palae. Coll. The right mandibular
ramus, lacking the coronoid process and part of the angle.
Cotype.—No. 5265, Univ. of Cal. Palae. Coll. An imperfect cranium.

Locality.— Potter Creek Cave, Shasta Co., California.

Numerous lower jaws of an Aplodontia were found in all
parts of the cave and at various depths beneath the surface of
the cave deposit. The jaws all show the characters possessed by
the type specimen. They differ from the typical Aplodontia
major in having the dental foramen generally wider trans-
versely. The ridge in front and below the masseteri¢e fossa, in
the fossil form, is usually continued across the lower side of
the ramus and connected with the inner prominence of the
angle, while in A. major a smooth space exists between the
angle and the ridge in front of the masseteric fossa. In the
fossil form the wall in front of the fossa above the angle, on
the inner side of the ramus, is vertical for a longer distance
below the opening of the alveolar canal than in the recent
major. So far as it is possible to compare its dimensions with
the measurements tabulated by Dr. ©. H. Merriam,* the
cranium agrees closely with Aplodontia major.

*Annals N. Y. Acad. of Sciences, Vol. III, No. 10, Table facing
page 328.

148 University of California Publications. [ GEOLOGY

MEASUREMENTS.
Least width of rostrum in front of zygomatie arches...... 17.25mm
IRE ie shaiKentoydoien| ywksldiy Reem acne gonumdcsongsobaccobenoac 10
Length of superior molar-premolar series (except P*)

measured! ON salveoltges. scission icine lino
Palatal width between alveoli of Pt ................ cece: 6.25
Palatal width between alveoli of M® ..................000. 6.5
Distance between alveoli of inferior incisor and P* .......... 13
Length of lower molar-premolar series measured on alveoli .. 18

TEONOMA SPELAEA, N. Sp.
Pl. 19, Figs. 4-7.

Type.—No. 5362, Univ. of Cal. Palae. Coll. The anterior two-thirds
of a skull of an adult individual, in which the teeth are not much
reduced by wear.

Locality.—Potter Creek Cave, Shasta Co., California.

Tconoma cinerea is the form nearest to this new species, but
the rostrum and incisive foramina are decidedly shorter in the
fossil! form than in cinerea. Also, the premaxillae extend far-
ther back beyond the nasals, the nasals taper more posteriorly
and the frontals have a greater interorbital width in the new
species than in 7. cinerea.

A large number of lower jaws were found in various parts
of the cave. They differ from the typical Teonoma cinerea in
having the enamel loops of the molars more evenly balanced
on the two sides of the axis of the tooth row. In cinerea the
loops are much longer on the inner side than on the outer side.
In the cave specimens there is comparatively little difference.
As but one species of Teonoma is represented in the Potter
Creek Cave, the mandibles are also referred to Teonoma spelaea.

MEASUREMENTS.
Length of rostrum from base of P* to anterior surface of

DMLCHSOY. <eygya wn Siasacariave sol agesane pees anc: See noes ueiteer ove fe eehensyeeeyemep conch cree 19 mm
Width of rostrum in front of infra-orbital foramina ........ 9
Depth of rostrum at middle of incisive foramina ........... 9
IbTssaveqlal uk ohaKihye) aonb) Bee soe achebanchonodoceeoddeue 13
Greatest width measured across both incisive foramina..... a}
Width across frontal! between orbits 2. shee ew cancers oere eo 6.5
Length of superior molar-premolar series measured on alveolar

WOT COTS Pye oy oe sativa cts eoscee es ale tac bemete Rede ode sen Rome eee 10.25
M’, antero-posterior diameter measured on alveolar border .. 4.3
M', transverse diameter measured on alveolar border at widest

ins mn One homoramnn loSeoe UA eno Oo cG nop Uo Eaetdoo ood 2.3

M?, antero-posterior diameter measured on alveolar border .. 3
M’. transverse diameter measured on alveolar border at widest
BEL casas eyances, cstarscanetes tcavehatyeuels eon MNO G GDA Doss ao nd.00 6 2.3

VoL.4] — Sinclair—Mammalia from Quaternary Caves. 149

PLATYGONUS (?), sp.
Text, Fig. 1.

Locality.— Potter Creek Cave, Shasta Co., California.

Three specimens from the Potter Creek Cave are doubtfully
referred to this genus. ‘lwo of them are superior molars which
are so poorly preserved and so badly worn that little can be
determined regarding them. When first examined, they were
thought to be referable to a large species of tapir and were
so listed in the writer’s preliminary paper.* The third speci-
men, a lower molar corresponding in size with the teeth of the

superior series, 1s represented in text figure 1. The crown

LCC oY
att

Fig. 2.
1. Platygonus, sp. Potter Creek Cave.
g. 2. Camel tooth. Potter Creek Cave.

is divided into two transverse lobes by a deep valley which
is unobstructed by ridges or tubercles. The notching of the
anterior crest is slight, that of the posterior crest deep. A
prominent extension of the cingulum posteriorly forms a heel
which appears to have been more or less continuous around
the external edge of the posterior lobe and to have joined a
small tuberele at the outer margin of the transverse valley.
This could not be well brought out in the figure as the enamel
has been broken off, exposing the dentine. Anteriorly, there
are traces of a narrow cingulum, but none exists internally.
If the generie position of the specimen has been correctly deter-
mined, the remains indicate a species of Platygonus larger than
any previously described.

MEASUREMENTS.
Antero-posterior diameter of inferior molar ................ 30 mm
Transverse diameter at widest part ............ cece cece eens 23.5

* Science, N.S., Vol. XVII, pp. 708-712, 1903.

150 University of California Publications. [GEOLOGY

CAMEL REMAINS.
Text, Fig. 2.

Although camels were abundant in California during the
Quaternary, they did not play an important part in the fauna
of the region about the Potter Creek Cave. Three molars of a
camel were found in this cave but their fragmentary condition
does not permit of a generic reference. One of them, a_third
inferior molar, is represented, natural size, in text figure 2,
The heel has been gnawed off by rodents. Most of the cement
and part of the external enamel layer have been removed by the
same means.

EUCERATHERIUM COLLINUM Furlong and Sinclair.
Pl. 20, Figs. 1, 2.

Pub. Univ. Cal., Am. Arch. and Eth., Vol. 2, p. 18; Bull. Dept. Geol.
Univ. Cal., Vol. 3, p. 412.

This ungulate is represented by abundant remains in the
Potter Creek Cave, where it occurs in all bone-bearine strata.
The specimens comprise numerous teeth from both jaws, loose
podial elements, and broken horn-cores, some of which are sup-
ported by a part of the frontal. The various parts of the
skeleton were not found associated, but there can be little doubt
that they all belong to this genus. The horn-cores and the teeth
of the superior series agree with the type specimen. As these
remains do not indicate the presence of more than one species,
the limb bones are also referred to FE. collinum.

The various podial elements of Euceratheriwm agree closely
in almost every particular with the corresponding bones in the
feet of Aplocerus, excepting in size. Both anterior and pos-
terior eannon-bones are short and robust. In the anterior can-
non-bone, the posterior margins of the proximal articular sur-
faces lie in the same plane, while anteriorly they meet in an
obtuse angle, producing an emargination of the anterior
proximal border which is less marked than in Aplocerus. (Com-
pare Pl. 20, figs. 2 and 3.) The nutrient foramen piercing the
anterior surface of the bone above the distal condyles is also
much smaller than in Aplocerus.

Vou.4] — Sinclair—Mammalia from Quaternary Caves. 151

In the hind foot (Pl. 20, fig. 1) there is the same close
agreement between the two genera. One of the most important
differences is the close approximation anteriorly of the external
trochlea and the condyle in the astragalus of Huceratheriwm. In
Aplocerus, the two articular surfaces are separated by a wide
groove.

The absence of close relationship between Huceratherium
and the existing North American cavicorns is well brought out
by a comparison of the foot structure, and especially of the
eannon-bones. In Ovibos the cannon-bones are short and robust
and agree, within a few millimeters, with the dimensions of
the corresponding elements in Euceratherium, exeept in the
length of the posterior cannon which is considerably greater
in Ovibos.* In the latter genus, the proximal facets of the
anterior cannon-bone do not lie in the same plane posteriorly
as in Euceratherium. Although there is close anatomical agree-
ment with the feet of Aplocerus, the difference in size of the
two genera is very great. The cannon-bones of the bighorn
sheep are much larger in proportion to their width and are
much less robust than in Huceratherium. In the domestic cattle,
these bones are in some cases as robust as those of Euceratherium
but are considerably longer. The extinct Bovinae of this Coast
all have much broader and heavier cannon-bones.

It is apparent from these comparisons that no close relation-
ship exists between Huceratherium and the goat-antelopes or the
sheep. The eattle are excluded by fundamental differences in
dental structure. The feet of Ovibos differ shehtly in size and
in minor anatomical peculiarities but the large horn-cores of
that genus are of a different type from those of Euceratherium.
No North American fossil forms are known from older forma-
tions which can be regarded as ancestral to the latter genus.
It is possible that Huceratherium represents an <Asiatie type
which reached North America in the Quaternary alone with the
goat-antelopes, and that its ancestors are to be sought among
the extinct forms of the Asiatic Pliocene.

* Dawkins, W. B. British Pleistocene Mammalia, Part V., Palaeont.
Soc., 1872.

by University of California Publications. [GuoLocy

MEASUREMENTS.

Length of anterior cannon-bone measured on anterior surface 175 mm
Width of anterior cannon-bone measured at proximal end.... 56
Width of anterior cannon-bone measured across distal condyles 61
Thickness of anterior cannon-bone measured at middle of

SWAT DM arc skenevens, seep seen) oaense ene tune eee ee ee eer 22
Length of posterior cannon-bone measured on anterior surface 180
Width of posterior cannon-bone measured at proximal end.... 49
Width of posterior cannon-bone measured across distal con-

CV LOS? HE ererecwe tists caevedeerastape tea weve Le gay Pen Toe oe ements 56.5
Thickness of posterior cannon-bone measured at middle of

SHALG Periyar scebe peer ce canine center mune ae caer eae Yee ene acre ee 27
Greatest lenoth of astnamalus Yieca-).ieictsee eae ieee: 62.5
Width of astragalus across proximal trochlea.............. 37
Width of astragalus across distal condyles ................. 42.5
Kaila Moni, ankehraKquilo anol eee es ane nod a goseecsanunoacoeun 51.5
Greatest proximo-distal width of naviculo-cuboid at anterior

Orders parc fel po cues ct vee Weta tEekape ceca cee We aareyees Pelecerane eee ees 18
length of a -phalanx of first row... 2.....).0.30)e....00%- 58.5
Width of a phalanx of first row at proximal extremity ...... 30.5
Width of a phalanx of first row at distal extremity ......... 26
ength ior a phalanx of isecomd row een csen. ees lee sens 43.5
Width of a phalanx of second row at proximal extremity..... 29

APLOCERUS MONTANUS Ord.
Pl. 20, Figs. 3 and 4.

Parts of two anterior cannon-bones from the Potter Creek
Cave are referred to this species. No. 4312 (Pl. 20, fig. 3) rep-
resents the proximal three-fourths of the right cannon-bone.
The specimen shows traces of rodent grawing and is further
disfigured by an exostitial growth at the proximal end, on the
inner side of the bone. The middle of the shaft is slightly wider
than the recent specimen of Aplocerus with which it is com-
pared, but otherwise the two correspond closely in structure
and dimensions. No. 4382 (Pl. 20, fig. 4), the distal half of
a left anterior cannon-bone, is slightly larger than the cor-
responding element in Aplocerus, but in other respects does
not differ from that genus. In the accompanying table, the
dimensions of these two specimens and of Aplocerus montanus
are given in parallel columns.

Vou.4] Sinclair—Mammalia from Quaternary Caves. 153

Cannon-bone No. 4312 No. 4382 A. montanus
Width at proximal end ........... 36° mm Perenecu act 35 mm
Width at middle of shaft ......... 29 eee 25
Greatest thickness at middle of shaft 13.5 estas 13
Width across condyles ............ hele 42.5 39.5
Width at nutrient foramen............. 35.0 32
Greatest thickness at nutrient foramen... . 15 14

NOTHROTHERIUM (?) SHASTENSE, n. sp.
Pl. 23, Figs. 1-5a and 8.
Type.—No. 8422, Univ. of Cal. Palae. Coll. An incomplete right
mandibular ramus without teeth.

Locality.— Potter Creek Cave, Shasta Co., California.

This ground-sloth is represented in the eave collection by a
large number of specimens. While teeth are wanting in the type,
the pecular shape and dimensions of the alveoli agree so closely
with a number of molars from the same.cave that there ean be
little doubt that they should be referred to the same species.

The type specimen lacks the greater part of the coronoid and
angle. The anterior part of the symphysis is wanting, and the
alveolar border is somewhat broken. The inferior border (PI.
23, fig. 2) is strongly convex with the major convexity below
the third lower molar. From this point it rises toward the
symphysis, which is quite oblique instead of being almost ver-
tical as in Megalonyx jefferson. The alveolar border in front
of the second molar is somewhat broken and there is no trace
of an alveolus for the first molar. The anterior opening of the
alveolar canal is visible at the anterior extremity of the ramus.
Its posterior opening is at the base of the coronoid process, on
the outer side of the jaw.

The molar alveoli extend to the lower border of the ramus.
from which they are separated by a thin shell of bone. All
have parallel vertical walls, indicating that the specimen is of an
adult individual.

In the second lower molar alveolus (Pl. 28, fig. 1) the
lateral walls are inclined toward each other and if produced
would meet anteriorly. The tooth occupying this alveolus was
grooved on both lateral faces, dividing the column into two
lobes of which the anterior was the smaller. Each lobe cor-

154 University of California Publications. [GEOLOGY

responds to a transverse ridge on the crown. The anterior wall
of the alveolus is plane, while the posterior is slightly convex,
with indications of a convex median rib.

The alveolus for the third molar is almost quadrangular in
outline. The anterior wall is slightly concave, while the pos-
terior is convex with a stronger convex rib situated about mid-
way. The lateral walls meet the anterior face at a right angle.
They are both grooved. <A third lower molar of the left side,
No. 8704 is represented on Plate 23, figures 4 and 4a:

The fourth molar alveolus is cordate in cross-section, with
the indentation on the outer side. The anterior lobe produced
by this groove projects beyond the posterior. The tooth is rep-
resented in the cave collection by three specimens, Nos. 8485,
8328 and 8339, but none of them have the triturating surfaces
preserved.

Fourteen molars referable to this species were collected from
the eave, principally from stratum E. Three were found in
stratum A and several in the Buried Gallery from stratum E or
F. Some of these are shown on Plate 23, figures 3-5a and 8. Sev-
eral are considerably curved and are doubtless of the superior
series. They correspond in size to the lower molar alveoli. The
last superior molar of the left side, No, 8497 is represented on
Plate 23, figure 8. It is a triangular tooth with the posterior
side plane, the anterior convex, and the outer plane and meet-
ing the posterior at a right angle. The triturating surface of
the crown has been injured by rodents.

MEASUREMENTS.

Length of inferior molar series measured on alveolar border... 53.5mm

Greatest antero-posterior diameter of the alveolus of M,...... 15
Greatest transverse diameter of the alveolus of M, .......... Tl
Greatest antero-posterior diameter of the alveolus of M, ......15
Greatest transverse diameter of the alveolus of M, .......... 17
Greatest antero-posterior diameter of the alveolus of M, ...... 16
Greatest transverse diameter of the alveolus of M, ........... 17
Depth of ramus below alveolar border of M; ................ 50

Least distance between alveolar border behind M, and inferior

border: OL awe Soa hacscieteles, Mhactebe costo eon tte eee 43.5
Superior molar No. 8702, antero-posterior diameter at triturat-
UNG! SUPL ACE: 02s coe ehewegesavasees tt arom veucne etre os tue cncneteeetepee meee 12

Superior molar No. 8702, transverse diameter at triturating
surface

Vout. 4] Sinclair.—Mammalia from Quaternary Caves. 1155

Third inferior molar No. 8704, antero-posterior diameter at

UMP RRaye neEKCY os Hetcn oacie coo oOo He eons Us aonobe 12
Third inferior molar No. 8704, transverse diameter at triturat-

DDO SUPLACE ovis. Sieh aie) saat tm rors ayo, Sa cuiere.ns we eee tyemenya sce are ee 15
Superior molar No. 8337, antero-posterior diameter at triturat-

MNO SSUTLACO! We i raaetdeevspesesexsi avers sve lorehelaliows wr eyehe areal aasle diana eve.< 12.5

Superior molar No. 8337, transverse diameter at triturating
SUMMA. C Ch Bee Netene ates shoes )s cliaueveuer aucpeueieiicge

MEGALONYX SIERRENSIS, Nl. sp.
Pl. 20, Figs. 5-8; Pl. 21, Figs. 1 and 2; Pl. 22; Figs. 1-3.

Type.—A lower jaw, in the Harvard Museum of Comparative Zoology,

Cambridge Mass., and No. 8130, Univ. of Cal. Palae. Coll. Left
scapula, seapho-trapezius, trapezoid and magnum; right caleaneum
and navicular; several imperfect metatarsals; a broken claw; part
of the tibia; several vertebrae and numerous fragmentary bones.
The Harvard specimen and the material at the University of Cali-
fornia belong to the same individual.

Locality.—Mercer’s cave, near the town of Murphys, Calaveras County,
California.

A part of the remains of this sloth were found when Mercer’s
eave was first discovered. The mandible was presented to the
Harvard Museum of Comparative Zoology in 1887 by Mr.
Z. A. Willard. <A broken tibia, a caleaneum and some other
fragmentary bones lay on a block of lmestone to which they
were cemented by stalagmite, and were for years an object of
eurosity to persons visiting the cave. Through the kindness
of Mrs. Mercer, these were presented to the University of Cali-
fornia in 1901, and permission was obtained by Professor J. C.
Merriam to search for additional material. At Professor Mer-
riam’s request, the writer visited the cave during the summer of
1902, securing several fairly complete bones, notably the scapula,
a number of podial elements and a few vertebrae. The bones
were found in the erevices between large limestone blocks in
the narrow part of the cave above the chamber known as ** The
Flower Garden.’’ Some were fairly well preserved, being
coated with stalagmite, others were exceedingly soft and spongy,
and a large amount of the material was too fragmentary to
be of use.

The cave is developed along a fissure, running parallel with
the strike of the Carboniferous limestone. Radiating from the
present entrance there is an earth fan, but deeper down the

156 University of California Publications. [ GEOLOGY

fissure is almost choked by large fallen blocks. From the posi-
tion of the sloth remains beneath some of these blocks it was
evident that many of the latter had reached their present rest-
ing place at a later date than the bones. The abrupt descent
preciudes the idea that the animal wandered into the cave and
there died. The best explanation of its presence seems to be
that it was killed by a fall into the eave.

Through the kindness of Dr. C. R. Eastman, the specimen in
the Harvard Museum was borrowed for examination. On the
accompanying label it was stated that fragments of human
erania were found associated with the mandible. Several
human skeletons were found on the surface of the earth slope
mentioned above, but these were probably comparatively recent
Indian interments, while the sloth remains were from a much
deeper part of the cave. Some of the human bones were
inerusted with a very thin shell of stalagmite. It seems once to
have been the custom of the Indians in this region to east the
bodies of the dead into such natural pits and caves as the region
afforded. The human remains in Mercer’s cave were apparently
introduced in this way.

The ground-sloth bones collected are those of a young animal
and differ in several respects from Megalonyx jeffersoni with
which some of the dimensions compare favorably.

Two views of the mandible are given on Plate 21. The jaw
is smaller than the corresponding element in Megalonyx jeffer-
sonn, but this is due in part to the youth of the animal, in
which the epiphytie elements were still distinct. The bone
is invested with a layer of stalagmite which increases its size
slightly. The second and fourth molars on the right side have
the trituratine surfaces broken. Some of the teeth are more or
less coated with stalagmite. The canine molars are not much
curved. The external dentine layer only could be distinguished.
The internal convex rib is not quite central, and the concavity
bounding it posteriorly is deeper than the anterior one.

A comparison of the dimensions tabulated on page 159 with
the measurements of the mandible of Megalonyx jefferson
given by Leidy,* shows that while the jaw is shorter and shal-

* J. Leidy, A memoir on the Extinct Sloth Tribe of North America
Smithsonian Contrib., Vol. VII.

Vou. 4] Sinclair—Mammalia from Quaternary Caves. aly

lower, the posterior molars are of the same size as in that
species.

The scapula (Pl. 22, fig. 1) is broken anteriorly, and lacks
the supraspinous fossa, the scapular spine, and the coracoid
process. These parts had disappeared before the specimen was
discovered. At the anterior border of the glenoid fossa there is
a rough surface for the attachment of a glenoid epiphysis like
that found in young individuals of Megalonyx jeffersoni.

The glenoid fossa as preserved in the cave specimen is much
longer and wider than in je/fersonii.

The anterior extremity of the superior border of that part
of the scapula preserved is greatly thickened; the posterior
extremity much less so. The posterior seapular border is
strongly coneave antero-posteriorly, differing in this respect
from jeffersoni.*

The subscapular fossa, so far as preserved, is smooth and
basin shaped, without the alternation of ridges and sloping
surfaces deseribed by Leidy for jeffersonii.+

The supraspinous fossa is not shown, and the thickening
of the antericr border mentioned above represents the base of
the scapular spine. The infraspinous fossa is convex in all
directions, with a low median ridge. In jeffersonit both fossae
on the lateral surface of the scapula are deeply concave.t

No foramina are indicated beneath the thin layer of stalag-
mite which preserves the specimen.

The scapho-trapezius (Pl. 20, figs. 7-8, s-t) is irregularly
tetrahedral in shape, with a broad convex proximal facet for
the radius. Distally, the most prominent facet is that for the
trapezoid, which extends from the dorsal almost to the palmar
margin of the bone, while in je/fersonii it is broadly separated
from the latter. The facets for the magnum and lunar are not
well preserved, as the specimen has suffered considerably from
decay which has reduced its dimensions at several places. <A
similar though slightly larger and somewhat less complete bone
was obtained from the Potter Creek Cave (No. 8201).

* J. Leidy, op. cit. Pl. VIII, fig. 3.

+ Ibid. pp. 24 and 25,
¢ Ibid. p. 25.

158 University of California Publications. [ GEOLOGY

The trapezoid (Pl. 20, figs. 7-8 ¢) is a small element, tri-
angular in section when viewed from below. The facet for
articulation with the scapho-trapezius which occupies the entire
proximal surface is convex in dorso-palmar section and sigmoid
transversely. The articulation is continued on the inner side
of the bone as a surface inseparable from the proximal one. An
oblong dorsal facet, concave in dorso-palmar section and a small
ellipsoidal convex palmar facet, separated from the former by
a groove, articulate with the magnum. A large distal facet,
sigmoid in dorso-palmar section, articulates with the second
metacarpal.

The magnum (Pl. 20, figs. 7-8 m) is broken, and has lost the
articular surfaces for the seapho-trapezius and the lunar.
There is an irregularly oval palmar facet for the seapho-
trapezius, a concave roughly quadrilateral distal facet for the
third metacarpal and two facets for the unciforme, a large
irregularly elongate facet proximally, and a small acutely
ovoidal facet on the anterior distal edge of the bone.

The calcaneum (Pl. 22, figs. 2 and 3) differs from the cor-
responding element in Megalonyx jeffersonu in the following
respects :

(a) he postero-inferior extremity of the tuber calcis is
directed toward the inner side, while in jefferson it is directed
toward the outer side.*

(b) The inner surface of the tuber ealcis is concave antero-
posteriorly, while in the vertical direction it is convex below and
plane or slightly econeave above. In jeffersoni, it 1s coneave in
both directions,

(c) In jefferson, ‘‘ posterior to the articular extremity, the
caleaneum forms a large plate nine inches in depth, and only a
fourth of an inch in thickness toward the center.’’+ In the
Salifornian species, this plate exceeds three-quarters of an inch
in thickness toward the center and is never less than half an inch
in thickness at the margin. :

(d) While the neck of the tuber, behind the articular sur-
faces is only slightly wider vertically, than in jeffersoni, the

* J. Leidy, op. cit., Pl. XII, fig. 6.
+ Loe, cit. p. 41.

Vou.4] Sinclair —Mammalia from Quaternary Caves. 159

length of the ealeaneum and the width across the fan-hke expan-
sion at the posterior extremity of the bone is far less.

The navicular (Pl. 20, figs. 5-6) has a shape slightly different
from that in jeffersoni, being irregularly triangular in outline,
with the angles broadly rounded. On the distal surface, the
facets for the cuneiform bones are separated posteriorly by a
sharp ridge, while in Leidy’s figure* of the navicular of je/fer-
sonu they are represented as separated by a groove.

Two vertebrae are preserved, a caudal and an anterior dor-
sal. In the caudal, the vertebral canal is low and broad and the
transverse processes, arising from the centrum are directed
posteriorly. The epiphyses are wanting and the sub-epiphytie
margins are bent inward toward the median plane of the
eentrum. In the dorsal, the transverse processes are broad and
are situated high up on the neural arch, rising above the zyga-
pophyses. The spine is short with acute anterior edge. The
neural canal is circular. The centrum is not preserved. Below
the prezygapophyses, a small, hemispherical process rises from
the anterior surface of the neural arch.

Fragments of several other bones were found, but they are all
too incomplete to deseribe.

The species is separated from the Californian forms of the
same genus described in the present paper by the size of the
teeth and the shape of the jaw, in which respect it resembles
Megalonyx jeffersonu, differing from that species, however, in
many skeletal particulars. It has not been identified from the
Potter Creek Cave, unless the doubtfully determined specimen
referred to Megalonyx jeffersonni can be shown to belong here.

The specifie name refers to the locality, in the foot hills of
the Sierra Nevada Range.

MEASUREMENTS.

Length of ramus from anterior extremity of symphysis to

CON vile! im CISL VC a eps 2 ee scan ey ca ciset she sone gs (eneftette Soiar cuca: eusuet ees ocvereer o%% 261.5 mm
Length of lower molar series (M.-M,) ...............00eeeee 63
Wenochwon Symphysisnexternalliy 22... ctw e sales is ee aes cies ats 81
Wepthmots maw BbelOw Wigs ysiesuersssrocsste re evsy eee erie evsteneruclereresb ein 75
Mepthwoten awe lbelow Misi as) snuscte se craae wlateteusr-isueGeushortefetaveuse 6 2 70

Diameters of lower molar crowns not including stalagmite:

* J. Leidy, loc. cit. Pl. XIII, fig. 8.

160 University of California Publications. [ GEOLOGY

M,, antero-posterior diameter of grinding face .............. 28) mm
M,, transverse diameter of grinding face ............+..2005 12
MM." antero-posterior diameters 2... tem. cers alee scsieue sees eis eee 17
WES andenchAcrecte Ouechosie senna hha nooo eae een aadagsnoede 20
M;) antero-posterior diameter! asec. vere seein sasachenetenenereteee 16
IME transverse scllameter sn sn ssc, snepcrses asic ieee a elcueectses aiotucteeerere 23
Mi; antero-posterior diameter fos seas os 2 ier teres 6s sie et cuteuat iff
Mee urdansverses Glam eters cerns cehemestrcesie a eisai aetna en tere 23.5
Greatest length from glenoid cavity of scapula to superior

Scapulars DOr er wc ves eee, aye ct tec teers cst ace cesscevensy «eh echo eNee eager OD
Distance from glenoid border to posterior inferior angle of

SCA PUA S o.ditcnrhrkae seks esd teen esas terse esac Seer eek eee ok ser eee ee 136
Greatest width of glenoid cavity of scapula................. 102
Greatest length of glenoid cavity of scapula ............... 100
Greatest leno thisot calcameumniy eject etre se tre estat etelcietoes) coat es 142
Greatest width of fan-like expansion of tuber calcis ......... 131
Width of neck of tuber calcis at narrowest point............. 67
Greatest width of posterior margin of tuber calcis........... 39
Least width of posterior margin of tuber calcis.............. 13
Distance from posterior extremity of tuber to inferior border

of wastrapalar: LACet: ssc cies wrsisidinnese cises nine. esin eo aie © Genet 106
Greatest dorso-plantar diameter of navicular ................ 70
Greatest transverse diameter of navicular .................. 64

MEGALONYX(?), sp.
Pl. 23, Fig. 6.

Locality.— Potter Creek Cave.

The large molar shown on plate 23, figure 6 (No. 8705) is
doubtfully referred to Megalonyx. It is oblong in outline, with
one of the narrow lateral faces convex and the other with a
median groove. The remaining faces are respectively broadly
concave, and convex. with a low median convex rib. At either
extremity of the deep groove crossing the triturating surface
there are shallow coneavities separated from each other by a con-
vex surface. In this respect, and in the shape of the crown and
its superior size, the tooth is unlike that of any species of
Megalonyx known from this state. In shape the tooth is also
unlike Mylodon. It is broken off a short distance below the
triturating surface.

MEASUREMENTS.

Antero-posterior diameter of molar at widest part .......... 16 mm
Niransverses diameter (Ol mMOlat qepricteatsett eer sere tonner ree: 27.5

VoL.4| Sinclair—Mammalha from Quaternary Caves. 161

MEGALONYX WHEATLEY! Cope (?).
Pl. 23, Fig. 7.

Locality.— Potter Creek Cave.

A single specimen (No. 8208) is referred to this species. It
has the characteristic triangular form of the superior molars of
Megalonyx, with the apex of the triangle rounded and the base
shehtly grooved. The remaining faces are respectively plane
and convex. In dimensions, it agrees with Cope’s Megalonyx
wheatleyr, and in the absence of negative characters has been re-
ferred to that species. Megalonyx wheatleyi was described from
material collected from the ossiferous deposit filling a fissure ex-
posed in a quarry at Port Kennedy, Pennsylvania. The poster-
ior molars can be distinguished from those of Megalonyx jef-
fersonu only by their inferior size. The tooth from the Potter
Creek Cave is intermediate in this respect between Nothrother-
tum shastense and M. sierrensis. It is slightly wider at the
base of the pulp canal than at the triturating surface, indicating
that the animal was not fully mature.

MEASUREMENTS.

Antero-posterior diameter of molar at triturating surface.... 12

Antero-posterior diameter of molar at margin of pulp canal... 12.5
Transverse diameter of molar at triturating surface.......... 19.5
Transverse diameter of molar at margin of pulp canal........ 20.5

MEGALONYX JEFFERSONI Leidy (?).
* Locality.— Potter Creek Cave.

This identification is based on a fragmentary eanine-molar
(No. 8620) which agrees in dimensions with Megalonyx jeffer-
sonu. Although not much curved, the obliquity of a small part
of the trituratine surface preserved indicates that the tooth
probably belongs to the superior series. The convex rib is situ-
ated midway on the inner side of the tooth with a well marked
coneavity on either side. It is possible that this tooth should be
referred to Megalonyx sierrensis, in which the upper molars
are not known, but the convex rib in the lower canine-molars of
that species is less centrally located than in the specimen in
question. If the tooth were entire, the measurements given below
would be slightly increased. In particular, the antero-posterior

diameter would be lengthened one or two millimeters.
MEASUREMENTS.
Antero-posterior diameter of canine-molar..................... 34mm
Transverse diameter of canine-molar ..............00.ceeeees 16

EXPLANATION OF PLATE 19.

Figures 1-7 are reproduced one and one-half times natural size; figures 8-11
are reproduced natural size.

Figs. 1-3. Thomomys microdon n. sp. Superior, inferior and lateral views
of the type specimen,

Figs. 4-6. TLeonoma spelaea, n. sp. Superior, lateral, and inferior views
of the type specimen,

Fig. 7. Leonoma spelaea. Superior view of the mandible.

igs. 8,9. Aplodontia major fossilis, n. sub-sp. External and internal
views of the right ramus of the mandible.

BULL. DEPT. GEOL. UNIV. CAL.

Werasy)
Aart 4
TE ESA

WAGE Mealy i)

!
|
i
1
|

ae

KXPLANATION OF PLATE 20.

All figures are reproduced one-half natural size.

Euceratheriuin collinum. Lett pes. Several dissociated elements

are combined in the drawing.

Kuceratherium collinum. Weft anterior cannon-bone.

Aplocerus montanus, Portions of anterior cannon-bones. — The
proximal three-fourths of the right cannon-bone is repre-
sented in figure 3, while 4 shows the distal half of the same
element of the opposite side.

Megalonyx sierrensis, n. sp. Views of the proximal and dis-
tal surfaces, respectively, of the right navicular.

M. sierrensis. Views of the dorsal and distal aspects of the
left scapho-trapezius (s-t), trapezoid (t), and magnum (7m).
One of the facets for articulation between the scapho-
trapezius and lunar is seen at (1).

BULL. DEPT. GEOL. UNIV. CAL VOET4, PIE 20

7

EXPLANATION OF PLATE 21.

Both figures are somewhat more than one-half natural size (1.e. X.62).

Figs. 1, 2. Megalonyx sierrensis, n. sp. Superior and lateral aspect of
the mandible. Reproduced from photographs of the speci-
men in the Harvard Museum of Comparative Zoology.

BUI DEPT. GEOLY UNIV, GAL VOL. 4, PL. 21

_
’ = * 1
ee '
or
‘
.
‘
- r
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:
Lary
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:

EXPLANATION OF PLATE 22.

All figures are reproduced one-half natural size.

Fig. 1. Megalonys sierrensis, nu. sp. Left scapula, external view. The
supraspinous portion has been broken away.

Fig. 2. Articular surface of the right caleaneum.

Fig. 3. Inner side of the right caleaneum.

BULL. DEPT. GEOL. UNIV. CAL. VO aaa 2

EXPLANATION OF PLATE 23.

All figures are reproduced natural size.

. 1,2. Nothrotherium (2?) shastense, n. sp. Right ramus of the mandi-

ble viewed from above and from the inner side.

. 3,3a. N. (?) shastense. A superior molar of the same crown and

lateral views, showing the curvature of the tooth and the
pattern of the triturating surface.

4,4da. N. (?) shastense. Lett third inferior molar, showing the
pattern of the triturating surface and the concave anterior
wall of the tooth.

. 5,5u. N. (?) shastense. Superior molar No. 8337, referred to the
i ,

same species as the above, showing the triturating surface
and the convex rib on the side of the tooth crown.

. 6. Megalonyx (?). View of the triturating surface of a molar (No.

8705, doubtfully referred to this genus.

=i

Megalonyx wheatleyi (?). Crown view of amolar. The triturat-
ing surface is slightly broken.

. 8. Nothrotherium shastense. Triturating surface of the fifth

superior molar of the left side. The tooth has been damaged
by rodent gnawing and its outline is restored by a broken
line. The restoration is based on the shape of the tooth
shown at the margin of the pulp canal.

4

BULL. DEPT. GEOL. UNIV, CAL. WAC ai AL 28)

Rinnai

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UNIVERSITY OF CALIFORNIA PUBLICATIONS

BULLETIN OF THE DEPARTMENT OF

GEOLOGY

Vol. 4, No. 8, pp. 163-169, Pls. 24-25 ANDREW C. LAWSON, Editor

PREPTOCERAS, A NEW UNGULATE

SAMWEL CAVE, CALIFORNIA

BY
Eustace L. FuRLONG

CONTENTS.

PAGE

IMtrOdMChLONT Ares secrets cata od ad ble done aisiecsiene aoa ie bee aera ne ee eae 163
REP LOCONAS MSEC lanier eevaaealeysmere senate lah eusi=ncanster= tates epee pete cacle ee etn ans 164
Gener GVCHATAGTENS: casleseusssic ee music See daue. a wie eo ebedguei tol toalieile. aero bie neste ecee 164
Specie aCharacters) eck were cisiecleidoncre tie iets Seige weer ions areas AG a cet 164
@CCUBFENCE: \yerarescrepsesiceaier eye) ev eays oe. Gre aus oie ave seoe cine wns op day eorecere BOE eee aT 164

(ha eaera Ua a oae cas Sav ota ce as fan weak aos ars Zecca arte ba cat sar ee bors Soar by atigh'ar2o ee ovei ons, oe “edo 165

NB STAT OVI Paves Se civere cece Zeurere eee Oeste genc eau cL Tearevaltns usr thsdarooatardoarencP Dae nvekatmeeh ee 166
EVIOTLE DTA.C ws coe stssn so 4 eka: se Nous vchien nuda mands Mifene (cor ofene Ge eustelere theca MAGib als Oa Oar 167
tamibs sandy Girdles = scccvetensece a: solsse sualersuste cousvaier stone ol ss yeiee a euctarerers aeetiecede 167
Affinities ........ MeieeaWlere ea ols arene test reuae Sion See ontiaes: Rubia: ween a Wik ds te Se 168

INTRODUCTION.

In the course of the exploration of the Quaternary Caves of
Shasta County, conducted by the Department of Anthropology
of the University of California during the past three summers, a
large quantity of ungulate material has been brought together
Through the kindness of Professor J. C. Merriam, it has been the
writer’s privilege to prepare and study this collection.

In the material from the Samwel Cave there is a nearly com-
plete skeleton of a large sheep-like animal differing from all
described forms. There are also the skull and horns of another
individual of the same species, and other more fragmentary
material. These animals were contemporary with Hucerather-
ium collinum* recently described from Potter Creek Cave; the

* Univ. of Cal. Bull. Dept. Geo., Vol. 8, No. 20, pp. 411-415, Pls. 50-51.

164 University of California Publications. [ GEOLOGY

remains of the two being found associated in the Quaternary
deposits of Samwel Cave.

While resembling Fuceratherium in general, the cranium and
horns are markedly different in many respects. These differ-
ences seem to warrant the placing of the new type in a distinct
genus for which the name Preptoceras is proposed.

PREPTOCERAS SINCLAIRI, hew genus and species.*
Pls. 24 and 25.

Type.—Specimen No. 8896, Univ. of Cal. Palaeont. Coll.

Generic characters.—Uorn-cores solid, on the posterior ex-
tremity of the frontals, well back of the orbits and rather widely
separated. Frontals rising at a steep angle from nasals to form
a greatly swollen area between and high above the orbits. Lach-
rymal pit broad and shallow. Teeth hypsodont, large, without
cement, superior molars with very small median accessory style
on the inner sides. Horn-cores with distinct burrs at the base.

Specific characters —Proximal third of horn-cores flattened
anteriorly. Proximal third directed outward and sheghtly up-
ward, distal third curving forward and downward with an
elevated point. Occiput with no median keel above foramen
magnum.

Occurrence.—The type specimen was discovered by the writer
in Samwel Cave on the McCloud River, Shasta County, Califor-
nia. It consists of the greater part of the skeleton of a young
individual. The skull lacks the median portion. This region is,
however, represented in another individual. The superior denti-
tion is complete on the left side. The left ramus of the mandible
was in articulation with the skull, as were also the cervical
vertebrae.

The remains were excavated from a shallow deposit in the
deepest chamber of the cave, at a depth of six inches to two feet
The bones were more or less covered by stalagmite varying in
thickness from one to twenty-five millimeters. A large quantity
of material from the same deposit is referable to this genus and
to Euceratherium.

+ [ take pleasure in naming this species in honor of Dr. Wm. J. Sinclair,
who was identified with the first extensive cave exploration in California.

VoL. 4 | Furlong.—Preptoceras, a New Ungulate. 165

From the associated fauna and the occurrence of the deposit,
Preptoceras is considered to be of Quaternary age, but prob-
y the principal

ably somewhat later than the epoch represented b
deposit at Potter Creek Cave.

Cranium.—The cranium is that of an immature individual
in which the last permanent teeth are being erupted. It is
slightly larger and more robust than the skull of Euceratherium.
Viewed from the front there is a strong resemblance to Budorcas
taxicola, and like the latter there is a suggestion of affinity with
the Musk Ox. The horn-cores of Preptoceras differ from those
of Budorcas and Ovibos in length and eurvature. In both of
these characters they closely resemble those of Bos.

The nasals and frontals are partly destroyed in the type
specimen, but in another individual from the same deposit they
are complete. The nasals are flat dorsally with steeply sloping
sides. The anterior ends are decurved and converge to form a
blunt point. Posteriorly, the ends slope upward to the fronto-
nasal suture. The posterior ends are not separated to form two
distinct points as in Budorcas.

The frontals rise from the nasals at a steep angle and are
much inflated dorso-ventrally above the orbits. In EHucerather-
ium the frontals, while slightly convex above the orbits, do not
rise from the nasals at a sharp angle, but present rather a plane
with uniform inclination from the nasals to the base of the horns.

The horn-cores grow from the extreme posterior and lateral
ends of the frontals, and show distinet burrs at the base. They
are situated rather wide apart at the base. The cancellous tissue
extends but a short distance above the burrs. In the proximal
two-thirds the anterior surface is flattened, and the posterior
surface strongly convex. The distal third is rounded and tapers
gradually. In Huceratherium the horn-cores are much closer to-
gether at the base, and in size and curvature suggest those of
Capra.

The parietals and frontals are fused just back of the horns,
the parietals forming the dorso-posterior roof of the cranium.
The parietals slope posteriorly at a sharp angle to the promi-
nent lambdoidal crest.

166 University of California Publications. [ GEOLOGY

In Preptoceras the occipital suture is midway between the
Jambdoidal crest and the foramen magnum, while in Hucerather-
cum the suture is much nearer the crest and gives a relatively
greater area to the occipital than in Preptoceras. The lamb-
doidal crest overhangs the occiput, forming deep fossae on either
side of the median tubercle. These are absent in Huceratherium.
In the latter, above the mastoid, where the squamosal, occipital
and parietal elements meet, prominent tubercles are formed,
from which a buttress-like ridge passes dorsally to the base of
the horns. This brings the parietals almost into the plane of the
occiput and gives the back of the cranium a square appearance.
This angulation is absent in Preptoceras. There is no ridge
from the lambdoidal crest to the base of the horns and the parie-
tals pass back of the horn-cores to the cranial roof in a uni-
formly eurved surface, making a deep concavity between the
erest and the horn-cores.

The elements of the basioccipital region are in general
broader than in Huceratherium, though the foramina occupy the
same positions. The occipital tubercles have not such well
defined anterior and posterior areas, the median constriction
being less marked in Preptoceras. The paroccipital processes are
relatively more robust and higher. <A raised posterior elongation
of the low-lying tympanic bullae rests against its base more dis-
tinctly than in Hucerathertwm.

The maxillae are greatly swollen at the sides as in
Euceratherium. This is apparently not due entirely to the im-
maturity of the individual. The palatal portion of the maxillae
differs in the relative measurements. The anterior margin of the
posterior nares is between the crescents of the last superior
molars, while in Huceratherium the margin is on a plane with
the posterior border of the last molars. The shallow fossae on
either side below the narial border in Fuceratherium are absent
in Preptoceras, this region being more like that in Aplocerus.

Dentition.—The dentition resembles even more closely that of
Ovibos than does Huceratherium, the length of the dental series
being the same, as that of an adult skull of Ovibos in the Univer-
sity collection.

VOL. 4 | Furlong.—Preptoceras, a New Ungulate. 167

The superior dental series on the left side is nearly complete,
with the last deciduous molar about to give place to the perma-
nent tooth, thus making the individual probably two years old.
The crowns of the teeth are unworn and present in general the
form seen in the Ovinae. They are hypsodont with no cement.
In the deep groove at the confluence of the walls of the inner
crescents of the molars there is a very small accessory style which
is not present in Hucerathertum. The inferior promolars of the
left side are missing, but those in the right ramus are present.
P,, is about to be shed, the permanent teeth just appearing above
the alveolar border. The second milk incisors are present and
the crowns of the permanent incisors visible. Their form is much
like those of Ovibos.

Vertebrae.-—The number of cervical and lumbar vertebrae
corresponds to that in the Ovimae. Their centra are not so
sharply keeled ventrally as in Capra and Aplocerus. They are
relatively shorter than in these latter genera and are much
heavier and robust in every way. The pre- and post-zygapophy-
ses of the cervicals are more like those in the domestic goat than
Aplocerus, in that there is no sharp lateral constriction separat-
ing them into distinct anterior and posterior limbs, but they form
an antero-posterior lamella. The lumbar and sacral vertebrae
closely resemble those of Aplocerus. No caudal or thoracic
vertebrae were present and they have been restored, the former
from Aplocerus, the latter from vertebrae associated with Prep-
toceras remains in Samwel Cave.

Iimbs and Girdles—The scapula in Preptoceras is rather
heavy compared with that in Aplocerus. The acromion is not
produced in a convex anterior surface in its distal half as in
Aplocerus.

The humerus is robust, it has a very broad head and stronely
developed tuberosities with a deep bicipital groove. The shaft
is heavy with prominent deltoid and supinator ridges.

The radius, ulna and distal elements of the fore limb are in
general like those in the Ovinae, though heavier. The articular
facets of the carpalia are placed so as to throw the knee toward
the median line, resembling Bos in this respect in a greater de-
gree than the Ovinae.

168 University of California Publications. [GEOLOGY

The pelvis is heavy and narrow, indicating an individual of
the male sex. Though no pelvis of Huceratherium has been
identified, the type specimen is judged to be of male sex. Por-
tions of the skulls of eight individuals in the collection are re-
ferable to Euceratherium and the differences noted in them indi-
cate difference of sex. The elements of the hind limbs, like those
of the fore limbs, are heavy and rugged compared with the
typieal Ovinae. The greater and lesser trochanter, gluteal
tubercle and all processes for muscular attachment are strongly
developed.

Affinities.—Preptoceras has interesting resemblances to
Budorcas and to Ovibos, though not nearly related to either. It
probably bears somewhat the same degree of relation to Ovibos
that Budorcas does. Its closest affinity is with its contemporary
Euceratherium. It stands in about the same relation to the
Ovinae as does the latter and is tentatively placed in that sub-
family. Preptoceras and EHuceratherium have unique character-
istics In common and will probably have to be placed in a group
by themselves when studied further.

MEASUREMENTS.

Basilar Jength of cranium from the anterior border of the

alveolus of “B® to icondyle:simclusivies cesses serene re eneyedc terete 300 mm
Greatest length of frontal from fronto-nasal suture to occiput,

AP PVOMIMNVATC, eatais cafe steescuse meme ae ena Meare soe Me neg eock eek onsh ok ese 143
Width between superior orbital rims ........... 00... eee e eee 160
Width across bases ot horn-Conesiescnstrarrereraietenetar sre et syenete st eler 144
Wadlthy ot spallart em ait, MES sv.sevcectenspkoe-yetsesrercusesman cr ctee caer ercielsne eden ce sneer 89
Greatest extent of molar arches measured between inferior

DOrderse LMS sca halt Res secreene ecuador sch oecenes omeeneres salcee ts) atone eMenees 180.5
Depthvot molar archi bel Ow cor Ditens ssp -eepeesesy)t ete etararuersreren secterane 48
Antero-posterior diameter of horn-core at base .............. 96
Transverse diameter of horn-core at base ............+-0000. 77
Length of superior dental series on alveolar border .......... 139.7
Antero-posterior diameter across head of humerus .......... 114
Ibfryearal One lbw oa eoe se oboneooccabuycouduneusobouedbs 300
Ibid dase emo ao ee oAneaeouod dere ouoos counDoDKouNcn oc 305
IbsMety One OWE) oseaop senna bons oo ousudounduobooeuonaDKe 305
enothe ot; a) metacanpallica. secter caressa t stele inane r aera 180
Ihength of Uist phalanx of fore! foot sei tecsrcete creer sepae reer 65.5
Length. of 2nd phalanx of fore foot ....1...6 cee ce ete wens 387.5

Ibfyaeady Cpe ey laveyone Oni Miley MOG Geog doogancogubogcooumontood 58

VoL. 4 Furlong.—Preptoceras, a New Ungulate. 169

cenothwot; pelvis. 4c jes ga de chee wee G6 cue eet sand oaleencans ONO
Menoth ol TOMUL 5 a icsescaeant cissrnseries sed aueeare aye Mesarne nai OOO,
Thength (of tba aku cis site gees emus eae eo ao caew aes BOO
hen ObHMOL samme Catan Sally semerensy hays neu seers teseneteteleencen nec). ret cee eee: 190
Length of Ist phalanx of hind foot.......................-. 64

Length of 2nd phalanx of hind foot ....................... 38
enothiot va hoot of hind foot 2... esse eee sees eee OS

University of California,
May, 1905,

a

EXPLANATION OF PLATE 24.
Fig. 1. Preptoceras sinelairi. Posterior aspect of cranium and horn-cores
*.22. Type specimen, No. 8896.

Vig. 2. Preptoceras sinclairi, n. gen. and sp. Lateral view of cranium,
.8. Specimen No. 1009.

BULL. DEPT. GEOL. UNIV. CAL. VOL. 4, PL. 24

AA I cs

ae

EXPLANATION OF PLATE 25.

Preptoceras sinclairi, n. gen. and sp. Temporary mount of the type speci-
men, X.081. The orbital and nasal regions have been restored
from specimen No. 1009. The inferior premolars, the dorsal
vertebrae, excepting the fifth, and the caudal vertebrae have
been restored from allied forms.

UNIVERSITY OF CALIFORNIA PUBLICATIONS
BULLETIN OF THE DEPARTMENT OF

GEOLOGY

Vol. 4, No. 9, pp. 171-175 ANDREW C. LAWSON, Editor

A NEW SABRE-TOOTH FROM CALIFORNIA

BY

JOHN C. MERRIAM

Some years ago Mr. Bernard Bienenfeld of San Francisco
very kindly presented to the University of California a collection
of fossil mammalian remains containing at least two carnivores
which are new to science. One of these has already been described
as the type of a new and peeulhar eanid genus, Hyacnognathus.*
The second form, which is deseribed below, represents a large
species of sabre-tooth differing considerably from those pre-
viously deseribed.

MACHAERODUS(?) ISCHYRUS, n. sp.
ext, Bigs t

The species is known only from a mandible (No. 8140 Univ.
Calif. Palae. Col.) found with the type of Hyaenognathus near
the foot of the Temblor range at Asphalto, Kern County. This
specimen, like the others found with it, is covered with a very
thin film of gypsum preserving the fragile bone.

The species is characterized by the great reduction of P., the
presence of a single posterior cusp on P,, the absence of both
metaconid and heel from M:, the shortness of the diastema, the
possession of a prominent flange below the symphysial region,
and the abbreviation and general robust character of the jaw.

The age of the beds in which the mandible was found is not
definitely determined. Such stratigraphie and palaeontological
evidence as has been obtained indicates Quaternary or late Plio-
cene age. In addition to this, the evidence furnished by the

*Bull. Dept. Geol. Univ. Calif., Vol. 3, No. 14, p. 278.

172 University of California Publications. [ GEOLOGY

stage of evolution of this species and of the associated Hyaenog-
nathus seems to show that they are probably not older than
Phocene.

The portion of the mandible present represents a large ani-
mal, and the species must have been one of the more formidable
members of the sabre-tooth group. The jaw is noticeably heavy,
while the inferior flange is wider and deeper than in the typ-
ical species of Smilodon and Machaecrodus but hardly as prom-
inent as in Hoplophoneus. In the symphysial region the infer-
ior portion of the anterior face is coneave on either side of

él pp

i Y wii)

ty

ply,

Fig. 1. Machaerodus(?) ischyrus, n. sp. * %.

the median line, but the whole upper part of this face is strongly
convex, and the portion of the alveolar margin occupied by
the incisors is bowed far forward. In the region of the cheek
teeth the alveolar margins are flared outward rather more than
is common in the cats, owing probably to shortness of the jaw.
The dentition is 3, 7, 3, 7. Iz is absent from both rami, but
its alveolus indicates the existence of a tooth approaching the
canine in size. I, is considerably larger than I,. P, is very
small and is single-rooted. P, possesses a single large accessory
cusp on either side of the protocone, but shows no trace of a
posterior basal cusp. The protoconid stands almost erect. In
M, the protoconid and paraconid are well developed and of
nearly equal size. The posterior portion of M, is somewhat

Vou. 4] Merriam.—A New Sabre-tooth from California. 173

damaged, but there appears to have been neither metaconid nor
heel present. ‘The transverse diameter is relatively large and the
tooth considerably heavier than in Smilodon neogaeus.

Of the North American species Machaerodus gracilis Cope,
fromthe Port Kennedy Fissure, resembles the Californian species
in the form of P,, while the heel of M, has almost disappeared.
M. ischyrus differs from this species particularly in the short-
ness of the diastema and probably of the whole jaw, in the
absence of a posterior basal cusp on P,, and in the complete
reduction of the heel of M,. Judging from Cope’s figure* of
the type of WM. gracilis the mandibular flange is not as prom-
inent and the jaw as a whole somewhat weaker than in WM.
ischyrus.

Smilodon fatalis Leidy, from the Quaternary of Texas, known
only from the dentition of the upper jaw, if a typical Smilodon
as it appears to be, would differ in the structure of P,, as also
of the mandible in general.

Dinobastis serus Cope, from the Texas Quaternary, does not
differ from JM. ischyrus greatly in size and had large external
incisors with a moderately elongated superior canine. The
superior sectorial has a large protostyle, but the basal cusp
anterior to this is rudimentary. This means that, as in Hoplo-
phoneus, the posterior part of P, opposing it was probably rel-
atively shorter than in Smilodon. The characters mentioned all
suggest correlation with WM. ischyrus, although there would at
present be no justification for considering them identical.

Felis imperialis Leidy, from the Quaternary of Middle Cali-
fornia, is known only from a fragment of the upper jaw with the
third premolar. It is evidently also a short-faced form but seems
to have been, as far as can be determined, of the true Felis type.

Machaerodus catocopis Cope, from the Loup Fork of Kansas,
has a relatively larger inferior canine, a deeper mandibular
flange, and is much narrower across the symphysis.

Machaerodus palaeindicus Bose, from the Siwalik beds of
India, very closely resembles this species in size, in shortness
of the diastema, and in the form of the anterior portion of the

*K. D. Cope. Jour. Philad. Acad. Nat. Se., 2nd Ser., Vol. 11, Pl.
20, fig. 1.

174 University of California Publications. [ GEOLOGY

mandible. It appears from the figures* that P, has but a single
posterior cusp. P. 1s, however, a heavy tooth apparently with
two roots and differing much from the corresponding tooth in
IML. ischyrus.

Compared with the later machaerodont forms this species
is relatively specialized in the reduction of P,, and the apparent
absence of both heel and metaconid from M,. It is relatively
prunitive in lacking a second posterior cusp on P,, and in the
prominence of the mandibular flange, which is secondarily re-
duced in the later sabre-tooths. The abbreviation of the dias-
tema, together with the flare of the alveolar borders, and the
robustness of the mandible show that this is a comparatively
short-jawed type.

The combination of characters appearing here is peculiar.
The stage of development of the mandibular flange suggests an
advanced form of Deinctis, such as is seen in the John Day
Pogonodon or in the more primitive Hoplophoneus species.
The reduction seen in P, and in the posterior portion of M,
equals or exceeds that in Smilodon and Machaerodus. The
character of P, is that of Hoplophoneus rather than of the later
sabre-tooths. As far as can be judged from the characters
present, this species could not consistently be referred to any of
the three machaerodont groups which it most nearly approaches,
viz: Hoplophoneus, Machaerodus and Smilodon. It may repre-
sent a new subgeneri¢ type, in which a peculiar set of conditions
suggested by the shortness and strength of the jaw have made
possible the combination of primitive and specialized characters
seen here. A knowledge of the cranium may bring out definite
relationship to one of the known groups, and I therefore refer to
the species tentatively under the more or less comprehensive

name of Machaerodus.

*R. Lydekker. Paleont. Indica, Ser. 10, Vol. 2, PL 43.

VoL. 4] Merriam.—aA New Sabre-tooth from California.

MEASUREMENTS.

Length of mandible from anterior side of I, to posterior

STCONOHE MG. oy gce aceesrao rene: raypnele raya etoh eupuoeaisas sr aianie. ebeue eee eiie dite enone
Length of mandible from anterior side of canine to posterior

side of M,
Width of anterior face of symphysial region
Depth of jaw across the middle of the flange
Depth of mandible below posterior end of P,
Length of inferior diastema
Width of I, transversely
Width of IL, transversely

Antero-posterior diameter of inferior canine ..............
Antero-posterior diameter of Py........50.s css ecessseees
Antero-posterior diameter of P,
Antero-posterior diameter of M,
Transverse diameter of M,

123

or Ol

oO

or or

mm.

UNIVERSITY OF CALIFORNIA PUBLICATIONS
BULLETIN OF THE DEPARTMENT OF

GEOLOGY

Vol. 4, No. 10, pp. 177-199 ANDREW C. LAWSON, Editor

THE STRUCTURE AND GENESIS

COMSTOCK LODE

BY

JOHN A. REID

CONTENTS. aie
Statement of thes Problems. ci. c« cenen< cies oe ie eas scree tare es eae | Soe ne 178
HW ast- Wiest AMA ULES vSesis sue cvacs alesis: lace Puacleusca dots: wane: cane aauenausr 3 e-sede nazar: asia svere 178
Mexican SH ality cists ecto: eys oo 0 ae elche sr ace aie wel ere elas) wieehe) oauekaeieie aie ans 179
BUT OM RA VAMC HAT crease a uweausre ete cretion cirstatcaycetceu/srreevetteienetleveilesene: eclleeseni-s etree 180
@ther Raw Me Wales: ecicie wistsauerc teenie: cuevatct secwe eee a rameders, Suanaus) sage eh: 180
Gedar Ravine and Cedar Hall Canon. ssc. eas cone eae ee ee = 181
Works? o£ Comstock) ode: cicissnecensie eiene si 01a. ¢eustavscensoneca ialerlacossnangie4eacests 182
Fault in Andes Mine and Central Tunnel..................-.... 183
HB OMAN ZS! vars eee sduse ves wees an. or dun Gao. ee uayaideapa aicealauenanetie teh atadi-c.dustial eta Ja auses arate 183
Waareainihy (Ohh arenes aoe Gann Moana cap mouo coy ote aoc cine crn 183
(GOV LSAT) a ses, seeker sare cSiceye tee rete cies ateareee et ee eee tek come ase tesa 185
Elaleranicdle Norcross utr Olina sesrelemenemeieks steteece sue mayememesusiisestaua iafeManeh «tals eteseeat 186
IDYerso MOREE) CHE MCP ea oe eu o te goneDon oma ea comoomc aemo 187
AmalysiseOds WWLCLS) gic c.cciens cneteumere sete ween edanle cashew sane eevee Gecene eres eye 189
iNecEy (ne WWRLOUS a aan ono dace ona v odo UouG Duco Dood OOo Go moc 189
Sunface Ores and Waters... «cassava conse wa ec ceis le ba @ Scie ee ed os 190
WAtmially sts wOL (Water: cos, x0 o2)o: eeau, loneeas orene (ai ey icederes eNevehfo'e:ioisiiels re) erstevescaners 192
PATS ScliyanO ug VV AILELS Ue eworcuses coaeusvarsbeteneicmsareyenane) erie sietins ieaeiei el ai lcievet araisness 192
Rocks of Hale and Noreross Tunnel Section............... ee cree? 193
WONCIUSTONS cic ichape sesnavete we Sap} loceuaneuas a, avaeedensieus euses dare Gieiltla ee cetera gerd vereee caine 195
THO TINO Ls GG LO. axl avid oh eh: isso toda. co tala osaea@ caer wledeatielievay slienarond cn Sab suaie cane: ena 195
MD GEPOSItLOI (Ot COTES) sade ae sieneitera carieere cl eget erwin / ones. + Giaeyeloieh sues stares 196
Tiocation. of Bonanzas: ose. cne1-.s ies ye esse ers Secehal ss cnaecauee 6, sciversus aes 197

Structure and Genesis of Mt. Davidson................ 000000 eee 198

178 University of California Publications. [ GEOLOGY

STATEMENT OF THE PROBLEM.

In these days of rapid advance in our knowledge of the genesis
of ore bodies, it becomes necessary constantly to test old ideas by
new conceptions. Particularly does this apply to our recent ideas
on secondary enrichments of ore deposits. The mining world is
awaiting eagerly more exact knowledge on the part of geologists,
that the cost of locating valuable ore bodies and developing them
properly may be reduced. The structure of the Comstock lode,
and the genesis of its ores, have been treated by several investiga-
tors, but even yet, many of the vital questions connected therewith
are unsettled. The somewhat overdone tendency to make every
ore deposit correspond to a ‘‘type,’’ and to regard much, if not
all, as already ‘“‘having happened,’’ has been productive of con-
siderable error. Fortunately, with our ever widening view, these
marks of immature science are disappearing. The Comstock is
yet largely an unsolved problem, withal we know much about it,
and the following notes contributed to its solution are the result
of numerous short trips to the lode while the writer was engaged
in other work.* The peculiar bonanzas of Virginia City have
never been satisfactorily accounted for, nor the form of the lode
as a whole. This paper is offered as a shght contribution to the
study of ore deposits, and on account of the immediate bearing of
its contents upon practical mining matters, it is issued at this
time.

EAST-WEST FAULTS.

There is a much greater development of east-west faulting
than has been noted by previous observers. These faults are of
the utmost importance, both in the structure of the lode and in

* The author’s acknowledgments are due to Mr. James McKinty and
Mr. Thomas McCormick, superintendent and foreman, respectively, of the
C. & C. mine, for their aid in obtaining deep mine waters; Mr. E. E. Everett.
for aid in obtaining mine waters and rock specimens; Mr. M. W. Fox, and
Mr. Frank Higginson, general manager and superintendent, respectively, of
the Hale and Norcross; and particularly to Mr. G. MeM. Ross, whose great
interest in these matters lies at the bottom of this short paper. Mr. Ross
was until recently superintendent of the Ophir and Mexican mines. The
author wishes also to state his indebtedness to former publications upon the
Comstock, particularly Becker’s Monograph and King’s Survey of the
Fortieth Parallel. These works have been freely consulted on points not
now to be determined in the mines.

Becker’s Atlas should be consulted for maps, etc.

Vou. 4] Reid —The Comstock Lode. 179

the genesis of the ores. Their importance to the lode lies in the
fact that they have most to do with the notable short length of the
main fissure. Their importance in regard to the ores lies in the
fact that they have caused the blocking out of the wall rocks
with the resultant opening to mineral solutions. These points will
be diseussed later. Becker* has noted the presence of such
faulting, but only ina general way, and as of little importance. He
says (p. 181) that the topography is due chiefly to faulting, ‘‘for
on the Sutro tunnel section, at least, there is evidence of but slight
erosion.* * * Fhe ravines which furrow the range are not there-
fore the results of erosion, but of faulting.’? And again (p. 184
et seq.) ‘‘To the north and south of Mt. Davidson the evidences of
faulting diminish (north-south faulting is meant). From the
Overman far into the Sierra Nevada claim, a distance of two and
one-third miles, the amount of fault has been great, and the indi-
eations unmistakable. Beyond these points the disturbance of
equilibrium has been to some extent adjusted in a different man-
ner. This is partly indicated by the union of the andesite fields,
which are separated near the center of the lode by diorite. To-
ward the ends of the lode the dynamic action seems to have been
distributed in part by the forking of the fissure and in part by
the formation of east and west cracks.’’? According to Becker,
these same east-west faults have their downthrow to the north.
Practically nothing more is written in the monograph of Becker
concerning these movements. But even now, with almost none of
the old workings accessible, their large development is well shown.
The most noteworthy examples are as follows:

Mexican Fault.—In the Mexican ground, on the Sutro tunnel
level, a very strong east-west fault was followed into the diorite
of Mt. Davidson, and east into the hanging wall block for several
hundred feet. No ore was developed, and the work was aban-
doned. Pyrite was very abundant, however, in the crushed zone.
This fault was nearly vertical, with a slight inclination to the
north. The throw, from all appearances seen, as striations, ete.,
was down to the north, making a normal fault. This line of mo-

*G. F. Becker. Monograph III. U.S.G.S. ‘‘Geology of the Comstock
Lode.’’

180 University of California Publications. [GEOLOGY

tion is directly in line with Ophir Ravine, and no doubt was the
main cause of its formation, as noted in general by Becker,
quoted above.

Bullion Ravine Fault—Bullion Ravine is likewise determined
by a fault plane, in this case shown largely by stratigraphic and
physiographic grounds. A new geologic map is necessary to show
this fully, as that of Becker * is in error at this point. In the
first place, this rocky ravine shows plainly that erosion has had
nothing to do with its formation, for its bottom has never been
occupied by a stream. Becker notes many times that the erosion
of the region has been little or nothing since the vein formation,
and this is merely a case in point. Moreover, in the second place,
here is a structural discordance between the walls of the ravine.
The north wall is solid diorite to the summit of Mt. Davidson. The
south wall is diorite farthest east, but andesite a short distance
west up the ravine. The contact between the two rocks appears to
be in the exact center of the ravine, but is obscured by surface
wash.

Other Ravine Faults —The ravine leading up to Mt. Butler,
and Crown Point Ravine farther south, have not been examined
in detail, but they partake of the characteristics of the others:
typical fault ravines. Becker, though noting this, fails to give
supporting evidence because he attached no importance to their
structure. Such evidence is plentiful for all these east-west
eulches, the most important of which is as follows:

1. The erosion of the country has been very little since the
faulting, so that we are driven to look for other causes for the
formation of the topographically striking ravines. In the ease of
Bullion and Ophir Ravines, at least, this cause has been shown to
be faulting. Becker’s reason for a lack of erosion seems to lie
in the close similarity of the contours of the actual faulted sur-
face with the theoretically deduced one. Further reasons, and
conclusive proofs, are: (1) there is little or no removal of the
thoroughly decomposed country rock near the lode; and (2) the
present surface of the lode, or its outerop, is that of the original
lode apex, formed under practically no pressure from above and

*G. F. Becker, Mon. III, Atlas, U.S.G.S.

Vou. 4] Reid—The Comstock Lode. 181

not yet removed by atmospherie agencies. The cross-section of
the upper portion of the lode, figure 1, shows this structure.

2. There is no stream worn material of any sort, except very
locally, in these ravines, nor any outside their mouths where a de-
posit would take place by stream action. The whole region is re-
markable in the lack of all such material.

No faults from Bullion Ravine in the hanging wall under-
ground have been seen, because this area is not accessible. But
on the surface, east of the lode, there are many very well defined
east-west faults, some of which are filled with calcite. A few have
been prospected and considerable ore extracted. The ridge run-
ning east from Bullion and Crown Point Ravines is a locus of
these movements.

Cedar Ravine and Cedar Hill Canon—These are the large
eulches on the north end of the lode. Cedar Ravine is due to the
surface effects of the east-west motion exposed underground in
the Sierra Nevada mine, as is Ophir Ravine the surface effect of
the fault shown in the Mexican mine. Cedar Hill Canon is rather
bevond the limits of the lode, yet deserves mention because it is
the sharpest cut of all the fault ravines, and, ike Bullion Ravine,
shows the faulting by the stratigraphic relations of diorite and
andesite. In both instances the andesite abuts against the diorite
in a plane which occupies approximately the center of the gulches.
In Bullion Ravine the andesite is south of the diorite; in the
northern fault canon, the andesite is north of the diorite. This
’ which has
been shown to be identical with the porphyritie facies of the di-

andesite is *Becker’s ‘‘earlier hornblende andesite,’

orite mass.+ Hence, an abutment of one of these rocks upon
the other indicates a fault plane.

There appears even yet to be a doubt in the minds of some
geologists, for instance, Lindgren,t as to the correlation of the
Comstock rocks. The evidence for this correlation is, of course,
of two kinds: (1) microscopical, and (2) macroseopical, includ-

*G. F. Becker, op. cit.
+Hague and Iddings, Bull. No. 17, U.S.G.8. ‘On the Development of
Crystallization in the Igneous Rocks of Washoe Co., Nevada.

¢ W. Lindgren, in one of his numerous papers, states that he believes the
Comstock rocks to be separate flows.

182 University of California Publications [ GEOLOGY

ing both field and laboratory work. The microscopical evidence
of Hague and Iddings needs corroboration on but one possible
point—that of the undoubted occurrence of fresh augite as the
chicf ferromagnesian mineral in the diorite. The field evidence,
however, seems to be insufficient regarding the diabase and dio-
rite. The present writer, through late mining work, is in posses-
sion of the facts necessary to prove beyond the shadow of a doubt
the conclusions of Hague and Iddings. The Hale and Noreross
tunnel into Mt. Davidson, just north of Bullion Ravine, has
brought to light these facts, and also a number of structural facts
of the most vital importance. The structures shown will be dis-
cussed later, and a note on the rocks will be placed near the end of
this paper.

Porks of Comstock Lode.—The main forks of the Comstock
lode, both north and south, are quite similar in their action on the
formation of the fissure as seen to-day. Of the Sierra Nevada
fork, which strikes nearly east and west, the writer can say
nothing, for so much of the old ground is not open. However,
the east-west shps are well shown underground in the present
workings, and this portion of the lode country appears to be a
locus of these movements. The large southeastward bearing
‘fork’? of the lode which runs toward Silver City, has some pecu-
harities which deserve mention. In the first place, this so-called
branch is not a mere fork of the lode, but as a fault continues west
of the lode into the mass of Mt. Davidson west of the summit.
3ullion Ravine exhibits this fault in the best manner. As already
noted, the south wall of the ravine is diorite for a few hundred
vards west up the gulch, when andesite appears from the bottom
of the south wall clear to the top. The topography also shows the
change, the diorite portion being steep and precipitous, while the
andesite is smoother and of more gentle slope. The transition
from one to the other is abrupt. Some prospecting has been
done along this line and some ore found. The gangue in the
Silver City portion or ‘‘fork,’’ as of a few of the east-west veins
east of Bullion Ravine, is largely calcite. Granting the identity -
of the rocks as set forth in the work of Hague and Iddings, this
difference in gangue mineral from the silica of the lode proper

VoL, 4] Reid.—The Comstock Lode. 183

ean be accounted for, in the most probable way, by assuming a
difference of age.

Fault in Andes Mine and Central Tunnel.—The Andes mine
workings and the Central tunnel show many east-west faults.
There is a great complexity of these in the surface workings, as
is to be expected in the great lode. The largest one in the Andes
cuts off sharply one of the bigger quartz bodies between the horses
of diabase. Others, of less extent, but still of some size, eut
across the vein proper, and act as channels for mineral solutions,
as will be mentioned later. These motions are shown by clay and
rolled pebbles of quartz. The east-west movements in all the
surface workings are characterized by identical features. A very
peculiar action is now taking place along one of these cross frac-
tures in the Central tunnel, where there is little circulation of
air, characterized by the deposition of pyrite from an acid solu-
tion.

BONANZAS.

Virgima City.—The formation of the Virginia City bonanzas
is peculiar, and has never yet been concisely presented. The
present developments in mining work have thrown much lght
upon this question of genesis. In the Virginia City portion of
the lode the ore occurs not in the main fissure, but in openings
or ‘‘veins’’ in the hanging wall, which oceupy nearly vertical po-
sitions (see figure 1). These

oe

veins’’ are more nearly allied to
gash veins than to what are usually ealled ‘‘fissure veins.’’ The
‘‘secondary vein’’ now so productive in the Ophir ground, has
brought to light some valuable and interesting facts. (1) It has
been found only in the lower mine levels, either as a mere fault
zone or a productive deposit. (2) From the lines of motion pre-
served finely in the clay gouge, the relative movement of the
walls is seen to have been nearly horizontal, whether north or
south the writer is not able to state definitely. From the parts

o

of the ‘‘vein’’ observed, however, chiefly on the 2050 level, it
seemed probable that the motion was to the south for the east
wall, dipping downward about four degrees in the same direc-
tion. This corresponds to the view that the vein itself is due to a

pulling apart of the rock mass, causing the greatest openings to

184 University of California Publications. [GEOLOGY

the north, in the concavity caused by the bending of the ‘‘vein’’
to the east at the north end. This northeastward swing causes
the secondary opening to become nearly parallel to the Sierra
Nevada fork, as shown diagrammatically in figure 2. The thick-

C.iC shaitt

Diabase in part

Foot Wall

Diorite

Fie. 1.—Cross section through the Comstock lode.

ness of the ore body within this opening increases with depth up
to the present time of working, and some very rich ore is being
extracted. Exact distances and figures cannot be given, on account
of the methods of mining now in vogue. The ‘‘vein’’ has been,
and is, productive up to the 1800 level of the C. & C. mine and
down to the 2250 level now being worked. The ore is not evenly
distributed, but is in more or less well-defined chimneys or
shoots, connected by material of too low grade to be worked. The
form of this secondary vein, then, is a nearly vertical fissure
about parallel to the main lode and east of it. In portions of this
vein, particularly where opened best in stoping, a dip to the east
is present. .

The lode at the surface shows an arrangement of vein filling
and ore in every way due to the same causes which produced the

VoL. 4] Reid. —The Comstock Lode. 185

secondary fissures at greater depths. The ‘‘west vein’’ and the
‘feast vein’’ at the surface have been carefully described many
times by previous observers,* and the fact that only the ‘‘east
vein’’ carried values has eaused much discussion. This ‘‘east
?

vein’’ is merely the gash which reached the surface, thereby ap-

Ravine

>>>

own Poiny

ian. am

Nevada

Foun — /

Fic. 2.—Ground plan of Comstock lode, showing disposition of faults.

pearing as a vein occupying a fault plane and resultant fissure.
These three gashes—the surface ‘‘east vein,’’ the famous bo-
now being worked, all have an identical

if ?

nanza, and the ‘‘ vein’
origin. Their formation hes in the fact that the lower part of the
hanging wall block has settled more than the upper, relative to
the foot wall, and has been torn apart by the stresses developed.
This form of ore deposit is rather new, and because of its evident
importance deserves a distinctive recognition. The term ‘‘gash

‘rift vein’’ is sug-

‘

vein’’ is not suitable, obviously, and the name
gested to cover the structure.
Gold Hill.—The bonanzas of Gold Hill are found in the lode
proper, near the east wall, and east of the low grade quartz. The
*G. F. Becker, op. cit. Clarence King, ‘‘Survey of Fortieth Parallel,’’

Vol. III. John A. Chureh, ‘‘The Comstock Lode—Its Formation and
History.’’

186 University of California Publications. [GEOLOGY

differences in the form of the bonanzas in the two portions of the
Comstock lode have been noted by other observers. In Becker’s
monograph,* von Richthofen is quoted as writing: ‘‘The ore is
distributed in a different way in the northern and southern parts
of the vein. * * * In the northern part the ore is concentrated
in elongated lenticular masses of which the greatest axis is not
far from vertical. * * * To the south the ore is concentrated in
continuous sheets, the principal one of which is very near and
parallel to the eastern wall.’’ This difference in the form and
occurrence of the ore bodies is a very important matter, both
from a scientific and an economie standpoint. This subject, and
what grows out of it, is the main reason for the writing of this
short paper, for a proper view may increase the life and output
of the mines very materially.

One peculiar bonanza occurred in the Gold Hill group, in the
Yellow Jacket mine. The explanation of this, as of the others,
will be given later.

HALE AND NORCROSS TUNNEL.

The structures shown in the Hale and Noreross tunnel will
be mentioned together, for the sake of simplicity. This tunnel,
running N. 75° W., enters the slope of Mt. Davidson at the Hale
and Noreross shaft (see figure 2). At a distance in of 1,080 feet
the footwall of the lode is reached, the so-called ‘‘black dyke.’’
1. Proceeding in, at a distance of 3,720 to 3,750 feet, appear ap-
proximately vertical slips striking N.W.-S.E. parallel and in line
with the Silver City lode as shown on the surface. A second
well developed slip parallel to these occurs at a distance of 4,550
feet in from the mouth. 2. In nearly all portions of the tunnel,
but particularly between the lode and 3,500 feet in the tunnel,
and from 4,500 feet to the end (5,085 feet on Feb. 12, 1905),
are seen slips parallel to the Bullion Ravine fault; that is, ap-
proximately parallel to the course of the tunnel itself. These
indicate unmistakably evidence concerning the existence of the
Bullion Ravine fault underground. 3. At a distance in the tun-
nel of 4,908 feet occurs a very strong vertical north-south fault.
The east wall is the diorite of Mt. Davidson, and the west wall

*G. F. Becker, op. cit., p. 17.

VoL. 4] Reid—The Comstock Lode. 187

is the same rock which forms the haneine wall of the Comstock
lode, the diabase of Becker. This rock continues to the face
(given above), and no doubt shades into augite andesite farther
west, Just as in the east country. Thus the diorite of Mt. David-
son is terminated east and west by identical structures. No
doubt tunnels north and south would develop the same conditions
on the other two sides, as indicated by the surface structures.
4. West of this west fault just noted, the prevailing slips are per-
pendicular to the tunnel and dip to the west, in contradistinetion
to the eastward dipping slips near the Comstock.

The west diabase, as it will be called, now shown in the tunnel,
is much fractured and filled with veinlets of pyrite. Some films
of galena and sphalerite up to one-eighth of an inch in thickness
also occur fifteen feet west of the fault. These gave some values
by assay.

DEEP ORES AND WATERS.

The ores are doubly interesting from that fact that their
deposition still continues, due to faulting opening up new fissures
and fractures, and from the fact that the mine waters are, for
such waters, rich solutions yielding very positive results to fire
assay methods. The ores are moving in two ways: upward and
downward.

That the ores have moved upward at more than one time has
been noted best by Becker.* He writes (page 219): ‘‘In the
great California and Virginia bonanza several streaks or veins of
very rich black silver ores, said to be largely stephanite, occurred.
These were separated from the surrounding quartz very sharply,
as if of later origin.’’ Again (page 221) he writes: ‘‘What I
have seen * * * leads to the belief that these rich concentra-
tions were of later origin than the rest of the ore. The quartz
in the C. & C. was almost everywhere a crushed powdery mass,
while the thin and persistent veins of black ore running through
it were very solid. A somewhat similar relation seems to have
existed near the croppings, and it is not impossible that these
ores were formed at the expense of others of the more usual
kind at a later date, and that they occupy spaces opened in the
ore masses by faulting action.’’

*G. F. Becker, op. cit.

188 University of California Publications. [ GEOLOGY

The writer had hoped to present even more conclusive evi-
dence of suecessive deposition and its receney, but owing to the
fact that the lowest mine workings are not open to outsiders,
this became impossible. However, such evidence as already pos-
sessed is as follows:

In the ore bodies opened within the last year on the ‘‘sec-
ondary vein’’ now worked, some pertinent facts presented them-
selves. The finest specimens of ore show often very perfect erys-
tals of stephanite and argentite coating, or wedged between,
quartz erystals. Coating one side, the downward side, of all the
minerals, is a thin layer of caleareo-siliceous material. Below the
surface crystals of ore and quartz is a layer of quartz, resting in
turn upon a second layer of caleareo-siliceous matter. This shows
below it a second layer of ore, resting upon quartz crystals. and
so on, the series often repeating itself several times more or less
perfectly. In that portion of the ore occurring in the lower
depths, from which the water has been drainea but a short time,
the surface layers of ore, quartz and caleareo-siliceous matter
showed clear and fresh, while on standing in the open, or in the
higher portions of the vein, the same minerals appeared dusty
and old. In some of the vugs in the lower portion of the ore
body, quite a number of small but perfect rhombohedra of calcite
were found; also, as noted by Becker, old fractures in the ore,
caused by faulting movements, are cemented with quartz and ore.
In the ores now worked, however, the motion appears to have
been a pulling apart, for breeciation, though present, is rare, and
the two sides of a cemented break are usually fully complemen-
tary. This process of successive deposition is not limited to the
Virginia City portion of the lode, but is found quite well de-
veloped in the Gold Hill mines, and in the calcite gangue of the
Justice ore body.

Further uncemented fractures present themselves as indi-
cators of motion up to the present time, since the withdrawal of
the waters by the mine pumps. The great volume of water still
entering the lower workings also contributes abundant proof of
fissures kept open by late motion, for the lode proper, where cut
by the shaft, is reported to have been completely filled with
quartz.

VoL. 4] Reid.—The Comstock Lode. 189

Analysis of Waters—The ore now being mined below the
2150 level, which was all below water level within a few months,
shows the same conditions, with the surface minerals in the fresh-
est possible condition, precisely as if just deposited from solution.
A notable fact of these lower deposits is the greater proportion
of gold to silver than was found in the ores above. On the 2050-
foot level and below, considerable free gold was found. The
actual process of deposition cannot well be watched, hence as the
best substitute the deep waters from the 2250 level of the C. & C.
shaft were analyzed and assayed, to determine if they were able
to do such work as indicated. They are exactly suited to this, as
the following facts will show. The water is the typical deep
water of the Comstock lode whose temperature has reached as
high as 170° F., and is always over 116° F.: ,

ANALYSIS OF MINE WATERS.*

Grams per liter.

DSTO) kart so oy cone eB ee a ees en cutee once eee eee 0.133
ATSOE, Anca suie core orte eee ae enh oe ee aus .0025
INGE OS teree nich aionce mee ie hata ps cd can amena eS .0091
CAO TS yds custo PART oe RR ToL eke .1404
INDO, elie isle esshesteuevermerr ss hGeats ce ees Ges .0097
Oe orev Sy dani ene take Maples Wemra dare tncos 3957
Qe pee etec dn ht apa Roa oceeeegemane) eeenentretay eS .0190
Oe. Bes seteseccs cea nae ee cae eet Re akiws cov eae SEEN Tee .0150
ERR OSS cach ero Ree PETE OSTEO aS .0643
EN ct; ps coeds cr cieskewzn ae se tome mentees ewe meee okra ter aes 1765
Total @Solid'siacesctas on cris ese sep are .9656

Assay of Waters—From an evaporation of 10 liters of the
water, the following assay values were obtained. This work was
most carefully done, and the results are accurate. The gold but-
tons obtained by parting were measured by a microscope and their
weight calculated. This result may therefore be a trifle high, be-
cause of the possibility of the gold being slightly porous. The
litharge used was remarkably pure, a number of test assays on
100-gram charges failing to show the merest trace of a button
under the highest powers of the microscope.

Silver.............2.92 mg. per ton of solution
CONDE Tacs csactote esr se 0.298 mg. per ton of solution

* Analysis by N. E. Wilson, Professor of Chemistry, University of
Nevada.

190 University of California Publications. [ GuoLocy

The analysis of the water showed it to be an alkaline sulphate
and carbonate solution containing a large amount of lime. The
presence of chlorine is important as affecting the gold in solution.
The CO, determined is low, for on standing, some of this gas is
given off and the silica separates out in sufficient amount to ren-
der the water milky. The writer has been unable, for stated rea-
sons, to test the water in the mine. The jugs of water stood
for from 48 to 64 hours before testing, hence the figures for the
carbon dioxide need considerable correction. On evaporating the
water and moistening the residue, a strong alkaline reaction is
obtained by litmus paper.

SURFACE ORES AND WATERS.

The ores are moving downward by the leaching action of the
acid surface waters. In this way they are extracted from their
containing rocks and redeposited below. This process in the past

)

has produced the striking ‘‘nodular’’ ores of the Andes mine,
noted by King * as occurring just below the level of ground
water. These ores are now in their turn being attacked and
again being carried below. <A striking example of the ore depos-
ited by the vadose waters was exposed on one of the levels of
the Andes mine. The presence of east-west slips has already

been noted as occurring here, and one of these, dipping south 60°,

,
had opened sufficiently to allow the free circulation of water.
The shp had cut across all other rocks, vein and country, and
was filled with about two inches of solid coarse black sulphides of
lead and silver. This small sheet of ore pinched out toward the
bottom of the drift, but broadened above. The grain of the ore,
and general characteristics of ratio of lead to silver, ete., were
all different from the ore which occurs below, deposited from the
deep circulation. The nodular ores consist typically of nodules
ranging in size from that of a pea up to a foot in diameter, and
composed of rich black sulphide ore in a matrix of fine crystals of
quartz. Each nodule is completely surrounded by barren quartz,
which at times may penetrate the nodule along later cracks.
These quartz crystals are built upon the nodules as centers, giv-
ing them a radial arrangement.

* Clarence King, ‘‘Survey of Fortieth Parallel,’’ Vol. III.

VoL. 4] Reid.—The Comstock Lode. 191

All the facts relating to these peculiar ores tend to confirm the
view of their deposition resulting from the intermingling of oxi-
dized surface waters with deep alkaline unoxidized solutions.
They are known to occur nowhere else on the lode in any mine
workings, although the exploration within the croppings is very
little in amount.

The acid surface waters which are now doing so much work,
have covered the walls and ecross-cuts of the Andes mine with
from six inches to a foot of sulphates containing traces of gold
and silver. The chief salt is the magnesian aluminum sulphate,
with also large admixtures of iron and copper, which results
in a remarkable variety of colors. The workings of the Central
tunnel likewise shown these sulphates, but in general the cireula-
tion of air is too rapid to allow of their great formation except in
some favorable localities. The composition of these salts is
shown as an average in the water analysis following. In the Cen-
tral tunnel in one particular spot, where the surface waters are
not fully oxidized, ferrous sulphate and pyrite are being de-
posited at the present time. Some sulphates are being formed
here in delicate needle-like erystals containing a large amount
of the ferrous salt. Bright, well-formed cubes of pyrite and
some few dark sulphides, too small in amount to admit of testing,
occur below and within the sulphates. Not infrequently a little
erystal of pyrite tips a needle of sulphate where the solution
is plentiful. Also, almost solid masses of the sulphide are found
within the wall in the partly decomposed country rock. The
water is descending along an east-west slip which dips to the
south. The clay, or clayey rock, upward along this slip is full of
pyrite, but this mineral is heaviest near the wall of the drift
where the solution is able to cover more ground. The clays of the
upper portion of the lode are all found to contain well formed
but small erystals of pyrite containing some value. There is
probably but one process responsible for all this, and a possible
reaction of the surface waters to produce such a result may be
expressed as follows:

FeSO, + 2H,SO, + 7H,SO,—FeS, + 8H,SO, + H,0.

This reaction is, of course, possible only when there is an

192 } University of California Publications. [GEOLOGY

insufficient supply of oxygen, as oceurs locally in this part of the
Central tunnel.

The water surrounding the sulphates and pyrite being de-
posited, is strongly acid, the most so where the pyrite is heaviest.
As the wall is worked into, the acidity becomes perceptibly less.
The ferrous sulphate appears to exercise the necessary protecting
influence over the pyrite to save it from attack by the free acid
or further attack by the small amount of free oxygen present.

Analysis of Waters.—The analysis of the vadose water, from
Central tunnel, taken from a dropping stream out of the wall on

the lower level, is as follows :*
Grams per liter.

DLO Macprarsdecce a eee icine eee 0.6160
ATS O 3A oxsheicvee te ed cee eee ole eee 18.2140
GRO8, .cessesitens feycup ae erok denn. Suaneve teers dkeneeaeeae 7.1786
MERON. Shel sacb racer ace tey eays rtm heme ates 1.2500
CAO Ie sacpesicd dco rce anette aie ie, Meath tere 1.7400
Mig © ug cistian centenary eG rote soaps een 10.8108
COs! foetied oD Goes er cctarentn crocsas aha aca 0.1850
NS Oye Fceenentie aucun Coane arene sieht) focsous tee 70.1154
CLAS cshteee ssp Sem ter ne rene ke Meme eer 0.1276
WE @)? See A. ses¥asice these shee eet aerate trace
IN a © ie ce eresccas Giinteyt caves eran vite meta coer veteanere hes 0.7209
EM OLALM SOM Siienera cxsscteta sy srermeteese eet 110.9583

Hreey EGS OW s-ccversusdekcksieesveue/ohetencese 125.0804

The remarkable properties of this water are evident. Silica
is noticeable in amount, in spite of the strongly acid solution.
The salt is seen to be essentially a magnesian ferrie aluminum
sulphate, with lime, copper and manganese. These mine solu-
tions vary, and the writer has taken from the roof of some of the
old stopes stalactites of quite pure copper sulphate. The water
analyzed was a fully oxidized solution; the water depositing the
pyrite is only partially supphed with oxygen.

Assay of Waters.——The assay of this vadose water gave the
following results: 250ce. portions were used for each test.

Silheiwera Aaa o 188.0912 mg. per ton of solution
Gold sa 2 cts wee 4.1528 mg. per ton of solution

It is necessary again to note the fact that some of the east-

west veins which exist east of Bullion Ravine on the line dividing

* Analysis by N. E. Wilson.

VoL. 4] Reid.—The Comstock Lode. 193

the Virginia City portion of the lode from that of Gold Hill, are
filled largely or wholly with calcite gangue. The same mineral
acts as vein-filling in the Silver City lode. Becker * favors the
view that the difference in gangue mineral between the Silver
City lode and the main vein, is due to differences of country rock.
But as the calcite veins exist in the augite andesite east of Bul-
lion Ravine, this idea cannot hold. On the fact, however, that
the two lodes are due to different faults, a more probable conclu-
sion is that the deposits are of different age. The proof of this
lies in the examination of the point where these two lodes inter-
sect, which is not now possible. Published reports and maps are
insufficient as a basis for judgment.

A further fact of importance regarding the lode, in the Vir-
einia City portion especially, is that the width of the vein is
often little or nothing in the lower levels. Moreover, the west
wall is not well defined in all places, because of a complexity of
slips in the west country. This portion of the ground in all the
lower levels has not been thoroughly prospected, in spite of the
many thousand feet of mine workings.

ROCKS OF HALE AND NORCROSS TUNNEL SECTION.

A full report of this section is not yet ready, nor would it be
proper at this time before the tunnel is complete. <A full set of
rock specimens, taken every fifty feet, and oftener over impor-
tant places, is now being collected for the writer. However, the
importance of the main facts concerning the roeks within Mt.
Davidson is too great to allow their complete reservation at this
time. These facts are briefly as follows:

1. The Hale and Norcross tunnel (see figure 2) strikes the
lode footwall at 1,080 feet in from its mouth. The first wall rock
encountered in the foot is the well known ‘‘black dyke,’’ of de-
composed basalt,y a few feet in width. Beyond this, in to a dis-
tance of 1,270 feet, is a fine-grained, dark rock looking much
hike a fresh augite andesite. In the Mexican ground, in the cross-
cut tunnel mentioned above (page 3), the same rock occurs
east of the lode, shading into diorite to the west. Under the mi-

* G. F. Becker, op. cit., p. 220.
y+ Hague and Iddings, Bull. No. 17, U.S.G.S.

194 University of California Publications. [GEOLOGY

croscope the rock is seen to be an augite rock of a texture be-
tween an augite andesite and a diabase, yet which in spots
is that of a fine-grained augite diorite. The augite is fresh, and
in more or less irregular grains or in well formed erystals, with
high birefringence, very faint pleochroism, and an extinction
angle of from 40° to over 50°. The feldspars are well formed,
and crystallized at about the same time as the augite. They all
show extinction angles of over 20°, and are labradorite. Some
few flakes of biotite and grains of quartz are also present. At
1,200 feet in there occurred what appeared to be a thin dyke of
diorite one-half an inch wide, intrusive in the dark augitie rock.
No well defined boundaries were shown, however. Farther
search showed many more such dykes at 1,250 feet, of apparently
the usual pinkish diorite, intrusive in the dark rock. The micro-
scope revealed the fact that the two rocks differ only in coarse-
ness of grain and alteration of feldspar, and that the change
from one to the other is gradual. The pinkish diorite was thus
found to be an augite rock with some of the large augites altered
to uralite, but identical in all particulars but grain with the dark-
colored stone. The dyke at 1200 feet seemed to show that some
motion took place in the mass when still plastic, as very often
happens in igneous magmas, for the transition from the fine to
coarse grain was more sudden than in the small dykes at 1250 feet.
Beyond 1250 the ordinary type of pinkish, coarse-grained diorite
comes in gradually. The microscope proved this to be a true
augite rock also, with many erystals of fresh augite, and more
such changed to uralite in part, and partly to chlorite, epidote,
and magnetite. This pinkish rock continues on until at 1358 feet
a small mass of diabase occurs, from six to ten feet wide along the
tunnel. One side of this diabase is bounded by a slip and some
breeciation ; the inner side passes into diorite very gradually.

Again at 2650 feet, and at 3725 to 3760 feet, diabase occurs,
in the latter case particularly, shading beautifully into diorite by
all possible gradations. Specimens taken here are either diabase,
or diorite, or both, as one may choose to call them. And the rock
is all augitic, though none of this mineral is wholly fresh. The
rock is much fissured and jointed, so that the alteration of the
minerals has proceeded quite far.

VoL. 4] Reid.—The Comstock Lode. 195

At 3350 feet an entirely new rock, as far as macroscopical ap-
pearances go, begins gradually to appear. This rock is of the
texture of the pinkish diorite so common on the surface, but is
almost black in color, with the peculiar luster of augitie rocks.
The microscope shows it to be a true augite diorite, precisely the
same rock as the surface stone except that its augite is fresh or
only slightly altered. The usual amount of free quartz is pres-
ent, as in all these rocks, and likewise some few flakes of biotite.
This phase of the diorite mass appears to be the core of Mt.
Davidson.

Proceeding farther in the tunnel, the pinkish rock tends to
reappear gradually beyond 4500 feet, and at 4700 feet a pecuhar
mottled facies shows itself. This has not yet been investigated,
but is merely a variety of the diorite. At 4908 feet im, the “‘west
fault,’’? as it will be called, occurs, beyond which appears the

’

‘‘west diabase.’’ The rocks of this section, when properly
studied, will complete the work of Hague and Iddings east of the
lode, and will serve to bring into greater relief the admirable
work of these men.

CONCLUSIONS.

Form of Lode.—-The Comstock lode is divisible on structural
erounds into two main portions: (1) the Virginia City portion,
and (2) the Gold Hill portion. The Silver City fault and lode, or
‘‘branch,’’ as now ealled, is a distinet unit, probably of later age.
The grounds for this belief are, as seen, the facts of it being a dis-
tinct fault, and that the vein filling is different from that of the
Comstock lode proper. The only grounds for a belief in a later
age are those of structure; it is well shown that much faulting
took place after the first formation of the main lode, and to com-
bine all the facts presented it is necessary to assume a period of
faultine not coineident with that which formed the bonanza
gashes, but later than the first faulting. In this country of great
and long continued faulting such an assumption is not without
a good basis.

The Virginia City portion of the lode is bounded on both
north and south by a series of east-west faults. Also, to the north,
‘some forking of the lode oceurs, with one strong branch bending

196 University of California Publications. [ GEOLOGY

to the east in the Sierra Nevada ground. The faults or slips to
the south are those approximately in and east of Bullion Ravine.
But few of these east-west fractures contain much secondary
mineral. The few which do become veins are largely calcite
bearing, and probably of different age from the others. Between
these two lines of east-west motion is located the Virginia City
portion, differing from the other part in having a greater rela-
tive movement of the foot and hanging walls. This motion has
been so great that an unequal movement of the hanging wall
block was produced, the bottom moving farther than the top,
with consequent rupture. These ruptures produced the second-
ary vertical gashes, or veins of rifting. This motion causing rup-
ture, however, was distinctly later in age than the first vein form-
ing movements. Hence, when the secondary openings were
formed, they were filled with concentrations from the previous
deposits as well as with original supplies from great depths. And
there is no good reason for assuming that either the movements
or the ore deposition have ceased, but rather all facts tend to
confirm the idea that ore is yet being moved from place to place
in the greater depths as well as fresh supplies from below being
brought up by the hot waters.

In the Gold Hill portion the relative movement of the walls
of the lode has been less; there have been no rift veins formed,
and the ore bodies are within the lode walls, near the hanging.
The same two periods of deposition of vein-filling were present
here, the bonanzas occupying later fissures near the hanging wall
of the earlier vein. No doubt deposition is still progressing in
depth here, though not enough mining work has been done to
allow a definite statement in this regard. The one exception to
form in this portion of the lode, in the Yellow Jacket mine, was
due to the fact that the vein, in its proper plane, did not reach
the surface, so that the relative movement of the hanging wall
block downward was taken up near the surface by a gash or rift.

Deposition of Ores—On account of the importance of the
subject, a reiterated statement is not out of place regarding the
two periods of ore deposition. Had the second of these periods
not existed, there would be practically no ore on the Comstock,
hence the relations of these two must be of vital concern. The

VoL. 4} Reid —The Comstock Lode. 197

first period of vein-filling was due to the primary faulting, and
iow-grade materials were placed in the open fissure. The second
and later period opened new fissures, rift veins in Virginia City,
and openings within the vein in Gold Hill, in which the rich con-
centrated ores of the bonanzas were deposited. This second
period probably continues in the depths, as it would surely do
above were the lode still intact from man’s hand. The details
of this ore deposition have not yet been thoroughly studied out,
nor can they be until our knowledge of the physical chemistry
of the subject is more complete.

Location of Bonanzas.—The deep ore bodies of Virginia City
have been, and will be, found within the hanging wall, in more or

«

less vertical fissures, of which the surface ‘‘east vein,’’ the Great
Bonanza, and the vein now being worked, are examples. More
such bodies should be found by properly-driven ecross-cuts and
drifts lower down and to the eastward. There is also a large
stretch of the lode above the 2150 feet level which has not been
thoroughly explored. The probable reason for the peeuliar rifting
of the hanging wall block is that the cementing of the first frac-
ture by quartz, and the concomitant weakening of the hanging
wall by the leaching action of the ground waters, enabled the
later stresses to fracture the hanging wall block as it is found.
The reason for believing in the existence of still deeper similar
rifts filled with ore is that the surface for two miles eastward
from the lode shows the hanging wall block to be greatly altered
by the action of hot waters, and therefore weakened. The Sutro
tunnel section corroborates this, and the mine workings also show
the rocks east of the lode not to be solid nor unaltered.

Also, there is considerable concentration of ore taking place
from above by the surface, or vadose, waters. These ores will
occur on or near the footwalls of the numerous branches of the
lode which outerop on the surface, within a few hundred feet of
the outerops. Such material is low-grade, however, and. in the
main, not yet available because of the high cost of mining and
milling. A body of future reserves is thus assured. The low-
erade of these ores has been proved by numerous assays. Fur-
ther, the west wall of the lode has never been thoroughly investi-
gated, and such work might prove very profitable.

198 University of California Publications. | GEOLOGY

Structure and Genesis of Mt. Davidson.—Mt. Davidson is a
diorite mass bounded on all sides by faults, and has risen rela-
tively to the surrounding country. The Comstock lode occupies
the fissure made by the east fault bounding the mass. The west.
fault now shown in the Hale and Noreross tunnel is not occupied
by a vein in the tunnel, because the compressive stresses have
been too great. Farther search, both along this fault, and partic-
ularly farther west, may easily result in the finding of ore. There
are no reasons for assuming the non-existence of ore in the west
country, nor elsewhere in the faulted region surrounding Mt.
Davidson, especially to the south, where the country is more frac-
tured and broken.

A further word concerning Mt. Davidson may not be amiss,
although the subject has not been fully investigated, on account
of the time necessary. On the Carson sheet* the mass of Mt.
Davidson is seen to be a roughly rectangular mass approximately
two by one and one-half miles, with the major axis north and
south, bounded on all sides by steep slopes. The eastern slope
is noted for the Comstock lode. The surface of this mountain
mass is that of an old eroded region, as noted by Becker t (page
184 et seq.), which has been uplifted above the surrounding
country. One standing on the summit of Mt. Davidson cannot
fail to be struck with the mature character of the topography.
This eroded, gently rolling surface exists well preserved in the
Sierra Nevada to the west, now broken and displaced by later
faulting action. The history of the Sierra and Virginia ranges is
identical in the main features. These statements will be proved
by a citation of facts in a subsequent paper now in preparation.
The results of this conception are obvious and far reaching. The
location of the Comstock is well known on the east. On the
south are other ore bodies in the American Flat region, but all
of the south has not been prospected. One well developed west
fault has recently been shown in the Hale and Norcross tunnel,
and more will follow. The maximum faulting on the west is
farther to the west than the present face of this tunnel. To the

* Carson Topographic Sheet, U.S.G.8.
7G. I. Becker, op. cit.

Vou. 4] Reid.—The Comstock Lode. 199

north several quartz bodies are known to exist on the surface over
the broken country, but the details here are not yet known. There
is abundant reason for suspecting the existence of ore on other
sides of Mt. Davidson than the east.

University of Nevada,
Reno, May, 1905.

Note.—At the present date, July 6th, 1905, it can be
definitely stated that ore has been discovered in well-formed
veins in the Jumbo District, about two miles west of the Com-
stock Lode, on the west slope of the Davidson Plateau. Also, the
Hale and Noreross Tunnel, though not yet far enough west to
develop ore bodies, has cut into a large flow of warm water in the
fissured ‘‘west’’ country.

UNIVERSITY OF CALIFORNIA PUBLICATIONS

BULLETIN OF THE DEPARTMENT OF

GEOLOGY

Vol. 4, No. 11, pp. 201-226, Pls. 26-27 ANDREW C. LAWSON, Editor

THE DIFFERENTIAL THERMAL CONDUC-
TIVITIES OF CERTAIN SCHISTS.

BY

PauL THELEN.

CONTENTS.

PAGE
ACY OCUGELOME caren tens areca es ban cneh eye soueeste Se agsnarnment rape L EER Lara air ee eee ase 201

The Use of the Wax-figure for the Determination of Relative Heat-
COMGUGTIVITRES Ue sect ee tsss bs eae icles ae tees oe anette: sreneye ev-osue.aaacenehaaitate 205
Methodstusedi by the Writer. ..4.0e qe estes suk seca ec se 0s wees ones 211
The Conventions used in speaking of the Schists..................... 215
The Rocks Investigated and the Results Obtained.................... 216
JETRO SUEY aye One Tale) ISOS ye pope ane aan dodo soe eon asa sas anes on 218
AMAMeS AalonmalolKevalGkey SieabisIns 44 oe soo ae ocr oe as 4 hn ead ee een oe 218
Mauer (CikenbicroyoNaenoKs SAWS i es ae ene anges gon. . 221
The Quartzose Schist...... Nas ee ers rns oe eae EEA ay
Mhreg Wren o ells IM Can S GIS te terereeeesdeeamenel et eisess ee teers espera eee

INTRODUCTION.

We know that in general the physical properties of crystalline
substances are functions of direction, that is, erystallographic-
ally similar directions show lke physical properties (conduc-
tivity for heat, light, and electricity, dilatation, cleavage, hard-
ness, solubility, ete.), while erystallographically dissimilar
directions may show unlike properties. Even isotropic sub-
stances, for instance, possess cleavage. Here the behavior toward
hght is the same in all directions, while the eohesion is not.
These phenomena, observed in all crystalline bodies, are referred
back to an internal molecular structure. This structure is sug-
gested to us, too, by the external geometrical form of the
erystals.

202 University of California Publications. [GEOLOGY

In the case of the heat and light conductivities of crystalline
bodies, we assume the properties of the ether to be affected by
this molecular structure. Increased conductivity in one direc-
tion is explained by an increase in the elasticity e of the ether
in that direction, the density d remaining constant (Fresnel) ; or,
equally well, by a decrease in the density, the elasticity being
constant and equal to infinity (Rayleigh) or equal to —K (Thom-
son) where A corresponds to the modulus of shear or coefficient
of rigidity. This is in accordance with the old elastic solid

é .
theory where V. =.| a The modern electro-magnetic theory of
—

Clerk Maxwell teaches that v=

inductive capacity and y is the permeability, and the value of

where A is the specific

this radical increases with an increase in = or with a decrease
in K. Whichever one of these views we adopt, we assume always
fundamentally that some property of the ether is affected by
any regularity in the arrangement of the molecules. ‘If we
arrange a number of material particles in orderly fashion we
have not affected the properties of the ether; if, as is probably.
the case in crystalline solids, we arrange a number of aggre-
gates consisting of many molecules each in orderly fashion, we
have affected the properties of the ether. Where is the dividing
line? The question that suggested itself was this: If light
and heat conductivity in a crystal are functions of internal
molecular structure and of conditions of internal strain, will the
heat and light conductivity of a rock depend similarly, in part,
at least, upon its internal crystallographic structure and its con-
ditions of internal strain?

In a schist which has been dynamically metamorphosed, we
assume that the internal strain has been relieved by the re-
crystallization of the constituent minerals; but this recrystalliza-
tion has set up in the rock a definite crystallographic structure
comparable to the definite molecular structure of a crystal.
Will this structure in itself affect the thermal conductivity of
the rock? Can we here consider the crystal as the physical unit
even as we have heretofore considered the molecule or aggrega-
tion of molecules?

Vou. 4] Thelen.—Thermal Conductivities of Certain Schists. 203

The answer seems to be very definitely, No! that the thermal
conductivity of a rock is not in any way a function of the
orientation in itself of its mineralogical constituents, but is en-
tirely the result of the integrated thermal conductivities of the
individual minerals.*

This result was the probable one. Experimental verification
is, however, always valuable and grateful.

When sufficient evidence shall have accumulated to verify
the above answer and the analogous statement concerning dilata-
tion effects, namely, that the dilatation coefficients of a schist
are unequal in different azimuths and computable from a micro-
scopic examination of the rock strueture and a knowledge of
the dilatation coefficients of the constituent minerals, we shall
have a new and potent tool to take into account in any discussion
of deformations of the earth’s erust by thermal effects. Sup-
pose, for example, a bed of erystalline schists undermined by a
molten magma. If the coefficient of thermal expansion in one
direction in the overlying plane is greater than in another diree-
tion perpendicular to the first, and in the same plane, then we
shall have a definite tendency toward differential deformation.
The effects will duplicate those due to compression by other
agencies. Take, for instance, a quartzose rock. This is a poor
example since quartz, though often found in schists with the
longer dimensions of the individual grains roughly parallel, is
yet never found with its c axes parallel. But the physical con-
stants of quartz have been worked out and can furnish the basis
of a numerical computation. For the range from 0° to 100° C,

Fizeau gives that parallel to c,

and perpendicular to ¢, tk; =lo (1+ .000013¢t+ .000000012 f)).
If we make ¢ = 100°C, we have (yoo = lp (1.00078) parallel to
¢ and 490 = 7p (1.00141) perpendicular to e.
Waldemar Voigt determined Youne’s modulus in various

“Such effects as total reflection, for instance, are probably not entirely
negligible. A Sillimanite needle, surrounded entirely by minerals of lower
index of refraction than its own, would propagate in the direction of its
length only any heat ray that entered a cross section of the needle nearly
parallel to its length. The effect may be observed by looking lengthwise
through a solid glass tube which points toward a source of light—lhght and
heat waves obeying the same laws in general.

204 University of California Publications. [GEOLOGY

directions for quartz, and his results bear out the conclusions
of Savart* that the elastic properties in various azimuths possess
the asymmetry characteristic of rhombohedral tetartohedral
crystallization. His results were computed from bending tests,

with the load applied in the middle, and # was the unknown
eae
4E bd®"
The values of H} expressed in grams per sq.mm. were:
Ey) = 10,304,000 parallel to c.
E45 = 13,050,000 perpendicular to —R.
Esa = i. 405,000 perpendicular to +R.

Eo) = 7,850,000 perpendicular to c¢.

Fl Fl
For linear dilatation, H# or J =——— or e=>_.
ea Ma

quantity in the bending formula y=

For thermal expansion, eI (t2—t) ¢
Combining, /—Ma (tz—h) ¢, which measures the force to be
applied to keep the body from expanding under the given con-
ditions. If we take a cubie foot of quartz in which the ¢ axes
are all parallel, we shall have the force of expansion for a rise
of temperature from 0° to 100°C to be

10,304,000 S 5 :
Goa p09 % (12 X 25-4)? X 00078 = 820 Tons per sq. ft. parallel to ¢
090.0 A, cUUU
and
7,850,000 hottie e .
453.6 < 2000" (12> 25.4)? ><.00141 = 1140 Tons persq. ft. perpendicular to ¢.
00.0 XK JUUU

These results are remarkable, but not nearly as startling as
they might be. For here the modulus is large where the thermal
expansion is small, and the two tend to neutralize each other.

A case that would come nearer to some of the schists studied
would be one in which mica or hornblende is the main mineral.
In many mica schists the micas all he in the same plane, having
their c axes parallel, while in some hornblende rocks the horn-
blendes have all three axes roughly parallel.

Gypsum has in the plane of its clinopinacoidal cleavage
moduli whose values vary from 3.1 10° to 8.6X10°£; but values
perpendicular to the cleavage have not been worked out because

* Pogg. Ann. Bd. XVI, p. 206, 1826.

+ Taken from his remarkable paper in V. 5 of the Beiblatter des Jahr-
buches fiir Cryst. Min. u. Paleont.

{ L. A. Coromilas. Wher die Elasticitatsverhaltnisse in Gyps und Glim-
mer. Inaug. Dis. Tubingen. 1877. Reviewed in Zeit. fur Kryst. V. I, p. 407.

Vou. 4] Thelen.—Thermal Conductivities of Certain Schists. 205

the bending test can not be applied here and no other method
has been successfully substituted for it. Mica shows less varia-
tion in the basal planes and values perpendicular to this have
also not been worked out. The physical constants of horn-
blende have not yet been determined. These two minerals will
doubtless show much greater differential effects than the quartz
does, and they are of more than theoretical importance.

The volume relations are interesting as they give an idea of
the relative insignificance of the synelinal and anticlinal de-
formations necessary to relieve the strains set up by thermal
changes. If we imagine a cubic mile of quartz similar to the
eubie foot discussed and heat this up for a thousand degrees, we
vet the expansion in the two directions (assuming rather dubi-
ously that Fizeau’s values for the coefficients of expansion as
determined for the range from 0° to 100° hold for this range
as well) to be

5280 .0078 41.2 ft. parallel to c, and

5280 .014 73.9 ft. perpendicular to c.

A similar block of augite would give expansions of 84.5, 32.7
and 96.0 ft. per mile in the three directions which correspond
to the three main axes of thermal expansion. Calcite shows
much greater discrepancies since ¢ is negative in one direction,
the values being

I, =o (1+ 0.0425 ¢ + 0.0708 2’) for parallel to ec.

1, = lo (1— 0.04057 ¢ + 0.0704 t’) for perpendicular to ec.
Hence the expansion for a thousand degrees (making the same
dubious assumptions) would be

5280 X (.025 + .008) = + 176 ft.

5280 X (—.0057 + .004)—= — 8.9 ft.
Again, one result of the differential thermal conductivities is its
effect upon the outlines of the zone within which the metamorphie
influence of an intrusive magma would make itself felt.

THE USE OF THE WAX-FIGURE FOR THE DETERMINATION OF THE
RELATIVE HEAT CONDUCTIVITIES.

J. Ingen-Houtz* was the first to suggest the use of wax-

figures. His work was done over a hundred and twenty years

* J. Ingen-Houtz. Sur les métaux comme conducteurs de la chaleur.
Jour. de phys. 34, 1789.

206 University of California Publications. [GEOLOGY

ago; although his numerical results were of no value whatever,
yet his name is remembered because he was the first to outline
the method. He took thin sheces of erystals cut so as to have
two faces parallel, bored a hole perpendicularly through the
center of each one, coated both faces with wax and through the
hole ran a needle or wire which could afterward be heated by
conduction or by an electric current.

Sixty years elapsed before anything more was done. Then
de Senarmont* took up the work. His results on quartz in par-
ticular and on about a score of other minerals in general have
become classic, and later investigations through half a century
have not cast any doubt upon their accuracy. Senarmont used
a silver wire which he heated at one end. The wire was either
driven through a hole in the section, or its end was lowered per-
pendicularly upon the face of the erystal. The wax surface was
shielded from any heat which might radiate from the flame or
wire. In his later work, Senarmont used also a hollow tube in
place of the silver wire. This was heated by passing a current of
hot air through it.

He found that every section of an isometric crystal and every
section perpendicular to c of a uniaxial erystal gave circular
wax figures. This means for the First System a spherical heat-
conductivity ellipsoid, and for the Second and Third Systems
an oblate or prolate ellipsoid of revolution with the ¢ axis as
the axis of revolution. Further experiments with crystals of
the Fourth, Fifth and Sixth Systems gave triaxial ellipsoids in
all eases. In the orthorhombic system, the three main axes lay
in the pinacoids, and hence were parallel to the erystallographie
axes. In the monoclinic system, one axis was parallel to the
orthodiagonal; and in the triclinic, not even one axis was
uniquely located by a knowledge of the orientation of the crystal-
lographic axes. Thus the orientation of the axes of elasticity
for heat conduction bears in every case a relation to the diree-
tions of the crystallographic axes which is entirely analogous to

* The scientific literature of the day is replete with brief outlines of the
results of his work. Ann. chim. phys. 1887, 1848, 1850; Ann. Pogg. 1848,
1849, 1850, ete.; Wied. Ann. of the same period.

Vou. 4] Thelen—Thermal Conductivities of Certain Schists. 207

that which the orientation of the optical axes of elasticity bears
them.

Senarmont’s values for the ratios of the axes of his wax figure
ellipses in sections parallel to ¢ in some uniaxial crystals are
given here, and reference will be made to these figures later. The
figures of the first column are proportional to the axis parallel to
c, and the axis perpendicular to ¢ is taken as unity.

Quartz 76 1.00
Tourmaline Pars 1.00
Caleite 90 1.00
Rutile 1.10 1.00

These were some of the results of Senarmont’s work, results
both general and specific. But this genius of the laboratory was
unable to state definitely whether or not there was any relation
between the thermometric conductivity in any direction and the
length of the radius vector of the ellipsoid in that direction. His
results, as interpreted by himself, merely showed that the ther-
mometrie conductivity varied in the different directions and that
the wax figures were symmetrical when there was within the
erystal no axis of elasticity which made an oblique angle with
the surface. (In this case, an oval was produced. )

We can at once come one step nearer our result by getting
the relation between the thermal conductivity HK, and the ther-
mometrie conductivity k. It is apparent that the rise in tem-
perature, by means of which thermometric conductivity is
measured, will be proportional to the thermal conductivity K,
and to the reciprocal of the thermal capacity d-s, where d is the
density, and s is the specific heat.

We have, then, k = K/d-s.
This agrees with Tait,* who uses s to represent thermal capacity

and writes k =I /s. It also agrees with Gruenstein and Giebe,+
who have a’ /d-s, where the thermometric conductivity is
expressed by a*. Such was probably the authors’ intention, since
a is generally used for distances, and could in this case be propor-

*Theory of Heat, Tait.

+ E. Giebe. Uber die Bestimmung der Wirmeleitvermégens bei tiefen
Temperaturen. Verh. der D. P. Gesellschaft, 1903.

208 Unversity of Caiforna Publications. [GEOLOGY

tional to the distance from the point source of the heat to the
point whose temperature is under consideration.

We have, then, for one direction, k =K/d-s;

and for another direction, WK? [de ss
and, since density and specific gravity are not directed quanti-
ties, and are constants for any one specimen, we have k:k’=
Te

The rest of Senarmont’s question was first answered by Duha-
mel* on the basis of a theory which he had worked out in 1828.
The foundation of this theory was the hypothesis that heat is
conducted within a solid body by radiation from one molecule to
another. Duhamel came to the conclusion that the ratios of the
axes of an isothermal ellipsoid are equal to the ratios of the
square roots of the thermometric, and hence also thermal, con-
ductivities in the corresponding: directions.

In the same year, G. G. Stokes; came to the same conclusion
from a perfectly general discussion of the conduction of heat in
erystals, in which no assumption was made as to intermolecular
radiation or any other means by which the heat might be con-
ducted. His differential heat equations and the beautiful line
of reasoning by which he finally gets his result would be out of
place in this paper. His result is that the axes of the ellipse
are proportional to the square roots of the thermal conductivi-
ties, and accurately so, for the shape of the ellipse is unaffected
by the losses from the surface.

The removal of the theoretical difficulties which had pre-
vented the interpretation of the laboratory results, at once gave
good opportunities for satisfactory research work.

EK. Jannetazt found that boring holes into the sections was
a tedious and unsatisfactory business, so he used a_ small
platinum bullet through which he sent an electric current by

* J. M. Duhamel. Sur les équations générales de la propagation de la
chaleur dans les corps solides dont la conductibilité n’est pas la méme dans
tous les sens. Jour. de l’école polytech. 13, 356, 1832.

+G. G. Stokes. On the conduction of Heat in crystals. Cambridge and
Dublin Math. Journal. 6, 215, 1851.

{ E. Jannetaz. Des Surfaces Isothermes en minéralogie et en géologie.
Notice sur les travaux scient. de M. E. Jannetaz. Meulan, 1882.

E. Jannetaz. Sur la propagation de la chaleur dans les corps cristallisés.
Annal chim. phys. (4) 29, p. 5, 1873. Bull. Soc. Géol. de France, 1873-
1878; 1881. Journ. de Physique, (1) 5, pp. 150, 247, 1876.

Vou. 4] Thelen.—Thermal Conductivities of Certain Schists. 209

means of two fine platinum wires. He took readings on a very
large number of minerals. Liebisch* says of Jannetaz’ attempt
to show a dependence of the thermal conductivity on the cleav-
age of the erystals, that the conductivity is symmetrical with
respect to other properties than that of cleavage,—‘‘dass die
Wirmeleitunesfihiekeit andere Symmetrieeigenschaften besitzt

;

als die Cohisionseigenschaften.’’ This matter will be brought up
again.

Roentgen} obtained his ellipses by an entirely unique method.
He blew his breath upon the polished surface of the crystal, set
a warm, pointed rod perpendicularly upon it, removed the rod
and hastily spread lyeopodium powder upon the surface.
Where the moisture from his breath had not evaporated, the
powder stuck; and on turning the erystal plate over, the loose
powder could be knocked off from the center, thus leaving a
negative ellipse with sharp borders.

S. Thompson and O. J. Lodget used Senarmont’s method to
verify the statement that linear conductivity depends upon the
direction of flow along the line. They obtained the results they
were looking for. The ellipses were elongated toward the
analogous pole of the tourmaline (section cut parallel to ¢)
with which they were working. The individual values for the
ratios of this elongation varied from 1.17:1 to 1.42 :1,—results
varying so much as to be considered valueless by the writer.
More aceurate methods of other observers gave determinations
of these values in which the maximum difference was under
one per cent.; and we may yet be able to devise means sufficiently
accurate to verify experimentally that heat flows with equal
facility in either direction along a given line, regardless of
pyroelectric or other properties. The only reason this matter
is mentioned here§ is to show what the personal equation can

* Liebisch. Physikalische Crystallographie. Veit & Co. Leipzig, 1891.

y W. C. Roentgen: Uber eine Variation der Senarmont’schen Methode
zur Bemessung der isothermen Flachen in Krystallen. Ann. Pogg. 151,
613, 1874.

W. C. Roentgen: Uber eine Methode zur Erzeugung von Isothermen
auf Krystallen. Zeit. f. Kryst. 3, p. 17, 1879.

¢ On Unilateral Conductivity in Tourmaline Crystals. Phil. Mag. (5)

8, p. 18, 1879.
§The matter is discussed in some detail in Liebisch, loc. cit.

210 University of California Publications. [ GEOLOGY

do in such a ease, and within what extremely wide limits the
results of good experimenters varied with this method. The
last point will be brought up again in discussing the probable
error of the results on the thermal conductivities of schists.

A fairly comprehensive list of ratios of thermal conductivi-
ties to the one-half power (this gives the ratios of the axes of
the isothermal ellipsoids) is appended herewith for future refer-
ence. Many of these have been checked by measurements of
absolute conductivities by the method of Forbes and in other
ways.

For the monoclinic minerals, ¢ will be replaced by ‘‘ parallel
; and the fourth

2

to that axis of elasticity which les nearest c’
row shows by its sign in which quadrant this axis lies. The sign
+ indicates that it lies in the obtuse angle between the c axis
and the clinodiagonal. The numbers show how far from the
c axis this axis lies. The third column will still indicate values
parallel to 0b.

Then the second column must indicate values along a line
perpendicular to 6 and to the direction indicated in the first
column.

The list includes no triclinic minerals.

c a b
ISOMETRIC All minerals ...... 1.00 1.00 1.00
IR AUCLLC2 saya euesseae eens 19 1.00 1.00
| ZAT COM: wateies a wines eee .90 1.00 1.00
HEURAGONAT -\ “Geapolite t%h-..s-1cs 085 94.00 1.00
| Vesuvianite ....... .95 1.00 1.00
@ Wart Zameenevettesesereee 76 1.00 1.00
( Specularite ....... 1.10 1.00 1.00
Wolomiter .2 eee. 1.05 1.00 1.00
a nee { Apatite .......0005 96 1.00 1.00
Tourmaline. ces 1.15 1.00 1.00
Calcite... a. see ess sol 1.00 1.00
iB amie mews cee 1.00 1.06 1.03
ORTHORHOMBIC § Amin yOriter cesta 1.00 971 . 943
| Staurolite ......... 1.00 97 901
/ Tremolite. 22-25 1.00 .60 15 — 5°
Hornblende ........1.00 a {fal . 80
MONOCLINIC Ve pidotery tee 1.00 .93 1.09 —14°5
( (Congiineal & B56 anes o0 1.00 .80 .65 +17°

Vou. 4] Thelen.—Thermal Conductivities of Certain Schists. 211

Mertriops Usep By THE WRITER.

The rock to be investigated was sawed or, where possible,
broken with a hammer, in such a manner as to give it a face
approximately parallel to the section wanted. This face was
then ground smooth and true, and coated evenly with a thin
layer of white wax.

The wax used had a melting point of 63.6°, as determined
by the mereury bath method. Lower melting points, down to
38° C, ean be secured at pleasure by adding turpentine in vary-
ing proportions. The wax was applied by dropping a few
shavings of it onto the previously heated face of the rock, tilting
the latter back and forth until a film of melted liquid covered
the whole upper surface, pouring off the excess, and then allow-
ing the whole to cool. The point of a hot copper wire was next
placed perpendicularly upon the prepared surface. As the heat
flowed outward radially from the point, a small, approximately
elliptical, area of the rock face became heated above the melting
point of the wax.

The area of the ellipse increased more and more slowly, until
the integrated radiation and convection losses per unit time
became equal to the rate of flow across the last section of the
copper wire. The area of the growing ellipse will depend on
the one hand upon the conductivity and the thermal capacity
of the rock, and upon those properties of the surface which vary
the surface losses; and on the other hand, upon the time, the
temperature of the copper wire and of the air, and very largely
indeed upon the temperature of the rock. Other causes affect
it to an inconsiderable extent.

The melted wax is drawn outward by its surface tension,
and, the point a being removed, it cools as shown in section in
fig. 1 (enlarged about 8 times). In this way, the 63.6° C.
isotherm is permanently fixed and may then be discussed and
measured at leisure. Usually 6 to 12 figures were thus fixed
on the same rock face before any measurements were taken.

The apparatus used had to be so arranged that no radiant
energy capable of vitiating the results could reach the rock sur-
face. With this and several other ideas in mind, the following

212 University of California Publications. [ GEOLOGY

scheme was finally evolved, and was considered satisfactory.
One end of a piece of No. 8 copper wire (diameter about 14
inch) was filed to a long point and the wire was bent into the
shape shown in fig. 2. A hollow glass cone was then fitted

ea eT, is)
Db
- |
W
E
Fig. 1. Fic. 2.

around the point, and stuffed full of a pasty mixture of plaster
of Paris and asbestos fibre. This dried firm. The Bunsen
burner flame was applied at the point B. As a further precau-
tion against radiation from the flame, a piece of 676” asbestos
sheeting, with a one-inch hole in the center, was slipped around
the glass cone from below until it was held safe by the friction.
This was soon dispensed with as an unnecessary refinement.

The apparatus, when in use, was clamped in a vise at D.
The weight W was removed. The Bunsen burner was adjusted.
The section E was placed, with the aid of ring-stand and clamp,
directly underneath the point of the wire and about one-fourth
inch from it; the prepared surface was then leveled so that it
would be parallel with the plane surface at the end of the wire
when the latter was lowered through the intervening one-fourth
inch. This lowering was accomplished by replacing the weight
W. On again removing the weight, the wire resumed its orig-
inal position, the melted wax solidified, and the ring-stand was
shifted so as to bring a new portion of the surface underneath
the point of the wire. This cycle of operations was repeated
until the entire surface was covered with wax figures. (See
Plates 26 and 27.)

This method is simple, inexpensive, and, if used with care
and a little skill, effective; moreover, it required but little appa-
ratus which was not at hand either in the petrographical or in
the physica! laboratories.

Vou. 4] Thelen.—Thermal Conductivities of Certain Schists. 213

A word as to the kind of point filed on the wire will not
be amiss. At first it was the tip of a long cone, but no heat
ean flow across a point, and the tip of the cone had to come off.
The question was how much of it, how large a section would
eive the best results. Without going into the details of differ-
ential heat equations, there are in general two limits to be dis-

Fie. 3.

ecussed,—a very large section or a very small section. In the
ease of the latter (fig. 4), the only objection is that the heat
which flows across can be dissipated from the surface of an
ellipse which is very small indeed. In the case of the former

Fic. 4. Fie. 5.

(fig. 3), both « and y would be greater, but a good contact of
the wire on the rock could hardly be expected. Figure 5 indi-
eates roughly what might be obtained in the way of a contact,
where the unshaded portion would show an air film between
the copper wire and the rock. Then, too, a large section that
is as nearly circular as it can readily be fashioned, would give
appreciably different values for the diameter in different direc-
tions, and d, would not be a true constant. Another element
which might be worth considering is that, in measuring many

214 University of California Publications. [GEOLOGY

hundred ellipses, the time consumed in racking the microscope
tube back and forth over a large dead area would be very consid-
erable.

The cone was trimmed back three times in the early stages
of the work, and was used for most of the tests with a diameter
d,—1.20 mm. The total diameters of the ellipses varied from
3.00—6.00 mm., most of them being very near 4.00 mm. The
traveling microscope which was employed read distances to
1/400 mm. and throughout the work this smallest reading of the
instrument was taken as unity. Thus the constant subtracted
for d, was 480, since 480 (1/400 mm.)=—1.2 mm.

Thus the ratio of two axes might be 1334/1673. From this,
the corrected ratio is found to be (1334-480) /(1673-480), or
Slits

To facilitate finding the limits of the wax figures under the
microscope, it was found advisable to scratch a number into the
wax on the inner flanks of the figure, and, in a few eases, to
delimit the field by scratches, as in fig. 6. Oblique natural light

Ges

Fic. 6.

was used. The shadows which it cast around the figure as a
whole were of no value, but it brought out very clearly, by high
lights, the extremely fine-grained, uniform texture of the twice
melted wax, as compared with that which surrounded the figure
and which had been melted but once. It was very easy, by ob-
serving this distinction, to follow the line of contact entirely
around under the microscope, and any figure which showed irreg-
ularity in outline was rejected.

The ratios of the three axes of the triaxial ellipsoidal iso-
therms are uniquely determined by measurements in two prop-
erly chosen sections, but a third section of each rock was taken
as a check.

Vou. 4] Thelen.—Thermal Conductivities of Certain Schists. 215

For the purposes of demonstration, that is, to obtain wax
fieures which would stand out prominently, and which could
easily be seen and photographed, numerous expedients were tried.
Paris white and various Diamond Dyes were dissolved in the
wax to give it body. Paraffin and beeswax were used. Nothing
more satisfactory than white wax developed, and the pictures
show that it was unnecessary to waste further time in experi-

menting along this direction. (See plates 26 and 27.)

THE CONVENTIONS USED IN SPEAKING OF THE SCHISTS.

For convenience of reference, the three axes will be denoted
by A, B, and C, as in erystallography, the rocks being set up
according to the following scheme. A plane parallel to that of
the schistosity always contains A and B, and will be designated
as the top face of the rock. If in this plane there exists also a
linear orientation of the erystals, this direction is A, and is placed
pointing directly away from the observer. If the schistosity,
however, appears to be linear, only the A axis is fixed, and the
choice of the top face is arbitrary until measurements on the
face perpendicular to A give the direction of the major axis of
the ellipse on this face. The direction of this major axis and
that of the linear schistosity then determine the basal plane. If
the schistosity is of two dimensions, but there is no linear orien-
tation of the erystals, only the top face is determined, and, if
the conductivity depended upon the structure, we would expect
to find equal conductivity in all azimuths in this plane. Hence
the directions of A and B become matters of indifference.

With our schists thus set up, we can imagine each rock eut
into the shape of a rectangular parallelopipedon, with the pina-
eoids each containing two axes, and then we may use the term-
inology of the orthorhombic system, since all four rocks yielded
heat conductivity ellipsoids which are analogous in every impor-
tant respect to the lght conductivity ellipsoids of the ortho-
rhombie system,—the axes of elasticity are unequal, are rect-
angular and coincide in direction with the three rectangular
crystallographic axes of symmetry.

We have then, in general, three sections to work upon: the
top or basal pinacoidal face (containing A and B) shows the

216 University of California Publications. [GEOLOGY

effect of the linear orientation; the end or macropinacoidal face
(containing B and C) shows the effect of the schistosity ; and
the side or brachypinacoidal face (containing A and C) shows
the effect of the schistosity superimposed upon that of the linear
orientation. The two effects were found in all cases to be super-
imposed in the same sense,—to have the same sign. However,
as the experiments indicate that the effect of structure in itself
is zero this coincidence is an accidental one and is to be explained
in terms of the thermal conductivities of the constituent minerals.

THE ROCKS INVESTIGATED AND THE RESULTS OBTAINED.

Four typical metamorphic schists were investigated. Each
specimen which was used possessed to a remarkable degree uni-
formity of distribution of mineralogical constituents, and uni-
formity in the strong development of the schistosity. Each rock
will be deseribed in detail later.

At the temperature of the melting point of the wax (63.6°)
C., the ratios of the three axes of the triaxial heat-conductivity
ellipsoids were found to be as follows:

(Observed. ) (Computed. )
A B/A C/A C/B C/A+B/A
Hornblende schist 1.00 942 .885 . 961 . 940
Glaucophane schist 1.00 . 961 . 743 . 769 773
Quartzose schist 1.00 - 906 . 860 . 947 . 949
Mica schist 1.00 . 894 .715 . 808 .800

(Fort Wrangell).

The fifth column is the quotient of the third by the second
and should equal the fourth column.

These results are the average values for a large number of
observations, and a few words as to their probable accuracy are
in place here. There is no doubt that each individual reading
truly represents the length of that line, measured to 1/40 mm.,
for the method of checking results showed that the lengths were
being measured accurately. The tube was racked across, read-
ings were taken at A and B, fig. 7, and the screw was given an-

Fig. 7.

Vou. 4] Thelen.—Thermal Conductivitics of Certain Schists. 217

other turn. Then the motion was reversed. As the lost motion of
the instrument was considerable, readings were obtained at C
and D which were numerically different from those at A and
B. If the two values of the differences of the readings agreed
within ten units, as they easily did, no further measurements
were taken on that axis.

It was found in the early stages of the work that the prob-
able error of the mean of a number of observations on different
figures on the same face could be kept under one per cent., with-
out taking an unreasonably large number of readings,—not that
the homogeneity of the rock was sufficient to give the same results
on spots a few em. apart, but the mean value represents the
average ratio over a large portion of the specimen. One per
cent., then, was set as the limit of the probable error of the
mean value of any one ratio, and the number of readings was
increased where necessary till this accuracy was obtained.
Columns 4 and 5 of the table show that this intention was prob-
ably realized.

Senarmont, working with the largest obtainable monoclinic
erystals, said: ‘‘Selten sind die drei Beobachtungen einer
solechen Genauigkeit fiihig dass sie einer numerischen Vergleich
gestatten.’’ But his material was not always. satisfactory.
With a good specimen of calcite, he obtained on one face ten
values varying from 1.09 to 1.19. Such is about the range ob-
tained in the most unfavorable cases by the writer. The end
section of the Wrangell schist yielded 19 results varying in value
from .773 to .892. The probable error of the mean, .808, com-
za 5 ae
- ame 009.

A rhombic section parallel to A of the same rock, yielded as

puted by the familar formula 1=.67454|

the most favorable case, seven values ranging from .810 to
.835, with a probable error of the mean, .823, of .002. Of
course the term probable error is really a misnomer, for this is
not a case of measuring the same quantity a number of times,
since neither the homogeneity of the rock, as before suggested,
nor its uniformity of structure, as will be shown later, are such
as to lead one to expect the same ratios at all points of any one
surface. (A fresh crystal, however, might be expected to do this.)

218 University of California Publications. [GEOLOGY

PETROGRAPHY OF THE SCHISTS.

The Hornblende Schist—This rock comes from Yum-Yum
Lake in the Rainy River District, Ontario, Canada. Under the
microscope it was the only one of the four schists whose sim-
pliity of structure was such as to enable a satisfactory deduc-
tion of heat-conductivity ratios from a knowledge of the struc-
ture, and of the thermal conductivities of the constituent min-
erals.

The rock is entirely crystalline. The structure corresponds
to the allotriomorphie granular of igneous rocks. Foliated strue-
ture is well developed. Quartz (x) is the only mineral that
shows the results of dynamic metamorphism well developed,
and even here wavy extinction is not prevalent.

The constituent minerals are :—hornblende, quartz (x), quartz
(y), orthoclase, acid plagioclase, epidote, titanite, apatite, mag-
netite, hematite.

The tendency toward idiomorphism of the constituent min-
erals decreases in the same order as in those igneous rocks in
which the normal order of erystallization is followed. Thus in
the order of strongly developed idiomorphism come (1) apatite,
(2) magnetite, (38) titanite, (4) hornblende, (5) the others.

Three slides of the hornblende schist were made, parallel
respectively to the bottom, side and end of the rock.

The hornblende makes up probably a good one-third of the
rock as judged from the slides. The idiomorphie character is
not very well marked. The prism faces and the eclino-pinacoid
are fairly well developed; in the case of the former, this may
be due to the well-marked cleavage rather than to any strong
idiomorphie tendency. The habit is elongated parallel to c.
The pleochroism is very marked. The colors are: Aa—light
brown or yellow; D—dark brownish black or greenish. black;
C—sea green (if very thin) to black. Absorption—b=c > a,

The hornblende shows a remarkable uniformity of erystallo-
eraphie orientation. The parallelism of the longer axes could
be seen macroscopically, and since the habit is elongated parallel
to c¢ in every ease, all ¢ axes are parallel. The bottom and
side rock sections but rarely showed any prismatic cleavage.

Vou. 4] Thelen.—Thermal Conductivities of Certain Schists. 219

The end section showed well developed prismatic cleavage in
nearly every specimen. Here none of the minerals were cut
even approximately parallel to c. The acute prismatic angle
varied but little on either side of 56°. The longer diagonals of
the cleavage parallelograms of the sections were roughly parallel
to b. The uniformity of the orientation was not as marked as
that of the c axes in the bottom or side sections of the rock, but
it was strongly developed.

The orientation of those basal sections which were devoid of
the traces of the prismatic cleavage was readily determined by
the pleochroie colors. In fact, the whole scheme of orientation
was first worked out independently by means of the pleo-
chroism, then by means of the cleavage.

The arrangement of the other minerals follows no law. If
the hornblende were eliminated from the rock, there would be
no reason why the wax figures should vary from the circle.
And the smoothness of the cirele would be marked because, in
general, the crystals are so small that their heterogeneously
arranged variations in conductivity could not seriously affect
the outline of the cirele.

The relative thermal conductivities of the rock are very
satisfactorily explained by taking account of the relative con-
ductivities of the hornblende.

These are 1.00: .71?: .80.

The first number is for an axis which very nearly coincides
with c; the third is for an axis parallel to 6, and the second
is perpendicular to these two.

If we assume one-third of the rock to be hornblende, or im-
agine the whole rock to be one large erystal of a hornblende in
which the differences in thermal conductivities have been
diminished by two-thirds, we would have a ratio of

1.00: 1.00—(1.00—.71?) /3: 1.00—(1.00—.80?) /8.
This yields a crude approximation to the values we should find.
The ratio reduces to 1.00: .914°: .938°. The rock shows a
ratio of 1.00: .885°: .942? for directions which nearly coin-
cide with those of the hypothetical hornblende erystal. The
coincidences of the second members is not remarkable, but that

220 University of California Publications. [GEOLOGY

of the third is. If this explanation is the correct one, then the
thermal conductivity of this rock is very definitely merely the
integrated effect of the thermal conductivities of its constitu-
ent minerals, and the structure of itself is of no consequence.

A brief deseription of the other constituent minerals of the
rock is essential in order completely to individualize it.

Quartz (x) occurs in large lenses in large fragments. <A
cross section of these lenses may be as much as .2 by 3.0 cm.
The individual fragments show no uniformity of orientation,
and some of them show a greatest dimension of .8 em. A wax
figure that covered a part of such a large fragment would natur-
ally be unsymmetrical. The non-uniformity of orientation of
the fragments of these lenses is shown by the diagram fig. 8,
the result of a few minutes of work with the quartz wedge. The
interference color shows how nearly the axis of elasticity is per-
pendicular to the section, and the line shows the projection of
this axis on the plane of the section.

‘i <—> ce

yellowish white indigo indigo. white. gt blue orange. orange.
Fic. 8.

The quartz (y) and the feldspars give the rock its uniform
allotriomorphie granular character. There is ttle variation in
size of the grains. <Albite twins are searce but not rare. The
extinction angles of the twins, measured from the traces of the
planes of composition, are low. This latter fact and the uniform
eray blue tints of the feldspars indicate the absence of any pla-
cioclase more basic than oligoclase or andesine. If we remember
that in non-igneous rocks the albite twins of the feldspars need
not be well developed, we find it impossible to separate the feld-
spars into orthoclases and plagioclases. Quite a few carlsbad
twins are present, however, and these tell us something.

The quartz makes up about 1% of this aggregate of feldspar
and quartz. It is easily recognized by its yellow interference

Vou. 4] Thelen.—Thermal Conductivities of Certain Schists. 221

tints and such identifications are always corroborated by the
characteristic undecomposed faces and by the Becke test.

The titanite is very uniformly and plentifully distributed in
small rounded or rhombic shaped sections.

The epidote oceurs in small fragments very sparingly distrib-
uted.

The apatite is very abundant in small idiomorphie crystals.

The magnetite is all in fairly large grains. One cross-section
shows a maximum diameter of over 1 mm.

The hematite occurs in a few blood-red blotches.

Broad zones of strongly developed kaolinization permeate the
rock. There are no fissures observable alone these zones and the
reason for their presence is not apparent.

The Glaucophane Schist—tThis is a local schist from Berke-
ley. The rock is wholly crystalline. The structure corresponds
to the allotriomorphie of the igneous rocks. Foliated structure is
well developed. The constituent minerals are :—glaucophane,
lawsonite, acid feldspars, and epidote.

Glaucophane makes up over 80 per cent of the rock. The
habit is elongated parallel toc. C:¢ is less than 6 degrees. The
optical orientation is very easily determined by the pleochroic
colors. These are as follows: C—sky blue to ultramarine blue;
b—reddish or bluish violet; @—yellowish to colorless (white) .

The individual erystals are small. The bottom slide contains
C of every erystal and @ and b, or components of both promis-
cuously. Thus with the upper Nicol out, the tint of the rock as
a whole varies uniformly as the field is rotated.

The side and end slides show a parallelism of the traces of
the ¢ axes, but the axis itself may he in the plane of the slide
or make any angle with it. Thus many sections show the pris-
matic cleavage, many sections contain @ and C, many contain
band ¢.

The structure of the glaucophane in the rock is then appar-
ently as follows:—all the longer axes (c) lie in planes parallel
to the bottom of the rock; in each plane the c axes point in all
azimuths indifferently. There is no uniformity of orientation of
a and 6 whatever.

222 University of Califorma Publications. [GEOLOGY

Then in the table on page 216 we would expect to find under
the glaucophane schist that B/A=1.00, and that C/A=C/B.
But B/A as measured on one face gives .961; and computed from
the two other faces,C/A—C/B=B / A=.743 /.769=.966.

The lawsonite in the rock may explain this discrepancy. This
mineral makes up from 5 to 30 per cent of the rock. It gives
the rock a tendency toward gneissic structure, some portions
being almost free from it, others very largely composed of it.
The rock slide parallel to the end shows elongated sections with
both C and b parallel to the elongation, and also parallel to A.
The side slide shows more nearly square sections; they are not
as uniformly oriented, nor are they as numerous.

The base shows very much albite and all kinds of orientation
of the lawsonite. Of the latter most sections are elongated, and
¢C is always perpendicular to the elongation.

No data are available for the thermal conductivity of either
elaucophane or lawsonite. If the glaucophane were the only
constituent, we might work backward and get a general idea of
the relative thermal conductivities of this mineral. As it is,
the study of this rock is of no value for our work. However,
it throws some further heght on the structure of schists, and
strenethens the idea that the structure of the rock in itself has
no effect upon the elasticity of the ether in different directions,
but that the thermal conductivity of the rock is the sum of the
thermal conductivities of the constituent minerals.

The Quartzose Schist (Whetstone).—This rock is used as a
whetstone. It comes from Telemarken, west of Laurdal, Nor-
way. The constituent minerals are muscovite, quartz, calcite,
magnetite, and biotite.

In the bottom and side slide the quartz appears in unelon-
gated grains.* There is no uniform orientation, as is seen by
all heights of interference colors, and all orientations of the
axes of elasticity. The quartz nearly all shows a stepping of
the colors with the Nicols crossed. This is due to the angular
nature of the fragments. In addition to this evidence of hard
usage, the quartz shows conditions of strain at present. It appar-
ently makes up over 70 per cent of the rock.

Vou. 4] Thelen—Thermal Conductivities of Certain Schists. 223

In both of these sections the calcite appears in elongated
rectangular sections parallel to the peneil structure of the rock,
but making various extinetion angles with this direction, as in

fie. 9.

ee

Fig. 9.

The muscovite is very abundant, filling in the spaces be-
tween the quartz. Some sections lie in the planes of these two
slides, others are apparently on edge; still others occupy inter-
mediate positions. These two sections would indicate the pres-
ence of 15 per cent of muscovite.

The end section presents an entirely different appearance.
The quartz grains seem much more numerous and closely packed,
none of them being masked by muscovite. The muscovite here
appears as foliae interstitial between the quartz, and forming
a network of red, green and violet ‘‘Fisseln,’’ as seen under
erossed Nicols. None of the characteristic elongated sections of
ealeite appear here.

Summary of the structure of this rock :

The muscovite occurs in minute flakes whose planes are
always perpendicular to the end section of the rock. Without
checking by chemical analysis and mindful of the deceptive
masking power of muscovite, we may assume it to make up 6 to
8 per cent of the rock.

The quartz makes up 90 per cent of the rock and in those
few sections which show one greater dimension of the fragments
these are generally parallel to A of the rock. But this dimension
has no relation to any axis of elasticity of the quartz.

The calcite occurs in pencil shaped forms with the ratio of
dimensions about 4:1:1. All the long axes are parallel. It shows
evidences of strain. It constitutes about 1 per cent of the rock.

A few flakes of biotite occur, also a few grains of magnetite.

A single case of polysynthetie albite twinning was observed.

*Cf. Rosenbusch’s Gesteinslehre, p. 501.

224 University of California Publications. [GEOLOGY

This rock is then again unsatisfactory for making numerical
comparisons. One would from this expect the heat conductivity
ellipsoids to be nearly spheres.

The Wrangell Mica Schist—This rock comes from the Stic-
keen River District in Alaska. Large, perfect crystals of andra-
dite* occur plentifully. The schistosity of the rock is due mainly
to the uniformity of orientation of the mica plates. The frae-
ture is roughly undulatory, not planar, and is good at as widely
different directions as those represented by 11 and 12 of the
figure. Almost any section perpendicular to A shows, when pol-
ished, beautiful mica spangles. Especially is this so of the bottom
section.

Under the microscope it is seen that the micas le with their
basal planes within 15° on either side of B. Hence slide 14 and
slide 10 (in the plane of the paper) show cleavage and pleochro-
ism in most sections. The cleavages are parallel enough here to
give the rock a uniform tint, and one which changes very decid-
edly as the stage is rotated; the pleochroism is very marked and
the absorption strong. The pleochroic colors are dark red brown
parallel to the cleavage and colorless to very pale grayish brown
perpendicular to the cleavage. The basal sections show slight
pleochroism. The extinction angle is uniformly very near zero.
The mica makes up a large part of the rock.

Silimanite is very plentiful in slides 14 and 12 as though
its distribution were roughly planar also. The needles are so
extremely fine that they defy detection, generally, if they occur
in cross section. They occur in long attenuated crystals, often
erouped radially. Their occurrence seems to be governed in
some way by the presence of the micas. The index of refraction
is very high, as compared to quartz by the Becke test, and the
dark total reflection borders generally meet and mask the color.
On some crystals, however, it can be seen that the color varies
from colorless to a very definite pale green or bluish-green. A
protracted search showed transverse cracks in only three of the
needles. The birefringence is quite high, as even these fine
needles affect the interference color of quartzes lying in the same
vertical plane. The extension is positive.

* Of. analysis by A. S. Kuntze. Dana’s System of Mineralogy, p. 444.

Vou. 4] Thelen.—Thermal Conductivities of Certain Schists. 225

The quartz is very abundant. It oceurs in small grains whose
angular character is well brought out by the stepping of the
interference colors. It is full of dark spots and fine inclusions
the latter largely apatite. Feldspars are very rare. A few ortho-
elases and acid plagioclases were found.

Apatite oceurs plentifully, both as inclusions in quartz and
as fairly large erystals between the quartzes.

The magnetite is very plentiful in small grains, usually asso-
ciated with decomposed micas. Pyrite oceurs irregularly. In
a few places half of the field is pyrite. It seems here to be oceu-
pying the place of micas too, though the latter contain no sul-
phur. Hematite and titanite occur rarely. A few large sections
of clinochlore were found.

The axes of the wax figures gave results of 1.000: .894: .715.
It is manifestly impossible to tie these results down numerieally
to the known thermal conductivities of the constituent minerals.
The undulatory fracture indicates that no results of any value
for our work ean be obtained. The presence of small garnets
and loeal impoverishments due to their formation points in the
same direction. The numerical results checked more poorly than

Fic. 10.

for any other rock, necessitating the reading of several dozen
ellipses on one face to get the probable error. Thus (fig. 10) read-
ings on the face y reduced to 100: 79.7 for 4: y; and on the face
x reduced to 100: 86.9 for A: x But on the face perpendicular
to A the values were 100: 80.8 for B: C. If we construct an

226 University of California Publications. [ GEOLOGY

ellipse with major and minor axes 100 and 80.8 and take B :y==

30° and B:7—20°, the equation of the ellipse gives us that
79.7 K cos 30°)? 79.7 K sin 30°)?
Oe) | Gana

and

(62 K cos 20" 2 cee K sin ae —_ 1
100 80.8

Kv is the same in both equations. Solving the first equation we
eet K==1.18. Solving the second equation we get K=—1.12. The
two values do not check satisfactorily, and emphasize the conelu-
sion arrived at from a miscrosecopie study of the rock structure,
namely, that it is wiser not to draw any conclusions from the
study of this specimen.

University of California,
May, 1905.

BULL, DEPT. GEOL, UNIV. CAL. VOL 4, PE: 26

Fic. 1.
Hornblende schist from Yum-Yum Lake, Canada. End _ section.

Fic. 2.
Glaucophane schist from Berkeley. End _ section.

Fic. 3.
Fort Wrangell mica schist. Parallel to 4 (y of text fig. 10).

BULL. DEPT. GEOL. UNIV. CAL. VOL. 4, PL. 27

Fic. 1.
Hornblende schist from Yum-Yum Lake, Canada. Side section.

Fie. 2.
Quartz schist. Laurdal, Norway. Bottom section.

Fig. 3.
Glaucophane schist from Berkeley. Side section.

UNIVERSITY OF CALIFORNIA PUBLICATIONS

BULLETIN OF THE DEPARTMENT OF

GEOLOGY

Vol. 4, No. 12, pp. 227-262, Pls. 28-30 ANDREW C. LAWSON, Editor

SKETCH OF THE GEOLOGY OF MINERAL
KING, CALIFORNIA

BY

A. KNopF AND P. THELEN

CONTENTS.

PAGE
Introduction —.................- Meee nate to oete ome c veers ceeraats Fo oe es Sere ee eee ae eres ee 227
GOT OF DIY, esac casera et as casee aaa cs ease Sec ona pee ise ease cea etaeeetearens Feet eae rs een eee OO
(GT eae biG riers eater en wwe eee ce cece acer oes sets ta cet ecees caSeau sptet ven te oweced aces uaaeesteeee-coasceeeestoate 230
JD cop MDAKoNaT he TH aNss MOY OLY SAY Ol hi ee a ee eee ee ZBI)
Evidence as to Mechanies of Glacial ErOon Be eee eras crate te eee eee OS
The Granitic and Associated Igneous Rocks ~......-2222022--22-- eee eee sp 2B YE
PINE R: CET ATINGLC MIEVOCKS ae tees ces ccn te cae nee stares re egies eee eet ee 234
HraXelhuksyKoy chsh shat recy (Ca feb abies) eee ere ee ere ee ee eee A]
Warten; UMGRUSIVOSs Bssecet es ece ce tteecccstceesde costs. sas cceethessseteeeesaeeee ee eeeemeser tees LOO
BY 01a LC 0911 Bs a ea nye eee meee ee eran 240
Tourmaline granite and andesitic dykes -...2.......2.220222222..22.2022-s22neeo- 241
Me pS Gra butted O CMS meres: sees cce sees eee crocs eee se rae een cory)
Grenier WRG) a G1 Oni Se cease een er ce ee eg ee ae eee ect 242
SKeenakoyal EXentoysis| Ura eyere (CRYO) ee eee 243
dA SU9 09 01 yn A ET re -e 244
Sheared Quartz Porphyries from the Little Kern .000000000...... 250
WVace) Wilrositss LER SHWE! YOM MANT OSS os eee ee ee 252
The Contact ...... Seas dade a anne Sc Sota ae sb eee oe eee cao web oven et ooR Sopa taster eeceste eases OL
CrovamPeKeL; INSTR MaMeN evs, a ee HY)
The Relation of the Mineral King Belt to the Granite 00000000000... 258

INTRODUCTION.

Mineral King is situated on the headwaters of the East Fork
of the Kaweah River near the western crest of the southern
Sierra Nevada. This portion of the range is known as the High
Sierra, and is preéminently distinguished by the sharply serrate
character of its profiles and the vast assemblage of lofty peaks.

228 University of California Publications. [GEOLOGY

Of these none illustrate more impressively the peculiar felicity
of the term ‘‘Sierra Nevada’’ than does Sawtooth, under whose
shadow Mineral King lies. Mineral King occupies very nearly
the north center of a narrow belt of sedimentary rocks, now
more or less schistose, some 14 miles long and 2 miles wide, and
striking N.N.W. This area of stratified rocks represents an
isolated remnant of the extensive terrane into which the Sierran
batholithic magmas were intrusive during Mesozoic time. The
hypsometric relations disclose the fact that the schists are deeply
sunk into the granites, and make it obvious that their preserva-
tion is in large part due to this favoring circumstance. The
belt has been strongly mineralized, whence its name, and has
invited a large amount of prospecting, but exploitation has not
proved profitable. The region was traversed by Professor
Lawson in his physiographic reconnaissance of the upper Kern
Basin, and its salient features outlined and discussed in concise
form. It was suggested by him to the writers as an interesting
field for more detailed study, especially in regard to its contact
phenomena and its stratigraphy. We wish here to express our
sincerest acknowledgments of his ever ready help and encour-
agement.
GEOMORPHY.

The portion of the region with which we are here concerned
cannot be said to constitute a geomorphic unit. In its longi-
tudinal extent it embraces a linear succession of strike valleys,
whose profiles show the glacial U-shape in splendid development.
The tributary streams, heading invariably in rock-rimmed
lakelets, drain across the upturned edges of the strata. and
enter the main valleys by series of waterfalls, often several hun-
dred feet high. This lack of adjustment between master stream
and lateral drainage is particularly well exemplified by the
valley in which Mineral King is situated. This valley is broad
and flat-bottomed in its lower extremity, its walls are sheer, and
have shed sufficient talus to yield a U-profile of ideal perfee-
tion. The floor of the valley is built up of glacial debris,
through which the stream meanders in short tortuous curves,
at an average grade of a hundred feet to the mile. Just below

VoL. 4] Knopf-Thelen— Geology of Mineral King. 229

Mineral Kine, the Kaweah suddenly swings through 90° and
commences its rapid descent down the western flank of the
Sierra Nevada at a rate exceeding 600 feet per mile. These
various physiographie features are readily discernible upon the
contour sheet, and hardly need comment.

The relief of the region is exceedingly bold and rugged,
varving from a maximum of 12,405 on Florence Peak to 6,500
feet on Chiff Creek, or over a mile in altitude. The crest lnes
are fierce and jagged, and consist characteristically of huge
angular spauls of rock recumbent in various unstable attitudes,
like a chaos wrought by the play of titanic forces. They are
impressive evidence of the vigor and destructive intensity with
which weathering progresses on alpine heights. Products of
secular decay are nowhere present.

Great talus heaps mantle the bases of the cliffs. These ac-
ewmnulations vary in character with the lithologie habits of the
parent chff: the schists, quartzites and plutonic intrusives yield
irregular confused aggregates of large angular blocks of widely
varying sizes; the clay slates, on the other hand, encumber
enormous slopes with fresh and unaltered debris which is uni-
formly of the size of a fist. :

Occasionally deep sand slopes are developed. The produe-
tion of these within this area seems to be determined by petro-
eraphical influences. The sand consists of the loose acemnuula-
tion of fragments of disintegrated granite, often up to the size
of a walnut, and grains of quartz and feldspar which still pre-
serve their pristine freshness.

Characteristic accumulations occur at Sawtooth Peak, where
the granite possesses a striking individuality. This granite is
a coarsely granular aggregate of quartz and orthoclase. with
very smal! amounts of hornblende and biotite. The quartz
occurs typically as anhedrons of the size of peas uniformly
seattered throughout the rock. The sand slopes are limited to
this particular variety of granite, and it is significant in this
connection, that the quartz-mica-diorites, which are rocks of firm
and closely coherent texture, do not yield sands under the same
conditions, but produce great talus heaps.

230 University of Califorma Publications. [ GEOLOGY

On the eranites west of Vandever Mt. is a plateau surface
whose profile against the sky line shows smoothly flowing linea-
ments, and which represents the nearly obliterated remnants of
an earlier geomorphie eycle.

GLACIATION.

Evolution of the Topography.—The region bears abundant
evidence of a former severe alpine glaciation, which, neverthe-
less, must be regarded as having been of comparatively limited
duration. There is a general absence of well-defined terminal
moraines. A heavy deposit of lateral morainic material flanks
the west wall of Mineral Kine valley some 800 feet above its
floor. Half a mile below Mineral King striations show that the
elacier was not less than 1,000 feet thick. At the confluence of
Deer and Chiff Creeks is a great medial moraine consisting
almost wholly of angular blocks of quartz diorite, which has
shifted the junction of the tributary considerably down stream
alone Cliff Creek. The evidence from the character of the
moraimie material indicates that the tributary glacier, having but
a feeble catchment area, receded before the main glacier of Cliff
Creek commenced to wane, which then dammed up the mouth
of its affluent. Toward the head of Cliff Creek not more than
a quarter of a nule from the cirque a low embankment of loose
angular blocks spans the canon from wall to wall. This is the
only typieal terminal moraine occurring within the confines of
the region under discussion.

The extreme recency of the disappearance of glacial eondi-
tions is shown by the preservation of highly polished surfaces
upon exposed granites, and of groovings and striations upon
soft schists, and perhaps still more emphatically, by the insig-
nificant amount of post-glacial stream erosion. This latter ree
limited itself to a slight notching of the cafion bottoms, but has
not yet advanced far enough to remove the veneer of glacial
material from the floor of Mineral King valley.

The glaciation has left its profound impress upon the
geomorphic configuration of the region: in the production of
numerous amphitheatres and encircling arrétes ; in the formation

VoL. 4] Knopf—Thelen.—Geology of Mineral King. 231

of strings of rock-rimmed lakelets, and in the development of
splendid U-shaped valleys. The ideal character of the U-profile
of the main valleys—Cliff, Mineral King and Little Kern, has
been alluded to and the strong discordance between lateral and
main drainage pointed out. This lack of stream adjustment is
all the more remarkable when considered in the leht of the
Pleistocene history of the range. The post-Pliocene uplift tilted
the Sierra Nevada orographie block to the west, the upheaval
in this portion of the range being not less than 10,000 feet, and
has thereby enormously accentuated the grade of the westward-
flowing streams. The drainage is still in the early consequent
stage, and the trunk streams have, in other portions of the range,
eut below their meridional tributaries and left them hung up. At
Mineral King, however, the orientation of the hanging valleys is

a strike stream erod-

irregular and unsystematic. Deer Creek
ing on ¢elay slates and flowing north—is in poor adjustment to
Cliff Creek, a stream flowine westward on granites. The
streams heading respectively in Monarch, Crystal and Silver
Lakes, and plunging down to the Kaweah at an average
rate of 1,800 feet to the mile across the upturned edges of the
schists, afford strong examples of hanging valleys. The two
tributaries from the western side of the valley of Mineral Kine
have not yet sueceeded in even gashing its wall. The valley in
these discordant relations to its lateral feeders is a strike valley
for the greater part of its length. Above its abrupt bend to
the west, it can be divided into two approximately equal por-
tions, a lower portion, which is veneered with glacial debris,
broad, flat-bottomed and of remarkable easy grade in spite of its
high altitude (7,800 feet); and an upper portion extending to
Farewell Gap, incised by post-glacial erosion, steeply graded,
but showing to some extent the step-lke progression character-
istic of the lateral valleys. The transition between the two por-
tions is relatively abrupt, and is coincident with the entrance of
two lateral hanging valleys—Silver Lake on the eastern side, and
White Chief on the western. Below Mineral King the valley
cuts across the slates and schists into the granite, but does not
change its essential character, except that it becomes broader.

232 University of California Publications. [ GEOLOGY

Below the lower limit of glaciation—the 7,000-foot econtour—it
assumes a strongly consequent character, becoming V-shaped
and taking on a grade of 500 feet to the mile. It is therefore
evident, as an observational fact, that a valley of strongly
marked individuality has been carved out coincident with the
leneth of the ice stream, and that its evolution has been inde-
pendent of lithologie control, inasmuch as its distinctive features
are found equally well developed in firm unweathered granite,
and aeross the strike of slates as well as along their upturned
edges.

The Little Kern River is bordered by high hanging valleys
in its upper region, but immediately below the lower limit of
elaciation, the lateral streams are in complete accordance,
notably the Shotgun and the Rifle. To sum up, the hanging
valleys do not show any systematic arrangement such as would
be produced by selective or differential erosion, or by faulting,
but are inseparably associated with the evidences of glacial oc-
cupation.

The lateral valleys consist of a series of irregular steps, the
suceessive treads of which are usually occupied by rock-rimmed
lakelets. These lakes do not owe their origin to morainal dams,
but fill basins eroded out of the solid granite. Their depth is
small, perhaps never exceeding 30 feet. Some few have become
silted up, giving rise to beautiful parks through which the
mountain streams wind leisurely. The uppermost lake always
occupies the circular basin of the amphitheatre at the crest of the
range; the succeeding lakes are separated by differences in alti-
tude of several hundred feet, and are invariably situated at the
foot of the abrupt changes of elevation. The tarns are not eon-
fined exclusively to the granitic rocks, but occur also upon the
sedimentary rocks.

In a number of instances cirques have been evolved partly in
eranite and partly in the sedimentary series, notably at Monarch
Lakes, Crystal Lake, Silver Lake, the lakes 8.W. of Florence
Peak, White Chief and at Eagle Lake, and it is a noteworthy
fact that in each case the symmetry of the amphitheatre has in no
way been impaired or diminished. (See Plate 28.) <A curious

VoL. 4] Knopf—-Thelen.—Geology of Mineral King. 233

feature, whose significance is not entirely plain, is the tendency
of the lakelets near the head of any lateral valley to associate
in pairs, of which the lower is the complete analogue of the
upper; see especially Monarch and Florence Lakes.

Evidence as to Mechanics of Glacial Erosion—The tributary
glaciers have not evolved the perfect U-profiles so characteristic
of the main drainage lines, but are more of the nature of broad
and relatively shallow troughs. The troughs upon the western
flank of Mineral Kine are flat-bottomed, of few steps of long
tread, and of nearly horizontal floor. On the eastern side the
treads are shorter and more numerous, and the floor less regular
and often approximating a V-shape. This V is not of post-
elacial origin, but is grooved and striated in its upper portion,
thus testifying to the efficiency of the subglacial streams. Every-
where are abundant evidences of the extreme receney of the
glacial evacuation of the region. It is as if the ice had ceased
its activity yesterday, and had left incomplete the work it had
inaugurated.

The lateral valleys, particularly that of Monarch Creek,
illustrate in no uncertain way the mechanics of the processes
coneerned in their evolution. The sides of the valleys consist
of an ascending series of stopes, like the benches of a quarry,
spreading laterally from the stream course as a medial ne. The
reeularity and persistence of this phenomenon is closely de-
pendent upon the perfection of the jointages, and is often truly
remarkable. The jointage to which the bed of the creek is
parallel controls the front face of the stopes, while a second
jointage intersecting the former at an angle near 90° deter-
mines the floor. The salient angle thus formed has been rounded
off to a slight extent, but upon the front face of the stope may
still be seen partially obliterated inequalities of surface. These
are jagged and angular in their innermost recesses and represent
uneven fracture planes of the rock masses torn out by the ice
from their positions. The front face of the stopes is nearly
vertical and may have a height of from six to eight feet, and
occasionally even up to fifteen feet. The rocks of Monarch
Creek are of stratified character, but similar bench-like forms

234 University of California Publications. [GEOLOGY

have been produced on the jointed granites at Silver Lake, and
it is obviously apparent that the phenomenon is independent of
lithologie control.

That the term ‘‘quarrying’’ is no mere figure of speech is
foreibly brought home by the photograph shown in Plate 29B.
This was taken on Crystal Creek at an altitude of 10,000 feet
in a valley hung up 2,000 feet above Mineral King. No less
than five benehes are shown, scarcely distinguishable in their
perfection from the labored handiwork of man. They are
quarried out of a strongly sheared andesite in steps up to fifteen
feet high, and display the efficient utilization of the two dominant
jointages. The ineffectiveness of glacial abrasion compared to
the process of plucking is also clearly revealed.

It has been mentioned that on Monarch Creek alone with the
numerous quarry-like benches evidences of a glacially striated
notch oceur in the bottom of the trough. Similar subglacial
channels are reported from the Unter Grindelwald glacier and
from the Yosemite Valley, and are held to furnish proof of the
feebleness of glacial erosion. At Monarch Creek, however, the
evidence is clear that the subglacial notch was an active co-
Operant with the glacial processes. The heavy grade of the
stream limited its energies to the downward corrasion of its
bed, and eaused the incision on the floor of the valley of a narrow
channel. To the ice was left the quantitatively much greater
task of excavating the main trough and maintaining the typical
character of the U-profile. It is a well-known principle to the
quarryman that the facility with which large blocks can be re-
moved is greatly increased by the number of free faces exposed
to attack. The downward channeling action of the subglacial
stream, therefore, afforded a vantage line for the quarrying
ability of the ice, and has enabled it, by utilizing the latent free

faces—the jointage planes,—to evolve the characteristic bench-

like forms.
THE GRANITIC AND ASSOCIATED IGNEOUS ROCKS.

The Granitic Rocks—The granitic rocks of the region com-
prise several strongly marked types, and represent somewhat

Von. 4] Knopf-Thelen.—Geology of Mineral King. 235

widely divergent products of the same irruptive magma. While
often maintaining their persistence of character over several
square miles, a gradual transition through the medium of inter-
mediate types frequently takes place. The prevailing rock upon
the eastern flank of the belt ig a very coarsely granular agere-
gate of orthoclase and quartz with subsidiary amounts of biotite
and hornblende. This granite readily becomes incoherent, and
disintegrates rapidly, forming great sand-slopes. The micro-
scope shows that the dominant potash feldspar is microcline,
usually to the almost complete exclusion of the orthoclase. As-
sociated with these are small amounts of acid plagioclase, and
occasionally, microperthite and microcline-microperthite. Be-
sides the usual accessories, magnetite, apatite, titanite and
zircon, the quartz is noted to contain eapillary rutile. This acid
potash granite is splendidly exposed at Sawtooth Peak, at Silver
Lakes and at Florence Lakes, and reappears on Shotgun Creek.

Passing south, the ferromagnesian minerals become more
abundant, and the amount of plagioclase increases. Toward the
southern extremity, the granite becomes noteworthy through the
development of large, imperfect phenocrysts of orthoclase scat-
tered somewhat sporadically throughout the matrix. They
often attain large dimensions, frequently measuring over four
centimeters in length and are broad in proportion. The ground
is a medium grained, eugranitie assemblage of orthoclase, plagio-
clase, quartz and biotite. The feldspars occur in nearly equal
proportions, placing the rock among the orthoclase-plagioclase
rocks as a porphyritic quartz monzonite.

West of Mineral King the granite is prevailingly of the horn-
blende-biotite variety. The rock is a typieal orthoclase granite
carrying a notable. quantity of dark constituents. Toward the
north, however, an interesting modification is met with. The gran-
ite becomes surcharged with lustrous black hornblende prisms,
strongly idiomorphic, and frequently attaining a length of two
centimeters. Splendent foils of biotite become conspicuous ;
sphene is macroscopically abundant, and quartz sinks to minor
importance. Systematic collection of hand specimens along a
normal to the contact showed a loss of the porphyritic habit with

236 University of California Publications. [ GEOLOGY

proximity to the sedimentary mass. The hornblende resumed
the ordinary hypidiomorphie form, the quartz content was noted
to increase, and at the contact the rock had become a quartzose
eranitite, barren of hornblende. Yet observation showed that
most frequently this particular variety of granite would pre-
serve its porphyritie habit to within two feet of the contact,
where it would become obliterated, and a slight enrichment in
the biotite content take place at the expense of the hornblende.
This tendeney toward the formation of a narrow peripheral zone
relatively richer in biotite can macroscopically be seen to have
been operative at numerous points, and even appears from
microscople evidence to have been effective in the leucocratie
eranites upon the eastern side of the area.

Inclusions in the Granites —Dark cireular and irregular oval
patches, varying in size from half a square inch to a square
vard, are exceedingly abundant in the granites of the region.
They are resistant to atmospheric agencies and weather out in
relief. Their outlines are sharp and distinct, though in detail
interlocking with the grain of their hosts. The term ‘‘schliere’’
when applied to these is a misnomer. On the basis* of textural
differences, two classes can be recognized: the first of which is
accurately deseribed as a pepper-and-salt mixture of the dark
and heht colored constituents; the second type is a dark colored,
medium granular aggregate in which oceasional porphyritiec feld-
spars are ineluded.

The distribution of these two varieties of inclusions is not
limited to any particular facies of granite, and is in general
fairly uniform throughout the region. Over wide areas a com-
mon perpendicular orientation of the major axes is often ob-
servable though the porphyritic hornblendes of the enclosing
rock are without definite disposition, either fluidal or gravita-
tional.

At Eagle Lake, the glaciation has laid bare a truly remark-
able phenomenon. Here the granite abuts against a_ white,
schistose quartzite, which thermal metamorphism has rendered
massive and vitreous over a breadth of a few inches from the
irruptive. Paralleling the contact, and forming a zone in the

Von. 4] Knopf-Thelen.—Geology of Mineral King. 23i

granite from three to four feet wide, is an enormous assemblage
of dark-colored ellipsoidal enclosures, so numerous as to con-
stitute more than one-half the bulk of the rock. The contact is
exposed to a vertical height of 20 feet at points, and horizontally,
several hundred feet, and the inclusions are seen to have sub-
ordinated the eranite to the function of a mere binding material.
They have been oriented parallel to the plane of the contact, and
show distinct evidences of plastic deformation, being somewhat
flattened in the direction of their major axes. Texturally they
are fine grained aggregates of the dark and leht constituents.
In thin seetion it is seen that the ferromagnesian minerals, rep-
resented by biotite, hornblende and augite, comprise half or
more of the bulk of the slide. The biotite exceeds shghtly the
hornblende plus the augite. The hornblende, which is of the
common ereen variety and strongly pleochroic, is frequently
regularly interegrown with pale green augite with the c axes
common. The feldspars present are orthoclase and ealeic oligo-
clase, associated together in nearly equal proportions. Quartz
is very subordinate; a small but variable amount of micro-
graphic (myrmectic) intergrowth is recognizable. The most
noteworthy feature, however, is an extraordinary abundance of
perfect apatite needles, often of long slender, acicular habit,
with a leneth exceeding fifty times the breadth. Such needles
must furnish sensitive indicators of any internal movements
since the consolidation of the magma. The apatite is perhaps
four or five times as plentiful as in its granite host. Zireon,
titanite, pyrite and magnetite are sparingly represented. The
structure is allotriomorphic granular, though occasionally the
biotite shows sharp idiomorphism.

The host is a fairly coarse grained quartzose granite carry-
ing a great deal of biotite and considerable hornblende. The
fohae of biotite show an incipient effort to congregate, and give
the granite a faint appearance of inhomogeneity. The miero-
scope shows that orthoclase is the dominant feldspar, and that
but a very small amount of acid plagioclase is associated with it.
Apatite (somewhat more abundant than in normal granites),

zircon, magnetite, and titanite comprise the accessories,

238 University of California Publications. | GEOLOGY

Throughout the hand-specimen can be observed small dark-
colored patches, approximately half an inch square, which are
pepper-and-salt aggregates of ferromagnesian minerals and
white. In thin section, the patches consist of panidiomorphic
equidimensioned aggregates of the above minerals with the dark
equaling the white. It is noted, however, that the triclinic
feldspars have become relatively more abundant, and that a
notable concentration of apatite has taken place. Each little
patch is apparently an integral unit which does not blend into
the enclosing rock, though the line of demareation is not abso-
lutely precise, and shows sympathy with the grain of the host.

At seventeen feet from the contact, the granite does not differ
essentially from that at but one foot, except, perhaps, in having
recovered completely its appearance of homogeneity.

From Chiff Creek was obtained a dark medium grained gran-
war inclusion, throughout which a few porphyritie feldspars
are seattered. The host, which was not in any near proximity
to the contact, is a hornblende biotite granite, conspicuous by
the porphyritie development of the hornblende and the macro-
scopie character of the titanite. Under the microscope the inelu-
sion appears to consist of biotite and green hornblende in equal
proportions, oligoclase and the accessories. Quartz is insignifi-
cant or absent. The feldspar is characterized by having a core,
or more frequently, a zone of sharp erystallographie habit con-
sisting of kaolinized feldspar succeeded by a peripheral growth
without exterior erystal outline. By far the most striking fea-
ture reveaied in thin section is the extraordinary concentration
of the accessories. Sphene is very abundant in sharp idiomorphie
rhombs. In one instance an ineluded cube of magnetite was
noted, and in another, a small striated feldspar lath. A horn-
blende cross-section was found in parallel intergrowth with a
titanite rhomb along their respective cleavage lines. Apatite
displays a profuse development of long slender needles and short
stout prisms. It is sometimes included in the sphene, and may
occasionally be seen jutting into the titanite rhombs. Octahedra

of magnetite are unusually plentiful. Zireon, however, is pres-

VoL. 4] Knopf-Thelen.—Geology of Mineral King. 239

ent in no more than normal amount. The structure is hypidio-
morphie granular.

The peculiar mode of occurrence of the enclosures at Hagle
Lake, and their great numerical abundance, seem to give the
contact some significance in their genesis. At first sight, it
would appear probable that here they represented partially
digested fragments of the invaded formations, but the micro-
scopic diagnosis, and the absence of the pronounced endomor-
phism which the assimilation of such large amounts of silica
would necessitate, areue strongly against such an hypothesis.
And furthermore, the deformation of the enclosures visible ma-
croscopieally should show corresponding structures microscopi-
eally. If the inclusions are of extraneous origin, and have suf-
fered magmatic corrosion and plastic deformation, the individual
mineral components should accordingly show ineipient fusion.
The deformation has necessarily been plastic, inasmuch as the
drawn-out inclusions are contained in an unsheared granite as
host. The thin section, however, reveals no evidence of incipient
fusion, and shows that the various minerals possess the sharp,
pyrogenic outlines characteristic of granular plutonic roeks. In
reviewing the petrographic details it is apparent that the inelu-
sions represent basic segregations from the granitic magma and
are characterized by high concentrations of the so-called usual
accessories. A close sympathy between host and segregation is
indicated by the dominance of a pecuhar accessory: apatite, in
the apatite-rich granites and titanite in the titanite-rich granites.

Later Intrusives.—Intrusive into the schists and granite on
Monarch Creek is a quartz-mica-diorite, which, wherever ex-
posed, exhibits a uniform and persistent petrographic habit. The
contact with the granite is marked by an irregular intrusion
breccia, wherein the invading magma has incorporated numerous
angular blocks of granite. Occasionally a light colored aureole
three-quarters of an inch broad has been developed around the
acid inclusions. Other evidence indicative of the irruptive nature
of the quartz-mica-diorite is furnished by the frequent appear-
ance at the contact of porphyritie facies resembling coarse, holo-
erystalline andesites.

240 University of California Publications. [GEOLOGY

Macroscopically, the quartz-mica-diorite is a medium grained
eranular rock, the tabular character of whose plagioclase feld-
spars is often apparent, even textured, and of gray color. Its
weathered surface is characteristically of blue gray tint, and
usually pitted, due to the atmospheric removal of the hornblende.
Under the microscope it is seen that the total ferromagnesian
content is relatively small and comprises biotite and hornblende,
the mica commonly predominating. Plagioclase is present in
large amount and is noteworthy from the strong tendency it
displays to assert its idiomorphism. Its habit is tabular, and
the feldspars aimost invariably consist of Carlsbad twins stri-
ated according to the albite law. An accurate determination is
therefore readily possible, and shows that the feldspar corre-
sponds to andesine Ab,An,. A variable amount of orthoclase
occurs, though usually in strict subordination to the soda-lime-
feldspar. It is always allotriomorphic, and occasionally twinned
according to the Carlsbad law. Strain shadows are observable,
sometimes culminating in a microcline structure. A not ineon-
siderable amount of quartz is distributed throughout the body
of rock so as to form an irregular mesostasis in which the tab-
ular feldspars lie embedded. It is probably owing to this inter-
stitial character that the quartz owes its macroscopic inconspicu-
ousness. A few minute occurrences of graphic intergrowths
were observed. The accessories are magnetite, titanite, zircon,
and apatite somewhat abundantly.

The characterization of this rock shows that it is closely
allied to the granodiorites, in the sense in which the term grano-
diorite has been most frequently employed (‘‘quartz-mica-dio-
rite carrying orthoclase’’). It also accords exactly with the
tonalite of vom Rath, to which, in the nomenclature of Rosen-
busch, it would unhesitatingly be placed. The dark colored seg-
regations so common in the granites are conspicuously absent in
the tonalite.

Closely resembling the tonalite of Monarch Creek is a body
of granite apparently intrusive into the hornblende granitite
on the Wet Meadows trail. More careful inspection shows that
the feldspars are largely unstriated and that the macroscopi¢

VoL. 4] Knopf—Thelen.—Geology of Mineral King. 241

resemblance is misleading and merely fortuitous. Under the
microseope it is observed that plagioclase is not abundant, and
that the potash feldspar is to a great extent intergrown with
albite in microperthitic fashion. Quartz is unexpectedly present
in no inconsiderable amount, though relegated to interstitial
habit. The ferromagnesian minerals are sparingly represented
by biotite.

Tourmaline Granite and Andesitic Dykes.—Cutting this
eranite at various places are intrusive masses of tourmaline gran-
ite and dykes of feldspar porphyrites. The tourmaline is quite
abundant in the shape of radial aggregates, averaging a centi-
meter in diameter. <A little plagioclase, orthoclase and quartz
form a rather fine grained ground throughout which the tour-
maline is distributed. The tourmaline spherulites are often
located in the center of areas of quartz of uniform optical orien-
tation. The porphyrites are characterized by an abundance of
white feldspar phenocrysts embedded in a dark gray-blue ground
of fine texture. Some biotite is noticeable, but is not conspic-
uous. In thin section the large feldspars display decided cor-
rosion phenomena, having had all the corners rounded off. They
correspond in composition to a ealecie oligoclase. A not very -
prolifie generation of much smaller plagioclase lathes succeeded
them. They show no evidence of magmatic resorption, and are
not connected with the first generation by intermediate sized
feldspars. Some basaltic hornblende, for the most part strongly
chloritized, and biotite represent the ferromagnesian minerals.
Magnetite and apatite constitute the accessories. The ground-
mass, in which a little accessory quartz was noted, is holoerystal-
line and contains a great deal of chloritic matter scattered
throughout it. The microscopic diagnosis shows, therefore that
the porphyrites should more accurately be called andesites.

The detailed petrography of the granitic rocks of the reeion
shows that in this portion of the Sierra Nevada there exist larve
bodies of typical orthoclase granites, and even highly acid potash
granites. The time relations between the tonalite (erano-diorite)
and granite magmas show that here the more acid preceded the
less acid (tonalite) intrusion.

242 University of California Publications. [GEOLOGY

THE STRATIFIED ROCKS.

General Relations.—The stratified rocks consist prevailingly
of clay slates and phyllites with interbedded lmestones, quartz-
ites, and large masses of tuffs and sheared volcanics, both acid
and more basic. Superficial oxidation has colored the series a
strong red and causes them to stand out in pronounced contrast
to the gleaming white granites.

The strike of the strata is fairly uniform throughout the
area, and does not vary greatly from N. 45° W. The dip is
nearly vertical, usually 85° to the southwest. The bedding is
in all cases found to be strietly conformable. At Mineral King
the series attains a maximum width of 12,000 feet. South of
Farewell Gap it narrows down to 5,600 feet. (See Plate 30.)

The roeks have been sheared to greater or less extent and
exhibit various degrees of schistosity, from perfectly massive
quartzites to highly micaceous biotite schists. The interbedded
limestone beds show that the foliation is always coincident with
the original stratification planes. This is further borne out by
the thin sections, which frequently show the parallelism between
the sedimentary banding and the superimposed cleavage.

The lithologie units are relatively small, and it was found
inadvisable to attempt to map them separately. The siliceous,
calcareous and argillaceous members are frequently stratified in
rapid alternation, and, as a further complication, even the larger
subdivisions are of strongly interdigitating habit and tend to
thin out in the direction of their strike. The voleanic rocks,
which constitute a large portion of the geologic series, are as
a general rule conformable in strike and dip with the sedimen-
tary rocks. They are strongly sheared, and have been invaded
by the granites and are, therefore, certainly pre-granitic. Asso-
ciated in conformable sequence with the quartz porphyries on
the Little Kern River are beds of tuffs, and the evidence is clear
that there the voleanies form an integral portion of the strati-
graphic column. At other points different evidence is obtain-
able. On Monarch Creek dykes of dark igneous rocks are intru-
sive into quartzites and are themselves cut by white aphanitie

VoL. 4] Knopf—-Thelen.—Geology of Mineral King. 243

dykes which are apparently apophysal from the tonalite
intrusive.

Owine to the nearly complete absence of fossil content, the
unreliableness of interealated voleanies as data planes and the
lenticular habit of the stratified rocks, correlations between va-
rious cross-sections can only be made in general terms. Where
thicknesses are given, it must be borne in mind that their accu-
raey is conditional upon the accessibility or inaccessibility of the
territory.

Section across Timber Gap—A section along the ridge at
Timber Gap reveals the following succession passing from west
to east:

ism WidOTIS RL ACLES MOLETLZ sp) OIG ly Tyg eee ee anes eseeacese seen sees reece ener 500 ft.
2) Bandedered and! white: QuMartzuer <2 seer aces eceee eee setenee meena neers 150
3. White and gray laminated limestone 50
(The two feet adjacent to the next following formation are
highly contorted and the laminae are often reversed. )
GiB VPA ny allt ia RO t={ 0) SOUS) eee acre gem Pe Dee peer rer er 50
5. Arenaceous slates, siliceous schists and clay slates -.................... 300
Grate hyllitesman diclaygSlates: te seecoscceccose ease ncseccex sc ceerexesJaeueenss Tune tares 800
(Contains a 2-foot bed friction breccia.)
7. Siliceous schists, with subordinate schistose quartzites inter-
beddedieeihaimm bands claiy Sta pes cesses eee oee eee cee eater eee 350
8. Sheared conglomerate, tuffaceous ........ Ss Seed ves S nes hs Stare Sta Sead 200
9. A few feet phyllite, tuffaceous slate and green schist with cherty
UE C5 a ee een ee 750
10. Clay slates Bd
ADSL ORIEL ree ee Se eB ee De ee eet A Ue Zo ened Seo tacos tees 175
12. Caleareous quartzite, occasional limestone lenses ~...............-..........- 180
MS CLA VIES ACCS) oe awk esc eece ese Ae ese eet cad, wn Re eee taxes emcee enn 300
BATS pSTClapsy oVsCey Aud abu ts) COMMS EVAN ete eee ere es ne ye ep 50
(Contains 4-foot bed blue limestone. )
NS eee CIUL CoC WELT Zam) Os OLN Vital CS ease eseenee eee eens Meteor sue enon creme eevee 400
a UG} TBH NCES emit saree le etry Ab i stole aeesee cea resets peavey eer ee ee, eee 500
INGE Sed are opWE- WEA oXo) eo) tly a Aes) eee ae se eee ee poe ore Se eS 350
IS 26 (2) tn Ee ZG ere scat ae cc ere ee eee ee eR Se go ee eee 50
IS relavereitelal TeClidlsyeyzbe jayeroleyyiny ees ye ee 800
Miotal thickness’ exposed) = :222e2cceceees eee secs eee 6,090 ft.

The series is completely conformable throughout its entire
thickness. The strike is very uniformly N. 60° W. (magnetic)
and the dip may be inclined a few degrees from the vertical on

244 University of Califorma Publications. [ GEOLOGY

either side. Of the 6,090 feet of strata, 3,175 feet, or very ap-
proximately one-half of the series, are of volcanic and pyroclastic
origin.

Petrography—Under the quartz porphyries included under
subdivision 1 is a light colored, strongly sheared rock which
presents the appearance of a fine grained gneiss upon its cross-
fracture, and that of a very fine grained biotite schist upon its
foliation planes. The mica, however, is not evenly distributed,
but is localized in patches. Across the schistosity minute augen
of quartz and feldspar are visible. These features are somewhat
variable, depending upon the degree of dynamic metamorphism.
Favorable sections show under the microscope an abundance of
quartz dihexahedra, which are often better preserved than ap-
pears consistent with the macroscopic habit of the rock. The
phenocrysts are cracked, and polarize in various colors, the dif-
ferent tints of which, however, persist over areas relatively
large. Inclusions of the groundmass do not occur. The quartzes
possess sharp and linear boundaries. More frequently they are
shattered and drawn out, and show strong strain shadows. In
somewhat less abundance than the quartz are the feldspar pheno-
erysts, chiefly orthoclase in a variable state of preservation. It
sometimes retains its idiomorphism, but is more commonly broken
up, and the cracked fragments are embraced in large muscovite
plates. Occasionally a nearly obliterated plagioclase feldspar,
surrounded by white mica, can be detected. The groundmass
is a fine mosaie of quartz and orthoclase, and contains much
flaky biotite scattered throughout it. The constituents are all
oriented with their major axes parallel, and the biotite flakelets
are arranged in concentric fashion around the quartz and feld-
spar phenocrysts. The accessories magnetite, apatite, zircon,
and titanite were found present in small proportions. A minor
facies is a much darker colored schist, very fine grained and
showing only small feldspar augen. It consists of a large number
of kaolinized feldspars, shattered, and their corners abraded off,
embedded in a finer feldspar mosaic, in which but a small amount
of quartz is scattered. Disseminated throughout the matrix is a
very large quantity of finely divided biotite, which serves to

VoL. 4 | Knopf-Thelen.—Geology of Mineral King. * 245

bring out the schistose structure of the rock. Its orientation
around granulated areas of feldspar surrounding unshattered
nuclei emphasizes the mode of reduction of the feldspars by
attrition.

An important variation of the gneissie quartz porphyry 1s
a strongly schistose facies showing abundant patehes of drawn-
out feldspar and a few augen of vitreous quartz. Upon the sil-
very white foliation planes of this schist are curious aggregates
of sheared biotite disposed in irregular orientation. They are
more or less rectangular in shape and eause the rock to simulate

’

the appearance of the so-called ‘‘ picture schists.’’ In thin sec-
tion a few shattered phenocrysts of quartz can be observed.
However, one was noted which was entire and of uniform polar-
ization tint, free from inclusions, and with but sheht shadowy
extinction. Its shape is such as to suggest its derivation from
the dihexahedral form, but can not be conclusively demonstrated.
Its boundaries are not geometric lines, but are crenulate. <A
peculiarity in the distribution of the interference colors sug-
gests a well healed gash running across the phenoeryst. In con-
vergent light the section shows an eccentric uniaxial cross of a
weakly birefringent mineral. The homogeneity and relatively
large size of the quartz erystal, and the sharp plication of the
lines of schistosity caused by it, accentuate strongly its pheno-
erystie character. A few kaolinized and shattered phenocrysts
of orthoclase also occur. The biotite is mostly flaky and is loeal-
ized in bands. The groundmass is very fine grained and consists
of quartz (?) more or less interwoven with sericite. Magnetite
and zircon occur as accessories. Other slides illustrate in equally
remarkable fashion the anomalous behavior of the quartz. The
presence of nearly undisturbed quartz phenocrysts in a highly
sheared, fine grained ground is an immediately striking feature
and ealls for an explanation.

The sericitic quartz porphyries included under 15 and 17
differ widely from the porphyries described in the preceding
paragraphs. The various facies of sericitie quartz porphyries
appear to grade imperceptibly from one to the other, and often
to become highly feldspathic and deficient in quartz. The com-

246 University of California Publications. [ GEOLOUY

monest variety of the sericitie quartz porphyries is a strongly
schistose variety presenting an irregularly mottled appearance
on its foliation planes. This mottled effect is due to the alter-
nation of areas black with biotite scales and areas of pale green-
ish gray color which shine with a distinctly oleaginous lustre.
On its cross-fracture the rock is exceedingly dense, and only
very sporadie, minute eyes of vitreous quartz can with difficulty
be distinguished. Under the microscope a few badly damaged
feldspar phenocrysts stand out in sharp contrast to the exceed-
inely fine grained ground. They are unstriated, apparently all
orthoclase, kaolinized, and strongly mashed. Biotite occurs spar-
inely in small flakes, occasionally localized in aggregates. The
eroundmass is holoerystalline, but irresolvable. Some white mica
ean, however, be identified with certainty. A little accessory
magnetite and zircon occur.

A subordinate facies of the series of quartz porphyries is a
strongly folated, very white variety which shimmers. with an
unctuous lustre upon its schistosity planes, due to the abundance
of small mica plates. Microscopically, the rock can be charae-
terized as a mosaie of quartz interwoven with white mica. The
mica, which is distinctly pleochroic in a light greenish tint, is
extremely abundant and possesses a definite linear arrange-
ment. At certain points, however, it flows around larger areas
of granulated quartz. A very little biotite is present. Some
few large aggregates occur which consist entirely of scaly white
mica. <A little accessory magnetite and zircon are also found.

The sheared feldspar porphyry is a rather remarkable ap-
pearing rock. It is light bluish-gray in color, and is closely
crowded with feldspar phenocrysts, which in consquence of the
shearing that the rock has undergone, cause it to split along
the foliation planes as if composed of small pebbles. In thin
section the feldspars are seen to be in poor preservation: they
are kaolinized, their crystallographic outlines are usually de-
stroyed, and the corners have been abraded off; they have some-
times been cracked and the groundmass has worked in between
the fragments. They have frequently been converted to seri-
citic aggregates, especially upon their peripheries: a band of

VoL. 4] Knopf—Thelen— Geology of Mineral King. 247

sericite was noted closely hugging a feldspar half way round its
perimeter. In another instance a sheaf-like aggregate of sericite
was found separating two feldspars in near juxtaposition. The
feldspars are largely orthoclase, though the plagioclase character
of some few is barely recognizable on account of advanced kao-
linization. An insignificant amount of biotite occurs, as does
also a little chlorite. The ground is a fine mosaic of quartz and
is often sericitic. A single large fragment of quartz, showing
strain shadows, differentiated itself from the ground, and ap-
peared to represent the remnants of a phenoeryst, but the evi-
dence was not decisive. Apatite in needles, and magnetite in
quite large aggregates, were relatively abundant. <A little epidote
and a piece of tourmaline were also found.

The rock called a tuff under formation 11 is of grayish-
green color and is dotted with rather numerous, small turbid
white phenocrysts in a very fine grained groundmass. The folia-
tion is rude, though very distinct. Under the microscope the
porphyritiec feldspars are found largely untwinned, though a
few show very narrow striations and small extinction angles
against the lamellae. The original character of the feldspars is
indicated by the cireumfluent sehistosity; by their oeeasional
strong idiomorphism and by the frequent peripheral granulation
zones ; and by their homogeneity and freedom from inclusions of
the minerals of the groundmass. In certain instances the sharp
abutment of the feldspars against the eryptoerystalline ground,
and the absence of granulation products seem to show in the
case of rounded corners evidences of magmatic corrosion.

The matrix consists of biotite flakes and some chlorite, dis-
seminated throughout a limpid, feebly polarizing paste. Mag-
netite occurs as accessory, and occasionally apatite needles are
included in the feldspars and more frequently le scattered in
the groundmass, where they show marked evidences of eataclastic
phenomena.

It is apparent that the microscopic diagnosis is not conclusive
as to the massive or pyroclastic origin of this rock. The field
relations, however, show that a continuous gradation exists be-
tween this type of rock and others whose clastic origin is more

248 University of California Publications. [ GEOLOGY

readily evident. It occurs as interdigitating masses with the
tuffaceous conglomerate, occasionally even forming the matrix
in which the pebbles lie embedded, and its gradual transition can
be traced on the one hand into the normal clay slates and into
the tuffaceous slates on the other.

The tuffaceous conglomerate presents an exceptional develop-
ment on the section across Timber Gap. Interdovetailing with
feldspar tuff are heavy lenses of coarse conglomerate consisting
of well rounded pebbles of quartz, red chert, shale and conglom-
erate up to the size of a man’s head. These occurrences are
local and thin out rapidly along the strike. The more tuffaceous
portions show oceasional drawn-out pebbles (three-quarters of
an inch long) ineluded in a strongly sheared schist of fine grain.
The color is slaty, tinged with green, and the foliation planes
show but a dull lustre, except where biotite has locally been
developed, or where infrequent patches of sericite occur. Some
httle eyes of glassy quartz can with careful search be discovered.

Under the microscope, the immediately noticeable feature is
the exceedingly large quantity of flaky biotite, with chlorite,
which is disseminated throughout the cryptocrystalline ground.
Some small lathes of white mica are apparent. Sporadic pheno-
erysts of feldspar occur, badly altered, and frequently con-
verted to sericitic ageregates. The foliation is around their
abraded corners. Between crossed nicols a long slender feldspar
rectangle was noted somewhat inclined to the foliation. Towards
one end it is bent and fractured, and definitely deflects the stream
of schistosity. It is twinned according to the Carlsbad law,
and the two halves give simultaneous extinction when the trace
of the twinning plane is parallel to the cross-hairs, and is there-
fore orthoclase. A few irregular fragments of quartz, showing
strain shadows, were found, and proofs of their pyroclastic
origin still remained undestroyed. These were found in the sur-
vival of pyramid faces, and the occasional presence of straight
edge boundaries indicative of their original idiomorphie char-
acter. Some tourmaline is present, and was found in three dis-
tinct forms: as a small stout prism; as sector of a spherulite ;

and as a spongiform aggregate. This is conclusive proof of the

non-allothogenie origin of the tourmaline.

VoL. 4] Knopf-Thelen— Geology of Mineral King. 249

The clay slates in general possess the plane-parallel cleavage,
but, nevertheless, frequently grade into finely foliated schists.
Transitions between clay slates, phyllites, and microcrystalline
biotite schists are of constant occurrence. In the strongly schis-
tose varieties the biotite becomes macroscopically visible in the
form of minute scales. The microscope shows that the clay slates
contain a large amount of flaky chlorite, which becomes replaced
by biotite with advancing schistosity. Interealated with the
clay slates and phyllites are beds of slates showing curious ellip-
tical depressions and pustular swellings about a tenth of an inch
in diameter upon the cleavage surfaces. This peculiar phenom-
enon was developed in extraordinary degrees in beds occurring
between a succession of normal clay slates exposed in a creek-
euttine northeast of Mineral King. The exposure was at the
maximum distanee possible from the granite. A thin section
eut from this rock when held to the light shows a remarkable
satiny shimmer, and reveals a large number of variously oriented
eye-like areas surrounded by carbonaceous bands. Under the
lens the rock is found to be exceedingly fine grained and dimly
polarizing. Some quartz, and an abundance of green chlorite
is recognizable with certainty. The chlorite is very feebly bire-
fringent and shows a faintly luminous ultra-blue. Large areas
are completely isotropic owing to the overlapping of chlorite
seales. Some thonschiefernadeln and a few minute prisms of
tourmaline were noted. Carbonaceous matter is quite abundant.
The elliptical areas previously mentioned are sometimes bounded
by bands of chlorite, but are more usually defined by carbona-
ceous material. They do not differ essentially in composition
from the ground, but in a few eases were found to contain

a
more brightly polarizing mineral.

It gave straight extinction,
and appeared to be white mica, but its identity could not be
conclusively established.

An interesting quartzite occurs near the Empire mine (alti-

tude 10,000 feet and N.E. of Mineral King). It is massive and

non-schistose, and shows three splendid jointages which cause

it to break in small polygonal blocks. Particles of a yellowish

green mineral are uniformly scattered through it, and lend it a

250 University of California Publications. [ GEOLOGY

somewhat granitic habit. Under the microscope, the clastic
origin of the rock is readily apparent. Numerous quartz grains
show their detrital origin in the subangular character of their
outlines. They have received a common orientation and show
strain shadows, and some have been crushed. Rounded grains
of altered plagioclase are quite abundant. <A portion of the
feldspar is unstriated, and may be monoclinic. A not inconsid-
erable amount of decomposed reedy hornblende is distributed
throughout the slide. With it is a little biotite and chloritic
material. <A fine grained, feebly polarizing paste, whose exact
nature is indeterminate, constitutes a sort of cement for the
clastic particles. Some accessory magnetite, pyrite, titanite, and
abraded zircon occur scattered through it. This rock seems,
therefore, to represent an indurated arkose sandstone.

Sheared Quartz Porphyries from the Little Kern.—Associ-
ated in conformable sequence with the sedimentary series on the
Little Kern in both strike and dip, are several hundred feet of
sheared quartz porphyries and tuffs. They are of pearl gray
color, of waxy, unctuous lustre upon their foliation planes, and
show numerous easily recognized dihexahedra of quartz, which
lie embedded in an aphanitie base. They are macroscopically
identical with the quartz porphyries described by Turner from
the Dewnieville Quadrangle, and placed by him as very probably
of Jura-Trias age. One facies here, however, shows also por-
phyritie glassy feldspars.

Under the microscope the numerous quartz phenocrysts show
severe strain shadows. Some have been seattered and granu-
lated. The outhnes of the quartzes are usually irregular, but
oceasionally bipyramidal forms occur showing corrosion and em-
bayment. A sheht conchoidal fracturing of the erystal edges is
sometimes apparent. Feldspars are not numerous, and are
poorly preserved, usually drawn out and kaolinized. The ground-
mass 1s extremely fine grained, presenting in ordinary light a
sort of shagreened appearance due to the interweaving of mica-
ceous material. The development of this material often serves
to bring out the former flow structure. Magnetite and some dis-
jointed apatite needles were noted as accessories. Small irreg-

Von. 4] Knopf—Thelen— Geology of Mineral King. 251

war groups of minute tourmaline prisms are of comparatively
frequent occurrence in the groundmass.

A section eut from a hand specimen taken from near the
intrusive granite showed somewhat surprising features. The
quartz porphyry at the contact is standing on edge and does
not differ macroscopically from the previously described facies,
which was taken from altitude 8,300, Little Kern trail. The
microscope shows that the porphyritic quartzes have retained
their integrity and idiomorphie habit in nearly perfect preser-
vation. They display strong undulose extinetion, and may ocea-
sionally be fractured to small extent, but rarely show traces
of granulation. The ferromagnesian minerals are conspicuously
absent from the quartz porphyries.

The tuff associated with these acid voleanics does not differ
ereatly from them in its physical aspect. It is, however, more
massive, and does not contain numerous porphyritic quartzes.
Included in it are dark lenticular patches, representing frag-
ments of extraneous origin. Under the microscope only a few
irregular fragments of quartz are apparent, and these are af-
fected by strain shadows. Phenocrysts of orthoclase are more
numerous, and frequently retain their idiomorphic habit. Some
are fractured, and the fragments, especially the corners broken
off from the phenocrysts, show cross-hatched twinning. <A few
of the larger feldspars display the microcline structure in
splendid perfection. The delicate cross-hatching is on a fine
scale, and has been developed uniformly over the area of the
feldspars. The plagioclases are less abundant than the potash
feldspar and have been somewhat capriciously affected by the
dynamie metamorphism. Some still show the re-entrant twin-
ning angles; others are peripherally granulated; and a lath was
found broken into three pieces and the fragments separated.

Phenoerysts are not abundant, and the ferromagnesian min-
erals are nearly absent. A few small strips of biotite were
found, as were some irregular patches which appear to represent
localizations of flaky biotite. The ground is eryptocrystalline,
and contains scattered through it very minute seales of biotite.
Some magnetite, a few zircons showing perfect terminations, and
some small prisms of tourmaline occur as accessories.

202 University of Califorma Publications. [ GroLocy

A continuation of the same tuff is found exposed near the
lakelet south of Vandever Mt. It is a gray-blue rock lberally
sprinkled with glassy quartzes, and contains abundant inclusions
of sharp angular slate fragments up to three-quarters of an inch
in length. The rock weathers to an ash-white, and the small
dark fragments lend it a strong porphyritic aspect. The schist-
osity is but feebly developed. Under the microscope the numer-
ous glassy quartzes are immediately noteworthy. They are ang-
ular and jagged, often assuming fantastic forms. Powerful
strain shadows are apparent, and the longer axes of the crystals
have received a common orientation. Occasionally the jagged
points are shattered, and sometimes the quartzes are surrounded
by a very faint granulation aureole, but usually the demarcation
between phenocryst and ground is absolutely precise. Some small
sericitie aggregates were found, as were a few inclusions of ear-
bonaceous shale. The groundmass is extremely fine grained, and
contains a great deal of flaked chloritic matter disseminated
through it.

On Monarch Creek at 8,500 feet is a strongly sheared seri-
citie quartz porphyry less than 100 feet thick. It is of light
pearl gray color and shows an oily lustre upon its foliation
planes. The porphyritic quartzes are quite abundant, and their
frequent idiomorphie character is often apparent to the unaided
eye. Under the microscope the outlines of the quartzes are seen
to be usually of geometric perfection. The dihexahedral form
is often modified by corrosion and embayment phenomena, and
sometimes by a shght conechoidal fracturing. Severe strain
shadows are frequent, and occasionally the phenocrysts have
been cracked, allowing the matrix to work in between the sepa-
rated portions. The feldspars, of which a little is triclinic, are
very sparingly represented, and are poorly preserved. A little
biotite is present in flaky aggregations. The groundmass is a
fine grained aggregate of quartz and sericite. In it occur some
disjointed and faulted apatite needles; cataclastie zircons show-
ing both sphntery and idiomorphie terminations; and some criss-
cross aggregates of minute tourmaline prisms. 5

The More Basic Volcanics—In the ereek descending from
the 9,883-foot Peak west of Timber Gap is a 50-foot thickness

Vou. 4] Knopf—Thelen.—G@eology of Mineral King. 258

of highly sheared voleanie rock intercalated between beds of
clay slates. The rock differs from the others of the region in
containing abundant triclinic feldspar and a weakly pleochroic
light green hornblende. Cataclastie phenomena are illustrated
in ereat abundance. The granulated remains of phenocrystic
quartz seem to be present, but are not conclusively demonstrable.
The chief interest attaching to this rock is due to the peeuhar
occurrence of tourmaline in it. The tourmaline was found occur-
ring as a peripheral fringe around a shattered feldspar, and
could be seen sending apophysal tongues into the core of the
phenoeryst.

The creek heading near the Empire Mine (N.E. of Mineral
Kine’) crosses several hundred feet of altered voleanic rock. The
rock is of bluish gray color, fine grained, and shows but a rude
schistosity. Its most conspicuous feature is the abundance of
sheared streamers of ferromagnesian material, commonly re-
placed by epidote. Under the microscope some drawn-out ag-
eregates of intensely pleochroic basaltic hornblende can be seen
to have escaped the general alteration. Some large masses of
eranular epidote surrounded by opaque earthy material occur in
considerable areal proportions. Cataclastie feldspars, too far
affected by decay to leave their exact nature determinable, are
present in no great abundance. The groundmass is eryptocrys-
talline. Broken apatite needles, and magnetite with associated
leucoxene, constitute the accessories.

Large bodies of sheared andesite (Pl. 29B) oceur on Crystal
Creek at an altitude of 10,000 feet. Its color is a dark grayish
green, interspersed with numerous regular patches of flaky bio-
tite. These aggregates assume rectangular forms, uniformly
oriented, and suggest a derivative origin from former pheno-
erysts. In this section a very abundant generation of large
feldspar phenocrysts, affected by dynamic agencies and nearly
obliterated by kaolinization, becomes apparent between crossed
nicols. Some of the feldspar erystals still show evidence of their
triclnie character, and upon a favorable section a symmetric
extinction angle of 22° was obtained. Dark ageregates of flaky
biotite are common, but nothing can be discerned as to their

254 University of California Publications. [ GEOLOGY

origin. The matrix is eryptocrystalline, and contains a great
deal of chloritic matter flecked through it. Some accessory mag-
netite with pyrite cores, and some secondary epidote are also
found.

THE CONTACT.

It has been pointed out that the sedimentary rocks form an
elongated belt surrounded by granites. The vigorous erosive
activity has laid bare the contact at numerous points and has
revealed clearly the intrusive nature of the plutonic rocks.

Porphyritie modifications, and in one instance, a rude gneissic
structure, are occasionally developed as marginal facies. The
porphyritie modification.is best displayed at the upper Monarch
Lake. The granite, here a coarse quartzose microcline granite
of normal hypidiomorphie habit, is converted at the contact
into a closely crowded assemblage of microcline phenocrysts
embedded in a fine grained mesostasis consisting of quartz and
small flakes of biotite. A similar modification is found on the
western side of the belt in the White Chief cirque.

The irruptive is accompanied by extensively ramifying sys-
tems of apophyses, which are, however, never very long. The
longest found was 20 feet thick and followed the strike of the
schists nearly a thousand feet. The larger veins, as a general
rule, cut across the schistosity at random, but the anastomosing
system of capillaries to which they give rise, tend to seek out
the planes of weakness. Their fineness, and acutely serpentine
character, argue a great degree of fluidity for the intrusive
magma.

In addition to the thermal metamorphic influence of the
granite, it has at points been active dynamically also. West of
the Timber Gap, the irruptive has locally bent the schists from
N. 45° W. around to N. 25° E. and back again to the normal
strike. Extensive shattering of the strata, especially in the
Silver Lakes region, has taken place, but the results are compli-
cated by the internal movements which the belt has undergone.

The granite at the contact frequently contains included large
numbers of angular fragments of schists. Occasionally they

VoL. 4] Knopf—Thelen.—Geology of Mineral King. 255

show some rounding of the edges, and even embayment, or may
be surrounded by a resistant aureole which causes them to
weather in relief.
the contacts and vicinity, and were noted to fault from two or

Aplite dykes and pegmatites are common at
three inches the basic segregations previously described.

CONTACT METAMORPHISM.

The conditions are distinetly unfavorable for the systematic
study of contact metamorphism. This is principally due to the
fact that in the great majority of eases the strike of the strata
is nearly parallel to the contact. Both ends of the belt are unfor-
tunately obscured, either by morainal debris or by decomposition
products. Other deterrent factors are the shattered condition
of the strata near the granites, and the frequently inaccessible
position of the contact on precipitous cirque walls.

This last cause was especially felt in the case of a meta-
morphie clay slate in the Crystal Lake cirque. The contact could
not be approached closer than about 400 feet. At this distance
the rock is dense and fine grained, massive, and of dark slate
blue color. Seattered through it in sparse porphyritic fashion
are small prisms of tourmaline, 1 mm. in diameter and several
mm. in length. Under the microscope the tourmaline shows
a nearly circular cross-section of yellowish brown color. The
section is fairly homogeneous and free from inelusions of the
eroundmass, but is surrounded by a heavy peripheral fringe
of carbonaceous material. The tourmaline contains some liquid
inclusions which are disposed in radial fashion. The matrix is
composed of rectangular and quadratic andalusite sections em-
bedded in a small amount of interstitial quartz, and a large
quantity of black opaque material, forming nearly half the bulk
of the slide. Ignition caused the rock to bleach, proving that the
included material is of organic origin. The andalusite is filled
with carbonaceous matter, which, however, shows little or no
tendency to systematic orientation. In one or two instances
only was a erude chiastolite cross noted. Pleochroism is absent,
and differences of absorption are feeble. Some small patches of
brownish biotite are also found.

256 University of California Publications. [GEOLOGY

The limestones have in all cases become marmorized near
the contacts. In the White Chief cirque north of Vandever Mt.
are large beds of coarsely erystalline white limestone paralleling
the contact, which is marked by a four-foot zone of garnet rock.
The limestone contains bodies of magnetite ore, and large meta-
somatic deposits of zine blende. Pieces of the sulphide ore are
frequently studded with small honey-yellow garnets (grossular-
ite). Under the microscope the garnet rock is seen to be com-
posed for the most part of common garnet, entirely isotropie.
Some monoclinic pyroxene of reddish brown color and of refrac-
tive index very near that of the associated garnet is present in
small amount. Its extinction angle exceeds 40°, and it there-
fore falls toward the hedenbergite end of the diopside series.
A little wollastonite is also found. Calcite forms an irregular
mesostasis serving to bind together the other constituents.

A local phase of the metamorphism of the limestone is a fine
erained variety specked with small particles of a dark greenish
mineral. The microscope shows that the dominant constituent
is a dusty looking carbonate. Associated with it in smaller pro-
portions is a clear limpid mineral displaying the characteristic
calcite twinning. <A qualitative test of the rock gave a large
precipitate of magnesium, indicatine that the brownish ecar-
bonate is probably dolomite. Subsidiary amounts of diopside,
which have frequently been converted to colorless serpentine
ageregates, are also found. Areas of fibrous chaleedony are
quite common. Some lttle reddish brown garnet and a few
eranules of magnetite, which were not associated with the ser-
pentine, constitute the accessories.

Along the creek descending from the 9,883-foot Peak the

(e)

following section is exposed across the strike, N. 45° W.:—

Porphyritic hornblende—biotite granite.

SJilernerdl (owen yoleie oleh anys oe eee yeeros 300 feet
Siliceous schist .........2-.2...------ Re Pee ire pe rrr rere eee Bima”
Glas] aibGs ess ime oe cee so ceenree aca svn ee Fe senr eee nee ees 50
Banded quartzite -........22.---.--:--seeeeceeeee eae ne ae 150
(containing a granite dyke 8 feet wide.)
Jeane yenexe le CleUNS rh Meme Meee eee ay
Crystalline limestone, banded blue and white... (fi 8
Blue crystalline limestone..................-.--.....- SP RNS PIES 50) 2
Ibe hmaminey eral ToqMen Ae ee ee eee ee eer 40”?
ds Eo) ch 00-1 KS ee Pee red ree eT LP Ee LO" 22

+e}

VoL. 4| Knopf—Thelen.—Geology of Mineral King. 257

The knotted schist is a slate-colored rock, distinetly schistose,
and owes its knotted character to the accumulation of biotite
flakes on its cleavage surfaces. Perpendicular to the foliation
planes the knots form flat lentils less than 1 mm. thick, and
varying up to 1 em. long. Under the microscope the very finely
eranular character of the rock becomes apparent. A large
amount of minute biotite seales, of chocolate brown color, is uni-
formly distributed throughout the shde. Equally noteworthy
are numberless smal! stout tourmaline prisms of sharp idio-
morphie habit. In some erushed quartz aggregates white mica
has been developed. The bulk of the rock is quartz, but all evi-
deneces of elastic origin have been obliterated. Some darker
colored areas of irregular elliptical shape are found, and seem
to owe their peculiar constitution to aggregations of overlapping
seales of mieaceous material.

The hornfels is an extremely tough and compact rock of
dense grain and dark slate blue color. The characteristic fea-
ture under the lens is the rather abundant development of anda-
lusite, usually in rude radial aggregates. Crystallographic out-
lines are rare, but the sections tend to assume a longitudinal
habit. They are colored brownish due to included carbonaceous
material; pleochroism is not appreciable. The absorption is
fairly strong and is a maximum in the direction of the length.
The main mass of the shde is finely granular quartz, containing
a large amount of pyrite and carbonaceous matter. This abund-
anee of included material masks the presence of the andalusite
in ordinary light, but between crossed nicols its brighter inter-
ference colors (yellows and blues of the 1st order) cause it to
stand out in conspicuous contrast.

Some limited cases of thermal metamorphism of the volcanic
rocks were found, chiefly to the west of Timber Gap. At the
contact of the granite and the quartz porphyries a narrow zone
of hornfels, two to three inches wide, has been formed. It is
perfectly massive, extremely tough, and has a sort of vitreous
lustre. Under the microscope quartz is found to be the dominant
constituent. It is characterized by containing numerous cir-
eular, and even rectangular liquid inclusions. Orthoeclase is

258 University of California Publications. [ GEOLOGY

quite abundant, and with it is a considerable amount of micro-
cline. Some little micrographic intergrowth is also recognizable.
Biotite and muscovite are present in subordinate proportions.
A eatalastic zircon was noted included in a muscovite plate.
Maegnetite and zircon constitute the accessories. The structure
is allotriomorphie granular.

A less unequivocal case of contact metamorphism was found
west of the ridge. Here the quartz porphyry, tn which the
original dihexahedral character of the quartzes is better pre-
served than ordinarily, contains a small amount of common
garnet. The garnet is completely isotropic: it possesses a ‘‘sieve
structure’’ and contains inclusions of quartz. This specimen
was taken 100 feet from the contact. The various other sheared

porphyries failed to show any traces of garnet.

THE RELATION OF THE MINERAL KING BELT TO THE GRANITE.

The relatively greater uplift of the southern portion of the
Sierra Nevada has long been recognized, and LeConte has pointed
out that the intensification of the erosive activities produced
thereby, has effeeted an almost complete denudation of the
irruptive eranites. In the High Sierras a few small detached
areas and narrow belts of schistified rocks are all that remain of
the extensive roof under which the plutonic magmas cooled.
Such isolated remnantal patches are known to occur at Mount
Tallac, Mount Dana, Mammoth, and Mineral Kine.

At Mount Dana and neighboring parts of the mountain
crest the stratified rocks can be seen resting in irruptive discord-
ance upon the more or less uneven surface of the granite and in
part sunk into it.* At Mineral King, however, the relations are
rather different. Examination shows that the schists instead
of reposing upon a batholitic surface, are embedded beneath the
eeneral surface of the granite. They occupy a trough-like depres-
sion the bottom of which is not revealed, in spite of the fact
that the hypsometric range within this limited area is more than
6,000 feet. This resemblance to a trough-like character is ac-
centuated by the deep strike valleys which selective erosion has

* Prof. A. C. Lawson, oral communication.

VoL. 4] Knopf—Thelen.—Geology of Mineral King. 259

carved out in the clay slates, and it is doubtless due to this de-
pression beneath the zone of most vigrous erosion that the rocks
of this belt owe their preservation. The sides of the trough are
occasionally visible, especially upon the cirque walls on the
eastern side, and at Silver Lake the contact is revealed to a
depth of over 500 feet. The exposure shows that the granite
abuts upon the sedimentary rocks in a locally uneven and irregu-
lar surface, but one which, in general, approximates verticality,
or even inclines slightly to the east. At other points it could
be seen dipping to the west. Detailed mapping on the contour
sheet shows that the contact planes depart indifferently from
the vertical. The fact that the belt becomes narrow on low
eround indicates, however, that the planes tend to converge,
rather than diverge, with increasing depth.’ The map shows the
close relation between the dimensions of the belt and its internal
structure. The great narrowness across the strike and the rela-
tively great length are immediately apparent. The correspond-
ence between strike and prolongation is complete south of Fare-
well Gap, but to the north a divergence sets in, amounting to as
much as 20°. In spite of the close accordance between the length
of the belt and the strike of the strata, it will be noted that the
eourse of the contact is often directly across the edges of the
schists. Along the entire periphery evidences of the intrusive
nature of the granites are abundant, and the various criteria for
the discrimination of irruptive contacts are everywhere visible
in the form of intrusion breccias, apophyses, marmorization of
the limestones, and the formation of hornfels zones. Numerous
fragments of schists included in the granites show that the
schistification of the series preceded the ascension of the plutonic
magmas, and this evidence is in confirmation of the relations
found to hold true throughout the Sierra Nevada that the
schistosity of the invaded formations is independent of the eon-
tact planes, and was not produced by the intrusive igneous
rocks.*

The post-granitie invasion of the sedimentary series on
Monarch Creek by the tonalitic magma has produced a deep

* Turner, however, cites an exception from the Bidwell Bar Guadrancle
gle.

260 University of Califorma Publications. [GEOLOGY

embayment in the contact line and has isolated a heavy body of
garnet roek which caps the summit of the 11,530-foot ridge. A
small patch of schists at the lake at the head of Chiff Creek
seems to owe its position to the same cause, and is now satellitic
to the main mass. With these exceptions the Mineral King belt
constitutes an isolated, integral unit, surrounded by granites of
synchronous origin.

The periphery of the belt is lined with granite peaks which
commonly exceed 12,000 feet in altitude—Sawtooth, 12,340 feet,
Florence, 12,405 feet, and other peaks unnamed as yet. West
of Vandever the granite plateau maintains a height of 11,200
feet with individual peaks rising to 11,800 feet. North of Cliff
Creek the vast assemblage of granite peaks ‘‘like the billows of
a choppy sea,’’ fall into a general level at 12,000 feet. The
lowest exposure of the sedimentary rocks on Cliff Creek was
found at 7,000 feet, or a difference of 5,000 feet. Even in the
heart of the belt, that is, at the site of Mineral King, the differ-
ence in altitude between the highest and lowest exposure of the
sedimentary series is more than 4,000 feet. If we assume that
Sawtooth. which is on the immediate periphery, approximates
toward the former surface of the batholith, the difference wil]
amount to more than 5,000 feet. The contact passes through

the region of maximum glacial degradation where the mountain

erests have often been reduced not less than one thousand feet.*
It is, therefore, evident that 5,000 feet represents a minimum
estimate of the amount of depression of the sedimentary series
beneath the general level of the granite surface.

A belt of stratified rocks thus surrounded and enveloped by
plutonic magmas was situated in extremely favorable environ-
ment for the operation of thermal metamorphic agencies. Yet
the alteration effected has been small, and always local. The
large body of clay slates, which examination shows to be the
most suseeptible to metamorphism, are practically unaltered.
This is all the more surprising when considered in the light of
the facts from other portions of the Sierra Nevada. Turner re-
ports upper Jurassic (Mariposa) clays slates metamorphosed to

* A. C. Lawson, Bull. Dept. Geol. Univ. Cal., Vol. 3, p. 361.

Vou. 4] Knopf—Thelen.—Geology of Mineral King. 261

chiastolite schists, over a distance of 6,500 feet along the strike.
At Cisco on the Colfax Quadrangle Lindgren has mapped in
several square miles of hornfels rocks, and has shown the exist-
ence of a broad contact zone half a mile wide and several miles
long. The conditions there parallel closely those obtaining at
Mineral King. The plane of intrusive contact is nearly ver-
tical, and is in its general trend closely coincident with the strike
of the invaded formations.

The belt of rocks with which we are concerned narrows down
south of Farewell Gap to as small a thickness as 4,200 feet across
the strike. The major portion of the series consists of normal
clay slates, and comprises the axis along which the valley of the
Little Kern has been eroded. Two conditions were unfavorable
to the metamorphie activity of the granite; firstly, the verticality
of the contact walls, and secondly, the parallelism of the strike
of the strata with the contact plane. Opposed to these unfavor-
able conditions were the great narrowness of the belt, and the
simultaneous supply of heat from two opposite sides. The de-
eree of metamorphism, therefore, appears relatively small, and
is but insignificant when compared with what has been effected
in other portions of the Sierra Nevada under less fayorable con-
ditions. The frequent occurrence of tourmaline in the invaded
formations, both sedimentary and voleanic, seems to show that
pneumatolytie processes, at least, have been comparatively ac-
tive.

The description of the intrusive nature of the contact shows
that the trough in which the sedimentary rocks lie embedded
cannot have originated through faulting, either of simple or
eraben character. The irruptive character of the granites nas
been sufficiently emphasized and the detailed evidence presented
as to the sunken condition of the stratified belt of rocks. It is,
therefore, evident that the Mineral King lens represented a por-
tion of the batholithie roof which has foundered during the intru-
sive ascent of the igneous magma. The granites were still in a
highly mobile condition when this event took place, but evidence
deduced from the incommensurate degree of thermal meta-
morphism seems to indicate that the submergence did not long
antecede the final consolidation of the magma.

262 University of California Publications. [GEOLOGY

Various severe internal movements have affected the strati-
fied rocks. At Timber Gap compressive forces acting along the
strike have caused severe buckling of the limestone beds. On
Crystal Creek the same forces acting as an oblique shear have
shoved the beds over one another, and have produced an appear-
ance resembling an erosional unconformity (Plate 29A). The
angular discordance amounts to 14°. The apex of the acute
angle is occupied by breeciated masses of quartzite, and crushed
horses of quartzite are common in the limestones. On the oppo-
site side of the ridge shown in the photograph the strata have
been intensely shattered and contorted. Owing to the near
proximity of the contact it is impossible to discriminate the
thermal rending from the crumpling due to a sort of buttress
action.

The granites of the region show no macroscopic evidences of
deformation. The microscopic investigation, however, showed
frequent straining of the quartz, and occasional faulting of
apatite needles. These minor ecataclastic phenomena constitute
the last page in the diastrophic record of the Mineral King area.

University of California,
May, 1905.

BULLE, DEPT. GEOL: UNIV. CAL, VORA plme2e

ZC

Yiew looking south-west from Sawtooth. Granite plateau behind Vandever Mt. in background; granite contact in
foreground, showing embedded character of the Mineral King belt of sedimentary rocks.

BULL. DEPT. GEOL. UNIV. CAL. NOI Gr, IG; 29)

A.—Angular discordance produced by oblique shear on Crystal Creek

B.—Glacial benches quarried out of sheared andesite on Crystal Creek.

Height, 15 feet. Showing utilization of jointages, and ineffective-
ness of abrasion.

i

BULL. DEPT. GEOL. UNIV. CAL. VOLE. 4; PE; 30

Re
ee

Z,
7
y
Popography hy USGS.
LIMESTONE CLAYSLATE = QUARTZITE 072, PORPHYRY TONALITE GRANITE BARNET ROCK GLACIAL LAKES
AN F.
Pe ee VT x ,mmtrro / re Tres Rai avn a
GEOLOGILAL MAP OF THE MINERAL KING HISTRICT:
1 z o 1 2 3 4s 5 Miles
— ee = SS SSS SS SS SSS)
TW Goo) 1 2 3 4. __5 Kilometers
= SS 2 SS SS SSS SS SS ESS

Contour interval 100 feet.

UNIVERSITY OF CALIFORNIA PUBLICATIONS

BULLETIN OF THE DEPARTMENT OF

GEOLOGY

Vol. 4, No. 13, pp. 263-286, Pls. 31-37 ANDREW C. LAWSON, Editor

COLD WATER BELT ALONG THE WEST
COAST OF THE UNITED STATES
BY

RuuirF 8. Houway

CONTENTS.

PAGE

Heri ONL CTUON Pano aten sncrasensvnc sea ode eta ecto oun eats reue Meat tenet aes tette eke eeitee, stn oats 263
Temperature Observations of the Tuscarora . .........:-......++s:: 266
Temperature Observations of the Albatross . ...............0..0000. 269
Inshore Belt, Of Cold! Water sec vs salience cee ae cine aie a 271
dU WiOmlaroblemsr Presented in. aaa. 1sceiwiae serene cosieueceristeee tereiesains cites cease 274
Cold Water alone Other Coasts 223... ens sede cies esse give gees as 274
General Temperature Conditions of the North Pacifie ................ 277
Maximum Surface Temperatures ........... 000. cc eee cece cee aes 278
Minimum Surface Temperatures ...............cee cece eecceees 278
Rane roi mourtace Mempera tiles ies a tenn te ntere rene mcs nee er 278
Memperaiume (ty © Cea nis OLLOUUsse it teens set ente rr a et ene 279
Hypothesis accounting for Cold Water Belt ...................000.. 28]
POUT IMA TY ea tgeeeye ys tstital es veya siege cis tue, weds aysaiceke sve sume casper ete eter |: tl adeeb Oe 285

INTRODUCTION.

Although considerable attention has been paid to the question
of ocean currents off the west coast of the United States. yet
much work remains to be done, that accurate information as to
the limits, direction and temperature during the year of the
various streams or drifts may be ascertained. The Pilot Charts
of the North Pacific, issued monthly by the United States Hydro-
graphic Office, give for each of the four seasons a somewhat
schematic current chart which is virtually a composite of the
observations received by that office. Upon the face of each
sheet there is a statement printed in red, calling attention to the

264 University of California Publications. [ GEOLOGY

meager data upon which the currents are charted. In the
preparation of the Pilot Charts, only actual reports by officers
erusing in the Pacific are considered and particular attention in
observing and reporting currents is requested of all mariners.
The amount of current reported by a vessel is the difference
in the position of the vessel each day as obtained by dead reckon-
ing and the position obtained by astronomical observation. In
vetting the position by dead reckoning, there are several sources
of error. Among these are the variation of the log in finding
the velocity of the ship, the failure of the man at the wheel to
hold the ship accurately to the prescribed course, and the un-
certainty as to the exact variation of the magnetic needle. This
last source of error may be of considerable amount. The North
Pacific Pilot Chart for February 1904 says: ‘‘Taking the
whole of the navigable world into consideration, it would be
conservative to state that the general uncertainty in the heading
of a ship at sea, arising from an inaccurate knowledge of the
variation of the needle, is as much as two degrees.’’ This alone
would make a discrepancy of 15 to 20 miles between the ecaleu-
lated and the true position of a fast steamer at the end of each
day’s run. Turning to the other half of the problem, it is
found that a probable error of 214 miles must be allowed in
obtaining the true position by astronomical observation.* The
difference between the ship’s position as determined by these
two methods with the possible sources of error is reported as
current or drift. It is well to note that the reports of steamers
have not the same value as those of sailing vessels. The sailing
vessel is occasionally becalmed for an entire day and then the
difference in position between two astronomical observations
gives a reasonably accurate determination of the drift. The
normal rate of a ship being known, it would seem as if it might
fully be allowed for, and hence the current might be determined
from a vessel under way, with an equal accuracy as from a
drifting ship. This would be true were it not for the fact that
ocean currents and drifts are not large masses of uniformly
moving water, but rather relatively narrow streams with bands

* Estimate by Professor George Davidson.

VoL. 4| Holway— Cold Water Belt. 265

of calm water or even counter eddies between. A steamer movy-
ing rapidly may pass through several narrow streams of differ-
ing velocity or even differing direction and its report of current
would then be the algebraic sum of the various currents en-
countered. A beealmed ship or even a slow-moving sailing-
ship is apt to remain in one stream for the entire 24 hours.
This is supposed to account for some of the widely differing
reports of sailing vessels and of steamers in traversing the same
region. With the increasing commerce of the Pacific the num-
ber of reports from both steamers and sailing vessels will in-
erease, and reasonably correct information will be obtained for
the zones traversed by regular vessels. For the parts of the
ocean out of the usual courses laid down, reliance must be placed
in the scientific expeditions devoted to oceanic research.

An important addition to the reports of currents encoun-
tered by vessels are the so-called ‘“‘bottle tracks.’’ Bottles
usually made of rubber are thrown overboard with an inclosed
slip giving the latitude and longitude of the ship at the time.
On the bottles is a printed request that they at once be returned
to the authority conducting the investigation, with a statement
of the time and place of finding. The bottle track is the line
connecting the place of starting and the place where found.
A minimum rate of drift is thus established. The line of drift
and the time that the bottle may be stranded on some coast
before being found are the elements of uncertainty. If the
bottle is so weighted as to expose practically no surface to the
wind, its movement depends entirely on current or drift and
‘bottle tracks’’ thus form a valuable element in current deter-
mination.

A third important source of information is found in the
constantly growing mass of data on ocean temperatures. The
thermometer is one of the most reliable instruments in deter-
mining currents. Unfortunately much of the data for ocean
temperatures on this coast is scattered through the reports on
file in the Hydrographic Office and is not accessible to the
public. It is to be hoped that more of this will be tabulated
and made available to investigators as has been done by Mr. C.

266 University of California Publications. [ GEOLOGY

H. Townsend* for the work of the Albatross for the years 1883—
1900. The original observations upon which this paper is based
are found largely in Mr. Townsend’s compilation and in the
valuable work of Admiral Makaroff; which tabulates tempera-
tures taken in the North Pacific from 1804 to 1890, but does not
include the work of the Albatross.

TEMPERATURE OBSERVATIONS OF THE TUSCARORA.£

Some of the most marked peculiarities in the temperature
distribution off the west coast of the United States are well
shown by tabulating the observations of Commander Belknap
of the U.S. S. Tusearora. In 1873 the Tuscarora had been de-
tailed for the purpose of finding a suitable route for a cable
between the United States and Japan. <A series of soundings
was made on lines running west from the Pacifie Coast to deter-
imine the slope and the general nature of the ocean bottom near
shore. Ineidentally the temperature of the ocean water was
taken—the series of observations is fairly complete for surface
and bottom temperatures but rather incomplete for serial tem-
peratures showing the conditions at intermediate depths. The
surface temperatures obtained on 14 lines running approxi-
mately west from the coast and at intervals from Cape Flattery
to San Diego are given in the table herewith. The first tem-
perature in each line is the temperature found nearest shore.
Unfortunately this is not at a constant distance from the coast
line. Where the difference is material, the first sounding is set
over a corresponding amount in the table.

The first line of soundings was made September 17 to 20,
1873; the eight lines from Flattery Rocks to San Francisco, Oc-
tober 20 to November 6; the lines between San Francisco and
San Diego from December 20 to 30. As these observations
were distributed over a period of three months, each line of
soundings must be taken by itself to avoid confusing seasonal

*U. 8. Fish Commission, Report for 1900, pp. 387-562.

7+ Makaroff, S. Le Vitiaz et L’Ocean Pacifique, St. Petersburg, 1894.

} Belknap, Geo. E., Deep Sea Soundings in the North Pacific. U. 8.
Hydrographic Office, 1874.

Found also in Makaroff’s work.

SURFACE TEMPERATURES BY COMMANDER BELKNAP, U.S.S. TUSCARORA
OFF AND ON SHORE SOUNDINGS FROM CAPE FLATTERY TO SAN DIEGO, 1873

|267]

Shore end of line |. Fixst Sounding a Temperatures Northing or
| Latitude Longitude Inshore Offshore Southing
N Ws 1873 | | ]
Cape Flattery | 48°35’) 125° 25’| Sept. |50.4/51.8|53.2| 56.5 54.6 59.0 58.0 12 aN
Flattery Rocks | 47 14 |} 126 42 Oct. 57.0/57.1 57.2 58.5 1 00 S
C: Ponla eatren! 44 52 | 124 47 | i 50.4] 51.2 | 52.3 | 53.3 57.0 59.0 59.5 9 26 N
Empire City 43 07 | 125 14 ” 153.2 52.1/54.9 57.6 017 N
Trinidad Head | 41 00 | 124 27 | as (48.5 | 49.4 | 50.2 52.0 51.0 54.6 58.1 54.8; 0 54 N
C. Mendocino 40 18 | 124 30 |» 49.6 55.6 51.6 53.2 55.0 0 09 S
Pt. Arena | 39 04 | 124 40 | Nov. |52.8 53.1] 55.8 0 02 N
Salt Point | 38 31/123 46 2s 51.7 | 52.8 57.9 58.0 0 06 S
San Francisco | 37 40 | 123 36 Z 55.0 58.2 0 06 S
Pt. Carmel | 36 25 | 122 04 | Dec. | 54.0 55.5 54.0 53.8 0 12 N
Pt. San Luis 35 15 | 120 58 i 04.3 | 55.0 | 55.0 | 55.0 | 55.0 54.1 0 13 N
Pt. Sal 34 59 120 47 ay 54.1/55.0|55.2 | 57.0 0 36 = S
San Nicholas 33 32 | 119 59 2? 56.4 | 56.0 | 56.8 | 57.0 | 55.6 | 57.0 0 37 N
San Diego 32 33 | 117 28 d 59.8 59.6 59.0 | By )aS) 59.0 58.0) 59.6 0 06 = S
Width of each column equals 15’ of Longtitude

268 University of Califorma Publications. [GEOLOGY

changes to changes due to differences in latitude or to distance
from the coast line. In the published records of the observa-
tions we are not given the time of the day nor the condition of
the weather. According to Buchan’s discussion of the Chal-
lenger observation, the daily variation of the temperature of
the surface of the sea does not exceed 1° F. In general the
differences considered in this paper greatly exceed that amount.

The first line of temperatures in the table is but a part of a
survey extending from Cape Flattery nearly to Dutch Harbor
on the island of Unalaska, made during the latter part of Sep-
tember, 1873. The first temperature near shore was 50.4°. In
voinge westward 120 miles and northward about 40 miles, the
temperature increased to 59°. From this point the rest of the
survey shows a gradually falling temperature, but the initial
temperature of 50° was not again reached until the vessel was
nearly 1,000 miles to the westward, about 370 miles north of the
starting point and only some 200 miles from the island of
Kadiak on the Alaska Coast.

This inerease of temperature on first leaving the coast and
the subsequent slow decrease are more striking when it is con-
sidered that the last records were made two weeks later in the
autumn than the first.

The next eight lines of survey represented in the table ex-
tend off shore from 100 to 200 miles. Their leneths are shown
approximately in the table where each column represents 15’
of longitude. These lines uniformly indicate that the water
near shore is colder than that further to the westward along
the entire coast from the Straits of Fuca to San Francisco.
The lowest temperatures obtained are at Cape Mendocino and
Trinidad Head and are at the two stations which are the closest
inshore. They are also near the change to the southeast in the
direction of the coast line. It is noteworthy that these lowest
temperatures are not those found further north. On the con-
trary, according to the data now at hand, it is more than 500
miles to the northward before surface water as cold as that near
the coast between Cape Blanco and Cape Mendocino is reached,
during the late summer and the early fall.

Vou, 4] Holway—Cold Water Belt. 269

Southward of San Francisco the temperatures in the table
all

north of Point Conception—are in harmony with the existence

do not show such marked variations. The first three lines

of an inshore belt of cold water. South of Point Conception
there is no evidence of such a cold belt. As indicated in the
table the leneth of the nes south of San Francisco is less than
that of those to the north. The Point Sal and the San Nicolas
lines also vary greatly from east and west lines.

South of Point Conception, the submarine plateau or econ-
tinental shelf is much wider; that is, there is a much broader
area of comparatively shallow water. This wider continental
plateau and the bend in the eoast line at Point Conception are
probable elements in the causes which determine the absence of
a marked inshore belt of cold water off southern California.

The temperatures in the table with those obtained by the
Tusearora in the cable survey from San Diego to Honolulu have
been laid off on the coast survey charts; the cable survey tem-
peratures, like the others already considered, give no indication
of a cold belt near shore, south of Point Conception. For the
first 150 miles from San Diego, the surface temperatures vary
from 58° to 59°. Beyond that, the temperature slowly rises as

the line runs to the west-southwestward to the Hawatan Islands.

TEMPERATURE OBSERVATIONS OF THE ALBATROSS.

In 1891-2 two surveys were made by the U. 8. 8. Albatross,
between Monterey Bay and Honolulu—the one on a great circle,
the other on a rhumb line. On the great ecirele line, the surface
temperatures for the first 150 miles vary from 54° to 56°. It
then rises to 59°, drops to 57°, and rises to 62°. After that it
rises slowly as the line runs toward the tropics. The observa-
tions on the Monterey end of the survey were made in October,
1891. On the rhumb hne in January, 1892, the temperature
off Monterey Bay was 52°, rising to 59° in 140 miles. Even
with a liberal allowance for the southing made on these lines,
the surface temperatures near shore are distinctly lower than
further to the westward.

270 University of Californa Publications. [ GEOLOGY

The vertical distribution of temperature on these two lines
is shown on the isobathymetrical charts accompanying the re-
port of the survey.* In both cases the isobathytherms in the
upper part of the ocean rise on approaching the California
Coast. They indicate that water near the surface close inshore
is as cold as that 1,000 to 2,000 feet below the surface 200 to 400
miles off shore.

From 1888 to 1900 the Albatross made several series of
hydrographic soundings along the Pacifie Coast. A line run in
September, 1888, off Cape Flattery falls between the first two
lines in the table of Tuscarora soundings. The stations are
close together and the temperature rises from 52° to 61° in run-
ning off shore about 50 miles and in the next 30 miles falls, but
only to 59°. The inshore cold belt is well marked, for the
temperature remains at 52° for the first 20 miles. Southward
from Cape Flattery to Cape Mendocino the series of surface
temperatures is quite complete but they are usually confined to a
coast belt of less than 30 miles in width. They are also scat-
tered through various months in the term of 12 years. For
comparison with the Tuscarora observations, temperatures taken
during the autumn months have been used. The general result
has been to confirm fully the conclusion that a belt of cold sur-
face water exists near shore. Of equal interest is the fact that
the temperatures show narrow belts of warm and of cold water
lying close together and frequently occurring in the area cov-
ered in one day’s observations. Usually these narrow belts are
at right angles to the coast. This peculiar arrangement of the
minor temperature belts seems to negative definitely the idea
that the cold coast water is due to an inshore Arctic current, for
such a current would give a stream of moderately uniform
surface temperature and the variations that did occur would
naturally extend in belts or lanes having the same longitudinal
direction as the main stream.

As an illustration of the results obtained in charting these
temperatures, a section of the coast extending about 150 miles
northwest from Cape Blanco is shown in Pl. 31. Close inshore

* Senate Ex. Doc. No. 153, 52nd Cong., Ist Ses.

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Surface temperatures along a portion of the Oregon Coast for August

or Septeml er.

indicate approximately the ocean depths.
ture observations made on the same day.

The 100-fathom line and an occasional deep-water sounding

The dotted lines connect tempera-

Vou. 4] Holway—Cold Water Belt. 2

the temperatures ran from 47° to 52° in the vicinity of Coos
Bay from September 10 to 12, 1889, while on the 11th a little
further off shore there is a short line running from 57° to 59°.
Notice also that on the same day within 10 miles on the north
and on the south, there are lines with temperatures varying
from 50° to 54°; that is, of the three short lines at right angles
to the coast just south of Coos Bay, the middle line averages
about 6° warmer than the other lines. Over the Heceta Bank,
it will be noticed that temperatures of from 60° to 63° oceur,
while close inshore a temperature of 49° occurs only ten days
later. The ten days’ difference in time can cause no appre-
ciable seasonal change in temperature and the variation from
63° to 49° very probably was true for the same day. The lines
of temperature for August 30 and 31 are typical in showing the
colder water inshore, the exceptions to this rule being few and
with sheht differences in temperature. No exception has been
found with east or west lines of 50 to 200 miles in length and
which run close inshore.

INSHORE BELT OF COLD WATER.

This general idea of a cold inshore belt has long been recog-
nized. Richter* discussed the Tuscarora temperatures and
ealled attention to the belt of cold coast water which they indi-
eate. Apparently without other observations he accounted for
the presence of this cold water by assuming the existence of a
eold surface current from the Arctic. Part of Richter’s argu-
ment is based on the strange error that ‘‘the western coast of
the United States trends northeastward from Cape Mendocino
to Tatoosh Island,’’ when in fact Tatoosh Island is shghtly west
of north from Cape Mendocino. As already stated, a study of
the temperature relations found in Pl. 31 renders highly im-
probable this idea of a cold polar surface current. Before dis-
cussing the hypothesis advanced in the present paper to account
for the cold inshore belt, the temperatures for greater areas of
the North Pacific should be examined. The temperature charts

* Richter, C. M. Ocean Currents Contiguous to the Coast of California.
Bull. Cal. Acad. Sci., vol. 2, p. 337.

272 University of Califorma Publications. [ GEOLOGY

for the entire west coast give a mass of detail which can be
studied best by expressing the figures for a limited period by
isothermal lines. In Pl. 32 is given the general result for the
month of August.

A salient feature of this chart is the area indicating warmer
water to the north of the inshore belt of cold water as well as
to the west and south. The fact of the presence of this warmer
water in addition to the minor belts of varying temperature
already shown in PI. 31 seems to exclude entirely the hypothesis
of a cold, polar surface current along the west coast of North
America. The only remaining explanation is that there exists
a belt of cold water upwelling from the adjacent ocean depths.
Possible reasons for this upwelling will be discussed later. A
prior consideration is the general trustworthiness and the de-
eree of accuracy of the isotherm in Pl. 32. The writer feels con-
fident that the location of the coldest part of the inshore belt in
the vicinity of Cape Blaneo and Cape Mendocino and the exist-
ence of warmer water to the northward are fully established.
The exact position of the isotherms is open to doubt but it is not
believed that the error is sufficient to affect the general relations
which can be shown on a map of the scale used in Pl. 32. More-
over the problems and conclusions of the paper will not be
changed by a future shifting of the boundaries of the tempera-
ture zones here represented.

The essential differences between the chart here presented
and previous isothermal charts of the North Pacifie for the
month of August will now be examined. The charts to be cited
show little if any variation in the location of the isotherms in
mid-ocean, but differ widely in the vicinity of the American
Coast. Marakoff in his work already quoted makes the isotherm
of 18° C. turn abruptly to the southward at about latitude 45°
and again bend to meet the coast in about latitude 36°. He thus
represents the cold belt along the coast as merely an extension
of the cold zone of the extreme North Pacific. The British
Admiralty charts (1886) show the isotherm of 60° as almost
touching the coast near the mouth of the Columbia River and
then as swinging out and southward, finally meeting the coast

BUI IDERT. GEOL. UNIV. CAL. VOWeaien o2

(70. {60 (50 (40 {30 (20 110

Isothermal chart of the eastern portion of the North Pacific for the
month of August. Lines represent approximate mean temperatures for the
month.

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VoL, 4] Holway—Cold Water Belt. 4

somewhat north of Point Conception. In other words, accord-
ing to this chart, the belt of cold coast water along California
and Oregon has a very narrow connection with the cold water
of the extreme North Pacific.

The temperatures for the cold belt are not so low as those
reported by the Albatross, but the latter were doubtless taken
much closer inshore than those used by the British Admiralty.
The loeality shown in Pl. 31 just north of Cape Blanco is marked
on the British Charts as having a variation exceeding 10° during
the month of August. This agrees with the belts of varying
temperature found by the Albatross in that vicinity and is prob-
ably due to alternate bands of the surface water proper and
of upwelling cold water from the ocean depths.

The isotherms of the Deutsche Seewarte chart are repro-
duced in Pl. 33. They show similar general relations to those
indicated in Pl. 32, but differ in making the cold inshore belt
much shorter and in locating the coldest part of the belt at two
San Francisco Bay and the Straits of

widely separated places
Fuea, the lowest temperature being shown by the isotherm of
14° C. (57° F.). The latest data available do not greatly change
the average temperatures for these points as marked on the
German charts. Davidson* gives the monthly averages in the
Golden Gate for 12 years of daily observations. The Aueust
mean for this period is 59.2°, with 57° the lowest average for
any one year. Lower temperatures are reported just outside
the bar.

The corrections to be made in Pl. 33, according to the recent
Albatross observations, do not consist in a revision of the tem-
peratures given for the cold water areas so much as in the loeat-
ing of much colder areas near Cape Blanco and in more than
doubling the entire length of the belt of cold coast water. The
occurrence of the coldest water in the vicinity of Cape Mendocino
and Cape Blanco has an important bearing on the theory to be
offered to account for the belt of cold water along this coast.

* Davidson, Geo. Bull. Calif. Acad. Sci., Vol. I, p. 354.

274 University of California Publications. [ GEOLOGY

TWO PROBLEMS PRESENTED.

The temperature relations of the surface water of the North
Pacific represented in Pl. 32 present two problems for solution.
First, what is the cause of the belt of cold water along the west-
ern coast of the United States? We have already seen that it
must be due to an upwelling of cold water from the adjacent
ocean depths, but what are the causes which produce this up-
welling? And secondly, why should the coldest part of this area
be in the vicinity of Cape Blanco and Mendocino, instead of
farther to the northward? Before attempting to answer these
problems, a brief review will be made of the discussions of cold
water in other portions of the world and also of the general tem-
perature relations of the North Pacific.

COLD WATER ALONG OTHER COASTS.

In Pl. 34 A is shown the belts of cold coast water as mapped
by Andrees.* Berghaus; gives practically the same areas omit-
ting the southeast coast of Arabia. Both authors make the belt.
extend along the entire Pacific coast of the United States and
of Lower California. Neither of them attempts any differentia-
tion of the cold water area into belts or sections of different tem-
perature. In the handbook accompanying Andrees’t Atlas, these
areas of cold water are attributed to a vertical current caused
by winds blowing off shore and dividing the surface water to
the leeward. The supposition is that the accumulation of water
to leeward would cause a return drift at the bottom of the ocean
and an upwelling near the shore.

A discussion and indorsement of this idea is given by Murray§
as a preface to his study of the effect of winds on the lochs of
Scotland. With such small bodies of water as the lochs, the
entire surface is under the influence of wind blowing in the
same direction and return surface currents are not possible.
Wich the ocean partial compensation may be made in other ways.

* Andrees. Allgemeiner Hand Atlas, 1900.

7¥ Berghaus. Atlas der Hydrographie, 1891.

{ Geographisches Handbuch zu Andrees Handatlas, 1899.

§ Murray, Sir John. Effects of Winds on Distribution of Temperature,
ete. Scot. Geog. Mag., 1898, p. 345.

BULL, DEPT. GEOL. UNIV. CAL. VOlLn 4) (Fl 34

°
st ae “o nn oo

A. Belts of cold coast water according to Andrees. Compare the West
Coast of North America as given here with the same region in Pl. 36.

wale
|
|

Longitude from| Greenwich.

B. Maximum Surface Temperatures, after Sir John Murray.

Vou. 4] Holway—Cold Water Belt. 275
Hann* accepts the theory that the rise of cold water along the
coast is caused by the ‘‘suetion effect’? of winds blowing off
shore. In his general discussion he incidentally remarks ‘‘that
the sharp deflection of an ocean current off shore may cause a
rise of cold water from below.’’ He does not apply the latter
ideas to any of the areas which he discusses, which are substan-
tially those mapped by Andrees. The whole California coast is
mentioned among others as if it belonged in the area of constant
trade winds.

Buchanan} discusses this subject and gives some data for our
coast. During his voyage from Valparaiso to San Francisco
in 1885 he stopped at Mazatlan. He states that on getting under
way from that port the surface temperature was 75.8° and ‘‘the
cold water must have been close to the surface, for water taken
from the wash when the steamer was going astern had a temper-
ature of 72.8
perature was 78° and the water a deep blue color. Approaching

oj?

Thence across the Gulf of California the tem-

Cape San Lueas the temperature of the water fell to 73.4° and
then to 64.4° close inshore. After passing the Cape the temper-

2)

ature rose to 66.8° as the shore was left. Thence northward to
San Francisco the water grew colder, falling to 50° degrees at
the entrance to the bay. The low temperature found in passing
Cape San Lueas is the most important part of this account. The
cold water he found on the further trip to San Francisco being
on a single line parallel to the coast furnishes little basis for dis-
eussion. Mr. Buchanan offers the following comment: ‘‘The
oeeurrence of these coast areas of abnormally cold water is ex-
plained when we recognize that they are the windward shores of
the oceans. The trade winds blow from them toward the equator
and in so doing mechanically remove water, which has to be
supplied from the readiest source. This source is the deep water
lying off the continental coast which is supplied by the gradual
drift of water from high latitudes. Hence, though the low tem-
perature of the coast water is referred to as due to the eold of
high latitudes, it is not supplied by a long surface current, but

* Hann, Julius. Handbook of Climatology, 1903.
7+ Buchanan, J. Y. Similarities in the Physical Geography of the Great
Oceans. Pro. Roy. Geog. Soc., 1886, p. 753.

276

a short vertical one.”’

University of Califorma Publications.

[ GEOLOGY

The limits of the trade wind belt off the

California coast will be discussed later, but it is needless to re-

mark that these limits never reach as far north as Cape Blanco.

Mr. Buchanan, it should be noted, does not discuss the conditions

on the coast north of San Francisco.

Possibly the most interesting instance of cold water rising

from ocean depths is found on the Somali Coast of Africa just

south of Cape Guardafui.

Captain Hoffmann’s account of the
I

voyage of the Méwe is becoming classic in these discussions. The

course of the Mowe was northward from Zanzibar along the coast

of Afriea to the Gulf of Aden.

The table of temperatures here-

with is taken directly from Captain Hoffmann’s account, chang-

ing the temperatures to Fahrenheit to agree with the use in this

OBSERVATIONS OF CAPTAIN HOFFMANN

FROM “REISE S. M. KR. MOWE VON ZANZIBAR NACH ADEN”*

Latitude | Longitude Date tr se) Latitude | Longitude
| Tune28| 12) 79°2 || 4°41’ N| 48° 14’ E
” 98/12) 75.2 |
4° 49’ S | 39 36 EI 2 DON Test, |
SPAY UPR ThatO) Iie fb 10 N| 49 33 E|
158 S/41 95 E| » 30/12| 79.5 | |
| » solie} 77.4 ||
1 15 N|43 15 E|July 1/12) 80.4 ||
|” 1/12) 78.1 |
2 35 N\46 24 B| » 9/12] 78.8 |
| » 9/12] 74.8 || 9 30 N[51 21 E
4 41 N|48 14 EB] ” 3/12] 77.4 |
| | » 3/4) m2 |
| » 3) 8] 68.0 11 56 N|51 05 E

==

Date |

July3 |

”

”

Oo WA Nn

|
Temperature

Water
68°0
65.6
64.8

68.0
73.9

6. Guardafui
90.3

* Ann. der Hydrogr., 1888. p. 345.

=a
a |

Cold Water Belt. ys

Vou. 4| Holway.

paper. The marked fall in temperature on July 3 and 4 was

accompanied by a fall in the temperature of the air and by a
change in the color of the water from blue to a deep olive green.
As in this loeality a cold polar current is an impossibility, unless
it persists directly across the equatorial region, we are forced
to the conclusion that the cold water rises from the ocean depths.
Captain Hoffmann reports a strong north flowing current that
makes a bend to seaward at this point where the fall in temper-
ature occurs. He states that the fall in temperature seems to
be related to the chanee in the direction of the eurrent. Bu-
ehanan attributes the cold water in this instance to the southwest
monsoon blowing off shore. Hann and Andrees do the same and
state that the cold water disappears with the coming of the north-
east monsoon.

The authorities quoted, with the exception of Captain Hoff-
mann, seem to be in general agreement in accepting winds blowing
off shore as a sufficient explanation of cold coast water in these
areas. On our coast from San Francisco to Cape Flattery, the
prevailing winds blow toward the shore, as shown in the Pilot
the
of the weather map—the winds may be temporarily re-

Charts. During the passage of an extratropical cyclone,
‘‘low’’
versed. As to trade winds on the California coast, the Pilot
Charts for 1903 show that the most northerly extension of the
trades—oceurring in August—was to Lat. 37° 30’. This was
only in mid-ocean nearly 1,000 miles to the westward of San
Francisco. Nearer the coast the northern limit of the trades is
further to the south. At all seasons of the year the Pilot Charts
show a belt of northwest winds between the Southern California
Coast and the trade winds. Alone Southern California where
the trades blowing off shore are the nearest to the coast is the
very locality that fails to show a definite belt of cold coast water.

GENERAL TEMPERATURE CONDITIONS OF THE NORTH PACIFIC.

For a brief summary of the temperature conditions of the
North Pacific we may take a recent article by that eminent
authority, Sir John Murray.* The charts which he gives afford

* Murray, Sir John. On the Temperature of the Floor of the Ocean, ete.
Geog. Jour. 1899, XIV, p. 34.

bo
-l
oe)

University of California Publications. [GEOLOGY

a summary of a vast amount of observational detail bearing on
the general problems of his paper. The charts showing maxi-
mum and minimum surface temperatures will first be examined.
These were prepared by laying off on 2° squares all the recorded
observations of surface temperatures. The tables of Admiral
Makaroff give 38,874 observations for the North Pacific. Murray
has supplemented these by the reports of the British Admiralty
Office and from other sources. The maximum and minimum
temperatures are taken for the months of August and February
respectively. Nearly 25% of the 2° squares in the North Pacific
have no recorded observations. This lack should be borne in
mind, but as nearly half of these omissions are in the Torrid
Zone, it is not likely that the mapping of maximum or August
temperatures in the broad belt of these charts has been seriously
affected.

Maximum Surface Temperatures.—P\. 34 B shows the results
for the North Pacific, the temperature zones indicating difference
of 10° F. So far as the problems of this paper are concerned, the
most marked departure from east and west boundaries to these
zones is found in the belt of 60°—70°. This shows a notable ex-
tension southward along the coast of the United States and re-
veals the belt of cold coast water, confirming the existence of a
southward flowing drift off the coast, as shown on the Pilot
Charts. The torrid belt of 80°—90° makes a northward extension
alone the coast of Lower California. This again confirms the
Pilot Chart which shows a northwestward flowing current off
the Mexican coast.

Minimum Surface Temperatures.—Pl. 35 A is the chart for
minimum surface temperatures in the North Pacific. Here again
is the southward extension of the cold belt along the western coast
of North America. An interesting fact here is the bend to the
southward along the 120th meridian showing that the currents
from the north leave the shores of America turning to the west-
ward.

Range of Surface Temperatures.—Pl. 35 B is from another
chart by Murray from the same data.* The annual range of tem-

* Murray, Sir John. Annual Range of Temperature, ete. Geog. Jour.
1898, Vol. XII, p. 113.

BURRS DERI GEOL SUINIVi CA, WAGE st Maledesesta)

[este t= i 4 Onrnies
4-~
a Ta |

eas EN

ra

‘Longitude from| Oreenwich

180)

A. Minimum Surface Temperatures, after Sir John Murray.

Longitude from! Greenwich.
‘ oe

160° 180° 160°

B. Annual Range of Surface Temperatures, after Sir John Murray.

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Von. 4] Holway.—Cold Water Belt. 279

perature is here shown. The great torrid belt with an annual
range of 10° or less shows a northward pointing extension off
Lower California similar to that on the map of maximum temper-
atures and to be accounted for in the same way. An interesting
minor point, bearing on the accuracy of the map, is shown by
the small area around the southern part of Lower California,
which is charted as having an annual range of 20°. This in-
eludes the locality where Buchanan reports cold water due to
upwelling. It will be seen by reference to the Pilot Charts that
while the main current from the southeast is constant during
the year, the inshore current varies with the seasons, sometimes
being from the north and sometimes from the south. This varia-
tion indicates of course a ereat annual range of temperature.
This mutual confirmation of the two maps in this small area is
worth noting as a correlation to the warning given by the authors
as to the insufficient data upon which their work rests.

Another variation in Pl. 35 B is the southward extension of
the belts of an annual range of from 10° to 15°. This occurs at
about 120° West Longitude and extends to Latitude 10°. This
is probably accounted for by a variation in the strength of the
south flowing California current and of the northwest flowing
eurrent off Mexico. This variation is somewhat indefinitely
shown on the Pilot Charts by a change in the extension of these
eurrents during the spring and the autumn seasons.

Temperature of Ocean Bottom.—Pl. 36 is a reproduction of
the Deutsche Seewarte chart showing ocean depths in the North
Pacifie. The principal areas which according to Murray have a
bottom temperature of under 35° are indicated by oblique pa-
rallel lines.

The contours on this chart are in meters; the first line indi-
catine 200 m. and the others the successive even thousands. In
the region to the eastward of Kamehatka these contours must
be modified to agree with recent soundings of the Albatross. A
sounding of 5,700 M. (3,117 Fm.) was obtained in Lat. 54°-51’,
Long. 163°—46’ E and other soundings indicate that a channel of
about 3,000 M. (1,640 Fm.) leads from the Pacifie into Bering
Sea. A dotted line shows the possible location of the 3,000 M.

280 University of Califorma Publications. [GEOLOGY

contour according to these late soundings. The distribution
of these areas of cold water on the ocean bottom is closely
related to the question of the source of the cold water
along the west coast of the United States. Of primary in-
terest is the larger area extending from near Alaska south-
ward far beyond Point Conception. The part of this mass
of cold water lying north of Lat. 50° is bounded on the
north and east by the contour line of 2,000 fathoms (nearly
4,000 M.). The western extension of this mass of cold and pre-
sumably heavy water hes just on the edge or slope of a sub-
marine valley that runs down to a depth of more than 3,000
fathoms (6,000 M.). If the distribution of cold water in the
ocean depths depends on convection as is frequently claimed,
why does not the cold water settle into this deep valley? This
might be answered by supposing greater density for the water
in the greater depths. A discussion of the varying salinity on
the bottom of the ocean in this region is at present impossible
from lack of accurate data. The uniform upper level of this
mass of cold bottom water is an interesting point when the North
Pacifie Pilot Charts of this region are examined. In this great
bight of the Alaskan coast there is represented an ocean eddy
turning contraclockwise for three-fourths of the year and being
reversed in direction during the winter months. Is it possible
that this eddy maintains a mass of cold water at the bottom at
a constant level? The idea of a casual relation here is so seduc-
tive that the writer feels compelled, in fairness, to quote a para-
eraph from the Pilot Chart :—‘‘ After a careful consideration
of the reports of vessels cruising near the Aleutian Islands and
in the Bering Sea, the Hydrographic Office warns mariners
against placing too much reliance upon eurrent predictions in
that portion of the North Pacific.’’? The warning is probably
intended to apply ‘to regions farther to the westward, but should
be eonsidered for this region as well. In connection with the
question of the existence of this Alaska eddy, it is to be remarked
that the isotherm of 55° bends to westward just south of Alaska
in a way to confirm the existence of such an eddy. (See Pl. 32.)
Setting aside theories and keeping in mind the thought of the

VoL. 4] Holway.—Cold Water Belt. 281

level upper limit of the cold bottom water as mapped by Murray
for the region south of Alaska, let us examine its great southward
extension.

From off Vancouver Island to San Francisco it has risen
above the 2,000 Fm. (4,000 M.) contour and lies upon the conti-
nental slope of the ocean bottom—again in defiance of gravity
unless there is postulated a peculiar arrangement of salinity in
the lower depths.

HYPOTHESIS ACCOUNTING FOR COLD WATER BELT.

To explain this apparentiy abnormal position of the cold
water, let us suppose, as a working hypothesis, that the direction
of ocean drift in the northeastern parts of the North Pacific is
not merely true for the surface, but that it holds throughout
the entire extent as far as the ocean bottom. In winter the cold
surface water to the south of the Aleutian Islands would sink
and at the same time be carried slowly toward the eastward.
It would thus be carried over the western portion of the Maury
Deep of Pl. 36 and would finally rest on the continental slope.
In the Alaska Bight it is conceivable that the eddy would give
a constant upper level to this mass of water. To the southward
along the coast of Vancouver to San Francisco, the upper drift
(except very close inshore) is toward the east and south. ‘If
this drift extends to the ocean bottom, the cold bottom water
would be driven up the continental slope, thus accounting for
the belt of cold coast water. Again it will be remembered that
the coldest coast water was found from the vicinity of Cape
Blanco southward to Cape Mendocino. In Pl. 36 the contours
of 1,000, 2,000, and 3,000 meters make a shoreward bend sli chtly
north of this latitude. That is, a great submarine valley heads
just under Cape Blanco and opens broadly out to the northward
and westward. The bottom drift on our working hypothesis
would thus be delivered most strongly against the coast in the
vicinity of Cape Blanco and carried southward by the general
drift.

282 University of California Publications. [GEoLoGy

The effect of the smaller submarine valleys near the coast
has already been discussed by Davidson.* Speaking of those
near Cape Mendocino he says: ‘‘They carry in the colder
waters coming from the north and outside of the influence of the
close inshore eddy current setting to the northward.’’

The writer fully agrees with this statement, but in the light
of the additional data discussed in this paper, he considers the
action of these valleys as but part of a general motion of the
deeper waters which affects the entire coast from San Francisco
to Vancouver Island.

Another instance where local temperatures seem to be influ-
enced by submarine valleys is found on Cordell Bank about 50
miles west-northwest from San Francisco and directly west of
Point Reyes. The 100 Fm. contour shows a valley opening to
the northward and heading just east of the Cordell Bank.
From June 12 to 17, 18738, Davidsont reports the mean water
temperature at 8 a.m. as only 49°. If the cold bottom water in
the deeper ocean has any motion or drift, it is not difficult to
recognize the fact that the submarine valley to the northward
might lead it to the surface in the vicinity of Cordell Bank.

A second point in favor of the theory of great depth to the
prevailing drift in the northeastern part of the North Pacific is
found in the shape of the areas of cold bottom water and in
their relation to the surface drift. The main area on the west
coast of North America has a longitudinal extension that agrees
with the prevailing surface drift. Tracing this area of cold
bottom water southward to Lat. 30°, it is seen to bend to the
southwestward as do the surface currents. The question also
arises as to the reason for a termination of the cold water at this
locality. It is certainly not the insolation received in the torrid
zone, for this penetrates but a short distance below the surface
of the ocean. Moreover, in the middle of the North Pacifie ex-
tending across the equator into the southern hemisphere is one
of the largest areas of water below 35° on the ocean bottom. A
ready explanation for the termination of the cold bottom water

* Davidson, Geo. The Submerged Valleys of the Coast of California,
etc, ro: Calit.) Acad) sci. Geol, Vol-memn. 99:
y~ Davidson, Geo. Pacific Coast Pilot, p. 236.

Vou. 4] Holway.—Cold Water Belt. 283

off Lower California is found in the northwest flowing warm
Mexican current previously mentioned. This current, accord-
ing to the charts of the Deutsche Seewarte, is more saline and
hence will sink and mingle with the colder water from the north-
ward.

Another interesting area of cold water on the ocean bottom
is found off Japan in the great Tuscarora Deep. The source of
this eold water is doubtless the cold polar current coming down
by Kamchatka. The southern part of this cold water area has
an extension off to the eastward. It has a direction that appears
to be the resultant of a conflict between the deep part of the
north-flowing Japan stream and the cold water of the Kamchatke
current. Here again the idea of great depth of drift would
account for the fact that we have represented a stationary body
of cold water resting on the sloping ocean bottom.

Of course, the hypothesis that these ocean currents and
drifts have a uniform direction to the bottom of the sea needs
additional evidence in its support. Meanwhile it offers a reason-
able explanation of the cold coast water on the North Ameriean
shore and of several peculiarities of the masses of very cold
water on the bottom of the North Pacifie with little indirect op-
position to the hypothesis.

The presence of the large area of cold water on the bottom
of the south central portion of the North Pacifie here challenges
attention. Can it be accounted for by the known direction of
surface or bottom drift? It must have some connection with
the cold water of high latitudes to maintain its low temperature
of 35° or under. There is no evidence to connect it with the
eold water off North America. From its position in equatorial
regions it must necessarily be supplied by subsurface currents.
There are few charts showing temperature below the surface in
the North Pacific. Turning to one by Makaroff* for the level
400 meters (218 Fm.) below the surface, the isotherms are found
to make a sharp bend to the southeast as may be seen in Pl. 37.
This indicates a southeast flowing portion of the cold Kamehatka
current which has underrun the warm Japan stream. The
~~ * Makaroff, 8. Le Vitiaz et L’Ocean Pacifique.

284 University of California Publications. | GEOLOGY

writer attempted to construct an isothermal chart for the depth
of 700 Fm. in order to follow further this cold undercurrent.
The number of temperature observations for this or greater
depths is few, and therefore not much reliance can be placed
in the results. The isotherms as drawn for the 700 Fm. level
show a narrow loop extending still farther to the southeast than
the loop in Pl. 37. It would thus seem from the evidence now
at’ hand that the cold water at the bottom of the south central
portion of the North Pacific is accounted for by a branch of the
Kamehatka current underrunning the upper portion of the
warm Japan stream and slowly sinking to the bed of the ocean.

In the provisional isothermal chart drawn for the depth of
700 Fm. a second narrow loop of the isotherms, starting farther
to the east of the Japan Islands, runs southeast toward the
Hawaiian Islands. This would account for the presence of
water below 35° F. that occurs to the northward of these islands
at the depth of 2,500 Fm.

The study of the areas of cold water at the bottom of the
central portion of the North Pacifie does not therefore in any
way contradict the hypothesis used for the cold water belt along
the west coast of the United States. In the northwest due to
the opening into Bering Sea between Kamchatka and the Aleu-
tian Islands, a southward flowing cold current disturbs the
otherwise great uniform clockwise drift of the North Pacifie.
In the north central and northeastern portions of the ocean
there are no cold currents from Bering Sea to interrupt the ac-
quirement of a uniform direction of drift to great depths.

The possibility of water at a great depth acquiring a slow
movement or drift from the action of surface winds has been
frequently discussed. A recent writer* thinks that the entire
body of water occupying the equatorial regions has a westerly
motion due to the action of the trade winds. In the northern
parts of the Pacific in the region of the prevailing westerlies,
contrary currents are frequently reported more or less in har-
mony with variations in the winds. But as the prevailing
westerlies have existed for untold ages, there has been ample

“Page, James. National Geographic Magazine, 1902, pp. 135-142.

‘soorsep operSryu0o ut somjzesoduis, ‘stojow OOF Jo yAdep oy} ye Vd WALON oy} FO sutroyjOsy

‘Horeyeyy 104FV

02)

0st

o1l

Ol)

os!

ols

‘Ld30 ‘11N8

o2)S)

71

“AINA

Wo

‘'y “1OA

“Vd

LE

i j
Ly
i
q
i
F ¢
i
eae one
{
b=
i
~
. rs sasaacommne D
Ae
a Yi!

yeu

Vou, 4] Holway—Cold Water Belt. 285

time for the development of a slow but constant deep water
movement in the direction of the prevailing wind. The north-
eastern part of the North Pacifie is pre-eminently the place for
the development of a uniform drift from surface to bottom, as
may be seen by studying the contours in Pl. 386. The contours
show a remarkable great ocean basin uninterrupted by islands
and bounded on the north and east by a regular but steep con-
tinental slope. This regularity of basin of the North Pacifie is
more noticeable if for comparison we examine a bathymetrical]
chart of the North Atlantic. In the latter we have the mid-
Atlantic ridge running in a general north and south direction
and making two great subdivisions of the basin. We have also
the wide openings on the west and on the east of Greenland and
connecting with the cold water of the Arctic Ocean. In the
Pacifie there is but one great opening into Bering Sea and that
sea is connected with the Arctic by Bering Strait, which is both
narrow and shallow. Considering then its practical lack of
connection with the Arctic Ocean and its uninterrupted basin
and relatively regular shores, it is a reasonable supposition that
the northern half of the North Pacific has a more regular system
of oceanic circulation than has the North Atlantic.

SUMMARY.

Several interesting points for future investigation are sug-
gested by the observations and theories discussed in this paper.
From the biological standpoint it will be interesting to find
whether the cold water and the variations in temperature near

rape Blanco are a barrier to species that might normally ex-
pand into the regions lying to the northward. The investiga.
tion of the area lying to the southwest of the coast from Point
Conception to San Diego, now being carried on under the direc-
tion of Professor William E. Ritter of the University of Cali-
fornia, should in the next few years give us more accurate in-
formation concerning the disputed temperature relations of this
portion of the Pacific as well as a better knowledge of the marine
hfe of the region and the temperature limitations of this life.

286 University of California Publications. [| GEOLOGY

The question of the accuracy of the charts herewith pre-
sented demands that the various gaps in the series of coast tem-
peratures be filled by reliable observations. If the theory of
this paper as to the final source of cold water lying along the
west coast be correct, serial temperatures in the region from 50°
to 55° N. Lat. and about 160° W. Long. should show, at certain
seasons of the year, inversions of temperature, that is, a stratum
of cold water should be found in intermediate depths overlying
warmer water on the ocean bottom.

In conclusion the following summary of observations and
hypotheses in reference to the belt of relatively cold water lying
along the west coast of the United States is presented :

(1) Recent observations indicate that the previous mapping
of this cold belt as extending southward to the coast of Lower
California is incorrect. The definite belt of cold water can not
be traced south of Point Conception.

(2) In summer the coldest part of this belt is in the vicinity
of Cape Blanco and Cape Mendocino.

(3) The source of this cold coast water is in the ocean depths
to the northwestward.

(4) This cold water at or near the ocean bottom has a slow
drift agreeing in direction with the average direction of the
surface drift and is driven to the surface on striking the slope
of the continental shelf. Local variations in the cold coast water
are due to the submarine valleys and other irregularities in the
slope of the continental shelf.

University of California,
September, 1905.

UNIVERSITY OF CALIFORNIA PUBLICATIONS
BULLETIN OF THE DEPARTMENT OF

GEOLOGY

Vol. 4, No. 14, pp. 287-357 ANDREW C, LAWSON, Editor

THE COPPER DEPOSITS OF THE ROBINSON
MINING DISTRICT, NEVADA.

BY

ANDREW C. LAWSON.

CONTENTS.

EET GVO) CLL 610 ete eee eat a se ee ee a ee eae 8

Wihite mPime Sho lee cca assess cetereec 2 ee sescee eee tues oes pvesstee a fesse eee OO
INGA C aialb iTS t O16 meetes meee sce tac Rcereens cores oeeee eras ares oe see seen re os dS 296
Correlation with the Wureka Section —....-..2...-.--..-sc:cce2---ssecceeeceecneneegese OOT
General iS truct ire: 2c cese arcs sete cee nee cree e este nse eee tess aacee ane fue eee otaseetes, BON
MMe mlx rp thViG: TRO CK S, Yess esceeaetes tesco tas c. nc scee. cate denes se =as0 Sen ttees¥egcnscshsceasesaesesuecesseesen 298
IWichaleqonamhiyey TREK Wao N Dele ee een eee eee 298
pNtore ot the; NUOmZ OTL erase orn osteo oeece asee cea eased ee Ae a eee 303
Gomtact) Whenomem ay s2iscs ccs sc eveaceva dese sovaes2 oeee. sacctexssuceeesscesdseceesescseeen cs 304
Jetehomayerstay aunce Nl OURO Pe ae ee eee etree ye erry een eee 305
RODueyrouteteH |) aX Cfop ant oY ays) 1109 ely e-em eet eee ayes POR ee 306
Monzonite Porphyry Dykes 308
POET OS LAPD Ye coset celia nce ce cs seee as so acacceneuaee douse des scbeeys oseedstececetacaeseenicdsseceeteace 308
Chemical Comp Oswtvon Serer ees nte ce wer cae a reece ere re soccer nce ernteerenaseteene= 310
Tnyetehnioner inoy MiNonbAonabhe: IBY HA aCOM MA ee eer aa eee ee 310

The (Copper-bearino (Porphyry aac soe a ance sence Pe nn cncnne Pes eae ccseeeantace? 311
DED) 0 ere ee ne I EEE Ee ae ee SEP eR eee 312
Hentrisivey ReLatLoms : Sc sc 255 8 swe eee ee seca see base cede shade eden ee cncn ce ecseecgensEieie cease 312
SHS E 01 0 Oe SP Pee OP 313
Contact Metamorphisma: 2. lceccscc:cc2-2ccece ce ceecteee scene costs cccevencenccceaceenssecuceesdens 315

Petrographical (Characters) -ecccc ce. css cesses eee cee eee ere ececes ats BLO

288 University of California Publications. [GEOLOGY

PAGE
Chem call “Comp OSU geeecen cece cae acon eee eee cee ee rare ae eee se esera eee se ieee ee 321
ROSIN c-. 1e orcas case gts oes tonaas cen seeen fue ae tes sttrace oz ece st eae tre ete eee 323
Porphyry atethe Chaimmerm (Mine ssa cee cee ee 823
Quartz lout: ais ic sis cert aoc ae, nce lseestebetce ns cetitucaes. 29 were tees 324
Mera: MCL WCU ee esses rescence scare eect carota neers 324
Biel) Relations), ssc. 2 resect soso cetcceccage cptsece eee oes saeee eee veneer eee ee 325
Warlettesmot Quartz eB Git escsscesccctecerescsetsce-ecceeeesseseves ceeeceeesseseee sess ee eeeneem 327
Relations to Copper Ores and Garnet Rock ..........20--22..222---22--2-00-20--++ 329
he Pomphryary: as a @opper Oxey es cscs ceeceeeeetese specs ore cs eeeseereee sop eeae teen 330
Mam et Ge Gress cee ee rere eae nee eee
Chemical Composition
Rhyolitie Tava amd dts ses eee ee ase secre esac eee cece tess ne ee eee eens 347
Three members of Volcanic Series -....-....-...-2-----00cecc0-teccceenesneecseneentereeess 347

Petrographical Character
CG) of) 6 7 ee ne aa Pe Meee ep ence
Other Metalliferous Deposits
P91 ge me ete roe eee Bene teh
Maneralioey “of the, (District 2ee-ncccsccccce-scesccee cores sta teeesoceces coe ees ce eee seeereae ees

INTRODUCTION.

The Egan Range is one of the larger members of the Basin
Range system of mountains traversing eastern Nevada with a
general north and south trend. The range has a breadth of
several miles and is separated from the neighboring parallel
ranges by broad, flat, alluvial valleys coextensive with the ranges
between which they lie. The chief formations which enter into
the structure of the range are, so far as at present known, sedi-
mentary strata ranging in age from the Cambrian to the Car-
boniferous. These strata have an aggregate thickness of many
thousands of feet, and the entire sequence has been compressed
in part into open, fairly symmetrical, folds, which locally
may be more acutely appressed and affected by dislocations.
The pre-Cambrian basement upon which the Palaeozoic rocks
rest is not exposed; but, at various places in the range, there
are intrusive masses of granitic and monzonitic rocks and some of
these have been supposed erroneously to represent the Archaean.
It is probable that these granitic rocks date from the mid-Meso-
zoic revolution, which affected the Cordilleran region from the
Wasatch to the Pacific, although it is only positively known that
they are post-Carboniferous. These intrusions would thus be
contemporaneous, in a general way, with the granites of the

VoL. 4] Lawson.—The Robinson Mining District. 289

Sierra Nevada, the Humboldt Mountains,* the Wasateh,+ Cen-
tral Idaho,t and the Coast of British Columbia.§

At a later date, probably in Tertiary time, there were local
intrusions of a light colored, acid, porphyritie rock which has
since been much kaolinized and silicified, in which or in con-
nection with which important ore bodies are now found. While
there is thus a certain degree of complexity of geological struc-
ture within the range, the structural lines seem to have had little
or no influence in determining either the east or the west border
of the range, both of which are remarkably linear, and would
appear, from a very partial and cursory examination, to cut
obliquely across various structures indifferently, a fact which
in itself justifies the conception of the range as an orographic
block of the Basin Range type. This independence of the bor-
dering lines of the range to the structure is in marked contrast
with the control which has been exercised by the structure upon
the geomorphic development within the range. Here the geo-
morphie expression is conditioned by the structure, and by the
differential resistance of the rocks to erosion. In the softer
formations the valleys are broad and the slopes are quite mature.
In the harder formations the streams run in eafions. In general
the montaine geomorphy is much more advanced than in the
case of the ranges of the same structural type recently described
by Louderback|| in the western part of Nevada, a contrast which
may be due, perhaps wholly and certainly in part, to the absence
of a cap of basaltic lava in the Egan Range. After the geo-
morphy of the range had been well advanced toward its present
condition there were local voleanic eruptions which caused some
of the valleys to be occupied to a limited extent with tuffs and
flows of lava. Since then the range has been faulted and a con-
siderable proportion of these lavas and tuffs has been removed
by erosion, and the valleys have been deepened below the floors
upon which the voleanie rocks rest.

The Robinson Mining district, with the geology of which this

* Louderback, G. D. Basin Range structure of the Humboldt Region
Bull. G. 8S. A., Vol. 15, pp. 289-346, 1904.

7 Emmons, 8. F. Am. Jour. Sci., 4th ser. Vol. XVI, pp. 139-147, 1903.

t Lindgren, W. 20th Ann. Rpt. U.S. G. S., Pt. IL, pp. 65-256.

§ Dawson, G. M. Geol. Surv. Canada Ann. Rpt., 1886, Pt. B.

|| Op. cit.

290 University of California Publications. [GEOLOGY

paper deals, is but a very limited portion of the Egan Range.
It lies in a pass through the range a few miles southwest of the
town of Ely. The district comprises a belt varying little from
a mile in width and having a length of about six miles. This
belt has an east and west trend and thus lies transverse to the
general course of the range. The mineralization of the district
which gives it its economic importance is intimately and genet-
ically connected with an irregular intrusion of ‘‘porphyry’’ cut-
ting Carboniferous rocks and occupying the center of the belt.
Ore deposits are found both in this porphyry mass and in the
sedimentary rocks which border it. In the porphyry itself are
found copper ores in large quantity. In the limestones on the
northern flink of the porphyry zone, particularly toward its
eastern end, are limited bodies of lead ores carrying some silver ;
and on the southern flank, also at the eastern end of the belt,
oceur gold ores in ledges in the sedimentary rocks. The silver
lead ores have as yet not been found in sufficiently large bodies
to warrant permanent mining operations, although considerable
prospecting has been done and some ore has been shipped. The
gold ores at the Chainman and Saxton mines have attracted the
attention of capital sufficient for the erection of extensive and
costly plants for their reduction, but the attempt to win the
gold has been apparently unsuccessful and both plants are now*
idle. The chief interest in the district now centers in the copper
deposits which give much promise of being mined on a large
scale in the near future. The chief localities in the district
where these ores have been developed by mining operations on
a notable scale are at the Ruth Mine in the eastern part of the
belt, at Copper Flat in the middle,-and in the vicinity of Pilot
Knob at the west end. Besides these, however, there are numer-
ous prospects and mining locations throughout the district.

In the following account of the geology of the district, its
limits will be assumed for purposes of description to be coter-
minous with these of the geological map which accompanies this
paper.y The topographic base of the map upon which the geolog-
ical formations are delineated was surveyed and drawn by Mr.

* 1905.

7 While this paper was passing through the press the map was destroyed
in the San Francisco fire. It may be reconstructed and issued later.—Ep.

VoL. 4] Lawson.—The Robinson Mining District. 291

F. S. Schmidt. The contours were sketched with the aid of as
many control points, established by transit and stadia survey,
as could be obtained in a somewhat limited time. The survey
plats of the numerous mining locations and traverses of the
roads constitute the chief frame work of the map. The altitudes
are approximate only, the nearest reliable bench mark being at
Eureka, some eighty-odd miles distant by wagon road, and the
only check to this being by aneroid. In relief the district has
a hypsometrie range of about 1,600 feet, the extremes of alti-
tude being 6,440 and 8,040 at the east end of the district. For
topographic details reference must be made to the map. For
the purpose of locating observations the mining claims named
upon the map will be freely used. The field was geologically
surveyed and the map constructed primarily for the purpose of
studying the conditions of occurrence of the copper ores, and
of delimiting the copper bearing formation. Attention in the
field being thus focussed upon a special problem, many phases
of the general geology received but incidental or hurried study ;
it thus happens that, in the attempt to compile the observations
into a consistent account of the geology, some questions have
arisen for the answer to which the data at hand are insufficient.
Notwithstanding this, the study has been sufficiently instructive
to the writer to warrant his thus attempting to set forth the
results obtained as a contribution to the geology of Nevada and
to the problem of the genesis of copper ores.

The literature of the Egan Range is rather secant. In the
Report of the Geological Exploration of the 40th Parallel, Vol.
II, pp. 486-489, is a brief note by Emmons on the general fea-
tures of the range based on observations made at its northern
end. In Bulletin 208 of the United States Geological Survey,
pp. 47-54, Spurr gives a somewhat more extended note on the
geology of the range. The only reference to the Robinson Min-
ing district, however, is a paragraph in the work just referred
to in which Spurr says: ‘‘At Mineral City, just west of Ely,
lead, silver, and gold, with some copper, are obtained. At this
locality a number of siliceous dykes cut up through the lime-
stone, and seem to be connected with the mineralization. In the
neighborhood of Ely there are considerable ore deposits.’’

292 University of California Publications. [ GEOLOGY

THE PALAEOZOIC ROCKS.

The sedimentary rocks of the Robinson Mining District are
confined to the Palaeozoic. The upper portion of the section has
been determined on palaeontological evidence to be of Carbon-
iferous age. In the study of the structure of the district it has
been found convenient to subdivide this Carboniferous series
into three formations and for these local names are used. The
lower part of the section has yielded no fossils, but falls into
two strongly contrasted members, and these, on the basis petro-
eraphic and other considerations to be mentioned later, are cor-
related with the two divisions of the Devonian recognized else-
where in the basin ranges, viz: the White Pine shale and the
Nevada limestone, and they will therefore be described under
these names.

THE CARBONIFEROUS.

The Ruth Limestone.—The highest member of the Carbonif-
erous series is the Ruth limestone, a formation of heavy, but
distinctly bedded, blue gray limestone, carrying Upper Carbon-
iferous fossils. This formation is characterized by an abundance
of flint or chert nodules and the fossils are to a large extent
replaced by such silica. The chert nodules are often several
feet in length, but generally they range in size from about an
inch to a foot in length. A very common form is oval or nearly
circular in random cross sections. The color of the chert is much
darker than the limestone in which it is imbedded. The rock
is otherwise remarkably free from impurities, weathers to a dull
eray color and forms but a scant regolith.* The outerops are
usually abrupt and the ridge tops are bare. This formation
being at the top of the local geological column and its upper
limit being determined by erosion, its full thickness can not be
here ascertained. There remains of it, however, not less than
500 feet.

A specimen of the chert from the Ruth limestone showing
a laminated structure was particularly studied. It consists of
blue-gray chert in layers from 3 to 6 mm. thick alternating with

* Merrill, G. P. Rocks, Rock-Weathering and Soils, 1897, p. 299.

VoL. 4] Lawson.—The Robinson Mining District. 293

thinner layers of limestone which on weathered surfaces are
etched out. The layers or laminae are distinctly curved. In
thin section the alternating laminae are distinct (the limestone
being turbid from impurities and the chert clear. The line be-
tween the chert and limestone is sharp but is irregular. The
chert is a crypto-erystalline aggregate of quartz grains showing
ageregate polarization effects. There are some shred-like areas
of calcite in the chert layers. The limestone is an allotriomorphiec
granular aggregate of calcite grains of rather vague boundaries.
There is an abundance of fragments of organisms both in the
limestone and in the chert layers. These organisms appear to be
chiefly foraminifera. In the chert the cavities of the organisms
are filled with an aggregate of quartz grains of much larger
size than those composing the chert matrix, but the chamber
walls are still composed of calcite. The same statements are true
of the organic remains in the limestone, but silicification of the
cavities is less pronounced. In several cases chambered shells
were found partly in the limestone and partly in the chert but
the character of the shells appeared to be the same for both parts.

Fossils—tThe time at the disposal of the writer while in the
Robinson district did not permit of a deliberate search for pa-
laeontological evidence of the age of the formations, but wher-
ever fossils were observed in the course of the stratigraphic
work they were collected. The localities at which such fossils
were found are chiefly confined to the Ruth lmestone. These
were submitted to Mr. George H. Girty, the well known specialist
on the Carboniferous who kindly identified the following forms:

Fusulina cylindrica.

Zaphrentis sp.

Stenopora sp.

Productus aff. P. porrectus Kut.
Fusulina elongata (7)

Seminula subtilita.
Lithostrotion mammillare (?)
Diphyphyllum n. sp.

Lonsdaleia n. sp.

Lonsdaleia n. sp. var.

Of this fauna Mr. Girty states that it belongs in the Upper
Carboniferous and rather well up. While some of the forms
possess more satisfactory evidence than others, he feels little

294 University of California Publications. [ GEOLOGY

doubt with regard to any. The most dubious as to age in his
opinion is the Diphyphyllum n. sp., and even in this case he be-
lieves that it may safely be regarded as Upper Carboniferous or
Pennsylvanian. All of these fossils occur in the same stratigraph-
ically continuous area of the Ruth hmestone, of which Fossil
Hill is the most prominent feature, on the south side of the
Ruth Mine. The Seminula subtilita appears to be the most com-
mon. The Diphyphylum n. sp. also oceurs on the Phenix claim
in the area of Ruth limestone two-thirds of a mile to the north
of the Ruth Mine. It is interesting and satisfactory to observe
that the palaeontological determination of the age of the Ruth
limestone by Mr. Girty entirely agrees with the conclusions that
had been reached by a comparison of the physical characteristics
and stratigraphic sequence of the Ruth section with those of the
standard section established at Eureka some 80 miles distant.*
The Arcturus Limestone-—Below the Ruth limestone is a
strongly contrasted formation of argillaceous, and in part sandy,
limestone which may be designated the Arcturus shaly lime-
stone, although the shaly character is not always apparent. This
formation is easily distinguished from the other formations of
the district by the abundance and yellow color of its regolith.
In general it yields to atmospheric erosion smooth slopes strewn
with small subangular or rounded residual fragments of yellow
limestone. In it there are occasional beds of a massive character,
but even these do not project prominently above the general
slope. Some of the limestone beds contain a notable proportion
of manganese, and when freshly broken present a faint pinkish
tint suggestive of rhodochrosite. This formation increases in
thickness from east to west, and passes in the country to the
northwest of Ruth into yellow, orange and red weathering, soft
shales, with thin beds of impure limestone. The formation car-
ries Carboniferous fossils but not so abundantly as the Ruth
limestone. Species of Zaphrentis and Stenopora were recognized
by Mr. G. H. Girty. Its average thickness within the district is
about 1,000 feet with a minimum of 900 feet in its more eastern
exposures.

* Hague, A. U.S. G.S8., Monograph XX, 1892.

VoL. 4] Lawson.—The Robinson Mining District. 295

The Ely Limestone.—Beneath this formation is the Ely lime-
stone, consisting of regularly stratified, thick-bedded, more or
less cherty limestone to a thickness of about 1,500 feet. Its
regolith is seant, the weathered surfaces are often of a light
lilae gray color, and it forms the boldest bluffs, the most precip-
itous slopes and the highest summits of the district. It also car-
ries Carboniferous fossils, but the only forms identified by Mr.
Girty to whom they were submitted are crinoidal fragments and
Productus aff. P. porrectus Kut.

THE DEVONIAN.

The White Pine Shale-—Below the Ely limestone are forma-
tions of supposed Devonian age. The first of these in descending
order is a body of shale of somewhat varied character. A good
deal of it is ordinary, blue-black, argillaceous shale. Most of the
formation is, however, rather siliceous and yields a regolith filled
with flat, angular rock chips, which have a yellowish color. Cer-
tain portions of the formation, as for example, to the north and
northwest of Copper Flat and in the vicinity of Pilot Knob, are
carbonaceous and have a dead black color. In other cases, as
in the vicinity of the Chainman Mine and Pilot Knob, the rock
while having an evenly and thinly laminated shaly structure is
almost wholly quartzose in composition. In several portions of
the shale belt, the shale has been bleached to a snow white or
a cream white color, due, it is presumed, to the action of emana-
tions from neighboring irruptive rocks, or more probably of
sulphurie acid arising from oxidation of the overlying pyritif-
erous porphyry. Some of these have a chalky consistency. <A
chemical examination of two samples of this bleached shale from
the gulch to the east of Jupiter Ridge was made for the writer by
Mr. Herbert Ross of the Ruth Mine with the following results:

I IT.
SiO, 65.0 Gf
Al,O; 28.5 28.1
CaO 1.8 1.0
HO Dell 3.7

296 University of California Publications. [ GEOLOGY

The formation to the northwest of Pilot Knob is traversed
by a heavy bed of light gray limestone about 150 feet thick, the
shale above and below it being not essentially different. The
total thickness of the shale is about 850 feet or with the included
limestone bed about 1,000 feet.

This shale formation, with its included limestone bed, agrees
well with the descriptions that have been given by Hague* for
the White Pine shale of the neighboring White Pine and Dia-
mond Ranges to the west of the Egan Range, and it is, there-
fore, tentatively correlated with that. This correlation is, more-
over, sustained by the fact that no other formation of similar
character has been described, so far as the writer is aware, from
the Basin Ranges for this portion of the geological scale. As
the White Pine shale is a fairly persistent formation in the
ranges to the west, it is quite probable that it should extend into
the Egan Range. Even the thick bed of limestone in the midst
of the shale has its analogue in the White Pine shale of the
Eureka and White Pine sections.+ There is one lack of agree-
ment between the Eureka section and the one here described
which seems to militate against the correlation suggested, and
that is the absence at the Robinson Mining District of the Dia-
mond Peak quartzite. At Eureka this formation has a thick-
ness of 3,000 feet and lies immediately above the White Pine
shale. It is to be noted, however, that in passing southeastward
from Eureka to White Pine, the Diamond Peak quartzite dimin-
ishes from 3,000 feet to a few hundred feet,} and that at this
rate of diminution of volume it would feather out before reach-
ing the Egan Range.

The Nevada Limestone-—The correlation of the shale forma-
tion of the district with the White Pine shale of the Eureka and
White Pine sections is the chief justification for suggesting that
the next lower formation is the equivalent of the Nevada lime-
stone of the standard section. This formation is a rather mas-
sive, gray limestone which agrees in petrographic character with
the description of the Nevada lmestone; but no fossils were

found in it by the writer, doubtless due to the lack of oppor-
We SEER Sh Wily, 2026
{ Hague, Op. Cit., p. 193.
+ Hague, Op. cit., p. 192.

VoL. 4] Lawson.—The Robinson Mining District. 297.

tunity for systematic search. Some of the beds of this forma-
tion are almost black limestone. The thickness of the formation
is unknown as only the upper part of it comes within the limits
of the country examined. It was estimated, however, that its
thickness was not less than 1,000 feet and might be much more.

CORRELATION WITH THE EUREKA SECTION.
For the purpose of comparing the geological column of the
district under consideration with that of the Eureka section, the
following correlation of all the Palaeozoic formations is sug-

gested :
Rosinson MINING DIstT. EUREKA.

Feet Feet
Ea, Vrs limestone ........ 500+ Upper Coal Meas......... 500
ee Arcturus shaly limestone. 1,000 Weber Conglomerate .....2,000
a* Ely limestone ......... 1,500 Lower Coal Meas......... 3,800
Diamond Peak Quartzite. .3,000
zy | Neva Pine shale....... 1,000 White Pine shale......... 2,000
BS Nevada limestone ...... 1,000+ Nevada limestone ........ 6,000

GENERAL STRUCTURE.

In the study of the general geological structural relations
of the Robinson Mining District several factors have to be con-
sidered. These are: (1) The stratigraphic sequence of the De-
vonian and Carboniferous formations as above outlined. (2)
The flexure of these strata. (3) The relation of the folded strata
to the irruptive masses which cut them. (4) The features intro-
duced in the process of mineralization. (5) The lavas and tuffs.
(6) The faulting of the region. Having in the previous section
deseribed the stratigraphic sequence, we may now conveniently
consider that phase of the structure referable to the deformation
of the Palaeozoic rocks anterior to the appearance of the irrup-
tive rocks leaving the discussion of the other factors till later.

The dominant feature in the structure of the Palaeozoic rocks
is a broad syneline, the axis of which runs nearly north and
south, through the Ruth Mine, and pitches northerly at a con-
siderable angle. In the central part of this fold les the Ruth
limestone with synelinal dips at moderately low angles. Flank-
ing the Ruth limestone on either side is the Arcturus shaly
limestone dipping under it. Flanking this on both sides is the

298 University of California Publications. [GEOLOGY

Ely limestone dipping beneath it at somewhat steeper angles.
As we pass along the southern border of the district as mapped
eastward and westward upon the Ely lmestone terrane, we pass
into the complementary anticlines of the Ruth syncline. That
to the east is of so low an arch that it is difficult to determine
with precision the direction of its axis. It is probably, however,
north-northeast. It may be referred to as the Saxton anticline
from the Saxton mine which is situated upon it. That to the
west is much more sharply flexed, and the trend of its axis is
northwest and southeast, the pitch being to the southeast. It
may be ealled the Rib Hill anticline from the most prominent
feature upon it.

In the heart of the Saxton anticline there appears a broad
belt of the White Pine shale dipping beneath the Ely limestone
on the foothills to the south of the Lane city. On this belt are
situated the Saxton and Chainman Mines. Flanking the White
Pine shale on the south side of Lane Valley are some areas of
limestone the relation of which to the shale is not clear. On
petrographical grounds they are mapped as Ruth limestone.

In the Rib Hill anticline, the White Pine shale again appears
beneath the Ely limestone, although the direct relationship is
largely interrupted by the porphyry of Jogalong Ridge and the
monzonite of Weary Flat. The dip of the shale with its included
bed of hard limestone beneath the Ely limestone may, however,
be clearly observed to the west and northwest of Pilot Knob. In
the same anticline, as it broadens out to the north on the north
side of Weary Flat, appears the Nevada limestone from beneath
the White Pine shale, extending as an important terrane in the
hills to the north of the western part of the district.

THE IRRUPTIVE ROCKS.
MONZONITE BATHOLITH.

One of the most interesting features of the geology of the
district is the occurrence of an intrusive mass of monzonite.
The chief interest attaches to the fact that it appears to be an
example of a rather frequent occurrence of plutonic intrusives
of granitic habit which have been reported from various parts

VoL. 4 | Lawson.—The Robinson Mining District. 299

of the Basin Ranges, and which have generally been referred
to the Archaean. In this case the mass is clearly of post-Car-
boniferous age and there is not wanting evidence that this will
be found to be true of many other similar rock masses. ‘The
monzonite appears in the Rib Hill anticline and underlies the
relatively low and gently sloping ground of Weary Flat in the
western part of the district. Its occurrence is marked by no
prominent outcrops nor even by hilly ground. The area oecu-
pied by it ean be delimited with a fair degree of precision. The
regolith which thinly veneers it is so characteristic of the under-
lying rock, that, taken with the occasional exposures of the latter,
and the opportunities afforded by the rather numerous prospect
holes that have been sunk upon it, particularly about its peri-
phery, there has been no serious difficulty in mapping it. The
longest diameter of the area is about one mile in a northeast-
southwest direction and its width is about half a mile.

The rock composing the mass is in general a rather coarse
grained, pinkish to gray hornblende-monzonite, with large por-
phyritic erystals of orthoclase, and has a characteristic plutonic
habit. When this rock was first met with in a rapid survey of
the field to be studied, the writer, relying upon previously re-
ported occurrences of Archaean granitic rocks in the basin
ranges, naturally supposed that he had here to deal with the
basement upon which the Palaeozoic rocks were laid down. In
testing this hypothesis, however, several facts came to light which
seemed to be inconsistent with it. It was remarked with surprise
that the lower part of the Palaeozoic column, including the Silu-
rian and Cambrian which form voluminous and persistent ter-
ranes throughout this part of Nevada, was here absent. The
lowest rocks in contact with the monzonite are those referred
in this paper to the Devonian. In meeting this objection it was
considered barely possible that a pre-Devonian disturbance and
erosion interval had removed the earlier Palaeozoic rocks, or
that this portion of the region had remained an insular mass in
Cambrian and Silurian times and had been finally submerged
only with the advent of Devonian time, and that the monzonite
might thus still be regarded as a portion of the Archaean floor
upon which the Palaeozoic in general was laid down. This possi-

300 University of California Publications. [ GEOLOGY

bility was, however, not supported by the facts observed in the
course of detailed mapping. It was found for example that
there was no trace of a basal conglomerate or even of an arena-
ceous formation at the contact with the monzonite, such as
would have been expected had the Devonian rocks been depos-
ited in a sea transgressing a subsiding Archaean terrane of this
character. It was found further that the stratification planes
of the rocks nearest to the monzonite were not parallel to the
surface of the latter but were in several instances in striking
discordance with the locus of contact and appeared to abut
directly upon it. It became, moreover, very apparent that the
monzonite was in direct contact with quite different and widely
separated stratigraphic horizons. For example, the monzonite
appears, in quite satisfactory exposures on the west and south
sides of Weary Flat, to be in direct contact with both the White
Pine shale and the Nevada limestone; and it appears to be
transverse to the entire thickness of the first named of these
formations. As such observations multipled, it of course be-
came evident that the original hypothesis was entirely at fault,
and its rejection cleared the way for the adoption of the hypoth-
esis that the monzonite is an intrusive mass of later age than
the rocks with which it is in contact. The facts which served
to overthrow the first hypothesis are quite in harmony with,
and indeed, strongly support the second. They do not, however,
establish its correctness beyond question; for there is still a third
hypothesis with which the same facts are not inconsistent. It
is possible that the relations subsisting between the monzonite
mass and the sedimentary rocks, in so far as they have been
described are due to complex faulting. The monzonite area
may be bounded by faults. The absence of the lower part of
the Palaeozoic section and of a basal conglomerate, the abutment
of the sedimentary beds at widely separated horizons upon the
monzonite mass, might all be brought about by faulting. As
between these two hypotheses, of intrusion and of faulting, the
field evidence distinctly favored the former. At the contact of
the monzonite with the White Pine formation the shales are
altered to a hard bluish hornfels which is in marked contrast
with the shales at a distance from the contact. The limestone

VoL. 4] Lawson.—The Robinson Mining District. 301

of the Nevada formation which is normally a gray fine grained,
ordinary sedimentary limestone is converted at the contact with
the monzonite into a snow white marble of much coarser texture.
At the contact of the monzonite with both shale and limestone
there are developed bodies of garnet rock which carries more
or less chaleopyrite and which can only be interpreted in a cer-
tain sense as a product of contact metamorphism. The mon-
zonite itself, moreover, has its character modified in the imme-
diate vicinity of the contact with the surrounding rocks. At a
shaft by the roadside immediately north of the Monarch claim,
for example, the monzonite at the contact is much finer grained
than at some little distance away, and presents the features of
a chilled edge of an intrusive mass. These facts, taken with
the others above enumerated, establish the intrusive hypothesis
upon a very satisfactory basis; and in the absence of any eyi-
dence of faulting leave it unquestioned.

A small isolated area of the monzonite, occupying a few
acres upon the Sacramento, Schley and Good Enough claims
north of Pilot Knob, is regarded as an integral part of part of
the large mass underlying Weary Flat. It is separated from
the latter by but a few hundred feet. It cuts both the Nevada
limestone and the White Pine shale and has a well exposed con-
tact zone of garnet rock against the limestone. If erosion had
eut but a little deeper, the roof of sedimentary rocks in the
intervening space would have been removed and the two areas
thus shown to be one as indicated in the section C—D on the
accompanying geological map.

Just beyond the confines of the map, however, on the Taylor
claim, north-northwest of Pilot Knob, there is another area of
the monzonite which may similarly be interpreted, or, inasmuch
as it euts considerably higher into the sedimentary rocks, it may
be regarded as an apophysis from the same mass. The rock
here has more the facies of a quartz monzonite, there being a
little quartz present. It has associated with it garnet rock earry-
ine chaleopyrite as shown by prospecting operations. While it
is clear that the mass of monzonite of Weary Flat is an intrusive
batholith (or possibly laccolith), it seems also certain that the
intrusive process was peculiar in certain ways. Usually in the

302 University of California Publications. | GEOLOGY

ease of plutonic intrusives that the writer has had opportunity
of observing there is evidence of greater intensity of action. The
magma is usually more or less thoroughly injected into the en-
casing rocks along their structural planes or across the beds in .
fracture fissures. The eneasing rocks are usually shattered and
angular fragments are scattered out into the body of the irrup-
tive. There is usually abundant evidence of more or less dynamic
metamorphism independent of the contact metamorphism. These
phenomena are lacking in connection with the Weary Flat bath-
olth. The rocks of the district are folded, to be sure, but they
appear to have been thus folded anterior to the batholithie inva-
sion, and the flexures are, besides, quite open. We must thus
conclude that the intrusive act was of a rather mild type and
that the pressures within the magma, which gave rise to the
invasion from below, were not far above the point of equilibrium
when it had reached this stage in its upward path through the
earth’s crust. Perhaps this is only another way of saying that
we have here to deal with the summit of a batholith, the level in
the quid column where its intrusive force was about spent;
and that at deeper levels, had they been exposed by erosion, we
should have had revealed to us the more commonly observed
phases of intrusive phenomena.

If we adopt this suggestion we have in it an explanation of
the peculiar geomorphy of Weary Flat. This is a very even
slope everywhere underlain by the monzonite. It lies at the
headwaters of a very feeble desert stream, with no catchment
area behind it, so that we can not interpret the flat slope as due
to stream planation. It is more probable that the present sur-
face of the monzonite is nearly coincident with its original upper
limit where it was overlain by the soft White Pine shale. In
this view of the case the geomorphic expression is strictly con-
trolled by structure and the structural feature involved is the
nearly flat contact plane between a batholith of hard rock and
the roof of an overlying soft rock.* If it were otherwise, then
the Weary Flat slope must be due to the planation of the mon-
zonite; but this is highly improbable, since there are no residual

* Cf. The Geology of the Upper Kern -Basin, Bull. Dept. Geol. Univ.
Cal., Vol. 38, No. 15, pp. 312 e¢ seq.

VoL. 4] Lawson.—The Robinson Mining District. 303

knobs of the latter, and the soft shale occupies higher ground
on three sides of the mass. It may, therefore, be safely as-
sumed that the batholith was nearly flat topped, and that this
flat top is practically the present surface as revealed by the denu-
dation of the shale roof.

Age of the Monzonite-—The only rocks actually penetrated
by the monzonite are the Nevada limestone and the White Pine
shale of the Devonian. At one point only, a little to the south
of Pilot Knob, does the monzonite, cutting across the entire
thickness of the White Pine shale, reach the contact plane be-
tween this formation and the overlying Ely limestone. It does
not appear to rise above this stratigraphic horizon. The evidence
is thus positive as to its post-Devonian age. The recognition of
the flat topped character of the monzonite bathoilth precludes us
from assuming that it ever penetrated higher into the Carbonif-
erous formations where they are now removed by erosion. Yet,
it requires but lttle reflection to make it clear that the date of
the intrusion is not only post-Devonian but also post-Carbonif-
erous. The investigations of the geologists of the 40th parallel
survey and those of Hague at Eureka and White Pine indicate
that the Carboniferous and Devonian formations of this part of
Nevada form a perfectly conformable sequence. This is con-
firmed by the writer’s studies in the limited field of the Robinson
Mining District. It seems to be quite inconsistent with this idea
of conformity that so important a disturbance as the intrusion
of a batholith could have affected the Devonian rocks in pre-
Carboniferous time. The strata of both the Carboniferous and
the Devonian are deformed to the same extent and seem to have
suffered this deformation anterior to the invasion of the mon-
zonite into the Devonian. If we should assume that the Car-
boniferous and Devonian are not in reality conformable, but
only apparently so, then, since the monzonite cuts across the
entire thickness of the Devonian, its upper surface must be due
to erosion, and we should expect a conglomerate or an arkose at
the base of the Carboniferous. But no such formation exists
here at the base of the Carboniferous. Moreover, since the mon-
zonite cuts across the entire thickness of the Devonian, if it were
intrusive in the Devonian prior to the deposition of the Carbon-

304 University of California Publications. [ GEOLOGY

iferous and were not exposed by erosion, it must have appeared
at the surface and would partake of the characters of a voleanic
extravasation. But it has none of these characters and is thor-
oughly plutonic in its habit. We are, therefore, constrained to
regard the time of the intrusion as post-Carboniferous.

Contact Phenomena.—Along the contact of the monzonite
with the Nevada limestone and with the White Pine Shale, it has
been mentioned that considerable bodies of garnet rock occur as
a product of contact metamorphism. These are not without
interest from an economic point of view since at their outcrops
they afford indications of the presence of copper ores. These
indications are usually in the form of malachite and azurite
stains and deposits in more or less decomposed and rusty rock.
Several prospect pits and tunnels have been cut into this contact
zone and have in several cases resulted in finding chalcopyrite
interlaminated or interspersed through the garnet mass. As yet,
however, no important deposits of ore have been found in this
situation, the most favorable being at the Taylor claim, near
the apophysis of the monzonite already mentioned to the north-
northwest of Pilot Knob, a little beyond the limits of the map.
Here very good ore is found in the garnet rock, but the question
as to its quantity had not been settled at the time of the writer’s
visit in 1904.

The Nevada limestone on the contact of which the garnet
rock is most abundantly developed is, in several cases observed,
thoroughly marmorized. <A typical sample of the garnet rock
from a pit to the north of Pilot Knob was examined microscop-
ically. It consists of a mesostasis of garnet partly isotropic and
partly doubly refracting. In this are imbedded rather numerous
irregularly bounded, but more or less elongated, colorless erys-
tals with a high refractive index and a strong double refraction.
These crystals have a cleavage parallel to the elongation and
the angles of extinction measured against this cleavage have a
high value. It is very probable, therefore, that the mineral is
diopside. With the diopside there are also numerous stout hex-
agonal prisms of apatite. There are also areas of calcite, of quite
irregular boundaries, and areas of limonite in the garnet. The
rock effervesces freely with dilute acid.

VoL. 4] Lawson.—The Robinson Mining District. 305

Another sample of garnet-chaleopyrite ore from the shaft
on the Taylor claim consists mostly of garnet with rough jagged
fracture shot through with chalcopyrite. The rock has a rudely
sheeted structure. In thin section the field is murky and con-
sists of nothing but impure doubly refracting garnet, more or
less distinetly idiomorphic, with interstitial chalcopyrite carry-
ing small irregular grains of quartz.

Petrographical Character—The normal facies of this intru-
sive mass is a medium textured gray rock composed of whitish
feldspar and black hornblende as a matrix in which are im-
bedded large flesh tinted fresh feldspars up to 15 mm. in size.
A very sparing amount of quartz may be detected with a lens
on weathered surfaces. The feldspar was assumed in the field
to be orthoclase and the rock was designated a syenite. A micro-
scopie study of the rock, however, shows that there is a large
proportion of plagioclase giving extinction angles in sections
normal to (010) up to 20°, and having a refractive power greater
than that of balsam. This feldspar, having the characters of
andesine, is not less in amount than the orthoclase, a fact which
clearly indicates that the rock should be classed with the mon-
zonites rather than with the syenites. The orthoclase is distin-
guished in general from the andesine by the absence of twinning
and by the fact that it shows a lower refractive power than the
balsam. The hornblende occurs in fairly idiomorphiec crystals
of small size. Quartz is very sparingly represented in the seec-
tion. The accessory minerals are apatite, titanite, and mag-
netite. The structure is hypidiomorphie granular as regards
the general body of the rock; but this serves as a matrix for
large phenocrysts of orthoclase. The phase of this monzonite
cutting the limestone and shale at the Taylor Mine to the west
of Pilot Knob shows some minor variations from the prevailing
character of the mass underlying Weary Flat. In the specimens
taken from this locality the ground mass is finer grained and
the phenocrysts are more numerous. The hornblende, where
fresh, occurs in longer prisms, but much of it is represented only
by pseudomorphs of limonite. Quartz is a little more abundant.
Apatite and titanite are more prominently developed. The large
phenocrysts of orthoclase attain a length of 25 mm. and they

306 University of California Publications. [GEOLOGY

often show Carlsbad twinning. <A contact facies of the mon-
zonite where it comes in contact with the Nevada Limestone on
the roadside just north of the Monarch Claim was studied in
specimens taken from a prospect pit on the contact. The rock
is a medium grained, gray, porphyritic rock made up apparently
chiefly of feldspar with a subordinate admixture of a dark min-
eral. In thin section the rock appears as an allotriomorphic
aggregate of orthoclase and plagioclase in which are imbedded
numerous phenocrysts of light green augite and a few green
hornblendes. The accessory minerals are apatite, titanite, and
zircon in rather numerous but small erystals and a few granules
of iron ore. Another specimen from the same pit is finer grained
and more decomposed. It effervesces feebly with dilute acid.
In thin section the rock is an aggregate of more or less idio-
morphic feldspars now wholly replaced by calcite and kaolin and
some yellow epidote. Nearly colorless chlorite occurs in nests,
representing, doubtless, the decomposition product of an original
ferromagnesian constituent. Large erystals of apatite are nota-
ble features of the slides, and considerable titanite is present. A
very little secondary quartz may also be detected.

Chemical Composition.—The identification of the rock as a
monzonite on the basis of microscopic study is confirmed by a
chemical analysis which has been made by Mr. Herbert Ross
since the above was written. The sample selected for analysis
was taken from a prospect pit on Weary Flat to the south of
the road between Copper Flat and Pilot Knob. The analysis
of the rock from Hodritsch, Hungary, quoted from von Hauer
by Brégger* as that of a typical monzonite is cited for compari-
son. The two analyses are given in the following table:

* Die Eruptionsfolge der triadischen Eruptivgesteine bei Predazzo in
Sudtyrol, p. 50.

Vou. 4] Lawson.—The Robinson Mining District. 307

ANALYSIS OF MONZONITE.

Weary Flat, Hodritsch,
Nevada. Hungary.
SiO. 61.69 61.73
Al,O; 17.26 17.45
Fe,O, 3.53 5.94
FeO 1-91
MnO .09 ja
MgO 1.45 2.2
CaO 5.49 4.52
Na.O 3.05 3.12
K.O 3.88 3.88
BaO sae
P.O; 34
Cl 03 Hewes
HO (ig) {he} 1.16
99.55 ; 100.09

The mineralogical composition of the rock as inferred froin
the analysis may be expressed approximately as follows:

Per cent.

Orthoclase 23.00
Albite 26.00
Anorthite 22.00
Hornblende 15.00
Quartz 13.00
Apatite 65

99.65

It would appear from this that a very large proportion, if
not all, of the orthoclase is present in the form of the large
phenocrysts, the matrix of the rock in which these are imbedded
having the character, when considered by itself, of a quartz
diorite which consolidated at the eutectic point of the cooling
magma. The amount of quartz revealed by the analysis is some-
what higher than was inferred from the microscopic study of the
rock. The presence of small quantities of manganese and ba-
rium is noteworthy. In spite of the fact that copper ores occur
at the contact of this monzonite with the encasing formations,
neither the results of the analysis nor the fresh condition of the
rock lend support to the idea that such copper was derived from
the monzonite. The absence of sulphides is a noteworthy feature
of the rock, and is a point of striking contrast with other igneous

308 University of California Publications. [ GEOLOGY

rocks, to be described later, which have an important relation
to copper ore bodies. It is to be remarked, however, that rocks
of the monzonite class are being more and more recognized in
regions where copper ore abounds. Possibly the rock contains
traces of copper which cannot be detected by the ordinary
methods of analysis, and this may be brought up from the deeper
portions of the irruptive mass, whence come the aqueous ema-
nations that induce the formation of garnet and other contact
metamorphic minerals, ineluding chalcopyrite.

MONZONITE PORPHYRY DYKES.

At several localities within the district, but most abundantly
on the border of the area mapped on the north side of Lane
Valley, there occur dykes of a remarkably coarse porphyritie
rock, a petrographical study of which reveals its character as a
monzonite porphyry. To the north of Lane City the dykes are
of large dimensions and at their contact with the lmestone
there is commonly developed an abundance of garnet rock.
Specimens taken here may be described as having a greenish
gray ground mass in which are imbedded huge crystals of fresh
orthoclase with flesh tinted, lustrous cleavages, smaller feld-
spathic phenoerysts and black hornblendes.

Petrography.—Under the microscope the ground mass ap-
pears as a microgranitic aggregate of non-striated feldspar and
quartz, the former predominating. In this ground mass are
imbedded idiomorphie phenocrysts of orthoclase, plagioclase,
ereen hornblende, green augite, abundant titanite, a few large
apatites, and an occasional much corroded crystal of quartz.
The plagioclase has the optical characters of oligoclase. It is,
however, commonly zoned. Combinations of Carlsbad and albite
twinning are of frequent occurrence. The hornblende is strongly
absorbent. The augite is of a clear chrome-green color, non-
pleochroie, octagonal in sections transverse to the prism, and
exhibits a strongly marked cleavage, against which the extine-
tion in longitudinal sections reaches 40°. The titanite is a re-
markable feature of the slides, some large crystals showing fine
twinning. The apatite is in part inclosed in the hornblende.
There are also a few grains of opaque iron ore. The smaller

Vou. 4] Lawson.—The Robinson Mining District. 309

feldspars range up to about 4 mm. in their longest dimension,
and the hornblendes attain a leneth of 6 mm., while the large
orthoeclases are usually from 10 to 20 mm. in length, though in
some phases of the rock they are as much as 50 to 75 mm. long
and proportionately broad. In other specimens of the rock from
the same locality no quartz can be detected with certainty, and
the orthoclase and plagioclase, the latter having a maximum ex-
tinction angle in the zone normal to (010) of 238°, oceur in about
equal proportions.

In the vicinity of the copper bearing porphyry four occur-
rences of this monzonite porphyry have been found, all of them
quite limited in extent. Of these, two are found in the Ruth
limestone, one in the Arcturus limestone, and one in the por-
phyry itself, but so near its contact with underlying limestone
that it is quite doubtful whether it really cuts the porphyry or
not. They all have the same general microscopic characters
and, although their actual contact with the surrounding rock
is In no case exposed, they can only be interpreted as dykes.
In the northwest corner of the Spion Kop claim the monzonite
porphyry dyke presents a greenish gray matrix in which are
imbedded flesh tinted orthoelases with Carlsbad twinning, an
oceasional erystal of yellow titanite, nests of epidote and some
scattered cubes of pyrite. In thin section the rock is seen to be
much decomposed. The ground mass is a holocrystalline, pan-
idiomorphie aggregate, consisting chiefly of feldspar in which
secondary calcite, epidote and pyrite occur very commonly. In
this are imbedded the large orthoclases, titanite, a little quartz
and a ferromagnesian mineral changed almost wholly to chlorite.
No lamellar twinning was observed in the feldspars, but it is
probably obscured by the decomposition which has affected them.

A similar dyke is exposed in a small prospect hole near the
forks of the road to the west of the Ruth Mine. The rock is the
same as that just described except that apatite is a notable fea-
ture of the slides.

Another occurrence is in the saddle of the ridge just north
of the Blair claim. The rock here has a compact gray matrix
in which are imbedded large orthoclase crystals up to 25 mm.
in length with Carlsbad twinning and fresh lustrous cleavages,

310 University of California Publications. [ GEOLOGY
smaller, dull white feldspars and numerous black hornblendes
up to 15 mm. in length. Under the microscope the ground mass
proves to be very murky. It is largely isotropie but with doubly
refracting areas in it. The smaller feldspars can not be advan-
tageously studied owing to their decomposition. Apatite is a
common accessory.

The fourth occurrence is about a quarter of a mile to the
southeast of the Ruth Mine. Macroscopieally it resembles the
occurrence on the Spion Kop claim and under the microscope
it differs from that rock only in the presence of apatite in the
thin shdes.

Chemical Composition.—A representative specimen of the
monzonite porphyry taken from the occurrence north of Lane
City was analyzed by Mr. Ross with the following results:

SiO, 59.79
Al,O, 17.70
Fe,O, 2.42
FeO 2.76
MgO 1.92
CaO 5.22
Na,O 2.64
K,O 4.19
BaO .21
MnO .09
OF 37
H.O (ig) 2.00

99.31

Relation to Monzonite Batholith.—The analysis is noteworthy
for its close similarity to that of the monzonite of Weary Fat.
This similarity of chemical composition suggests an identity of
magma for the two rocks. So far as the field evidence is con-
cerned there is little that can be adduced in opposition to this
suggestion. The monzonite porphyry may be the dyke facies
of the monzonite of Weary Flat. The one doubt that arises is
due to the occurrence of a very small mass of the monzonite,
porphyry within the area of the copper-bearing porphyry near
the north boundary of the Blair claim. This, however, is so
near the contact of the porphyry with the underlying limestone
that it may be interpreted as a portion of the floor upon which

Vou. 4] Lawson.—The Robinson Mining District. Buell

the porphyry rests, that is, as a dyke cutting the limestone but
not the porphyry. If the monzonite porphyry is thus to be re-
garded as directly and genetically connected with the monzonite
of Weary Flat as a dyke facies, it is remarkable that the pheno-
erysts of the small intrusive masses (dykes) are as a rule many
times larger than the erystals of the same mineral in the larger
batholithie mass of which the dykes are apophyses. In support
of the correlation of these dykes with the Weary Flat monzonite,
the further fact may be mentioned that the contact phenomena
of both rocks against the limestones is closely the same, particu-
larly in the development of large bodies of garnet rock. On
the other hand it is somewhat remarkable that none of these
dykes have been observed anywhere on the immediate periphery,
or, indeed, in the vicinity, of the main mass of monzonite at
Weary Flat. In view of the absence of direct evidence of con-
nection between the two rocks, it must be confessed that the
question of their relationship remains as yet unsettled, but the
view that the dykes are apophyses of the batholith seems fairly
probable.

THE COPPER-BEARING PORPHYRY.

The term porphyry is here used in the popular sense. In
mining communities the term is applied very freely to the lighter
colored voleanie and intrusive rocks in much the same way that
the expression trap is used for the darker rocks of basaltic
character. It is very rarely applied to rocks of plutonic habit.
It is particularly used for intrusive and voleanie rocks with
which ores are directly or indirectly associated. The usage is
not definitive and affords little or no intimation as to the place
of the rock so named in any system of classification. To the
petrographer the term is simply descriptive of the presence of
a porphyritie structure which is common to many different kinds
of rocks; but in the popular usage even this is not essential

In the present case the popular term is the more readily
adopted as a preliminary designation from the fact that owing
to its very thorough decomposition the rock we are here con-
cerned with is difficult to classify. It is a light yellowish or
whitish feldspathic rock with a prevalent porphyritie structure

312 University of California Publications. [GEOLOGY

and a general absence of ferromagnesian minerals. Its more
precise characterization and its variations will appear from the
detailed descriptions to be given after its broader features as a
factor in the geology of this field have been considered.

Extent.—An inspection of the geological map of the district
will show that the porphyry occupies two quite distinct areas.
One of these extends from Copper Flat westward to Rusty
Ridge at the west of the map. This area has an east and west
extent of nearly three miles and a maximum width of five-sixths
of a mile. The area is continuous and there are no outlying
patches of the same rock in its vicinity.

The second area extends from Ocher Valley eastward to a
little beyond the eastern limit of the map near the Chainman
Mine. This area has also an east and west extent of about three
miles and a maximum width at the Ruth Mine of about three-
fifths of a mile. This area is more irregular in outline and less
continuous than the western area. It has in fact, in consequence
of its dissection by erosion, been separated into two distinct
parts, the jess extensive of which is in the vicinity of the Saxton
and Chainman Mines. These two areas of porphyry lie in a
distinct east and west allignment and form a belt of rock tra-
versing the district which has determined not only the distribu-
tion of the economically important minerals but also the evo-
lution, under erosion, of the geomorphic features of the region.
It is noteworthy that this alignment and the features deter-
mined by it are transverse to the general trend of the Egan
Range and to its dominant structural lines.

The break in the continuity of the porphyry belt at Ocher
Valley in the central part of the district might on a rapid survey
be referred to its dissection by erosion, but a more careful ex-
amination of the contact between the porphyry and the adjacent
rock shows that there is little warrant for this view, and that
the two areas probably have always been distinct at the surface,
although doubtless connected at depth.

Intrusive Relations—The evidence as to the relations be-
tween the porphyry and the adjacent Palaeozoic formations is
in general quite satisfactory and establishes the fact that the
porphyry is intrusive in the sedimentary rocks. This evidence

VoL. 4 | Lawson.—The Robinson Mining District. oils,

is of two kinds: (1) the structural relations of the porphyry
mass to the surrounding strata; and (2) the contact metamor-
phism displayed at several points on the margin of the porphyry.

Structure.—The structural evidence of the intrusion of the
porphyry is perhaps most apparent in the eastern area and
particularly in the vicinity of the Ruth Mine. Here the por-
phyry belt les transverse to a well marked northerly pitching
syneline of the Ruth limestone. On the south side of the por-
phyry belt different stratigraphic horizons of the Ruth limestone
abut upon it and the plane of contact does not conform to the
planes of stratification, but in general appears to dip under the
porphyry. On the north side of the belt, the Ruth hmestones
overlie the porphyry, dipping away from it but again meeting
it at different stratigraphic horizons. It is evident from this
relationship not only that the porphyry is intrusive in the Ruth
limestone, but, also, that the intrusion occurred subsequent to the
establishment of the synclinal structure.

The way in which the upper surface of the porphyry passes
beneath the limestone at low angles on the north side of the
belt, the strata dipping away from the intrusive mass, suggests
strongly that the structure is, in general, for this part of the belt,
laceolithic. On both flanks of the Ruth syncline the porphyry
comes in contact with the underlying Arcturus shaly limestone.
On the west flank it appears to pass beneath the Arcturus for-
mation although cutting across various horizons. On the east
it passes over upon the Arcturus formation.

On Jupiter Ridge and from thence eastward to the Chain-
man Mine, the mapping of the porphyry indicates that it lies
upon the White Pine shale as a warped sheet, partly removed
by erosion, but eutting across the contact of the shales with the
overlying Ely limestone. On the lower flanks of this slope at
the upper end of Lane Valley, it is mantled by the remnants of
a roof of limestone and it probably sustains a similar relation
to two other areas of limestone between this and the Chainman
Mine although this relationship was not established in the field.

In the western area of porphyry the laccolithic character of
the intrusion is even more apparent. Along the eastern edge
of this area, in the vicinity of Copper Flat, the upper surface

314 University of California Publications. [ GEOLOGY

of the porphyry passes beneath the western edge of the Arcturus
shaly limestone at a rather low angle. To the west of Copper
Flat, however, beyond the northeast-southwest fault shown upon
the map, the base of the porphyry mass may be traced without
a break for about two miles and a half, resting first upon the
White Pine shales, then upon the Weary Flat monzonite, then
upon the Ely limestone, then upon the shales again and finally
upon the Ely limestone to the north of Rusty Ridge. West of
Weary Flat, the trend of this lower edge of the porphyry mass
is transverse to both the strike and dip of the strata upon which
it rests; and it is evident from the mapping that the rupture,
through which the porphyry magma welled up from below, was
formed, as in the case of the mass lying in the Ruth syncline
quite independently of the preéxisting structure as expressed in
stratification and flexure.

On the south side of this western area of porphyry, the upper
surface of the intrusive mass cuts across the strata of the Ely
limestone in the Rib Hill anticline and appears to pass beneath
it. On the western flanks of this anticline it cuts similarly
across the strata of the Arcturus formation while plunging be-
neath it. At the extreme western limits of the porphyry belt
the intrusive mass seems to wedge out rather abruptly but this
point did not receive as much attention as the writer would like
to have given it.

From the above summary statement of the structural rela-
tions of the porphyry to the rocks which are adjacent to it,
there can be left no room for doubt as to its intrusive character.
The suggestion that the intrusion is of the nature of a laccolith
may, perhaps, be questioned on the ground that the mass cuts
across the strata of the encasing formations. That it does so is
probably due to the fact that the strata were folded anterior to
the intrusion. The laccolithic chamber for the reception of the
magma, particularly in the western area, has a floor, which while
uneven, appears to have an approximation to the horizontal, and
the impression that one gets from the mapping is that the hori-
zontal dimensions of the mass are much greater than the vertical.
There seems to be httle question but that the sedimentary rocks
once arched completely over all of the porphyry, although there

VoL. 4] Lawson.—The Robinson Mining District. 315

may of course have been vents in the arch to the surface as it
existed at the time of the intrusion.

Contact Metamorphism.—The conclusion which has been
reached on purely structural grounds as to the intrusive char-
acter of the porphyry is confirmed by evidence of contact action
which has been detected at various points on the periphery of
the mass. The southern border of the porphyry to the east of
the Ruth Mine is characterized by a zone of vermilion colored
earthy material which les between it and the limestone. To
the south of the porphyry, immediately opposite the Ruth Mine,
the first rock that one meets is passing from the intrusive to-
ward the Ruth limestone is a body of yellowish green garnet
rock associated with magnetic and lmonitie iron ore.

The garnet rock has frequently a miarolitie structure, show-
ing cavities with drusy crystals of garnet up to 2 mm. in diam-
eter. Occasionally there is a green copper stain. Even the most
massive phases of the rock appear in thin section to be made up
of an aggregate of fairly well formed erystals. The garnets are
isotropic. There are occasional small veins of quartz traversing
the garnet, and small areas of yellow stained quartz aggregates
oceur. The iron ore with which this garnet rock occurs is found
in considerable bodies over several acres of ground but is not
intermixed with the garnet. In hand specimens it is feebly
magnetic, shows yellowish stains and has the yellow streak of
hmonite. In thin section it is chiefly opaque, but is shot through
with irregular areas and veinules which are translucent to red-
dish yellow lhght. The ore is evidently a mixture of limonite
and magnetite. A sample analyzed by Mr. Ross contained 65.6
per cent. iron.

At the contact of the porphyry with the Ely limestone on
the Jupiter claim, there have been developed bodies of yellowish
green garnet rock which, in thin section, is seen to be an aggre-
gate of more or less idiomorphie crystals of doubly refracting
garnet, with angular spaces between the erystals filled with
ealcite.

At the same contact on the Emma G. claim, the limestone
has been changed to a white marble or a mixture of calcite and
earnet. In places it may be called a garnet rock with a subor-

316 University of Californa Publications. [GEOLOGY

dinate proportion of calcite, in which are imbedded irregular
grains and idiomorphic erystals of quartz. Associated with the
calcite is a biaxial mineral with lamellar structure, a refractive
index less than that of quartz, a double refraction about that
of quartz or less, a pronounced cleavage and a twin structure,
which is thus identified as gypsum. Where the garnets prevail
the structure is miarolitic; where the calcite prevails the garnets
occur in nests and stringers through it.

At another locality on the same contact a yellowish garnet
rock occurs with drusy surfaces, in cracks, of small yellow gar-
nets and small veins of calcite. The garnet in this case has a
zonal structure and is doubly refracting. Nearly colorless epi-
dote occurs in aggregates of grains enclosed in the garnet.

Just to the west of Copper Flat and at Pilot Knob occur
considerable bodies of iron ore which seem to have the same rela-
tion to the porphyry that the iron ore at the Ruth does, although
the porphyry, particularly at Pilot Knob, has been well removed
by erosion from the immediate vicinity of the ore. The iron ore
at Pilot Knob is a black to metallic gray magnetite with a some-
what vitreous luster. It is compact and shows no granular struc-
ture. Thin sections are quite opaque except for a few areas and
veins translucent to reddish yellow lhght. This is the largest
body of iron ore observed in the district.

It is noteworthy that all the observed occurrences of this
contact garnet rock and iron ore are on the lower side of the
porphyry mass. It is also to be remarked that, while these pro-
ducts are regarded as the result of contact metamorphism, they
can in no sense be ascribed simply to thermal metamorphism in
the same way that common limestone is converted into marble,
or a clay state to an andalusite hornfels* without change of bulk
composition. It is evident that they are the products of a reac-
tion between the intrusive porphyry and the adjacent limestone.
The lime of the garnets was doubtless derived from the lime-
stone, but the carbonic acid was eliminated and the silica must
have been derived from the porphyry. The most probable means
whereby the reaction was effected was aqueous solutions ema-
nating from the porphyry and, this being the case, the process

*e.g., The contact zone at Barr Andlau described by Rosenbusch.

VoL. 4] Lawson.—The Robinson Mining District. 317

of garnet formation might have gone on, and probably did go
on, after the actual solidification of the intrusive mass.

Regarding the origin of the iron ore little can with confi-
dence be stated. This much is known, however, that bodies of
iron ore similar to those occurring in this district, and often on
a much larger scale, are common at the contact of intrusive rocks
with limestone. In some eases these ore bodies are known to
have originated long after the solidification of the igneous rock
and to have resulted from the leaching of the iron from it and
its precipitation at the contact with the lmestone. It would,
therefore, again not seem necessary to regard the iron ore as
in any way the product of the direct reaction of the molten
magma upon the limestone, but an after product, due to the
precipitation of the iron oxide at the contact of the limestone
from soluble salts due to the downward leaching of the por-
phyry. The particular reaction which has effected the precipi-
tation of iron oxide by carbonate of lime under such cireum-
stances is not known, but doubtless a chemical investigation
would make it clear.

At the contact of the porphyry with the monzonite of Weary
Flat the former is curiously modified locally. In some prospect
pits that have been opened along the wagon road between Copper
Flat and Pilot Knob, the monzonite is exposed in proximity to
the overlying porphyry. Here, the only part of the monzonite
that is left is the large porphyritic crystals of orthoclase, and
even these are charged with limonite giving them a yellow color.
The form and cleavage of the orthoclases are intact and the
faces reflect the hght well. All the rest of the rock, or the entire
matrix in which the porphyritic orthoclases are imbedded, has
been altered to a reddish cellular aggregate of limonite and
sihea. In thin sections of this altered rock the orthoclase is
perfectly fresh, showing no kaolinization products, although con-
taining much limonitie pigment. Carlsbad twinning is common,
and in some sections free from limonite a good biaxial figure
was obtained. The index of refraction is less than that of bal-
sam. The matrix in which these large orthoclases are imbedded
appears under the microscope to be composed of nothing but
limonite and secondary quartz in rather large grains and agere-

318 University of California Publications. [GEOLOGY

gates of such grains. There are some dusty inclusions in the
quartz, but no liquid inelusions could be detected.

The modification of the monzonite just described is clearly
a contact phenomenon, but it can not be ascribed to the direct
influence of the porphyry magma upon the underlying rock. It
is with little doubt due rather to a subsequent action in which
the chief reagents concerned were derived from the porphyry
by a process of downward leaching, though why all the feldspars
of the main body of the rock should have been destroyed and only
the porphyritic orthoclases left intact, remains a mystery.

Petrographical Characters—The porphyry in general has
suffered so much alteration since its solidification that it has
proved difficult to find material upon which to make a study
of the rock in its original condition. At a few localities, how-
ever, specimens were obtained which being less decomposed than
the rest of the mass have contributed some information on this
point. They are not, however, uniform in character and doubt
still remains as to the prevailing petrographical features of the
rock prior to its alteration. Some of these will now be briefly
described.

At the head of Lane Valley, on the south side, a tunnel has
been run into a mass of the porphyry where it emerges from
beneath a limestone capping. Here the porphyry has a bluish,
light gray color and may be seen in hand specimens to consist
of a dense matrix in which are imbedded numerous small pheno-
erysts of dull feldspar up to 3 mm. in length and fewer large
phenocrysts of another feldspar of fresh glassy appearance up
to 126 mm. in size. The rock is shot through with pyrite
mostly in disseminated grains but also in nests and small veins.
The rock effervesces freely in acid.

In thin section the ground mass is a microgranitic aggregate
of untwinned feldspar with a subordinate amount of quartz
and a great deal of secondary calcite. In this are imbedded
idiomorphie feldspars of small dimensions thoroughly altered
to an aggregate of decomposition products and also much larger
phenocrysts of fresh orthoclase containing shreds of calcite, some
phenocrysts of bleached biotite and grains of pyrite with blurred
outlines. None of the pyrite is enclosed in the feldspar pheno-

VoL. 4] Lawson.—The Robinson Mining District. 319

erysts. The feldspar of the ground mass has a distinctly lower
refractive index than the balsam and this taken with its non-
twinned character indicates that it is orthoclase.

Across the road from the last locality, a few hundred feet
distant, a shaft has been sunk into the porphyry at the base of
a vertical lhmestone bluff. Here the rock is of a light gray color
and strongly porphyritic. A blue-gray dense matrix holds abun-
dant dull white phenocrysts of feldspar ranging up to 4 mm.
in length, besides occasional much larger phenoerysts of ortho-
clase in Carlsbad twins up to 15 mm. in length. Throughout
the rock is disseminated much pyrite which is locally bunched
in nests and veins, and in portions of it there are large erystals
of fluorite the cleavage faces of which range up to 25 or 30 mm.
in breadth. The pyrite does not occur in the phenoerysts but
occurs freely in the fluorspar. The rock effervesces with acid.

In thin section this rock shows remnants of a holoerystal-
line feldspathic ground mass, much replaced by ealcite, with
grains of quartz scattered through it. In this are cloudy feld-
spar phenocrysts wholly altered, shreds of white mica of consid-
erable size and small seattered grains of pyrite. The larger
phenoerysts of orthoclase are fresh and show Carlsbad twinning.
The white mica is probably a bleached biotite. Some portions
of the rock are so charged with sulphides as to constitute ore.
A specimen of such ore shows numerous parallel and obliquely
intersecting seams of chaleocite and pyrite alternating with thin
sheets of rock more thoroughly kaolinized than the rest. The
seams vary from 1 to 2 mm. in thickness. A little gypsum is
plastered on the surface of the specimen.

At the first fork of the road east of the Ruth Mine, the rock
has a bleached white appearance with occasional yellow iron
stains. The porphyritic structure is very pronounced. The
phenocrysts are of two kinds: (1) Remains of sharply idio-
morphie feldspars of a dull white color and ranging usually
from 2 to 5 mm. in length, though sometimes attaining 10 mm.
(2) Lustrous white blades—evidently pseudomorphs of some fer-
romagnesian mineral from which the iron has been leached.
These phenocrysts are imbedded in a matrix which under the
lens appears to consist almost altogether of silvery white scales

320 University of California Publications. [GEOLOGY

lying in a felt work. This felted matrix is quite open and porous
in texture. Under the microscope the white scaly mineral of
the matrix has the properties of kaolin and has some quartz
associated with it. The feldspar phenocrysts are represented
by an aggregate of white mica scales and quartz. The broad
blades prove to be white mica probably a bleached biotite. One
crystal of zircon was detected and a few minute crystals of brown
hornblende.

On the hill to the west of Copper Flat shaft house the por-
phyry is yellowish in appearance and with the lens is seen to
be of a porous or boneycomb texture. Quartz veins 5 or 6 mm.
thick traverse it, also small zones of secondary quartz without
definite walls. The porphyritic structure is quite apparent, but
the feldspars are of a dull earthy appearance, as is, indeed, also
the matrix in which they le. There is no effervescence with
acids.

In thin section much of the field is turbid with yellow stained
scarcely translucent decomposition products. Between patches
of this kind is an aggregate of untwinned feldspar and quartz.
Cavities are numerous. Pseudomorphs of sharply idiomorphie
feldspars, in a very turbid condition, are numerous.

On the south side of same hill as that on which the last
specimen was taken, the porphyry is a dull white rock with
drusy cavities and irregular patches of blue gray quartz. There
are very faint traces of a porphyritie structure. In thin section
the ground mass consists of untwinned feldspar and some quartz
in which are occasional phenocrysts of orthoclase with Carlsbad
twinning and numerous larger grains and areas of secondary
quartz. A brownish isotropic decomposition product occurs in
patches through the slide and there are besides these stains of
limonite.

At the Copper Flat Mine the porphyry when charged with
sulphides becomes a copper ore. A sample of the ore from the
dump of the mine is a dull white rock showing occasional cleav-
ages of feldspar phenocrysts which is traversed to the extent of
half its volume with hght colored quartz stringers ramifying
in all directions. Both the dull white rock and the quartz have

VoL. 4] Lawson.—The Robinson Mining District. Bel

chaleocite and pyrite disseminated through them. The pyrite
also occurs in nests and veinlets.

A thin section shows only quartz in allotriomorphie granular
ageregate with numerous irregular grains of opaque sulphides.
In the quartz are abundant liquid inclusions with bubbles and
numerous small ragged nearly opaque solid inclusions are scat-
tered through it.

Another sample of the porphyry taken from near the bottom
of shaft No. 2, of the same mine, is a light gray rock with vague
and uneertain traces of porphyritie structure. Rather large
stringers of quartz, large nests of bronzy mica and stringers and
disseminated grains of chaleocite and pyrite are common in the
rock.

In thin section the rock is seen to be an allotriomorphie gran-
ular aggregate of quartz and biotite, with a small shear zone
running through it. The biotite is evidently secondary with the
quartz and the sulphides.

A specimen of the porphyry from the Josephine claim ex-
hibits a characteristic phase resulting from extreme silicifica-
tion. Microscopically it is a mass of honeyeombed quartz with
patches of light yellow ochre. Under the microscope the rock
is composed only of quartz in an aggregate of fairly uniform
sized anhedrons, with patches of yellow ochre.

Chemical Composition.—It is evident that a rock varying so
much in degree of alteration as the porphyry is difficult to char-
acterize chemically. Searcely any two of the specimens described
above as representative facies of the formation would yield the
same results on analysis; and the results in every case would
differ greatly from the original unaltered rock. The best that
can be done in such a case, where the chief object is to deter-
mine the character of the fresh rock, is to select the least altered
material available and subject it to analysis in the hope that,
thereby, some light may be thrown upon the nature of the altera-
tions which have affected it. This has been done. <A sample of
the rock from a tunnel at the upper end of Lane Valley, on the
south side, was analyzed by Mr. Herbert Ross with the following
results :

322 University of California Publications. [| GEOLOGY

ANALYSIS OF ORE-BEARING PORPHYRY.

SiO, 58.31
Al,O, 16.69
Fe.O,
FeO aster
MnO .19
MgO 1.27
CaO 5.29
Na.O .20
K.O 6.11
BaO .35
P.O; .31
Fe 2.27
S 2.79
Cl trace
co, 3.47
H,0 2.42
99.67

Approximately this corresponds to the following mineralog-
ical composition :

Per cent.

Orthoclase eile
Albite 1.5
Anorthite 2.
Biotite (residues ) 3.5
Apatite 6
Kaolin 22.
Pyrite 5.
Quartz 20.
Calcite 8.

99.6

The analysis agrees with and confirms the description of the
rock based on microscopic study (page 318) which was written
before the analysis was made. It seems quite certain from the
data thus obtained that the original rock was, as it still is, rich
in orthoclase and that this mineral, part of the quartz and the
apatite are the only constituents which have escaped alteration.
It is clear from the analysis that water, sulphur and carbonic
acid have been introduced into the rock from outside sources.
Since the kaolin is probably chiefly derived from the breaking
down of feldspars, it would seem probable that originally there
was a notable proportion of plagioclase, the soda of which has
been leached out and the lime of which has been converted into

Vou. 4] Lawson.—The Robinson Mining District. Bet

ealeite. The surplus silica of such plagioclase over and above
that fixed in the kaolin has probably also been removed. The
pyrite has doubtless resulted from the reaction of sulphur bear-
ing solutions upon the iron of the biotite which is now bleached
white, thus accounting for the absence of oxides of iron in the
analysis of the rock.

In view of this interpretation it seems pretty certain that
structure of this facies of the rock is much better preserved
the original rock had the characters of a rhyolite. The original
than its mineralogical character and seems to have been holo-
erystalline. This, however, may be due to its rather deep seated
situation and more superficial portions may quite possibly have
been hypoerystalline.

Resumé.—Reviewing now the petrographical deseriptions of
the porphyry from various localities, it would appear that we
have a gradation in the degree of alteration to which the mass
as a whole has been subjected, ranging from that exemplified
in the specimen analyzed to cases where every trace of the orig-
inal minerals has been removed and nothing has been left but
an ageregate of cellular secondary quartz constituting a phase
of the quartz blout. This extreme end product is, however,
probably quite superficial since in all underground openings in
the porphyry there is an abundance of kaolin in the rock with
notable quantities of residual feldspars. It probably represents
a result of the weathering of the kaolinized and silicified mass
as it became exposed to the direct attack and downward leaching
of meteoric waters above the ground water level. Setting aside
this extreme facies of the altered porphyry as a superficial phe-
nomenon, we may safely characterize the porphyry in general
as a very much kaolinized, silicified, carbonated and pyritized
rhyolite.

Porphyry at the Chainman Mine.—Near the Chainman Mine
mill there is exposed, in a road cutting, a mass of porphyry which
is quite different in its general physical characters from the
main body of the copper-bearing porphyry above described. It
is very probably, though not certainly, a distinct intrusion from
the general body of the porphyry. It is, however, mapped with
the latter. The rock is quite fresh and shows little or none of

324 University of Califorma Publications. [ GEOLOGY

the tendency to kaolinization and silicification to which the com-
mon facies of the porphyry seems so prone. In hand specimens
it is a compact, light yellowish gray rock, showing numerous
small porphyritie feldspars of a fresh glassy aspect.

Under the microscope this is seen to consist of a fine holo-
erystalline ground mass made up of allotriomorphie and inter-
locking feldspars, some of which show lamellar twinning. These
are approximately equidimensional and generally free from de-
composition products. In this ground mass are imbedded nu-
merous phenocrysts of plagioclase, colorless augite, and apatite.
The feldspar in sections normal to (010), showing both Carls-
bad and albite twinning, have extinctions corresponding to the
composition Ab, Ang.

The rock thus appears to be a pilotaxitic augite andesite.
The fresh condition in which this rock occurs promised satis-
factory results on analysis. A selected sample was, therefore,
placed in the hands of Mr. Herbert Ross of the Ruth Mine, who
kindly made a chemical analysis with the following results:

SiO, 63.30
Al,0, 17.90
FeO 1.83
MgO 2.53
CaO 10.45
Na,O 2.30
K,0 aoe
P.O; .69
ae lig Tats

100.18

QUARTZ BLOUT.

Term Defined.—Perhaps the most remarkable feature of the
porphyry is the occurrence, in the areas occupied by the latter,
or on their periphery, of large bodies of quartz of somewhat
varying character. These bodies of quartz are by no means un-
common features of decomposed and mineralized eruptive rocks
in Nevada and elsewhere; and the prospectors and miners, who
have to deal with them practically, usually distinguish them
from ordinary vein quartz by characterizing them as ‘‘blow

VoL. 4] Lawson.—The Robinson Mining District. 325

>

outs.’’ This discrimination appears to the writer to be well
warranted. They cannot be regarded as veins or lodes; and
while, as will be shown !ater, they are to a large extent replace-
ments of other rocks, they may not be wholly so. They consti-
tute a particular mode of occurrence of quartz which the writer
desires to distinguish both from vein quartz and from replace-
ments of country rock by silica in the vicinity of veins. To
signalize the distinction and to simplify their discussion, the
miners’ term ‘‘blow out’’ will be adopted in the modified form
of blout, and.they will, therefore, be referred to henceforth as
quartz blout, much in the same sense as one would use the ex-

20)

pression ‘‘quartz vein.’’ Similarly as we designate the quartz
of a vein specifically as ‘‘vein quartz,’’ so here we may refer to
the quartz of which the blouts are composed as blout quartz.

Field Relations —The most striking feature of these quartz
blouts is their vast size as compared with ordinary veins. <A
glance at the map will show that in the vicinity of the Ruth
mine they occupy a very considerable fraction of the area of
the porphyry ; perhaps one-third is occupied by the blout.

The mapping indicates that the greater part of the quartz
blout hes on the periphery of the porphyry mass and occupies
an intermediate position between it and the surrounding lime-
stone; and although some important occurrences are more cen-
trally situated, these from the mapping appear to be of the
nature of caps upon the hill tops and ridges. If we accept the
suggestion thrown out in an earlier portion of this paper, that
the porphyry mass is of the nature of a laecolith, then these cen-
trally situated quartz blouts are also peripheral, and represent
a contact development between the porphyry and its roof of
limestone now removed by erosion. Indeed, we can form a very
consistent hypothesis to explain the distribution of the blouts
by supposing that they were once a more or less continuous
envelope, easing the porphyry, particularly on its upper side,
and intervening between it and the over arched roof of lime-
stone. The removal of the limestone roof by erosion and the
dissection of the envelope of quartz blout, leaving exceptionally
thick or resistant portions of it as residuals reposing upon the
porphyry, would well explain most of the occurrences. This

326 University of California Publications. [GEOLOGY

hypothesis is borne out by the way in which the porphyry in
the vicinity of the Ruth Mine passes at comparatively low angles
beneath the Ruth limestone to the north, with considerable bodies
of blout along the contact. On the west of the same porphyry
mass the mapping of the blout is also very instructive, for there
it is revealed as a sheet of considerable thickness flanking the
porphyry. and extending from the summits of the hill down the
slope to the floor of Ocher Valley, where it passes beneath the
limestone. Mapping in other parts of the field shows the same
general relations. We may thus assume with considerable confi-
dence that the quartz blout is of the nature of an eneasing shel!
developed, so far as the field evidence goes, chiefly upon the
upper side of the porphyry laccoliths. It is, however, pretty
clear also from the failure of the blout to appear at certain loeal-
ities, where the contact of the porphyry and overlying lmestone
may be mapped narrowly, that this shell was not perfectly con-
tinuous. It is also very probable from a study of various occur-
rences, that the shell of blout was not only a partial one, but
that it was of very variable thickness, and that the contact be-
tween the quartz and the porphyry was extremely irregular in
detail, the quartz often penetrating down into the porphyry
quite sharply. Some of this irregularity, however, may be ex-
plained by the excessive minor faulting, which as will be shown
later, affects the porphyry throughout. Faulting must also be
resorted to to explain certain subordinate occurrences of blout
in depressions in the surface of the porphyry below the general
level of the original shell, as for example, on the Josephine claim
to the northeast of the Ruth Mine.

Besides these occurrences in immediate association with the
porphyry, in the relations above indicated, there are others of
minor importance as regards the scale on which they are devel-
oped, but which are nevertheless of much interest in throwing
light upon the question of the genesis of the quartz blout. These
occur not in the porphyry, nor on its contact with the limestone
but wholly in the limestone. Some of these, while they are now
quite disconnected from the porphyry, may have at one time
been connected with it. The quartz blout of the Twin Peaks,
for example, to the southeast of the Ruth Mine, may with much

VoL. 4] Lawson.—The Robinson Mining District. 327

reason be regarded as representing a mass of peripheral blout
about the porphyry in the vieinity of the edge or margin of the
laceolith, which has since been caused to shrink in area by ero-
sion, leaving the more resistant blout behind as a residual. If
this view be accepted for such occurrences, they would need no
special discussion as apart from the blout now found in the
porphyry areas. There are, however, occurrences which can not
be so explained. They lie wholly in the limestone and extend
down into it as irregularly bulging and tapering masses which
have some resemblances to veins but differ from these in the ex-
tremely abrupt and short lenticular habit which they affect.

Varieties of Quartz Blout.—The quartz of the blouts is by
no means constant in character throughout the field. There are
a great many varieties. These need not, however, be described
in detail and it will suffice for purposes of description to class
them under four subdivisions made on structural grounds. These
are the (1) solid, compact quartz, (2) ecavernous-weathering
quartz, (3) breeciated quartz, and (4) cellular quartz. The
first of these is the most common. It resembles closely a mas-
sive quartzite of granular but compact texture. Sometimes it
is nearly pure quartz, glassy or whitish or but shghtly yellowish
in appearance, but for the most part it is deeply stained with
iron oxide. The colors are sometimes disposed in a eutaxitic
fashion, or it may be seamed with intersecting veinlets of more
deeply colored jaspery quartz. It weathers in smooth, rounded
knobs, or breaks down into a talus of irregularly angular blocks.
Oceasionally this variety shows a stratiform appearance but with
no tendency to part along the planes between the different lay-
ers. The difference in the layers is usually due to both color
and texture, flinty or cherty layers alternating with those of a
more granular character. The cherty portions may be dark to
almost black or may be light colored—yellowish or milky white.
The granular portions, where not heavily stained by iron oxide,
may be glassy or gray or very dark.

The cavernous variety of the blout quartz differs from the
last described by its weathering out in extremely irregular forms
with rugged chambers and straggling channels. In the bottom

328 University of California Publications. [GEOLOGY

of the pits and chambers which characterize the weathered ex-
posures of this phase of the blout quartz, remnants of limestone
may be occasionally detected. In one case a mass of limestone
about 8 inches in diameter showing abundant traces of fossils
was found imbedded in the quartz at the bottom of a depression.
In other cases the presence of the carbonate in such situations
was proved by effervescence on the application of dilute acid.

The third general variety of blout quartz shows a pronounced
breeciated structure, the whole being made up of sharply angular
fragments, mostly less than an inch in diameter but often as
much as three or four inches. The breccia is generally well
cemented, and firmly bound together. The cementing materia!
in most cases observed is quartz, but in some cases where the
breccia has been exposed to the weather, the cement is etched,
leaving the angular fragments in sharp relief. In these cases
the cement proved to be, in part at least, carbonate of lime by
testing with dilute acid. In the breccia with siliceous matrix
the angular fragments are often free of color while the matrix
is strongly colored by iron oxide and appears as a compact red
or yellow jasper. All three of these varieties of blout quartz may
occur together in the same mass.

The stratiform facies of the solid compact variety of the
quartz has been alluded to. But the cavernous and brecciated
varieties are often also stratiform. In this case the stratification
is so similar to the stratification of the neighboring limestones,
that no one in the field could have any doubt but that the quartz
is the result of the silicification of that formation. Not only is
the quartz stratiform, but the individual beds are quite distinct
from one another and separate under the weather along the
original bedding planes. When in such stratiform quartz, re-
sembling an outcrop of limestone, one finds residual masses of
fossiliferous limestone imbedded in it, in the bottom of depres-
sions due to weathering, the evidence amounts to a demonstra-
tion that some of the blout quartz at least is the product of the
silicification of the limestone adjacent to the intrusive porphyry.

This conclusion cannot, however, be extended with certainty
to the solid, compact varieties of the blout quartz, which make
up the greater part of the occurrence, and the stratiform appear-

VoL. 4] Lawson.—The Robinson Mining District. p29

ance here may well be due to other causes than the replacement
of an original sedimentary structure.

There is still another variety of the blout quartz which merits
especial attention because its origin is not less clear than in the
case of the cavernous, stratiform varieties with residuals of
limestone. This is a light colored rock free from deep ocherous
stains, although it may be distinctly yellowish. It possesses a
prevailing spongy or cellular structure on weathered surfaces
and tends to break down into fragments of small size which
mantle the upper and flatter slopes of the porphyry areas. In
consequence of the tendency to break down, this variety of blout
does not present such bold croppings as in the case of the other
varieties. It is found occasionally, however, as on the Minne-
sota claim, as a cap of some prominence on the summits of the
hills. This variety of blout quartz occasionally shows traces of
porphyritie structure and it passes by insensible gradations,
representing stages of less intense silicification, into the well
characterized porphyry. ;

It thus appears that the blouts, which form so prominent a
feature of the porphyry areas, and which from their mapping,
appear to be remnants of a discontinuous shell or envelope which
once encased the porphyry, are in part the result of the replace-
ment of the adjacent limestone, and in part the result of the
extreme silicification of the porphyry itself on its margin, but
in greater part can not with confidence be referred to either of
these origins on the basis of direct evidence, although it seems
probable from analogy that most of it is due to the replacement
of limestone.

Relations to Copper Ores and Garnet Rock.—The more or
less ocherous iron stain which affects most of the blout crop-
pings has generally attracted the attention of prospectors to
them and not a few pits have been sunk upon them. It is only
rarely, however, that ore is found in these croppings and it is
then, almost in every case, in the form of sparing quantities of
malachite, azurite and chrysocolla. <A little fresh pyrite is not
infrequently found and it is the oxidation of this that gives the
blout its ocherous appearance. A number of shafts which have
been sunk in the blout appear to pass through it at no great

330 University of Califorma Publications. [ GEOLOGY

depth. Some of these pass into a massive greenish or brownish
rather soft rock, evidently a decomposition product, and then
penetrate a garnet rock, or garnet and quartz, in which is usually
found fresh chaleopyrite and pyrite, although in no great quan-
tity. This is true of the Morris shaft near Pilot Knob, and of
a shaft sunk on the Emma Nevada claim. <A similar occurrence
was found in the third level of the mine at Copper Flat, the
gradation from the fresh garnet rock with some chalcopyrite
into an olive brown or greenish decomposition product being
perfectly apparent in the abundant material on the mine dump.

It is not proposed at this place to discuss the genetic rela-
tions of this garnet rock and its decomposition product to the
quartz blouts; but it is well to note that the field evidence indi-
cates that they are associated to the extent that there are bodies of
garnet rock with chalcopyrite in the midst of the porphyry in
the vicinity of, or beneath, the blout.

THE PORPHYRY AS A COPPER ORE.

Certain portions of the porphyry mass, notably at the Ruth
Mine and at Copper Flat, have been so mineralized as to con-
stitute an ore of copper. In considering the characteristics of
this ore and its genesis, it will be first necessary to recognize
the fact that the porphyry, considered as an ore, is, like most
metalliferous deposits, separable into two zones: the zone of
oxidation near the surface, and the unoxidized zone beneath
this, extending to depths at present unknown. The porphyry
of both zones may constitute a copper ore but each in a different
way. At the Ruth Mine the porphyry of the oxidized zone is
almost wholly if not quite devoid of sulphides. It has a pre-
vailingly yellowish color, but is in many places of a deep red
color due to the abundance of iron oxide. It carries never more
than a small fraction of one per cent. of copper, and frequently
none can be detected. The passage from the oxidized zone to
the unoxidized is very abrupt and sharp, and, below the divid-
ing line, the porphyry throughout the mine is bluish white, and
is usually well sprinkled with erystals of pyrite and chalcocite
of small size, probably averaging half a millimeter in diameter.
The immediate appearance of these two sulphides at the divid-

VoL. 4] Lawson.—The Robinson Mining District. 331
g

ing line between the oxidized and the unoxidized rock and their
absence above that line leave no room for doubt but that these
minerals formerly existed in the upper zone, and have been oxi-
dized and leached out by meteorie waters descending from the
surface.

While there is thus a very sharp line between the two condi-
tions of the porphyry in the mine, that line is hypsometrically
extremely irregular, and has no reference to the present level
of the ground water. The water level stands in the mine at
present at about 335 feet below the shaft mouth, and the mean
lower hmit of oxidation is somewhere between 100 and 150 feet
below the shaft mouth. But the various levels and cross euts
of the mine have shown that tongues or wedges of oxidized rock
extend irregularly down into the unoxidized zone as far as the
500-foot level, with occasional limonitie stains alone seams to
still greater depths. It appears to be elear from this state of
affairs that the level of the ground water has been lowered prob-
ably not less than 250 feet and possibly much more in quite late
geological time at such a rate that the oxidation process failed
to keep pace with it; so that about a couple of hundred feet
of the unoxidized zone has been left stranded, so to speak, above
the water plane. The irregular tongues and seams of oxidized
rock that project down into the sulphide zone, of course, merely
represent the loci of more efficient oxidation by waters perco-
lating down from the surface, in the general tendency of that
process to overtake the retreating ground water.

This lowering of the ground water may be explained in more
than one way. As will be shown later, the region has suffered
deformation by faulting and tilting at quite a late date in its
eeological history and this deformation would, or at least might
easily, have affected the position of the water plane. Again the
district lies in a geological province which, as has been so well
shown by Gilbert* and Russell, has been affected in Quater-
nary time by an advent of arid conditions extending to the pres-
ent, which may well be considered as an adequate cause of the
lowering of the ground water throughout the Great Basin. In

* Lake Bonneville, U. 8. G. 8., Mon. I.
+ Lake Lahontan, U. 8. G. S., Mon. IX.

Boe University of California Publications. [ GEOLOGY

this point of view the descent of the water plane in the Egan
Range would be the subterranean correlative of the last desic-
eation of Lake Bonneville. The discriminating test between the
two suggestions above made as to the lowering of the ground
water would be the generality of the phenomenon. If, in va-
rious mines distributed over the Great Basin, it should be found
to be a fact that the ground water has in general been lowered
to a similar extent, then local causes would be eliminated except
as modifying conditions, and the general cause, the advent of
arid conditions, would seem to be the true explanation. If such
should prove to be the case, it would be an interesting addition
to the accumulating facts which go to show a definite dependence
of certain important features of ore deposits upon climatic
conditions.

The temperature of the mine water at the bottom of the in-
clined shaft on June 15, 1904, was determined to be 16° C. A
sample of the water had previously been sent to San Francisco
and was there analyzed by Dr. Harry East Miller, with the re-
sult tabulated below. It is probable that the proportion of ferric
sulphate is higher than is actually the case in the mine owing
to the difficulty of preventing oxidation of the ferrous salt. The
result is interesting as an indication of the materials which are
being leached from the porphyry by the descending meteoric
waters. There is no evidence or suggestion of ascending waters

in the mine at present.

ANALYSIS OF MINE WATER AT THE RUTH MINE.

Grains per Gallon of

231 cu. in.
SiO. + insoluble matter 5.50
NaCl 4.88
KCl 55
FeSO, 5.77
Fe,(S0O,)s 8.78
K.SO, 2.96
CaSO, 20.99
MgS0, 7.61

Organic matter + water of sulphates 6.96

64.00

VoL. 4] Lawson.—The Robinson Mining District. 333

Another sample of the mine water, collected by the writer
and analyzed in the mine laboratory as expeditiously as possible
after collection, by Mr. Herbert Ross, gave the following results,
for the ferrous and ferric sulphates:

FeSO, 9.36
Fe,(SO,)s 4

From this it would appear that the iron of the mine water
is nearly all in the ferrous state and that the high proportion
of ferric sulphate in Mr. Miller’s analysis is ascribable to oxida-
tion in the interval between the taking of the sample and the
time of his receiving it. If this be so, it clearly indicates a
deficiency of oxygen in the mine waters, thus promoting the
maintenance of a supply of SO, which, as has been so well shown
by Winchell,* is favorable for the reduction of copper sulphate
to cuprous sulphide and the precipitation of the latter as chal-
cocite upon pyrite. That the chalcocite is secondary upon the
pyrite is very apparent in several samples of the ore that were
examined, the chaleocite being frequently a shell encasing, or
partially eneasing, pyrite.

From what has thus far been stated it appears certain that
the copper ore of the Ruth Mine, porphyry impregnated with
chaleocite and pyrite in sporadic erystals, owes its value in part
to secondary enrichment by downward leaching from the zone
of oxidation. The fact that the oxidized zone might easily be
robbed of its copper ore by the leaching action of sulphate of
iron, was experimentally verified by placing a mixture of pulver-
ized chaleocite and porphyry in a burette and causing a 10 per
cent. solution of ferrous sulphate to pass through it in presence
of the atmosphere. The chalecocite was taken into solution and
passed from the burette as copper sulphate, CuSO,, at a fairly
rapid rate. While this secondary enrichment of the porphyry
below the zone of oxidation is unquestionable, two important and
significant facets remain to be noted. The first of these is that
the products of this enrichment are not localized at any partic-
ular horizon in the porphyry, so far as the development of the
mine has yet gone. The copper values are by no means evenly

* Bull. G. S. A., Vol. 14, pp. 269-276, 1903.

334 University of California Publications. [ GEOLOGY

distributed in the ore bodies thus far blocked out. But the richer
eround is apparently rather determined by freedom of flow of
descending solutions, that is, by local structural conditions in
the porphyry, than by any horizontal control such as the present
level of the ground water. In so far as the sulphides are uni-
formly distributed, this may possibly be ascribed to a steady
retreat of the ground water level, whereby the additional copper
ore leached from above was distributed fairly uniformly over
the range of that retreat, although at any given stage it was
precipitated chiefly at the contact with the ground water. It is
more probable, however, and more consistent with the distribu-
tion of chaleocite at Butte, Montana, that the products of the
down leaching from the zone of oxidation were not precipitated
at the ground water level, but more diffusely through the region
of the ground water, in the course of a slow circulation, which
is implied in the maintenance of a fairly constant level of that
water in the face of additions from above. In this view we
might expect below the level of the ground water an appreciable
but very moderate enrichment of the ore as compared with the
values in the still unoxidized ore above the ground water to
which the mine developments are at present chiefly confined.
This generally very moderate enrichment will doubtless be found
to be greatly modified by structural differences affecting free-
dom of circulation of the ground water, and may only be de-
teeted when considerable bodies of the country have been blocked
out so as to permit of a satisfactory average value, which may
properly be compared with average value of the ore in the un-
oxidized ground above the present water plane. This zone of
probable moderate enrichment might from the experience at
Butte be expected to gradually decrease in value with depth.
The second significant fact to which it is here desired to
advert, is that the ground which is being leached in the course
of oxidation differs in no essential particular from that which
is being enriched in consequence of that leaching. It has been
shown that the line of contact between the oxidized and the un-
oxidized zones, while quite irregular, is exceedingly sharply de-
fined and that the result of oxidation and its attendant leaching
is simply to lower the upper surface of what may be termed the

VoL. 4] Lawson.—The Robinson Mining District. ooo

ore bearing country. It has been shown also that this irregular
surface is far above the ground water. It thus appears clear
that the oxidized rock was before oxidation simply the bluish
white decomposed porphyry sporadically impregnated with py-
rite and chaleocite. This ore then, which by oxidation has con-
tributed secondary sulphides to the lower ground, must itself
have been mineralized by a similar secondary process. In other
words, the copper ore which yields by oxidation the materials
for the enrichment of the lower ground, is not a primary de-
posit, but has been derived from some primary source not yet
apparent; and our so-called secondary enrichment is in reality
at least a tertiary enrichment. This conclusion immediately
raises the question as to the original unenriched copper deposit,
or the product of the primary concentration. The answer to
that question cannot be given on the basis of direct evidence,
but only as an inference from certain suggestive facts observed
throughout the district.

The only primary deposits of copper that have been observed
in the district are limited bodies of chalcopyrite intimately asso-
ciated with garnet rock, or with garnet and quartz. These pri-
mary ores occur in two distinct situations. One of these is at
the contact of intrusive rocks, particularly the monzonite and
monzonite porphyry with the Carboniferous limestones. Here
they are clearly referable to a process of contact metamorphism.
By this is meant not merely thermal metamorphism, but reac-
tionary metamorphism, whereby solutions bearing silica and iron
from the intrusive mass react upon the lime carbonate and give
rise to the lime-iron silicate, garnet. These same solutions ap-
pear to have brought with them the materials necessary for the
deposition of the chalcopyrite, and sometimes there was an excess
of silica which was precipitated as quartz.

The other situation in which primary copper ores have been
detected is in the quartz blout and here again it is intimately
associated with garnet. From considerations set forth in pre-
vious pages, It appears very probable indeed, if not a demon-
strated fact, that the quartz blout is largely the result of a silici-
fication of the limestone, chiefly on the periphery of the copper
bearing porphyry, but also partly along fissures in the limestone

336 University of California Publications. [ GEOLOGY

in the vicinity of the porphyry. At the surface, and often for
considerable depths below the surface, these ores are now in the
form of the carbonates, malachite and azurite. But these car-
bonates are regarded as the result of the alteration of chalco-
pyrite i situ. In other localities, particularly at the Morris
Shaft near Pilot Knob and at a pit near the road between Copper
Flat and Pilot Knob, the quartz blout at depth carries consid-
erable garnet, with pyrite and chaleopyrite. In the Copper Flat
Mine on the 300-foot level there is an extensive body or so-called
‘““dyke’’ of garnet rock with nests of pyrite and chalcopyrite.
The garnet rock is for the most part thoroughly decomposed to
a greenish or brownish material which, when moist, has a cheesy
consistency and on drying on the dump, slacks in the air. All
eradations may be observed between the perfectly fresh garnet
rock and the decomposed material.

It thus appears that the only traces of primary copper ores
in the district are in the form of chalcopyrite associated with
garnet, and that certain of these occur in the quartz blout either
as the original chaleopyrite or altered to carbonates.

On this basis the hypothesis may be favorably entertained
that the secondary copper ore of the Ruth Mine has been de-
rived from the downward leaching of copper from bodies and
disseminated particles of chaleopyrite in the course of superficial
oxidation of the blout in which they were originally deposited.
There are at present vast bodies of blout at the surface imme-
diately above the Ruth Mine, but these are only remnants. The
ereater part of the blout has been removed by erosion. The
product of this leaching was deposited as chaleocite in the por-
phyry at a time when the water level was much higher than at
present. And finally, when in consequence of the subsidence of
the ground water to lower levels the zone of oxidation extended
into the porphyry, this chaleocite was in turn taken into solu-
tion and redeposited as chalecocite at still lower levels. This,
leaving out of account for the moment the source of the chalco-
pyrite, appears to be the history of the copper deposits in the
Ruth stated broadly. |

The modifying factors are the structural features. These
fall into two categories. (1) The thoroughly sheared and in-

Vor. 4] Lawson.—The Robinson Mining District. 337

ternally deformed condition of the porphyry which while open-
ing up the rock to the permeation of the ground water, with its
mineral matter in solution, would render that permeation irreg-
ular and so give an irregular distribution of the values. (2)
The presence of a dyke of dense fine textured minette to the
northeastward of the present mine workings would undoubtedly
affect the underground circulation, although what its effect
upon the deposition of the ore may have been is not yet clearly
apparent. ,

In order to get an idea of the average contents of the ore of
the Ruth Mine, an analysis was made at the writer’s suggestion
by Mr. Herbert Ross of an average sample. In the development
of the mine samples have been taken for assay every five feet of
the ground traversed. As there are about 5,000 feet of drifts,
shafts and crosscuts in the mine, the ore of all kinds was repre-
sented at the time of the analysis (1904) by about 1,000 samples.
Of these every fifth sample was used in equal proportions and
thoroughly mixed. By the process of quartering this was re-
duced to a convenient quantity and analyzed. Owing, however,
to the adverse conditions under which the analysis was made,
the results were not satisfactory except as regards the determin-
ations of sulphur, 6.00 per cent., iron, 5.384 per cent., and copper.
2.61 per cent. These results show that on an average the ore
of the mine contains 10 per cent. of pyrite and 3.25 per cent. of
chaleocite. It is to be noted, however, that much is included in
the sample taken which would not be regarded as ore and mined
in regular mining operations, so that the average copper content
of the actual ore is higher than the analysis shows and is prob-
ably about 3 per cent. The development of the mine and its
carefully maintained assay chart show that there is a very ex-
tensive body of ore of this average value with considerable
ground running well above the average, and in spots reaching 8
and 10 per cent. There are no well defined boundaries or limits
to the ore body except the oxidized zone above and the dyke of
minette on the northeast. This dyke is probably of limited thick-
ness and under the general conditions of deposition of the ore
above set forth, it should be regarded as of the nature of an
interruption to the ore and not as its final limit, it being quite

338 University of California Publications. [ GEOLOGY

probable that the porphyry on the north side of the dyke below
the zone of oxidation is impregnated with chaleocite just as it
is on the south side. In fact, the general conditions of deposition
lend much support to the belief that a large part of the por-
phyry mass below the zone of oxidation will be found to carry
more or less copper and will be well worth prospecting, particu-
larly where the capping of quartz blout is strongly developed.
At Copper Flat the general conditions are analogous to those
at the Ruth. There is the same porphyry intrusive in Carbonif-
erous limestones, and although, as the map shows, this area of
porphyry is separate from that of the Ruth yet the two may be
continuous in depth. The fact that, on its western border, the
porphyry of the Ruth area plunges beneath the limestone, while
that of the Copper Flat on its eastern border passes similarly
beneath the limestones in the opposite direction, renders this
subterranean continuity of the porphyry of the two areas quite
probable. On the hills about Copper Flat there are remnants
of a once extensive body of quartz blout. In general it is diffi-
cult to specify any significant difference in the general condi-
tions affecting the porphyry and those which prevail at the Ruth.
Yet in one important particular the porphyry regarded as an
ore of copper is very different from that at the Ruth. This
difference lies in the fact that, in the zone of oxidation, the
copper ores, over a very considerable acreage at least, have not
been leached out of the porphyry but have been fixed in the
form of carbonates. Over an area of perhaps 10 acres numerous
prospect pits have been sunk in the porphyry and show a very
general impregnation of the rock with green and blue carbonates
and carrying on the average an attractive percentage of copper
said to range up to 7 per cent. Many of these pits are fairly
deep and the dumps about them show that the copper carbonate
extends to their bottom. Not having had access to the record of
these prospect pits or to the assays of the samples taken from
them the writer can form no very exact idea as to the depth and
value of the ore. The exposures are, however, excellent and
enough is apparent at the surface to warrant the statement that
there is a vast tonnage in sight, both of unoxidized and of oxi-
dized ore, that could be mined by steam shovel methods. Unfortu-

VoL. 4] Lawson.—The Robinson Mining District. 339

nately the carbonates of copper disseminated as they are rather
diffusely through the porphyry do not lend themselves to ordi-
nary processes of concentration as does the chalcocite. In order
to handle this ore, therefore, it may be necessary to resort to some
leaching process.

The porphyry thus charged with copper carbonate has other-
wise the character of the zone of oxidation at the Ruth, except
perhaps, that kaolinization has not proceeded so far and that
the rock is fairly strong and coherent. Between this zone of oxi-
dation with its content of copper carbonate and the ground
water, there is as in the case of the Ruth a certain depth of the
sulphide zone in a dry condition down into which the oxidized
rock extends irregularly. This sulphide zone both above and
below the level of the ground water resembles closely that at the
Ruth. It is a bluish white porphyry impregnated with pyrite
and chaleocite. Locally it has in it nests of bronzy or brownish
mica in foils of considerable size. The mica appears to be sec-
ondary and is said by the miners to occur in those portions of
the porphyry where the content of the chaleocite is highest.

The upper part of the unoxidized zone at Copper Flat carries
higher copper values than the deeper ground, and doubtless rep-
resents a zone of enrichment by downward leaching at a former
higher stage of the water plane. The general average value of
the ore in the unoxidized ground differs but little from that at
the Ruth.

It is probable that the copper ore of the oxidized zone ex-
isted earlier as chalcocite, itself a product of secondary concen-
tration, and that in the oxidation process an excess of carbonic
acid determined the carbonatization of the copper ore dissem-
inated through the rock. The presence of this carbonic acid
may perhaps be ascribed to a later period of eruptive activity
which gave rise to flows of rhyolite, remnants of which are to be
found in the vicinity of Copper Flat.

With the exception of the mines at the Ruth and Copper
Flat practically all other attempts at copper mining in the dis-
trict have been made upon rather unsatisfactory and limited
deposits of chalcopyrite either on the contact zones of the intru-
sive rocks or in the quartz blout.

340 University of California Publications. [GEOLOGY

A discussion of the porphyry considered as an ore of copper
would be far from complete without some reference to what is
perhaps its most remarkable feature. This is the contrast which
its internal structure presents to that of the surrounding rocks.
As has been shown in an earlier part of this paper the Carbon-
iferous limestones have been folded; but the folds are open and
there is no evidence of intense compression resulting in plication
or shearing anywhere in the sedimentary terranes. Similarly
the monzonite which is the earhest intrusive into these sedimen-
tary rocks shows no evidence of deformation or of notable shear-
ing. The same is true of the monzonite porphyry. The latest
eruptive, a rhyolite lava, is similarly devoid of evidences of com-
pressive stresses. All of these rocks are, it is true, traversed by
faults but these are not numerous and do not in any case appear
to have affected the internal structure of the rocks dislocated.
It is probable that they are the local manifestations of general
movements of the earth’s crust in this part of the Great Basin
occurring at a late date in its geological history. The ore bear-
ing porphyry on the other hand, although occurring in compara-
tively small and definitely limited masses in the midst of these
unaffected or but gently folded and broadly faulted terranes, is
internally intensely deformed. In the series of long drifts and
numerous crosscuts of the Ruth Mine, which the writer examined
closely, scarcely a step can be taken without passing slips and
shear zones in the body of the porphyry. These have quite va-
riable orientations both as regards dip and strike, but in spite
of this variation a series of observations in all parts of the mine
shows an interesting general tendency. Of some 74 observa-
tions for the direction of the dip of these slips and shear zones,
only nine were found to bear southerly. In all other cases the
direction of dip was in some azimuth to the north of the mag-
netic east and west line. That is, the prevailing dip is in the
direction of the general dip of the mass of porphyry considered
as a whole. - The angle of dip ranges from 10° to 75° and the
average value of the 74 observations is 40°. Many of these slips
and shears intersect one another, the abutment of older slips
upon later ones being commonly observed. Many of the shear
zones have a black gouge from a few inches up to about a foot

VoL. 4] Lawson.—The Robinson Mining District. 341

or a foot and a half in width, the black color being due to the
pulverization of the pyrite and chaleocite in the zone of crush-
ing. In other cases, there is a notable deposit of these sulphide
shears which has been made subsequent to the movement and
which, therefore, shows no evidence of crushing. In those cases
where the black gouge is present, it is most probable that the
movement was progressive, the first rupture having afforded
conditions favorable for the deposition of the sulphides, and the
recurrence of the movement having effected their attrition, to-
gether with the adjacent porphyry. In some cases there are
seams of fresh sulphides in the midst of the gouge. At the lower
limit of the zone of oxidation it is not uncommon to find that
the oxidation has extended downward along the shps and shears
below the general limits of the zone. It appears thus that these
structural features of the porphyry are important factors in the
process of mineralization, and it becomes an interesting question
to inquire into their origin. The contrast which is presented
between the intensely broken and sheared porphyry and the
unmoved condition of the surrounding country indicates at once
that the cause of the movement is an internal one, intrinsic in
the mass of the porphyry, and not either general or local earth
movements. The fact that the prevailing dip of the slip planes
and shear zones is in the same direction as the dip of the por-
phyry mass, though probably at steeper angles, indicates that
the movement has been one of repeated and complex normal
faulting, and that this faulting is but an expression of the ten-
dency of the mass to adjust itself to a new and diminished vol-
ume. It is further clear that such a tendeney would not have
found expression in faulting, had the shrinkage of volume been
uniform in degree and in time throughout the mass.

Our inferences thus lead us to a picture of the porphyry mass
shrinking in volume unequally in different parts and at different
times. The only cause that can be suggested for such a shrinkage
of volume is a chemical change within the porphyry and an elimi-
nation of certain of its chemical constituents. This suggestion
is well borne out by the abundant evidence of kaolinization and
allied changes within the body of the porphyry as far as it has
been yet explored. The change from orthoclase to kaolin, with

342 University of California Publications. [ GEOLOGY

the partial elimination of alkalies and silica and the addition of
water, involves a very considerable diminution of volume, and
since this process has been general throughout the porphyry, it
seems reasonable to make it accountable for the shrinkage mass.
The tendency to collapse as the process proceeded would be ad-
justed by shpping and shearing on normal fault planes and as
these developed the mass would be rendered more and more ac-
cessible to permeating solutions.

The process of kaolinization is probably most commonly in-
augurated by the attack of carbonated waters, whereby a portion
of the alkalies is removed as carbonate, carrying off with it a
portion of the silica in solution, in the form of alkaline silicate.
It has been shown that the slipping and shearing of the mass
of porphyry was progressive and the process of kaolinization
was probably also progressive extending over a long period of
time. If this be conceded, there is nothing violent in the assump-
tion that the process may have started immediately after the
solidification of the porphyry, the source of the carbonic acid
being the decomposition of the surrounding limestones by econ-
tact with the hot intrusive mass. This, at least, is the hypothesis
which the writer entertains to explain the chemically altered
and mechanically sheared condition in which we now find the
porphyry.

The hypothesis finds support in the fact that it affords at the
same time a consistent explanation of certain other important
phenomena connected with the porphyry, particularly on its
periphery. It also suggests an adequate explanation for the
original source of the copper ore and its associated pyrite. Un-
der the hypothesis, the carbonic acid would be in the ascending
waters arising about and through the recently consolidated por-
phyry, the ascending tendency being due to the disturbance of
the equilibrium of the ground water of the region by the inva-
sion of the intrusive mass. This ascending water charged with
carbonic acid would inaugurate the kaolinization of the por-
phyry. Lime would be present in these waters in the form of
the bicarbonate. Under these circumstances, certain chemical
reactions would take place from the recognition of which there
appears to be no escape. The potassium silicate formed in the

Vou. 4] Lawson.—The Robinson Mining District. 343

course of the kaolinization of the orthoclase would react upon
the ealeium bicarbonate. Potassium bicarbonate would be

formed and ealcium silicate precipitated, thus:

K,Si0,-+-CaH,(CO,).—CaSi0,+2KHCO,.

The calcium silicate thus formed would in turn be decomposed
by earbonie acid, with the precipitation of insoluble silica, thus:

CaSiO,+H,CO,—CaH, (CO,).+H,O+S8i0,.

These reactions were verified experimentally for the writer
by Mr. Herbert Ross, and while it is not insisted that they repre-
sent the detail of what must be a complex series of chemical
reactions, yet they indicate with great probability the source of
the silica which is so abundantly found in the form of quartz
blout on the periphery of the porphyry mass, and the general
mode of its derivation from the porphyry. It accounts also for
the secondary silica in the body of the porphyry. Moreover,
since lime silicate is formed in the process above outlined, it may
have been locally precipitated, in combination with iron, in such
situations, on the periphery of the porphyry, as to escape decom-
position by excess of carbonic acid and so give rise to the garnet
rock found sporadically at the contact with the limestone and
to some extent also in the midst of the quartz blout. Further,
since the copper ores of the district are intimately associated
with the porphyry, except for certain unimportant occurrences
on the periphery of the monzonite which probably have an anal-
ogous history, there seems little escape from the conclusion that
the copper was originally minutely disseminated through the
porphyry in its unaltered conditon; and that the same ascending
waters which robbed the porphyry of part of its silica to form
the quartz blout also leached it of its copper, depositing it as
chalcopyrite in the blout, whence by oxidation and the agency
of descending waters it was carried down into the porphyry
again and deposited as chalecocite, the permeation of the rock
by such descending waters being greatly facilitated by the rup-
turing and collapse of the mass due to the kaolinization.

344 University of California Publications. [GEOLOGY

¢

MINETTE.

In the underground work at the Ruth Mine there have been
brought to light two occurrences of lamprophyres neither of
which were detected at the surface of the ground. Both of these
have the mineralogical characters of minette. The first occurs
as a small dyke a few feet in width in No. 1 level east. The
dimensions and extent of the dyke are difficult to determine since
it has been affected by the various shearing movements in the
porphyry, which it cuts. Its exposed width is about 3 or 4 feet.
It strikes N. 45 E. and dips to the N.W. at 30° and conforms to
the direction of the slip planes in this part of the porphyry. It
is best seen at the first cross-cut east of the station on No. 1 level,
but may be traced for perhaps 50 feet beyond this point.

The rock of the dyke is fine grained and has a dark pepper-
and-salt gray appearance. It is traversed by quartz stringers
in much the same way that the porphyry is but is not notably
mineralized. Under the microscope it is readily seen to be com-
posed of about equal proportions of brown biotite and feldspar
in an allotriomorphic granular aggregate. The feldspar is un-
twinned and in all sections has a lower refractive power than the
balsam.

The second occurrence of the minette is a finer grained, com-
pact, bluish green rock, which, in the zone of oxidation, decom-
poses to a soft yellowish or brownish mass of almost cheesy con-
sistency. The thickness of this mass is not known since the mine
workings have not pierced it, and, owing doubtless to its soft
decomposed condition, it ean not be traced at the surface. It
seems, however, to form a somewhat irregular wall limiting the
ore-bearing porphyry to the northeast, thus forming an impor-
tant element in the geology of the copper deposit. All of the
mine workings in the copper-bearing porphyry lie to the south-
west of it; but the main shaft of the mine and the upper levels to
the east have penetrated it for some distance.

In thin section the rock appears as a microcrystalline mosaic
of untwinned feldspar having a lower refractive power than
balsam, throughout which are abundant shreds of brown biotite
and numerous areas of secondary white mica. Besides this there

Vou. 4] Lawson.—The Robinson Mining District. 345

are grains of a blue, pleochroic mineral with an enormous re-
fractive power and a moderately weak double refraction. Its
maximum polarization tints range from yellow of the first order
to blue of the second order, while the orthoclase for the same
thickness shows gray blue of the first order. The grains show
extinction parallel to the direction of elongation where such
elongation can be recognized. The sapphire blue color is not uni-
form but patchy in its distribution, and the pleochroism is from
blue to colorless. The blue ray corresponds to the axis of less
elasticity. Surrounding the grains of this mineral is usually a
border of white micaceous mineral, evidently secondary, and
derived in part from the grains which it envelops. These char-
acters are those of corundum, and it thus appears that we have
here to deal with a corundiferous minette, a fact which is of
course suggestive of the possibility of finding a facies of the rock
which might yield sapphires of value. Those revealed in the
study of the thin sections are of microscopic dimensions; but
inasmuch as sapphires have been found in similar rocks in Mon-
tana,* their discovery here is a hint which may some day be of
service in the search for gems.

Besides the minerals above described there is considerable
pyrite scattered through the rock in isolated crystals.

- Chemical Composition—tThe corundiferous minette, consti-
tuting as it does an important feature of the mine as a wall or
barrier lmiting the distribution of the actually developed ore
body on the north, was subjected to analysis for the writer by
Mr. Ross with the object of settling as definitely as possible its
petrographical character and its possible relations to the ore-
bearing porphyry. The results of the analysis are as follows:

*U.S. G. 8. 20th Ann. Rpt., Pt. ITI, p. 554 et seq.

346 University of Califorma Publications. [GEOLOGY

ANALYSIS OF MINETTE.

SiO, 53.69
A1,O, 25.86
FeO, sate
7 FeO 1.71
MgO 1.91
CaO .65
Na,O .89
K.O 8.11
BaO Boll
P.O; #25
Fe . 88
Ss On
co, ilal
H,O 3.66
F .07
99.17

From this analysis the following percentage of minerals in
the rock has been ecaleulated as probably representing its com-
position although the estimate is not altogether satisfactory :

Orthoclase al.
Albite Mee
Anorthite alg
Biotite WG:
Muscovite 8
Corundum 4,
Apatite ar
Calcite Are
Pyrite 2
Kaolin 21.
Free Silica 8.
99.4

From this it is evident that. the rock, although much kaolin-
ized, pyritized, silicified, and otherwise altered, is rich in ortho-
clase and biotite and corresponds in a general way with what
might be expected of a much altered minette. The high content
of alumina in the analysis can only be accounted for on the as-
sumption that some of that oxide exists in the rock uncombined,
thus confirming the microscopic detection of corundum.

Vou. 4] Lawson.—The Robinson Mining District. 347

RHYOLITIC LAVAS AND TUFFS.

In the general statement of the geology of the district it has
been said that the latest rocks with which we have to deal are
certain rhyolites and tuffs which were erupted after the geo-
morphie evolution of that region was well advanced toward its
present condition. In the district as mapped there are two con-
siderable areas of such rocks besides some outlying patches. The
first of these is at Quarry Hill which occupies the western medial
portion of Ocher Valley. The hill has a north and south extent
of about 4,000 feet and a width of 1,500 to 2,000 feet. The vol-
eanie rocks which compose it clearly rest upon the eroded sur-
face of the Arcturus limestone and have a thickness of about
180 feet. The lava is not now connected with any eruptive vent,
and is evidently the remnant of a much more extensive sheet
which once occupied the valley, and doubtless was once contin-
uous with an area of similar rocks about two miles down the
valley near the old Ely stage road. One may completely encircle
the hill without leaving the exposed Arcturus shale limestone ;
but on the northeast side of the highest part of the hill the limit
of the lava is a fault which has dropped it down against the
limestone. It is evident from the situation of this lava that,
although, as will be shown later, the region has been deformed
and faulted since its eruption, the valley which it occupies must
have had locally pretty much the same general configuration as
is now presented to us by resurrection due to removal of the
ereater part of the lava by erosion.

Three Members of Volcanic Series—The section afforded by
the abrupt faces of Quarry Hill shows that there are three dis-
tinct members in this voleanic accumulation. The first of these
is a white tuff exposed at the base of the hill, on its east side.
where the wagon road from the Ruth Mine to Copper Flat passes
it. The rock is composed of fragments of pumiceous glass and
rhyolite with broken crystals of quartz and feldspar. The frag-
ments are usually small but some of them are a few inches in
diameter. The tuff is rather firmly cemented. The full thick-
ness is not exposed but it was estimated to be not less than 10
feet. To the north and northeast of Quarry Hill beyond the
limits of the territory mapped, this tuff formation is well ex-

348 University of California Publications. [GEOLOGY

posed in artificial and natural cuttings, and is there shown to
be well stratified and to have a thickness several times greater
than the estimate given above. The tuff has been quarried to
some extent at various croppings for the building of fire boxes
for steam boilers at the various mines of the district.

Above the tuff les a sheet of black glassy porphyritic lava
having the greasy luster of a pitchstone. This lava is best ex-
posed on the north slope of the hill but its thickness could not
be satisfactorily determined. It may be 40 feet. Above this the
bulk of the hill is composed of a purplish red lava of lithoidal
aspect with abundant phenocrysts of feldspar and black quartz.
This rock extends to the summit of the hill where a small quarry
has been worked which gives its name to the hill. This purple
lava is traversed by structural planes of parting which appear
to be parallel flow planes of the lava and dip to the northeast
at angles of about 23°, indicating a tilting of the formation
since its solidification. Traversing these flow and parting planes
are several well marked jointages. The best defined system
strikes N. 65° E. with a dip of 70° to the south-southeast. The
next best defined system has a similarly steep dip to the south-
west. In the absence of all suggestion or evidence of compres-
sive stresses, these joints are most simply explained as due to
relief from tensile stresses. There is no columnar structure in
the rock.

At Copper Flat village and a little to the north of it there
are three outlying patches of the purple variety of the lava
lying partly on the Arcturus limestone and partly on the por-
phyry. The largest of these les on both sides of the main street
of Copper Flat but chiefly on the east side. It has a length from
north to south of about 1,000 feet and a width of about 500 feet.
Neither the black pitchstone nor the white tuff appear to be here
present beneath the purple rhyolite.

The second important area of rhyolite is found on White Hill,
the summit of which is about a mile and a half from Copper
Flat to the southwest. This is a roughly triangular area, the
longest side of which is to the north and is determined by a
fault which has dropped the rhyolite against the porphyry, the
Ely limestone and the Arcturus shaly limestone. It is nearly

VoL. 4] Lawson.—The Robinson Mining District. 349

a mile in greatest length along the line of the fault. On the
south side the purple rhyolite reposes partly upon the porphyry,
partly upon the Ely limestone and partly upon the Arcturus
shaly limestone. The thickness of the lava is estimated to be
here not less than 300 feet. At its base where it reposes upon
the older formations, no exposures were found of either the
black pitchstone or the white tuff and it is probable that they
are here absent from the section. he purple rhyolite of White
Hill differs somewhat in detail from that described at Quarry
Hill. It is of a more compact texture and a lighter color and
shows a more pronounced flow structure. It breaks down readily
into thin slabs or shaly fragments, a tendency which was not
observed at Quarry Hill.

Petrographical Characters——Hand specimens of the dark
pitchstone variety of the rhyolite present the characters of a
back glass thickly studded with sharply defined phenocrysts of
vitreous to dull white feldspar, from 1 to 4 mm. in length, small
dark quartzes and a few flakes of brown biotite. Under the
microscope the ground mass is a stippled gray glass, the stippled
appearance being due to the sporadic distribution of clusters of
polygonal microlites and stellate trichites. The glass has a lower
refractive power than balsam. In this glass are imbedded nu-
merous phenocrysts of cracked sanidine, more or less corroded
quartz, a little plagioclase and a few crystals of greenish brown
biotite. The plagioclase is in some eases enclosed in the sanidine
which also holds occasionally inclusions of glass. The sanidine
has a small optic angle giving in isotropic sections a nearly un-
laxial figure and a negative sign.

The more abundant variety of the rhyolite of purplish tint
is composed of a compact ground mass in which are imbedded
numerous vitreous phenocrysts of feldspar ranging in size up
to 5mm., and dark quartz rarely exceeding 3 mm. in diameter.

In thin section the ground mass is a turbid glass with nu-
merous small vaguely defined doubly refracting areas. The
feldspar is mostly sanidine with a little plagioclase. The quartz
has well defined boundaries of the usual dihexahedral habit, but
is occasionally somewhat resorbed. The microscope reveals a few
foils of biotite not apparent in the hand specimens.

350 University of California Publications. [ GEOLOGY
y

OBSIDIAN.

On the Josephine claim, near Versan’s cabin, is a small ex-
posure, not exceeding 30 feet in diameter, of obsidian, which
appears to be intrusive in the porphyry. It is the only occur-
rence of the kind which has been observed within the area of
the district examined, and is very probably connected with the
voleanie activity which gave rise to the rhyolite flows, although
there is no direct evidence bearing upon this correlation. In
the midst of this exposure a wide pit has been sunk to a depth
of perhaps 12 feet, and fresh obsidian is well exposed on the
walls of the pit. Surrounding the exposure on all sides at the
surface there is nothing but porphyry as far as can be made
out from an examination of the soil and hillside wash. As the
mantle of debris is here rather heavy, however, it is possible that
the obsidian has a much greater extent than is revealed in the
exposure. The actual contact with the adjoining porphyry is
nowhere exposed.

The obsidian is a somewhat resinous looking, dark, vitreous
rock which might from its luster be called a pitchstone. The
most remarkable feature connected with the occurrence is that
the rock contains numerous inclusions of dark altered shale
ranging from half an inch to 2 or 3 inches in diameter. These
inclusions indicate that the intrusion has pierced the White Pine
shale in depth, and has derived its inclusions from that for-
mation.

Under the microscope the obsidian appears as a brownish
glass with a well marked flow structure containing occasional
fragments of crystals of sanidine and quartz. Under high pow-
ers the glass appears whitish and the brown color is seen to be
due to numerous: brownish, irregularly shaped, ragged or floe-
culent inclusions. These are drawn out in lines and give the
rock its flow structure. The glass has a lower refractive index
than the balsam as is clearly indicated by the Becke test.

One of the fragments of shale inclosed in the obsidian was
examined in thin section. The fragment was subangular and
had dimensions about 111434 inches. Its color was bluish
black. The most interesting fact revealed was the evidence of
thermal metamorphism shown in the presence of numerous erys-

Vou. 4] Lawson.—The Robinson Mining District. 351

tals of chiastolite. The ground mass of the rock is murky and
much obseured by particles of carbonaceous matter. Through
this are disseminated small flakes of brown biotite. The chias-
tolite, in beautifully idiomorphie erystals with geometrically dis-
posed carbonaceous inclusions, les in this matrix. The sections
are square, oblong and rhombie, and the carbon is arranged in
the usual way so characteristic of chiastolite. The size of these
chiastolites is generally about .56 mm. in longest dimension. The
discovery of such pronounced evidence of thermal metamor-
phism under such conditions is most interesting as indicating
that no greater time is required to effect such changes than is
required for a magma to solidify as a glass—a period which is
generally conceded to be quite short.

OTHER METALLIFEROUS DEPOSITS.

Before the Robinson Mining district became known as a pros-
pective copper camp, various attempts had been made to mine
lead-silver, and gold ores. Up to the present these attempts can
not be said to have been successful in the sense of having led
to profitable mining operations. But a considerable amount of
capital has been sunk in the district in gold mines and an un-
certain amount of selected ore has been shipped out from the
lead-silver mines.

The writer has made no special study of these deposits and
eannot, therefore, undertake their discussion here. It is de-
sired, however, to call attention to certain features of these de-
posits, particularly as regards their relation to the ore-bearing
porphyry. The lead-silver deposits form a fairly well defined
belt confined to the Ruth limestone and lying to the north of
ore-bearing porphyry and Lane Valley. The gold deposits occur
in various Palaeozoic formations, particularly the Ruth lime-
stone and the White Pine shale, and are distributed in a belt
on the south side of the ore-bearing porphyry and Lane Valley
although just beyond the area mapped there are some gold pros-
pects on north of Lane Valley. This general distribution of
the two kinds of deposits appears to the writer to be significant
of a genetic relationship with the same porphyry which has
given rise to the copper ore. In the vicinity of the Ruth Mine

352 University of Califorma Publications. [ GEOLOGY

the gold ores have not been exploited to any notable extent and
the writer has only seen the gossan of one deposit. The gangue
is a silicified limestone more or less stained with ocher from the
oxidation of pyrite. The deposit, so far as could be judged from
the collar of a prospect pit, is disposed parallel to the stratifica-
tion of the Ruth limestone. The writer was informed that the
ore ran at $18.00 per ton but can not vouch for the fact.

This deposit lies in the limestone a little below the porphyry
in which the Ruth copper mine is situated.

The lead-silver deposits to the north of the Ruth are above
the porphyry. On the Phoenix claim a considerable amount of
development work has been done and the character of the de-
posits can to some extent be observed. The ores are for the most
part distributed along the planes of bedding in the limestone.
The latter is inclined at quite low angles (18° to the N.E.) and
mineralization has occurred at different stratigraphic horizons
one above another. These successive sheets of ore are connected
with one another by a vertical, mineral-filled fissure, and the
tabular deposits so connected seem to pinch out at no great dis-
tance from the vertical vein. The tabular deposits near the ver-
tical vein vary from one to three or four feet in thickness and
the vertical vein was at one place observed to be two feet wide;
but in both the vertical vein and the tabular deposits parallel
te the strata the thickness varies rapidly. The occurrence of
the ores in the deposits is, also, so far as could be observed, far
from uniform. The prevailing color of the ore in the mass is
light ocherous yellow and iron minerals appear never to have
been abundantly represented in the deposits. The chief gangue
is silica which appears to be a replacement of the limestone and
the croppings at the surface resemble closely the quartz blout
of the neighboring porphyry. Some of the limestone imme-
diately adjacent to the deposits is of a dead white chalky char-
acter and is somewhat slickensided. It resembles massive kaolin
but effervesces freely with acid. The siliceous vein matter car-
ries galena, a sample of which was examined by Mr. Ross and
found to contain 22.4 ounces of silver to the ton and $1.49 in
gold. Besides the galena there are azurite, malachite, and chrys-
ocolla in sparing quantities, a little cerussite and considerable

Vou. 4] Lawson.—The Robinson Mining District. 353

ealamine. With the quartz of the gangue are also chalcedony,
opal, fluorspar, and calcite. There are also some dendritic films
of manganese oxide.

While in general the chief feature of the mineralization has
been the silicification of the limestone, there is abundant evi-
dence of minor fracturing and crustification and much of this
has occurred after the chief deposition of silica.

From the general facts above set forth, it appears that in
the vicinity of the Ruth, without considering the mines farther
east, there are three well marked zones of metalliferous deposits,
Viz. :—

1. <A central one containing sulphides of iron and copper in
the porphyry.

2. A southern one carrying gold in the limestones below the
porphyry.

3. A northern one carrying argentiferous galena with sub-
ordinate zine and copper minerals in the limestones above the
porphyry.

The segregation of the metals in this stratigraphic or struc-
tural relation to the porphyry is a most interesting fact but
with the limited data available it would be perhaps unwise to
attach too much significance to it. The fact is here recorded in
the hope that it may prove useful when considered in connection
with similar observations elsewhere in sufficient abundance to
lead to an inductive hypothesis.

FAULTS.

The general structure of the district, particularly as regards
the folding of the Palaeozoic strata, has been briefly described
in an earlier part of the paper. The essential features of the
structure are the Ruth syneline with an axis pitching northerly,
the rather flat Saxton anticline pitching southerly flanking this
on the west, and the broad spreading Rib Hill anticline, pitch-
ing to the southeast, flanking it on the west. These folds appear
to have been established before the advent of the earliest intru-
sive, the Weary Flat monzonite, which appears in the axis of
the Rib Hill anticline cutting across the folded strata. The sim-
plicity of these folds is interrupted by the more or less contin-

354 University of California Publications. [ GEOLOGY

uous belt of ore-bearing porphyry which traverses the district
with a trend in general transverse to the strike of the sedimen-
tary strata. It is probable that the rupturing of these folded
formations, incident to the injection of the intrusive masses,
was accompanied by more or less pronounced dislocations; but
such dislocations were more of the nature of laccolithic lifting
of the formations, one part from another, than of faults in the
usual sense of the term.

The only true faulting subsequent to these intrusions that
has been detected in the district is of very late date, since the
faults traverse the sheets of rhyolite which were poured out over
the surface at a time when the latter had been reduced by ero-
sion approximately to its present general configuration. These
rhyolitic lavas may be early Pleistocene and. are certainly not
older than late Pliocene, judging from the degree of degradation
which the region has suffered since their extravasation. It is,
therefore, believed by the writer that the faulting is not older
than early Pleistocene.

Of these faults traversing the district perhaps the most prom-
inent in the geological mapping is that which crosses the north-
ern flank of White Hill and throws the rhyolite capping of that
eminence down into the Palaeozoic rocks. This fault has a
general northeast-southwest trend, and the mapping shows that
it hades to the southeast at a small angle from the vertical. This
is the direction of the down throw and it is thus a normal fault.
The down throw brings rhyolite against the Arcturus and Ely
formations and against the ore-bearing porphyry. The mini-
mum estimated value for the amount of the down throw is 200
feet and it may be much more than this, depending upon the
reduction which the surface on the upthrow side has suffered
since the faulting transpired.

To the northeast, in the vicinity of Copper Flat the fault has
dropped the ore-bearing porphyry against the White Pine shale,
and the northeastern boundary of the porphyry has thereby been
heaved to the northeast, a distance of about 3,000 feet.

A second fault of some importance is that which traverses
Ocher Valley with a general east-west trend and drops the rhyo-
lite of Quarry Hill against the Arcturus limestone. The throw

VoL. 4] Lawson.—The Robinson Mining District. 355

here is downward on the south side of the fault and its minimum
amount is about 100 feet. This fault curves somewhat on its
strike and if continued for about half a mile beyond the point
where the dislocation is apparent on the northeast face of the
Quarry Hill, it would converge upon the White Hill fault in
the vicinity of Copper Flat. In attempting to follow the fault
to this intersection, it was found that the fault appears to fade
out and no dislocation was observed of the west boundary of
the Quarry Hill area of rhyolite. Followed to the eastward the
fault is observable in the dislocation of the quartz blout near
the grade up from Ocher Valley to the Ruth Mine. The trend
of the fault from this point would be toward the Ruth Mine
and it is possible that the precipitous bluffs which rise above
the mine are in some way an expression of this fault, but no
dislocation of the rocks could be here detected. Beyond the
mine, however, there is an obscure line of dislocation of the
quartz blout, porphyry, and limestone, extending from the north-
east corner of the Ruth claim to the east end line of the Kimbley
elaim.

The remarkable geomorphic character of Lane Valley and
the -stratigraphie relations of the formations on either side of
the valley suggest that the course of the valley has been deter-
mined by a fault; but as the valley is deeply filled now with
alluvium, the nature of the fault, if such there be, is obscure
and difficult to decipher. In the lower part of Lane Valley be-
yond the limits of the map, there is an important fault trans-
verse to the trend of the valley, the dislocation of the strata
being observable on the precipitous north side of the valley. The
alluviation of Lane Valley is probably due to a disturbance of
the drainage caused by this dislocation. Below the flat-bottomed
alluviated portion of the valley, the drainage is through a rather
steep grade, rocky gorge.

Besides these more important faults, a number of minor dis-
locations were observed, but they could not be traced for more
than short distances and they do not appear to be factors in the
structure which call for more than the briefest mention. One
of these is on the east flank of Rib Hill; a second crosses a gulch
about 500 yards west of the head of Lane Valley with a north

356 University of California Publications. [GEOLOGY

and south trend and is best seen in a tunnel which has been
driven on the west side of the gulch; a third lies about 400 yards
west of Copper Flat and appears to be a spur or branch from
the main White Hill fault already noted; a fourth lies about
800 yards northwest of the Saxton mine and brings the Ruth
limestone in abutment upon the White Pine shale and a similar
fault oceurs on the north side of Lane City.

MINERALOGY OF THE DISTRICT.

In addition to the minerals enumerated in the petrographical
descriptions of the rocks of the district, the following minerals
have been encountered and are here summarily listed with brief
notes for convenient reference, in the expectation that the list
will grow larger as the district becomes better known.

Pyrite in small cubes and pentagonal dodecahedra common
in the ore-bearing porphyry and minette below the zone of oxi-
dation.

Chalcopyrite in nests and irregular masses usually associated
with garnet at the contact of the monzonite with limestone and
shale and in the quartz blout of the ore-bearing porphyry.

Chalcocite the valuable copper ore of the district, and so far
as known confined to the ore-bearing porphyry below the zone
of oxidation through which it is disseminated in small grains.

Native copper found rarely in the ore-bearing porphyry of
the Ruth Mine.

Chrysocolla occurs to a limited extent in the ore-bearing por-
phyry and more abundantly in croppings of ore in isolated
bodies of quartz blout, and then associated with the carbonates
of copper.

Azurite in the superficial or oxidized zone of the ore-bearing
porphyry at the Copper Flat mines and in various isolated crop-
pings of quartz blout.

Malachite same occurrence as azurite.

Chalcanthite as incrustations of current formation on moist
surfaces of the ore-bearing porphyry protected from the rain.

Melanterite same occurrence as chalcanthite.

Olivenite (?) a green mineral determined qualitatively as a
copper arsenate. A rare occurrence in the Ruth Mine.

VoL. 4] Lawson.—The Robinson Mining District. oD

“

Turquois oeceurs sparingly in the ore-bearing porphyry of the
Ruth Mine.

Galena occurs somewhat abundantly in silver-lead deposits to
the north of the Ruth and to the north of Lane Valley.

Molybdenite thin films in the minette of the Ruth Mine.

Calamine found rather commonly in the zone of oxidation of
the silver-lead deposits to the north of the Ruth.

Fluorspar gangue mineral of the silver-lead deposits and also
in nests in the ore-bearing porphyry near the head of Lane
Valley.

Calcite a gangue mineral in the silver-lead deposits.

Magnetite in considerable bodies at the Ruth, Copper Flat,
and Pilot Knob at the contact of the ore-bearing porphyry with
limestones. Apparently only on the lower side of porphyry
intrusive.

Limonite same occurrence as magnetite but more limited:
also common in the oxidized zone of the pyritiferous rocks.

Garnet common at the contact of monzonite, monzonite por-
phyry, and ore-bearing porphyry with limestones; both leght
yellow garnet, grossularite, and a red lime-iron garnet, andra-
dite; occur. The andradite also occurs in the quartz blout below
the zone of oxidation.

Cliastolite in fragments of black metamorphic slate enclosed
in obsidian on the Josephine claim.

Rhodochrosite ; presence inferred from the pink color of cer-
tain limestones which weather to a brownish black color and give
reactions for manganese.

Wad rarely found in the porphyry of the Ruth Mine.

Talc oceurs in a notable body in a tunnel run into the ore-
bearing porphyry on the west side of a guleh about 500 vards
west of the head of Lane Valley.

Gypsum occurs as a current deposition on the rubble of cer-
tain dumps near the head of Lane Valley.

Opal sparingly in small veins in silver-lead deposits.

Biotite a notable occurrence in the form of nests in the ore-
bearing porphyry in Copper Flat mines and to a much less ex-
tent in the Ruth Mine.

University of Califorma,
May, 1906.

UNIVERSITY OF CALIFORNIA PUBLICATIONS
BULLETIN OF THE DEPARTMENT OF

GEOLOGY

Vol. 4, No. 15, pp. 359-396 ANDREW C, LAWSON, Editor

I.—CONTRIBUTION TO THE CLASSIFICA-
TION OF THE AMPHIBOLES.
II.—ON SOME GLAUCOPHANE SCHISTS,
SLENITS ate

G. MurRGOocI.

CONTENTS.

PAGE

TANGO CUCELO Me SER. oh. SEE cs Bee ees se Ceee sotee ace ag est Sa eae ese eit eee ae 309

I Ammphibolesvot the Glaucophane Schists ics :.2e.: cesses: cee cae cece see seen nase een eeeeee 361

Glaucophane—Crossite—Rhodusite .........2...2.-.2--2.---2020---eeeeeteee- See 362

Gastaldite——Gilaucop hanes s22.gcs Merce soeeeanee ee ease sce ee ee ence es oyster 362

(OR OSSIGC| 22520 <s.2s: Saececazosites cue sbccteseeausesbavsstueaeucausssese Saves actestsceaxtecetesiiiessokts- 365

Rhodusite (Abriachanite) -................222..------ SE ee ees eee 368

@rocudolites (18))- cree. eee soe wc eects se eee ee See onan gee ees eeces a 369
Relation between Optical Properties and Chemical Composition

vinal, qwlaker (CHP HUK Coy oak E HAN es LEVIS, oe me ee 371

Karinthine Amphiboles; Common Hornblende.................2....-...22---2.-.----- 379

Vee estan orb Velen) fees bso) Ceeeeee nee epee peer ene eee ee eer 379

HN HeUTV CUE GT (Opie) eee cecen cee reeaetaces se eeateae Se ee eee 384

Actinolite; an Actinolite with Transverse Axial Plane.................... 386

dole Material se Stacie lt 2 te. F 25 acest eee vee eee pees steed eee eae 387

Gilaicophame) Schists yess ee ressses sees rere eae ee eee eee oa Pane ee eee a eae ac 387

SA MSMUN eS TNCs eye eg aoe a are tee elena 2 oe te 393

(CONCIISTOTS tyrants oo hs okt ee meno Re ee 2 ee BOD

INTRODUCTION.

Recent researches on the amphiboles have shown quite clearly
that in this important group of minerals, especially in the mono-
clinic series, there are still many questions to be solved. The
amphibole family is, far from having the same simplicity and
clearness in classification, the same facility in the identification
of minerals and names, or the same precision in the physical and

360 University of California Publications. [ GEOLOGY

chemical properties of the species, as the equally important fam-
ilies of the feldspars and pyroxenes.

This comes naturally from the complicated chemical consti-
tution, and from the difficulty of bringing into close and con-
tinuous relation the physical properties and the chemical compo-
sition of these minerals. Yet, when we try to introduce order
into this group, taking as our basis either the chemical composi-
tion or the optical or other physical properties (e.g., etch-figures,
ete.), we find ourselves confronted by very many species, sub-
species, and varieties, where often the different individuals stud-
ied are variable in their composition and properties, forming
intermediate terms not easy to classify.

Isolated mineralogical investigations of different members of
this family, whether well erystallized or not, occurring fre-
quently in small quantities, differing from each other in loeality,
in occurrence, and in genesis, will hardly give the possibility of
a natural classification. We should much more easily attain re-
sults by an investigation of these minerals when they occur in a
series of rocks from a petrologieal provinee. Following the
changes in the mineralogical and chemical composition of the
rocks, we can learn the variation which the minerals themselves
undergo, and perceive the direction of the variation in their
chemical composition and physical properties. Such a study must
include, besides a precise and detailed determination of the phys-
ical properties, also a series of exact chemical analyses of the
individuals studied.

During a visit to America I had the opportunity of studying
two important series of rocks with amphiboles: roeks with rie-
beckite (from Massachusetts, Dobrogea, ete.) ; and rocks with
elaucophane (from California). These two series comprise large
numbers of rocks with various amphiboles from hornblende to
riebeckite, or from actinolite to crocidolite. In these investiga-
tions defects which the classification and nomenclature of the
amphiboles present become evident, yet I was fortunate enough
to find some facts which throw heht on the whole question. It
has become clear that the determination of even the most common
amphibole must not be limited merely to the measurement of the
extinction angle and pleochroism.

Vor. 4] Murgoct.—Classification of the Amphiboles. 361

Although my investigations have not been conducted accord-
ing to the plan mentioned above, I wish to present in the fol-
lowing pages the results obtained in the glaucophane series. The
rich material which I used in these investigations has been put
at my disposal by Professors J. Perrin Smith (Stanford Univer-
sity), Andrew C. Lawson (University of California), and Charles
Palache (Harvard University), to whom I wish in this place to
express my heartiest thanks. Especially in frequent consulta-
tions with Professor J. P. Smith, who has accumulated the rich-
est and most interesting colleetion of glaucophane and lawsonite
rocks, much light was thrown on the subject. Further, some
ideas have been generously suggested to us by Dr. A. C. Lane,
who several years ago made, but did not publish, some observa-
tions in this field.

i

AMPHIBOLES OF THE GLAUCOPHANE SCHISTS.

In the glaucophane schists and some other rocks from Cali-
fornia which I had the opportunity of investigating may be
distinguished many amphiboles which show a color and pleochro-
ism in blue, violet, or green more or less pronounced. Two or
more of these amphiboles may occur at once in the same rock and
slide, and often one single lamella has zones or patches of two
or even three amphiboles quite different from one another. Of
course the separation of one type for a detailed chemical and
physical investigation is almost impossible. Shght variations in
the properties of the same amphibole are general and obvious
under the microscope; thus it is very difticult to determine the
chemical composition of one type, and if one has an analysis of
an amphibole separated from a given rock, one cannot always be
sure to what variety it would best correspond.

The nomenclature and classification which it is sought to
establish here are made on the basis of the best analyses available,
together with an exhaustive determination of the optic properties
(under the microscope), and with a careful study of the litera-
ture on the minerals. I have distinguished: (gastaldite) glauco-
phane, crossite, crocidolite, rhodusite, karinthine soretite (?), lan-
cite, actinolite, ete. Actinolite, karinthine, and glaucophane seem

362 University of California Publications. [ GEOLOGY

to form, as E. Weinschenk* has stated, a series from lime-magne-
sian to soda-aluminous amphiboles; the others seem to come in
some side ferruginous series; this is quite certain for gastaldite

—glaucophane—crossite—rhodusite—abriachanite.

Now it is generally admitted that blue amphiboles or amphib-
oles with blue pleochroism contain more or less alkali (soda) in
their constitution; this is always the case with the amphiboles
from glaucophane rocks.

Further, many petrologists have observed that some green
amphiboles become bluish at the periphery, and also undergo
some changes in their birefringence. Dr. A. C. Lane attributed
this phenomenon to the increase of the soda content, and has
given an empirical formula which connects the birefringence with
the soda content of the mineral. It seems to me that this for-
mula is not applicable in general, especially not in the glauco-
phane series. The chemical constituent with the most influence
on the physical properties seems to be Fe,O, (viz., Fe,Si,0,),
and that not only in the glaucophane series, but in general in the
amphibole family.

We know that the optic orientation, the optic constants, and
the pleochroism vary very much in the alkali amphibole group
from one member to another; but we can state that the pleochro-
ism always varies on c’ to blue, on b (axis of symmetry) to green,
on a to yellow, whatever the orientation of the ellipsoid of elas-
ticity may be.

Further, the size of the angle of the optic axes, the position of
the axial plane, and even the angle of extinction, up to a certain
point, are in relation with the amount of Fe,O,.

A. GLAUCOPHANE—CROSSITE—RHODUSITE.

Gastaldite—Glaucophane.—There is a very extensive litera-
ture about glaucophane, so that its identification is in general
not difficult. It is well known, however, what a variation glau-
cophane shows both in its optical properties (extinction angle,
pleochroism, birefringence, optic angle, etc), and in its chemical
constitution.

*E. Weinschenk. Die gesteinsbildende Mineralien 1901. Amphibol-
gruppe.

VoL. 4] Murgoci.—Classification of the Amphiboles. 36:

As regards the chemical composition, the ideas of G. Tscher-
mak are generally admitted, namely: isomorphic mixtures of
Na,A1,8i,0,., (Na,Fe,Si,0,.), and (MgFe)SiO,. A recaleula-
tion of all the analyses* of glaucophane and related minerals
(Table I) shows that Al and Na do not behave as if they were
in a single formula of a double metasilicate. In the gastaldite
of Striiver, in the glaucophane of Yoshida, ete., Al,O, enters
with the coefficient 21, Na,O with only 10. If Al and Na are in
one single formula, their coefficient must be equal, which in gen-
eral is the ease with the other glaucophane analyses. We find
again the independence of Na,SiO, from Al,Si,O, in the abriach-
anite, erocidolite in the riebeckite series, ete.

In the same way the consideration of FeO, MgO, CaO, forces
us to admit the direct and independent mixture of single for-
mule FeSiO,, MgSiO.,, CaSiO,, as well as H,SiO,, the importance
of which Berwerth and others emphasized years ago.

Further, Table I shows that Striiver has defended with good
reason the view that gastaldite (I) is different from glaucophane,
although the optic properties are almost the same. It is easy to
see that the constitution of

( Na.SiO,

(
| FeSiO, | FeSiO,
Gastaldite is { 2A1,S8i,0,; and Glaucophane is , 2(MgCa)SiO,
(MgCa) SiO, | A1,Si0O,
H,SiO, | +H.Si0,
Mg: Ca=5:2 Mg:Ca=6:1
or (R’2)» Rk", (Al,). (Si0,) 10 or (R’2)s (R”’) 33 Al,(Si0,) ;

where R’= Na+ H and R’”= Fe + Mg( + Ca)

Gastaldites or glaucophanes containing Al only are very rare;
they have faintly or moderately intense colors and absorption,
small angle of extinction (0°-6°), large (40°-60°) angle of the
optic axes, with negative acute bisectrix.

In general some Fe replaces the Al and, as we shall see far-
ther on, the properties vary much and the varieties have been
given names, as crossite, rhodusite, abriachanite, ete.+

*In table I, are represented the analyses by the molecular proportions
of the constituent oxides, obtained from the percentages divided by the
respective molecular weights of the oxides.

7+ The alkali amphibole studied by A. Johnsen (Neues Jahrbuch 1901,
IJ. p. 117) is related more nearly to gastaldite than to glaucophane, as
Johnsen emphasizes (see XXI Table I). It is a lime free gastaldite with
Al:Fe= 4:3, Fe:Mn= 2:1, and poor in alkali, a member intermediate
between riebeckite and gastaldite.

364 University of California Publications. [ GEOLOGY

In the Californian rocks I have met with many glaucophane-
like amphiboles very faintly colored, with small angle of extinc-
tion and variable axial angle, but as we have no analyses of them
I do not know if they may be identified with gastaldite. In fact,
there was no difference from the gastaldite of St. Mareel, ete.
(slides in collection of Dr. Palache), which I have investigated.

As type of the glaucophanes for the Californian rocks, I con-
sider the blue hornblende from North Berkeley (XI) described
and analyzed by W. C. Blasdale.* I had the opportunity of
seeing the original specimens, and of verifying and completing
the optical determination of Blasdale. Pleochroism brillant: ¢

=azure blue, b=violet to purple, a = yellowish to colorless;
os
on cleavage lamellae about —8° (in the most deeply colored even
more) ; birefringence as usual; 2 V not very large. The first
bisectrix (negative) is almost perpendicular to the orthopinacoid.
Blasdale has, however, analyzed another glaucophane (XII)

c>b>a. Angle of extinction on clinopinacoid, €:¢=-5

which is in some respects different from others. It is a very dark
blue-violet glauecophane, which oceurs in large prisms apparently
homogeneous and pure, but showing under the microscope many
patehes of green amphibole (actinolite or karinthine) just as in
crossite described by Palache. Sp. gr. 3.119-3.116. Pleochro-
ism: € = dark Prussian blue, ) = intense violet, a = yellowish;
c >b>a. Angle of extinction on clinopinacoid, -8°, on cleay-
age lamellae, —11° but variable with the intensity of the color;
in some faintly colored specimens only —9°, in others very in-
tensely colored up to -13°. It extinguishes in the same direction
as the green amphibole, which has an angle of extinction of —18°.
Birefringence: y—a== 0.018, somewhat smaller, y— 8, how-
ever, very small; 2 V very small, some lamellae being uniaxial
negative. The axial plane is parallel to the plane of symmetry,
the first (negative) bisectrix being almost perpendicular to (100).
The analysis indicates, as compared with the former, a de-
crease in Al,O,, and some increase in Fe,O,. The increase of
Na,O compensates for the decrease of MgO and CaO.
Glaucophanes with very small optic angles, or sometimes even

*W. C. Blasdale. Contribution to the Mineralogy of California. Bull.
Dept. Geol. Univ. Cal., 1901, 2, p. 327.

VoL. 4] Murgoct.—Classification of the Amphiboles. 365

uniaxial, occur frequently in the glaucophane schists of Califor-
nia, and some are faintly colored. Unfortunately there are no
analyses of these varieties to show us precisely in what the chem-
ical variation may consist. We ean discuss the question from
the chemical point of view better after the consideration of the
next minerals.

The constitution of the uniaxial elaucophane is that of a glau-

cophane with Al:Fe= 3:1, viz.:
( Na,SiO,
| FeSiO,
{ 2Mgsi0, Misy:'Ca == 621 Al:Fe=3:1
| (Fe’’A1).Si,0,
L H.SiO,

Crossite—Charles Palache gave the name of crossite to a
blue amphibole-like glaucophane, which oceurs in an albite schist
in the hills near Berkeley.* The chief property of crossite, which
on the original section I have determined independently of for-
mer observations, had been remarked already some ten years ago
by Dr. A. C. Lane, but has never been published. In the last
edition (IV) of Mikroskopische Physiographie I, Bd. II, Halfte,
H. Rosenbuseh gives almost the same properties determined on
specimens presented by Palache. My determinations were made
on the original sections just at the time of the publication of that
book and were communicated to Professor Rosenbusch in a let-
ter.+ Later I had the opportunity of finding this interesting
mineral in several rocks of the Coast Ranges of California, some-
times with characters even more distinct than in the original
sections. (See the material studied. )

The properties of crossite are so important for the general
question of the amphiboles that I shall give more details here.

The chief property of crossite is that the plane of the optic
axes is perpendicular to the plane of symmetry, the optic normal
making an angle of —16° with the vertical c’ axis. Accordingly
the pleochroism, which is identical in its colors and erystallo-
graphic orientation with that of glaucophane, is: @ = brillant
yellow, b = dark Prussian blue, ¢ = dark violet. Very strong
absorption, € = b> a, sometimes b> C, and almost opaque.

*C, Palache. On a new Soda Amphibole, ete. Bull. Dept. Geol. Univ.
Cal ep smliSils
+ Rosenbusch’s observation, loc. cit., p. 246-247; my communication, p. 395.

366 University of California Publications. [GEOLOGY

The color and absorption on one hand, the strong dispersion
on the other hand, make the determination of the optic orienta-
tion and of the color of birefringence very difficult. The use of
the gypsum plate is to be recommended, but at the same time
the determination should be controlled by the mica plate, and
especially by the character of the figure in convergent light.

The angle of extinction is difficult to determine in white light
because of the dispersion of the optic normal, besides the hori-
zontal dispersion of the bisectrix (bp:b,=6°). Palache gives

a:¢ = 133°; Rosenbusch gives b:¢ =-20° (max. -30°). I have
determined in different specimens € :¢ = -+71° max. 74°), or
b:¢=-19° (in Palache’s slides, -16°). It is certain, how-

Fig. 1.—Stereographic projection on (010) of the optical orientation of
common glaucophane Gl, uniaxial glaucophane wu, and cross-
ite Cr.

ever, as in glaucophane, that the maximum angle of extinction

measured in the slides does not correspond to the angle on (010),

but to a plane near the prism face, as Daly has demonstrated.

Measurements on cleavage lamellae gave 15°—20°, according to

the color and the size of the angle of the optic axes.*
0.008, y
parallel to the base; both pinacoid sections show a cross (by using
the oil immersion) which by rotation of the stage passes over into
a hyperbola with widely separated arms. The angle of the optic

a, ——

B= variable, very small. The axial plane is almost

*We often find in the literature glaucophanes with large angle of
extinction (16°-20° in glaucophane of New Caledonia and M. Vanoise,
21°—28° in glaucophane of Syra and Saasthal, and even more), but we do
not know either the chemical composition or the exact optic properties of
these.

VoL. 4] Murgoct.—Classification of the Amphiboles. 367

axes is variable, in Palache’s specimens very large, so that the de-
termination of the optie character is not easy, but for blue plainly
negative; Rosenbusch’s specimens show 2 V large, character neg-
ative; in some other rocks (see the material studied) I have
found ecrossite with quite small optic angle, character negative,
obvious in the orthopinacoidal sections. The sections perpendic-
ular to an optic axis may be recognized by their very intense
blue-violet color, of course with little or no pleochroism; on ac-
count of the dispersion there is no extinction.

The dispersion is so strong that it appears even in parallel
light; p>v; bp:c> by (almost 6°). The hyperbole which ap-
pear in convergent light in the sections near or perpendicular to
an optic axis are composed of several broad colored bands, red
and blue very distinct.

A glaucophane with transverse axial plane (like ecrossite) has
been deseribed by Michel Levy* in a schist of Versoix (Genéve).
The pleochroism is like crossite, in blue and violet, but the angle
of extinction only 3°; the first, negative bisectrix almost perpen-
dicular to (100). y—a—0.021; y—8 = 0.003; 2V = 35° —40°;
optic character negative.

Another amphibole with the properties of crossite, except the
strong absorption, has been described by F. Becket in a green
schist from Limmerbtichl] (Duxer Thal). I have seen this min-
eral, and can state that only the intensity of the colors is differ-
ent. Pleochroism: €—dark blue to violet, 6 = dark greenish
blue, €@= yellowish green. b—c; b:¢ =-18° ca.; Be:e<hy:
e; 2V =90°. y—a=0.0lea. The dispersion of the optic
axes p<v, All these properties are exactly the same as I have
determined for the crossite from the Coast Ranges of California.
Further, the origin and occurrence of Becke’s crossite is the
same as that from California.

The analysis of Palache’s crossite, made by W. S. Tangier
Smith, shows in comparison with Blasdale’s analyses and those
by Washington, ete., of the glaucophane from Syra, Zermatt, ete.,

* In Barrois’ paper, Mem. sur les Schistes met. de 1 ’ile de Groix. Ann.
Soe. Geol. du Nord, Lille, 1883, II., p. 50.

7 F. Becke. Uber cine merkwiirdige Hornblende. Tscherm. M. und
P. Mittheil, 21 p. 247, and Rosenbusch’s Mikroskopische Physiographie I.
II. A, p. 247.

368 University of California Publications. | GEOLOGY

only this difference (except water) that Al:Fe 3:4. The con-
stitution is that of a glaucophane:

- Na.SiO,

( FeSiO, Mg:Ca=6:1

( 2MeSi0, Al: Fe= 3:4

. (A1Fe).S8i,0,

as P. Groth* has stated; but because of the characteristic prop-
erties and chemical constitution, I propose to retain the name
crossite for such glaucophanes with transverse axial plane. I
add here that this ttle variation in the chemical composition
(Fe > Al) has a great influence on the cohesion, so that erossite
cives etch-figures quite different from those of glaucophane.

Dr. A. C. Lane has remarked (in a letter to Dr. Palache, No-
vember 27, 1895), and I can confirm the observation, that crossite
is not identical with Cross’s amphibole.; Cross has identified,
with good reason, the blue amphibole of Silver Cliff with La-
eroix’s crocidolite.t I was not fortunate enough to find schists
with crocidolite, such as have been deseribed by Lacroix, S. Fran-
chi,§ ©. Smith,|| ete. Professor Louderback has shown me, how-
ever, a quartzite with crocidolite (?) (from the Coast Ranges)
which is very similar to the description of Lacroix. I may add,
however, that among the ecrocidolite-like minerals there are sey-
eral kinds of amphiboles.

Rhodustte (Abriachanite).—Almost all mineralogists have
considered Foullon’s rhodusite** as being related to glaucophane.

Foullon himself describes it as an asbestos variety of glauco-
phane. According to the occurrence (in a ‘‘breecia’’ and in the
‘* Asbest-artiger’’ schists of eocenic flysch), form and few prop-
erties given, and especially according to the analyses, rhodusite
is a member of the glaucophane group of amphiboles related to
crossite and crocidolite, as Rosenbusch has emphasized in his new

*P. Groth. Tableau des mineraux d’aprés leurs composition chimique,
1904. Edition Pearce and Jourowsky.

y W. Cross. Note on some secondary minerals of the amphibole and
pyroxene groups. Amer. Jour. Sci., XX XIX. May, 1890.

} A. Lacroix. Sur la crocidolite. Bul. d. 1. Soc. de Mineralogie, Paris,
1890. XIII. 10. Mineralogie de la France, p. 691, 1893.

§S. Franchi. Contrib. allo Studio delle roccie a glaucofane. Extr.
del. Bollettino del R. Comitato geologico, 1902. No. 4.
: || C. Smith. Untersuchungen einiger Gesteine. Zeits, fiir Kryst. 1904,
8, p. 201.

** In Bukowski’s paper in Sitzungsberichte d. k. Akademie, Wien 1890,
p. 226. H. B. Foullon, Ibidem, 1891, 100 p. 169.

VoL. 4] Murgoci.—Classification of the Amphiboles. 369

book. One ean see (in Table I) that rhodusite is the Fe-end
member of the glaucophane series. Its constitution is that of a
elaucophane where Al is replaced by Fe:

( Na.SiO,

| Fe’SiO,

4 2MgsiO, (very little Ca.)

| FeSi,O,

| H.SiO,

It is a pity that, except pleochroism like that of glaucophane
and an uncertain angele of extinction (4°?), we possess no other
properties of this interesting end member of the glaucophane
series.

We find in the hterature (Hintze p. 1267, Dana p. 401) an-
other mineral, which in its occurrence, form, and chemical com-
position is quite similar to rhodusite, viz.: Heddle’s abriachanite,
a blue fibrous substance found in the clefts of the Old Red con-
glomerates, underlying schists, granite, ete., from Abriachan
(Seotland), ete. Dana and others have considered abriachanite
as related to ecrocidolite, but that is not the ease. Abriachanite,
like. rhodusite, is an iron amphibole very poor in lime, rich in
magnesia (like glaucophane), while ecrocidolite is an iron am-
phibole very poor in lime and also in magnesia (like riebeckite,
as Lacroix has stated).

One analysis of abriachanite (XV) poor in soda (Hintze p.
1268) seems to represent the Fe’’— glaucophane corresponding
to the gastaldite formula. But, as we have no other details about
the properties of abriachanite regarding its similarity with rho-
dusite, and as rhodusite is better known, I propose to identify
abriachanite with rhodusite, and to retain the name rhodusite for
the end member (rich in Fe) of the glaucophane series.

Crocidolite (?).—I had the opportunity of studying some
blue amphiboles like crocidolite, in some syenites which show ex-
actly the same mineralogical composition and phenomena as have
been deseribed by Chestner, W. Cross, A. C. Lane, and others, in
many such rocks. The occurrence, the form, and the rather ob-
scure properties make the determination of these minerals very
difficult and their identification with other minerals (crocidolite,
rhodusite, etc.) almost impossible. As the properties of crocido-
lite are insufficiently known (pleochroism and absorption like

370 University of California Publications. [GEOLOGY

riebeckite and crossite-rhodusite, @:¢c = 10°-21°, optie character
positive), an identification of the mineral without analysis is
valueless.

The constitution of ecrocidolite is:

N.Si0,

3(FeMg) SiO,
Fe.8i,05 Fe’: Mg = 4:1 minimum.

+ H.SiO,

v.e., the formula of a rhodusite where almost all Mg is replaced
by Fe’; except for water, it is the identical constitution of the
riebeckites of Colorado and of Cape Ann, Massachusetts.

The blue asbestos-like amphibole in the syenite of Spanish
Peak, Plumas County, California, is identical (optically) with
the blue amphibole from Rosita Hill described by Cross. Pleo-
chroism: &—= Prussian blue, 6= lighter blue, ¢ = greenish
blue. Absorption very strong: a>b>¢c; the colors are very
intense. Angle of extinction (in the opposite side of that of
katophorite) @:¢ = +21° (€:¢ =-69°). The axial plane seems
to be longitudinal; on account of the absorption and dispersion
(p<v) one cannot determine the optic character. y—P very
small, almost zero; B—a = 0.004 ea.

It is very important to note that some sections from this sye-
nite and some from Rosita Hill (a section in the collection of Dr.
Palache) show such orientation on (001) and (010) that we can
suppose the axial plane to be perpendicular to the plane of sym-
metry: a@:¢c,C—b. This fact indicates that crocidolite under
goes the same variation in its properties as glaucophane, and in

the same way.”

Fig. 2.—Crocidolite (Cross’ amphibole) with axid@ plane normal to the plane
of symmetry. a, basal section, b, clinopinacodal section.

*JIn Vienna I discussed the chief points of this paper with Professor
F. Becke, and Dr. C. Hlawatsch. The latter showed me an arfvedsonite-like
amphibole with transverse axial plane (a:¢;¢—b), which he was studying.
In the same rock there occur arfvedsonite and ossanite (n.s. Hlawatsch),
like the crocidolite from Rosita Hill and Spanish Peak, with transverse
axial plane.

VoL. 4] Murgoci.—Classification of the Amphiboles. 371

‘These amphiboles are optically related to crocidolite ; the ero-
cidolite is related, optically and chemieally, to arfvedsonite and
riebeckite on one side, to rhodusite, and to glaucophane on the
other side. .

Another similar blue fibrous amphibole in the quartz from
Oak Ridge, California, is very probably crossite; the optical
orientation (8:¢==-17°) and pleochroism are identieal with
crossite.

Fig. 3.—Stereographie projection on (010) of the optical orientation of
common crocidolite, Cd., with normal axial and osannite, Os.

Relation between optical properties and chemical composition
in the glaucophane series —Comparing the analyses of the am-
phiboles from the glaucophane series (Table I), we see that Na,O,
FeO, and MgO undergo little or no variation, while Al,O, and
Fe,O, show variation in opposite directions.

(a). The intensity of color and pleochroism (absorption) are
not due only to the amount of Na,O (or Na,SiO,), because the
elaucophanes of Zermatt, Syra, San Pablo, ete., are very differ-
ent in their absorption, and still have almost the same amount of
Na,O. Very probably the Na,SiO, determines the shade of the
color, but not the intensity.

A. Lacroix* has emphasized the fact that the glauecophanes
rich in iron have more intense colors; Broggery states too that
amphiboles rich in iron (but without Ti) are blue. The accom-
panying analyses verify these statements in respect to Fe,O,.
The amount of FeO, however, seems to have no influence on the

* A, Lacroix, Mineralogie de la France, p. 700.
7 W. C. Brogger, Eruptivgesteine des Kristiania Gebiet, I, 37.

[ GEOLOGY

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VoL. 4] Murgoci.—Classification of the Amphiboles. ayia.

eolor of absorption, all glaucamphiboles having almost equal
FeO. Grunerite (FesSiO,) and the amphiboles related to it are
very faintly colored, with almost imperceptible pleochroism, and
it is known that by heating glaucophane Oebbeke* has obtained
a variation of the pleochroism on € = reddish brown, on 6 and a
= yellowish green to colorless, explained as due to the oxidation
of FeO to Fe,O,. Inspection of the analyses shows clearly the
influence of Fe,O, on the absorption of these minerals; gastal-

dite and glaucophane very faintly colored, glaucophane uniaxial,

in general strongly colored, crossite and rhodusite very intensely
eolored and with strong absorption. I may further add that the
other series of blue amphiboles with extremely strong absorption,
osannite, arfvedsonite, riebeckite, crocidolite, ete., are the am-
phiboles richest in Fe,O,; then philipstadite and others (with
only 1 or 2 per cent. Na,O but rich in Fe,O,) show a strong ab-
sorption and pleochroism in blue.

(6). Laeroix has stated also that the angle of extinction is
smaller in the normal glaucophanes than in those passing over
into common hornblende or actinolite. Many of our slides which
show glaucophanes and karinthine or actinolite as forming one
single prism verify this suggestion.

Further, I have remarked in the glaucophane series that with
the increase of intensity of color, an increase in the value of the
angle of extinction occurs, €:¢ (glaucophane) or B:c¢ (erossite).
A comparison of the whole group of Al Fe” amphiboles has con-
vinced me that in general the size of the angle of extinction C:c
(or f:c) is related neither to the amount of AlsOs (as Wiik has
emphasized), nor to the amount of Fe,O,, but to the proportion
of their molecular coefficients of combination in the amphibole
constitution.; In this way we ean explain why the different
members of the glaucophanes, riebeckites, barkevikites, common
hornblendes (soretite, karinthine, ete.), and basaltic hornblendes
are minerals in general of constant formula, but are very differ-
ent in their optic orientation; e.g., in the glaucophane series:

* Oebbeke, Zeits, fiir Kryst, 1887, 12, 286.

+ Brégger was the first to state that the angle ¢:c increases with the
amount of iron and alkali. Blasdale says, loc. cit., in respect to glauco-
phane ‘‘there is perhaps a connection between the position of the acute
bisectrix and the relative amount of ferric and aluminum oxide.’’

374 University of California Publications. [GEOLOGY

Fe,0,:A1,0, c:c or b.e
Gastaldite and Glaucophane 0—1/4 0— 6° (rarely larger)
Gastaldite of Skikoku 2/5 —11°
Mn Gastaldite of Miask 3/4 (+ ?2)36°
Glaucophane uniaxial 1/2 —10° to —13°
Crossite 1/1—3/2 —16° to —20°
Rhodusite >10/2 2(4°)
In other series:
Crocidolite >10/1 S70
Riebeckite, Osannite >10/1 >75°
Amph. of Karbéle 2/1 —15°
Barkevikite <2/3 —14°
Barkevikite 2/3 —20°
Hudsonite <1/2 —= We
Hastingsite 2/3 —25°
Soretite Pays —17°
Basaltic hornblende <1/2 0 to —12°
Kiarsulite <1/2 —10°
Kataphorite (Sao Miguel) 3/2 —23°

Ete., ete.

So far as I know, only some arfvedsonites and common horn-
blendes (karinthine, pargasite, ete.) seem not to follow this rule,
but there is an explanation for this, as the corresponding series
is not well known. Very probably a large quantity of FeO to-
gether with Fe,O, affects the increase of the angle of extinction
in greater measure than Fe,O, only: e.g., in the ease of croeido-
lite, arfvedsonite, riebeckite, ete.

(c). An interesting, perhaps the most obvious, influence of
the amount of Fe,O, on the optic properties is the variation of
the birefringence, y — 8. Dr. A. C. Lane, as well as many other
petrologists, has remarked that the green amphiboles in some
alkali rocks become bluish at the periphery, and the birefringence
decreases. He explains this as an influence of the feldspars on
the amphiboles, and has given an empirical formula which con-
nects the amount of Na with the birefringence ring:

90
Na = — (0.012—b),
if

where Na= soda content of the amphibole, and b= the bire-
fringence of the orthopinacoid section which is to be taken posi-
tive or negative according as the vertical axis is £ or a (resp. B)

Table I shows us that this formula is not general, because the

VoL. 4] Murgoci.—Classification of the Ampluboles. 37:

elaucophane from Zermatt, ete., and the uniaxial glaucophane
from San Pablo, have almost equal Na,O, but are very different
in their y— 8. Nevertheless, the ideas of Lane served as a start-
ine point for the following discussion.

The statement of Tschermak (Min. Mith., 1871, 38, 40), that
with the increase of Fe in the aluminous amphiboles the optic
angle increases around ¢€ and decreases around @ (usually the
first biseetrix), is well known. If we consider the Fe” (better
Fe,8i,0,), this statement is quite true, not only in the glauco-
phane series but in general in the FeAl amphiboles with meta-
silicate formula. Of course, when 2 V becomes smaller around
a negative bisectrix, y — B also becomes smaller, and finally at-
tains the value zero when the amphibole becomes uniaxial. But
the rule is still more general; the variation of y and £8 can pro-
ceed in such a manner that y — 6B passing through zero then be-
comes negative, t.e., 8 takes the place of the former y, and vice
versa. In this ease we have an amphibole with transverse axial
plane, and have established a continuous variation from the com-
mon amphibole with parallel axial plane, through the uniaxial
amphibole to the amphibole with transverse axial plane.

| |
c Cc

I
NK

a. b. ch
Fig. 4.—Ellipsoid of elasticity, section parallel to c and b , of glauco-
phane, a, uniaxial glaucophane, b, and crossite, c.

We have seen this whole series with all possible intermediate
members in the glaucophane group, and it is easy to see that it
is a function of Fe,Si,0,. The more Fe,SiO, replaces Al,SiO,,
the more the axial angle and y — 8 decrease: for Fe”: Al —1:3
corresponds to the uniaxial glaucophane (y=), while for Fe:
Al= 6:5 we meet with a crossite with transverse axial plane and
2 V almost 90°. Perhaps rhodusite, which is the Fe” glauco-
phane, is a crossite of positive optic character, or even a uniaxial
positive glaucophane, with the optie axis perpendicular to the

376 University of California Publications. [ GEOLOGY

plane of symmetry. The whole phenomenon ean be clearly indi-
cated ina diagram: Ina system of codrdinates, let the ordinates
represent the indices of refraction, and the abscissae represent
the amount of Fe,O, causing the variation of the former. <Ac-
cordingly we have Fig. 5, which shows that we can have the fol-
lowing glaucamphiboles:

Fh?

Fe; 0 3
Al, 0;

Fig. 5.—Diagram showing the variation of y— 6 and y—a with the ratio
of Fe,O,: Al,O,; Gl=glaucophane; Cr—crossite; Rh? =

rhodusite.
up aee ue cs ig KOE 2y on : Formua*
259 ies plane :¢) acter
Gastaldite 21-15 0—6 | (010) 0— 6° 40°—60° = — 2G+M’; (6/4G+2/4R+M)
Glaucophane 14— 9 0— 3 | (010) 0o— 6° 30°—50° =— G+M; (3/4G+1/4R+M)
Glaucophane 8 Che Lees 10° 0° — 2/3G4+1/3R+M
uniaxial
Crossite 6 6 £(010) 152 50° —)s:1/2G+1/2R+M
Crossite 4 7 4(010) 20°—30° 90° — 1/3G+2/3R+M

Rhodusite 0— 2 12—10 4(010) (>40°) (50°—30°) (+) R+M,(1/5G+4/5R+M)
Abriachanite 0— 3 21—18 (2) (?) (2) (2) 2R+M

We shall see further on that just the same optic variation
takes place in the karinthine series and in the riebeckite (crocid-
olite) series. As regards karinthine, we shall discuss it later on,
but we may dwell on crocidolite and riebeckite a little in this
place.

I do not know the constitution of Cross’s erocidolite, and still
less that of the crocidolite with transversal axial plane, but I
*In these formulae G—= A1,Si,0,; R= Fe.Si,0,; M, (or M’); the sum

of the other metasilicates—=Na.SiO, + FeSiO, + 2 (or 1)MgSiO,
(+H.Si0,).

tt
t

fication of the Amphiboles.

Sst

iI

‘gocl.

Mw

Vou. 4]

SiO2
T. Arfvedsonite, Greenl. 80
II. Arfvedsonite, Greenl. 73
III. Arfvedsonite, Sardinia 82
IV. Riebeckite, Colorado 83
V. Riebeckite, Cape Ann 83
VI. Riebeckite, Jacobdeal 76!
VII. Riebeckite, Sokotra 83
VIII. Riebeckite, Jacobdeal 83
IX. Arfvedonite (?) Christinia 83
X. Osannite 81
XI. Hornblende, Sao Miguel 81
XII. Kataphorite, Sao Miguel 76
XIII. Barkevikite, (?) Brevig 77
XIV. MHornblende Hochenkrochen 75
1 Obtained by difference. °*+ZrO,.

TABLE OF ANALYSES.

TiOe AlsO3 Fe203

— 1 1
= 4 2
= 5 3

2 — 9
= i 11
= tle 2)
—- _- 18
= = 18
= 2 21
— a 10
— 6 aes
a 4 6

2 3 —
= 8) 5

The mineral incloses some zircon, haematite, and aegirite.

FeO
49
46
39
26

35
31

MnO

rca Peers ers cue ran|

CO ip

“a

Jol.
MgO

1

=|

CaO
5

NavO

11
13
ily
13

12

KeO

H:O
11

Analyser.
EF. Berwertl
Lorenzen.
Bertolio.
Koenig.
Gregory.
Mrazec.
Sawer.

Rordam.
Dittrich.
Reiss.

Osann.
Plantamour.
Fohr.

378 University of California Publications. | GEOLOGY

believe that they must be very rich in Fe,O,. As a rule, all
analyses of crocidolite show a large amount of Fe,O, (16 to 20
per cent.) ; unfortunately we lack optical determinations of these,
and no analysis has been made of Lacroix’s positive crocidolite
(axial plane parallel to (010) ). Fortunately the question in the
riebeckite series is quite clear. There are many riebeckites
known; some poor in Fe,O, but very rich in FeO, the end mem-
ber being arfvedsonite; some others very rich in Fe,O, but poor
in FeO, including in the latter osannite, the new amphibole of
Hlawatsch. (See the analyses in Table IT.)

The variation within wide limits of the optic constants of
those arfvedsonites which have been studied, as well as of the
riebeckites, is well known; nevertheless we see a great difference
in their chemical constitution. We can, however, in general state
that the analyses of some arfvedsonites (of San Piedro IIT, Sao
Miguel XI, Hochenkréchen XIV), and of some riebeckites (Colo-
rado, Cape Ann) give a formula of the type of glaucophane
(crossite or rhodusite) where Mg is replaced almost entirely by
Fe (and Mn) and Ca by Na,.

In the hope of bringing some order into this interesting group
of amphiboles, I propose the following classification :

ays Optie
Fe2Q03 a:c Axial 2V_ char- Formula
plane mane
Arfvedsonite very —70°—80° |\(010) very + From 5FeSiO3, NazSiO3, (H2S8i03) to
poor large 4-5 FeSiO3 1-2 NagSiOg + FeA1Si309
Riebeckite rich ca—85° |\(010) small — From 3FeSiOs, 2Na2SiO3, Fe2Si30y to
(Colorado) 2FeSiO3s, NagSiOs, 2Fe2Sis09 +
HesiO03
Osannite* rich ca—80 (010) very —
large

(d). Both the literature and my own observations show that
the dispersion of the optic axes and bisectrices stands in close
relation to the intensity of the blue color and to the intensity of
the absorption. As the latter are a function of Fe,Si,O,, as has
been stated above, the dispersion must also be a function of Fe,
Si,O,. I believe that the above is sufficient to demonstrate the
influence of Fe,Si,O, on the optic properties in general in the
AlFe amphiboles of metasilicate type.

*T owe the information about the optical properties and the chemical
composition of osannite to the courtesy of Dr. C. Hlawatch.

Vou. 4] Murgoci.—Classification of the Amphiboles. 319

KARINTHINE AMPHIBOLES ; COMMON HORNBLENDES.

Karinthine, pargasite—Karinthine is the name given by Wer-
ner to the dark hornblende from the eclogites of Sanalpe in
Karnten or-Carinthia (Hintze, p. 1201). Many mineralogists
(Tschermak, Naumann, Lacroix, Dana, Rosenbusch, and others
have ineluded this material among the common hornblendes. E.
Weinschenk, in Gesteinsbildende Mineralien, has brought it to
notice as a member intermediate between the common green horn-
blende and blue glaucophane or gastaldite. I use the name in
the same sense for bluish green or blue-black amphiboles which
under the microscope show a bluish green color parallel to the
length of the prism. I believe that Barrois was the first to iden-
tify this amphibole from the glaucophane schists with karinthine.
The Californian bluish green karinthine is identical with the
Alpine karinthine (Val d’Aosta, Zermatt, and elsewhere) which
I was able to examine (slides in the possession of Dr. C. Palache),
and with those from Val Canaria, Val Pioia, Mt. Taunus, ete.
(Rosenbuseh). It is certain that this kind of hornblende has
sometimes been described as glaucophane, and perhaps the deter-
minations of glaucophane with ¢ = ultramarine or bluish brown,
6b = bluish green or lavender blue, and with a large angle of
extinction, refer to karinthine, which occurs in almost all glau-
cophane schists. Lacroix* has distinguished betwen these aim-
phiboles and glaucophane; they are namely ‘‘glaucophane pas-
sant a la hornblende,’’ or members ‘‘intermediaires entre la glau-

2:

cophane normale et les amphiboles dépourvues d’alealis.’’ Ros-
enbusch,+ who states that between glaucophane, or rather gastal-
dite, and common hornblende or actinolite there is a series of
intermediate forms, suggests that Weidmann’s hudsonite may be
such an intermediate form (see Table IIIT). I may add that the
chemical composition of hudsonite hardly differs from that of
hastingsite and of barkevikite, especially of Montana, Beverley,
ete., which minerals together with noralite seem to be both chemi-
cally and optically members intermediate between common horn-
blendite (soretite) and arfvedsonite.t (See Tables II and ITI.)

* A, Lacroix, Mineralogie de la France, 1903.

+ H. Rosenbusch, Microscopische Physiographie, I. 2, 1905, p. 240.

{The glaucophanes (or glaucophane-like amphiboles) described by
Szadecky, Washington, etc., as occurring in many igneous rocks enter per-
haps into the same category of amphiboles.

380 University of California Publications. | GEOLOGY

From the chemical point of view we find karinthine (and par-
gasite) as a form intermediate between gastaldite on the one
hand, and common hornblende (edenite or soretite) on the other
hand. (Table III.) Karinthine and pargasite are more or less
similar in their metallic constituents, but pargasite contains an
appreciable quantity of fluorine, which replaces silica (in an
equal coefficient, 10). This chemical difference, together with
the positive optie character of the amphiboles of Pargas, justifies
us in distinguishing between pargasite and karinthine. Besides,
pargasite is quite different from karinthine both in its genesis
and in its occurrence, which is another argument for the identifi-
cation of the bluish amphibole from the glaucophane schists with
karinthine. On the Californian karinthine (?) I have made the
following determinations: Pleochroism: € = greenish blue to
bluish green, b = olive green, €@= pale yellow to greenish yel-
low. Absorption ¢<b >a. Angle of extinction variable, C:c
= 17-22, in obtuse angle 8. The angle measured on cleavage
lamellae is hardly different from the maximum angle measured
in slides and on (010). The axial plane is parallel to (010). 2 E
B=ca. 0.022. Small

very large, optic character negative.
dispersion, p < v.

In some schists from California (and also in some from the
Alps) I have found a dark green or black hornblende with:

c — greenish blue to light ultramarine,
Pleochroism : 6 olive green to dirty green,

a —honey-yellow to greenish yellow.

Angele of extinction in general larger than in the former karin-

thine, €:¢ = 20°-28? Other properties almost the same. In
one section only (II, 6). I found also a positive hornblende as-

sociated with glaucophane: ¢ = Db = greenish, €a= colorless, €:¢
—=-48°; 2 V very small, axial plane (010). Unfortunately we
possess no analysis of the Californian karinthine to see whether
the conclusions stated for glaucamphiboles hold in the karinthine
series. I may remark, however, that some Al (and Fe”’) in the
existing analyses belongs to a syntagmatite formula (orthosil-
cate), as in the syntagmatite of Jan Mayen, philipstadite, sore-
— free; philipstadite, hud-

my

tite, ete. Karinthine is almost Fe

VoL. 4] Murgoci.—Classification of the Amphiboles. 381
sonite, and other such amphiboles contain some Fe’” which re-
places Al. Perhaps the darker varieties correspond, as in the
elaucamphiboles, to those richer in Fe”. TI have found karin-
thine-like amphiboles in many rocks, generally alkali rocks. other
than schists, an occurrence which is also put on record in the
literature of the subject. As I possess no analyses, the identifi-
eation with karinthine or soretite is doubtful.

In fact, if we consider the analyses of pargasite, karinthine,
soretite, philipstadite, hudsonite, hastingsite, noralite, ete., we
notice that while alkah, CaO, and the sum of Al,O, and Fe,0O,
remain almost constant, FeO and MgO vary in opposite direec-
tions; karinthine has 7 FeO : 48 MgO, noralite 40 FeO : 5 MeO,
and the others have intermediate proportions. As far as the
hterature is known to me, I do not know of a continuous varia-
tion in optical properties which could be explained by this vari-
ation of chemical composition, and I may state again that the
amount of iron as FeO (not Fe.O,) has no influence upon the
physical properties of the amphiboles. This does not hold for
FesO,. The sum of the coefficients of Al,O, and Fe,O, in the
above named series is almost constant, = 14 (the extremes being
12 and 18, karinthine and noralite being almost free from Fe”,
while the analyses of the other members give more or less Fe” in
the proportion of 24 to 4%). I have tried to prove above that the
size of the angle of extinction in this series also is a function of
this proportion.

Further, in the ease of karinthine we have seen, and in the
ease of barkevikite, plilpstadite,* hudsonite, hastingsite, ete.,
the literature supports the suggestion, that the angle of extine-
tion is proportional to the intensity of color and absorption; the
phenomenon is quite clear if these amphiboles show a zonary
structure, as frequently happens.

Unfortunately we have not always good and complete deter-
minations of the optical properties corresponding to the analyzed
individuals, and accordingly we cannot, in general, verify the
dependence of the angle of extinction and the intensity of ab-
sorption on the proportion Fe,O,: Al,O,, but the few precise

*R. Daly, On a New Variety of Hornblende, Proc. American Academy
of Arts and Science, XXXIV. 16, 1899.

382 University of California Publications. [GroLocy

data (philipstadite, hudsonite, hastingsite, barkevikite, etc.)
which we have seem to show that the rule is quite general.

If this suggestion holds, then the making of new species in a
type because the pleochroism and angle of extinction differ more
or less, is worse than unnecessary, for we have seen clearly in the
glaucamphiboles that the replacing of Al,O, by a small quantity
of Fe,O, brings about a noticeable variation in these two prop-
erties and also in the etch-figures. There would be an unlimited
number of species in any series.

In order to make the nomenclature more simple and natural,
I should like to propose the following classification :

; Plane Optie
AloO3 Fe203 C:¢c of 2V— char- Formula*!
axes acter
Pargasite 14—11 0—3 ae (010) 50°—60°° + S$+0to1G+4 to 3K (+Fe)
Karinthine 14-12 0—2 17° to —28° (010) verylarge — S+0 to 1G+4 to 3K
Soretite™ 10 6 —17° to (—28°) (010) 80°—90° — S+1 to 2G+3 to 2K
3arkevikite*? 16—10 0—4 12° to (—25°) (010) t+large — 8+3G+K
Noralite*# 12 2 ? 2 — $+3 to4G+1 to 0K

*IWhere: S=Syntagmatite molecule, = (Al1Fe,) (CaNa,); Si,0,, G=
grunerite mol., = FeSiO,; K—=kupferite mol., = MgSiO,.

“Under soretite are to be included the hornblendes corresponding to the
analyses XI, XII, XIII, XCI, CXXITI, CXXTV, CXCVITI, CCXL, ete., in
Hintze’s Manual; further, philipstadite (also CX XVI, CXLVIII, CXLVI,
ete.) and camsigradite which is a Mn-—containing philipstadite. See for
details, Hintze, Handbuch der Mineralogie, II.

“Under barkevikite could be included the hornblendes corresponding to
the analyses CCL, CCLII (see Table II, No. XI and XII), ete., in Hintze’s
book. Also hudsonite and hastingsite, (Tab. III), although they have very
pronounced pleochroism in blue; I may remark that the brown barkevikites
are not only titaniferous but are also very poor in Fe,O,.

“*Under noralite (Dana) must be included also the hornblendes corre-
sponding to CCXLVI, CCLII, ete., in Hintze’s book. See V and III in

Mabe: Eh)

Perhaps to karinthine, soretite, or barkevikite corresponds a
series from aluminous to ferruginous amphiboles parallel to that
of glaucophane rhodusite, these known members being the most
aluminous.* As we ean see in the accompany table (for details
see Hintze’s manual, Rosenbusch’s, ete.), analyses of karinthine
amphiboles rich in Fe”’ are quite unknown. Very probably it is
to this unknown catgeory of karinthines that the green or bluish

* T may remark that in the riebeckite series the members rich in Fe’” are

almost the only ones known; that of Jacobdeal analysed by L. Mrazek
(Table IT., No. VI) has 7% A1,0, (+2ZrO,, ete.)

3

¢
t

38

f the Amphiboles.

von O

Classificat

rgoct.

Mu

VoL. 4]

I.
18g

IIL.
IV.

V.

VI.
VII.
VIII.
ip.@
ae
Sal.
Xe.
XLV.
eve
XVI.
XVIL.
XV LE:
Da D.¢

Karinthine, San Alpe
-argasite, Pargas
Hornblende, Teneriffa
Noralite, Nora
Hornblende, Kikertars
Barkevikite, Greenl.
Barkevikite, Greenl.
Barkevikite, Montana
Hudsonite

Hornblende, Beverley
Hastingsite
Bergamanskite
Philipstadite
Philipstadite
Camsigradite

Soretite (mean)
Hornblende, Jan Mayen
Kaersutite

Basaltic Hornblende (mean)

SiO»
82
70

TiO»
({- TEI)
(+10F1)

ba |

TABLE OF ANALYSES. III.
AleO3 = FeoO3; FeO MnO MgO CaO NavO KkeO HO
12 1 if, —_— 43 19 4 1 6
11-16 3-0 14-2 33-49 27-21 5 3-4

9 —- 4] — 12 17 = = =
12 ~- 40 — 5 20 — — 4

2 3 40 a a 22 1 2 i

6 4 30 2° 9 18 5 3 1
11 4 27 1 3 19 9 2 =
16 2 30 —_— 6 19 5 2 =
12 5 33 1 iz 19 5 2 =

9 6 34 2 — 12 8 5 17
al 8 30 1 3 18 5 2 3
15 9 32 — 2 9 7 — 2
12 3 Alyy i 30 24 1 3 =

7 5 24 —_— 2 22 1 — 4
13 — 18 9 20 16 5 1 =
10 6 14 — 30 22 4 1 3
14 8 8 —_ 2 20 4 a 2
14 6 5 _ 35 22 4 2 —_
15 7 5 —_— 35 20 + 2 —

Analysers
Rammelsberg.

St. Cl. Deville.
Klaproth.
Janovsky.
Rammelsberg.
Flink.

Lind.g Melv.
Weidmann.
Wright.

Adams &§& Harin.
Lucehetti.
Rammelsberg.
Daly.

Miiller.

Dupare § Pearce
Scharizer.
Lorenzen.

384 University of California Publications. [ GEOLOGY

green amphiboles, uniaxial or with transverse axial plane, be-
long; these amphiboles are described in the literature, and I was
fortunate enough to find some in the rocks studied.

If the relation between Fe,O, and optic properties exists also
jn the karinthine group (as I have tried to prove above) as in
the glaueamphiboles, then the following amphiboles with trans-
verse axial plane must be very rich in Fe,O,.

Laneite (n. v.).—As far as I know, Dr. A. C. Lane was the
first to make known (in 1895, in a letter to Dr. C. Palache) an
amphibole with transverse axial plane in a theralite from Michi-
gan; at the same time he suggested that there might be an am-
phibole which was uniaxial, or even for a definite composition
isotropic; he connected this phenomenon with the amount of Na.
Some hornblendes with very weak birefringence (nearly iso-
tropic) have been deseribed by Milch,* and hastingsite with
AlsOs: FesO3 = ile tele C:¢= 25°-380°; 2K = 30°-45°,, optic
character negative, @—= yellowish green; b=—f —deep blue-
ereen, by F. D. Adams and J. Harrington.; Such blue-green

hornblendes with very small optical angle have been often men-
tioned as occurring in the alkali rocks. Dr. C. Hlawatscht has
described a uniaxial amphibole as occurring in the gabbro-diorite
from Jablanica (Bosnia) @—deep yellowish brown, b =¢ =
deep blue-green; C:¢ =18°, 2 V =40°-0° (in the blue horn-
blende, in the brown one very large). He considers it as inter-
mediate between the common hornblende (with the axial plane
parallel to 010) and the hornblende with transverse axial plane
which he himself has found in the eleolite syenite porphyry from
Viezzena Thal (Predazzo): &=light yellow, b= dark blue-

green, C =dark brown-green, D:¢ = 25°; 2 V = 45°; optic char-
acter negative.

It is a pity that these hornblendes, as well as the following,
have not been analyzed; very probably they belong to the sore-
tite or barkevikite type, and are very rich in Fe,O,. Optically,

* Milch, Die Schiefer des Taunus, Zeitschr. d. D. Geol. Gesellsch., XLI,
pp. 394 and 423.

7 Fr. D. Adams and B. J. Harrington, Amer. Jour. Sci., I. 1896, p. 210.

Also in Rosenbusch.

+ C, Hlawatsch, Tscherm. Mittheil., 1903, p. 499, 4. Ibidem, XX, p. 43.

VoL. 4] Murgocit.—Classification of the Amphiboles. 385

except for the position of the axial plane, they are similar to the
hornblende of Wright* found at Beverley.

In the course of an investigation of riebeckite rocks and their
inclusions (from Quiney, Massachusetts, Jacobdeal, Dabrogea,
ete.) I was fortunate enough to find this kind of amphibole,
which in my notes I have ealled Lane’s amphibole. It is a dark
colored amphibole (like barkevikite), with a very strong pleo-
chroism: a@ = brownish yellow, 6 = green or brownish green, C
=h)luish ereen or greenish blue; C>b>a. Angle of extine-
tion C:¢ = 13° in the darker colored, up to. 20° and even 26°
(in this ease b:¢). The birefringence y—e is large enough to
be noticed, but y

B is very small, almost zero. 2 V of course
very small or zero; very strong dispersion; p < v; optic character
negative. In the darker colored lamellae with an excessive dis-
persion (bp:c<by:¢), we meet with a transverse axial plane, 2 V
very small around the same negative bisectrix.

Besides the inclusions of riebeckite granite, I have observed
this mineral in a section (No. 304, the property of Dr. C. Pa-
lache) of glaueophane schist from Riffel Alp (Zermatt). In this
section we have in some lamellae the blue-green amphibole with
the axial plane parallel to (010) ; in others it is transverse to the
plane of symmetry; angle of extinction ¢ (or Bb) : ¢e=18°-20°;
optic character negative.+ All these amphiboles are optically
similar; there is also another which differs only in the angle of
extinction.

In Rosenbusch’s new manual we find a communication by W.
Freudenberg about an amphibole from the shonkinite of Katzen-
bueckel: blaek (transparent brown or greenish), ‘‘very rich in
iron.’’ Pleochroism: = straw color, b (or €) =deep red-
brown, ¢€ (or b) = green to yellow-green. Angle of extinction:
¢ (or b) : ¢ variable up to 65° (2); be:c<by:c; 2 V very small
around a negative bisectrix. Axial plane in the central lamellae
parallel to (010), in the periphal zones perpendicular to (010).

These observations all show that crossite-like amphiboles oc-

* FP. E. Wright, Alkali syenit von Beverley, Tscherm. Mittheil, XX p.
310. See Table II. No. X.

y This amphibole must occur very frequently; for example, I believe that
I recognized it in a slide of riebeckite granite from Socotra, although I

studied the slide, the property of Professor A. Pelikan, No. 41, for a few
minutes only.

386 University of California Publications. [GEOLOGY

cur in the group of common hornblende, and are very probably
Fe’”’—amphiboles corresponding to the karinthine, barkevikite,
or soretite formula. Until more detailed knowledge about this
kind of amphibole is published, I propose to retain for such the
neme laneite, in honor of Dr. A. C. Lane, who has introduced
new ideas and made new observations in this group of minerals.

Actinolite and an Actinolite with Transverse Axial Plane.—
As a type of the actinolite from the rocks with glaucophane,
we may take the actinolite of North Berkeley and San Pablo
studied and analyzed by Blasdale (loc. cit.). It is very similar
in its physical properties to the actinolite described by C. Pa-
lache as occurring in erossite schists, ete. Color, bluish green;
pleochroism: € = bluish green, = yellowish green, a= yel-
lowish to colorless; absorption faint, ¢ >b >a. Angle of ex-

tinction €:¢ =15°; birefringence as usual; 2 E very large; the
section (100) shows a negative bisectrix and one axis.

In one glaucophane schist (VIII 10) I found an interesting
mineral which seems to be an actinolite with transverse axial
plane. The relief is like zoisite. Pleochroism, ¢ = colorless, b

= green, more or less dark, a = yellowish to colorless; angle of
extinction, B:¢ =—-7° (measured on hemitropie lamellae which
extinguish symmetrically). In the sections with parallel extine-
tion the axial plane is transverse, with 2 E small around a posi-
tive bisectrix. Some lamellae show patches of glaucophane.

From the occurrence and optical properties of this mineral,
it can be no other than an amphibole, viz., an actinolite. I have
met with it only in one rock (3 slides), and in so small a quan-
tity that it was not possible to isolate it for further investigation.

I may here again remark that the position of the axial plane
is near to the vertical, as in crocidolite and osannite, and not near
to the horizontal, as in crossite and laneite.

VoL. 4] Murgoci.—Classification of the Amphiboles. 387

1B,
MATERIALS STUDIED.

GLAUCOPHANE SCHISTS.

On the Californian glauecophane schists there is an extensive
literature, but in California, as in other countries, the problems
are far from being solved. I add here some petrographic notes
on some of these rocks merely as suggestions for future work, and
especially as proofs in support of the theories advanced in the
preceding section of this paper.

The numbers in these notes refer to the collection of slides of
Professor J. P. Smith.

Eclogite—Arroyo Hondo, Calaveras Valley. I. (4, 5.) Gar-
net in large erystals with inclusions of titanite, rutile, apatite,
and karinthine, with patches of glaucophane. Ilmenite with
edges of magnetite; hematite, golden yellow rutile sometimes in-
eluded in titanite, epidote; lawsonite. Karinthine, with inelu-
sions of zircon with halos of titanite rutile, ete., shows: ¢—=
blue-green, b—dark olive-green, &= yellowish to colorless.
Patches and edges of blue-violet glaucophane, max. ext. == —24°.
2 V large; the basal sections show an optic axis. Negative.

In another slide with much titanite, the karinthine with edges
and patches of glaucophane gives a max. ext. —27° with stronger
absorption (the colors much darker).

Another slide shows a karinthine: £= blue green, b = dirty
olive-green, &@ = yellowish green; ext. —-28°; 2 V very large;*
y—a large; negative; axial plane= (010); a basal section
shows an optie axis at the edges of the field of the microscope.
Glaucophane shows: €—azure blue to ultramarine blue, b =
violet, & = bluish to colorless; 2 V large; negative; intergrown
with karinthine.

Greenstone.—Calaveras Valley. I. 8,8 (No. 10). Titanite,
rutile, ilmenite, hematite, epidote, lawsonite (?), karinthine. chlo-
rite, glaucophane intergrown with karinthine. Karinthine shows:
C= bluish green, f = olive green, a = yellow to colorless; ab-
sorption sheht; ext. —-20° ; negative; basal sections show a second

* Very large is over 60°; large is 60°—40°; small is less than 40°.

388 University of California Publications. [ GEOLOGY

bisectrix and an optic axis. Glaucophane variable in pleochroism
and absorption from pale colors to very dark ones; 2 V also va-
riable from large to zero; negative.

Greenstone (eclogite).—Calaveras Valley. I. 7. Well de-
veloped erystals of titanite; rutile with halos of leucoxene; karin-
thine, clinozoizite (colorless epidote) in large crystals, lawsonite,
lotrite (?), quartz, chlorite with biotite and muscovite. Glauco-
phane occurs in lamellae with variable pleochroism and absorp-
tion, with remains of karinthine faintly colored like the glauco-
phane in general. As veins, or mixed with the other minerals in
the rock, we find a yellowish mineral here and there with some
greenish pigment; it oceurs as lamellae and fibers with cleavage
sometimes very well pronounced, often disposed in fans, forming
sometimes a radial spherulite. The refractive index is 1.67; the
occurrence and properties suggest lotrite. The lamellae with
strong birefringence (y—a) extinguish symmetrically; some
other lamellae give wavy extinction, and those with 8 —a very
small show an angle of extinetion of 15°. Relief and birefrin-
gence a little higher than in glaucophane. Pleochroism: a= tC

= colorless; b= greenish. The length of the lamellae is parallel
to B; axial plane perpendicular to the cleavage; 2 V large down
to very small around a positive bisectrix, even uniaxial. Accord-
ing to these properties this mineral is very similar to lotrite, from
which it differs only shghtly in the angle of extinction.* The
lotrite (?) seems to be in genetic relation with the glaucophane
and karinthine; some lamellae of glaucophane and karinthine
pass into a mass of lotrite lamellae. The glaucophane, however,
at the contact with the vein of lotrite (?) shows clearly a trans-
formation into crossite. (Fig. 6.) It becomes very intensely
colored (blue and violet), almost uniaxial, and the edges and
lamellae which project into the interior of the vein have a much
stronger pleochroism and absorption, and the optic orientation
of crossite: £ = dark violet; f= Prussian blue to indigo; a=
eray-violet ; ext. -19° ; birefringence very small; 2 V very large;
dispersion very great. Karinthine shows an extinction of 19°,
* For lotrite see: Granat-Vesuvianfels von Paringre by the author in

Bulet. Soc. Sciinte., Bucharest 1901. Refer. Groth’s Zeitschrift; Neues
Jahrbuch, ete., and Rosenbusch.

VoL. 4] Murgoci.—Classification of the Amphiboles. 389

elaucophane less (6°-10°), and erossite also 19° in the same
direction as glaucophane and karinthine.

Fig. 6—Glaucophane, g, with patches of karinthine, k, shows edges of cross-
ite at the contact of a lotrite?, 1, with actinolite, a, ete. «30.

The transformation of glaucophane into crossite seems to be
posterior to the genesis of glaucophane and karinthine, probably
at the same time or even posterior to the filling up of the vein
with lotrite (?), actinolite, and iron mica. It seems that at the
time of the formation of the vein the glaucophane had suffered
an unpregnation with a foreign substance, or a transformation
of FeO into Fe,O,, which had altered its chemical constitution
and optical properties. It is to be remarked that in some other
parts where glaucophane comes in contact with lotrite (?) one
cannot observe a pronounced variation in the color or in the op-
tical properties of the glaucophane.

Eclogite—Oak Ridge, Calaveras Valley. I. 10. Garnet with
rutile and ilmenite, the fissures filled with smaragdite (?), epi-
dote, titanite with rutile; rutile with leucoxene, karinthine.

Eclogite—Calaveras Valley. 1. Garnet with veins of chlo-
rite. Lawsonite, much titanite, omphacite.

Glaucophane-gneiss—Melitta, near Santa Rosa. II. 2, 3, 4.
Quartz, titanite, garnet with the fissures filled with tale (?);
much ehlorite and margarite. Orthoclase, smaragdite. Karin-
thine with glaucophane very faintly colored; some patches of
more intensely colored glaucophane show 2 V very small.

Another section of the same rock (II. 5) shows very large
erystals of titanite; garnet; rutile with leucoxene. Karinthine
shows: €= greenish blue, }= green, a= yellowish; ext. =
20°; forms erystals with glaucophane showing: ¢ = ultrama-

390 University of California Publications. [ GEOLOGY

rine blue, bh = pale violet, &=—gray yellow. (Fig. 7.) Some
lamellae of glaucophane with intense colors are almost uniaxial.
In another section (II. 6.) besides a glaucophane with ¢ =
azure blue, 8 = purple violet, a = yellow to colorless, y— 8B =
0.002, 2 V large, we find a greenish amphibole with patches of
glaucophane. Pleochroism ¢ = b = greenish, a@ = colorless.
Birefringence weak; 2 V very small; positive; axial plane (010) ;
ext. (€:¢)=-48°

Fig. 7.—Glaucophane erystal, g, with patches of karinthine, k, quartz, q,
x30.

Quartzite—San Luis Obispo. II. 12. Reerystallized quartz
in some zones undisturbed, in others crushed. Garnet, titanite,
spinel grown also in glaucophane. Glaucophane with variable
colors, some lamellae rising up to those of the crossite. Angle of
the optic axis varying inversely to the intensity of the color.

Gneiss—Belmont School, Belmont. JI. 17. Garnet, ilme-
nite with hematite, rutile with leucoxene, much musovite. Glau-
cophane in radical lamellae with very weak absorption; angle of
extinction very small; 2 V large; negative.

Quartzite—Oak Hill, San José. II. 20. Idioblastic quartz,
earnet inclosed in glaucophane; rutile and titanite in beautiful
crystals; muscovite (paragonite?), lawsonite. Glaucophane with
intense colors; 2 V very small; in some ultramarine lamellae al-
most uniaxial. Muscovite with rutile inclosed in glaucophane.

Mica schist—Calaveras Valley. II. 22. Brown garnet in-
closed in glaucophane; little muscovite. Glaucophane with in-
tense colors and strong absorption; € = ultramarine blue, 6 =
purple violet, @ = yellowish green; ext. angle very small; y —«
= 0.021; y —B=0.005 ca. 2 V very small, negative; axial
plane (010).

VoL. 4] Murgoct.—Classification of the Amphiboles. 391

Lawsonite gneiss. Three miles west of Redwood. II. 2, 7.

Ophitoblastie structure. Titanite, lawsonite, ilmenite, hema-
tite, rutile with leucoxene. Glaucophane in large erystals: € =
Prussian blue, 6 = purple violet, €& = gray; some lamellae are
quite uniaxial. In sect. III. 7 the glaucophane has paler colors;
2 V small. ,

Lawsonite gneiss. Helmann ranch. III. 3, 14.

Ophitoblastie structure. Glaucophane in some lamellae very
pale with 2 V very large; extinction angle very small. Titanite,
lawsonite in glaucophane, but also glaucophane in the lawsonite
erystals.

Epidote schist. Hooper Dairy, Schrader Tract, near Red-
wood. III. 11.

Epidote, lawsonite, pyrite, chlorite. Karinthine: € = green-
ish blue, b = dirty olive-green, a= yellowish to colorless. ¢=b
>a; ext. -14°; hemitropie lamellae; grown together with
glaucophane. Glaucophane: ¢ = ultramarine blue, 6 = purple
violet, &@= yellowish to colorless; ext. -15° (probably not on
(010)); y—a as usual. y—B=—0.006; 2 V large. In some
lamellae a colorless zone occurs between glaucophane and karin-
thine. Karinthine passes into chlorite.

VI. 38. Loe.? Ilmenite with leucoxene, chlorite, actinolite.
Hornblende (karinthine or soretite): € = dark brown green, 6
= brown-green, @—= straw yellow, with edges of bluish karin-
thine and here and there patches of glaucophane, especially on
the prolongation of a chlorite vein. Karinthine shows hemitropic
lamellae. Ext. -19°, y — @=0.009 ca.; axial plane (010); 2 V
large; negative.

Eclogite. Hilton guleh, Oak Ridge. VII. 5, 9, 6.

Epidote and zoisite, margarite, rutile, inclosed in amphibole
and free, titanite. Karinthine: ext. -23°; negative; 2 V large;
axial plane, parallel to (010) ; with edges and patches of glauco-
phane in pale colors.

Glaucophane schist. Belmont School, Belmont. VII. 19.

Margarite, much titanite (leucoxene) with centers of rutile,
lawsonite, chlorite in veins and fissures. Glaucophane in colors
of medium intensity; karinthine: £—bluish green, ete. Ext.
—23°.

392 University of Califorma Publications. [ GEOLOGY

Epidote schist. VII. 20.

Much epidote, margarite. Karinthine: ¢= blue, 6 = dirty
olive-green, @ = yellowish; ext. -19°; 2 V very large. Glauco-
phane in pale colors; € = azure blue, § = violet, a = yellowish
to colorless; ext —5°; 2 V small; negative.

Quartzite (gneiss). Belmont. VIII. 6, 7, 8, 9.

Brown garnet, magnetite, leucoxene, hematite, rutile, ilmenite,
muscovite, glaucophane in pale colors as sheaves and radial
spherulites.

Quartzite. Pine Flat, Sonoma County. VIII. 10, 11, 12.

Garnet, zoisite, leucoxene, ilmenite, hematite, muscovite (para-
gonite?) iron biotite. Glaucophane: ¢ = Prussian blue; ext.
—6°; negative, 2 V small; with patches and nucleus of karin-
thine: ext. —18°, ¢ = bluish green, ete.; axial plane parallel to
(010); 2 V large, negative. Polysynthetic lamellae. Here also
the actinolite with transverse axial plane described above.

Eclogite. Reed Station, Tiburon.

Karinthine (or soretite) as lamellae with end faces: ¢ —bluish
green, { = olive-green, A= yellow. Ext. (€:c) =-26° axial
plane, (010); 2 V large; negative. Some lamellae with patches
and edges of glaucophane. (Fig. 8.)

Fig. 8.—Karinthine crystal, k, with edges and zones of glaucophane. 30.

Quartzite (and mica schist). Tiburon, 14 miles southeast of
Reed Station.

Idioblastic quartz with many inclusions of liquids with bubbles.
Zircon, garnet in small erystals with optic anomalies, sometimes
inclosed in erossites; titanite. Muscovite, bent in the crushed
zones of the quartz. Brown iron biotite, often in radial lamellae,
with a slight pleochroism: ¢ = dark brown, @ = yellow brown;
negative, nearly uniaxial. Crossite: ¢ = violet, 6 = Prussian
blue, a = yellow; it occurs as needles and lamellae; some needles

Vou. 4] Murgoci.—Classification of the Amplhiboles. 393

a= 0002 2 V

recall those of tourmaline. Max. ext. —12°, y
small, axial plane transversal to cleavage.
Glaucophane and titanite. San Pablo (studied and analysed
by Blasdale, loc. cit.). No. 126. See my determinations on uni-
axial glaucophane in the first part of this paper.
Glaucophane schist. North Berkeley.

Glaucophane, ext. -54; on cleavage lamellae —7°; 2 V small;

negative; y—a and y — 8 as usual.

Glaucophane (boulder). San Pablo. No. 123. Analysed by
Blasdale. The colors of the pleochroism not intense; ext. on
cleavage lamellae, —10° (8°-10°), 2 V small.

Eclogite with glaucophane. Russian River. No. 2144.

Glaucophane quartzite. Wildeat Creek. North of Berkeley.

Garnet; titanite; glaucophane in pale colors, ext. —-4°-6° on
cleavage lamellae (one lamella gave —14°) ; the prisms have the
orthopinacoidal faces more developed than the clinopinacoidal
ones; 2 V very large.

Mica schist. North Berkeley.

“Pale glaucophane, ext. on cleavage lamellae, -8°; 2 V large.
Chlorite.

Quartzite. North of Berkeley.

Crossite quite identical with that of Palache. Very intensely
colored; absorption and dispersion very large; max. ext. —20°;
B—a > y—B8; axial plane transverse to the prism; ¢ = opaque
violet, f = Prussian blue; @ = yellowish green.

SYENITES, ETC.

Syenite. Spanish Peak, Plumas County, California.

Apatite as needles and bunches; rutile as formless grains, often
as pseudomorphoses of fragments of amphibole; leucoxene as
halo around some rutiles, or as patches; ferruginous patches;
chlorite and biotite with weak pleochroism, very small angle of
the optic axes; negative. Albite, katophorite. Secondary quartz
and erocidolite.

The katophorite is smoky yellow, without appreciable
pleochroism; ¢>6 >a. The color seems to be due to a
pigment which is not evenly distributed through the whole min-
eral; at all events, the periphery is lighter in color and clearer

394 University of California Publications. [GEOLOGY

than the center. Sometimes the pigment forms zones and patches
in the neighborhood of the clearer region, as if brought from
there through secondary influences. <A fibrous crocidolite occurs
around and in some eavities of the katophorite in close connection
with the light zones. Between erocidolite and katophorite there
are always definite lines of demarcation, although the crocidolite
zone begins with a greenish yellow substance. For katophorite :
f:c =-31° The longitudinal and transverse sections show
many hemitropic lamellae on the (100). The optic orientation
as usual f = b; axial plane parallel to (010). 2 V large, posi-
tive; no appreciable dispersion.

Fig. 9.—Katophorite, k, with halo of crocidolite, Cr. a= prismatic section;
b=basal section; ¢=polysynthetic lamellae parallel to
(100); d=pseudomorphs of rutile, r, after katophorite;
e=kataphorite with a circle of crocidolite; f and g=
same with halo or sheaf of crocidoliet. 30.

Some fragments are very dark colored, and we find some grains
of rutile surrounded by fibrous crocidolite; clearly they are
pseudomorphs of katophorite. The pseudomorph is more distinct
in some prisms which show a periphery of rutile and a center
of katophorite with some fibers of crocidolite. (Fig. 9.) Very
probably we meet here with the phenomenon of separation of the

VoL. 4| Murgoci.—Classification of the Amphiboles. 399

TiO, from the Ti-bearing amphiboles during the transformation
of the eruptive rock in a erystalline schist.*

The crocidolite was deseribed above (Part I). The relations
with katophorite are the same as in the rocks of Rosita Hills,
etc. The angle of extinction of crocidolite (@:c¢) is opposite to
that of katophorite.

Another specimen of the same syenite of Spanish Peak shows
no katorphorite nor crocidolite; the structure is hypidiomorphic.
The amphibole is here a soretite; it oecurs as long prisms with
(110) and (100) more developed than (010), with many inclu-
sions of albite (and magnetite) in a poikilitic structure. Pleo-
chroism: € = greenish blue, b = olive-green, a@ = honey-yellow.
c<b>a. Angle of extinction -24° (f€:¢); axial plane
parallel to (010). y—B@=0.012 ca. y—a—0.024 ca. 2 V
very large, negative. Apatite, chlorite, albite.

Quartz diorite. 4m. from Flume, Oak Ridge (5 m. east of
Calaveras Valley). IV. 1.

Ilmenite, hematite, titanite as large reddish yellow, crystals,
chlorite, biotite, acid ohgoclase with erystals of lawsonite, pegma-
titie and granophyrie quartz.

Katophorite: € =reddish brown (if altered: greenish or
bluish); b= olive brown, €a=light yellow. c2b>a. The
colors not uniform, with dirty patches and zones; ext. —26°;
hemitropic lamellae; axial plane parallel to (010) ; negative.

The katophorite passes over into fibrous ecrossite (?) at the
periphery, as the katophorite from Spanish Peak does into croci-
dolite.

Ferruginous biotite as pseudomorphs of hornblende with zones
of leucoxene or rutile, chlorite, and a bluish actinolite result also
as a secondary product of katophorite.

CONCLUSIONS.

From this short description of some of the most interesting
rocks of California we may conclude:

I. The glaucophane schists are in general crystalloblastic
rocks:+ lawsonite, epidote, zoisite, sometimes titanite, ilmenite,

* BF, Becke. tsber Mineralbestand und Structur der Krist. Schiefer. C. R.
IX. Congrés de Géologie, Vienne 1904.
+ The nomenclature proposed by IF’. Becke, loc. cit.

396 University of California Publications. [GEOLOGY

and even quartz are idioblastic elements. Sometimes the structure
of the glaucophane schists is ophitoblastie.

2. The statement of Rosenbusch*, ‘‘die Arfvedsonitamphi-
bole treten nur in Eruptivgesteinen, die Glaukamphibole dagegen
mie als urspriinghche Gemengtheile solcher, auf’’, is quite true.

3. The glaucamphiboles rich in Fe,O, (crossite, rhodusite, ete.)
are in general characteristic of the most acid schists (quartzites,
albite schists, gneiss, mica schist with muscovite, just as arfved-
sonite amphiboles rich in Fe,O, (riebeckite, ete.) are character-
istic of acid eruptive rocks} (pegmatites of granites, quartz
syenites, ete.

4. The origin of the glaucophane schists is very complicated,
and nothing but detailed investigations in the field will solve the
problem. The phenomenon of the metamorphism of various
rocks into glaucophane schists seems to be a kind of piezometa-
morphism (Weinschenk), as stated by S. Franchi.

5. Many kinds of amphiboles, glaucophane, karinthine, actino-
lite, ete., may be formed synchronously in the same rock and
erystal.

6. During the metamorphism of the eruptive rocks into glau-
cophane schists, many changes of the homogenous mixtures into
non-homogenous rocks take place. Besides the formation of rutile
and titanite from brown amphiboles, of lawsonite (epidote,
zoisite, lotrite (?), ete.) and albite from a basic plagioclase, the
occurence of various amphiboles (glaucophane, karinthine, aetino-
lite, ete.) can also be explained in this way from katophorite,
barkevikite, ete., or a similar complicated amphibole.

* L0G. Cve.

7G. Murgoci. The Genesis of Riebeckite and Riebeckite Rocks, Amer.
Journal of Sei., 1905.

Bukarest,

March, 1906.

UNIVERSITY OF CALIFORNIA PUBLICATIONS
BULLETIN OF THE DEPARTMENT OF

GEOLOGY

Vol. 4, No. 16, pp. 397-409 ANDREW C. LAWSON, Editor

THE GEOMORPHIC FEATURES OF THE
MIDDLE KERN.

BY

ANDREW ©. LAWSON.

Two years ago the writer published a paper* descriptive of
the genesis of the salient features of the Upper Kern Basin, in
which one of the most interesting points was the recognition of
a great rift which had determined the course of the Kern Canon.
The rift was traced as far as the southern end of the Trout
Meadows defile which was the limit of the writer’s field observa-
tions. With the object of extending those observations, the
writer last summer made a somewhat hurried trip through the
middle Kern Canon in the hope of discovering evidence of the
prolongation of the rift to the south of the junction of the Little
Kern with the Kern River. The most convenient approach to
this portion of the mountains is by the wagon road from Caliente
at the southern end of the Great Valley, by way of Walker
Basin, Havilah, and Hot Springs Valley to Kernville, and thence
up the Kern Canon by a saddle trail to the mouth of the Little
Kern. On this route of travel certain observations were made
which it is here desired to record. From Caliente, altitude 1286
feet, the road follows the terraced canon of Caliente Creek for
a few miles with a very gentle grade and then climbs up to the
left in the steep-grade canon of Oyler Creek to a summit, on the
north side of which there is a rapid descent to Walker Basin.
The summit is ten miles distant from Caliente and about 2800

*Geomorphogeny of the Upper Kern Basin. Bull. Dept. Geol. Univ.
Cal., Vol. 3, No. 15.
7 Aneroid.

398 University of California Publications. [GEOLOGY

feet above it, or 4086 feet above sea level. From this summit the
observer looking north obtains a fine view of the profile of Breck-
enbridge Mountain, and of Walker Basin, both very remarkable
geomorphic features. Breckenbridge Mountain is an asymmetric
ridge, the general trend of which is north and south, and which
lies immediately to the west of Walker Basin. The summit is
probably about 6500 feet above sea level. Its western slope is
exceedingly gentle and descends uniformly toward the great
valley in the latitude of Bakersfield. Its eastern side is a very
precipitous mountain front overlooking Walker Basin. The mere
inspection of the profile suggests immediately that the mountain
is a tilted orographie block and that its eastern front is a fault-
scarp. This suggestion is confirmed by its relation to Walker
Basin. The latter is a triangular shaped valley having an area
of ten or eleven square miles. One side of the triangle is the
base of the steep eastern face of Breckenbridge Mountain, and
the other two sides converge in a narrow canon at a point about
four miles to the east of the mountain base. The valley bottom
is wholly alluviated with a nearly flat slope to the west. It
stands at an altitude of about 3300 feet above sea level. It is
in entire geomorphic discordance with the erosional features of
the surrounding mountains. On all sides are narrow high-grade
canons and gorges. The outlet of the basin itself is a narrow
gorge, which hes between the south end of Breckenbridge Moun-
tain and the ridge over which the road passes from Caliente.
This geomorphic discordance with the erosional features of the
region can only be explained as the result of an acute deforma-
tion, such as would be produced by uplift of an orographic block
along a fault parallel to the east front of Breckenbridge Moun-
tain.

The route to Kernville follows the east side of this great
mountain searp from the southwest corner of Walker Basin to
Hot Springs Valley, a distance of fifteen miles with a bearing
a little east of north. From the northwest corner of Walker
Basin the road ascends about 1000 feet to cross a divide which
connects the lower portion of the Breckenbridge scarp with the
mountains to the east and separates Walker Basin from a much
narrower depression in which Havilah is situated. This is a

Breckenbridge Mountain and Walker Basin. <A fault-scarp overlooking an alluviated valley.

Vou. 4] Lawson.—Features of the Middle Kern. 399

longitudinal valley lying between the scarp and the mountains
to the east. In its lower part it has been alluviated, but the
alluvium is now dissected by the stream which drains the valley
to the Kern. This drainage is by a narrow gorge which les
between the scarp and a mountain spur from the east which
separates Havilah Valley from Hot Springs Valley. The exten-
sion of the searp beyond the Kern, if it persists, hes in a rugged
country difficult of access and was not pursued further. Beyond
the Kern at the point where the drainage from Havilah Valley
enters it, Breckenbridge Mountain may have its counterpart in
the Greenhorn Mountains, but this ridge is not known to present
an abrupt searp to the east such as exists to the south of the
Kern, and it is much more symmetrically dissected with reference
to its north and south axis. It would seem probable, therefore,
that the Breckenbridge fault dies out about where the Kern
river crosses it and that beyond this point the deformation of
the region took, in part at least, the form of an arch, the erosion
of which gave rise to the Greenhorn Mountains. Havilah Valley
then may be interpreted as a structural trough, formed at the
time of the faulting along the Breckenbridge fault, which has
been considerably modified, first by alluviation before its outlet
had eut back along the lower part of the trough, and subsequently
by stream erosion. But while it appears probable that the Breck-
enbridge uplift was continued in part beyond Havilah as an
arch, it was also in part extended, as will appear in the sequel, as
a fault of more moderate throw to the east of this arch up the
eanon of the Middle Kern.

The next point of interest on our route of observation is Hot
Springs Valley. This is reached from Havilah by a road which
crosses a notch in the mountain spur above referred to. The
descent from this divide to the Hot Springs is about 1300 feet
and the latter are situated at an altitude of about 2600 feet. This
pass over which the road passes from Havilah to Hot Springs
Valley is asymmetric in cross profile and has a steep straight wall
on the west side which is strongly suggestive of a degraded
fault-searp.

Hot Springs Valley from Vaughn at its southern end to
Isabella at the junction of the South Fork with the Kern River

400 University of California Publications. [ GEOLOGY

is a little over four miles long and is about a mile wide. Its
trend is north-northeast and south-southwest. This valley is
divided longitudinally into two parts by a low median ridge of
granitic rock. On the east side of this ridge is a flat bottomed
alluviated plain from one-half to three-quarters of a mile wide.
In this plain are situated the Hot Springs from which the valley
is named. The springs emerge from the alluvium of the plain
in its middle part but toward the east side. On the west side
of the median ridge is the somewhat tortuous channel of the
Kern River. The stream flows in a succession of low rapids with
intervals of smooth water over bare granite with a descent of
about 25 feet to the mile. The trench in which the stream flows
is a typical erosional feature. The stream enters this rocky
trench through a stream-worn notch in the north end of the
median ridge immediately at the junction of the South Fork and
the Kern River near the town of Isabella. Here we encounter
a totally different character of stream bed, the moment we pass
to the east of the median ridge. Both the Kern and the South
Fork are flowing upon expansive and far extended flood plains
and their confluence occurs upon a common flood plain. This
flood plain strewn with boulders and gravel extends north up
the Kern for a distance of over ten miles from Isabella with a
breadth diminishing from a mile and a half to a few hundred
feet. Up the South Fork to the east it extends for probably
fifteen miles, with a width in its lower part of over a mile. But
here the flood-plain silts and sands mantle the stream gravel in
large part and make agricultural land. Above the present flood
plain is a terrace about 25 feet in height, indicating that the
valley at one time was filled that much higher than at present.
The alluviated plain which forms the eastern moiety of Hot
Springs Valley is about on the grade of this terrace.

To complete the description of that portion of Hot Springs
Valley which lies to the east of the median ridge, it should be
stated that the alluvium which forms its floor is derived from
three incoming streams. The largest of these is Erskine Creek,
which enters the valley at its southeast corner and there builds
up a notable fan which spreads out over its entire width. The
second is Vaughn Creek which enters at the south end and gives

BULL. DEPT. GEOL. UNIV. CAL. VOL. 4, PL. 39

A. Looking north along the median ridge of Hot Springs Valley
from a point opposite Hot Springs, showing the dual character
of the valley.

B. Looking down the rocky course of the Kern on the west side of

the median ridge of Hot Springs Valley.

Vou. 4] Lawson.—Features of the Middle Kern. 401

rise to a less important fan which is confluent with that of
Erskine Creek. The smallest creek is that which drains an incip-
ient cafion in the face of the steep mountain slope which bounds
the valley on the east side between Erskine Creek and the South
Fork. This creek lies to the north of the Hot Springs and the
latter are situated in a depression between its fan and that of
Erskine Creek. For half a mile around the springs the soil in
dry weather is white with an incrustation of alkaline salts. But
this is more probably referable to seepage from the lower edge
of the fans than to the water from the springs.

The median ridge which divides Hot Springs Valley into
two parts is continuous from Isabella to a point opposite the
Hot Springs where it attains its maximum height of about 400
feet above the flat valley floor to the east. South of this point
there is a notch in the ridge which is on a level with the west
side of the flat valley and about 60 feet above the Kern. Beyond
this to the south the ridge is lower and in less than a mile there
is another notch in the ridge eut below the level of the valley
floor through which Erskine Creek finds its way to the Kern.
At the southern end of the ridge there is still another notch
which separates it from the mountain slope which forms the
south boundary of the valley. Through this notch Vaughn Creek
flows to the Kern with a drop of nearly 100 feet.

From the above brief outline of the geomorphic features of
Hot Springs Valley, it is evident that we have here to deal with
conditions induced by diastrophie interference with the normal
course of erosional evolution. Below Hot Springs Valley the
Kern flows in a normal mountain gorge. Above their aggraded
flood plain at their confluence, both the Kern and the South Fork
flow in sharp, deep canons. Two anomalies are to be accounted
for:. The first is the aggradation of both streams above their
confluence and the second is the dual character of Hot Springs
Valley.

It has been pointed out that the asymmetric ridge of Brecken-
bridge Mountain with its steep eastern fault-searp passes in part
northerly into the more symmetrical ridge of the Greenhorn
Mountains, on the east side of which no great scarp has been
detected. It has been further suggested that the deformation

402 University of California Publications. [GEOLOGY

which resulted in faulting along the face of Breckenbridge
Mountain found its expression in arching in the Greenhorn
Mountains. Now the Greenhorn Mountains lie to the west of
Hot Springs Valley and any deformation such as is here sug-
gested would have the tendency to pond back the Kern. That
tendency would, however, be effective only if the corrasive action
of the Kern failed to keep pace with rate of uplift. But for
several miles below the region of aggradation, and still on the
east side of the uplift, the Kern is flowing in a rocky trench and
it would thus appear that the Kern had been fully able to keep
pace in its rate of down-cutting with the rising arch in its path.
We cannot, therefore, adduce this special phase of the deforma-
tion of the region as the cause of the aggradation of the Kern
and the South Fork above their confluence; and even if such a
cause were admitted, it would offer no explanation of the dual
character of Hot Springs Valley. No amount of simple aggrada-
tion due to the ponding of the Kern would account for the
notched median ridge between the two portions of the valley. A
more fruitful hypothesis is suggested by the notches in this ridge.
They have the character of very short residual trunks of
beheaded stream valleys. If such be their origin, then the valleys
or canons of which they once formed a part could only have
been beheaded by a fault along the east side of the median ridge,
with a downthrow to the east. The straight and quite precipi-
tous east side of the median ridge becomes under this hypothesis
a degraded fault-scarp, the notches in which are antecedent to
the existence of the ridge. Does this hypothesis afford an ade-
quate explanation of the two classes of phenomena with which
we are here concerned? Seemingly it does.. By the development
of a fault along what is now the east side of the median ridge
with a downthrow to the east, a trough would be formed, the
aggradation of which would give us the flat bottomed eastern
moiety of Hot Springs Valley. If the fault-secarp were rather
rapidly formed, as it probably was, the waters of the Kern would
be impounded against it and a process of aggradation inaugur-
ated. The impounded waters would rise to the level of the lowest
noteh in the face of the fault-searp, which would probably be
the trench of the Kern itself, and so resume their former channel

BUELL, DEPT. GEOL, UNIV, (CAL. NAGI apse 40)

A. View of east part of Hot Springs Valley, looking southeast.
Fault-scarp of median ridge on the right.

B. Expansive flood-plain at the confluence of the South Fork and
the Kern at Isabella.

t wy

Vo. 4] Lawson.—F eatures of the Middle Kern. 403

beyond the scarp. Owing to the impounding of the stream
detritus in the lake thus formed, the downward corrasion of the
trench beyond this notch would be slow. Meanwhile deltas
would be rapidly extended down the Kern and South Fork arms
of the lake. The embayment of the lake to the south of Isabella
would be filled partly by the silt of the river and partly by the
deltas of Erskine and Vaughn Creeks. The final result would
be an expansive flood plain sloping up in all directions from the
rock barrier in the notch of the fault-searp through which the
river passed out to its normal channel. As soon as the flood plain
was completed by delta extension on to this point, coarse detritus
would begin to pass through the notch and the deepening of the
Kern trench beyond the scarp would proceed comparatively
rapidly. In consequence of this, the flood plain would be dis-
sected leaving terraces at the level of the flat floor of the infilled
trough to the south of Isabella.

Pursuing now our observations up the Kern River above
Kernville, we find the stream flowing in a profound but remark-
ably straight canon. The general trend of the cafion is much
more nearly a straight line than is the course of the stream which
flows in it. On the west side of the canon the crest of the moun-
tains is in general about ten miles back from the river. Numer-
ous tributary streams enter from this side and all of them, as far
as Tobias Creek, twenty miles above Kernville, have built up
huge alluvial cones which indicate a marked lack of accordance
between the action of these affluents and the main stream, which
is itself running on bedrock and deepening its trench. The
material of these cones is in large part of a very coarse bouldery
character. It seems probable that the deformation of the country
on this side of the Kern which has been recognized in Brecken-
bridge Mountain and in the Greenhorn Mountains has in late
Quaternary time accentuated the grade of the upper reaches of
these affluents and caused them to deject great quantities of allu-
vium into the main canon. It is even quite probable as an infer-
ence from the existence of these cones that, if the country a few
tiles back from the stream were examined, a fault scarp would
be discovered, the dissection and degradation of which has given
rise to the alluvium.

404 University of California Publications. [ GEOLOGY

Beyond Tobias Creek for the next twenty miles to the mouth
of the Little Kern, no such alluvial cones are found on this side
of the Kern. The trail for this stretch of the cafon passes over
a rolling terrace, the more expansive portions of which are known
as Dry Meadows, Peppermint Meadows, and Kern Flats, the last
being the high terrace of the Little Kern described in a former
paper.* This rolling terrace is mantled with a heavy regolith of
decomposed granite. Occasionally residual hills rise above its
average surface and the streams which cross it from the high
eround behind it do so in open swails and then plunge suddenly
through chasms to the Kern which flows at from 1200 to 1500
feet below. It is evident that this rolling terrace is a remnant
of a very mature valley land which has been dissected by the
down-ecuttinge of the Kern, and is to be correlated with little
question with the high valleys of the upper Kern. At the conflu-
ence of the Kern and Little Kern this high valley is mantled
with lava as more fully described in the paper? above referred to.
It appears, however, that the writer did not from his former
observations fully appreciate the degree of inequality of the lava-
mantled surface. The dissection of the Kern Flats by the Little
Kern shows that the lava is in places 400 feet thick. This would
indicate that the surface prior to the outflow of lava was similar
in its degree of relief to the very mature but rolling valley rem-
nants at Dry Meadows and Peppermint Meadows. There can be
little doubt that these high valley remnants once formed a
continuous valley through which the Kern flowed anterior to the
general uplift of the Sierra Nevada which inaugurated its dis-
section. It was, however, a more or less sinuous valley and in its
dissection one portion has been isolated from another. Thus
Kern Flats are separated from Peppermint Meadows by a moun-
tain spur, known as the Needle Rock, which extends out to the
west wall of the deeper portion of the canon. Similarly a mature
rounded divide which separates Peppermint Meadows from Dry
Meadows reaches the deeper part of the cafion and the trail from
one meadow to the other has to cross this divide. The notable
features, then, of this side of the Kern cafion between Kernville

* Bull. Dept. Geol. Univ. Cal. Vol. 3, No. 15.
7 Op. Cit.

VoL, 4] Lawson.—Features of the Middle Kern. 405 |

and the Little Kern are: (1) The extension for twenty miles
below the Little Kern of the same high valley system as was
formerly noted in the Upper Kern basin. (2) The absence of
alluvial cones where the valley terraces prevail. (3) The promi-
nence of alluvial cones between Tobias Creek and Kernville
where the valley remnants fail. (4) As an inference from these
facts a probable rather acute diastrophie disturbance of the latter
stretch of the canon on its west side.

The geomorphic features of the east side of the Kern Canon
from the vicinity of Kernville to the mouth of the Little Kern
are in remarkable contrast to those of the west side. In general
the east side of the canon is more precipitous than the west side,
and it appears to be the edge of a high uneven plateau. The
streams are shorter and frequently fall in cascades over the
steeper portions of the cafon wall in notches of no great depth.
The Kern in the first twenty miles of the stretch under consider-
ation is crowded to the east side of the canon by the large alluvial
cones on the west side and similar cones are only feebly developed
on the east side. These facts indicate in themselves a rather
striking contrast in the geomorphie aspects of the two sides of
the canon, but the most notable feature of the east side, and one
which is entirely absent on the west side, is a series of high and
prominent ridges and butte-like peaks which are arranged along
the canon side in an almost straight line. These ridges and buttes
extend along the whole length of the cafion from near Kernville
to the Little Kern. They he within the canon and reach in gen-
eral from about one-half to two-thirds the height of the cafion
wall, and they are separated in each case from the main canon
wall by a defile or col which is generally several hundred feet
lower than the summit of the ridge or butte. Between these
ridges or buttes flow transversely the affluents of the Kern from
the notches in the main canon wall. The entire series presents
the appearance of a continuous ridge, separated from the main
canon wall by an equally continuous narrow defile, which has
been dissected by the affluents of the Kern which now pass
through it. In attempting to explain these remarkable features
the writer has considered several hypotheses. It is possible that
they might have originated wholly by the subsequent erosion of

406 University of California Publications. [GEOLOGY

lateral branches of the affluents of the Kern if we suppose the
existence of a zone of exceptional weakness paralleling the main
canon wall. Such a zone of exceptional susceptibility to stream
erosion might inhere in the character of the rocks themselves or
it might be purely a structural feature such as a rift, which, it
may be recalled, was found to exist along the cafion of the Upper
Kern in what is practically the projection of the line we are
now considering. As regards the possibility of a zone of weak-
ness in the rocks themselves, it is to be noted that for several
miles along the cafion of the Kern there is a belt of crystalline
schists which is sunk down into the granitic rocks of the region
in much the same way as is the similar belt of schists at Mineral
King described by Knopf and Thelen.* These schists are, however,
common to both sides of the cafon, whereas the peculiar features
noted are confined to the east side. In several cases, noted only
from the trail on the west side of the cafion, the ridges and buttes
are composed chiefly of erystalline schists, in other cases of a
mixture of crystalline schists and granitic rocks, and in other
cases toward the upper end of the cafion they appear to be com-
posed chiefly of granitic rocks. It would appear, therefore, that
there is no good warrant for assuming a zone of weak rocks
which might be easily removed by subsequent erosion so as to
produce in straight alignment the series of defiles which separate
these ridges and buttes from the main ecafion wall. Moreover, if
such a zone of weak rocks existed, it would undoubtedly have
been discovered by the Kern in the course of its downward corra-
sion and have become the main line of cafon cutting. But the
main course of the canon crosses granite and schists indifferently
and has evidently not been greatly influenced in its course by
peculiarities of these rocks.

We are forced, then, still under the assumption that the series
of defiles is due to subsequent corrasion along a line of weakness,
to the view that the weakness postulated must be structural, a
line which is common to both granite and schists. Such a struc-
tural line might have existed prior to the development of the
Kern Canon, or it may have come into existence after the cafon
trench in its main features had been established. If the first

* Bull. Dept. Geol. Univ. Cal. Vol. 4, No. 12.

BULLE, DEPT. GEOR UNIV. ‘CA VOL, 4, PL. 41

A. Looking down the canon of the Kern from Needle Point, showing

, line of buttes and ridges on the east side.

B. The Little Kern Plateau at the confluence of the Little Kern and
the Kern, from Needle Point.

VoL. 4] Lawson.—Features of the Middle Kern. 407

were the case, then it is difficult, as before, to see why it should
not have determined the main line of canon corrasion instead of
the one now followed by the stream. If the supposed structural
line, a rift for example, had come into play after the main canon
trench had been deeply incised, results might ensue by subse-
quent corrasion which would be consistent with the facts
observed. We have in this set of assumptions, therefore, a pos-
sible explanation of the phenomena. It is, however, less prob-
able than another hypothesis discussed below.

Another hypothesis which the writer attempted to apply was
suggested by the resemblance of these features to the kernbuts
of the Upper Kern and the possibility of their having the same
origin was considered. The analogy of these features with the
kernbuts breaks down, however, under examination. In the
Upper Kern Cafion the kernbuts cause constrictions in the cation
and in the interval between them the canon bottom has its full
width. In the case of the ridges and buttes of the Middle Kern,
the width of the lower portion of the canon is not affected by
their presence. The intervals between the buttes and ridges are
purely erosional products and the prominences which are thus
separated cannot be regarded as portions of a long narrow fault
block which have failed to sink as far as the intervening portions.

There are two other hypotheses which must be examined as
possible explanations of the phenomena under consideration.
Both of these involve faulting and they differ essentially in the
position of the fault, its hade, and the direction of the down-
throw. The first of these supposes that the long but now dis-
sected defile was originally the trench of the Kern, and that
when in the course of its downward corrasion it had reached this
depth, a fault occurred on the west side of the cafon with a
downthrow to the west. In this way a trough might be formed
deeper than the trench of the Kern and into this the drainage
would naturally flow leaving the old channel stranded above the
brink of the new diastrophie canon. The erosional modification
of this stranded channel and of the ridge between it and the new
channel might give us the feature we are seeking to explain.

The second hypothesis states that after the canon of the
Middle Kern was well advanced, a fault occurred within the

408 University of California Publications. [ GEOLOGY

canon but on the east side with downthrow to the east. The
trough thus formed was not as deep as the cafion when the dislo-
‘ation occurred. Again by erosional modification of the purely
diastrophic features the present forms would be evolved. In this
case the notches in the ridge between the older erosional cafion
and the new diastrophiec trough would be antecedent to the dislo-
cation and would correspond to the affluents of the Kern. In
making a choice between these two diastrophic hypotheses the
facts which have been narrated in the earlier part of this paper
seem clearly to limit us to the second. It has been shown that
from the south end of Walker Basin through Havilah Valley,
and Hot Springs Valley on the same line as that on which the
Middle Kern flows, there has been a very notable downthrow
to the east and an uplift to the west along a north and south
fault. It would seem necessary, therefore, if we resort to fault-
ine to account for these remarkable geomorphic features of the
canon of the Middle Kern that we must adopt the fault hypo-
thesis which gives us the same downthrow. By doing this, more-
over, the series of ridges and buttes which adorn the east side
of the canon of the Kern consists with and is the perfect analogue
of the median ridge of Hot Springs Valley from the genetic
point of view. The same considerations which favor this
hypothesis as against the one which postulates downthrow to
the west on a fault on the west side of the canon are adverse
to the first hypothesis considered, viz: the evolution of the trough
or defile by purely erosional processes along a rift developed
within the cafon but without dislocation. The fault line along
which the country was downthrown to the east from Walker
Basin to Kernville would pass straight up the canon of the
Middle Kern and there seems to be no good reason for doubting
that the peculiar features of the canon are just as much the
result of that faulting as are the equally remarkable features
deseribed to the south of Kernville.

The question now arises: Is the occurrence of a fault within
the canon of the Kern and strictly coincident with it in direction
more than a coincidence? In view of the observations made on
the Upper Kern* it is clear that it is not merely a coincidence.

* Op. cit.

VoL. 4 | Lawson.—Features of the Middle Kern. 409

For the Upper Kern the conclusion was reached that the canon
had been controlled as to its course by a rift line antedating the
canon and that at a later period faulting had occurred along
this rift with partial engulfment of a narrow orographic block
or wedge. The Middle Kern lies along the southward projection
of this rift line through the Trout Meadows defile, and there
seems little room for doubt but that its course, lke that of the
Upper Kern, was determined primarily by a great north-south
crustal rift. At a later period when the canon had been deeply
incised the region was deformed and dislocation was effected
along the general line of the rift.

University of California,
April, 1906.

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UNIVERSITY OF CALIFORNIA PUBLICATIONS
BULLETIN OF THE DEPARTMENT OF

GEOLOGY

Vol. 4, No. 17, pp. 411-423 ANDREW C. LAWSON, Editor

NOTES ON THE FOOTHILL COPPER BELT
OF THE SIERRA NEVADA.

BY

A. KNOPF.

CONTENTS.

PAGE

NISTGTEO CLA C TO Tiga eases sess ras eee ma, SN Te ee eg ae ae suet geese eee c senses 41]
Spenceville, Nevada County, and Vicimity.........0..2...2.ecec:ceeeeceeeeeeeeeeeeeeeeeeeees 4192
ime MEI PNeva dla, Comunity -2es2.ccccese 2s cce ceees eaee cere cce seen ee eee geese sree 413
ADIGE, NYEMIU eS PENA 491 C p00 ae lee ee RIE eee eee ee 414
ID Few cys elt eho ee ANY 80a pres a ee aoe een ere cna Oye Retin eee geen eee 414
Valley View Mine ............ eo ee ee ee A 415
Cedar Mine, near Wolf Creek .................-.--.-;e00cccsese-ceeseeeeeeeeeeeeeeeeneeee ee 415

Campo Seco, Calaveras County
Wopperopolis, «Calaverase Count yy. sce 22g. -sceeeceeeececeesessene- sees ese seeeseeeee eee -
Napoleon Mine, Calaveras County
Resumé

INTRODUCTION.

The existence of a belt of copper deposits along the western
foothills of the Sierra Nevada has long been known, but its
economie importance has been overshadowed by the richness of
the Gold Belt immediately to the east of it, and by the extensive-
ness of the copper deposits of Shasta County.

Owing to the discovery of rich carbonate croppings in Cala-
veras County, California experienced an intense copper excite-
ment as early as 1861. Upon the exhaustion of the oxidized ores
a period of stagnation and idleness ensued, lasting well up to the
present time. Only within the past decade has an extensive
exploitation of the unaltered sulphide bodies commenced, notably
at Campo Seco and Copperopolis.*

* For an account of the historical and economic features of the copper

resources of the State, Bull. 23 of the Cal. State Mining Bureau should be
consulted.

.

412 University of California Publications. [GEOLOGY

The formations of the Sierra Nevada region are according to
the United States Geological Survey grouped together as the
Bedrock Complex and the Superjacent Series. The Superjacent
Series is composed of the Tertiary auriferous gravels of fluviatile
origin, and the succeeding heavy accumulations of rhyolites,
andesites, and basalts, all resting upon the eroded edges of the
Bedrock Complex. This Complex includes a succession of closely
appressed rocks in belts paralleling the general trend of the
range, and dipping steeply towards its axis. They comprise
quartzites and microcrystalline mica schists (Calaveras forma-
tion, Carboniferous), black clay slates (Mariposa formation,
Upper Jurassic), meta-andesites and their schistose equivalents.
At the close of the Jurassic these were all extensively intruded
by plutonic magmas, chiefly granodorites and peridotites.

The meta-andesites and their associated pyroclastics often
attain enormous thicknesses, freqently reaching five miles, with-
out doubt, however, due in great part to folding, although as
yet unrecognized in the field.* In the earlier folios of the Gold
Belt they were mapped as diabases and augite porphyrites, but
in the later publications (notably the Mother Lode Folio, F. L.
Ransome) they were designated meta-andesites in order to
emphasize their essentially extrusive character. Their exact posi-
tion in the stratigraphic column is still a moot point in the geol-
ogy of the Sierra Nevada, though the evidence, both petro-
eraphic and stratigraphic, favors a late Jura-Trias age for the
bulk of the series.

We propose to describe the copper deposits in geographic
order from north to south. A number of small idle or unworked

prospects were not visited.
SPENCEVILLE, NEVADA COUNTY, AND VICINITY.

North of Spenceville toward the head of Little Dry Creek
numerous copper prospects have been opened up in the meta-
andesites. The country rock is usually massive, but in the vicin-
ity of the copper deposits has been slickensided and sheared, and
belts of strongly foliated chloritic schists up to 4 feet thick have
been produced. The strike is N. 45° W. and the dip vertical.

*H. W. Turner, Jackson Folio.

VoL. 4] Knopf.—Foothill Copper Belt. 413

Clay and gouge are frequent, as on the other hand are lenses of
massive, unsheared rock in the midst of the schists. The ore
consists of chaleopyrite in a gangue of a spherulitic zeolite (Sp.
er. 2.17) replacing a chlorite schist. The microscope shows radial
stilbite,* quartz charged with liquid inclusions, areas of chlorite,
often consisting of small partially developed spherulites, and
accessory epidote and calcite. The most nearly massive wall rock
obtainable is composed largely of green, reedy hornblende,
chlorite, highly altered plagioclase, and accessory epidote, pyrite,
and magnetite.

At Spenceville the ore body occurs in andesites whose extru-
sive character is readily apparent. Facies carrying numerous
quartz amyedules occur in the bed of Little Dry Creek, and the
eryptoerystalline facies on the brow of the hill just behind the
mine dump is rich in epidote amyedules. A few hundred feet
to the west, however, typical ophitie diabase occurs. This has
been cut by fine grained dykes of similar chemical composition.
The dykes show that minor faulting has taken place, not exceed-
ing half a foot in individual cases. Some two hundred feet east
of the Spenceville mine the greenstones are intruded by a large
eranodiorite boss. Lindgren has characterized the Spenceville
deposit as a ‘‘local massing of copper on the granodiorite
contact.’ ’t

The mine has been a quite large producer in the past, but is
now idle and filled with water. From report it appears that the
ore body consisted of one huge kidney of chalcopyrite which
pinched out in depth.

PINE HILL, NEVADA COUNTY.

This locality has been described by Lindgren, who drew atten-
tion to the unusual fact that here barite acts as a carrier of gold.t
The deposit was characterized as of the general type; ‘‘veins and

* The optical properties of this zeolite diverge from those of stilbite in
two important particulars; it shows an absorption equal to that of muscov-
ite, and displays brilliant interference colors of the 2nd and 3rd orders.
Otherwise the physical and chemical properties are identical with those of
stilbite.

+ Smartsville Folio.

{ W. Lindgren, The Gold Deposit at Pine Hill, California; A. J. S. 3rd
ser., vol. XLIV., pp. 92-96, 1892.

414 University of California Publications. [GEOLOGY

seams of barite, carrying gold and silver, distributed through a
kaolinized zone in diabase and diabase porphyrite.’’ Since 1892
more development work has been done, but at present the mine
is tied up by litigation, and the shafts flooded with water.

Pine Hill itself consists of augite andesites, ophitic diabases,
amyedaloids, and tuffs. Interealated with the porphyries is a
lens of fissile black slate 50 feet thick. Near the summit of Pine
Hill the tuffs have been crumpled and brecciated. This has been
the locus of most intense mineralizing activity. Extensive gossan
croppings often containing much heavy spar have formed. Large
masses of pure solid barite occur. The gossan when panned yields
numerous coarse colors of gold. The pure barite assays $2 per
ton. .

Tunnels run into the hill show that the porphyries have been
thoroughly leached by sulphurie acid. They still retain their
porphyritice aspect, but are soft enough to be kneaded. A very
white kaolin, theoretically pure,* is of frequent occurrence, but
seems limited to zones of movement. This movement may be
correlated with the arching upward of the floors of abandoned
drifts—1 foot rise in 43 feet. The tunnels show that the
porphyry has been fractured and stained with iron oxide along
the cracks and fissures. At open spaces porous platy masses of
limonite have formed, and lying loosely upon these are numerous
small glassy crystals of barite.

The gossan has long been mined as a free milling gold ore.
At 75 to 100 feet in depth oxides, carbonates, and native copper
were encountered, and the barite disappeared. The copper ore
below this consists of a crumbly mass of bluish black sulphide
in which the frequent glint of pyrite can be detected. A thin
section of leaner ore shows grains of pyrite surrounded by per-
ipheral coatings of copper sulphide. The gangue is fine grained
quartz. Unfortunately, the flooding of the mine did not admit
of a closer investigation of the extent of the secondary enrich-
ment.

THE VALLEY VIEW GROUP.

Dairy Farm Mine.—A large lens of solid pyrite 60 feet thick,

carrying 2 per cent. copper, parallel to the foliation of the enclos-

* W. Lindgren, loc. cit.

Vor. 4] Knopf.—Foothill Copper Belt. 415

ing schists, is reported from here. Amphibolite schist is the pre-
vailing country roek, but numerous lenses of quartz porphyry
schist occur in the immediate vicinity.

Valley View Mine.—The gossan deposit here has been worked
for gold during many years.* At greater depth chalcopyrite and
eovellite were struek. Development is in active progress.

The gossan occurs in a quartz porphyry schist lens, some three
hundred feet wide and nearly a thousand feet long, intercalated
in the prevailing amphibolite schists.

Cedar Mine, near Wolf Creck—The country rock is meta-
andesite and augite porphyry tuff, roughly schistose N. 60°
W. The ore is chaleopyrite in a gangue of quartz and calcite.
The vein is a strong fissure vein, about 20 feet wide, breaking
at right angles across the country. Inelusions of country rock
occur in the ganeue. The property is at present idle.

Two miles south of this is the Ace Mine, also idle. The shafts
are sunk upon a mineralized shear zone in the otherwise massive

meta-andesite.

CAMPO SECO, CALAVERAS COUNTY.

Just west of the Campo Seco copper mines is a belt of black
clay slates (Upper Jurassic aget). Passing eastward across the
strike these graduate by an easy transition, as seen at the old
engine house, into tuffs and coarse breccias, more or less schistose.
A typical specimen of these greenstone schists examined micro-
seopically showed a large abundance of chlorite and epidote,
especially the latter, and a few small plagioclase feldspars. Inter-
ealated with these breccias are some green glossy slates, well
exposed along the Mokelumne River. In this section they are
found to be irregularly layered, consisting of ealeite and chlorite.
A little quartz was noted, as also some clouds of magnetite dust.
These rocks, therefore, represent metamorphosed calcareous tufts.
The breecias are frequently quartz-bearing, and are probably the
ejectments of a dacitice magma. Their thickness is 1000 feet.

These are succeeded by quartz porphyry flows, which in turn
are sueceeded by schistose greenstone breecias. To the eastward

* W. Lindgren, Sacramento Folio.
+H. W. Turner, Jackson Folio.

416 University of California Publications. [GEOLOGY

heavy accumulations of auriferous gravels mantle the bedrock °
geology. Along the bluffs of the Mokelumne River and in the
region north of the river the greenstone schists are literally
charged with long angular fragments of an aphanitie quartz
porphyry in which the quartz phenocrysts are small and infre-
quent.

The quartz porphyry flows are the copper bearing members.
In the exposures along the river, especially on the north bank,
the base of the quartz porphyry is found to interleave with the
green glossy slate, and with coarse angular breecias. In the vicin-
ity of the new shaft two main flows, separated by 300 feet of
tuffs, are discriminable. A few hundred feet to the south they
become confluent, but diverge almost immediately, becoming
separated by a mass of greenstone schists whose coarsely pyro-
clastic character is still obviously patent.

The quartz porphyries have as a general rule been very thor-
oughly foliated, though some unsheared lenses have escaped
metamorphism. The schistosity is occasionally crumpled and
bent back on itself, and a slip-strain cleavage produced. The
unsheared rock is remarkable on account of the abundance of
large quartz phenoerysts, in a light flinty groundmass. In addi-
tion to the quartz, the microscope shows some porphyritic plagio-
clase (16°, maximum symmetrical extinction), orthoclase in
nearly equal amount, and a few chlorite-epidote aggregates, which
may possibly represent former ferromagnesian minerals. The
groundimass is a microcrystalline aggregate of feldspar, part of
which is striated, abundant chloritic matter in small flakes, and
some magnetite. A few rather large grains of chalcocite were also
noted. Mineralogically and structurally, the rock may be desig-
nated a quartz monzonite porphyry.*

The following is described as a type uncommon at Campo
Seco. The rock is a dark colored quartz porphyry upon whose
flow banding a rude foliation has been superimposed. Under the
microscope is revealed an intricate fluidal structure characteristic
of stiffly moving acid voleanices. Quartz phenocrysts are numer-
ous, but bipyramidal forms are wanting. Certain minor flow
bands consist of magnetite, while others are rendered opaque by

* W. Lindgren, Mon. 43, U. S. G. S., p. 81.

VoL. 4] Knopf.—Foothill Copper Belt. 417

magnetite dust. A few small magnetite phenocrysts are involved
in the convolutions of the flow lines, much lke the numerous
larger quartzes. The flow bands are feebly polarizing mosaics,
probably eryptoerystalline quartz and feldspar. Epidote grains
are abundant in some, or yellowish chlorite in others, or both
together in yet others.

Numerous augen of glossy quartz in a highly schistose matrix
of taleose appearance is the most characteristic feature of the
sheared quartz porphyries. The schists from the mine workings
are very light colored with a tinge of bluish green. Under the
microscope the original bipyramidal character of the quartz is
often recognizable. Many of the quartzes have been affected by
a process which gives them a frayed appearance: short streamers
of quartz have grown out from the main mass of the phenocryst
parallel to the schistosity. The matrix consists of quartz and
sericite intimately interwoven. Sections cut parallel to the schis-
tosity show aggregate polarization of a scaly character. The
interference tints are quite low (yellow to gray), which may be
due to a compensatory effect of overlapping scales of finely foli-
ated sericite. . The tale-like mineral fails, however, to react for
alkalies, but yields silica, alumina, and water at high tempera-
tures. It appears probable that with the sericite a large amount
of a hydrous aluminum silicate mineral is present.

- The chaleopyrite present in the quartz porphyry schists has
been sheared along with the other minerals, appearing now as a
plating between the foliation planes. In this section it is seen
to oceur in long narrow streamers conforming to the schistosity,
except where partially replacing quartz phenocrysts.

At the site of original location (malachite-azurite eroppings)
some barren lenses of vein quartz, 1 to 2 feet long, occur in the
schists. Certain unschistified horses of quartz porphyry have
escaped mineralization, but have undergone a profound meta-
somatie alteration. The original glassy quartzes of the quartz
porphyry now appear as phenocrysts in a eryptoerystalline
ground of silica. Under the microscope this ground is shown to
be composed of fine granular quartz, portions of which assume a

299)

rude form of the ‘‘retiform structure’? of Spurr. Some minute

fibres of white mica can be detected under the highest power.

418 University of California Publications. [GEOLOGY

The large quartz phenocrysts (3mm) visible macroscopically,
frequently show in thin section the smoothly rounded outlines
characteristic of porphyritie quartz modified by magmatic corro-
sion. In one particular instance, however, the metasomatie alter-
ation of the groundmass has also affected the phenocryst. In
this case the quartz, which possesses a very nearly perfect hexa-
gonal outline as indicated by a peripheral arrangement of inclu-
sions, is surrounded by a narrow zone of secondary quartz in
optical continuity with itself, but fading irregularly into the
quartz of the groundmass.

The first-class ore at Campo Seco consists of chalcopyrite
running about 8 to 10 per cent. zine. The ore is often banded
with black granular sphalerite. The gold content varies from
one to three dollars; the silver values are about the same. In
spite of the greater losses in the metallurgical treatment with
high zine content, it is found that the gold and silver values
increase with the amount of zine present.

The ore bodies are lenticular in shape, and attain a maximum
thickness of 30 feet.

COPPEROPOLIS,*” CALAVERAS COUNTY.

The meta-andesite belt attains a great thickness here, and
displays in unusual perfection the evidence of its extrusive
origin. Various amygdaloids, coarse breccias, and tuffs graduat-
ing into clay slates largely preponderate over the massive por-
phyries. In addition to the angular blocks of andesite, and at
times fragmental quartz porphyry, the breccias are often thickly
crowded with granitic material—hornblende gneiss, diorites, and
hornblendites. The intimate association of the clay slates with
the finer pyroclastics suggests a possible submarine origin for
the entire series.t Dynamic movements have affected the region,
shearing the massive voleanics but slightly, while often imposing
a very thorough schistosity upon the finer tuffs, parallel to the
bedding.

The Copperopolis Lode, which has been traced over a length
of 10,000 feet, occupies a rather persistent horizon of clay slates,
microcrystalline chlorite schists, and chlorite schists whose width

* J. D. Whitney, Geology of California, vol. I., pp. 254.
7 A. Geikie, Textbook of Geology, vol. I., pp. 339.

ol Decne

VoL. 4] Knopf.—Foothill Copper Belt. 419

approximates 100 feet. Within this zone, however, typical augite
porphyrites and coarse breecias may occur, as the croppings at
the Empire shaft show. The general strike is N. 60° W., and
the dip 61° to the northeast.

Four thousand feet south of the Union shaft (the present
hoisting shaft) is found a small gabbro boss, which from the
nature of its inclusions, is determined to be intrusive in the green-
stones of the footwall country. The gabbro consists essentially
of abundant diallage, often altered to actinolite, and basie plagio-
clase feldspars, largely converted to aggregate of minute zoisite
prisms. Toward the southern end of the boss a more basic modi-
fication of the gabbro is met with, which may descriptively be
designated a feldspathic hornblendite. A similar rock occurs
in small isolated croppings 200 feet southeast of the mill in
the hanging wall of the lode, surrounded by schistose augite
porphyries. The hornblendite here consists of numerous stout
hornblende prisms bound together by a mesostasis of basic plagio-
clase feldspars which poikillitically enclose small perfect idiomor-
phie hornblendes. This hornblendite is cut by a system of
quartzose biotite granite dykes. The main gabbro boss is intruded
by thin albite dykes containing some faintly pink zoisite. At
two points on the periphery of the gabbro, and on opposite sides
of the boss, are lenses of serpentine, not exceeding 30 feet in
thickness. Discrete areas of this serpentine, attaizing a maxi-
mum width of 60 feet, appear intermittently along the footwall
of the lode as far north as the Union shaft. It is occasionally
altered to a tale schist. Along the footwall are also limited expos-
ures of a deeply decayed rock of granitic habit, which fresher
samples from the mine workings show to be a quartz monzonite.
The greatest thickness exposed is 50 feet, and the northernmost
cropping is 4000 feet north of the Union shaft, or about 8000
feet north of the gabbro boss. The mutual relations of the quartz
monzonite and the serpentine were not discoverable. The quartz
monzonite is intrusive into the chlorite schists of the lode, the
actual contact showing a limited degree of fusion and assimila-
tion over an inch or two. The quartz monzonite is composed of
hornblende and biotite, both entirely chloritized, oligoclase, and
orthoclase in equal amounts, and abundant quartz, with accessory

420 University of California Publications. [GEOLOGY

apatite, zircon, and chalcopyrite, which by preference replaces
the chlorite. The quartz monzonite shows evidence of severe
movement and fracturing, and is often highly sulphuretted.

Another type of igneous rock is found in the hanging wall
country just east of the mill. This is an aphanitie white rock,
heavily pyritized, showing a few small glassy feldspars, which
the microscope shows to be largely orthoclase. It may represent an
offshoot from the quartz monzonite, which a prospect shaft shows
is intrusive in the greenstones a hundred feet or so to the east.

Northward from the original location the Copperopolis Lode
occupies the center of a broad strike valley ; to the south, it forms
the summit of a low, gentle ridge. At present the ores are being
entirely hoisted from the northern portion of the lode, consist-
ing of microcrystalline chlorite schists (locally known as ‘‘black
pyritous slates’’) ; in the southern portion the ore rock is thor-
oughly seamed with quartz stringers, which by their resistance
to weathering, have elevated the lode above the surrounding
topography.

The ore bodies consist of a series of lenses parallel to the
foliation of the schists, about 200 feet long, 150 feet high, and

to 60 feet in width. They are not necessarily located in align-.
ment, but frequently occur en enchelon. The shoots are stated
to pitch 45° to the north in the plane of the dip.* The footwall
is often defined by soft, putty-like tale, which has a tendency to
run. There is no definite hanging wall, the ore shoots fading
into barren rock, and the extent to which ore is stoped out is
governed by the dictates of economic expediency.

Below the shallow zone of oxidation, 30 feet in depth, lie
the unaltered sulphide masses. The ore consists of chalcopyrite,
singularly free from admixture with other minerals, included in
a fine-grained chlorite schist as gangue. The absence of the ordi-
nary gangue minerals is so marked that ore containing quartz
is retained as specimen material. The chalcopyrite occurs as
thin bands, from an eighth to a quarter of an inch in thickness,
ribboning the schist parallel to its foliation planes, though fre-
quently anastomosing irregularly across the schistosity.

* According to Mr. G. MeM. Ross, Mgr., whose great courtesy it is the
writer’s pleasure to acknowledge.

VoL. 4] Knopf.—Foothill Copper Belt. 421

The appearance of the typieal ore is adequately expressed by
its local designation: ‘‘black pyritous slate.’’ From the slaty
forms the transition to the chlorite schists is not great. Under
the microscope the typical ore presents a uniform deep green
eolor with little or no individualization of the chlorite into dis-
tinct flakes. Between crossed nicols a few rude shadowy crosses
-become apparent, and a general streaked effect, expressed in low
blue gray colors, indicates the trend of the flow cleavage. The
chaleopyrite is distributed in small stringers parallel to the cleav-
age, and is often accompanied by a fringe of epidote grains.
Some of the large granules of chaleopyrite are associated with
a little quartz and chaleedony. A very small amount of chalcocite
was noted, some of which was peripheral upon the chalcopyrite.
The quantity of secondary sulphide, however, is nearly insig-
nificant.

The chlorite schist ore differs from the preceding only in the
fact that the chlorite is in well-developed plates, many of which
show evidence of internal movements. Some grains of titanite
occur.

Ore rock taken from near the footwall of Level 4 shows a
few additional features. In sections cut normal to the schistosity
the rock is seen to be composed almost exclusively of chlorite,
often in minute spherulites, and a few ‘‘porphyritie’’ plates of
elhnochlore. The discrimination, clinochlore, is made on account
of its superior birefringence and deeper pleochroism. In certain
plates chaleocite can be seen replacing the eclinochlore parallel
to the cleavage lines. The amount, however, is inconsiderable.
A few rectangular sections of andalusite occur. Grains of
titanite, sometimes partially idiomorphie, are rather abundant.
Splendid rutile prisms, surrounded by strongly pleochroie halos
of deep olive green color, constitute a characteristic feature of
this variety of chlorite schist.

The andalusite may indicate contact metamorphism by the
quartz monzonite intrusive, and lends weight to the probability
suggested by the petrographic and stratigraphie data that the
Copperopolis chlorite schists represent argillaceous andesite tuffs
dynamically metamorphosed.

Since the deposition of the ore much movement has taken

422 University of California Publications. [ GEOLOGY

place, shearing the chalcopyrite and plating the foliation planes
of the chlorite schist with yellow mineral.

The introduction of the ore has been subsequent to the latest
intrusive, for the quartz monzonite is often impregnated with
chalcopyrite, especially along fracture zones. The amygdules of
the flows west of Copperopolis occasionally show a speck of
chalcopyrite in the interior of the solid filling.

NAPOLEON MINE, CALAVERAS COUNTY.

The Napoleon mine is six miles southwest of Copperopolis.
The section between them is composed largely of the meta-
andesites, including, however, about 5000 feet of Upper Jurassic
clay slates and an intrusive mass of granodiorite.

The prevailing rock in the vicinity of the Napoleon mine is
a massive quartz porphyry whose characteristic feature is its
abundance of glassy quartzes in an aphanitiec base of flinty
appearance. The microscopic petrography of this rock shows
numerous idiomorphie quartz phenocrysts, often affected by
magmatic corrosion, and a large number of porphyritie feldspars,
untwinned, turbid, opaque, and frequently containing much sec-
ondary epidote. Femie constituents were nearly absent, and are
now represented by chlorite. The groundmass is a microcrystal-
line assemblage of feldspar, quartz and minute spherulites.

Two thousand feet east of the shaft the tuffs, breccias,
amyegdaloids, and porphyries of the meta-andesite series appear in
great thickness. In the immediate vicinity of the mine is an
interealated flow of hornblende andesite, which having a thick-
ness of about a hundred feet at the hoisting shaft, rapidly thick-
ens towards the southeast to 500 feet. The distinguishing fea-
tures of this rock are the presence of hornblende prisms and the
ereat abundance of calcite amygdules. Certain highly feld-
spathie facies are associated with the hornblende andesite. The
quartz porphyry where resting upon the andesite was found to
show a narrow chilled selvage against a scoriaceous amygdaloid.

The lode hes along the contact of the feathering end of the
andesite flow with the quartz porphyry. This contact has been a
locus of exceptional dynamie activity, along which the horn-
blende andesite has been reduced to a chlorite schist, and the

VoL. 4] Knopf.—Foothill Copper Belt. 423

quartz porphyry has been breeciated, and more rarely, converted
to a sericitie quartz porphyry schist. The width of this shear
zone is about 30 feet, though within this belt there are horses
of unschistified rock. The lode strikes N. 75° W., dip 62° 8.
The hanging wall is quartz porphyry and is fairly regular; the
foot is the meta-andesite, is soft and rotten, and more irregular.
The ore is solid chaleopyrite, massively schistose and often
roughly banded with ruby zine. Calcite and some galena are
occasionally noted. The unschistified lenses of rock noted in the
croppings form horses of second-class ore, 6 inches to 2 feet in
diameter and several feet long. They are more poorly mineral-
ized, and contain a larger proportion of iron pyrites. Where
eubes of pyrite have developed in the vicinity of the calcite
amyedules of the hornblende andesite, they fail to replace the
earbonate, but remain imperfect and have grown around it.

RESUME.

The Foothill copper belt les west of the main gold-produc-
ing region, and ineludes a series of copper deposits occupying
the lower foothills of the range. Great stress cannot be laid on
the unity of this belt as a metallographic province, Inasmuch as
two typical occurrences, notably Pine Hill and Valley View, were
long worked as gold mines, until deeper exploration revealed the
unsuspected presence of copper. Along this belt are also the
gold mines of Ophir, described by Lindgren.* Copperopolis and
Napoleon are held to be on separate branches of the copper belt.
Between them is a great thickness of black clay slates, upon which
is located the Royal, a large gold-quartz mine (120 stamps).

The copper deposits are, however, all closely associated with
the meta-andesites, and belong to the general type of replace-
ment deposits along shear zones. This gives a certain geologic
unity to the entire belt. The replacement has been equally thor-
ough in very diverse rocks, producing the large ore bodies of Cop-
peropolis in chlorite schists, and the extensive, and more massive,
ore bodies of Campo Seco in quartz porphyry schists.

* W. Lindgren, 14th Ann. Rept., U. 8. G. 8.

University of California,
May, 1906.

UNIVERSITY OF CALIFORNIA PUBLICATIONS
BULLETIN OF THE DEPARTMENT OF

GEOLOGY

Vol. 4, No. 18, pp. 425-430 ANDREW C. LAWSON, Editor

AN ALTERATION OF COAST RANGE
SERPENTINE.

BY

A. KNOPF.

In the vicinity of North Berkeley bold massive eroppines of
a curiously weathering rusty red rock form conspicuous features
of the foothill slopes. They frequently attain a height of 40 or
50 feet, and owing to the striking character of their superficial
alteration, readily attract attention. Under the action of the
weather they yield cavernous, honeycombed masses of great var-
iety of form, gnarled and twisted, and often of fantastic fash-
loning.

The unweathered facies of this rock consists of an aggregate
of chaleedony and rhombohedral carbonates, whose relative pro-
portions may vary within rather wide limits. Highly siliceous
phases are common, while the other extreme is represented by
phases indistinguishable from crystalline limestones. In the
typical roek, however, the carbonates are dominant, and the
chaleedony subordinate. The structure is often peculiar and
characteristic, and is due to the intimate lenticular interlamina-
tion of the two main constituents. On a fresh fracture the rock
is colored a sort of terra-cotta red, and is seamed with small
vitreous quartz veinlets, and bunches and veins of white waxy
chaleedony. Chromite occurs in numerous small specks, and
upon isolation gives a good chromium reaction with borax. Ocea-
sionally a deep green mineral of lamellar habit can be found.
Cleavage flakes show the emergence of a negative acute bisectrix
of small axial angle. The extinction is parallel to a well-defined
cleavage, the relief low, and the birefringence feeble. These

426 University of California Publications. [ GEOLOGY

properties, together with a fibrous habit, unquestionably identify
the mineral as bastite. The presence of chrome micas was sus-
pected, but could not be verified.

The rocks under discussion have an extensive distribution in
the hills north of Berkeley, occurring as lenticular masses in the
Franciscan sandstone. The invariable presence of glaucophane
schists is suggestive. They occur at numerous other points
throughout the Coast Ranges, and are locally known as ‘‘the
quicksilver rock,’’ on account of their frequent association with
cinnabar deposits. They were described as forming a subordi-
nate member of the Franciscan series (lowermost Cretaceous ?),
and were provisionally designated as a silica-carbonate sinter.*
This was attacked by Fairbanks,? and in particular the sugges-
tion that the formation might be used in correlating isolated
portions of the Franciscan. His contention was based on the fact
that the rock occurs as the gangue of the quicksilver ores which
are known to be of post-Miocene age, and that the silica-carbonate
sinter may, therefore, occur at any stratigraphic horizon.

Becker,t however, seems in part to have recognized the deriva-
tive origin of the rock under consideration, but his views are
largely obscured by his conceptions of the metamorphic char-
acter of the Coast Range serpentines. Von Groddeck,|| in a
remarkable paper on the Quicksilver Deposits at Avala, Servia,
was the first to draw attention to the pseudomorphiec character
of the ore rock at New Almaden.

His conclusions, both as to the Servian and California oecur-
rences, were vigorously denied by Becker.

The recent finding near North Berkeley of some exceptional
material allows the origin of the carbonate rock to be fixed
beyond question.

Under the microscope a thin section of typical carbonate rock
is seen to consist of an intimate mixture of lime-magnesia carbon-
ates and chalcedony. The carbonates are without crystalline
boundaries and are frequently stained with yellow iron oxides.
The unusually strong differences of relief for O and E indicate

* A. C. Lawson, 15th Ann. Rept. U.S.G.S., pp. 435.
7; H. W. Fairbanks, Jour. Geol. V. 63-67, 1897.

¢{ Monograph XIII. U.S.G.S.

|| Zeit. fir Berg, Hutten-u-Salinenwesen, vol. 33.

VoL. 4] Knopf.—aAn Alteration of Serpentine. 427

magnesian carbonates, and in exceptional eases even siderite. The
chalcedony is composed of aggregates of beautifully formed
minute spherulites. Granular and automorphic magnetite, and
grains of chromite occur as accessories. The chaleedony com-
monly occupies small lenticular areas surrounded by narrow
bands of carbonate, and the structure produced thereby is char-
acteristic of the silica-carbonate rock.

At North Berkeley this type is found grading into a rock
whose characteristic feature is the abundance of lamellar pyrox-
enes of decidedly bronzy metallic lustre. Veinlets of chrysotile
under a millimeter in thickness form a reticulate network tra-
versing the rock.

In thin section large plates of orthorhombie pyroxene become
apparent. Their color is brownish yellow, and the deeper colored
sections show a faint pleochroism. A strongly colored plate was
found to give a decided pleochroism: green parallel to er and
yellowish green transverse to c. The pyroxene is therefore,
bronzite. Small grains of chromite are ineluded in the bronzite.

The pyroxenes are partially serpentinized and the remaining
bronzite plates represent the survivors of the process of serpen-
tinization. Even these show strong variations in the degree of
relief, varying from the characteristic high relief of the pyrox-
enes down to that of Canada balsam. The latter probably repre-
sent the bastite modification, though the position of the optic
axial plane could not be tested. The pyroxenes are, moreover,
traversed by a ramifying system of carbonate fibres. Certain
banded veins of serpentine which intersect the slide are found not
merely cut across by the carbonate, but show also a progressive
replacement by means of numerous small apophysal tongues.
These paragenetice relations show that the carbonate is epigene
upon the serpentine, and not merely a residual product of the
process of serpentinization.

In certain sections the carbonate can be seen replacing the
pyroxene directly without the intervention of the serpentine
stage. The advancement of carbonatization appears easiest in the
direction of the vertical axis.

Often a sort of net structure is produced by capillaries of
carbonate encircling areas of serpentine. From these, grada-

428 University of California Publications. [GEOLOGY

tions can be traced wherein the carbonate has completely sup-
planted the serpentine. It is not unusual to see the characteristic
antigorite structure displayed by carbonate.

Certain larger veinlets of carbonate also occur, and usually
show a well-developed rhombohedral cleavage. The usual strong
differences of relief are displayed, and from the very high index
for O, dolomite and magnesite are suggested. ‘

The remaining portions of the sections are composed of con-
fused aggregates of serpentine, which render inferences as to
their derivative origin unsafe. Only oceasionally is the charac-
teristic antigorite structure visible. No olivine, or structure cer-
tainly referable to its former presence, could be found. A few
mosaic polarizing veinlets of quartz seam the slides.

Under medium high power some tangled trichite-like agere-
gates can be discerned embedded in the carbonate and quartz.
They possess a metallic lustre, inclining to brassy. <A straight
and relatively stout prism showed a hexagonal cross-section.
These characteristics serve to identify the mineral as millerite.

Summarizing the petrographic details, we find that the rock
is composed of allotriomorphie plates of bronzite, often serpen-
tinized, and magnesian carbonates epigene upon both the serpen-
tine and the pyroxene. It, therefore, conforms to a partially
altered pyroxenite.

From the rock at North Berkeley whose origin is thus appar-
ent, the series of changes involving the transformation to the
carbonate rock may readily be followed, and may even be seen
in the hand-specimen whose typical pyroxenite character is
macroscopically obvious. Throughout the Coast Ranges, how-
ever, the carbonate rock often occurs in isolated croppings, highly
weathered, or associated with serpentine in obscure relations,
hence the uncertainty which has existed as to its origin.

The approximate chemical composition of the original unal-
tered bronzitite as computed from the mineralogical content is:

SiO. = 60
Fe.O, nN =
AO 8 =) Cee
MgO = 28-30
CaO= 2

Sum = 100%

—

VoL. 4] Knopf—An Alteration of Serpentine. 429

Analysis of the silica-earbonate rock (excluding macroscopic
quartz veinlets) yielded the following result after digestion in
hydrochlorie acid:

Insol. residue = 16.24% (96.4%Si0.,)
Fe.0; \__ x o¢
ALO, "0

CaO = 13.20

MgO= 25.89

Theoret. % CO, - = 38.61
Total’ HELO Fal

Sum = 100%

The analysis represents the end product of two successive
processes: first, serpentinization, and secondly, dehydration and
carbonatization. The former involved a large increase of volume,
the latter a decrease. This latter process has been attended by
the formation of vitreous quartz veinlets, whose frequent comb-
in-comb structure indicate their deposition in open fractures.
The above analysis when compared with the composition of the
bronzitite shows several noteworthy features. An exact diseus-
sion is not possible on account of the uncertainty of the volu-
metric relations involved, but the following points appear well
established: that there has been a large expulsion of silica by
earbonie acid; that a notable enrichment of lime has taken place ;
and that the magnesia and total sesquioxides (largely iron) have
practically remained constant.

It has already been pointed out that in thin section the silica-
earbonate rock often presents a highly unique and characteristic
structure, due to an anastomosing system of carbonate capillaries
enclosing discrete eye-like areas. These small lenticular areas are
composed of allotriomorphie carbonate, or spherulitic chalcedony,
or both together.

The carbonate veinules possess a fibrous structure, the fibres
not being continuous across, but growing from both walls toward
the center. The center line is occupied by yellow iron oxide,
which frequently extends in between the carbonate fibres, thus
producing a sort of stiff, orthogenal dendritic structure. The
above phenomena represent a pseudomorphie replacement of a
schistose serpentine, the carbonate capillaries occupying the

430 University of California Publications. [ GEOLOGY

foliation partings produced by movement consequent upon vol-
ume expansion during hydration.

The production of the silica-carbonate rock, then, illustrates
an extensive case of hydro-metamorphism, effected by solutions
highly charged with carbon dioxide, and carrying calcium ear-
bonate and metallic sulphides.

University of California,
May, 1906.

UNIVERSITY OF CALIFORNIA PUBLICATIONS

BULLETIN OF THE DEPARTMENT OF

GEOLOGY
Vol. 4, No. 19, pp. 431-462, Pls. 42-51 ANDREW C. LAWSON, Editor

THE GEOMORPHOGENY

OF THE

TEHACHAPI VALLEY SYSTEM.

BY

ANDREW C. Lawson.

CONTENTS.

PAGE

TERA Gre{ 6 6 EDLCL V0 1 ie greeter eee nN OS eI PS ye ee 431
Tehachapi Valley ................. Sosa aiendeced ieee ses ue sareeteseceeeseeascemteasceeetAca Statens Focus lem 432
Greneralimulea tt ess 26 ee fe ee nee Pa een en Seen ee eee ree eee 432

RS GTEC 21010 9 i ee cae ae ee ea ce a te 432
PAN Munya 2101 0 30 Spee i ce ee as es eS AS ee oe ee 433

ES Oi 2 GE Cie EVI S pieces cence tc reece. seer sneer ese enone RO dR ene ee 435
Jayerangnliats: (oe 7 Wilhaaahaevoyiay eee ee 436
Rocks of Surrounding Mountains 2202000 437
@utlets of Dehachapi Valley 2 eee eects eee eee 438
PACGLEVS ELOWIN abl O Duets ese ele nse ea es oo 440
SBE WaM Se) AVON eraN rat tS} Me toe So oe eR Nc 441
Chalks Ionia poi 92 ee en 441
AWGN KO ney oM Ilo feae none oe ee 443

(2 lameyti0 pecs eee ace eee ee SCORE Soin asa ae 445
Dissection and Reversal of Drainage 20000 447

MWleneiite) (Cron eVov OLR 5c ee
Western Boundary of Valley
Geological History
Brites Valley
Cummings Valley
Bear Valley

INTRODUCTION.

At the southern end of the Sierra Nevada there are certain
high valleys, situated about 4000 feet above sea level, which, by
reason of their abnormal position, their peculiar drainage, their
large dimensions, and their discordant relation to their geomor-
phic environment, invite geological inquiry as to their genesis.

432 University of California Publications. [GEOLOGY

The largest of these valleys is Tehachapi, and, as it forms the
pass over the mountains for the railways connecting the Great
Valley with Southern California, it was the first to attract the
attention of the writer. An attempt to get familar with its
features led to the discovery, however, that it was but one of a
system of similar valleys which characterize the region. In the
country to the west of Tehachapi lie Brites Valley, Cummings
Valley, and Bear Valley. It is the purpose of this paper to give
a brief descriptive account of these valleys, to indicate something
of their geological history and in so doing suggest at least a
partial explanation of their rather unique features.

TEHACHAPI VALLEY.

General Features.—Tehachapi Valley is situated on the sum-
mit of that portion of the Sierra Nevada which les between the
southern end of the Great Valley and the Mohave Desert. Its
extent from east to west is about 12 miles. Its breadth in its
middle part, at the town of Tehachapi, is about 44 miles. At
its west end it is 6 miles wide and at its extreme east end it
narrows to about half a mile. It has thus in ground plan the
form of a right angled triangle, the right angle being at the
southwest corner of the valley. Its area is about 36 square
miles.

The boundaries of the valley are for the most part bold.
mountain slopes, which rise to crests at no great distance from
the valley. The area of the hydrographic basin in which the val-
ley lies is about 130 square miles. From this statement it will
be apparent that the streams which flow into the valley from
the surrounding mountains are small. The annual rainfall is
103 inches.

Strcams.—Of these streams the two largest are on the north
side of the valley toward its east end, and are known as Cache
Creek and White Rock Creek. Both of these enter Tehachapi
Valley through trumpet-shaped side valleys, which in their stage
of geomorphic advancement and in their degree of alluviation
are seemingly homologous to, and harmonious with, the main
valley to which they are tributary. These tributary valleys are
of the nature of embayments in the monntains on the south, and,

O

BULL. DEPT. GEOL. UNIV. CAL. VOEP aR 42

Limit sof
this—orea—of racks
Bre mei ty congtteraye

a |

Mountainous Early Tertiary Atlas i Alluviated
Slopes of the Sandstones Tank Forma-_ Valleys.
Bed-rock Complex. and tuffs. Cable tions.

Tehachapi

Physiographic Sketch Map of the Tehachapi Valley System showing their relation to the Great Valley and to the Mohave Desert.

Scale: 1 inch=4 miles.

oe SEE Se RW os ipa oly 4 ee

i
:
}
i
ji 4

-

VoL. 4] Lawson.—Techachapi Valley System. 433

as their floors are accordant with the floor of the main valley,
they cause the ground plan of Tehachapi Valley to have in this
part a distinctly indentate contour. There are three notable
streams entering the valley from the high sharp mountain ridge
which forms the southern boundary of the valley in its western

part. These are from west to east, China Hill Creek, Antelope

Creek, and Blackburn Creek. These three creeks are in marked
contrast to Cache Creek and White Rock, Creek on the south
side. They emerge upon Tehachapi Valley through narrow
rocky gorges, whose bottoms are not yet cut down to the level
of the main valley floor, and the alluvial fans which they have
built up apex wholly outside of the mountain pass, within the
confines of the valley. These canons are so narrow that they
effect no appreciable indentures in the ground plan of the valley
boundaries, and the mountain front is here remarkably even
and straight, as well as steep.

Alluviation.—The floor of Tehachapi Valley is for the most
part a surface of alluviation, and appears to the cursory glance
uniformly flat. Unfortunately the region has not yet been
topographically mapped and we have, therefore, no exact meas-
ure of the slopes of this apparently flat floor except such as are
afforded by the railway levels. The altitude at Tehachapi station
is 3963 feet; at the summit, 2 miles to the east, it is 4025 feet;
and at Sullivan’s, 34 miles from Tehachapi, it is 3980 feet. These
figures give the altitude of the central part of the valley along
its north side, which is the lower side. From the line of the
railway the floor of the valley slopes up to the south on the sur-
face of the confluent alluvial fans of China Hill, Antelope and
Blackburn Creeks. In the eastern part of the valley, on the
contrary, the alluvial fans of White Roek and Cache Creeks from
the north dominate the slope of the valley and cause its lower
part to be on the south side.

Between the alluvial fans of these two creeks there is on the
south side of the railway a saline lake, the expanse of which
varies with the season, but which at its largest is less than a
square mile in area. This lake receives the waters of White
Rock Creek. The waters of Cache Creek are sometimes shed
down the west side of its fan to the lake and at other times to

434 University of California Publications. [GEOLOGY

the east side out through the rocky gorge at Cameron to the
Mohave Desert, the position of the stream upon its fan being
unstable and fluctuating. Usually the lake has no outlet and
the waters are strongly saline. It is said that deposits of salts
have been worked in the clays which underlie the lake to a depth
of 8 feet. Occasionally, however, the lake appears to overflow
around the lower edge of the Cache Creek fan into the gorge
leading out to Mohave.

The depth of the alluvial infilling of the valley is not known.
Certain wells that have bene sunk indicate that it is by no means
a Shallow veneer. A well sunk for water on the railway about
three-quarters of a mile above Cameron at the extreme east end
of the valley passed through 125 feet of alluvial gravel, sand,
and clay without reaching solid rock. On Spencer’s ranch a well
was sunk for water on the northwest quarter of Section 34,
Tp. 828., R. 33 E. This well is said by the driller to have passed
through 10 feet of black clayey loam, then 125 feet of yellow
clay with fine gravel, and then through 30 feet of gravel with
coarse boulders at the bottom up to 10 inches in diameter. At
this depth no water was found and for practical reasons the
well was abandoned. Another well was sunk in the immediate
neighborhood, to a depth of 344 feet through gravelly sandy and
clayey alluvium, water being found at a depth of 248 feet and
rising in the well to within 120 feet of the surface. In this well
very few pebbles were found larger than one’s fist and only
rarely was a boulder found as large as a man’s head. The
writer visited the well and examined the material that had been
taken from it. The well is situated less than a mile north of
the base of the steep mountain slope which bounds the valley
on the south. We have thus in the record of this well evidence
that the alluviation of the valley reaches a depth of not less
than 344 feet. Several wells have been sunk in the town of
Tehachapi, and these are said to yield water first at a depth of
35 feet and again at about 90 feet below the surface. One well,
however, is said to have been sunk to a depth of 166 feet, mostly
in clayey alluvium with gravel at the bottom. The alluvial floor
of the valley is in part suitable for cultivation, and the greater
part of it is fenced for ranch purposes, but there are probably

BULLE DERI GEOEP UNIV.CAIE VOL, 4; PL. 43

A. Looking west across Tehachapi Valley from the east end. Saline
Jake in the foreground.

B. Southwest corner of Tehachapi Valley. Looking southwest toward

the barrier which separates Tehachapi and Brites Valleys across
the alluvial cone of China Hill Creek.

Vou. 4] Lawson.—Tehachapi Valley System. 435

not more than a dozen ranchers actually engaged in the cultiva-
tion of the soil. Portions of it are, however, utilized as cattle
ranges.

Another indication of the volume of alluvium in the valley
is afforded by the dissection of the alluvial cone of Antelope
Creek at its apex. Here Antelope Creek has greatly deepened
its rocky gorge within the mountains since the apex of the alluvial
cone was established, and this deepening of the gorge has necessi-
tated the dissection of the cone. The extension of the gorge
through the apex of the fan reveals a section of alluvium 250
feet thick above the stream. In the vicinity of the apex of the
China Hill alluvial cone a much greater thickness may be
inferred. Here the coarse gravels of the upper part of the cone
have been hydraulicked for placer gold.

Isolated Hills ——An interesting feature of the valley floor is
the occurrence of certain isolated rocky hills which project as
island-like masses through the alluvium. There are two such
hills of prominence, both on the north side of the valley and
both composed of the granitic rocks of the surrounding moun-
tains. One of these lies to the northeast of Tehachapi and less
than a mile distant from the town. It rises to an altitude of
perhaps 100 feet above the surrounding plain as a rugged more
or less conical mass of bare rock. The other is at the east end
of the valley and lies at its confluence with the wide-gaping tribu-
tary valley of Cache Creek. It is surrounded by the alluvial fan
of that creek, the stream, which is now to the east of the hill,
having formerly flowed to the west. The hill is about half a
mile in length from north to south and about half as wide at its
base and it is probably not less than 200 feet high, its bare rocky
precipitous slopes being in striking contrast to the surrounding
alluvial plain. The isolation of these hills from the neighboring
mountain slopes affords additional suggestion as to the great
depth of the aliuvial infilling of the valley, and indicates some-
thing of the irregularity of the rock surface upon which the
alluvium, in parts of the valley at least, rests. The best actual
exposure of alluvium of the valley floor which came under the
writer’s observation was that afforded by a trench at the extreme
eastern end of the valley at from one-half to three-quarters of

436 University of California Publications. [GEOLOGY

a mile above Cameron station. The trench is a new feature of
the topography and was cut by the exceptionally heavy run-off
due to the rains of the winter of 1904-5. The trench is 13 feet
deep below the floor of the valley. In the bottom of the trench
there is exposed a dark gray or drab-colored, stiff clay with
remains of plant stems in it, to a thickness of 3 feet. Upon this
clay with a sharp horizontal contact rests 10 feet of the ordinary
alluvium of the valley, consisting of light colored granite sands
with lenses of gravel. The contrast of this sandy and gravelly
alluvium with the underlying stiff clay is significant of a change
in the conditions of deposition. This contrast is the more signifi-
cant when it is stated that the exposure occurs in the narrowest
part of the valley, practically in its outlet to Mohave, the width
of the floor here being only 200 yards, between steep rocky walls.
It would be interesting to know the thickness of the clay, but
unfortunately this could not be ascertained.

Remains of Mammoth.—About a mile and a quarter to the
westward of Tehachapi station on the line of the railway, certain
trenches were cut by the Southern Pacifie Railway Company for
the purpose of developing a supply of water for one of their
tanks. In this work a large bone was found and was forwarded
to the University of California by Mr. de Heur, the resident
engineer of the company at Bakersfield. The bone has been
identified by Professor J. C. Merriam as the tibia of a mam-
moth.* The writer subsequently visited the locality under the
euidance of one of the workmen who was present when the bone
was found. The trench is now boxed in, but enough of the section
was seen to establish the fact that it cut through about eight
feet of black adobe clay, then through three feet of yellow clay.
This yellow clay rests upon gravelly alluvium, the rock frag-
ments of which are angular and little water worn, and range in
size from minute fragments with sand up to pieces the size of
one’s fist. The depth of this gravelly alluvium is not revealed.
The mammoth bone was found at a depth of between 11 and
12 feet, or just below the yellow clay. The yellow clay and the
eravelly alluvium represent with little question the lower edge

* This is now in the Collection of Vertebrate Palaeontology, Univ. Calif.
Accession No. 9842.

VoL. 4] Lawson.—Tehachapi Valley System. 437

of the China Hill Creek cone. But the black adobe clay is the
product of more recent accumulation, under marshy conditions,
due to springs, on the narrow flood plain of the modern creek
where it has trenched the cone.

Rocks of the Surrounding Mountains —The prevailing rocks
of the mountains which eneirele Tehachapi Valley, as well as the
other valleys to the west of it which are described in this paper,
are those of the Bed-rock Complex of the Sierra Nevada. They
comprise a series of metamorphic rocks, represented chiefly by
erystalline limestones and mica schists with quartzites, and vari-
ous plutonie irruptives of granitic habit which have invaded the
metamorphic series. The limestones occur in isolated patches in
numerous localities and appear for the most part to be large
inclusions which sank down into the granite when the latter was
viscous. The mica schists occur in more persistent belts of no
ereat width. Both limestones and schists have a persistent north
and south strike with easterly dip at angles of from 45° to 60°,
though sometimes vertical. The granitic rocks, however, greatly
preponderate throughout the region, and constitute the great
bulk of the mountains. The limestone is quarried at a number
of localities, but most extensively at the mouth of Antelope
Canon to the south of the town of Tehachapi where it is burnt
for lime.

The superjacent series of the northern portion of the Sierra
Nevada is represented in this region by two formations of strati-
fied rocks, which rest uneonformably upon the Bed-rock Com-
plex. The lower of these is well exposed in the middle and
upper parts of the tributary valley of Cache Creek. It consists
of a great volume of coarse arkose sandstones and conglomer-
ates with some thin beds of sandy shale. On the northwest side
of the middle part of Cache Creek they dip at an angle of 60°
to the southeast, and their superposition upon the granite is well
exposed. On the east side of Cache Creek these sandstones
appear to dip to the northwest and to strike to the northeast,
curving around the granite traversed by the creek in its lower
part. In certain of the shale beds referred to there are abundant
fossil leaves in a good state of preservation, and their oceur-
rence here renders it probable that the formation is a fresh-water

438 University of California Publications. [GEOLOGY

deposit. The age of the beds is not known but it is probable
that they are early Tertiary. The second formation of stratified
rocks is well exposed in the vicinity of Sullivan’s station and
thence up White Rock Creek. It is probably stratigraphically
above the sandstone and conglomerate formation of Cache Creek
but this was not certainly determined. The formation is almost
wholly made up of regularly stratified voleanic tuffs and agglom-
erates, well cemented, but there are with these near Sullivan’s
station some beds of greenish gray sandstone which may be com-
posed only in part of voleanie ash. These stratified tuffs and
agglomerates he in a well marked synecline, the axis of which
pitches to the northeast. The formation lies chiefly in the coun-
try between White Rock Creek and Cache Creek, but the nose
of the syncline above referred to crosses White Rock Creek,
toward the west, and in this direction one passes in a few hun-
dred yards from the tuffs to the underlying rocks of the Bed-
rock Complex. The dip of the strata on the southern lmb of
the syneline, near Sullivan’s, is from 25° to 30°.

The most interesting feature of these superjacent formations
is their degree of deformation, and the evidence that they thus
afford that orogenic movements have occurred in the southern
end of the Sierra Nevada which seem not to have affected the
same series in the middle and northern part of the range. That
is to say, while the superjacent series in middle and northern
California have been profoundly faulted by the movements
which gave rise to the Sierra Nevada tilted block, there appears
to have been no folding of such rocks; while here on the north
side of the east end of Tehachapi Valley the evidence of flexure
is marked.

Outlets of Tehachapi Valley—Perhaps the most remarkable
feature of Tehachapi Valley is the fact that it has two outlets.
Both of these are incisive stream gorges cut in the granite rocks
of the Bed-rock Complex. One drains the western portion of the
valley to the Great Valley and is occupied by Tehachapi Creek
which leaves the valley at its northwest corner. The other drains
the eastern part of the valley to Mohave Desert. The Tehachapi
Creek gorge has a higher grade than that leading out to Mohave,
carries more water and is more sharply cut. The cafion draining

VoL. 4] Lawson.—Techachapi Valley System. 439

out to Mohave is wider in its bottom, carries little water except
during heavy rains, and in its upper part is encumbered with
stream gravels and sands. In its lower part, however, the grade
becomes too steep for this stream drift to linger on the cafon
floor and the stream runs on bed rock. On the whole, the
Mohave outlet of the valley presents a more mature aspect than
the gorge of Tehachapi Valley. The divide between these two
drainages lies in the nearly flat, expansive, alluviated floor of
Tehachapi Valley near its middle part. The explanation of this
anomalous drainage must be deferred till certain other features
of the geology of the valley are presented.

Although the fossil leaves of the sandstones and shales of
Cache Creek indicate that they were laid down in a fresh-water
basin, it is not supposed that this basin had any structural rela-
tion to the present Tehachapi Valley. The Cache Creek beds
are apparently much more extensive to the northeast than the
limits of the valley in that direction. Cache Creek Valley, more-
over, is a valley of erosion cut in part out of the sandstone
formation. As will be seen later there is ground for believing
that Cache Creek Valley, as a geomorphie feature, probably ante.
dates the main Tehachapi Valley. The tuffs and agglomerates
of White Rock Creek are probably of about the same age as
the sandstones and were doubtless laid down in the same basin.

In the northwest corner of Techachapi Valley, however, there
is a group of formations which seem to have a somewhat more
intimate relation, as regards their basin of accumulation, with
the present Tehachapi Valley. These formations will be first
listed in the order of age and their characters and relationships
will then be brietly reviewed:

1. An Ancient Alluvium, here designated the Atlas Forma-

tion.

2. <Andesitic lava flows and tuffs, here designated the Tank
Volcanics.

3. Fresh-water lake beds, here designated the Cable Forma-
tion.

4. Post-lacustrine alluvium, here designated the Tehachapi
Formation.

440 University of California Publications. [ GEOLOGY

Atlas Formation.—tThis formation is known from three ex-
posures, one at the nose of the ridge one mile west of Tehachapi
station on the north side of and immediately adjacent to the
railway; another in the eut one-eighth of a mile below Cable,
just north of the steel bridge; and the third in the bottoms of
certain canons tributary to Tehachapi Creek on the east side of
the railway and about midway between Cable and Tehachapi
stations. In all three of these exposures the formation has the
same characters and the same stratigraphie position. It is made
up of angular fragments of rocks of the Bed-rock Complex
including schists, quartz-diorite, granite, ete., pieces of quartz
and considerable granite sand or arkose. The fragments are
frequently from 6 to 12 inches in diameter but are prevailingly
less than 6 inches across. This aggregate presents the normal
characters of a typical alluvium, such as is deposited at the
mouth of a high grade, short mountain stream. This alluvial
debris has been well cemented; but since its cementation it has
been thoroughly decomposed, so that the blocks and smaller
fragments of the erystalline rocks are now soft and incoherent
and crumble under the pressure of the fingers. Independently
of the stratigraphic position of this formation, it is easily recog-
nized and distinguished from other alluvial accumulations of the
region by these two characters: viz: 1ts cementation and its de-
eayed condition. In the railway eut one-eighth of a mile below
Cable, near where one enters the rocky Tehachapi canon, there
are exposed 12 feet of this formation. Above it and resting strat-
igraphically upon it are 3 feet of yellowish white volcanic tuff;
and above this there is a thick sheet of andesitic lava. There
is no doubt, therefore, that the alluvium antedates the only vol-
canie rocks that are known in the region.

The same relations are revealed in the canons east of the
railway between Cable and Tehachapi. Here the streams have
eut down through stratified tuffs into the Atlas Allauvium which
is thus revealed to a thickness of perhaps 30 feet.

The thickest exposure of the formation is the first one men-
tioned at a point about a mile west of Tehachapi station. Here
there are about 50 feet of the formation shown in the railway
cut and in the adjacent steep slopes. <A little beyond this point

VoL. 4] Lawson.—Tehachapi Valley System. 441

on the railway grade there is exposed an area of 20 or 30 acres
of andesitie lava which probably overlies the decomposed allu-
vium. The entire absence of fragments of lava in the alluvium,
although carefully looked for, is in accord with this interpreta-
tion which is, however, based on independent structural evidence.

Tank Volcanics—These rocks are best exposed in the vicinity
of the railway tank which is situated about 2 miles below
Tehachapi station on Tehachapi Creek. The lava is exposed
over an area of 20 or 30 acres with a slope of 5° to the west and
a vertical range of about 150 feet. Its relations here are not
as well revealed as in other localities, but it appears to rest
in part upon the Atlas Alluvium mentioned above, and is cer-
tainly below the Tehachapi formation. The Cable formation is
not here exposed.

Another occurrence of the lava is on the west side of
Tehachapi Creek to the west of the high ridge, composed of the
Cable and Tehachapi formations, which is situated southwest of
Cable station. Here the lava rests upon an old surface of the
Bed-rock Complex composed of granitic rocks, schists and
erystalline limestone and is clearly stratigraphically below the
easterly dipping beds of the Cable and Tehachapi formations. A
third occurrence has already been mentioned in speaking of the
exposure of the Atlas Alluvium below Cable. Here it was stated
that the Atlas Alluvium was overlain by a bed of yellow tuff
and a thick sheet of andesitic lava. The same section shows very
clearly the superposition of the Cable lake beds upon the sheet
of andesite.

The tuffs and agglomerates which le upon the Atlas Allu-
vium in the country between Cable and Tehachapi station are
without question to be correlated with the lava as part of the
same voleanie extravasation. These voleanics as has been shown
are clearly above the Atlas Alluvium; but they are no less clearly
below the Cable lake beds which are well exposed by the same
dissection as that which has revealed the underlying beds.

Cable Formation.—The rocks of this formation are best ex-
posed in the vicinity of Cable station on both sides of the canon
of Tehachapi Creek. They comprise limestones, cherts, gravels,
clays, and fine light colored volcanic tuff. These rocks are for

442 University of California Publications. [GEOLOGY

the most part well stratified and have a thickness which is esti-
mated at about 250 feet. Where the base is exposed, the forma-
tion rests in some places upon the Tank Andesite, as on the
west side of Tehachapi Creek below Cable, in some places on a
coarse agglomerate made up of andesitic fragments, and in other.
exposures directly upon the rocks of the Bed-rock Complex. In
every case where it is exposed it is overlain by the alluvium of
the Tehachapi formation. The limestones are cherty and contain
fresh-water molluscan remains such as species of Planorbis and
Physa in a good state of preservation. The clays are more or
- less admixed with fine voleanic ash and in such beds there are
often remains of roots and stems which have been thoroughly
silicified. Not only are the limestones cherty but they pass along
the strike into beds which are composed almost wholly of evenly
stratified light colored to white cherts. These cherts outcrop
rather boldly and as they occur near the base of the series they
facilitate the delimitation of the area of the formation. The
pebble beds are not more than a few feet thick and are composed
of smoothly rounded pebbles of small size. These beds of course
indicate shallow water conditions and proximity to the shore
line of the lake. The occurrence of voleanic ashes in the clays
and as distinct beds may indicate a survival into the lacustral
period of the voleanie activity, which gave rise to the pre-lacus-
tral and underlying Tank Voleanies; but it may also be explained
as due to the erosion of these earlier voleanic deposits. To the
east of Tehachapi Creek these fresh-water beds strike southeast
from Cable and dip southwest beneath the overlying Tehachapi
alluvium at angles varying from 12° to 20°, for a distance of
nearly 3 miles, beyond which the outcrop can no longer be fol-
lowed with certainty. The strike at the point where the outcrop
ends probably swings around to south and follows the lower east
flank of the ridge extending toward Tehachapi station. To the
west of the creek below Cable they dip southerly and thence
going south the strike swings around to north and south with
an easterly dip and at a point about a mile north of Cable sta-
tion the dip of the beds is vertical. About three-quarters of a
qnile southwest of Tehachapi station near the cemetery there is
an outcrop of calcareous clays from beneath the Tehachapi

BUEE DEPT: GEOL UNIV] GAL VOL, 4, PL. 44

The fresh-water limestones of the Cable Formation, south of Cable.

VoL. 4] Lawson.—Tehachapi Valley System. 443

alluvium. These clays are probably a portion of the fresh-water
formation and if so, they indicate a northerly dip of the forma-
tion.

It thus appears that the Cable fresh-water beds he in an
asymmetric synelinal trough, the nose of which is situated below
Cable at the point where the strike changes its course from
northwest and southeast to north and south. An interesting
fact indicating at onee the former extent of the lake beds and
the nature of the deformation to which they have been subjected
is the occurrence, on a spur of the mountains to the north of
Tehachapi, at a point about 2 miles north of the station, of an
outlying patch of cherts plastered as it were on the face of the
mountain slope, the dip of the beds determining the angle of
dechivity. The projection of these beds to the northeast would
earry them over the entire southerly slope of the mountains on
this side of the valley.

Tehachapi Formation—In the trough above indicated lies a
great body of coarse alluvium, the Tehachapi Formation, repos-
ing upon the Cable fresh-water beds and having approximately
the same areal distribution as those beds. It is well exposed in
many steep slopes and railway cuttings in the canon of Tehachapi
Creek above Cable. In these exposures it is seen to be composed
of a coarse aggregation of rock fragments such as is usually
found near the apex of the alluvial cone of a steep-grade stream.
These rock fragments are in a fresh undecomposed condition
and are but slightly cemented together so that separate blocks
may be detached from the aggregate with ease. These materials
comprise, not only granite rocks, schists, Lmestone and quartz
of the Bed-rock Complex, but in certain portions of it there are
numerous blocks of the Tank Andesite. In the lower part of
the formation where it rests upon the uppermost beds of the
Cable formation, the rock fragments are comparatively small,
masses the size of a fist and less predominating and there is a
considerable admixture of sand. Here the material is rudely
stratified and where the contact is exposed in the railway cuts
above Cable the dip of this stratification is the same as that of
the underlying lake beds, about 12° to the southwest. In the
higher parts of the formation the angular blocks of which it is

444 University of California Publications. [GEOLOGY

composed are much larger in size and in the highest portions
spauls of rock 10 feet in diameter are occasionally met with while
masses from 3 to 5 feet in diameter are quite common. In gen-
eral, stratification is not apparent throughout the formation even
in excellent exposures except at its base, as above mentioned,
and it is difficult to estimate its thickness. Some idea of its vol-
ume may be obtained, however, from the fact that the highest
part of the formation is 350 feet above the level floor of the
valley at Tehachapi Station and assuming a gentle syncline for
the structure of the formation as a whole this figure may be
taken as a value for its thickness.

This thick accumulation of coarse alluvium is the record of
an important event in the diastrophic history of the southern
Sierra Nevada. It is considered by the writer to have been,
anterior to its deformation and degradation, a great cone such
as is found commonly where high grade streams emerge from
narrow mountain canons and spread out abruptly upon a lower
erade valley. Their situation is always along lines of geomor-
phie discordance, or where the geomorphic features of the moun-
tain are completely out of harmony with those of the adjacent
valley from the point of view of erosional evolution. Such situa-
tions are produced by faulting or by other acute deformation of
the region, whereby the mountain mass has been uplifted rela-
tively to the valley. Occasionally a trunk stream may flow in a
canon which has been overdeepened relatively to its tributaries
and the conditions may in such cases be favorable for the devel-
opment of alluvial cones at the mouths of the hanging valleys.
These conditions, however, are most commonly found in glaci-
ated regions, and even then the geomorphic discordance between
the overdeepened cation and the tributary hanging valley is
slight compared with that which obtains between the recently
uplifted mountain ranges and the broad diastrophic valleys
which parallel them in Southern California and in Nevada.

On the assumption which is here made of the strictly
fluviatile origin of the Tehachapi formation it is evident that an
acute deformation of the region occurred at the close of the Cable
lacustral period, and caused a rapid dejection of coarse moun-
tain detritus into the basin formerly occupied by the lake from

VoL. 4] Lawson.—Tehachapi Valley System. 445

country where no high grade streams had previously existed. It
is noteworthy, moreover, that the position of this coarse alluvial
material, in the northwest corner of the present Tehachapi Val-
ley, establishes the fact that its souree was in the mountains to
the south. In other words, it is clear that at the time of the
accumulation of this great alluvial cone the drainage was from
the north, and was approximately, in part, along the line of the
present deep canon of Tehachapi Creek which flows from south
to north. The present drainage then, to the Great Valley of
Jalifornia has a direction which is the reverse of that which
formerly obtained along the same general course. This fact is
one of prime significance in any attempt to explain the present
dual outlet of Tehachapi Valley.

But while it is clear that orogenic movements inaugurated
the accumulation of the great cone, it is no less clear that
orogenic movements subsequent to its upbuilding have deformed
it. What is left to-day of the great cone is but a remnant of
its original mass and extent. It now lies in a synelinal trough.
Whenever its base is exposed it reposes upon the Cable lake
beds and the rude stratification of the lower part of the forma-
tion where exposed above Cable Station is parallel to that of
the lake beds. It probably nowhere extends at present beyond
the rim of the synelinal trough formed by the lake beds. It
certainly does not in the numerous and often persistent expos-
ures where the two are seen in juxtaposition. The lake beds are
nowhere horizontal but dip in all observed cases for several
miles of outcrop on different sides of the trough under the
alluvium, and on the west side of the trough they are well ex-
posed in one locality in a perfectly vertical attitude. It is evi-
dent then that the whole body of the alluvium has been subjected
to the same measure of deformation as that which can be made
out clearly from the attitude of the underlying regularly strati-
fied lake beds.

Planation.—Sinee its deformation the Tehachapi alluvium
has been broadly terraced by stream action, the terrace has since
been deeply dissected and the mass has otherwise been degraded
by the forces of erosion. The broad terrace which truneates a
large proportion of the total area of the formation is a most

446 University of California Publications. [ GEOLOGY

interesting feature of the geomorphy of the region. The terrace
is not confined to the alluvial formation, but extends, as a broad
even plain, indifferently across the alluvium, the soft beds and
hard cherts of the Cable formation, and the schists, limestones
and granite of the Bed-rock Complex. The terrace slopes down
to the south at a low angle. Its expanse increases also in this
direction and it eventually passes beneath the present floor of
Tehachapi Valley where it meets the opposite slope of the China
Hill alluvial fan. The terrace becomes constricted to the north,
and leaving the valley it passes into the mountains, which lie on
this side of the valley, in the form of bench-like remnants high
up on the eastern slope of Tehachapi cafion. Just before passing
into the mountains north of Cable, it is bounded on the west for
a short distance by a sharp residual ridge of the Tehachapi
alluvium. Beyond the south end of this ridge, however, the ter-
race extends over to the steep, rocky mountain slope which forms
the western boundary of the valley. On the east side of the
railway above Cable, the stream which carved the terrace, in
the course of its meandering and lateral corrasion, cut an embay-
ment over a mile in breadth out of the main mass of the
Tehachapi Alluvium. This embayment is bounded on the east
and south by a relatively high semicircular residual ridge of the
alluvium. This semicircular ridge, together with the similar
residual ridge on the west side of the railway nearer Cable, are
so disposed as to give these prominent residuals of the Tehachapi
alluvium the configuration of a terminal moraine. This super-
ficial resemblance to a moraine is enhanced by the numerous
spauls of rock of considerable size which weather out of the allu-
vium and lie strewn over its surface. The facts above cited
prove, however, that the resemblance to a moraine is quite super-
ficial and accidental as regards at least its form.*

It has been pointed out that the source of the materials for
the Tehachapi Alluvium was probably in the mountains to the

*Tt is to be observed that on the basis of its composition alone there
might be considerable doubt as to whether the Tehachapi formation were
fluviatile or glacial in origin. But as the mountains of the region do not
exceed 7000 feet in altitude, and present no traces of glacial sculpture,
and as the material rests on a non-glaciated surface and is in part stratified,
the writer was forced to reject the glacial hypothesis and interpret the
accumulation as an alluvial cone.

BULE DEPT. (GEOESUINIVa CAL Vi@ ere ea evaet

A. Tehachapi Creek as it leaves Tehachapi Valley near Cable, show-
ing the degree of dissection of the terrace shown in Plate 46.

B. Stream terrace near Cable on the sides of the cafion of Tehachapi

Creek. The terrace slopes up to the north, the direction of the
present drainage.

lord

VoL. 4] Lawson.—Tehachapi Valley System. 447

north of the present Tehachapi Valley, these materials having
been brought to the seat of deposition by a high grade stream
engaged in the rapid dissection of a recently uplifted mountain
block. It has been shown further that the later orogenic move-
ment which deformed the Tehachapi Alluvium was characterized
by a recurrence of the uplift on the north side of the present
Tehachapi Valley. The stream which gave rise to the Tehachapi
Alluvium would, by this second uplift, have had the grade, to
which it had attained, again accentuated. This accentuation of
grade would apply now to the country occupied by the alluvial
cone and the latter would consequently be dissected. The dissec-
tion of the cone would continue till a grade profile was estab-
lished, when the stream would begin to meander and evolve an
ever-widening flood-plain on a stream-cut terrace. This terrace
would be eut out of the alluvium and the rocks adjacent to it
or under it indifferently. The history thus sketched appears to
be that of the broad stream terrace which has been described as
traversing the Tehachapi Alluvium, the Cable lake beds, and the
various rocks of the Bed-rock Complex above Cable.

If this interpretation be correct, then it is clear that the
drainage, at the time that the terrace was functional as a flood-
plain, was from the north and not towards the north as at
present.

Dissection and Reversal of Drainage.—Sinece its completion
the terrace has been deeply dissected and this dissection has been
effected by a northerly flowing stream, the present Tehachapi
Creek which drains into the Great Valley. In the vicinity of
Cable this dissection amounts to 350 feet or more; and in the
tributary creek, which comes in from the left from China Hill,
and which joins Tehachapi Creek about half a mile above Cable,
cutting through granite, schist, limestone, Cable lake beds and
Tehachapi Alluvium, the dissection is about 250 feet in depth.
The valley of this stream where it cuts through the hard rocks
has a width of about 150 feet and in the soft rocks of over
300 feet on its bottom.

Two circumstances seem to have conspired to bring about
the reversal of the drainage above indicated. It has been shown
that the terrace surface slopes to the south and passes beneath

448 University of California Publications. | GEOLOGY

the modern alluvium of Tehachapi Valley, or, more particularly,
beneath the alluvium of the China Hill cone. What its extent
may be beneath this alluvium is unknown but it is clear that
the accumulation of this alluvium upon the southern extension
of the flood-plain would tend to pound back the waters coming
from the north and cause them to seek another outlet if such
were available.

Such an outlet was provided by the headwater erosion of a
stream on the Great Valley side of the mountains. The two
orogenic movements which have been recorded as affecting the
mountains in this direction greatly accentuated the grade of the
streams on the north side of the divide, and one of these, the
present Tehachapi Creek, caused the divide to migrate southerly
till it reached the terrace of the southerly flowing stream, and
not only effected its capture but provided an outlet for its
beheaded portion, the waters of which, in greatly diminished
volume, were obstructed by the excessive accumulation of allu-
vium upon its flood-plain. The question now arises as to the
cause of this excessive accumulation of alluvium. The answer
to this question is very pointedly suggested by a consideration
of the geomorphic features of the region which is the source
of that alluvium. The alluvium all comes from a few sharp,
torrential cahons which emerge, above grade, upon Tehachapi
Valley, from the straight, bold wall of Tehachapi mountain
which forms the western half of the southern boundary of the
valley. The geomorphic discordance which these canons present
to the broad, alluviated Tehachapi Valley is in itself ample
proof of the fact that the mountain mass which they dissect is
a fault block. The northern slope of the mountain is steep and
on the whole not greatly degraded. This face has a regular east
and west trend, transverse to the strike of the schists and lime-
stones which together with granitic rocks make up its mass. The
canons which discharge the alluvium are relatively so insignifi-
cant that they do not greatly notch the longitudinal profile of
the mountain and their mouths can scarcely be perceived at a
distance of a few miles. If such evidence that the face of the
mountain is a degraded fault scarp were not sufficient, more
direct evidence may be observed at the point where Antelope

Dissected stream-cut terrace at the northwest corner of Tehachapi Valley sloping down from the outlet to the valley floor.

Vou. 4] Lawson.—Tchachapi Valley System. 449

Creek emerges upon the valley. Here it is apparent that the
apex of the alluvial cone which spreads out from this point across
the entire breadth of Tehachapi Valley was established when the
rock bottom of the ereek within the mountain was much higher
than it is at present. The cafion bottom has been corraded down
to a depth of 250 feet below the apex of the cone and this deep-
ening of the rocky cafion has necessitated the dissection of the
higher part of the alluvial cone. There is thus exposed in the
walls of the cafion the contact betwen the buried face of the
mountain and the alluvium which reposes against it through a
vertical range of 250 feet. This contact, while not absolutely
vertical, is so nearly so that the rock surface against which the
alluvium rests can be interpreted only as a fault scarp. That is
to say, it is the lower portion of the general fault scarp of the
mountain front which has been preserved by burial from the
greater part of the degradation which has affected the upper
portion. :

In the recognition of the fault scarp nature of this moun-
tain front we have evidence of a third orogenic movement, and
its discreteness in time from the other two movements, which
have been recorded as affecting particularly the north side of
the present valley, is proved by the fact that the alluvial debris
which was produced by the torrential corrasion of the uplifted
block, was dejected upon the broad terrace which had been in
part cut out of the deformed Tehachapi Alluvium.

Mature Geomorphy.—tlf now we continue our consideration
of the south boundary of Tehachapi Valley into its more eastern
part beyond the portion which has just been identified as a fault
scarp, we come upon a totally different type of geomorphic
expression. Here the valley is bounded on the south by a range
of hills of gently flowing profiles and contours. The hill tops
are flatly rounded and there are no incisive canons dissecting
them. The slope to Tehachapi Valley is not steep and abrupt
but descends as an undulating surface, on the lower parts of
which there are remnants of stream terraces strewn with well
washed cobbles and pebbles. The height of these hills is prob-
ably about 1000 feet above Tehachapi Valley or less than half
the height of the fault block mountain immediately to the west

450 University of California Publications. [GEOLOGY

of it. The edge of these mature hills where they meet the floor
of Tehachapi Valley is not a straight line, as is the case with
the fault scarp to the west, but is more or less indentate and on
the whole sinuous or coneave to the north. It is evident from
the facts cited that we have here to deal with a quite mature
geomorphy which has been entirely unaffected by the disloca-
tion upon which the fault block to the west was uplifted. When
first viewed from a distance the contrast between these two por-
tions of the south boundary of Tehachapi Valley was so striking
that the writer supposed that the underlying rocks must be to-
tally different. But an inspection of the ground showed that this
was not the case. The rocks which underlie the geomorphically
mature hills to the east have the same granitic character as those
which form the bulk of the fault block mountain to the west with
its bold, youthful features. It seems clear, then, that the fault
scarp does not extend eastward beyond the dividing line between
these two contrasted types of geomorphy. It follows from this
that the dividing line between the fault block mountain and the
unfaulted, mature hills immediately to the east of it is a trans-
verse or north and south fault, and that the fault block is tilted
to the west as well as to the south.

Such a mature geomorphy as has been above indicated is
evidently but a remnant of what was once the general condition
of the region, and as this mature surface passes down beneath
the floor of Tehachapi Valley, it is probable that we have beneath
this part of the valley an earlier mature valley of erosion quite
different in its configuration from the modern feature. Towards
the eastern outlet of Tehachapi Valley, the north and south sides
of the valley converge and here the edge of the mature hills is
quite abrupt, but their acclivity appears to be that of a stream |
cliff of a stream no longer functional, whose rocky bed is deeply
buried in the alluvium from Cache Creek.

Western Boundary of Valley—There remains to be noted
the western boundary of the valley. This is a steep mountain
slope of very even and but feebly notched front, except for the
gap into Brites Valley. This as will appear later is the revet-
ment end of a rather narrow fault block and as such has but
little water to discharge to Tehachapi Valley and so has been

BUILE. DEPi “GEOR. OUNIV, CAE. VOL. 4, f

A. Degraded fault-scarp forming the western half of the southern
boundary of Tehachapi Valley.

B. Mature topography of the mountains forming the eastern half of

the southern boundary of Tehachapi Valley.
, ] y

VoL. 4] Lawson.—Tehachapi Valley System. 451

but slightly affected by stream erosion. It can scarcely be
regarded as other than a somewhat degraded fault scarp. The
date of its origin is, however, not quite clear. It appears to
have antedated the broad terrace which lies at its foot, and may
with much probability be referred to the period of orogenic
movement which deformed the Cable Lake beds and _ the
Tehachapi Alluvium, since the western edge of the trough in
which these formations lie is parallel to its trend and the trough
on this side is most acutely deformed so that, as before stated,
the Cable Lake beds and the plane of contact between them and
the overlying alluvium are in vertical altitude. It is probable,
however, as will appear in the sequel, that a second movement
of minor extent took place on this same fault at a later date.

GEOLOGICAL HISTORY.

Reviewing now the data that have been presented, the history
of the evolution of Tehachapi Valley in so far as the writer has
been able to decipher it, in the lmited opportunities at his dis-
posal, may be summarily stated. It is not presumed that the
statement is complete. When the region is mapped and _ its
features are more closely studied it will doubtless be amplified,
and perhaps in some respects modified.

After the profound degradation of the mountain mass which
resulted at the time of the mid-Mesozoic revolution in conse-
quence of the invasion of the region by the Sierran batholith, a
basin of deposition was developed in which accumulated the sand-
stones, conglomerates and shales of Cache Valley, and the tuffs
and agglomerates of White Rock Valley. The basin was prob-
ably lacustrine in character and is probably to be correlated with
early Tertiary lake basins of other portions of the Great Basin.
These lake beds and tufts were folded, but not closely appressed,
and were then largely removed by erosion, the bed-rock surface
upon which they were deposited being in this way in large meas-
ure resurrected and subjected to renewed degradation. The next
event of which we have note is an orogenic disturbance of the
region and the formation of diastrophie valleys bordered by
abrupt mountain fronts. This event is an inference based on
the occurrence of a coarse alluvium. Alluvium of this character

452 University of California Publications. [GEQLOGY

is only known as the product of torrential streams emerging from
narrow high grade canons upon broad open valleys. Such valleys
are geomorphically discordant with the erosional features of the
mountains whence the streams emerge, and such discordance can
usually only be explained as due to diastrophic movements. This
accumulation of coarse alluvium was followed by an outburst
of voleanic activity, which gave rise to showers of ashes and
scoriae and a flow of andesitic lava. Upon the new surface con-
figuration of the region thus established, a lake basin, or possibly
several of them, interrupted the normal course of the drainage.
In this basin there accumulated the Cable formation consisting
of limestones in which fresh water molluses were entombed, beds
of clay, more or less calcareous, and, in the vicinity of incoming
streams, beds of gravel and sand. Interstratified with these
lacustral beds is an abundance of volcanic tuff also for the most
part well stratified. These probably represent the recurrence of
voleanie eruptions during the lacustral period, although they
may also in large part at least, be explained as the product of
the erosion of the surrounding ash mantled country.

This lacustral condition was brought to a close by another
orogenic movement which uplifted the mountains to the north
of the valley in which the lake lay. The lake was displaced and
its deposits were buried under a vast accumulation of coarse
alluvium, the Tehachapi Formation, evidently the cone of a tor-
rential stream actively engaged in the dissection of the new
mountain mass. The source of the alluvium was from the north.

The next event of which we have record is another orogenic
movement which deformed the region both by flexure and fault-
ing. At this time the pre-Cable volcanics, the Cable Lake beds,
and the Tehachapi alluvium, or at least so much of these forma-
tions as are left for our inspection, were together folded in an
asymmetric syncline, the most acute deformation occurring on the
west side of the trough where the beds are now vertical. At this
time the fault scarp which forms the boundary of Tehachapi
Valley on the west was also probably formed. This period of
acute deformation was succeeded by a period of vertical stream
corrasion till the streams attained their base level and then began
to evolve a broad flood plain by lateral corrasion. This flood

BULLE DEPT GEOR UNIV CAL VOE 4, Pies

A. The eastern end of Tehachapi Valley, looking southeast toward

the eastern outlet at Cameron.

B. Looking down the eastern outlet of Tehachapi Valley toward
Mohave Desert from Cameron.

VoL. 4] Lawson.—Tchachapi Valley System. 453

plain was developed as a very notable feature of the region, being
eut across hard and soft rocks alike with great evenness. It is
very probable from our general notions of the conditions which
attend the evolution of stream-cut plains, that this flood plain
stood at a much lower level than its remnants do to-day (4000
feet A. S.). It marks an important datum plane in the evolu-
tion of the Sierra Nevada and is the probable correlative of
the high valleys of the Upper Kern.*

Up to this time there was probably no such feature as the
modern Tehachapi Valley. But now the process of flood plain
expansion was abruptly terminated by another orogenic move-
ment, which besides effecting a general elevation of the region
far above the base level of the streams, also raised Tehachapi
Mountain as a fault block on the south of the present valley
and gave the latter its modern configuration as regards its
boundaries. The uplift of this block caused the dejection upon
the flood plain of the alluvium which forms the greater part of
the floor of the valley. Co-eval with this progressive obstruction
of the drainage on the flood plain, the head waters of its stream
were captured by head water erosion cutting back from the
Great Valley into the upraised mountains. The beheaded stream
was unable to cope with deluge of torrential debris from the new
mountain mass on the south and its course was reversed into
the same stream that had captured its head waters. Since this
reversal of the drainage the flood plain has been dissected.

The geological history of the eastern outlet of Tehachapi Val-
ley is not so complex. The outlet is a rocky gorge so deeply allu-
viated as to give a rather broad bottom (200 yards). If we
imagine the alluvium removed below the depth of certain wells
that have been sunk in it but have not bottomed it, and suppose
the rocky slopes projected down we would have a quite narrow
and somewhat tortuous mountain gorge. This character estab-
lishes the fact that it was not the outlet for the stream that
corroded the broad terrace at the western end of the valley. The
gorge, with its present direction of drainage, could not very well
have been evolved after the present boundaries of Tehachapi Val-

* Geomorphogeny of the Upper Kern Basin, Bull. Dept. Geol. Univ. Cal.,
Vol. 3, No. 15.

454 University of California Publications. [GEOLOGY

ley were established. It must, therefore, antedate the modern
Tehachapi Valley, 7.e., it must antedate the fault block which
forms the south boundary of the western half of the valley. This
being so the gorge must have been coexistent with the stream
which evolved the broad terrace at the west end of the valley,
and if this be coneeded then the gorge was that of a small eastern
affluent of the larger stream. From this line of reasoning we
thus reach the conclusion that the drainage of this outlet was
also at one time toward the area of the present Tehachapi Valley
and that this drainage has been reversed. The causes of the
reversal are doubtless two-fold. The uplift which terminated
the process of flood plain expansion in this region was without
doubt effected by a movement on the great fault which bounds
the Sierra Nevada on the east and southeast and which here
separates them from the Mohave desert. Such a movement
would have beheaded this gorge and have rendered it an easy
matter for the rapidly accumulating alluvium in the now moun-
tain-girt Tehachapi Valley to congest the gorge and cause the
waters to flow out to Mohave.

It thus appears that both of the outlets of Tehachapi Valley
antedate the valley as we know it to-day, and that they are both
cases of reversed drainage brought about by orogenic move-
ments, inducing stream capture and the obstruction of the
beheaded streams by great alluvial cones.

BRITES VALLEY.

Brites Valley opens into Tehachapi Valley at the southwest
corner of the latter through a gap between the fault scarp which
bounds both valleys on the south and the northeast corner of
Bear Mountain. The trend of the valley is northwest and south-
east, in which direction it has an extent of 34 miles. Its breadth
is about 14 miles. Its southern boundary is the western exten-
sion of the same degraded fault scarp as that which bounds
Tehachapi on the south. Its northeastern boundary is a moun-
tain wall with a very straight trend and a steep, even, little
notched slope, which can only be interpreted as a fault scarp,
The bearing of this scarp is northwest and southeast, thus mak-
ing an angle of about 45° with the strike of the rocks. It may

VoL. 4] Lawson.—Tehachapi Valley System. 455

be referred to as the southwest scarp of Bear Mountain. The
western boundary of the valley is a sharp low ridge with north
and south trend which spans the space betwen the two converg-
ing searps above noted. This ridge is composed largely of erystal-
line schists, the strike of which is north and south with the trend
of the ridge. The ridge separates Brites Valley from a larger
valley on the west known as Cummings Valley, which lies at a
much lower level. At the southeast end of the valley a mountain
stream comes in from a gorge in the southern scarp. This stream
has built up an alluvial fan which is co-extensive with the limits
of the valley. The floor of the latter is the surface of this fan
and its general slope is down toward the northwest end of the
valley, where the outflowing waters have cut a gorge down
through the edge of the fan and deep into the underlying bed-
rock, and so find their way to Cummings Valley. Along the base
of the southwest scarp of Bear Mountain, the debris from the
degradation of the scarp interdigitates with the edge of the fan
and being locally dominant reverses the slope.

The gap through which one enters Brites Valley from
Tehachapi is a platform of bedrock or flat-topped ridge between
the two valleys. But over this ridge some of the alluvium from
the fan which fills Brites Valley has spilled into Tehachapi
Valley. <A terrace-like shoulder on the south side of this flat-
topped rocky barrier, where it is crossed by the wagon road is
544* feet above Tehachapi station. The lowest part of the
gap is about 500 feet above Tehachapi station. The floor of
Brites Valley at the farm house at its west side, just before
entering upon the descent to Cummings Valley, is 446 feet
above Tehachapi station. From these figures it will be appar-
ent that Brites Valley is on quite a different level from
Tehachapi Valley, a fact, which, considering their immediate
juxtaposition and open connection, can only be explained on
the hypothesis of their diastrophie origin. The eastern edge of
the rocky platform which separates the valleys is in direct line
with the western scarp of Bear Mountain and we have in this
fact a pointed suggestion that Brites Valley has been dislocated

* This and other altitudes were determined, where not otherwise stated,

by means of a mercurial barometer, using Tehachapi station, elevation 3963
feet, as a base.

456 University of California Publications. [GEOLOGY

from Tehachapi Valley by a movement on the fault which estab-
lished this scarp. The gap which connects the two valleys over
the rock platform is about half a mile wide, and the rock plat-
form is with lttle doubt a surface of stream planation. This
suggestion is confirmed by the section afforded by the gorge at
the outlet of Brites Valley. Here the base of the alluvium may
be seen reposing upon the bedrock surface, and that surface is
again a platform which can only be regarded as a product of
stream corrasion. It would seem, therefore, that, flanking the
southwest scarp of Bear Mountain where it bounds Brites Valley,
there is a stream terrace in large part buried by alluvium. It
seems a fair hypothesis in the absence of any other suggestion to
correlate this stream-cut terrace with the broad terrace already
described as occurring in the northwestern portion of Tehachapi
Valley; and in this hypothesis we have the farther suggestion
that the stream, which evolved the now dislocated and partly
buried terrace, flowed out westward through the present site of
Brites Valley.
CUMMINGS VALLEY.
Cummings Valley les immediately to the west of the sharp

north-south rocky ridge which forms the western boundary of
Brites Valley. It lies at a much lower level than Brites Valley,
the drop from the one valley to the other being rather precipi-
tous. In the northeast part of the valley where the wagon road
to Bear Valley leaves the main road through Cummings Valley,
the altitude is 4056 feet, or 353 feet below the lowest part of
Brites Valley, while in the middle of Cummings Valley the alti-
tude is 3924 feet, or 485 feet below Brites Valley. The general
contour of the valley is that of a trapezium. Its eastern bound-
ary, as already indicated, trends north and south and has a
length of about 4 miles. Its southern boundary is the same east-
west, degraded fault scarp which bounds Tehachapi and Brites
Valleys on the south. This side is also about 4 miles in length.
On the northeast, the southwest scarp of Bear Mountain forms
its boundary for about 2 miles. The fourth side of the valley
is the more or less serrate edge of a mountainous tract which
rises to several hundred feet above the level of the valley on
the west. The trend of this boundary is north-northeast and its

BULLE DEPT. GEOEY UNIV. GAL VOLES a peat

A. Looking east across Brites Valley. Tehachapi Valley in the
> * L ”

distance.

B. Looking southwest across Cummings Valley from near the outlet
of Brites Valley.

VoL. 4] Lawson.—Tehachapi Valley System. 457

extent is 54 miles. The valley thus bounded contains about 13
square miles. There are two principal lines of drainage through
the valley. One of these is a stream that comes into the valley
at its southeast corner from a high grade canon in the mountain
on the south. This stream has built up an extensive alluvial
cone which spreads out over almost the entire valley. The drain-
age from Brites Valley skirts the northwest edge of this alluvial
slope and catches part of thé water that flows down the slope
of the fan. The entire drainage of the valley converges on its
southwest corner and after flowing for a short distance over a
bedrock platform enters a narrow gorge and drops rapidly to
the Tejon Valley. This gorge descends about 2500 feet in a dis-
tance of 4 miles. In the northern part of the valley this alluvial
fan mects the waste slope from the southwest scarp of Bear
Mountain, and it is the trough between these two opposing slopes
which determines the path of the stream from Brites Valley for
the first two miles of its course. Beyond this it is crowded over
well toward the base of the hills on the northwest side of the
valley. The valley thus largely occupied by alluvium is an
artesian basin, and in the middle part of the valley a well has
recently been sunk to a depth of 125 feet which yields a flow
of water at the surface. The mouth of this well is but little
above the rock platform over which the drainage flows before
escaping from the valley. The well, therefore, proves that the
valley, independently of the alluvium which fills it, is a rock
rimmed basin. The rocky platform at the southwest corner of
the valley is a most interesting feature. It extends out from the
base of the hills which bound the valley on its northwest side a
distance of half a mile and appears to pass under the feather
edge of the alluvial fan with a uniformly flat slope, as is indi-
eated by occasional protuberances of rock for some distance
within the area of the alluvium. This platform is interpreted
as a surface of stream abrasion and is correlated hypothetically
with the similar stream-cut terraces above described, in
Tehachapi and Brites Valleys. This platform probably extends
as a flanking terrace, but thinly veneered with alluvium, along
the greater part of the northwest side of the valley. The hills
‘which rise above the valley on this side harmonize with this

458 University of California Publications. [GEOLOGY

supposition. Although rocky slopes, they have a mature aspect,
and the contour of the valley edge is indented with broad, wide-
open embayments separated by narrow ridges or points of rock,
the crests of which pitch down toward the valley and eventually
pass beneath the alluvium. Frequently, off from the base of the
hills, there are isolated knobs of rocks and rocky hillocks rising
from the alluvium like islands. In general, then, the valley is
bounded on this side by geomorphically mature slopes which pass
down, a little below the present floor of the valley, into an uneven
or lumpy terrace, which, however, is well exposed at the south-
western corner of the valley. There is thus no suggestion of
faulting on this side. But such a terrace could not have been
evolved with the present drainage scheme or the present configur-
ation of the valley. It clearly antedates the valley. In its south-
ern extension it abuts upon the fault block mountain to the
south of the valley and it thus appears to have been cut off in
the same way and at the same time as in the case of the stream-
eut terrace of Tehachapi Valley, with which it is correlated.

The sudden drop from Brites Valley to Cummings Valley
would seem to indicate with little question a fault along the
eastern edge of the latter. In general it thus appears that on
three sides Cummings is bounded by fault scarps and that as a
result of the movements on these a geomorphically mature sur-
face, including a stream-cut terrace, now situated at an altitude
of between 4000 and 5000 feet above sea level, and immediately
above the edge of the Great Valley, has been tilted down toward
the southeast, so as to form a rock-rimmed trough, which has
sinee been filled by alluvium, arising from the degradation of
the fault block on the south.

This conception of the character of Cummings Valley involves
the recognition of the fact that, before it became filled to its
present level by alluvium, it must have been occupied by a lake.
Should the central part of the valley, therefore, even be pierced
by wells deep enough to reach its rocky floor it may confidently
be predicted that such wells will pass through lake sediments.
It is questionable whether this lake had an outlet or not. The
present catchment area tributary to Cummings Valley is only
about 45 square miles, or 34 times the area of the valley floor.

BUEE. DEPIW GEOE. UNIVGICAE VOL, 4, PL. 50

A. Fault-scarp forming the northeast boundary of Cummings and
Brites Valleys. Ridge between the two valleys in the middle

ground,

B. Main fault-scarp on the northeast side of Bear Valley, with alluy-

iated fault-terrace in the foreground.

Vou. 4] Lawson.—Tehachapi Valley System. 459

With this limited catchment and an annual rainfall of only 104
inches it seems quite certain, under present climatic conditions,
that the lake could not have attained the expanse necessary for
it to reach the level of the lowest part of the rim of the basin.
Assuming a run-off to the lake of 50 per cent. of the rainfall
for a rocky region such as we have to deal with, and an evapora-
tion of 60 inches per year under a more humid climate than now
obtains, it would require a rainfall of at least 35 inches to enable
the lake to attain the necessary expanse to escape at the present
outlet. Such a rainfall is not an improbability for this end of
the Sierra Nevada during glacial times. But it is to be noted
that the present drainage outlet of the valley is through a gorge
which has been cut down probably 300 feet since the enclosure
of the basin by faulting. To attain this increased altitude for
the original lowest place in the rim of the basin, the expanse of
the lake would be considerably greater than the present area of
the valley floor and the rainfall necessary to effect this would be
correspondingly greater. A further objection to the lake ever
having had an overflow at the original level of the outlet is that
we should expect to find strand lines scored on the sides of the
valley well above its present floor and no such strand lines have
been detected. It seems thus that we are not warranted in assum-
ing that the lake which once occupied Cummings Valley ever had
an outlet, and that the drainage outlet which now exists has been
evolved without the aid of an overflow. The outlet is a gorge
about 300 feet deep at the point where it leaves the valley. Here
the geomorphically mature surface to the north of the gorge abuts
upon the precipitous mountain scarp which bounds the valley
on the south. Where these two surfaces meet there is an asym-
metric notch in the mountain profile which constituted, at the
formation of the valley, the lowest part of its rim. This notch
lay in the line of the fault scarp and could not be missed by
a stream cutting back into the very precipitous mountain slope
which rises from the Great Valley only a few miles distant. Cum-
mings Valley has been tapped, then, by the headwater erosion
of a tributary of Tejon Creek eutting back in a structural ~
trough. A consequence of this conclusion is that the great moun-
tain wall which confines the south end of the Great Valley on

460 University of California Publications. [GroLocy

the east, between Caliente and the Tejon Ranch House, is itself
a fault scarp, and dates from about the same time as the fault-
ing which gave rise to Tehachapi, Brites and Cummings Valleys.

BEAR VALLEY.

Bear Valley lies to the northwest of Cummings Valley along
the base of the southwest scarp of Bear Mountain. Its longer
diameter is parallel to the line of the scarp and is about 3 miles
in extent. The general width of the valley is about 2 miles. Its
area 1s about 6 square miles. The valley is in two levels. Along
the immediate base of the southwest scarp of Bear Mountain is
a well defined terrace about 1000 feet wide mantled by the allu-
vial wash from the scarp which rises steeply at its rear. This
terrace is bounded on the southwest by a rather sharp rocky
ridge which is in general less than 100 feet above the terrace,
and which is notched down to the level of the terrace in a num-
ber of places. On the southwest side of this ridge there is an
abrupt drop to the level of the main floor of the valley. The
latter has an altitude of about 4300 feet at the Fickert ranch
house. The terrace is from 300 to 500 feet above this, its highest
point being at its southwest end where the wagon road from Bear
Valley begins to descend to Cummings Valley. From this cul-
minating point the terrace slopes down to the northwest in the
direction of its extension. It is evident that this remarkable
feature is a fault terrace. It is a narrow strip of the mountain
mass lying between the main fault of the Bear Mountain scarp
and a subsidiary parallel fault, the scarp of which forms the
descent from the terrace to the main valley. The terrace prob-
ably sloped originally down toward the main Bear Mountain
scarp and owed that slope to rotation of the fault-bounded block.
The trough thus formed has since been filled by the debris shed
from the scarp above. In its essential features this narrow fault
block flanking a major fault scarp is identical with the kernbuts*
of the Upper Kern. The main portion of the valley below the
fault terrace is constricted near its middle by a narrow sharp
ridge of small height which projects as a spur from the moun-

* Geomorphogeny of the Upper Kern Basin. Bull. Dept. Geol. Univ.
Cal., Vol. 3, No. 15, p. 331.

Looking down Sycamore Creek from the outlet of Bear Valley to the Tejon Plains.

VoL. 4] Lawson.—Techachapi Valley System. 461

tain slope on the south, part way across the valley. The geo-
morphy of this side of the valley is that due to the normal pro-
cess of erosion and presents no suggestion of faulting. The
edge of the valley is indented and the slopes above it are mature.

No stream of importance comes into Bear Valley so that no
notable alluvial cone occurs in it as in the other neighboring
valleys. But the various streamlets and the general wash from
the surrounding mountain slopes have contributed to its infilling
and have given it a floor of alluvium except at its west end near
its outlet by way of Sycamore Creek to the Great Valley. Here
the alluvium which forms the floor of the valley feathers out
and there is exposed a rock platform which is the counterpart
of that already described near the southwest corner of Cummings
Valley. This rock platform passes eastward and southeastward
with an almost flat slope beneath the alluvium, and evidently
underlies a considerable portion of the valley. It is with little
question a remnant of the same system of stream-cut terraces,
relics of which have been detected in Tehachapi, Brites, and Cum-
mings Valleys. Its original relation to those relies is not clear,
but that is not surprising in a region of such acute diastrophie
deformation as that with which we have here to deal. In gen-
eral, then, Bear Valley may be briefly stated to have originated
by the downward tilting of a tract of mature geomorphy on
the south, including a stream-cut flood plain, against a dominant
fault along the southwest scarp of Bear Mountain; and that
against this fault there was left in the down plunge a slab, or
kernbut, which failed to drop as far as the rest and the top of
which forms the ridge-bordered terrace on this side of the valley.
valley.

Beyond this rock platform a narrow gorge opens in the moun-
tain ridge which bounds the valley on the west and through this
the waters of the valley find their escape by a very precipitous
descent to the Great Valley 3000 feet below and only 4 miles
distant. This gorge in its upper part lies on the line of the sub-
sidiary fault searp and the same suggestion for its development
is here made as for the gorge which drains Cummings Valley,
viz., that it is due to the headwater erosion of a high grade stream,
Sycamore Creek, cutting back in the face of the northwest scarp

462 University of California Publications. [GEOLOGY

of Bear Mountain and finding the notch formed by the sub-
sidiary fault, which notch was originally lower, as it now is,
than the analogous notch made by the main southwest fault of
Bear Mountain. Prior to the capture of the valley by Sycamore
Creek it must have been occupied by a lake, since it is entirely
rock rimmed, but the hydrographic basin which includes the
valley is so small relatively to the area of the valley, that it is
quite improbable that the lake had an outlet by rising to the
level of the notch which was afterward deepened by the head-
water erosion of Sycamore Creek.

University of California,
March, 1906.

INDEX TO VOLUME 4

Norer.—Italicized page numbers indicate maps or illustrations.

ADAMS, F. D., cited on hornblende
ALBATROSS, observations of ocean tem
peratures
AMPHIBOLES, Classification of
ANALYSES:
—, Altered serpentine
—, Amphiboles
—, Biotite diorite
—, Glaucophanes
—, Granite-porphyry
, Minette
Mine Waters at Ruth Mine
Monzonite
Monzonite porphyry
—, Ore-bearing porphyry
Porphyry at Chinaman Mine ..
, Quartz biotite diorite -..
—, Rhyolite
,

dike

Waters in Comstock Lode
White Pine Shale ....
ANDERSON, KF. M., cited on Monterey
formation
— —, cited on Point Reyes Peninsula 42
cited on last shore of Bodega

>

TB ayaiectee nce se nceeccss-2
ANDESITE
ark West ....
ANDRERS, cited on inshore “cold water
Ne LSC ooo eco cond = 5s cs ccsacuzcnccuccausseenaeseea 274
ARNOLD, RALPH, cited on age of Mer-
(Lea bad BY 8 US ae Pee 86
AsHBuRY, C. H., cited on name Sing-
PLUG 20.) Run custeeaccscpuacctttepeusptacscestsasosécetascim
ATLAS FORMATION of Tehachapi re-
gion
BASALT ......

BEAR VALLEY
BrckE, F., cited on hornblende
— —, on crystalline schists -.

Brecker, G. F., cited on alter ser-
DO IMGINLG ete - cee ccecons sez cess eocnee+cucs ccenac-setsenevnns 426
— — —, on asperite and andesite ..... 71

on Comstock Lode
179, 185, 186, 187; 193, 198

— — —, on Eocene 52
— — —, on Knoxville series 51
—_— — on Basalt 86
BERGHAUS , cited on inshore cold water
belts 274
BIOTITE-DIORITE 43

BLASDALE, W.
Amphiboles
Buout, defined -
BODEGA DIORITE
BODEGA PENINSULA, field aspects of
—— —, petrography of .
BONANZAS of the Comstock Lode
—, location of -...
BRECKENRIDGE MOUNTS
BRITES VALLEY
BROGGER, cited on monzonite
, on amphiboles
BUCHANAN, J. Y., cited on coastal cold

Wa LOLA CLUS i oes ccesess cate cecee ea soe ce arena
BUKOWSKI, cited on rhodusite

C., cited on analysis of

[463]

PAGE
Tehachapi re-
....441, 442

CABLE FORMATION of

gion
CANYON of the KERN ..
CAPAY VALLEY, pre-volcanic beds of...
CHURCHILL Canyon

Sens cx noes caee ec edeaue Soe cettagstasesecsicacrato eect: 39, 68, 78
— —, map of, north of San Francisco 43
— —, pre-Franciscan sedimentaries of 42
CoLp WATER, inshore belt of, Pacific

WO BShgee ces terest ee eee
— —, — —, along other coasts
, hypotheses for
Comstocy Lopr, bonanzas of .

» Cross section through ...

, deep ores and waters of ..

, faults of 78, L779, 180;
—, forks of =

ground plan of
Hale and Norcross tunnel of....
rocks of
— —, structure and genesis of A
CONTACT PHENOMENA ..uuu..222.2.------- 304, 315
Corr, EK. D., cited on Tertiary verti-
brata - eae
Copper, native
, deposits
— —, at Pine Hill, Nevad

a Co.

— —, at Campo Seco, Calaveras Co. _ 415
— —, the valley group .........................- 414
— —, at Copperopolis, Calaveras Co. 418

— —, at Napoleon Mine,

Co.
COPPER-BEARING PORPHYRY
, Intrusive Relations of -
—, Structure of
— —, Petrographical Characters of....
Corominas, L. A., cited on elasticity

Calaveras

of gvpsum and mica 204
CoRUNDUM in minette -.... 345
Cross, W., cited on Amphibole 2 O08
CUMMINGS VALERY q:.-.22--2-c-<--0--s2-p--- 456,458
Dau, W. H., cited on Martinez for-

T0018, til O Te eee cemes cee oe eeseens eee ee 104, 112
DaAty, R., cited on hor nblende ............ B81
DAVIDSON, cited on astronomical ob-

SOV MALOINSI ese ercsed so kece ect oee ete aoerene 264
— —-, on California inshore cold wa-

tex? Del tert ee 273, 282
DAWKINS, W. B., cited on Ovibos ~.... allyl
Dawson, G. M., cited on granite of

British Columbia 289

DIKES AT MINERAL KING .
DUHAMEL, J. M., cited on hes

tivities of minerals
MGLOGITE, (-2...2-2-2-----: 387,389, 391, 392,
Emmons, S. F., cited on granite of the

Wasatch Range
Errore ScuHist
FAIRBANKS. H.

Serpentine
— —, on Chico-Tejon ..
FAULTS ....- 78, 79, 82, 450, 458
—, in Comstoe 178, 179, 180, 183

—, in Robinson mining district 258

464 University of California.

—, Ampullina striata
—, Aplocerus .........

—, Astrodapsis tumidus ..
—, Astyris gausapata ...
—, Aucellae -.............
—, Awinea patula .
_—, aad SDs, seckes-scesecosues

—, Bulla nebulosa ......
—, Bullinula subglobosa

—, Clypeaster brewerianus
—, Conus californicus ...
ee oe TSP ete eaceneeen
—, Crassatella unioides .
—, Orepidula Grandis .....--....--.----0-----=--

PAGE PAGE
FLOOD PLAIN on KeEeRN at Isabella -..... 402 TOY OSH. --.n.sncnccecctere tere 94
FOOTHILL COPPER BELT .......0--cc--sncceceee 411 — —, princeps . ZT 393)
FOSSILS: — —, dorsata ..... 93
—, Acila castrensis —, Crustacean remains -. stitial
—, Aemaea sudis .. —, Cryptichiton, ef. stelleri 94
—, Actaeon lawson —, Cryptomya californica .... 93, 94

i

—, Agasoma barkerianum ........------------ 97

— —, kernianum ..........-- Be EE
meri TNS Dice coset casccecesace anaseuwarersoneeeaecsetene O7
—, Allomeryx planiceps 144

— —, montanus . eee 152, 162

——, Aplodontia MAJOT ..2.5----nssecanncenvoversen-s 147
— — —, fossilis
—, Arca biloba
— —, canalis .....
— —, camuloensi

“108, 110, 115, 124
93, 94, 96, 99, 100
_..98, 100

— —, congesta ... 99

—, grandis ee aS
— —, microdonta ..90, 94, 96, 100
— —, montereyana . .--96, 100
— —, obispoana ... 99
— —— SCRIZOCOM GF ncatieeceiac~nsoseceseneosan=ee 93

— a sulcicosta ...
, trilineata ....
Besccestestiase 68, 75, 91, 92, 93, 94, 96, 99, 100

—, Architectonica tuberculata ...........-

ay ai ere = =
—, Brachysphingus liratus -108, 110
—, Budorcas tawicola ... .165, 168

et eee caer 108, 110, 122, 124
Qg

—, Calliostoma costata 93
—, Calyptraea filosa ..... - 94
— —, inornata ........ . 94
—, Cancellaria, sp. 97,98
sarees es DIL ES UNG eset encccecatecnscecssavexseene 93
— —, ef. vetusta 94
— —, tritonidea 94
—, Cancer breweri ee, 795
—-—s TT, 123
—, Capra ....... 1655-67;
—— (Cardata RON: ser2.20-sece-s-n50----2---=- 108, 110
—_ —, OCCIDENEAUIS .2.0.222-2----.2--0neeeeeseeeeenne 95
— —, subtenta ..... 91
— —, ventricosa ..... 93
—, Cardiuwm blandum . 95

— —, breweri ....

— —, cooperi

— —, corbis ..

ert emer TTL E Gap teenies seeerd nan caseauctentvn-accesresem 98
— —, meekianum _ 94, 95
—, Caryatis barbarensis - 95
—, Cerithidea sacrata - 91
—, Chaenohyus decedens re Us Pees I 9
—, Ohione succinta .............--------- aoe 93, 97
— —, simillima .. 94
— —— ‘SD sesi-s-e-s 97
—, Chorus belcheri. .. - 94
—, Ohrysodomus tabulatus . 68, 94
——— —, RUMEN OSUS? <iccrnccceensecanensnceeecesnesse= 94
— —, n. sp. Santos's cdcsesneeeees 98
—, Clementia subdiaphana 55, 98

—, Delphinosaurus ..
—, Dentalium hexagonum
— —, cooperi
— —, stramineum
—, Dicotyles ...........
—, Dinobastis serus .........--
—, Diodora crucibuliformis
—, Diphyphyllum ..........--...- a
—, Discohelix californicus _...22.2.020.222----

—, Dosinia ponderosa .

—, Flabellum remon

—, Cucullaea mathewsoni 108, 110
—~, Cylichna costata ..............-
—, Cymbospondylus petrinus
—, Cyrena californica
—, Daonella dubia ....

Dewctism

Sonali Serres eee ee 108, 110, 118, 124
94, 97

os ASD A ccecs soz covaseecteee Pareme?)7/
uaa torosa . 94

ie DOUY. Soh neescate Be 5)

— Sitios calkinsi 132, 144
— —, ingens ........ --- 133
— —, imperator 133

Buceratherium co
451, 162, 168, 164, 165, 166, 167, 168
Entoptychus ‘cavifrons Lac ae 127
—, crassiramis E
—, lambdoideus

, minor ...
—, planifron

rostratus ...
—, sperryt .......
, Felis imperialis .
, Ficopsis remondi
—, angulatus

Foraminifera. ...-2222-/4-
, Fusulina cylindrica Bs
—, elongata .......... -- 293
, Fusus ambustus -
—, equilateralis -.
—, martinezensis .
—, M.. SDa ede
, Glycimeris

-- L087 1105

121, 124

, Glycimeris generosa 94
, Hemifusus, sp. -..----- 97
, Heteroterma gabbi . 109, 118
——, SENVHER: ...5c0s ee 11

—, trochoida 109, ae
—, indet. ............. 109, 110

. Hipparion richthofent -....---2---.--------
, Hoplophoneus
, Hyaenognathus . ,
, Hypertragulus, sp... 128, 131, 144
» LLY PUSOGUS: 2.2.2 eee 131
Janira bella ..... v
, Leda alaeformis (ie mera eee
—, gabbi ....
—, taphria
, Leptomeryx

, Lima multiradiata 2-108) ko)
, Liropecten estrallanus ........---.---------- 94
, Lithostrotion mammillare . 293
y LONE CALCU avecees tescete reas 203)
, Lucina borealis po, GONE
—,. “‘richthofent <..-sen cee 293597
—, turneri ....... == SLO
5 UNG ORT concesenen cere sorensote==eeene 110
—, lewisii ........- --93, 94, 97
EM STH LLNs 1) MPR ee rH ES repr 5 95
—, richthofeni ....---..------ 298)
, Lrautiricolan Uta csseene ee eee ses DD:

Index to Volume 4. 465

PAGE
Machaera patula .......... -55, 98, 95
Machaerodus catocopis
—, gracilis
—, ischyrus
—, palaeindicus
Macoma edulis ..
—, expansa ..... - 95
—, inquinata
—, nasuta
PE OCURG SSDs: (atontscasstanenccccesteccnccssedeent 95, 97
—, falcata
— (pseudocardium), sp. -
Megalonyx jeffersonit
Be ee ere £53, 156, 157, 158) 159) 161
commen SE SUCTNEMSUG. 1 ccaxctctccbalaacacse 155, 161, 162
—, sp.
—, wheatleyi ..
Megistostoma striata
Meretria, sp. ..

"173

—, traskii 95
—, uvasana 53

Mesohippus acutidens ...
:--. 140,

anceps

—, bairdi .. é
—, brachystyl - 142
—, equiceps 143
oF pruestans .. - 143

Zodiola flabellata 95

—, multiradiata
—, merriami
—, ornata .....
—, recta ....
Morio tuberculatus
Mulinia densata .

Mya truncata eth)
Mylodon, ....2..:-.-- = 160
Mytilus californianus 95, 97
—, edulis ............-.-- 4) seh
Myurella simplex . 94
SSDs | secs seeezetecciccce Seon Oat,
Nassa californiana ... 94, 96, 98

—, near californiana
» fossata

—, clausa
—, lewisii

—, ocoyana 97
—, sp. indet. Beare) s)
—, Sp... 109, 111
Neohipparion ..... so
Neptuna tabulata .. 95
Neptunea altispira 95
—, humerosa ....... ..93, 94
—, mucronata 108, 111
——- et ag (Sse cnane ee LYE
—, recurva =, ©6353
—, tabulata .... 93

Neverita recluziana ... 91, 93, 96, 97
Nothrotherium shastense.. 153, 161, 162
Nucula truncata ....

TS Dah esses 98
WOlivetta biplicata ..68, 93
—, boetica 47 9)5)

Ostrea, sp.
, veatehti

Ovibos

Ovinae ....

Pachydesma inezana ... 95

cep mS gibberosum 94
sp. 98

iBindora bilirata .... - 938

—, seapha ........ : 97

Pecten caurinus ED. DF "94, 95

—, cerrosensis .. 98

—, estrellanus 97

— —, canaliculata .....
— —, saxicola
—, Sanguinolaria nuttalliana
—, Sawvidomus gracilis ..
— —, gibbosus

—, Schizothaerus nuttalli
—, Seutella gibbsi
— , interlineata

— —, putula

— —, fatalis

— Tellina bodegensis -

— Teonoma cinerea

— Thinohyus decedens

PAGE

— —, pabloensis .....22.22....00------- OL. 95, oR
—, propatulus .. ee. 40D
ce SD rae cess cnn eoas 96, 97
—, Pectunculus veatchi ..........--2.---.------ 110

( POTISSOLAL DIGHEU. -.-c-cc0en---0 109) LL 127
—, tricarnatus ..108, 109, 111, 121, 124
, Peromyscus nematodon ..... 126
—— i MOTUS) sees cences-o reese ..126, 144
Pholadomya nasuta - “108, 110, 116

,
READS TUT OP GUS ake secet" ctaceas nena sonssaepee 94.
, Platygonus, sp. 149
eA LCUPOC OND) Vraktensekcaccteseeeenswontecee 69, 93, 97
, Plicatula ostretformis ..........0::1----- ie)
WeEELOG.ONUO MOU se sceanaees ee oa TA
HE TEPCOCENAS SUN CLOUT) cece te cecceeeen seas

bee -LO4) LGD, LOG, Onl, MOGs 27.0,

5 P) ENE OVEDONEMNSUS <cc.ccncsaee--- anna 95, 98
—, Priscofusus devinctus 95
— —, oregonensis ........--.-- 95
—, Productus aff. porrectus 293
nN) LE TOL ONE TY ieee cccecnee 10
—, Psammnobia rubroradiata 95
ERS CDIVUS) LOTOY, sacseescee seta 95

, Pseudocardium gabbi . 95

, Purpura crispata 94

—, uaratus

, Schizaster leconteti ..

Sharks’ teeth -

,
ye BOTDULG, -2ste-a---rcn
, Siliqua edulata

, Similodon ....

—, neogaeus .....

—, Sinum planicostum a 93
—, Siphonalia lineata _.108, 109, igi
—— SOLON. seen ns ate -55, 69, 93, 97

m— —, POSHCOWS) 2.22 sccheececcasea ces sscazJeencend a 95
— —, sicarius .
— —, stantoni- ..
—, Standella californica

, faleata

— —, indet.

— —, nasuta

— —, planulata 95

— —, sp. 93

— Stenopora - 293
Strepsidura pachecoensis - 109, 111
Surcula carpenteriana =.-94,°9'7
Tapes aft. quadrata .... 108, 110

— —, staleyi ....... 68, 93, 95
—, staminea 93, 95, 96
—, tenerrima 93, 95, 97

—, hornii _........
—, martinezensis
BSD sp ceveeecseece-cs

—, u ndulifera

VSN CUG CO os: 85 weeostncesto Pees

— Terebratulina tejonensis ............-...-. 110

Teredo sp.

erase Reread fe ceeen 134, 135, 139, 140, 144
—, lent 135, 140
—, osmonti . .136, 138, 140, 144

——, ONUSEUNUG) .-ronssdevedusesendiostotececcestee 140

rostratus :
socalis .. i re 135

466 University. of Califorma.

— —, subaequans
— —, trichaenus secs
—, Thomomys microdon. ........-------- 146, 162
— —, mazama 25,

MAG EN zeseaze
—, Thracia karquinesensis -.

109, 111, 120, 124

— —, impressum

— —, pulehrum ......------ 109, 111, 120, 124
—, Vrochita costellata 91
= y) SDo oceiecves ste eeacs Bee AON

—, Trochocysthus zitelli_ ...
—, Trophon aft. T. ponderosum .
—, Turbinella crassitesta ...........---
—, Turris sp. indet.
—, Turritella conica -
— —, cooperi .........-.
— —, infragranulata
— —, jewetti
— —, n. sp.

— —, ocoyana
— —, puchecoensis -...22...----- is
—, Urosyea caudata ......108, 109, 111, 119
— —, robusta 208, 121, 119, 724
—, Venericardia ventricosa .............--- 94
==, Voluta mn. ‘SDo q2sccc--ceeccee

—, Volutilithes indurata ..
—, Xenophora zitteli .....

—, VYoldia cooperi .

— —, impressa 95
—, Zaphrentis ........ 293
. Zirphaea crispata 95

FRANCHI, 8., cited on glaucophanes... 368
WRANOLISOAN, \SERDUS! 2-22 ---<--cc-cerecece-ce----1s 48
FREESTONE, pre-voleanie beds near .... 54
GABB, W. M., cited on fossils of Mar-

finez formation’ 2..:.:.1..- 102
— — —, on Mesozoic fossils 9
— — —, on Arca trilineata 92
— — —,, on fossils at Kirker’s Pass... 58
GFIkiz, A., cited on clastic rocks ....... 418
GipLEey, J. W., cited on fossil horse’s

OOO LINN 2 = cote ie eee ae recone A eda Sere of (Papal fs)
GIEBE, E., cited on heat conductivities

(spebp sot ash 6f7)) (oh) are een pees eset PR eerre nena 207

GILBFRT, G. K., cited on basalt sheets
of Great Basin
, on Lake Bonneville boas
GLACIATION at MINERAL KING, re-
cency of
GLAUCOPHANE

. optical and chemical prop-
1 SOG, tL

GRANITIC ROCKS ............
— at Mineral King
GREENSTONE 3
GrotTH, P., cited on glaucophanes ei 368
HAGUE and IDpDINGS, cited on rocks of
Comstock Lode

— cited on White Pine shale .... _. 296
HANN, cited on coastal cold water
WWE] tSie <ceee serie ues nee ey eee eee sb Nie eae 275

HEAT CONDUCTIVITIES of minerals - 205
HbLAwatTscnu, C., cited on amphibole... 384
HOFFMANN, CAPTAIN, cited on coastal

cold water belts -. 276
HORNBLENDE ANDESITE 20

——, “SGH ISM 2 222:.:2-deccesse280: 218, 226
Hot SpriInc VALLEY
KERN, Canvon of

==» Mood-plaimitOh es-c.csee sees sees ees, 402
—. plateau at confluence of Little
OYE Ds. ctt ress Mee cs. sack, eer Tea ee 406

PAGE

IGNEOUS ROCKS, unconformity and rel-
ative age: of \-2..521..s:ctis-2.3:.20 kee eee
— —, sequence of
—- —, on Bodega Peninsula
— — at Mineral King
ICHTHYOSAURIAN LIMB, a primitive... -- 83
INCLUSIONS in granites =
INGEN-Hovutz, J., cited on

ductivities in minerals ..............---..-----
IRRUPTIVE ROCKS, Robinson mining
district. ..2..2-:..b eee 298
— — — —~, Monzonite batholith ...... 298
— — —-—, Monzonite porphyry
ike; .ss2.80. ti eee
—- — — — Copper-bearing — por-
PBYIY «nese neh ics ee eee
— — — —, Porphyry at Chinaman
Mine .-- 823
— — — —, Minette .. 844
— — — —, Rhyolitic lavas and
Cutis gece eee = B47

Obs 350
JANNETAZ, I., stir on heat conduc-

tivities im minerals|.....J/:.21 sees 208
KING, CLARENCE, cited on ores of
Comstock Lode. ....... 222-32). 190

KNopF and THELEN, cited on schists
at, Mineral! Kang ..22:2 Se eee
LACROIX, A., cited on crocidolite..
, on amphiboles ...........
LATER PLIOCENE ...
— —, age of ......
— , thickness of .. ieee
LAWLOR’S RANCH, lignitic beds of
Lawson, A. C., cited on Santa Clara-

San Benito Valley .....022 22 85
— — —, on folding of Merced beds... 86
— — —, on coast terraces ................-- 87

— — —, on quicksilver deposits .
— — —, on geology of San Fran-
Cisco. peninsula) ft. eee 48
— — —, plutonics of Montara Moun-
TAIN! . jeecseds- ee
— — —, on silica-carbonate sinter... 426
— — —~, on Upper Kern Basin ........
397, 404, 408, 453
rocks of Mt.

wpseudtececstibesestleceee ee ee te 258
— —, on Karquines series ...........- 104
LAWSONITE: -GNIEISS) 2.2-22-2.0.--0-oeose = 39
Letpy, J., cited on extinct mammals.... 131.

— — , on extinet sloth... 156, 157, 159
— — —, on saurian species from

Cottonwood Canyon .2-2..2.2 34
LIrBIScH, cited on heat conductivities
im: ‘minerals: ..4:.2..05.212 se eee 209

LINDGREN, W., cited on granite of
Idaho

, on rocks of ‘omstock Lode
— — —, on copper ore of Spence-

WH lee nccscecshec eee 413
— — —, on gold deposit of Pine

DM) p33 ane eee 413, 414, 415
— — —, on quartz monzonite por-

PITY cic. ere 416

, on age of granite in Sierras 48
Lovage, O. J., cited on heat conductiv-

ities, im minerals: fics oes 209
LOUDERBACK, G. D., cited on granite

of Humboldt Mountains ~.................. 289
MAKAROFF, ADMIRAL, cited on ocean

temperatures

Mark West CREEK,
— —, andesite
Marsu. O. C., cited on Thinohvus .....-
“on. Mesohinnus <.2-se eee
MARTINEZ GROUP, palaeontology of -.... 101
— —, Historical review of -............ =

— —, Geographic distribution of

Index to Volume 4.

PAGE
— —, Stratigraphic relations of ........ 105
— —, Correlation of ......... re af
MERCER’S CAVE -. 146
Merriam, C. H., cited on Aplodontia.. 147
MerRRIAM, J. C., cited on Martinez
group 103
MERRIL, G.
ing 292
Mica scuistT 393

Micuen-Levy, cited on elaucophane... 367
MippLE KERN, geomorphic features of B97
-— —, Character Of CANVOM! <tcccccccccec- 403
, Rolling terrace dissected by .... 404
, Crystalline schists of . 406
— —, Contrast between opposite

OTMREG ATUV.O Were ences teecsecartee Seas ssettereec aan - 405
— —, Hypothesis to

origin of
Miucnu, cited on hornblende .-
MONTEREY FORMATION
MINERAL KING, location -.
— —, geomorphy
— —, glaciation -

rocks (on

, Native copper
, Olivenite
(pall.
, Pargasite
a eVIte: <--2
Rhodochro
, Rhodusite ...
, Stilbite
i ENC
—. Turquois ..
—, Wad
MINETTE Se
MoONzZONITE in Robinson mining dis-
trict ---. 298
— — —, age of ........ g eos
— — — —, petrographic characters 305
—, chemical composition.... 306
* MONZONITE-PORPHYRY dykes
, petrography of .............1...
— —, chemical composition of ............ 310
Mr. DaAvipson, structure and genesis

— —, contact metamorphism Ge sees 255
— —, geological map of ............--......-- 262
MINERALS:
BPA CUINIO LE TO Mt ateeeecece=e focestedeneczensswz see eeees 386
—, Amphiboles of the glaucophane
SCNISUS hese ccdec acd scorned aeeee Se iesneeevene eee 363
—, Azurite 35
—, Biotite -.. 357
—, Calamine . B57
—, Calcite ...... 357
—, Chalcanthite 356
—, Chalcocite ... 356
—, Chalcopyrite 356
—, Chiastolite _. 3BbT
—, Chrvsocolla - 8356
—, Crocidolite 371
—, Crossite -.... ..365; 393
—, Fluorspar Bow
—, Galena B57
—, Garnet ... 357
—, Gastaldite- glaucophane Seas 362
—, Glaucophane .... 9%
—, Gypsum ...... 3
—, Katophorite
—, Laneite
—, Limonite
—, Magnetite
—, Malachite
—, Melanterite -
—, Molybdenite

of 198
Mr. St. HELENA, fault origin of - 82
MvurRAY, StR JOHN, cited on coastal

cold water DOES Coe stesseeeere eres 274, 277

>

NEOCENE STRATA, correlation of
——, StLUCtUTe (Of or... -cereencceccents2ecvevecaes
NortH PActric OCEAN, temperature,
conditions of a
Surface temperatures .
--270, 272, 273,
pera u ocean bottom...

— — — —, Hypothesis relative to....
OBSIDIAN
OCEAN TEMPERATURE,

eee Sar |

IPERATURE, observations of
...266, 269,

OnE KE, ec
ORE beroene of. MVallter River pada,
geology of

, formation of

ORINDAN FORMATION
OSBORN, cited on Mesohippus ..
PAGE, JAMES, cited on motion of ocean
waters
PALACHE,
PENEPLAIN, elevated, of Coast Ranges
OheCalifOryi aly csecsecescese--eeeeee ceases
PETALUMA CREEK, sedimentaries be-
neath andesite
PORPHYRITE
PORPHYRY in Robinson ‘mining x district
“308, Siu

a: copper or
PoTTeR CREEK CAVE

PRE-TERTIARY and surfaces

Tertiary
compared with present relief -..........

QUARTZ BLOUT, defined ........
Field relations of -
— —, Varieties of
Relation to
garnet rock
QUARTZ DIORITE
QUARTZITE
QUARTZ PORPHYRY
QUATERNARY of
IRAN GOS, i cess neee eset = teeta sees 22 enc osen eee astee
— Caves of California, mammalia of.
QUICKSILVER DIUPOSITS! -.....--2 cc cecccsceeces
Reposst, cited on Mixosaurus ............--
RHYOLITE
IREYWODITIO GAVAS: cciccccecvecccacaeceseeecneceeeceace
Ricnrer, C. M., cited on California
inshore cold water belt
ROBINSON MINING DISTRICT ... se
Ruth limestone, fossils in..
— — —, Arcturus limestone .......
, Elv limestone ........
— — —, White Pine shale
— — —, Nevada limestone ......
Structure of rocks of .......
ROENTGEN, W. C., cited on conductiv-
MICS OL MINGPAalS: 2. ccc cee Neceexseeteeee
ROSENBUSCH, cited on andalusite
hornfels ee
—, cited on amphiboles .....
RUSSELL, cited on lake Lahontan -
—. cited on mammalian fossils ..
SABER-TOOTH from California z
SAMWEL CAVE, a new ungulate from..
San PABLO FORMATION
SANTA ROSA VALLEY,
ScuHIsTs
ScuHIstTs, thermal conductivities of
—, petrography of
— —, glaucophane schists
— —, quartzose schist .....
Wrangell mica schist —.
Scort, W. B., cited on Hypertragulns
era sor eRe Parnes A rece Pe op nape eneer ee 128,
—, on osteology of Blotherium
. on osteology of Mesohinpus
SERPENTINE, alteration of, in North
BE Yond 02) (2h eee er er cee ea te

ores and

copper

red gravels of-_.

C., cited on soda amphibole 2

390, 392,

80

133
142

468 University of California.

PAGE

SINCLAIR, Wm. J., cited on Potter
Creek Cave ........ oss . 146
fae a cmon mammali - 10
SING-ATS’-E RIDGE, rocks of Ce Sn LL
Smiru, C., cited on crocidolite - 368
—, J. P., cited on Tertiary fossils . 9

SONOMA TUFF
SpuRR, cited on Great Basin
STranton, T. W., cited on Ma

Fale aly ease serie tec ie Np ee ee ea
Stokes, G. G., cited on conductivities

OL gmme ral seco caeeccccnven eeeseseeecocesseceuee 208
STRATIFIED ROCKS at Mineral King .... 242

STREAM TERRACES ..
SUBMERGENCE, rece

Ranges 82
SSVENIDE) cscccses cpsveccsccccencsctvveodeseccteceovsteorsensd 393
TAIT, cited on conductiv of min

OUR BY copeseseeetecroetets bececat tcengn weet evesvoxeeeanee ee 207
TEHACHAPI VALLEY SYSTEM, general

PE ALUT CS o22.22-2e22 ease tan ceae thee seesmeonecteece 432
—_———, Alluviation of .. -- 433
— — —,, Isolated hills in -....... 435
— — —, Mammoth remains in .. 436
— — —, Outlet of -..0.2.222222222.... -- 438
— — —, Atlas formation of .. 440
— — —, Tank volcanics .................--- 441
— — —, Cable formation of ...... 441, 442
— — —, Tehachapi formation of .... 443
— — —, Planation .....22222.2022222222. 2-2. 445
— — —, Dissection and reversal of

OU AINE LC coo ccce seve ecereweew eco .. 447
= —, Mature geomorphy ... 449
— — —, Western boundary of .. 450
— — —, Geological history of ........-. 451
— —, views showing physiographic

PEAGUTES! 2....cssee-2 = 434,446, 448, 450, 452
TEJON FORMATION 53
DT RRA OM Sys NCARUNG Wie 2. occ. cece cue teee ences 81

PAGE

THOMPSON, S., cited on conductivities
of minerals
TIMBER GAP, section across ...

TRENTON, pre-voleanic beds at DD

TURMALINE GRANITE ..........---2-------00--e-+ 241

TURNER, H. W., cited on San Pablo
sandstone 22... 54

— — —, on schists of Sierra Nevada 259
— — —, on folding of Sierra Ne-
vada os
— — —, on age of clay slates 4
UNconFormiry between Bedrock com-
plex and. Dertiary (te sees cosets cen
— between Tertiary and Quaternary...
UPPER REGION of the MAIN WALKER.. 1, 4

— — — —, Location of 2
— — — —, First Ridge ... 4
— — — —, Third Ridge .... uf

— — — —, Mid-valley buttes .......... 9
— — — —, Bedrock complex, struc-
TUTE: (Of ..2202 cece eee
— — — —, Tertiary, structure of 10,13
VIRGINIA CITY, bonanzas of -
WOLGCANIOS! (fo--ccscccct-.cecenssese eee 3
VON GODDECK, cited on altered ser-
pentine ....
WALKER RIVE
sentation of
— —, Upper region of ... Bic,
WEINSCHENK, cited on amphiboles .... 362
West coast of United States, cold |
water belt of -...
WHIRLWIND Moun
— —, rocks of ~.......
— —, profile of
WHITNEY, J. D., cited on Copperopolis 418

region, Ideal

WILSON’S RANCH, marine beds of .....- 59
WINCHELL, cited on composition of
MONG Waters: ccn-.ate 333

Wricut, F. E., cited on hornblende.... 385

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