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THE
JOURNAL OF GEOLOGY
JULY-AUGUST, 7593.
THE BASIC MASSIVE ROCKS OF THE LAKE
SUPERIOR REGION.
Introduction. — Before the application of the microscope as a
geological instrument the classification of rocks was dependent
largely upon their apparent similarities and dissimilarities as
noted by the unaided eye. When the use of this instrument
became almost universal it was found that many rock types
similar macroscopically were very different from each other in
microscopic appearance, and very dissimilar genetically, while
many of the apparently dissimilar types were discovered to owe
their differences in appearance simply to the ordinary processes
of weathering, which masked their original essential character-
istics with the products of mineral alteration.
The rocks now known as gabbro are quite well characterized
by peculiarities that are strikingly uniform in their essential
features, though formerly the term was made to cover a large
~ number of closely related but quite different rock types. Their
history affords a good illustration of the manner in which rock
classification developed from its early independent form to its
present highly differentiated but well defined one.
In the case of the gabbros, as well as in the case of other
rock groups, there were at first included under one name all rocks
whose superficial features were similar to those of the type
originally described. Later, more discriminating study separated
this group into a large number of subordinate groups, based on
Vol. I. No. 5
433
434 THE JOURNAL OF GEOLOGY.
slight differences noted in the characteristics of their components.
The number of such groups became larger and larger until
eventually there were almost as many sub-groups recognized as
there were students who had investigated them. Thus the
classification grew complicated, because the criteria upon which
it was based were mainly unessential, though prominent, pecu-
liarities in the components comprising the classified bodies. The
next step, following the use of the microscope in rock investi-
gation, consisted in the consolidation of several sub-groups into
one larger group—a result due directly to the comparative ease
with which the microscope enables the student to distinguish
between the primary and secondary—the essential and unessen-
tial—properties of rocks. After careful work of this kind had
finally established the various varieties on the basis of mineral-
ogical composition, attention was directed to the manner in
which the rock components are associated —to the rock structure
—and an explanation of variation in structure was sought in the
environment of rock masses. The study ot the gabbros thus
became a geological study rather than a mineralogical one.
The brief historical sketch of the classification of the
granular basic rocks, with special reference to the differentiation
of the gabbros from the remainder of the group, will thus serve
to illustrate the successive steps with which rock classification in
general has progressed. But the sketch is not offered here
solely as an illustration of the development of rock classifica-
tion. It was originally written with a view of emphasizing the
distinctive differences between the gabbros and the coarse dia-
bases. In the Lake Superior region there exist many coarse
basic rocks that have been called indiscriminately ‘ gabbros.”
Some of these possess the features of true gabbros, as defined
by a study of the history of this group of rocks, and others the
peculiarities of diabases. Until the distinction between these
two types is clearly recognized, it will be impossible to discuss
the causes of their differences. It is hoped that the present
contribution will serve partly to clear the ground for a careful
study of the coarse basic eruptive rocks of the Lake Superior
DDB A SHOCMNEAS SIVLE TO CLES, 1 1G. 435
province, which the writer desires to make as opportunities and
time permit. The present plan proposes a series of papers ap-
pearing in this Journal at irregular intervals. The first follows
this introduction. The second will embrace a sketch of previous
work on the basic rocks of the region, and the succeeding ones
will treat of the gabbros and coarse diabases in the Huronian
and Keweenawan areas on both sides of the lake.
I. BRIEF HISTORY OF THE CLASSIFICATION OF THE GABBROS
AND NEARLY RELATED ROCKS.
At about the same time the names Euphotide and Gabbro
were applied, respectively by Hatiy* in France and von Buch? in
Germany, to rocks composed essentially of a foliated augite and
a “compact feldspar.”” Haity describes the Euphotides as con-
sisting of a compact feldspar and diallage, for which combina-
tion he constructed the name from the two Greek words éy
(blessed) and das (light), in allusion to the green and white
mottling in the hand-specimens from many localities. Von
Buch’s name, gabbro, was adopted from the Florentines? to
cover a group of rocks that had been described at various times
under a great number of different names, of which perhaps jade
was the most common. Although gabbro was used by the
Italians to designate what is now known as a diallagic serpen-
tine, it has been accepted by nearly all geologists outside of
France as the name to be applied to the group of rocks which
von Buch so clearly and definitely separated from other allied
rocks, and defined as made up of jade, feldspar and smaragdite.
Between the time of the appearance of von Buch’s paper and
the publication of the first microscopic description of gabbros
by Rose in 1867,4 many descriptions of these rocks appeared in
tTraité de Mineralogie, 2d Ed., IV., p. 535.
* Ueber den Gabbro, mit einigen Bemerkungen iiber den Begriff einer Gebirgsart.
Geol. natur. f. Freund. zu Berlin, Mag. etc., 1810, IV., p. 128; 1816, VIL., p. 234.
3Cf, T. S. Hunr: Contributions to the History of Euphotide and Saussurite.
Am. Jour. Sci., 2d Series, Vol. XXVII., 1859, p. 336.
4G. RosE.—Ueber die Gabbroformation von Neurode in Schlesien. Erster Theil.
Zeits. d. deuts. Geol. Ges. XIX., 1867, p. 270.
436 THE JOURNAL OF GEOLOGY.
the various geological journals. In 1835 Gustav Rose* separated
the rocks composed of labradorite and hypersthene, with acces-
sory olivine, mica, apatite and ilmenite, from the gabbros, and
‘mat, thessame
time suggesting that the term gabbro be confined to rocks con-~
taining labradorite and diallage. Many rocks were described as
hypersthenites or hypersthene rocks, because of the supposition
included them under the name “ Hypersthenfels,
that the highly foliated augite in them really belonged to this —
variety of pyroxene. Delesse? and others showed that the com-
pact feldspar of Haitiy, and the jade mentioned by von Buch as
an essential constituent of gabbros (afterwards called saussurite
by de Saussure Jr., and by Beudant) is in some cases a true
plagioclase; and Hunt? showed that in other cases it consists of
zoisite, of white garnet mixed with serpentine, or of meionite,
and that the rocks containing these substances usually also con-
tain hornblende, with the characteristics of Rose’s uralite.
Hunt, further, declines to regard the rocks containing a triclinic
feldspar and pyroxene (either augite, hypersthene or diallage)
as true gabbros. He places them among the dolerites, and
declares that the true euphotides described by Hatiy and de
Saussure are mixtures of smaragdite and saussurite; a declara-
tion that Cocchi+ made for the Tuscan rocks a few years later.
Rocks composed essentially of diallage and saussurite Cocchi
called granitones. Whatever may be the virtue of the objec-
tions raised to the use of the name gabbro for plagioclase-
diallage rocks, it still continued’ to be apphed to rocks thought
to be of this composition, just as hypersthenfels or hypersthenite
™Ueber die Gebirgsarten, welche mit den Namen Griinstein und. Griinsteinporphyr
bezeichnet werden. Poggendorf’s Annalen, XX XIV., 1835, p. 16.
? Recherches sur |’ Euphotide. Bull. Soc. Géol. d. France, VI., 1848-49, p. 547.
3T. S. Hunr.—On Euphotide and Saussurite. Am. Jour. Sci., 2d Series, Vol.
XXV., 1858, p. 437; and Contributions to the History of Euphotide and Saussurite.
Ibid., XX VIL. 1859, p. 326.
41. Coccut1.—Description des roches ignées et sedimentaires de la Toscane dans
leur succession géologique. Bull. Soc. Géol. d. France (2) XIII., 1856, p. 267.
5Cf. P. KerrBEL.—Analysen einiger Griinsteiner des Harzgebirges. Zeits. d.
deutsch. geol. Ges. IX., 1857, p. 569.
THE BASIC MASSIVE ROCKS, ETC. 437
was used to designate those in which hypersthene was supposed
to occur.*
When Naumann? wrote the chapter on rocks for the second
edition of his ‘Lehrbuch der Geognosie”’ he defined the gabbros
_as characterized by the possession of labradorite or saussurite
and platy augite, and divided them into two varieties—the
gabbros, consisting of labradorite or saussurite, diallage and
smaragdite, and the hypersthenites, containing hypersthene as
the pyroxenic constituent, and sometimes a little secondary
hornblende. Naumann recognized the difficulty of distinguish-
ing between the gabbros and the diabases, even at this early
day, before it was known that augite could have imposed upon
it a parting as the result of pressure, for he says ‘‘ Diese Familie
wurde sich vielleicht mit der nachstfolgenden des Diabases
vereinigen lassen” (p. 573); and again, in a foot-note to diabase
“Wenn der feldspathige Bestandtheil der Gesteine dieser Familie
wirklich in allen Fallen Labrador ware, so wiirde es zweckmassig
sein, die Familie des Gabbro mit ihr zu vereinigen” (p. 578).
The norites described by Scheerer3 and Esmark, were thought
probably to belong with the gabbros, but their true relations to
the group were not known.
A few years later Kjerulf+ discussed the results reached by
‘himself and other Norwegian geologists, and ended by dividing
the Norwegian rocks of the gabbro type into gabbros and
norites, the former consisting of labradorite, augite, hornblende,
and the latter of labradorite and diallage.
*VON RATH: Geognostische Bemerkungen iiber das Berninagebirge (?) in Grau-
biindten. Ib. IX., 1857, p. 246.
RAMMELSBERG: Bemerkungen iiber den Gabbro von der Baste (Radauthal im
Elarz) lbs 1850: p. Tol.
VoN RICHTHOFEN: Geognostische Bechreibung von Siid-Tyrol. 1860, p. 146.
? Lehrbuch der Geognosie. B. I. 1860, p. 573-577.
3 Geognostisch - Mineralogische Skizzen, gesammelt auf eines Reise an der Siid-
kiiste Norwegens. Neues Jahrb. f. Min., etc., 1862, p. 668.
4Zusammenstellung der bisherigen Ergebnisse der geologischen Untersuchung
Norwegens. Neues Jahrb. f. Min., etc., 1862, p. 144.
438 THE JOUKRNAE (OF (GEOLOGY,
The macroscopic examination of the rocks of this type con-
tinued to give rise to many different methods of classifying
them, but the general tendency after this time seems to have
been toward the union of the gabbros and the hypersthenites
into one group. Von Cotta,’ for instance, embraces the gabbros
hypersthenites and norites under the single head ‘“‘gabbro,”’? and
then divides this group into five sub- groups— gabbros cane
tone of Cocchi and other Italians), with labradorite or saussurite
and diallage, or saussurite and smaragdite (gabbro of Cocchi,
Hunt and others); euphotides, equivalent to the saussuritized
gabbros of later authors ; norites of Scheerer, which are
regarded as gabbros containing a soda-orthoclase and some
quartz; hypersthenites, consisting of plagioclase and hypersthene,
and finally, Monzoni-hypersthenites, afterwards discovered by
de Lapparent3 to belong to an entirely elhigteat group since
they contain no hypersthene.
In the same year in which von Cotta’s classification appeared
Aug. Streng+ began the task of reducing the number of varie-
ties that had been separated as distinct sub - groups of the gene-
ral group gabbro. In his article on the gabbros and associated
rocks in the Harz he describes the former as made up of
labradorite, diallage, hypersthene, augite, hornblende, brown
mica, and ilmenite. Of the hornblendic constituent he says, it
is ‘“‘ Kein selbstandiger Gementheil des Gabbro, und es werden
daher durch ihre Anwesenheit keine besonderen Abanderungen
erzielt.” It is fibrous and is intergrown with the augite and dial-
lage. The labradorite is saussuritized (p. 935) and the saus-
surite is therefore regarded as an _ unessential component.
The hornblende- gabbros and the saussurite gabbros of the Harz
™Die Gesteinslehre. 2, Aufl. Freiberg, 1862.
?Cf. also Rocks Classified and Described. A Treatise on Lithology. By Bernhard
von Cotta. An English edition by P. H. Lawrence, London, 1866.
3DE LAPPARENT: Sur la constitution géologiqué du Tyrol meridional. Annales
des Mines. (6) VI., 1864, p. 259.
4AuG. STRENG: Ueber Gabbro und den sogenannten Schillerfels der Harzes.
Neues Jahrb. F. Min., etc. 1862, p. 932.
DEAE BASIC MASSIVE, ROCIES, EG. 439
are nothing but altered forms of the fresh gabbro. It is rather
surprising to one accustomed to the use of the microscope as a
means of studying rocks to learn that such correct conclusions
as to the inner constitution of rock masses could be reached
without the aid of this instrument as were reached by Streng in
his study of these rocks.* A few years later the same geologist
examined the gabbros and serpentines of Neurode in Silesia and
discovered that all of the so-called hypersthene of these rocks
is probably diallage, and that the serpentine rock, which from
very early times had been known under the name of forellen-
stein, is really an altered gabbro, containing but a small amount
of pyroxene. While Streng was examining the rocks of Silesia
and deciding that the so-called hypersthenite is a true gabbro,
Des Cloizeaux,? was investigating the hypersthenites and gabbros
of France, with a view to their better classification. Des
Cloizeaux declared as the result of his investigations that dial-
lage, which is only a lamellar augite, and saussurite form eupho-
tides and gabbros, and that many rocks that had been called
hypersthenites or hyperites contain no hypersthene, but that the
supposed hypersthene is diallage. He further proposes that dis-
tinctions between gabbros and hypersthenites be made more clear
by the use of the name diallagite for labradorite and diallage
rocks, and hyperite for those composed of labrodorite and
hypersthene or bronzite. Although the use of Des Cloizeaux’s
name diallagite was not accepted by petrographers, all workers
acknowledged the correctness of the statement that very many
of the hypersthenites described from various localities are noth-
ing more than gabbro in which the cleavage of the diallage is
well marked. :
Thus far the study of the gabbros and related rocks had pro-
ceeded without the aid to be obtained from the microscope.
Many rocks had been described as belonging to the gabbro- type,
1A, STRENG: Ueber den Serpentinfels und Gabbro von Neurode in Schlesien.
Neues Jahrb. f. Min., etc., 1864, p. 257.
2 ALF. Des CLOIZEAX: Sur les Classifications des roches dites hyperites et eupho-
tides. Bull. Soc. Geol. d. Fr. XXI, 1864, p. 105.
440 THE JOURNAL OF GEOLOGY.
as defined by von Buch, and these had been given distinct names
in accordance with the usual custom of distinguishing between
the different varieties of a rock containing different character-
istic mineralogical components. The years between r860 and
1862, perhaps, marked the height of the wave of differentiation.
After this time the classification of the numerous varieties took
the direction along which it was to be carried farther by micro-
scopical methods. Some of the hornblende gabbros, the forel-
lenstein, many of the hypersthenites and some of the norites had
been shown to be altered or fresh forms of true gabbros. The
characteristics of the components of the two groups of the gab-
bros and the hypersthenites had been fairly well determined, and
the similarity between many of the gabbros and the diabases had
been pointed out.
The best résumé of the state of knowledge at this time con-
cerning the rocks under discussion is to be found in Zirkel’s*
“Lehrbuch,” published a year before the microscope was
brought into use for the purpose of studying these rocks. Zirkel
collected the observations of the different workers and incor-
porated them along with his own in sucha way as to give an
excellent impression of the value of macroscopic rock determi-
nations, when undertaken by competent observers and aided by
chemical analyses. He distinguishes as gabbros those rocks con-
taining labradorite and diallage, at the same time agreeing with
Bischof? in the view that the latter mineral is merely a variety
of augite. Saussurite he regards as sufficiently characteristic of
some gabbros to warrant their separation from others. He like-
wise looked upon smaragdite, which was thought to be an inter-
growth of augite and green hornblende, as an essential constitu-
ent of some gabbros, and these he separated from the diallage
gabbros under the name of smaragdite gabbros. The hypers-
thenites are described at some length, with the appended state-
ment that many hypersthenites are probably gabbros. The
{
*F. ZIRKEL: Lehrbuch der Petrographie. Bonn, 1866, p. 112.
* BiscHoF: Lehrbuch der chemischen und physkalischen Geologie. Bonn, 1864.
2 Aufl. II, p. 654.
THE BASIC MASSIVE ROCKS, ETC. 441
norites of Scheerer are classed among the gabbros and the hypers-
thenites, and those of Esmark are said to belong partly with
these and partly with the diorites.
In the year succeeding the appearance of ZGirkel’s book, as
has been stated, Rose* made the first microscopical examina-
tion of gabbros that has been recorded. He found among the
Silesian gabbros two varieties, one of which is black and con-
tains olivine, and the other green and free from olivine. Tscher-
mak? followed Rose with a description of some Austrian gab-
bros, and an announcement that many serpentines are altered
gabbros, and that Streng’s forellenstein is only an olivine gabbro.
He concluded, further, that augite and diallage differ only in
physical properties, and therefore that gabbro ‘“‘ist eine Abtheil-
ung des Diabas”’ (p. 168).
In the few years succeding Tschermak’s paper several con-
tributions of great importance were added to the literature of
the gabbros. Zirkel3 recognized olivine varieties of these rocks
among the Tertiary formations on the islands off the west coast
of Scotland, and succeeded in showing that the hypersthenites
described by Macculloch from the island of Skye contain no
hyphersthene. He further pointed out as important the fact
that the plagioclase associated with diallage is rich in inclusions,
while that associated with ordinary augite is free from them. In
the same year Hagge‘ continued the work that had been so
ably begun by DesCloizeaux in 1864. He made a careful micro-
scopic examination of all the important gabbro and hyphersthe-
nite occurrences recorded, and reached a result very similar to
that of Des Cloizeaux. He found that very many of the rocks
™G, RosE: Ueber die Gabbroformation von Neurode in Schlesien, Erster, Theil.
Zeits. d. deutsch. geol. Gessel. XIX, 1867, p. 270.
2Die Porphyrgesteine Oesterreichs aus der mittleren geologischen Epoche.
Wien, 1869.
3F, ZIRKEL: Geologische Skizzen von den Westkiiste Schottland. Zeits. d.
deutsch. geol. Gessell. XXIII, 1871, pp. 58 and 92.
4R. Hacce: Mikroskopische Untersuchungen uber Gabbro und verwandte
Gesteine. Kiel, 1871.
442 THE JOURNAL OF GEOLOGY.
heretofore described as containing hypersthene, have none of
this mineral in their composition. He divided the gabbros into
those containing olivine and those without this constituent, and
from the latter separated a group which he called saussurite
gabbros, recognizing at the same time, however, that saussurite
is an alteration product of labradorite. He described it as con-
sisting ‘‘of small. crystal needles, prisms and grains, which are
colorless or light-green, and are scattered irregularly in a ground
mass with the appearance of a colorless glass, which often forms
clear patches in the saussurite’’ (p. 52).
Six years after Rose’s description of the Neurode gabbro,
and seven years after the appearance of Zirkel’s masterly class-
ification of rocks based almost entirely upon their macroscopic
properties, the latter geologist was enabled to issue a second
volume containing a classification of rocks based on the micro-
scopical characters. In this volume‘ he defines the gabbros as
granitic in structure, and consisting principally of plagioclase
and diallage, usually with the addition of olivine. The plagio-
clase is usually labradorite. It usually contains fluid inclusions
and numerous little dark needles and prisms arranged in a defi-
nite order. The diallage is filled with small brown plates and the
olivine is characterized by thousands of fantastically shaped hair-
like bodies. The structure of genuine gabbros is described as
coarsely or finely granular. They contain no porphyritic crys-
tals and no unindividualized ground mass.
The group of hyphersthenites had by this time become almost
depleted of its members. Most of the hyphersthenites had
been found to be diallagites, in the sense of Des Cloizeaux, so
that but four undoubted occurrences of this rock were left to be
included by Zirkel in the group. On the other hand, the number
of ‘‘forellensteins”’ had increased to such a degree that a group
was formed of the same classificatory value as that of the hyper-
sthenite group. These rocks were described as having the
structure of gabbros, while at the same time they contain but
‘FR, ZIRKEL: Mikroscopische Beschaffenheit der Mineralien und Gesteine.
Leipzig, 1873.
THES BASIC MASSIVE ROCKS, ETC. 443
little diallage. Their separation from the gabbros and the hyp-
ersthenites seems to be upon mineralogical grounds solely ; since
emphasis is laid upon the fact that their feldspar is apparently
anorthite. Of such great importance was the-mineral constitu-
tion of rocks regarded at this time, that we find no statement made
with respect to the similarity between many diabases and many
gabbros. The facts pointed out by earlier investigators to the
effect that augite and diallage are but slightly different varieties
of the same mineral, had been overlooked, or ,had, at any rate,
been regarded as of little importance, since these expressions of
opinion had for the most part not been founded on the study of
thin sections. The microscope was used principally for the
determination of the nature of the constituents of rocks, and
had therefore emphasized their mineralogical composition out of
due proportion to its importance.
The influence of Zirkel’s book upon geologists in all parts
of Europe was soon felt in the increased number of purely pet-
rographical papers published in the journals; and this increased
interest soon manifested itself in studies that included more than
a mere description of rock sections. Vogelsang* had, years
before, shown that there were great possibilities in the new
science of petrography, but in the flush of excitement over the
discovery of an easy and exact method of rock analysis, these
possibilities were left unexplored until geologists became quite
well acquainted with the essential components of the most im-
portant rock types.
Soon after the composition of the important rock types
became fixed, attention was turned more particularly to their
structure. Professor Judd? examined the gabbros in the denuded
cores of Tertiary volcanoes in Scotland, and found that while
diallage is the prominent pyroxene of the lower portions of the
™H. VOGELSANG: Philosophie der Geologie und Mikroskopische Gesteins-
studien. Bonn. 1867.
2J. W. Jupp: The Secondary Rocks of Scotland. Second Paper. On the
Ancient Volcanoes of the Highlands and the Relations of their Products to the Mes-
ozoic Strata. Quart. Jour. Geol. Soc., XXX. 1874, p. 220.
444 THE JOURNAL OF GEOLOGY.
masses, in their upper portions the diallage is replaced in large
part by augite. Many other papers of importance were publish-
ed, and in most of these the structure of the rocks described
was more or less briefly alluded to. Wiik* announced the fact
that many of the Finnish rocks classed by Zirkel among the
hypersthenites are olivine-diabases and olivine gabbros, while
Stelzner? filled the gap thus produced in this group by the dis-
covery of a bronzite gabbro from the Monte Rosa district in the
north of Italy. Vallee- Poussin and Renard? made a thorough
examination of the plutonic rocks of Belgium and the eastern
part of France, and discussed the composition and structure of
some gabbros.
The result of these and other workers were collected and
edited by Rosenbusch* in his well-known book on the micro-
scopical characters of massive rocks, in which the fixing of rock
types which had been begun by Zirkel was carried out ina
scheme which was not improved upon until the same author
published the second edition of his treatise ten years laters. In
the scheme proposed in 1877, the gabbros were placed among
the pre- Tertiary massive granular rocks. The group was made
to include all pre- Tertiary rocks consisting essentially of diallage
and plagioclase in their unaltered state, either with or without
olivine. Saussurite was recognized as a secondary product pro-
duced by the alteration of plagioclase, and green hornblende
(actinolite and smaragdite) as the result of an alteration of dial-
lage. The saussurite and the hornblende gabbros were no longer
‘F, J. Wik: Mineralogiska och petaografiska meddelanden. Ref. Neues Jahrb.
f. Min., etc., 1876, p. 206.
2A. STELZNER: Briefliche Mittheilung. Zeitz. d. d. geo. Gessell., XXVIII.
1876, p. 623.
3 Ch. de la VALLEE-PoussIN, et A. RENARD: Memoire sur les caracteres miner-
alogiques et stratigraphiques des roches dites plutoniennes de la Belgique et de I’
Ardenne francaise. Bruxelles, 1876, pp. 62-76 and 125-128.
4H. RosenpuscH: Mikroskopische Beschaffenheit der Massigen Gesteine.
Stuttgart, 1877.
5H. RosENBUSCH: Mikroskopische Beschaffenheit der Massigen Gesteine. 2te
Aufl. Stuttgart, 1887.
THE BASIC MASSIVE ROCKS, ETC. As
regarded as sub-groups of the gabbro family, but were looked
upon merely as altered gabbros. Magnetite and titanic iron
oxide as well as apatite were mentioned as accessory in all mem-
bers of the group, and hornblende, rhombic pyroxene, brown
mica and quartz were spoken of as occurring in many (p. 459).
The difficulty of distinguishing between a gabbro and a diabase
was Clearly appreciated. -The distinction between diallage and
augite, upon which is based the mineralogical distinction between
gabbro and diabase, is acknowledged to be of doubtful value for
this purpose, since some rocks with the other properties of gab-
bros have an augite devoid of the diallagic parting, while others
with many of the properties of diabase possess an augitic con-
stituent with the parting highly developed. ‘ Héchstens
diirfen sie (the gabbros) als ein unterabtheilung der Diabase,
welche sich durch eine eigenthiimliche Structur und Theil-
barkeit ihres Pyroxens charakterisirem.’’ The structure of the
gabbros was said to vary within narrow limits. They are always
coarse-grained rocks whose different structures depend princi-
pally upon the different amounts of their constituents. Since
they are so well characterized by the monotony of their texture,
and since no gradations* between them and porphyritic or glassy
forms were known, while on the other hand the structure of the
diabases varies so widely between holocrystalline and glassy, the
former were regarded as a distinct rock type. Rosenbusch,
however, declined to regard the gabbros as dependent for their
individuality upon the mere possession of an augite with pinacoi-
dal parting, but was inclined to look upon them as rocks occu-
pying a position in the scheme of classification intermediate
between that of the diabases and that of the norites, the latter
*MR. T. T. Groom has recently described a gabbro glass associated with gabbro
at Carrock Hill in the Lake District, England, under the name carrockite. Since this
glass occurs only as a narrow selvage where the gabbro has cooled rapidly in contact
with preéxisting rocks, it cannot be considered as contradicting the above general
statement. The structure is not one connected genetically with the rock itself, but is a
local phenomenon dependent upon extraneous circumstances. See T. T. Groom: On
the Occurrence of a new form of Tachylyte in Association with the Gabbro of Carrock
Fell, in the Lake District. Geol. Magazine. Jan. 1859, p. 43.
446 THE JOURNAL OF GEOLOGY,
consisting of plagioclase and an orthorhombic pyroxene, and
therefore corresponding in part to Zirkel’s hyphersthenites. The
- principal difference between the gabbros and diabase was, then,
one of structure, while subordinate to this was a difference
in mineralogical composition. In his sentences closing the dis-
cussion of the gabbros Rosenbusch writes: ‘‘ Man miusste aber
alsdann das Hauptgewicht fur die Absonderung der Gabbros
nicht auf den eigenthimlich struirten Diallag legen, sondern
darauf, dass sie einen pinakoidal spaltbaren klinorhombischen
Pyroxen als wesentlichen und daneben einen rhombischen Pyrox-
en als accessorischen Gemengtheil enthielten.” The distinction
here made is evidently a strained one, for quite a number of
gabbros were known in which the structure is the typical gabbro
structure, while at the same time they are entirely free from
rhombic pyroxenes. The new group name “ Norites”’ is borrowed
from Esmark and Scheerer, although the rocks described by
these geologists are by no means typical of the group. The
advantage of the name over ‘‘hyphersthenite”’ is readily appre-
ciated when it is remembered that the rhombic pyroxene of
these rocks is not always hyphersthene.
The publication of Rosenbusch’s classification of the massive
rocks fixed the characteristics of the various types with some
degree of scientific accuracy. There was, however, much to be
learned concerning the less well known types, and much more
to be discovered concerning the relations of the various types to
each other.
The work of Judd, referred to above, was the beginning of a
severe attack on the wavering line of geologists who still clung
to the belief that mineralogical differences alone should deter-
mine the class to which a rock should be referred. It would be
unprofitable in the present place to mention all of the important
articles treating of gabbros and their varieties. It will be suf-
ficient for our purposes to refer briefly only to those papers in
which new types of gabbro are described and a little more fully
to those which treat of the classification of these rocks.
The existence of true hyphersthenites (norites), of gabbros,
THE BASIC MASSIVE ROCKS, ETC. 447
and of types intermediate between these, was established at the
time that Rosenbusch’s book appeared. In this year (1877)
Toérnebohm* suggested that the name hyperite be used for the
latter classs, composed essentially of plagioclase, diallage and
an orthorhombic pyroxene, that the term gabbro should be used
to designate plutonic rocks in which the pyroxene is diallage, and
that hyphersthenite (or norite) should be restricted to those
containing a rhombic pyroxene as their principal augitic constit-
uent. This suggestion has not met with a very wide acceptance
because the gradation between the three types is very gradual,
and in all cases the geological relations of the types are the
same. It is convenient, however, asa descriptive name for those
gabbros containing two pyroxenes.
In the same year Streng’ investigated the crystalline
rocks of Minnesota and described a gabbro from near Duluth,
in that State, to which he gave the name hornblende- gabbro,
because of the supposition that the brown hornblende it
contains is primary. Irving,3 however, has shown that
much of the brown hornblende in the rocks of the Lake
Superior region is secondary. He thought that nearly all, if not
all, of the hornblende of the hornblende gabbros is of this
nature. Williams‘ has also shown that compact brown horn-
blende is often a secondary product of the alteration of augite;
and Wadsworth’ holds to the view that this is the character of
all the hornblende in the Lake Superior gabbros.
™A. E. TORNEBOHM: Ueber die wichtigsten Diabas und Gabbrogesteine
Schweden. Neues Jahrb. f. Min., etc., 1877, p. 387.
2A. STRENG and J. H. Kioos: Ueber die krystallinischen Gesteine von Minne-
sota in Nord Amerika. Neues Jahrb. f. Min., etc., 1877.
3R. D. Irvine: On the Paramorphic Origin of the Hornblende of the Crystal-
line Rocks of the Northwestern States. Am. Jour. Sci., Vol. XXVI, 1883, p. 27; Ib.
XXVII, 1884, p. 130.
4G. H. WILLIAMS: On the Paramorphosis of pyroxene to hornblende in Rocks.
Am. Jour. Sci., XXVIII, 1884, p. 259.
5M. E. WapDsworTH: Preliminary Description of the Peridotytes, Gabbros,
Diabases and Andesytes of Minnesota. Bull. No. 2. Geol. and Nat. Hist. Surv. of
Minn., St. Paul, 1887, p. 66.
448 THE JOURNAL OF GEOLOGY.
If Irving, Williams, and Wadsworth are correct in their opin-
ion, the hornblende-gabbro of Streng is merely an altered form
of gabbro, and therefore it does not deserve a distinctive name
(except for the mere purpose of description), any more than do
the saussurite-gabbros.
Another type of gabbro to which a distinctive name has been
given is also found in the region surrounding Lake Superior.
This is an orthoclase-gabbro which has been carefully described
by Professor Irving. An unstriated feldspar taken to be ortho-
clase had been discovered in gabbros from European localities
by various petrographers, but it was usually present in such
small quantity that but little importance was attached to it. In
this country Pumpelly’ and Julien? identified orthoclase in cer-
tain gabbros from Wisconsin, and Irving? discovered it in simi-
lar rocks from both Wisconsin and Minnesota. The latter author
describes the orthoclase as often reddened and charged with
secondary quartz. He mentions in detail the characteristics of
the rocks containing it, and regards the differences noted between
these and the non-orthoclastic gabbros as of sufficient importance
to warrant their separation from the latter under the variety
name orthoclase-gabbro.
Within the past few months still an additional gabbro variety
has been brought into prominence by Adams‘ and by Lawson$
working in different portions of North America. This consists
essentially of plagioclase with gabbro characteristics, with which
is associated only now and then a grain of pyroxene or magnetite.
in containing no olivine, and from
It differs from ‘‘forellenstein”’
™R. PUMPELLY: Geology of Wisconsin, III, 1880, pp. 38, 40, 41.
7A. A. JULIEN: Microscopical Examination of eleven rocksfrom Ashland County,
Wisconsin. Geol. of Wisconsin, III, 1880, p. 233.
3R. D. Invinc: The Copper-Bearing Rocks of Lake Superior. U. 5S. Geol. Survey,
Monograph V, pp. 50-56.
4F. D. Apams: Ueber das Norian oder ober-Laurentian von Canada. Neues.
Jahrb. f. Min., etc. B.B. VIII, p. 419.
5A. C. LAwson: The Anorthosytes of the Minnesota Coast of Lake Superior.
Geol. and Nat. Hist. Surv. of Minn. Bull. No. 8, p. 1.
THE BASIC MASSIVE ROCKS, 1G. 449
gabbro proper in the absence of diallage and orthorhombic
pyroxenes. To this variety belong the norite’ of New York
State, the labradorite rock of Labrador, and the ‘anorthite
rock”’ of Irving? from the north shore of Lake Superior.
But if we are to regard the anorthosites as gabbros in which
pyroxene and olivine are wanting, we must pass to the other end
of the series and include in the gabbro group those rocks in
which plagioclase is wanting, and in which the sole essential
components are pyroxene and olivine, or the pyroxenes alone —
the peridotites of most authors and the pyroxenites of Williams.3
Judd# has shown conclusively that the peridotites of Scotland
are but phases of the gabbro with which they are associated, con-
sequently they may with good reason be included within the
gabbro group. But other peridotites and many of the pyrox-
enites must be regarded as distinct rocks. They are the products
of the cooling of magmas of an essentially different composition
from that of the gabbros, hence their consideration may well be
excluded from this history.
The varieties of gabbro that depend upon mineralogical com
position, so far as known, have been carefully described and
named by their investigators —the names referring for the most
part to the nature of their iron-bearing constituents. These are
gabbro and olivine-gabbro, hyperite, norite, peridotite and pyrox-
enite, together with the alteration products of the first named, viz.:
hornblende, saussurite, orthoclase, and perhaps quartz-gabbro,°
the latter of which is more properly a quartz norite, since it con-
tains no diallage. The varieties whose names have reference to
rCf, F.D. Apams: 1. c., p. 475 and 483.
2R. D. Invinc: Copper-Bearing Rocks of Lake Superior. Mon. V. U.S. Geol.
Survey, p. 438.
3G. H. WitiiaAms: The non-Feldspathic Intrusive Rocks of Maryland and the
course of their Alteration. Amer. Geologist, VI, 1890, p. 95. Not the pyroxenites of
the French authors, which are mainly augite gneisses or schistose gabbros.
4J. W. Jupp: On the Tertiary and older Peridotites of Scotland. Quar. Jour.
Geol. Soc., XLI, 1885, p. 357.
5Cf. U.S.GranT: Note on the Quartz-Bearing Gabbroin Maryland. Johns Hop-
kins Univ. Circ. No. 103.
450 THE JOURNAL OF GEOLOGY.
the feldspathic component are the orthoclase-gabbro of Irving
and the eukrites’ of the older authors. The latter name was
proposed to designate rocks whose feldspar is anorthite. It
never received a very wide application owing partly to the diffi-
culty of distinguishing positively anorthite from the other plagio-
clases. Since the discovery by Tschermak that the plagioclases
form a series of isomorphous compounds, the value of the dis-
tinction recognized by the name has disappeared and the name
itself has fallen into disuse.
In addition to these there are two other varieties that seem
to be sufficiently well characterized to deserve special names.
One of these, the anorthosite, consists exclusively of gabbroitic
plagioclase and the other ‘“forellenstein” contains olivine and
plagioclase.
During the past few years nearly all the work on the gabbros
has tended toward the separation of these rocks from the dia-
bases by sharper lines than those based merely on mineralog-
ical distinctions. All those who had attempted to separate the
two groups by the methods in use had failed, and some had
thought it well to include the two in one group. The views of
the earlier petrographers on this subject have been referred to.
Later petrographers have accorded with these in their recog-
nition of the fact that the value of the pinacoidal parting of
diallage is not of great importance for the purpose of rock classi-
fication. The discovery of Judd, referred to above, produced a
marked effect on the work of those who followed him in the
same field.
In 1883 J. Roth? declared that the position of the gabbros
with respect to the diabases depends upon the significa-
tion given to diallage. If we regard it as an altered augite
with a pinacoidal parting produced by twinning it is found,
as Rosenbusch has already stated, that the parting may
occur in the pyroxene of some rocks without the presence of
‘For a discussion of the eukrites see J. RorH: Allgemeine und Chemische Geol-
ogy, II, 1883, p. 200.
2 Allegemeine und Chemische Geologie, II, p. 185.
WUE AHA SHOVES SUMED TAO GIES WS aC. ASI
twinning lamellae. On the other hand, the pinacoidal parting
is entirely absent in cases where twinning lamellae are present.
Consequently not much dependence can be placed upon this
constituent as a means of distinguishing between gabbros and
diabases. The former rocks are evidently related to the latter,
whose typically granular, holocrystalline forms they are. Irving,’
in his work on the geology of the Keweenawan series in Michi-
gan, Wisconsin, and Minnesota, was compelled to make use of
coarseness of grain as a means of distinguishing between diabases
and gabbros, both of which were thought by him to occur as
flows. ‘It is evident,’ he writes, ‘“‘that my observations on
these north Wisconsin gabbros bear out the conclusions reached
by certain European lithologists, as to the subordinate import-
ance of the foliated condition of augite, by which gabbro is
ordinarily separated from diabase, of which it would seem to be
merely a phase. Nevertheless, the name is here retained, not
only because most of our rock is very close to the typical Euro-
pean gabbros, but more especially because it is so sharply con-
trasted with the typical Keweenawan diabase that a separate
name seems necessary.” And again, when speaking of the dia-
bases, he says,? “Although grading through coarser kinds into
the coarse olivine-gabbros, the fine-grained rocks here considered
deserve a place by themselves. The gradation into the coarser
kinds has never been observed in any one bed, and they are very
strongly marked by their external characteristics, both in the
fresh and altered states.”
The prime distinction between the two classes of rocks is,
then, one based upon structure and not upon the difference
between the augitic and diallagic nature of its pyroxenic con-
stituent. The structure of the most typical gabbros was recog-
nized by most geologists to be granitic and that of the diabases
as ophitic. Professor Judd3 proposed to restrict the name
* Geology of Wisconsin, III, 1880, p. 171.
2 Copper-Bearing Rocks of Lake Superior, p. 69.
3J. W. Jupp: On the Tertiary and older Peridotites of Scotland. Quart. Jour.
Geol. Soc., Vol. XLI, 1885, p. 354; and On the Gabbros, Dolerites and Basalts of
Tertiary age in Scotland and Ireland. Ib. XLII, 1886, p. 49. ;
452 LHE JOOCKRNALE OR GEOLOGY,
gabbro to granitic forms of plagioclase pyroxene rocks, and to
designate as diabases the ophitic, porphyritic and glassy forms.
He agrees with Zirkel* and Lasaulx? in regarding the Hebridean
rocks as Tertiary in age, and at the same time as corresponding
in all their characteristic features with older augite-plagioclase
rocks of granitic structure. These rocks possess not only the
structure of the most typical gabbros, but their various constitu-
ents are marked by the same microstructure. The plagioclase,
olivine, and augite contain the numerous inclusions that were so
early recognized as characteristic of these minerals in gabbro,
and the latter mineral, the augite, is marked by the diallagic
parting, which is the result of the action of a secondary process
upon ordinary augite. The process, called by Professor Judd$
schillerization, is moreover shown to be a function of the depth
at which the original rock magma cooled, and the granitic struct-
ure of the rock mass is demonstrated to be likewise due to the
. fact that the rock possessing this structure crystallized at some
depth below the earth’s surface.
The work of Professor Judd established two great facts, viz.:
first, that the age of a rock cannot serve as a basis for rock
classification, since it has but little to do with the development
of a characteristic structure; and, second, that the geological
position of a rock mass is the condition determining not only its
structure, but also the peculiar features possessed by its constit-
uents. The rocks which it is proposed to call gabbros are
marked by both of the characteristics of deep-seated rocks,
while the diabases possess neither of them. The differences
between the two groups of rocks, as expressed by their structures,
~ are probably differences that are dependent upon the geological
conditions under which they solidified.
Zeits. d. deutsch. Geol. Gesell. XXIII, 1871, pp. 58 and 93.
? Min. u. Petrog. Mitth. I, 1878, p. 426.
3Cf. also J. W. Jupp: On the Relations between the Solution-planes of Crys-
tals and those of Secondary Twinning; and on the Mode of Development of Negative
Crystals along the former. A Contribution to the Theory of Schillerization. Min-
eralog. Magazine, VII, p. 81.
IED IASC: MHAS| SINE, IROCIGS, 12 ING. 453
Professor Rosenbusch* clearly appreciated the value of the
work on the basic rocks of the Hebrides, for, in the second edi-
tion of his Mikroskopische Physiographie, he defines the gabbros
as hypidiomorphically granular plutonic rocks,-consisting of a
basic plagioclase, diallage, or a pyroxene resembling diallage,
rhombic pyroxenes and often olivine. The important feature in
this definition is the characterization of the gabbros as plutonic
rocks. The diallage no longer defines the gabbro. The condi-
tions which determined the characteristic structure of the rock at
the same time produced the diallagic structure in its pyroxenic
constituent. The structure of the typical gabbros, as defined by
Rosenbusch, is granular, with the components all equidimen-
sional. Notwithstanding the fact that some plutonic rocks of
this class seem to lack the granitic structure, it remains true that
the typical gabbro is well described by this definition.
When, however, we seek to separate the gabbros from the
diabases we are met at the outset with the same difficulties that
have always stood in the way of an exact separation of these two
rocks. Rosenbusch? describes the diabases as possessing some
of the features of plutonic rocks, while at the same time they
possess other features that are eminently characteristic of rocks
that have flowed out upon the surface of the earth. He never-
theless includes them with the plutonic rocks, stating, however, at
the same time that they occur principally as dykes and interbedded
flows ; are more frequently interstratified with schists than are
any other plutonic rocks; and that their predominant structure
is the ophitic. That there is a fundamental difference between
the two rocks is shown by the fact that the typicial gabbro can
not be traced into porphyritic or hyprocrystalline varieties, nor is
it ever accompanied by tufas. Whereas the diabases are often
porphyritic, and are not infrequently associated with diabasic
tufas. A consideration of these phenomena, together with the
great differences in the structures of the typical gabbros and
diabases, have led Loewinson-Lessing to regard the gabbros as
1 Mikroskopische Physiographie, der Massigen Gesteine, 2, Auf. 1887, p. 132.
2 Mikroskopische Physiographie, 2 Auf. II, pp. 174 and 195.
454 THE JOURNAL OF GEOLOGY.
the intrusive? equivalents of the diabases, which he thinks were
effusive under water, with the augite porphyrites as their equi-
valent terrestrial effusives. The conclusions of Loewinson-Les-
sing are not at all startling in their originality, for the wide
separation in origin of the two groups of rocks here discussed
has been suspected by petrographers ever since the classification
of rock-types based on age, mineralogical composition and struc-
ture, gave way to the classification founded on geological rela-
tionships. The placing of the diabases with the effusive rocks
will probably be looked upon with favor by all petrographers,
especially since Professor Rosenbusch? has treated of them as
members of this group in his Heidelberg Lectures, and Brauns3
has shown that a typical-lava flow of a suitable composition may
have the diabasic structure developed in it but a few feet below
its upper surface.
Lawson,‘ on the other hand, has shown conclusively that the
coarse grained, ophitic diabases, jnterbedded with the Huronian
slates and quartzites on the north shore of Lake Superior, are not
effusive, but are intrusive, and that their intrusion between the
fragmentals with which they are associated, must have occurred
at a time when these were deeply buried under a great thickness
of overlying rocks. Consequently these coarse, holocrystalline
diabases must be regarded as intermediate in their geological
relationships, as they are in their structural features between the
hypidiomorphic, holocrystalline, plutonic gabbros, and the typi-
cally ophitic, hypocrystalline effusive diabases.
But if the hypocrystalline diabases are classed with the effu-
sives, their position with respect to the melaphyres and _ basalts
*F. LOEWINSON-LESSING: Quelques considerations genetiques sur les diabases, les
gabbros et les diorites. Bull. d. 1. Soc. Belge. de Geol. etc., II, 1888, p. 82.
* Cf, Zeits. d. deutsch. geol. Ges. XLI, 1890, p. 533.
3R. BRAUNS: Mineralien und Gesteine unf dem hessischem Hinterland II, 3,
Diabas mit geflossener Oberflache (Strick oder Gekroselave) von Quotshausen. Zeits.
d. deutsch. geol. Ges. XLI, 1890, p. 4o1.
4A. C. Lawson: The Laccolitic sills of the northwest coast of Lake Superior,
Geol]. and Nat. Hist. Surv. of Minn. Bull. No. 8, 1893, p. 24.
THE BASIC MASSIVE ROCKS, ETC. 455
must be defined. Brauns,* in the article referred to in the last
footnote, has attempted this correlation. He finds, after review-
ing the opinions of various writers on the subject, that ‘It is not
possible to distinguish between diabase and melaphyre on purely
petrographical grounds, whether olivine is considered as an
essential component of melaphyres, as Rosenbusch holds, or
whether it is regarded as unessential in these rocks.” In order
to construct an exact definition for these three types of rock
Brauns is compelled to fall back upon distinctions of age, although
Rosenbusch? in his last article, in which he refers to this subject,
declares it as his opinion that ‘it requires no great foresight to
prophesy that in the not very distant future, this separation [ of
the effusive rocks into an older and a younger series| will be
proven untenable.” In spite of the almost certainty that Braun’s
classification will meet with but little favorable acceptance, it is
given here in order to complete the sketch of the history of gab-
bros and the related rocks. According to Brauns, the basalts
are made to include rocks of this class from recent time to the
beginning of the Tertiary age. The limit of separation between
the melaphyres and the diabases passes through the productive
' coal measures; rocks older than this are regarded as diabases,
while the melaphyres extend from the Carboniferous to the Ter-
tiary. Each group is divided into varieties, according to struct-
ure, and into sub-varieties according to mineralogical composi-
tion. A tabular grouping of the principal divisions of the
effusive rocks of the composition of diabase follows:
HEEL UO. “Oa ee Mesozoic to Tertiary to
ductive Coal Terti R
Measure ce ertiary. ecent.
Granular - - - Diabase. Melaphyre. Basalt.
Porphyritic - - Diabase-porphyrite. |Melaphyré-porphyrite.| Basalt-porphyrite.
Glassy - - - - Diabase-glass. Melaphyre-glass. Basalt-glass.
It is very evident that the introduction of the diabases among
™R. Brauns: Ib. 5. Systematik der Diabas, Melaphyr und Basaltgesteine. Ib.
Pp. 532.
2H. ROSENBUSCH: Ueber die chemische Beziehungen der Eruptivgesteine. Min.
u. Petrog. Mitth. XI, 1890, p. 146.
456 THE JOURNAL OF GEOLOGY.
the effusive rocks has created a disturbance in the melaphyre-
basalt group that can only be quieted by the ejection of one of
the members of the group, probably the melaphyres, from the
position it now occupies. When this is done it is probable that
the diabases will take the position thus left vacant, and the
plagioclase-augite rocks will be found to occupy these places
with respect to each other: the gabbros, the position of a deep
seated rock, the diabases that of the corresponding holocrystalline
effusive, and the basalt that of the hypocrystalline equivalent.
WWE Ss IBAIGLIB,
WATERVILLE, ME., June 1, 1893.
NOMES OWN Wels, SIVAIMS Islets JUN Welle, MMUNBES
AND MINING BUILDING *AT.THE WORLD'S
COMUINNBIVAIN IS 2XIPOSIMMIOIN,, » ClsUUCevGrO),
THE Mines and Mining Building at the World’s Columbian
Exposition contains exhibits of the different mining industries
of the various states of the United States and of foreign coun-
tries, exhibits of many of the manufactured products derived
from these industries, exhibits of various kinds of mining and
engineering machinery, and many private mineralogical and pet-
rographical collections of great value and interest. To describe the
whole would require a volume, and it is the intention of the present
paper to discuss only some of the more important features of the
state exhibits, with occasional references to the foreign exhibits.
A mining exhibit should seek to show the actual resources
of the region it represents, whether these resources be developed
or undeveloped, and to give the different products prominence
according to their present or prospective importance to the
region. The products of present importance should be exhib-
ited as showing what the region actually produces; the pro-
ducts of prospective importance should be exhibited as show-
ing what the region contains in bountiful quantities, but what
is not yet utilized, either from lack of knowledge on the part
of the public concerning it, from temporary inaccessibility, or
from some other cause. By this means many valuable mate-
rials, which have not yet been developed, are brought to the
attention of the general public, and often to that of specialists
on such subjects, and in this way receive quicker development
than if they had not been exhibited. It is often difficult to
give the proper relative importance in an exhibit to products
actually being mined and those which have not yet been devel-
457
458 THE JOURNAL OF GEOLOGY.
oped, but an effort can be made in this direction, and it is always
possible to state that a given material is not being mined.
A properly arranged mining exhibit affords advantage in
two directions. In the first place, it benefits the exhibitor in
calling attention to his products, and in the second place it is of
great educational benefit to the general public as showing what
different regions produce. The best interests of the exhibitor
are served by a true exhibition of his products; while the educa-
tional value of an exhibit depends almost entirely on the exact-
ness with which the exhibit reproduces the actual state of
affairs, for if the exhibit is exaggerated in one direction or
neglected in another it leaves with the uninitiated a false idea of
the resources of the region.
Most of the state exhibits have been collected and arranged
by commissioners appointed by the state, and are supposed to
fully represent the resources of the state. Many of the foreign
exhibits, however, are made up of the individual exhibits of
different mining companies, and often show only a certain class
of the products of a given region. They are, therefore, not
claimed to always represent the whole of the mining industries
of a region’ and cannot be criticised for not doing so. The
state exhibits, however, should fairly and honestly represent the
mining industry within their borders, giving undue prominence
to no one product, and neglecting nothing that should be repre-
sented. In this feature some of the states have been highly
successful, while others have done worse than make a failure, for
they have misled those who are not sufficiently acquainted with
the resources of the country to know that the exhibit is not char-
acteristic. Some of the states have exhibited and made very
prominent great amounts of materials which they do not possess
in paying quantities; other states have actually exhibited mate-
rials which they do not possess at all, and which have been
obtained from other states, a proceeding which is very mislead-
ing to the general public.
«A notable exception to this is the New South Wales exhibit, which is one of the
best in the building.
EXHIBITS. IN MINES AND MINING BUILDING. 459
lit-bas becnmthe object of Mir oh gia Vi .Skith Chret or’ the: -
Mines and Mining Building, to make the mining exhibit truly
characteristic of the states and foreign countries represented,
and thus to give it the greatest possible value to the general
public and to the individual exhibitors. His supervision has
been wise and systematic, and it is to him that a large part of
the success of the mining exhibit is due. Where failures have
been made they have been the fault, not of the Chief of the
Mines and Mining Building, but of the commissioners under
whose charge the exhibits were prepared, or else of the govern-
ment of the state or country which they represent. Very often
the commissioners have been so hampered by the fancies of the
mine owners or others in their districts that, though entirely
capable of doing so, they have been unable to make a creditable
exhibit of the regions they represent. Many of the state exhib-
its contain a large amount of good and characteristic material
which is often rendered useless and often ridiculous by bad and
ignorant arrangement; while many otherwise good and charac-
teristic exhibits are rendered very unattractive by the slovenly
way in which they are exhibited and the untidiness of the cases
and specimens. Of course the last mentioned defects are minor
ones, especially to those interested in the subject; but at the
same time the neatness of presentation has a great influence on
the attractiveness, and hence on the benefits, of an exhibit to the
general public. An exhibit which has no natural beauty may be
made very attractive by neat and systematic arrangement, while
on the other hand, an exhibit of beautiful things may be made
actually repulsive by a slovenly and dirty mode of presentation.
The different state exhibits have been collected and dis-
played by means of the appropriations made by the various state
legislatures for such work. As the amount and conditions of
the appropriation varied very much in different states, the size
and costliness of the exhibits vary accordingly, and often give a
very great advantage to the state with the larger appropriation.
In criticising an exhibit, therefore, these circumstances must be
borne in mind.
460 THE JOURNAL OF GEOLOGY.
Among the best American exhibits are, beginning with the
Eastern states, those of Massachusetts, New York, Pennsylvania,
North Carolina, Michigan, Minnesota, Missouri, Colorado, Mon-
tana, Arizona, Idaho and California; and in Canada those of the
Provinces of Quebec and Ontario. Among the other foreign
exhibits that of New South Wales is preéminent in the quality,
nature and mode of arrangement of the exhibit. The exhibits
of Great Britain, Germany, Norway, Sweden, Denmark, Spain,
Greece, Austria, Switzerland, Belgium, Italy, South Africa, Cey-
lon, Japan, and other foreign countries, are good as far as they
go.
Many of the mining exhibits of both states and foreign coun-
tries are divided, and put partly in the Mines and Mining Build-
ing and partly in the individual buildings of the states or coun-
tries in question. . Such a course is a great mistake, as it renders
the exhibit in both buildings imperfect, and those who see the
exhibit in one building without knowing that it is supplemented
in another, receive an incomplete, and therefore an erroneous,
idea of the products of the country represented. Each mining
exhibit should be kept together, whether it be in the Mines and
Mining Building or in another building.
The exhibits of the New England states are naturally repre-
sentative of less economic value than those of some of the other
states, because, with the exception of building and ornamental
stones, most of their mining products are of subordinate import-
ance ; but at the same time they display what they have ina sys-
tematic and consistent manner. The Massachusetts exhibit is
thoroughly characteristic and well arranged, showing not only
the economic products, but also many rocks and minerals of
purely scientific interest. The Maine exhibit is also character-
istic of the state, while the New Hampshire and Vermont exhib-
its are small but appropriate, consisting largely of building
stones, with mica and other minerals from New Hampshire. The
granite of New Hampshire and the granite and white marble of
Vermont are displayed on a small but sufficient scale.
Coming westward, the New York exhibit is the first one we
EXHIBITS IN MINES AND MINING BUILDING. 401
find which is representative of great economic importance. It
displays its clays, sands, iron ores, building stones, petroleum,
salt, etc., in a thoroughly systematic and creditable manner, and
gives a very good idea of the relative importance of the differ-
ent products.
The Pennsylvania exhibit is somewhat more elaborate than
that of New York, as it should be, on account of the greater
value of its products. Its immense coal and oil resources,
together with its iron, clays, glass-making materials, slates, build-
ing stones, etc., are very well displayed. A model showing the
method of coal mining and relief maps of the anthracite basins
and of the whole state add to thé attractions of the exhibit. A
large series of samples of crude and refined petroleum are an
appropriate and interesting feature of the exhibit. A large col-
umn of anthracite in a conspicuous position in the centre of the
building, and apart from the rest of the Pennsylvania exhibit,
represents a vertical section of the ‘‘mammoth seam” on the
property of the Lehigh Valley Coal Company. A second column,
near the main Pennsylvania exhibit, is composed of blocks of the
different products of that state, varying in size according to
their importance, the smaller blocks being’ placed successively
higher in the column.
New Jersey makes a much less elaborate exhibit than either
New York or Pennsylvania, though it is neatly arranged and in
some respects it is good. The magnetic iron ores of the north-
ern part of the state, and the clays, marls, and other products
are well exhibited. The zinc deposits of Sussex county, how-
ever, are only poorly represented, and in this respect the exhibit
might have been improved. A _ glass-plate model of the zinc
mines at Mine Hill, Franklin Furnace, Sussex county, is an
attractive feature.
Virginia makes a very characteristic and well arranged
exhibit, though the fact that the materials exhibited are not in
cases detracts from their neatness. A large display of coal and
coke, so rapidly becoming the most important products of the
state, is made; while the characteristic brown hematite (limon-
462 THE JOURNAL. OF GEOLOGY.
ite), the manganese ores, zinc ores, clays, fire-brick, and slate of
that state are represented. The Bertha Zinc and Mineral Com-
pany displays the zinc ores of the southwestern part of the state
and the spelter made from them, as well as statues, wire, etc.,
made from the spelter.
West Virginia makes a fine display of coal and coke, at pres-
ent two of its most important industries. Such an exhibit is very
appropriate when we consider that forty-eight out of the fifty-
two counties of the state are said to contain more or less coal.
The salt, mineral waters, crude and refined oils, iron ores, and
building stones are also displayed.
North Carolina makes a véry neat and characteristic exhibit
of iron ores, auriferous quartz, mica, kaolin, asbestos, building
stones, gems, etc. The gems include diamond, sapphire, topaz,
ruby, beryl, garnet, rutile, chalcedony, etc. A number of inter-
esting models of gold nuggets are also displayed. A number of
photographs of different districts form a part of the exhibit,
which is neatly and systematically arranged.
South Carolina makes a good exhibit of its great phosphate
industry, displaying the crude phosphate and also the manufac-
tured superphosphate. The phosphate industry far eclipses in
importance all other mining industries in that state, and the
others, such as gold, iron, and manganese mining, in the western
part of the state, are of very little and very unstable importance,
and are not represented.
Florida, long unknown to the mining industry, has suddenly
become of great importance on account of the recent discovery
of its phosphate deposits. A small exhibit of these phosphates
is made in the Mines and Mining Building, but it is not suffi-
ciently extensive to do credit to a young and rapidly growing
industry.
Louisiana makes a very appropriate exhibit of its mining
products, among which are lignite, oils, salt, sulphur, marls, clays,
chalk, building stones, grindstones, mineral waters, and other
minor materials.
The Tennessee exhibit consists mostly of a ‘‘ Mineral Exhibit
EXHIBITS IN MINES AND MINING BUILDING. 463
of Harriman, Tenn.,” and shows the coal, coke, fossil and mag-
_netic iron ores and brown sandstone produced in that district,
together with the pig iron manufactured. The exhibit is
creditable to Harriman, but it is a pity that the state of
Tennessee in general did not make a full display of its coal, iron,
marble, and many other mining resources. The Cleveland Fire
Brick Company of Cleveland, Tenn., makes an exhibit of its clays
and bricks.
Kentucky makes a good and extensive exhibit of coal and
coke, with smaller collections of iron ores, building stones, clays,
Diteks,e ete. oy felich imap) otythe state is alsoman jattractive
- feature of the exhibit. The exhibit contains a large amount of
good material, but it might be displayed to better advantage.
Ohio makes a good exhibit of coal, its most important min-
ing industry, and also displays on a smaller scale its crude and
refined oil, its salt, clays, iron ores, whetstones, etc. It presents
a good model of a salt refining works, and makes a very attrac-
tive display of the bricks, tiles, etc., made from its clays.
Indiana makes a good business-like exhibit of just what it
has and no more, including a display of coal, clays, building
stones, oil, mineral waters, and tiles, and glass manufactured
from native products. The exhibit is well arranged and shows
all that is necessary.
Illinois makes an extensive display of its clays and the various
manufactured articles made from them. A much more exten-
sive mining, mineralogical, and geological exhibit of the state is
made in the large state building elsewhere on the World's Fair
grounds. This exhibit is well arranged, and truly indicative of
the products of the state.
Michigan makes one of the most elaborate exhibits of all
the states. The three great mining products of this state are
iron, copper, and salt. The first two are excellently repre-
sented ; the last is much neglected. The different kinds of iron
ore are illustrated with numerous specimens ; anda large colored
cross-section of the Cleveland Cliffs Iron Company’s mine is
given. A wooden model of the No. 4 Ore Dock at Marquette,
™;
404 THE JOURNAL OF GEOLOGY.
on the Duluth, South Shore and Atlantic Railroad, gives a good
idea of the method employed in handling large quantities of ore.
The different modes of occurrence of the copper of Michigan
are shown by a number of well selected specimens ; ‘while the
copper in ingots, sheets and wire is well displayed. . Interesting
wooden models are given of the shaft house and mills of the
Calumet and Hecla mine, and of the rock and shaft house of the
Tamarack mine. Other interesting features of the exhibit are a
number of pre-historic copper implements from Michigan, and ©
arches and columns of brown sandstone produced in the state.
The Wisconsin exhibit contains some good material, but it
seems to be arranged more to give prominence to fine specimens
than to show systematically the products of the state. The lead
and zinc industries of the southwestern part of the state are well
represented, but the great iron interests of the northern part of
the state are neglected, one pile of ore indefinitely marked ‘iron
ore” and a few other odd specimens being all that are displayed.
Some good specimens of granite and columns of red sandstone
are also exhibited. - In addition, various mineral specimens are
displayed, some of which have come from other localities than
Wisconsin, and are therefore misleading to the uninitiated.
Minnesota confines its exhibit almost entirely to its greatest
mining industry, z. e., the iron of the northern part of the state,
and in this department the exhibit is very good. Some building
stones and a few mineral specimens are also displayed. A
wooden model of the Chandler mine, and a number of maps
showing the mines and the geology of the state also form a part
of the exhibit.
Iowa makes a small but fairly characteristic exhibit, consist-
ing mostly of coal, building stones, etc. A feature of the exhibit
is an artificial “drift” in a coal mine, showing the mode of
working and transporting coal on underground tramways. A
model of a coal shaft and breaker is also given.
The Missouri exhibit is excellently arranged, and is
thoroughly indicative of the resources of the state. The lead,
zinc and iron industries are well represented, and pig lead and
EXHIBITS IN MINES AND MINING BUILDING. 405
zine spelter are displayed with the ores from which they are
derived. A model of the dressing works of the Saint Joseph
Lead Company and a relief map of Iron Mountain, colored to
show its geology, are interesting features of the_exhibit. The
coal industry of the state is also represented, together with a
number of building stones, ochres, etc., and a fine collection of
calcite and other mineral specimens from the lead and zinc
mines.
The South Dakota exhibit consists largely of tin ore, aurif-
erous quartz, mica and some argentiferous galena, and is
essentially a Black Hills exhibit. ‘ Lode” tin ore and stream
tin, as well as pig tin manufactured from the ores, are exhibited
in large quantities. A large column of tin ore, from the property
of the Harney Peak Consolidated Tin Company, contains a
placard stating that the capital invested is $3,500,000, a fact
it is difficult to understand they should wish to make so promi-
nent in view of the unproductive history of their operations.
The auriferous quartz is a good exhibit and characteristic of the
quartz deposits of the Black Hills. Some beautiful pieces of
Arizona silicified wood, which were polished in Dakota, are
exhibited, but in lack of the proper explanation as to their source,
they are misleading, as they suggest Dakota as the region from
which they were derived.
Kansas makes a very good exhibit of lead and zinc ores with
the pig lead and zinc spelter derived from them. The exhibit
also includes a display of rock salt, gypsum, building stones and
other minor products. The exhibit is small, but it is character-
istic of the state and is well arranged.
Montana makes a good exhibit as far as it goes, but many
localities and many important deposits are not represented. The
best exhibits are from the great mining camp of the state, 7. ¢.,
Butte City. The great copper and silver interests of this district
—especially the former—are well presented, and large quan-
tities of sulphide copper ores, and the metallic copper made from
them, are displayed. A quantity of gold quartz, and an inter-_
esting collection of gold nuggets are also a part of this exhibit.
400 THE JOURNAL OF GEOLOGY.
The most prominent feature of the exhibit, however, is a solid
silver, life-size statue of the celebrated actress, Ada Rehan, stand-
ing on a globe which in turn rests on a base of solid gold.
The whole work represents several hundred thousand dollars
worth of precious metals, all the products of Montana mines.
Wyoming makes a neat and effective exhibit. It consists
largely of coal in columns and blocks, jars of petroleum, blocks
of sulphate of soda and sulphate of magnesia, “lode” tin ore
and stream tin ore from the northeastern part of the state,
adjoining the Dakota tin region, iron ore, copper ore, auriferous
quartz, lead carbonate, asbestos, agates, clay, sulphur, building
Stones CLG:
Colorado makes a fairly good display of its silver-lead ores,
copper ores, gold ores, coal and manufactured lead and copper.
Some of the building stones and iron ores of the state are shown,
but these materials are not fully represented. An instructive
feature of the exhibit is a series of cases of gold nuggets, dust
gold and sheet gold from Breckenridge, Colorado. Many of the
important mining camps in the state are represented, especially
Aspen, Leadville, Creede, Cripple Creek, etc. The exhibit is
fairly good, but a state of such immense mining wealth as Colo-
rado could have made a much better one.
The Utah exhibit contains a large amount of valuable
material, but it is too much crowded and badly arranged. The
desire for a display of brilliantly contrasted colors has in some
cases entirely upset the systematic arrangement of the exhibit,
and has given part of it the appearance of the toy boxes with
pieces of minerals glued on the outside that are sold to confid-
ing tourists in our western states as works of art and value.
The exhibit represents the varied mining industries of the terri-
tory, among the most important substances being coal, gilsonite,
albertite, elaterite, asphalt, oil shales, sulphur, salt, iron ores,
copper ores, silver and gold ores, building stones, etc. The exhibit
of articles “‘japanned” by the gilsonite varnish are of interest.
Some large specimens of silver-lead ores and ores containing
chloride of silver are characteristic of the mines producing them.
EXHIBITS IN MINES AND MINING BUILDING. 467
The New Mexico exhibit contains some good material, but
is not very well exhibited. The silver ores, one of the most
important products of the territory, are well represented, being
grouped according to the localities from which they came. A
small cabin in the centre of the exhibit is composed of silver,
lead and gold ores from different localities. A stuffed burro
carrying a prospector’s camping outfit is a somewhat sensational
feature of the exhibit. A column of coal from Blossburg and
Los Cerillos represents the growing coal industry of the terri-
tory.
The Arizona exhibit is very good and well arranged. It is
truly indicative of the products of the territory. The most im-
portant features of it are the copper ores, the silicified wood and
the gold ores. The copper ores especially are well represented,
and a beautiful column of green and blue carbonates of copper
from Bisbee forms the most prominent feature of the exhibit.
While in the Michigan exhibit we see only native copper, in the
Montana exhibit only sulphides of copper, here in the Arizona
exhibit we see mostly carbonates of copper with some silicate
and oxide of copper. Thus in these three copper districts we
have representatives of three great classes of copper ores. An
interesting feature of the Arizona copper exhibit is a series of
models showing the underground workings of the Copper Queen
Consolidated Mining Company at Bisbee. The Old Dominion
Copper Company whose mines are at Globe, Arizona, makes a
very excellent exhibit of its ores and its copper ingots in a cabinet
alongside the main Arizona exhibit. The gold ores of Arizona
are well represented, and some of the silver ores are also shown,
while the beautiful polished sections of the celebrated silicified
wood of Arizona form an attractive and interesting feature of
the exhibit. Some of the so-called “onyx”
in polished slabs.
Nevada makes a fairly good exhibit of its mining products,
mostly the silver ores abundant in this region, and the accom-
panying minerals. A ‘special exhibit”’ from Eureka, Nevada,
contains a number of interesting specimens.
is also exhibited
408 THE JOURNAL OF GEOLOGY.
The Idaho exhibit is fairly good, but not thoroughly charac-
teristic of the state. The most prominent features are the silver-
lead ores from the northern part of the state, green copper car-
bonates, and a mineral water known as ‘‘Idanha”’ from Soda
Springs. A number of photographs of different mining dis-
tricts are of interest.
Washington makes a fairly good, but poorly arranged, ex-
hibit of gold ores, silver ores and silver-lead ores, and a few
other products. The coal resources of the state are entirely
neglected, though they are well represented in the Washington
state building. This separation of the mining products of a
region, and their distribution partly in one building partly in
another, is a great mistake, as it gives a person who sees only
one of the exhibits an incomplete and therefore an erroneous
idea of the resources of the state. The exhibit should be all in
one or the other building.
Oregon makes a large exhibit of auriferous quartz and shows
a very good working model of hydraulic mining. Some build-
ing stones are also represented. The exhibit is very good so far
as it goes, but it does not do justice to the state, as many of its
developed and undeveloped resources such as iron, coal, etc., are
not represented.
California makes a good exhibit, and one characteristic of
the resources of the state. It is very appropriately composed
largely of gold ores and a display of the methods of gold min-
ing. The auriferous quartz of the celebrated Grass Valley and
other localities is well represented. An interesting feature is a
wooden model by A. C. Hamilton showing a system of mine
timbering. Stibnite from San Benito county and the metallic
antimony derived from it are also represented. Among the other
prominent features of the exhibit are iron ores, asphalt, oils,
slate and a beautiful display of ornamental and_ building stones.
The so-called “onyx” from San Luis Obispo county, and the col-
ored marbles from Inyo County are exceedingly beautiful. The
exhibit is entered through arches built of the various ornamental
stones of the state, while blocks of rock containing the beauti-
EXHIBITS IN MINES AND MINING BUILDING. - 469
ful rubidolite, or pink tourmaline, are displayed at the entrance.
Elsewhere in the building is a fine and beautiful exhibition of
the so-called “onyx” from New Pedrara, in Southern California.
Besides the California exhibit in the Mines and Mining
Building, an interesting collection of the mining products of the
state, especially gold ores and native gold, are contained in the
California state building. Somewhat similar specimens, how-
ever, are in the Mines and Mining Building, so that the division
of the collection in this case is not especially injurious.
Among the foreign collections, that of New South Wales
stands preéminent. The great mining wealth of this province
is exhibited in a very systematic and thorough manner, and an
excellent idea is given of the resources of the region. There is
no attempt at a display of a sensational character as is seen in
some of the exhibits, but everything is shown in a plain business
way, in large quantities and in properly selected samples.
Among the most prominent features of the exhibit are its tin,
gold, silver, lead, antimony, copper, iron, manganese, and chromium
ores, its coal, graphite, building stones, etc. The ores exhibited
are average samples such as are sold in the market, and there-
fore give a true idea of the deposits represented. In many
cases, as in antimony, tin, etc., the metals are exhibited in blocks
or pigs, with the ore from which they are derived. The ores of
the great Broken Hill silver mine and the statistics of its pro-
duction are of interest to those acquainted with this famous
mine. The exhibit of the tin industry is of great interest as rep-
resenting the development of this comparatively new tin region,
which has only been much developed since 1872; while the coal
exhibit shows not only the bituminous coal of the region, but
also the kerosene shales, etc.
Among some of the other foreign exhibits those of the prov-
inces of Ontario and Quebec are very good, showing as they do
the various products of those provinces in a thorough and syste-
matic order. The other provinces of Canada do not make such
good exhibits. A collection of the rocks of Canada by the Geo-
logical Survey is of great interest. Mexico exhibits a great
470 LLL] OORAN ALES OTHE GTR OTE OG NG
amount of material, but it is so arranged that it loses much of
the benefit that it might afford to the exhibitors and to the
public. Brazil makes a fairly good exhibit, while Chile, Ecuador
and other South American countries are also represented. The
South Africa diamond exhibit is very interesting as showing the
mode of occurrence, methods of mining and washing, and cutting
the diamonds. The exhibits of Great Britain, Germany, Japan
and other foreign countries are also of interest. La Societé ‘Le
Nickel” of France makes a very interesting exhibit of its nickel
ore in New Caledonia, the nickel derived from it, pictures of
the mine and various other interesting features of the industry.
Many others of the numerous exhibits of American and
foreign products in the Mines and Mining Building might be
mentioned, but lack of space forbids further elaboration. The
same cause makes it necessary to discuss in another article the
extensive and excellent exhibition of the United States Survey
in the Government Building.
R, AvP: PENROSE, JR
=
Waa; ILA) SUNIOWUANS). (GuEVAC CIDE IR
One of the largest of the extinct glaciers of the Rocky
Mountains was that which occupied the valley of the Las Ani-
mas river. This stream originates in the San Juan mountains
in southwestern Colorado, and flows nearly south to its junction
with the San Juan river in New Mexico. The San Juan moun-
tains, with their outlying spur, the La Platas, are the first high
mountains encountered by the moist winds from the direction of
the Gulf of California on their way northeastward; and although
so far south, this region has perhaps the heaviest snow fall in
Colorado, as Fremont found to his cost. His expedition up the Rio
Grande attempted to penetrate the snowiest part of the mountains.
Silverton -is situated about fifteen miles from the head of the
valley, and Durango about sixty. About one mile north of Du-
rango, near Animas City, two well defined morainal ridges extend
across the valley of the Las Animas, and from thence a plain or
series of terraces of water-washed morainal matter extends for
several miles down the river. I have not explored far below
Durango, and do not know the extreme limit of the ice. At
Durango the ice rose to about the same height as the mesa lying
east of the city, on which is the reservoir of the water- works, 300
or more feet above the valley terrace. This is proved by the fact
that a thin sheet of morainal matter covers the slopes of the bluff
and extends back for a short distance on top of the mesa (up to 100
feet); whereas, beyond that the top of the mesa is a base level
of erosion in the sedimentary rock, with none of the far- traveled
bowlders that abound in the moraine stuff. The glaciated
bowlders are largely composed of rocks found only near the
head of the valley, such as volcanic rocks, Archean schists and
granites, Paleozoic quartzites, etc. Most of these must have
traveled thirty to sixty miles.
471
472 THE JOURNAL OF GEOLOGY.
About a mile above Durango, at the most distinct of the ter-
minal moraines thus far noted, the valley widens to about one
mile, and continues pretty broad for twelve miles or more north-
ward. The valley is here covered with rather fine sediment.
It is marked on Hayden’s maps as alluvium, but the glacial char-
acter of the terraces near Durango is not recognized, though
deposits substantially the same, situated a few miles northwest
of Durango in the La Plata valley, are markedly morainal. :
The post-glacial history of the valley was as follows. The
terminal moraines near Durango formed a dam that held ina
lake. This lake was partially filled with sediments, and at the
same time the river was cutting down through the morainal bar-
rier. The outlet is now so low as to drain the lake, except there
are some low, marshy flats where the water stands only a short
distance below the surface of the ground.
I have visited many of the tributary valleys of this river
above Silverton. Every cirque had its glacier that flowed down
into the larger valleys. The volcanic rocks of that region
weather readily, so that one seldom finds glacial scratches
except at recent excavations for roads and mines. It has there-
fore been a matter of considerable difficulty to determine the
depth of the glacier of the main valley. By degrees the esti-
mated depth increased until a few months ago, when I found
scratches well preserved on quartzite at a height estimated at 1,500
feet above the Las Animas river. This was near the Mabel mine,
about four miles southeast from Silverton, and not more than
500 to 800 feet below the top of the ridge which here borders
the valley on the east. The glaciated rock is situated on a long
gentle westward slope, while the scratches have a north and south
direction. Local glaciers would have flowed westward. These
scratches are therefore parallel with the movement in the main
Las Animas valley, under conditions where no local glacier could
have produced them.
It thus appears that near Silverton (elevation of valley about
gooo feet) the Las Animas glacier was 1,500 or more feet deep,
while at Durango (elevation about 6000 feet) it had a thickness
LHE LAS ANIMAS GLACIER. 473
of about 350 feet and a breadth of one-fourth mile or more.
Its extreme length was more than sixty miles, probably about
seventy miles. The average slope of the upper surface was
eighty-three feet or more per mile. For fifteen miles its breadth
was one or more miles.
From the terminal moraines near Durango, the valley of the
Las Animas is for several miles southward covered by a plain of
water-washed material, from coarse gravel up to bowlders three
to five feet in diameter. Some of these have glacial scratches,
though most have been so much rolled and polished as to pre-
serve no distinct scratches. The lower terraces at Durango are
of this character. They are typical of the overwash gravels found
in many of the Rocky mountain valleys. The subglacial streams
poured out their load of sediments in the valley in front of the
ice, where they were mixed with some material dropped directly
from the ice, and hence not rolled far enough to obliterate the
glacial scratches. More or less of this glacial gravel is found in
* all the wider parts of this valley and its tributaries above Silverton
until we reach within five or ten miles from the heads of the val-
leys. During the retreat of the tributary glaciers they poured
out much less glacial gravel after they came to be ten miles or
less in length, and what there was is usually but little water-worn.
Since the above was written further exploration reveals the
fact that a large glacier originated on the eastern slopes of the
La Plata mountains, and flowed southeastward down the valley
of Junction creek and joined the Animas glacier in the northern
part of Durango. Five hundred or more feet above the creek it
left a lateral moraine on the top of the narrow ridge which
borders the valley on the south. The moraine consists chiefly
of the eruptives and metamorphosed sediments found in the La
Platas, and but little of the local rocks.
The drift terraces near Durango are found at different levels.
The lowest terrace is that above described, and consists of
glacial gravel mixed with matter that has been but little rolled.
The higher terraces have the appearance of ordinary valley
terraces as seen from the river, but in some cases do not extend
A74 THE JOURNAL OF GEOLOGY.
back to the sides of the valley. The largest of these lies on the
east side of the Animas river, between Animas City and Durango.
It is more than a mile in length, and the outer or distal side ends
in a bluff twenty to forty feet high.» At its north and south ends
this curved terrace approaches near to the mesa bordering the
valley, thus enclosing a depression several hundred yards wide
that is occupied by a small lake in time of violent rains. A
basin of this kind could not have been hollowed out by the
river, and, besides, the terminal moraines of Animas City extend
across the north end of the basin. It is evident that this terrace
was formed laterally to the glacier in substantially its present
form. It contains great numbers of boulders up to fifteen feet
in diameter, but a large portion of it has been very much water-
rolled. The most probable interpretation is that these higher
terraces began to be deposited at the outer edge as a lateral
moraine. Then as the ice gradually receded morainal matter
and glacial gravel were simultaneously deposited in the space
between the moraine and the retreating ice. This hypothesis
well accounts for the fact that morainal and water-rounded
matter are so intimately mixed in the terrace, also that the
overwash did not spread laterally back to the margin of the
valley. We thus have the terraces ending distally in the steep
slope characteristic of the moraine rather than the more gentle
slope of the overwash apron. Most of these higher terraces end
proximally (next the river) in rather steep slopes or bluffs rising
twenty to seventy-five feet above the lower terraces. No city of
Colorado has so much of glacial interest within its limits as
Durango, unless it be Leadville.
It is an interesting fact that the cols of the mountain ridges
of this region are glaciated almest or quite to their tops. Thus
at Stoney Pass, the first pass north of Cunningham Pass, I saw
well- glaciated rocks within 200 feet (horizontally) from the top
of the pass. From the top of this pass the mountain slopes
steeply northwestward toward the Las Animas valley, and in
the opposite direction down the Rio Grande valley. The rocks
at the summit were weathered, and it was not evident whether
THE ELAS ANIMAS GEA CTER. 475
the top of the ridge had been glaciated, but it is certain the ice or
snow flowed in opposite directions from the col. On each side of
the pass, peaks of the Continental Divide rise above the col to a
height of 1000 to 2000 feet. It is evident that the snow from these
peaks would flow or slide from each side down into the pass, and
maintain a supply of névé or ice right on top of the ridge in the
pass. The pass is about 11,800 feet high. It thus appears that
the snow fields reached nearly to the tops of the mountains, say
about 12,000 feet in the cirques and passes, while above this the
discharge was probably in large part by avalanches.
Durango city is situated in about N. Lat. 37° 16’, a few miles
north of the end of this glacier. It is to be carefully noted, in
the study of the climates of the glacial epoch, that a glacier
nearly seventy miles long reached so far south. Apparently the
most snowy part of Colorado now was also the most snowy then.
During the retreat of this glacier it left numerous small
retreatal moraines, both in the main valley and in the tributary
valleys above Silverton. One of the most accessible is near the
junction of the two branches of Mineral creek, about three miles
northwest from Silverton.
It is noticeable that the proportion of moraine stuff left by
this glacier is small as compared to the glacial sediments. No-
where have I yet found very noticeable ridge or terrace lateral
moraines. This is in part due to the steepness of the hills that
border the sides of the Animas valley. There is usually a
scattering of glaciated matter on these hill slopes, and where
they are less steep, or in lee of ridges projecting out into the
valley, local morainal sheets are sometimes found that have a
depth of twenty feet or more. Small terrace-like lateral
moraines extend for a mile or two north of the terminal
moraines of Animas City near Durango. Probably the snow
avalanches and flowing névé carried down débris and incor-
porated it with the glacier proper, so that there were no
large surface lateral moraines as in some of the valleys of the
Alps, or in the Arkansas and some other valleys of Colorado.
In other words, the débris of this glacier was largely englacial
and basal. GEORGE H. STONE.
STUDIES BOR SUD ENES
CONDITIONS OF SEDIMENTARY DEPOSITION.
EROSION.
Erosion consists of fragmental reduction and abrasion of rock
masses, chemical disintegration of rocks and transportation.
The three sub-processes may be called rock-breaking, rock-decay
and transportation. They are conditioned by declivity, lithologic
character and climate.
ROCK-BREAKING.
Favorable conditions:
(ay Steep slopes.
(0) Bare rocks.
(c) Cleaved and jointed rocks.
(dz) Alternation of hard and soft beds.
(e) Rapid changes of temperature.
(f) Aridity and high winds.
g) Abundant rainfall, in the absence of vegetation.
(2) Sea cliffs.
Products: Shingle, gravel and sand of mixed mineralogical
composition.
ROCK-DECAY.
Favorable conditions :
(z) Gentle slopes.
(6) Porous soil.
(c) Soluble rock constituents.
(@) Carbonic acid and other acids of organic decay.
(e) Abundant rainfall in the presence of vegetation.
(f) Prolonged transportation of gravel and sand.
476
CONDITIONS OF SEDIMENTARY DEPOSITION. 477
Products: Rock cores of disintegrated masses, sand, (chiefly
quartz-sand), residual clays, and lime, magnesia,
iron, etc., in solution.
TRANSPORTATION. =
Favorable conditions:
(az) Steep slopes.
(6) Abundant rainfall.
(c) Absence of vegetation.
(d) Floods
(@) Fine detritus.
By comparison of the statements of favorable conditions for
rock-breaking, rock-decay and transportation it becomes apparent
that breaking and decay are favored by opposite conditions in
nearly all respects, while breaking and transportation are most
efficient under like conditions. But breaking promotes decay,
and decay aids transportation, by reducing the size of the parti-
cles to be decomposed and carried, and the maximum effect of
erosion is probably attained when rock-breaking is active
among greater elevations, and rock-decay and transportation are
both proceeding energetically on lower slopes. *
The amount of material furnished by erosion is an important
consideration in reference to the rate of accumulation of sedi-
ments over a given area, and is a condition not to be overlooked
in comparing thicknesses of deposits with the lapse of geological
ages.
SEQUENCE OF SEDIMENTS.
Shingle, gravel, sand, clay and silt are products of ero-
sion of rock masses. They are produced either by mechanical
breaking or by chemical disintegration. These two sub-
processes of the general process of erosion are favored by
unlike conditions. Those conditions which render breaking
most efficient are unfavorable to immediate disintegration ; and
those conditions which promote disintegration limit breaking.
Breaking, the reduction of a rock mass to small pieces, is usually
tGilbert, Henry Mts. p. 105.
478 THE JOURNAL OF GEOLOGY.
the antecedent of disintegration, of decay, but the two are not
most efficiently active at the same time. Now their products
differ. Rock breaking yields shingle, gravel, coarse sand of
mixed mineralogical composition, and no chemical ‘solutions.
Rock-decay yields directly no shingle or gravel, but produces
sand, chiefly quartz-sand, clay, silt and chemical solutions.
Hence, if the products of rock-breaking are deposited unchanged
in the sea, there will result one class of sediments from which we
may infer corresponding conditions of erosion of the parent land ;
and if the products of rock-decay are deposited we must infer
other conditions of erosion.
Declivity is the chief factor which determines either rock-
breaking or rock decay. Rock breaking occurs on steep slopes,
that is, among hills or mountains ; rock-decay takes place chiefly
on gentle slopes, that is, in valleys or on plains. Hence the
sediments may indicate the topographic phase of the parent-land.
They may indicate topographic phase, not permanent topo-
graphic character, for relief of the land surface is transient. The
steeps of mountains become the slopes of hills, the hill slopes sink
to plains and plains to base-level; and erosion pauses till renewed
by uplift. So the conditions of rock-breaking pass into those of
rock-decay, and the product of the two processes may appear in
sediments, the older gravel and sand beneath the younger sandy
clay and clay.
The possible sequence of unlike sediments does not stop with
the finer mechanical products of disintegration; chemical solu-
tions may be related to chemical or organic deposits, and these
have their place among strata. The amount of lime and mag-
nesia carried annually from a given land area is directly related
to the efficiency of rock-decay, and so among other factors to
slope. Rock-decay is limited on the one hand by declivities,
which promote the rapid running off of rainfall, and on the other
hand by the accumulation of a deep covering of soil, which pre-
vents percolation. Other things being equal, it is probably most
efficient during the period corresponding with the life of low
hills and sloping plains. If at any time chemical solutions from
CONDITIONS OF SEDIMENTARY DEPOSITION S. - 479
the land determine the deposition of calcareous formations they
will do so most efficiently during this topographic phase, and
in the absence of mechanical sediments the corresponding de-
posits will be limestones or dolomites. As the topographic phase
passes to its close and the sloping plains sink to base-level, the
power of streams to transport mechanical sediment fails, and
rivers finally carry only silt in lessening proportion; hence the
upper portions of a great limestone deposit may be less clayey
than the lower. Furthermore, the mantle of residual clays,
accumulating upon the extended base-level, will check solution,
and thus, in so far as the deposition of limestone is influenced
by contributions from the land, will limit the growth of the for-
mation; and with the cessation of both mechanical and chemical
supply, terrigenous deposits will cease to form beneath the sea.
Then, while these conditions endure geologic ages may pass with-
out record in sediments unless there is a marine source of supply.
Thus far this statement has tacitly assumed a constant relation
of elevation between coast and ocean. Assume that the long
quiet, which has been necessary for the reduction of a mountain
range to base-level and the deposition of the corresponding sedi-
ments, is interrupted by sinking or heaving of the landarea. The
surface is low, flat and covered by a mantle of residual sand and
clay intimately mingled. Moderate subsidence must lead to ex-
tensive transgression and the invading sea, margined by tide flats,
will spread arenaceous, clayey deposits, bearing the marks of
shallow water formations and resting unconformably upon the
aneient rocks. If the residual soil be red, the sediments will be
of similar color, since the process of deposition on tide flats does
not involve much attrition and the ferruginous coating of the
grains will remain.* The base of the deposit may be a zone of
transition, composed of cores of undecomposed rocks, imbedded
in more or less re-arranged products of partial decomposition.’
‘Bull. U. S.G.S. No. 52. I.C. Russell, Subaérial Decay of Rocks and Origin
of Red Color of Certain Formations.
2R.Pumpelly. The Relation of Secular Rock Disintegration to Certain Transitional
Schists. Bull. Geol. Soc. of America. Vol. IL., p. 209.
480 2 HE, JOORINALG OFA GTSOL OGM
Or, on the other hand, moderate uplift of the base-leveled conti-
nent, must cause the revived streams rapidly to sweep into the
sea the mass of insoluble clay and sand which formed the resi-
dual mantle. Thus the limestone deposits will be succeeded by
a thickness of shales of a more or less arenaceous or clayey
Characters
From these considerations it follows that a complete
topographic cycle may be related to a sedimentary sequence
composed of a sandy base, a limestone middle and a shale top.
Newberry first noted the frequent recurrence of this sequence,
and sought an explanation in conditions related simply to the
sea; its advance, presence and retreat. When he made his gen-
eralization the base-level had not been recognized as a result of
continued erosion, nor had Gilbert analyzed the process of
erosion; and Davis had not described a topographic cycle.
These contributions to the science have widened the field of in-
ference, and the topographic phase of the land can no longer be
disregarded in the discussion of the deposits of the sea.
But it should not be forgotten that the inference from sedi-
ments should be confined to the topographic phase of a belt of
land extending back from the shore to a moderate distance only.
The products of rock-breaking disintegrate during prolonged
transportation and mountains remote from the coast are not in-
dicated in deltas of great rivers. A student of the deposits of
the Mississippi would not infer the height of the Rocky moun-
tains, but the sands of the Klamath river bear witness to the near- »
ness of the coast range.
The analysis and discussion of conditions which govern the
character of the material contributed from land to sea might be
extended in detail, and illustrated by descriptions of sediments
in existing rivers, but the subject is worthy of independent treat-
ment.
SEDIMENTATION.
Sedimentation consists of three sub-processes, sorting,
distribution and deposition. These are effected by waves and
undertow, tides, winds and oceanic currents and are modified
B
CONDITIONS OF SEDIMENTARY DEPOSITIONS. 48%
by the relation of volume of sediment to the force of waves or
currents. If the analysis be based on the sub-processes and
conditions which favor them, it may be stated and discussed as
follows:
=
SORTING.
The conditions under which sorting is more or less efficiently
carried on are three in number.
Favorable conditions:
(z) Vigorous wave action accompanied by strong
undertow.
(6) Prolonged transportation in consequence of
deep water and continuous currents.
(c) Moderate volume of sediments.
The conditions under which sorting is not accomplished are
the reverse of these, namely:
Unfavorable conditions :
(z) Feeble or diffused wave action.
(6) Concentrated deposition.
(c) Excessive volume of sediments.
It will be profitable briefly to discuss these positive and neg-
ative conditions.
(a) Vigorous wave-action.—The force of waves is determined
by their fetch and the strength of winds. In the study of mod-
ern beaches the latter is important, since it controls the form and
the greatest storm’ fixes the maximum size of detritus moved;
but in considering fossil beaches as strata we deal with sands
which have been so rearranged during submergence that the
beach form is lost. However the former condition, the fetch
of the waves is more constant, and the force of the waves
determined by it may be inferred from the nature of the beach
deposits.
The efficiency of waves of a given force is determined by the
concentration of their blows, and this is conditioned by the slope
against which they break. If relatively deep water prevails
For full discussion of wave erosion and deposition, see Lake Bonneville, by G. K.
Gilbert. Monograph 1, U.S.C. 5.
482 LE JOUTANALE OL NGHOLO. GAVE
to the shore, whatever force the waves may have is expended
at the water’s edge. On a bold coast they carve sea-cliffs
and grind shingle with sand. Such are the coasts of
New England, Oregon, California, and of all the Pacific
side of South America. The resulting sediments are com-
posed of worn but fresh rock fragments and thus bear witness to
rapid mechanical erosion, like the products of rock breaking on
steep declivities. Ona shore of incoherent materials waves stir,
wash and separate fine and coarse, light and heavy particles.
Under favorable conditions of depth of water and long fetch,
waves thus sort a heterogeneous mass of gravel or of residual
sand and clay more efficiently than any other agent, and leave
clean cross-stratified beach sand and gravel with boulders, while
the finer materials are swept away. The southeastern shore
of Long Island presents a conspicuous example of this, and
the westward drift of the beach-sands is illustrated in the fact
that shingle beaches prevail toward the eastern end of Montauk
point, and the sands there washed from the bluffs of glacial
gravel form long barriers along the coast to the westward.
If, on the other hand, waves break in shallow waters at a dis-
tance from shore they there build a barrier, and the height to
which they build it above high tide is the measure of their max-
imum power during great storms. Within the barrier then ex-
tends a lagoon. The whole Atlantic coast from Long Island to
Florida is thus fringed by the features of prevalent wave action,
due to the great fetch from off the ocean and the gradual slope
of the continental platform.
(6) Prolonged transportation—Sorting is also accomplished
to some extent, though less perfectly, by deep water and con-
tinuous currents. Sediments settle unequally according to size
and specific gravity of particles; therefore the largest and heav-
iest reach bottom first, the finer and lighter later, and the finest
and lightest last. If the conditions of supply or current be in-
termittent over any area then each incident of deposition will be
marked by a layer composed of coarsest grains below and finest
grains on top. This is the nature of deposition in tidal estua-
CONDITIONS OF SEDIMENTARY DEPOSITION. 483
ries. If,on the other hand, currents be continuous and constant,
the zones of sand, clay and silt deposits will occur each beyond
the former. But this is a question of distribution as well as of
sorting of sediments. ae
(c) Moderate volumes of sediments.—Sediments are also
more or less completely sorted by waves or currents according
to the relation between the volume of sediment and the force of
the sorters. When waves breaking upona coast have only the
product of wave erosion to handle they sort most completely;
the material is washed again and again until no trace of clay
remains mingled with the sand grains ; and the under-tow, bur-
dened only with the clay washed out by the waves and the fine
products of abrasion, ¢arries them all away. But where a river
pours out a large volume of sediment, and waves or currents are
consequently overloaded, both sorting and transportation fail to
a greater or less degree. Deposition takes place too rapidly for
the separation of fine from coarse and the deposit is of mixed
character. _The effect of waves is then seen in ripple-marked
and ill-assorted beds of tide flats.
DISTRIBUTION.
The conditions under which sediments are more or less widely
distributed, depend upon movement of the waters and the nature
of the sediment; those favorable to distribution are:
Favorable conditions :
(a) Efficient wave action prevailing from one direction
oblique to the shore.
(6) Continuous currents.
(c) Uniform or gradually increasing depths of water.
(2) Fine or light sediment.
The reverse of these conditions favor deposition, and will be
discussed in that connection.
(a) Efficient, oblique wave action.— Distribution of shore
drift is fully discussed by Gilbert, and has already been referred
to in stating the effect of sorting by waves of the Atlantic on
484 LPHE, JOOKINALE OF NGE OLOGY.
the south shore of Long Island, and the formation of barriers of
wave-washed sand.
(2) Continuous currents.—Distribution by continuous cur-
rents is the condition usually assumed as having controlled the
arrangement of sediments in seas of past geologic periods. In
consequence of the sorting which results from different rates of
settling clay is carried beyond sand, and silt is distributed more
widely than clay. The prevailing current, which thus distrib-
utes, is under-tow more or less checked and assisted by tides.
If the submarine slope descends from the shore steeply into
oceanic depths, the force of undertow must rapidly be dissi-
pated, but pebbles and sand move easily down the steep
incline, and form a sequence of continually smaller particles,
which is usually not very extended. This is the case on
themenwestern coast Oks SOuUrhna Americas If on) thesrother
hand, the seaward slope is very gentle, undertow loses
force more gradually and fine sands may occur to great dis-
tances from the shore, with clay and silt deposited beyond
them. This is the case off the Atlantic coast of the United
States where tides probably form a powerful alternating influ-
ence; there the continental plateau is covered with sand to its
outer rim, as is shown by soundings by the Coast Survey. But
the force of undertow is determined in the first place by the
force of waves, and it can be effective in distributing only where
waves are powerful. It fails in limited seas except in a very
narrow zone along shore.
Ocean currents also distribute sediments very widely. The
terrigenous deposits of the Bay of Bengal and Arabian sea,
mapped by Murray," covering 1,600,000 square miles, owe their
wide spread distribution apparently to the ocean currents which
circulate east and west alternately with the changes of season in
these great bays.
(c) Uniform depths —Changes in depth of water affect the
velocity of a current and thus modify its power to distribute sed-
iment. Narrowing channel or shallowing water may cause a
*Scottish Geogr. Mag., Vol. V. No. 8, Aug. 1889.
CONDITIONS OF SEDIMENTARY DEPOSITION. 485
current to scour and take on more load ;. but broadening channel
or deepening water tends to cause it to deposit. The Gulf
stream scours the straits of Florida and the Blake plateau, but
deposits a silt bank on the lee side of the latter.?~ Only in the
broad expanse of deep water does it widely distribute sediment.
_(d)_ Size of particles —Fine or light sediment is most widely
distributed. The ‘blue muds” which form the terrigenous de-
posits beyond the littoral zone consist of particles of an average
diameter of .05 mm.
Deposition occurs whenever a body of water becomes over-
loaded with substances in suspension or in solution. According
to the condition which determines the result the deposits may
be classified as mechanical, chemical and organic.
MECHANICAL DEPOSITION.
Favorable Conditions :
(a) Arrest and retreat of waves; beaches and sand deposits
from undertow.
(0) Current entering still water and slowing; lake-deposits.
(c) Alternating currents in fresh and salt water; estuarine
deposits.
(d) Rise of salt water surface at a river’s mouth in conse-
quence of winds, long continued from one direction ;
delta of the Mississippi.
(e) Flotation of fresh water on salt; bars of the Mississippi.
(f) Floculation of sediments in salt water.
(¢) Expansion and diffusion of a current in rapidly deepen-
ing water; silt deposits on the edge of continental
plateaus.
(Z) Final subsidence from oceanic circulation.
Arrest of Waves.—(a) Beaches are formed where waves
break. The rotary oscillation which constitutes waves in deep
water becomes a motion of translation when the water shallows
sufficiently and the mass of the broken wave, rushing forward,
t Agassiz. Three Cruises of the Blake. Bull. Mus. of Comp. Zodlogy. Har-
vard College. Vol. XIV.
486 THE JOURNAL OF "GEOLOGY,
carries up material stirred from the bottom. The finer particles
are swept back by the undertow, the coarse are placed by the
greater waves beyond the reach of the lesser. Thus waves, con-
stantly in advancing, take material from the lower part of the slope
to carry it up, and in retreating sweep back more or less of their
load with them. If the slope be gentle they thus take from the
lower to add to the upper part, and therefore they increase the
declivity until the seaward profile becomes so steep that the load
carried in retreat balances that advanced. This is the profile of
equilibrium, which waves perpendicular to the trend of the beach
do not change, unless they are of unusual force. Waves oblique
to the beach-slope, scour, transport and deposit the same sands
repeatedly, and if the oblique advance be prevailingly from one
direction the effect is to move the beach longitudinally. _Then
the beach, in any one section, continues, while the supply of
sand is continuous; but when the supply ceases the beach is
gradually moved onward in the direction of the prevailing wave
action, and the material beneath the beach sands is exposed to
Wave erosion.
A beach itself is but a narrow zone; it cannot constitute a
wide-spread formation any more than a line can constitute a
plane. But if a line be moved in one direction parallel to itself
it will develop the plane, and in the same manner if a beach ad-
vances landward it may spread a formation. This advance may
be a result of wave erosion, which carving a sea cliff on a bold
shore planes a surface of marine denudation. The beach deposit
is then a basal conglomerate. Or, the land reduced to a low sur-
face by subaérial erosion may subside slightly in reference to sea
level,and the sea, transgressing, will rearrange the superficial for-
mations. If the waves have power to handle the material the sea
is margined by beach sands. If they cannot efficiently sort it
the land will merge in tide-flats with the water.
A beach is not only narrow, it is also shallow; waves build
on the surface over which they break, and the height to which
they may build does not exceed a few feet. Therefore, beach
deposits cannot form thick strata.
CONDITIONS OF SEDIMENTARY DEPOSITION. 48 7
The undertow rolls coarser sand and. pebbles down the slope
of the bottom, and carries out in suspension silt and clay with
more or less fine sand. The rolling of coarser sands is promoted
by a steep slope. The transportation of finer sands depends on
the endurance of the undertow of a given initial strength; and
this endurance will be the greater the more gradual the seaward
slope and the stronger the tides. The amount of sand thus de-
posited is limited only by the supply, and sandy strata may,
therefore, attain great thickness and have great extent seaward
from a fixed beach line. If the coast be continually maintained
by uplift or renewed by volcanic flows the work of the waves
may be of like duration and the record will be correspondingly
voluminous. Professor Chamberlin mentions the great conglom-
erates of Lake Superior in this connection.
Beach deposits, strictly speaking, are usually of quite coarse
sand, clean and characterized by marked and irregular cross-
stratification. Sand deposits from undertow graduate from clean
to muddy sands, becoming ever finer seaward, and are horizon-
tally bedded or massive.
Therefore the interpretation which may be put on strata, de-
posited by the arrest and retreat of waves, are:
(1) A basal conglomerate is significant of an horizon of
wave erosion, due to transgression of the sea and probable sub-
sidence of the land. If the basal contact be clean and sharp the
waves probably carved a shore cliff in hard rocks. If, between
the parent rock and the later sedimentary formation, there pera
zone of transition composed of boulders, sand and clay of mixed
mineral composition, the waves probably rearranged the cores
and finer products of a surface of partial subaérial rock decay. A
basal conglomerate of any variety is a definite proof of an un-
conformity by erosion; it is often the only fact by which such
an unconformity can be distinguished from an overthrust fault.
(2) A deposit of clean sands is proof of the former existence,
somewhere, of a beach on which they were washed; but the
place of deposit may have been remote from the line of the
beach. Coarseness of grain suggests proximity of land and vice
488 THE JOURNAL OF GEOLOGY.
versa, but such suggestions need to be qualified by considering
the probable fetch of the waves, the corresponding initial strength
of the undertow and the declivity of the seaward slope.
A thin stratum of coarse cross stratified sands may represent
a transgression by a beach-building sea over a subsiding land.
A thicker stratum may have been formed by deposits from under-
tow behind a stationary or advancing beach line, and if such a
deposit shows cross-stratification throughout, it was washed by
conflicting currents, probably tidal, during its accumulation. ;
The deposition of beach-washed sands is consistent with con-
stant or subsiding level of the land in relation to the sea. It
does not appear that it is likely to occur during uplift from the
sea except in the comparatively rare case of the rapid ele-
vation of a bold coast range with preponderance of rock-break-
ing over rock-decay.
The occurrence of a stratum of sandstone is not evidence that
during its formation the land furnished no other detritus. If the
sands be of mixed mineralogical composition, bold declivities on
land and prevalence of rock-breaking are indicated; but if the
sands be chiefly quartzose it is more probable that the waves
have sorted the waste of a residual mantle. :
Quiet Water—(6) When a current enters a body of quiet
fresh water, unvexed by tides or winds, as a stream enters
a lake, the inertia of the greater mass and the diffusion of
the stream in the greater volume checks the current, and it drops
whatever sediment it may have carried. The laws of this simple
case can be formulated mathematically, and Babbage has calcu-
lated the distance to which sediments of an assumed character
would be transported by a river current of assumed velocity
entering a salt-water body, whose bottom has an assumed slope ;
he neglects the difference of density between fresh and salt
water, and assumes an off-shore current equal to that of the river
at its mouth. The conclusion is determined in advance, and
cannot be applied to the interpretation even of lake sediments,
since the assumed conditions of sediment and current are hypo-
‘Hand Book of Physical Geology, 1884. A.J. Jukes-Browne, p. 185.
CONDITIONS OF SEDIMENTARY DEPOSITION. 489
thetical. An existing case, which approaches the conditions
assumed by Babbage, is that of the Rio Uruguay, which is
described by Revy.* .
“The little town of Higueritas, also called Nueva Palmira,
is situated in latitude 33°52’S., long. 58°23’ W.,in the Banda Ori-
ental, at the junction of the Uruguay with various branches of the
Parana, all of which discharge jointly their volume into the La
Plata. Three miles below Higueritas, at Punta Gorda, the La
Plata proper commences; three miles above Higueritas the
Uruguay opens into a lake from 4 to 6 miles wide and about 56
miles long. There are no islands on this lake, although, with
the exception of a deep channel half a mile wide of steep sides
and submerged, the lake is shallow ; it may be called the estuary
of the Uruguay. A little above Fray Bentos, 58 miles from Hig-
ueritas, the first islands appear within the lake; and, their num-
ber soon increasing, we enter the delta of the Uruguay, which for
25 miles more retains the width of the lower lake, breaking,
however, up into a great number of large and small islands, until,
a little below Paysandu, the river proper commences within a con-
fined channel. At Paysandu, a commercial town of importance,
125 miles from Higueritas, the delta of the Uruguay commences.
At Fray Bentos the visible delta terminates ; and from the latter
place to the La Plata the future delta of the Uruguay is now in
COURSE OloOnmMations @ a...
. During the survey of the Uruguay there was a period-
ical rise of the river, viz., on February 3, 1871, and a sample of
-water was taken on that day at the Salto section, about 200
miles above Higueritas. The water was turbid, of deep brown
color ; and the analysis of the sample showed that it contained
one part by weight of solid matter in suspension in 9524 parts of
water. There was no perceptible change in the color of the
water or in its analysis, until we reached Fray Bentos [142 miles
below Salto | on the 5th February, 1871, and here it contained 1
part solid matter in 11,200 of water by weight in suspension. At
Higueritas, on the same day, the waters of the Uruguay ap-
t Hydraulics of Great Rivers. J.J. Revy, pp. 134-135.
490 THE JOURNAL OF GEOLOGY.
peared clear, and we could only trace one part of solid matter
held in suspension by 25,925 of water. Nothing could more
forcibly illustrate the formation of deltas. The river retains
matter held in suspension by its water within its ordinary chan-
nel as long as its velocity is maintained ; as soon as itenters a lake
or an estuary checking regular currents, the matter held in sus-
pension is dropped.”
That is to say, in flowing 142 miles in its navigable channel
and through its delta the river dropped about 15. per cent.
of the load which it bore at Salto; and beyond the delta in
still water it dropped 48 per cent. more; leaving it but 37
per cent. of the original load to be carried past Higueritas to the
estuary of the La Plata. Or stating the proportions in terms of
the sediment brought through the delta to the head of the lake,
57 per cent. was deposited and 43 per cent.escaped. It would be
desirable to determine in what ratio the deposit is made in the
upper and lower reaches of the lake, but Revy gives no data
between Fray Bentos and Higueritas. He states however that the
lake is without islands, although it is shallow with the exception
of a deep channel half a mile wide ; but just above Fray Bentos
islands indicate the present front of the delta. The occurrence
of these advance elements of the delta only in a limited distance
indicates that the bulk of deposition is on the delta’s front, and
that the sediment which passes beyond is that which the slower
current of the lake can hold in suspension.
The deposits of the extinct lakes Bonneville and Lahontan
have been fully described by Gilbert and Russell, but the lake
beds of the west still present rich fields for study of deposition
under simple conditions in fresh and salt water.
(c) Alterations of Current—Whema land-locked water body
is open to the ocean it is subject to influx and reflux of tides, but
the rivers pouring into it may possess volume sufficient to exclude
salt water; it is then a fresh-water estuary, which receives the
sediments as well as the waters of its tributaries. The currents
in such an estuary are periodic, changing with the flood and
ebb, and the conditions of deposition vary accordingly. The
CONDITIONS-OF SEDIMENTARY DEPOSITION. 491
Atlantic coast is fringed with estuaries which are carefully
mapped by the Coast Survey, but variations of deposit with
changes of current have apparently not been described. Writing
of the La Plata, an estuary 125 miles long, where the tide from
the Atlantic contends with the current of the rivers Paraia and
Uruguay, Revy says: * |
‘At this point, where the power of the tidal wave balances
that of the rivers, there will be no current; the level of the estuary
will rise slowly like that of a lake receiving supply from all
round its border. It is here—where the rivers and the tidal wave
contend for supremacy, each trying to establish its own current,
and where for hours the power of either of them trembles in the
balance without any sensible movement in any direction—that
deposit copiously takes place ; matter, held in suspension by the
rivers as long as their currents are maintained agitating their
water, is dropped as soon as they cometo rest. It is here, within
about 10 or 20 miles of the river's mouth that banks are most
rapidly growing and islands are forming, and the ultimate result
of these daily contests is invariably in favor of the rivers which
slowly but steadily encroach on the estuary and ultimately annex
its whole territory. The progress of the tidal wave is, however,
never checked an instant, the rivers only check the currents orig-
inating with the wave. . . . . A tidal wave is never visible to
the eye, and can only beconceived from observation, by a suc-
cessive measurement of its dimensions, which are very large. We
may, from an elevated position, see 10 or 15 miles, but a tidal
wave onthe La Plata is about 258 miles long... . .
“.. . . During the second half of the tidal wave, viz., from
flood to ebb when the surface of the La Plata is falling, there is
much more uniformity in the directions of the currents, which
for a time will be the same for the whole estuary, all tending to
the Atlantic. The wave will again proceed faster in the deeper
than in the shallower portions of the estuary, and will accord-
ingly make the level fall a little faster in the deeper channels, and
‘Op. cit. pp. 29-30.
492 THE JOURNAL OF GEOLOGY.
the current will now set from shore into the estuary; the reverse
of what happened with the rise of the La Plata.
‘By degrees the level of the estuary will again adjust itself to
mean sea-level. All the water which the tidal wave brought
from the sea will now have to be returned, and in addition the
whole volume which the great rivers have discharged into the
estuary ; and the currents will not only be stronger, but they will
also last longer, of which circumstance the outline of the tidal
wave bears evidence, the duration of the rise of the La Plata
being about six hours, its fall continuing for about seven hours.”’
Revy further calls attention (page 23), to the fact that the
current with a given fall of the river is swifter in deeper, slower
in shallower water therefore deposit during flood-tide is
more copious over shallows, and is there less liable to scouring
during the ebb. It follows that the shallows become tide-flats,
tide-flats are raised to rush-grown islands, and the islands unite
to extend the river’s banks. Thus the Parana has filled two-thirds
of the La Plata, which was 325 miles long, and the river will
ultimately replace the estuary, so that the future delta will be
built into the Atlantic, as that of the Mississippi extends into the
Gulf.
If the sediment thus deposited consists of mingled sand and
clay it will be sorted to some extent by the alternate checking
and starting of currents. As with rising tide the current slows,
sand will first be dropped; during the period of quiet water both
sand and clay will sink together, though at unequal rates; and
when the ebb restores the outward current, the surface of the
latest deposit may be scoured, removing clay and leaving sand.
Furthermore the swifter currents of the channel may carry clay, ;
even though dropping sand, while the slower currents of the
shallows drop both. Hence there must be a tendency toward
alternation of more sandy layers with more clayey ones, and of
horizontal passage of sands into clays.
Where rivers enter bays of such depth or expanse that the
fresh water does not displace the salt water, other conditions
than those governing estuarine deposition prevail. It is there
CONDITIONS OF SEDIMENTARY DEPOSITION. 493
probable that the influence of tides is often subordinate to that
of winds, of the difference of density between fresh and salt
water, of mechanical and chemical reactions of salt water on
sediments, and of currents prevailing along shore.-
The influence of tides upon undertow, tending alternately to
retard and accelerate the seaward current, may be important and
may lead to alternate episodes of deposition and scouring as it
does in estuaries; this is probably the case on all submerged
continental platforms, and particularly where tides sweep in from
a great expanse of ocean, as on the Atlantic coast of the United
States. The effect, where conditions favor it, would be more
regular than among the shoals and channels of an advancing
delta, and the alternation of strata would be more distinct and
even; it is possible that thinly interbedded strata of unlike
character may be thus interpreted.
The well recognized characteristics of tidal formations are
the evidences of shallow water, ripple marks, sun cracks, organic
trails, etc., peculiar to sections of the shore where sediment is
abundant. The strata are shales, and shaley sandstones
irregularly bedded and often red. Such deposits are direct evi-
dence that:
(1) The land from which they came presented gentle slopes
and was mantled in residual formations to a distance from the sea.
(2) Since the zone of tide-flats along any shore is limited in
width, if the distribution of such strata be wide, either great
rivers gradually filled a shallow basin, as the Mississippi, the
Amazon and Parafia have done, or the sea transgressed upon a
low-level land. In the former case the land was built outward
by volumes of muddy fresh water, and the deposits would be of
fresh or brackish water types. In the latter case the sea pre-
vailed and the deposits would be of marine character.
(3) Since the level of tidal deposits is near the surface of
the water, and they are therefore limited in thickness, if a con-
siderable thickness shows the characteristic marks throughout,
the area of deposition subsided at a rate approximating to that
of accumulation.
494 THE JOOKINATIZOFNGEOLOGM,
(4) Since tidal deposits are imperfectly sorted, they form
under shelter from waves or in the presence of waves of force
insufficient to handle the volume of sediment. The shelter may
be a point of land before a bay or a barrier of beach sand
before a lagoon; in either case clean sands and mud deposits
may be contemporaneous. Or the feeble waves may be
unequal to the task of sorting, because of short fetch in a nar-
row sea.
(2) Long continued or powerful winds.—The fall of a river
determines its current, other things being constant, and therefore
its transporting power. The fall near the mouth is lessened in
any given stream if the level of discharge is raised, and vice
versa, and the influence of tides in this respect has just been
discussed. Winds may exercise a no less important influence.
Revy (p. 27) describes an instance in which the effect upon the
tides of a storm approaching from the east, combined with its
subsequent direct effect in heaping up waters, was to raise the
level of the La Plata fifty inches at ebb tide, and to reverse the
current of the Parafia fora hundred miles. An extraordinary
result like this is probably balanced in its effect upon deposition
by the scouring which takes place when the wind changes direc-
tion, or calms, and the mass of water returns to its normal level.
But the influence of long continued winds blowing periodically
during certain seasons of the year must be effective in causing
deposition from silt-laden rivers. Humphreys and Abbott briefly
discuss the nature of winds affecting the level of the gulf at the
mouth of the Mississippi, and assign an important share of the
results from deposition to the influence of the southeast winds.*
(¢) Flotation of fresh water on salt-—Fresh water is lighter
than salt water, hence a river discharging into the ocean rises
and spreads over the surface. The volume of the river, advanc-
ing, holds back the salt water, and the fresh water flows up an
incline which is the surface of contact between the media of
unlike densities. This checks the river’s current and forms a
‘Physics and Hydraulics of the Mississippi. Page 450.
CONDITIONS OF SEDIMENTARY DEPOSITION. 495
vertical eddy or ‘‘ dead angle,” in which material rolled on the
river’s bottom is left and some sediment is dropped. Thus bars
are formed in advance of deltas.* With rising tide or on shore
winds the elevation of the salt water surface will-increase this
effect and force the zone of maximum deposition shoreward,
while the reflux with the ebb or change of wind will lower the
incline and assist wider distribution of sediment. Hence there
is most rapid accumulation in the comparatively narrow strip
of deposition during rising tide.
Flocculation in salt water.— Acids and salts in solution cause
fine particles of sediment to draw together in flocculent form
and therefore to settle more rapidly than they would in fresh
water. W. H. Brewer states that clay which has been in sus-
pension thirty months in fresh water had not settled out as
clearly as the same clay from a solution of common salt in less
than thirty minutes,” and he describes a number of experiments
tending to show that ‘‘when a muddy river enters salt water
chemical laws interfere with the purely mechanical ones. Then
the rate of deposition is affected by the salt more than by the
current, and velocities which would be more than sufficient to
carry the finer suspended matter indefinitely, if the water were
fresh, entirely fail where the water is brackish or salt. Practi-
cally it is the degree of saltiness which controls deposition.”’
Brewer applies this principle to a discussion of the formation
of the bars of the Mississippi and concludes that the zone of
maximum deposition retreats and advances as the greater or less
volume of the river changes the position of the opposing salt
water. It is obvious that this condition would be combined with
that of the ‘dead angle” produced by the rise of the fresh
water on salt.
The phenomena of flocculation have been attributed by
Hilgard, Brewer and Barus to chemical reactions, but Milton
Whitney finds a readier explanation in the forces of attraction or
*Humphreys and Abbott; op. cit. p. 445.
* Memoirs of the National Academy of Sciences, Vol. II, 1883, p. 168.
496 THE, JOCKNALE VOR (GHOLOGN.
tension existing among the fine particles of a solid in suspension,
which are modified by the presence of salts.* But whatever
the conclusion may be as to the nature of the controlling law,
the influence of salt water in this respect is an important cause
of deposition of clays at the mouths of rivers.
(g) Inequalities of depths; lee banks. —When any volume of
flowing water expands, it loses velocity and, if muddy, deposits
sediment. This well recognized condition of river deposition
has been considered in reference to a river entering a lake; it is
equally true of an ocean current or of undertow, where the for-
mer passes from a narrow strait to the broader sea, or where
either one flows from shallow into rapidly deepening water. The
condition needs no explanation—it requires only illustration.
From the Atlantic the southern equatorial current sweeps past
the mouth of the Amazon and Orinoco; as the Gulf stream it
crosses before the Mississippi delta, and pouring out through the
Straits of Floridaenters the North Atlantic. From the rivers tribu-
tary to its course it receives fine sediment escaped beyond the deltas.
In its passage through the Caribbean sea and the Gulf of Mexico
it flows over the eastern Caribbean deep, Bartlett’s deep and
Sigsbee’s deep, and where it leaves the Blake plateau north of
the Bahamas it falls over the continental rim into ocean depths.
Between these basins it traverses relatively shallow seas, whose
bottoms are floored with modern limestone and green sand.
These deeps of 2,500 to 3,000 fathoms and shoals at 100 to 500
fathoms are result of epeirogenic forces probably, but they are
now floored with deposits which consist of the shells of pelagic
organisms mingled with terrigenous silt, forming ‘ modified
pteropod ooze.’”’? This deposition, if it has gone on long enough
since the depression at the deeps, or fast enough to mask the
details of deformation, possibly continued up to a recent time,
determines the profiles of the slopes from shoal to abyss. In
*U. S. Dept. Agric. Weather Bull. No. 4, 1892, ‘Some physical properties of
soils,” pp. 19-23. Milton Whitney. $
? Geologic and bathymetric maps of the Atlantic in ‘“ Three Cruises of the Blake,”
by Alex. Agassiz, Vol. I.
CONDITIONS OF SEDIMENTARY DEPOSITION. 497
the Eastern Caribbean deep the declivities are such as would
thus be determined; the northern and southern slopes between
which the current flows are approximately equal and steep; the
slope of the eastern side is also steep and lies at right angles to
the course of the current in the position of a bank forming in
the lee of a terrace, and the rise from the abyss westward in the
direction of the current is relatively gradual. *
This basin is the one most advantageously situated to exhibit
slopes of deposition. Bartlett's deep lies like a narrow cafion
across the course of the current, and the small triangular basin
immediately east of Yucatan, while it shows a steep slope north-
ward in the direction of the current, presents similar declivities
along its other two sides which are possibly scoured by the
waters converging to pass out at the apex, the Yucatan channel.
The steepest slope of the Gulf of Mexico from the 1ooth to the
2000th fathom line, is in the position of a lee-bank northwest
of the Yucatan plateau, and the contours elsewhere are appar-
ently modified by the scouring action of the current as it sweeps
around the basin, and by terrigenous deposits from the adjacent
shores and rivers. The Blake plateau, over which the Gulf
stream sweeps north of the Bahamas, is clean, hard limestone,
but a lee-bank of mud and ooze is forming on its short, steep
slope into deep water. Agassiz says (p. 277): ‘There we pass
from the comparatively coarse shore mud to finer and finer ooze,
which becomes an impalpable silt in the deeper water beyond
one or two thousand. fathoms, assuming at the same time a
lighter color.”
Another illustration may be found in the deposits of silt
which form the edge of the continental plateau off the North
Atlantic coast of America. Agassiz has mapped the width of
the plateau as covered with “silicious shore deposits,” and
examination of some of the samples of bottom in the Coast
Survey office, for which opportunity has been most courteously
extended to the writer, shows that the surface of the plateau is
*See bathymetric map opp. p. 98, “Three Cruises of the Blake.”
498 THE JOURNAL OF GEOLOGY.
composed of sands which are indeed fine near the eastern edge,
yet are distinctly granular and incoherent. But soundings on
the steep slope beyond the 100 fathom line have brought up
very fine silt from the bank of which that slope is the surface,
and this silt passes at its foot into globigerina ooze. The zone
of transition from clean sand to silt is as sharp as the edge of
the slope and is coincident with it. It is evident that the sus-
pended mud which escapes beyond the estuaries and sounds of
the littoral is swept out until the undertow expands over the edge
of the escarpment, and is diffused in deep water; there the silt
forms a great bank 10,000 feet high, with a slope of 3 to 8
degrees, which has grown seaward during geological ages, and
continues to expand as erosion continues on the land.
The structure of this deposit can only be inferred, but it is
worthy of consideration. The surface of accumulation, to which
bedding planes are probably parallel, is inclined at a considerable
angle, and traverses the bank from top to bottom obliquely to
the vertical thickness. The direction of the growth is outward,
not upward. The conditions of deposition are similar to those
of a delta advancing into fresh water, and the structure of the
deposit is probably similar to that shown by Gilbert for a fresh -
water delta. (Fig. 14, p. 68, Lake Bonneville). If the detritus
was sand, instead of silt, the conditions would be identical, and
the bedding which would be exposed by removal of the hori-
zontal upper layers would represent an enormous thickness of
strata, inclined at a dip corresponding to the slope of the bank.
Russell rejects explanations of the attitude of the Newark beds
so far as they are founded on sedimentation," but it seems possi-
ble that they may present the structure of lee banks. It may
also be probable that isoclinal structure, where repetition of strata
does not occur, is evidence of this form of deposition and of the
conditions essential to it.
Deposits of this character, consisting usually of clay or silt,
are significant of extended rock decay on the land, of currents
‘Bull. U.S. G.S. No. 85, Correlation Papers—— The Newark System, p. 78. I.
C. Russell.
CONDITIONS OF SEDIMENTARY DEPOSITION. 499
capable of distributing the sediment, and of shoals and deeps in
the sea. The amount of difference in depths is not indicated,
but the rapid descent from the edge of the bank to the foot is
essential to diffusion of the current and the consequent deposi-
tion. A lee-bank is a submarine terrace of construction. Where
such a terrace extends into an abyss it argues prolonged devel-
opment, and, therefore, antiquity of relation between continental
platform and oceanic basin.
(h) Subsidence from oceanic circulation—The greater part of
terrigenous sediment must be deposited in deltas and estuaries,
on continental platforms, and in silt banks along great deeps. But
a very considerable amount of fine silt brought out by rivers and
undertow, quantities of volcanic dust fallen on the ocean, and the
calcareous and silicious parts of pelagic organisms are taken into
oceanic circulation, and find a resting- place more or less remote
from their place of origin. These deposits constitute the deep-
sea formations; they are not clearly recognized among the strata
of past geological periods now exposed in land surfaces, and on
this fact rests the principal argument for the antiquity of the con-
tinents and oceans. They have been fully described by Murray,'
and their mode of deposition need here be indicated only
by reference to the blue muds of the Bay of Bengal and the
Arabian Sea.
The blue muds are composed of minute mineral fragments
derived from the disintegration of the land, of a diameter of .05
-mm., or less, which may contain calcareous remains amounting
to 50 per cent. of the whole, or may be almost free from lime.
The description of a typical sample, taken about 275 miles south
of the mouth of the Ganges, is given by Murray? in an article
which is accompanied by a map showing the distribution of dif-
ferent formations. From this map we may gather that terrigen-
ous deposits form a belt, 50 to 125 miles wide, along the eastern
coast of Africa, the western coast of Australia, and the Malay
™Challenger Reports; Narr. of the Cruise, Vol. I, Part II.
2 Scott. Geog. Mag., Vol. V, No. 8, Aug., 1889, p. 420. John Murray on “‘ Marine
Deposits in the Indian, Southern and Antarctic Oceans.”
500 THE JOURNAL OF GEOLOGY.
archipelago, but in the Arabian Sea and the Bay of Bengal they
extend to distances of 800 miles from the mouth of the Indus
and Ganges, and cover areas of more than 700,000 and g00,000
square miles, respectively. By reference to a map of the ocean
currents it may be seen that their courses affect the distribution
of these deposits. Sweeping at all seasons past the west coast
of Australia and directly toward the east coast of Africa, paral-
lel to which it then diverges, the principal current prevents any
extended distribution of sediments in a direction normal to these
coasts. But the currents of the Arabian Sea and the Bay of Ben-
gal, flowing alternately east and west around these great embay-
ments, past the mouths of the two great silt-bearing rivers,
distribute fine material in suspension throughout the area of their
circulation.
CHEMICAL DEPOSITION.
Favorable conditions:
(a) Evaporation from an enclosed sea.
(6) Precipitation of lime and magnesia from ocean waters,
charged by solution from the land, through evaporation,
through reaction of salt water on fresh, and through varying
atmospheric conditions at the surface of the sea.
(a) Evaporation of an enclosed sea—When a limited body of
water, such as a lake, is subjected to a change of climate, so that
evaporation exceeds precipitation of rain, the volume will shrink,
outflow will cease, and the solution of salt will be concentrated. If
the process is sufficiently continued the solution will become satur-
ated, first for one salt, then another, and they will be deposited
in the order of their insolubility. This process is important as
an indication of climatic variation in the past; it has been
fully described by Gilbert, Russell and Chatard for Pleistocene
lakes and the chemical relations, and these studies suggest
the conditions to which appeal must be made to explain the less
exact facts known in ancient formations of the kind.
(0) Precipitation from brackish waters—The chemical precipi-
tation of lime and magnesia from sea-water is a much mooted
question. There are two lines of evidence relating to it which
CONDITIONS OF SEDIMENTARY. DEPOSITION. Sol
are apparently opposed. On the one hand, the scientists who
have described material obtained by soundings on modern lime-
stone deposits have recognized only organic remains. The
Challenger in the open océans, remote from great rivers, the
Coast Survey vessels in the Caribbean, the Gulf of Mexico and
off the Atlantic coast, the Norwegian expedition in the North
Atlantic and English vessels in the Indian ocean have found cal-
careous oozes of various kinds and rocky limestone formations,
but in every case the calcareous matter is described as composed
wholly of the tests of pelagic organisms, many of them of micro-
scopic size. It is known that carbonates of lime and magnesia
are to a greater or less extent soluble in waters containing car-
bonic acid, and that the proportion of these carbonates dissolved
in ocean waters is small. According to Dittmar the salts in solu-
tion in ocean waters contain 0.345 per cent of carbonate of lime
and 3.600 per cent of sulphate of lime,t and the ocean is capable
of dissolving all the lime poured into it by rivers.2 This view
being accepted, it follows that pelagic organisms, which possess
the power of secreting solid carbonate of lime from solution,
alone can cause lime deposits. Chemical precipitation is, accord-
ing to this view, impossible, or, if it occurs, is followed by speedy
re-solution, and all limestones deposited under conditions of the
existing oceans are of organic origin. On the other hand, there are
many limestones, deposited at different periods of geologic time,
from Algonkian to the present, including some now forming, which
consist of more or less clearly crystalline calcite, devoid of organic
structure. If this calcite was originally built into organic forms
they have been entirely obliterated. Such limestones do indeed
contain fossils which sometimes exhibit more or less crystalline
texture, but the occurrence of these organic forms in the holo-
crystalline matrix only raises the question: If the mass was
originally all organic and has undergone secondary crystallization
after lithifaction, why was the process so complete in the matrix
*Report on the Scientific Results of the Voyage of H. M.S. Challenger. ‘‘ Physics
and Chemistry.” Vol. 1, p. 204.
Z@psiciteaps22ir
502 THE JOURNAL OF GEOLOGY.
and relatively so ineffective in structures whose delicate anatomy
can still be traced even to microscopic details? Thin sections
of limestone which show a mass of interferant crystals suggest
that this was the primary structure of the rock, and organic
remains appear to be foreign bodies which are accidentally
of the same substance as the matrix. If this view be correct,
then only the alteration of the organic carbonate is the
measure of the alteration of the rock-mass. If it can be
shown that limestones now forming by chemical precipitation
possess a crystalline structure, which resembles that of ancient
limestones, the resemblance will constitute a presumption in favor
of similarity of origin for the modern and ancient formations.
And the fact that limestone is now being precipitated would, if it be
established, leave the geologist free to weigh the evidence in the
case of any ancient limestone for and against its organic or chem-
ical origin. It is not proposed here to argue that limestones are
prevailingly of one origin or the other, but only to show that the
assumption of organic origin for all the calcareous deposits of the
stratified series is too sweeping. To this end it is desirable to
consider the chemical and mechanical conditions which affect the
precipitation of carbonate of lime, to estimate the solubility
of the carbonate in salt water, to review the conditions under
which lime is contributed to, and distributed in, the sea, and
to describe several cases of modern limestone formation by
precipitation.
Schloesing made a number of experiments on the solubility
of carbonate of lime in carbonic acid and water ; he thus describes
his method and results. 7
‘‘ Experiments :—The method adopted was to cause to pass
through pure water, which was maintained at a constant temper-
ature and contained an excess of carbonate of lime, a mixture of
air and carbonic acid, of a composition varied at will, but con-
stant, for each experiment; this mixture was constantly supplied
until a perfect equilibrium was established between the substances
*Comptes Rendus, Vol. 74, 1872, pp. 1552-56, and Vol. 75, p. 70.
CONDITIONS OF SEDIMENTARY DEPOSITION. 503
entering into the reaction, then the quantities of carbonic acid
and of lime were determined in the filtered solution.
“Then to run through the scale of pressures of the car-
bonic, acid from the most feeble to the strongest-that could be
obtained. 5
“Then to change the temperature and re-commence anew
the series of experiments in order to eliminate the influence of
heat.
“The experiments establish the fact that pure water in the
presence of carbonate of lime, and of an atmosphere containing a
determined proportion of carbonic acid, dissolves simultaneously
free carbonic acid according to the law of absorption of gases,
neutral carbonate according to the solubility of this salt in water
free from carbonic acid, and bicarbonate of lime.”’
The relation found between the tension of the carbonic acid
and the proportion of bicarbonate formed is such that: “ Equil-
ibrium being established in the solution, the slightest diminution
of the tension of the carbonic acidin the atmosphere determined
the decomposition of a corresponding quantity of bicarbonate,
with precipitation of the neutral carbonate and the emission of
carbonic acid gas.”’
The veteran chemist Dumas, in an article on the normal car-
bonic acid of the atmosphere, says: *
“In recent times, by a happy application of the principle of
dissociation, M. Schloesing has shown that the proportion of
carbonic acid contained in the air was in relation with that of
bicarbonate of lime held in solution in the waters of the sea.
When the amount of carbonic acid (in the air ) is diminished the
bicarbonate of the lime in the sea is dissociated, the-half of its
carbonic acid passes into the air, and the neutral carbonate of lime
is precipitated from solution” ( ‘deposé”’ ).
Another condition which may decompose bicarbonate of
lime is simple mechanical agitation of the water holding it in
solution. Dittmar in examining samples of ocean water for car-
*Comptes Rendus, Vol. 94, 1882, p. 70.
504 LTTE J OULINATE OLA GIOLO GN.
bonic acid, was led to make a series of experiments on the effect
of shaking with air an artificial sea-water, Containing a known
amount of carbonic acid. He found that he shook out 27 per
cent of the carbonic acid originally present, and this did not
represent the greatest possible loss. After describing the experi-
ments he says :*
eosin experiments reported inthis chapter . . . are sufficient —
to prove . .. that, supposing a sea-water which contains its
carbonic acid as bicarbonate, associated or not with free carbonic
acid, to be exposed to the air even at ordinary temperature, such
a water will soon lose not only its free but part at least of the
loose carbonic acid of the bicarbonate (7. ¢., of what is present
over and above that existing in the form of normal carbonates ).”
Dittmar also discusses the dissociation tension of bicarbonates in
sea-water and suggests that the water of the tropics constantly
gives out carbonic acid to the air, and water of cooler and of
arctic zones constantly absorbs it. *
Thus the chemists describe two conditions under which bicar-
bonate of lime may be decomposed into neutral carbonate and
carbonic acid: Ist, by diminution of the tension of the carbonic
acid in the atmosphere; 2d, by agitation of the solution.
Theoretically, either one of three things may occur to the
neutral carbonate of lime if it be thrown out of solution by either
one of these processes, which we may admit are active on some
portions of the salt water surface. The carbonate may be redis-
solved, or deposited as a calcareous mud, or built into organic
structures. We may discuss these alternatives in turn.
The solvent action of sea-water has been the subject of direct
observation in the ocean and of experimental determination.
Deep-sea shells, dredged from the bottom of the Pacific and now
in the Smithsonian collection are corroded, some of them on the
outside only, some of them through and through. In the former
‘Report on the Scientific Results of the Voyage of H. M.S. Challenger. ‘“ Physics
and Chemistry,” Prof. Wm. Dittmar, F. R. S. Vol. I, p. 115.
ZOp a cit. pp e2t2-213%
3 For an opportunity to examine these my thanks are due to Dr. Dall, B. W.
CONDITIONS. OF SEDIMENTARY DEPOSITION. 505
case the creature still inhabited the shell and preserved the
essential parts of its house; in the latter case the decomposition
of the fleshy parts may have assisted the solution of the cal-
careous skeletons. To this last point Murray calls attention :?
“Tt is probable, however, that carbonic acid does play an im-
portant part in the solution of shells of animals sinking through
the water. The organic matter of the animal on being oxidized
produces carbonic acid, which, being itself liquid at all depths
over 200 fathoms, will form a locally concentrated acid solution
inside the shell, which it will attack with vigor.”
The shells which were corroded while still inhabited were also
exposed to unusually active solvent influences since they lay upon
the bottom, of which Agassiz writes :*
“The pelagic animals derive a large part of their food supply
from the swarms of large and small pelagic alge covering the
surface of the sea in all oceans. On dying, both surface animals
and plants drop to the bottom, and still retain an amount of
nutritive matter sufficient to serve as food for the carnivorous
animals living on the bottom. A sort of broth, as it has been
called by Carpenter, collects on the bottom of the ocean, and
. probably remains serviceable for quite a period of time; the
decomposition of the organic material which has found its way
to the bottom takes place gradually, and its putrefaction must be
very slow.” Thus these more or less corroded shells, dredged
from the deep sea, bear witness to the solvent evolved ina bottom
layer of decomposing organic matter.
A more direct line of evidence as to the solvent action of the
sea-water itself is afforded by observations on the depths to
which calcareous skeletons will sink undissolved. The pelagic
pteropods and foraminifera, living at the surface, sink on dying
and are slowly dissolved; if the water be too deep they never
reach bottom. The limits below which they are not found are
about 1500 fathoms for pteropods, thin shells exposing large
* Narrative of the Cruise of the Challenger, Vol. I, Second part, p. 981.
* Three Cruises of the Blake, Vol. I, p. 313.
506 THLE, JOUKNALE OF IGEOLOGV.
surfaces to solution, and 2800 for globigerina, smaller shells,
relatively more massive. Commenting on this, Dittmar says :"
‘At the greatest depths of the oceans all these calcareous
shells disappear from deposits in all latitudes. The cause of
this, in my opinion, is not that deep-sea water contains any
abnormal proportion of loose or free carbonic acid, but the fact
that even alkaline sea-water, if given sufficient time, will take up
carbonate of lime in addition to what it contains.”
The solvent action indicated by the disappearance of delicate
and microscopic shells, which enclose decaying organic matter,
yet sink through gooo to 16,000 feet of water, is very moderate.
Dittmar says:? ‘‘Sea-water is alkaline; all the alkalinity
must be owing to carbonates, and of these carbonate of lime is
one.” Now the very moderate solvent power of this alkaline
solution may be satisfied so far as carbonate of lime is concerned
by two sources—by organic tests in suspension, and by chemical
precipitate. The lime used by organisms is derived from the
solution to which it is partly returned by re-solution, but an-
other part is deposited, and the sea thus suffers constant loss.
This loss is supplied by the land. If this terrigenous supply is
less than the amount of organic deposit the sea will become less -
alkaline, and will more efficiently dissolve calcareous tests until
the solvent is satisfied. If the land contribution is continuously
equal to the amount organically subtracted, there will be equili-
brium. If the land yields more carbonate of lime than that which
is being locked up in organic limestones, the alkalinity of the sea
will gradually increase until there is chemical precipitation. This
condition is favored by the entrance of lime-bearing fresh
water into a sea free from active currents and exposed to evapora-
tion which balances the inflow.
Since the amount of lime in the ocean is thus balanced be-
tween that contributed by the land, and that precipitated by
organic or chemical means, it is worth while to review the con-
VOpwcit-sapa22ue
2Op. cit., p. 206.
\ CONDITIONS OF SEDIMENTARY DEPOSITION. 507
ditions under which lime is carried from the land, and to consider
how it is distributed in the sea. As was stated early in this paper,
the amount of lime carried annually from a given land area is
directly related to the efficiency of rock-decay; rock-decay is
most efficient over surfaces which have suffered prolonged de-
gradation, and on such surfaces the development of drainage
systems has usually resulted in the growth of great rivers.
Hence the lime contributed from continents to oceans is delivered
chiefly at a few places, the mouths of extended systems, and
there is great inequality in the distribution of these along differ-
ent coasts and among different seas. Of this fact South
America is the most conspicuous example, with all its great
rivers pouring into the Atlantic, and not one considerable stream
entering the Pacific. More limited seas, which receive vast quan-
tities of solutions are the Caribbean and Gulf of Mexico, Arabian
Sea, Bay of Bengal and Yellow Sea.
At the mouths of great rivers there exist several conditions
which influence the solubility and distribution of lime in the
adjacent seas; these are: Ist, the amount of lime in solution
in the river water; 2d, chemical reactions between substances
in fresh and salt water; 3d, the relative solubility of lime in
fresh and salt water; 4th, the conditions of evaporation and agi-
tation of the brackish water; 5th, the effects of currents.
The proportion of solids in solution ina river is dependent
not only on the extent and slopes of its basin, but also on the
nature of the rocks exposed, and the influence of climate on
decay. Under like topographic conditions, silicious schists and
a cold climate probably yield a minimum contribution; crystal-
line rocks and a warm, moist climate yield more; limestone areas,
though resistant in a dry climate, suffer most rapid degradation
under a humid atmosphere, and the deposits of the later geo-
logic periods, including as they often do quantities of soluble
salts, charge the drainage most strongly. The following
analyses present specific contrasts, traceable to these geologic
and climatic conditions. Each analysis represents but one phase
of composition, which varies in each river with high and low
508 THE JOURNAL OF GEOLOGY.
stages, and the analyses of our great rivers are incomplete, but,
strange as it seems, no other analyses of their waters have
been found, after diligent search.
SAMPLES.
(2) Ottawa river; sampled March 9g, 1854, before the melting
of the snow, at head of St. Anne lock; water was pale amber yel-
low, free from sediment and derived froma region of crystalline
rocks covered with forest and marsh vegetation." ;
(6) St. Lawrence river, sampled March 30, 1854, before the
melting of the snow, on the south side of the Pointe des Cas-
cades, Vaudreuil; water was clear, colorless, and represents the
drainage of areas of glacial drift, crystalline rocks and paleozoic
sediments, clarified by passage through great lakes."
(c) Mississippi river;* sampled in the autumn of 1887 at very
low water, inthe main channel above the mouth of the Missouri;
water represents drainage from areas of glacial drift, crystalline
rocks and paleozoic sediments, including large expanse of lime-
stone and cultivated lands. |
(@) Missouri river;* sampled on the same day as the preced-
ing ; water represents drainage most highly charged with the sol-
uble salts of the more recent and little consolidated geologic for-
mations; potash was no doubt present but was not determined.
(¢) Mississippi river;* six miles below the mouth of the Mis-
souri ; sampled on the same day as the preceding in the current
of Mississippi water as shown bya float dropped on taking sam-
ple c; sample represents Mississippi and Missouri waters, appar-
ently with excess of the latter.
(f) Mississippi river ;* twelve miles below the mouth of the
Missouri, above St. Louis ; sampled on the same day as the pre-
ceding inthe current indicated by the float; sample represents
Mississippi and Missouri waters apparently more thoroughly
mixed.
"Geology of Canada, 1843-63, Logan, pp. 565-568.
*Annual Report of the Water Commissioner, St. Louis, 1888, pp. 309-310. Anal-
yses by St. Louis Sampling and Testing Works, Wm. B. Potter, Manager.
CONDITIONS OF SEDIMENTARY DEPOSITION.
ANALYSES——PARTS PER I,000,000 OF WATER.
509
St. Missouri and Missouri and
Constituents. Ottawa. Lawrence. | Mississippi.| Missouri. Mississippi. Mississippi.
a C (oa
Morale Solids: ss | awe see 253.69 | 1207.66 1058.98 787.12
Filtered sedi-
DOGIME sa 69.75 167.80 20.90 638.26 622.33 389.36
Tn 8 2 ae cee 1.52* I.15* | notgiven | notgiven | not given not given
UN fees reel ap fat 2.39% 5.03% B Aas 2707 g.16* 10.37%
Mig @ aes 2.30*)| 12.08% 28.26 41.96 37.51 39.40
CaO se 13.88*| 44.92* 52.93 IIO.15 109.63 94.90
(Gils een) .76 2WA2 5.31 19.53 14.22 1S 3)
SO peak awee 1.61 6.87 10.28 89.76 73.66 69.89
SiOpgses esse 20.60 37.00 | notgiven | notgiven| not given not given
69.75 167.80 20.90 638.26 622.33 389.36
Iron and al-
umina ____ traces traces none 55-84 20.90 26.80
According to Gooch* the combination in these analyses should
be calculated im the order ME), NaC) AG SO; Na, sO), Me sSOy,
Cas Oj iceO nr Cac@nwNae EO. Tete: vam tints is) the order,
followed in the Canadian analyses. Hence the following is the
hypothetical combination.
a b C ad e if
etal Solbiglgsi 2254 |) “eesece 253.69 | 1207.66 1058.98 787.12
Filtered sedi-
TAME — 552 69.75 167.80 20.90 638.26 622.33 389.36
Klee ane 1.60 2.20 | notgiven | not given| not given not given
INE Cobos os Mi een el D LPs 8.57 32.03 23.30 26.38
Kan ofece Tye22 tah |e en not given | not given} not given not given
Nias SOZ 222= 1.88 12.29 | notgiven | notgiven| not given not given
Me SOn S522 none none 15.41 125.90 118.49 104.83
Ca, SOnsesse none none none 9.93 none none
Mg CO, ___- 6.96 25.37 19.63 none 137, 4.28
CACORE 24.80 80.83 94.56 189.35 195-79 169.47
Nas COe 2222 4.10 0.61 none none none none
Fe,O3-++ ----
Als On 2 traces traces none 55-84 20.90 26.80
The chemical reactions which take place between substances
dissolved in river waters and those contained in salt water are no
doubt complex; but that which is most significant in relation to
possible precipitation of carbonate of lime depends upon the
fact that organic matter may decompose sulphate of lime. Ac-
* Calculated from combinations given in the original publications.
t Analyses of Waters of the Yellowstone National Park, Bull. U.S. G.S., No. 47,
p. 24.
510 THE JOURNAL OF GEOLOGY.
cording to Dittmar,’ the greater part of the lime in ocean water
is there combined as sulphate, which in contact with organic mat-
ter would be reduced to sulphide with evolution of carbonic acid;
the latter would attack the sulphide with formation of carbonate
of limeand sulphide of hydrogen. Thus organic matter in river
waters tends to increase the proportion of carbonate of lime in
the zone of brackish water. The carbonate thus formed is added
to that already existing in the river water.
The solubility of carbonate of lime in fresh water and inl
salt has been an object of consideration by several experiment-
ers. Sterry Hunt testing artificial solutions found that 1 litre of
water which contained 3 to 4 grams of sulphate of magnesia
could dissolve 1.2 grams of carbonate of lime and 1 gram of
carbonate of magnesia; but after standing a long time all the
lime was deposited as hydrated carbonate. Thus it would
appear that the presence of the sulphate assisted the solution of
the carbonates.
Experiments made by Daubrée, which contradict Hunt's re-
sults, led Thoulet to conduct a series to determine the question.?
He took several minerals, marble, shells, coral and globigerina
ooze, and subjected the comminuted samples of each separately
to the action of filtered ocean water and distilled water during
five weeks in each case. The solutions were shaken several
times each day and the water waschanged from time to time.
At the close of the experiments the samples had lost in weight
and the amount taken into solution, reduced to that dissolved
per cubic decimeter per day, was found to be, in grammes
In ocean In fresh
water. water.
Shells, - . - - - .000039 001843
Coral, - - - - - .000201 .003014
Globigerina, - - - - .000137 .003091
Opry Cite pier 204.
2 Dittmar, op. cit., p. 209.
3 Oceanographié (Statique) par M. J. Thoulet, 1890, p. 263, and Comptes Rendus,
t. CVILI, April, 1889, p. 753.
CONDITIONS OF SEDIMENTARY DEPOSITION. S511
‘“‘One sees that the solubilityin ocean water, itself very feeble,
is also notably more feeble than the solubility in fresh water.”
When river water enters salt water it is. exposed in different
form and under different physical conditions from those which
existed in the river. As the fresh water is lighter than the salt,
it floats upon it and spreads out in a sheet not unlike a fan. As
compared with its depth and width in the river the layer is very
shallow and widens from the mouth. Through waves and cur-
rents the fresh and salt water mingle, and the expanse of brack-
ish water may be of great extent. Forchhammer attributes the
minimum salinity which he found for surface water from the
north Atlantic, goo miles from the mouth of the St. Lawrence,
to the volume of that river, and he found the ocean water fresh-
ened at a similar distance from the La Plata. This thin sheet of
brackish water is exposed to variations of temperature and baro-
metric pressure produced by changing winds, now on, now off
shore, and is in constant agitation with the rise and fall of waves.
Thus the conditions which produce varying tension of carbonic
acid, and which aid the escape thereof, exist at its surface, and
the bicarbonate of lime in solution must be in unstable equili-
brium, with constant formation of neutral carbonate and more or
less constant recombination of it. If the neutral carbonate be
present in sufficient quantity it will remain in suspension, undis-
solved and unused by organisms, and will ultimately be deposited
as calcareous ooze.
Oceanic circulation maintains an approximately uniform com-
position of ocean water in all parts of the open seas, and great
currents sweeping past river mouths distribute the contribution
of fresh water and its solid matters, whether in solution or sus-
pension. Thus the lime brought down by rivers, though meas-
urable by hundreds of thousands of tons per annum, is so widely
diffused in the vast volume of the ocean that it escapes recog-
nition.
There are, however, several instances of modern limestone
formation which, though local, illustrate the processes of chemi-
cal deposition on a large scale. The descriptions of these may
512 THE JOURNAL OF GEOLOGY.
close these suggestions concerning limestone deposition by other
than organic means. f
Chemically deposited limestone is forming in the southern
part of Florida, probably over extensive areas. The Everglades,
4,000 to 5,000 square miles in extent, lie nearly at sea level, mar-
gined by barrier reefs which confine the surface waters; in the
dry season the drainage consists of numerous small streams—in
the wet season the region is all submerged save the numerous
muddy islands. Explorations on the western side, from Cape
Sable north to Punta Rasa, were made by Mr. Joseph Wilcox,
whose observations are stated by Dall as follows :*
“At the north end of Lostman’s Key (on the west coast, in
about latitude 25° 30’) they entered the river of the same name
and succeeded in penetrating 12 or 15 miles inland. No hard
ground was seen except near-the mouth of the river, and the
highest land at the latter place was not over 3 feet above high
tide. Wide, shallow bays, with muddy bottom, interspersed with
low, muddy mangrove islets, comprise the scenery. The boat
frequently grounded, and was obliged to wait for the rise of the
tide. A small fresh-water stream was finally reached, the cur-
rent of which had scoured a channel 4 to 6 feet deep, with a
rough, hard, rock bottom, fragments of which were broken off.
It consisted of large masses of Polyzoa more or less completely
changed into crystalline limestone, the cavities filled with crys-
tals of calcspar. The rock is very hard and compact.”’
‘“Allen’s creek, emptying into Walaka inlet, anarm of Chuko-
liska bay, was also visited. Ata point 8 or 10 miles east from
the Gulf of Mexico the party were able to land on soft, wet soil,
a little higher and drier than that at the head of Lostman’s river.
A third of a mile eastward from the head of the creek specimens
were obtained of a few rocks which project above the soil. They
presented molds of recent shells with the interior filled with calc-
spar, and an occasional Pecten dislocatus or Ostrea virginica, still
retaining its shell structure. The cavities between the shells
* Bull. U.S. G.S. No. 84. Correlation Essays—* Neocene,” by Wm. H. Dall, pp. 99—
IOI and 154.
CONDITIONS OF SEDIMENTARY DEPOSITION. 513
were filled with hard, coarsely crystalline limestone. The rock
was not coquina modified, but looked more like a fossilized oyster
reef. It contained no corals, and was obviously Pleistocene.
The rock formed the base of small islets of drier soil amid the
marsh, on which islets grew pine trees. The marsh, apart from
these islets, is probably entirely submerged in the rainy season.”
In the bulletin referred to Dall speaks of the rock obtained
by Willcox as being of organic or of partly organic and partly
chemical origin, but at the time that manuscript was prepared
the observations were less complete than now. Ina recent let-
ter he says: ‘‘Mr. Willcox’s observations on the deposition of
the flocculent mud from lime-bearing water were later than the
original statement. The precipitated mud is more or less me-
chanically mixed with masses of the corrallia of Polyzoa and
bivalve shells driven in shore by the sea, but these creatures do
not live in the muddy water, but in the clearer water outside.”
Through the courtesy of Dr. Dall the writer has examined
specimens of this rock. It is a light cream-colored mass of
crystalline calcite formed around the included fragments of
shells. Under the microscope the unaltered structure of the
organic fragments is strikingly different from that of the coarse
holocrystalline matrix, in which it is apparent that the crystals
developed in place. Were this a limestone of some past geo-
logic period it would be concluded, on the evidence of the crys-
talline texture of some parts of it, that it had been metamor-
phosed and that the organic remains now visible had: escaped
the process which altered the matrix. But the observed condi-
tions of its formation preclude the hypothesis of secondary crys-
tallization. Apparently, the crystalline matrix is one primary
product from solution, a rock formed in contact with the
bottom, the calcareous mud is another, which, being precipitated
in the solution, remains an incoherent sediment.
- These results may perhaps be thus explained: The drain-
age of the peninsula contains an unusually large amount of lime,
in consequence of the abundant supply of carbonic acid and
other products of vegetable decay in the sub-tropical climate and
514 THE JOURNAL OF GEOLOGY.
of the calcareous nature of all the rocks of Florida. In the
Everglades this water is exposed in broad shallow sheets to ac-
tive evaporation, agitation and variations of atmospheric temper-
ature and pressure. Concentration of the solution and escape
of carbonic acid, including some of that in the bicarbonate in
solution, follow, and the neutral carbonate is produced in
excess of the amount that can be retained in dissolved form. It
is therefore precipitated in two forms—first, from the mass of the
water as a flocculent mud ; second, from the lower layers of the
water in contact with limestone as crystals forming an integral
part of the solid rock..
The alternation of dry and wet seasons is accompanied by
concentration and sluggish flow, alternating with dilution and
flood currents. Therefore there are seasons of more active pre-
cipitation interchanging with those of more vigorous transporta-
tion and, perhaps, partial re-solution. In these latter seasons the
calcareous mud is swept beyond the shallow basin where it
forms, and enters as a suspended sediment into the Gulf circula-
tion. What part, if any, is dissolved, what is deposited as mud
in the lagoons along the coast, and what is swept into the silt
banks of the Atlantic, is not known.
Conditions which produced similar results are described by
Gilbert as having existed in Lake Bonneville.t Tufa was depos-
‘ited on the shores of the lake at various stages, but most abund-
antly at the Provo stage, during which the water lingered longest
at one level. The occurrences are thus described:
“The distribution of tufa along each shore is independent of
the subjacentstenrane; “ys, a) No deposit is found in sheltered
bays, and on the open coast those points least protected from
the fury of the waves seem to have received the most gener-
ous coating. These characters indicate, first, that the material
did not have a local origin at the shore, but was derived from the
normal lake water ; second, that the surf afforded a determining
condition of deposition.”
"Monographs of the U.S. G.S. Vol. I, p. 167-168.
CONDITIONS OF SEDIMENTARY DEPOSITION. 515
Dittmar’s experiments in decomposing bicarbonate of lime
by agitation indicate the nature of the condition afforded by
the surf, and it appears that the neutral carbonate is capable of
lithifying at the point of, and immediately upon, separation. Gil-
bert also says that: ‘‘Calcareous matter constitutes an important
part of the fine sediment of the lake bottom, and this was chiefly
* and to explain the forma-
tion of the coherent and incoherent deposits of the same mater-
or wholly precipitated from solution,’
ial from the same water he suggests that ‘‘separation was pro-
moted by aération of the water. All precipitation being initiated
at the surface during storms, coalescence at the shore may have
resulted from contact at the instant of separation.”
Mr. Gilbert states (pp. 178-179), that the concentration of the
waters of Lake Bonneville at the Provo stage is not definitely
known. The lake had an outlet at the northern end of Cache
bay, and the principal tributary, Bear river, emptied into this
bay near the outlet. Cache bay was connected with the main
body of the lake only by a deep but narrow strait, and it is
possible that evaporation from the greater expanse of the lake
exceeded the inflow of fresh water into it, while the overflow at
the outlet was supplied by Bear river. In that case there would
have been circulation through the strait between Cache bay and
the main body, an upper current from Cache bay and an under-
current from the lake. The straits were the scene of peculiarly
copious deposition of tufa.
The tufa deposited in Lake Bonneville is of the variety
described by Russell as ‘‘lithoid tufa,’’ ‘‘of a compact and stony
structure” and he concludes that it was formed when the lake
waters were moderately concentrated (pp. 210-222). A limestone
of similar structure is now forming on the shores of Florida, where
the waves break on the beaches under conditions quite like those
which determine the growth of tufa, where the surf dashed
against the shores of Lake Bonneville. This rock is deposited in
irregular layers, sometimes three or four feet thick, on the quart-
* “Geological History of Lake Lahontan,” p. 190.
516 THE JOURNAL OF GEOLOGY.
zose beach sands. Like the tufa, it is independent of the material
upon which it gathers, but the possibility of a local supply of
lime exists in the discharge of surface waters below low tide.
Under the microscope the material shows a dense, fine-grained
groundmass of lime with admixture of fine clay, including grains
of quartz and cavities filled with coarsely crystalline calcite.
A case, which is probably more typical of what may occur
now, or may have occurred in past ages at the mouths of rivers
and in shallow seas, is that of the limestone deposited beyond the
delta of the Rhone: This is) referred to by Thoulet anders
described by Lyell,’ who says: ‘In the museum at Montpelier
is a cannon taken up from the sea near the mouth of the river,
imbedded in crystalline calcareous rock. Large masses also are
continually taken up of an arenaceous rock, cemented by calcare-
ous matter, including multitudes of broken shells of recent
species.” Lyell attributes the precipitation of lime to evapora-
tion of the Rhone water, which, when it is spread upon the salt
water, he compares toa lake. But this one cause is no doubt
combined with the chemical and mechanical conditions which
have been suggested in the preceding discussion. These con-
ditions are favored at the mouth of the Rhone by the salinity of
the Mediterranean and the absence of strong currents.
The examination of a few thin sections of limestone of dif-
ferent ages, from Cambrian to the present, shows that they have
three principal types of structure. There are those which re-
semble the Everglades limestone in that they consist of more or
less coarsely crystalline calcite, yet include unaltered organic
remains. Of these the Trenton limestone and the marbles of
corresponding age in Tennessee, which occur interstratified with
unaltered calcareous shales, are the most striking examples
examined. Cambrian limestones and the Knox dolomite show
similar crystalline structure. The second type, the precipitated
sediment which forms the muds of the Everglades and which
was deposited in Lake Bonneville is represented by specimens
2@pcit.5)p. 27,0.
? Principles of Geology, Vol. I, p. 426.
CONDITIONS OF SEDIMENTARY DEPOSITION. 517
composed of exceedingly fine grained, apparently pulverulent,
material; the best of these are from the Knox dolomite
and the Solenhofen lithographic stone. The third variety of
limestone consists of the thoroughly crystalline marbles, which
contain no unaltered material, and which occur in such field
relations that they are known to be completely metamorphosed.
Extended study is required to determine the nature of deposition
of the first and second types. They may have been organic and
have suffered moderate alteration only, but there is a reasonable
presumption that they did to some extent crystallize in place
from sea-water, and were, to a still greater extent, precipitated
from the outspread fans of fresh water, radiating from rivers’
mouths, whence they spread as fine silt over the bottom of the sea.
ORGANIC DEPOSITION.
Since deposits of this character are composed chiefly of the
calcareous or silicious remains of marine organisms, their
formation is conditioned primarily by the circumstances con-
trolling marine life, and secondarily by the insolubility of the
skeletons under circumstances of wide distribution and gradual
sinking.
Favorable conditions —(a) Warm waters.
(6) Clear waters.
(c) Abundant food supply.
(@) Depths less than 1500 fathoms.
(e) Expansion and diffusion of currents in rapidly deepening
Conditions favorable to life.
water.
For a description of the oceanic deposits and of the biological
conditions which promote their accumulation, the reader may be
referred to the Narrative of the Challenger Expedition, Vol. I,
second part, pages 915 to 926. The oozes which are character-
ized by the predominance of remains of globigerina, pteropods,
diatoms or radiolaria are there described, and it is shown that
the nature of the deposit is determined by the conditions of tem-
perature, light and motion which favor the generation of multi-
tudes of the minute creatures whose living forms swarm at the
518 THE JOURNAL OF GEOLOGY.
surface of the sea, and whose remains only enter into deposits
when they have escaped being used by other creatures, or being
dissolved in the ocean waters.
Agassiz, writing of the physiology of deep sea life,? points out
that in marine, as in terrestrial, life the primary source of food
for animals is in plants. The lower types of marine life, it would
seem, must derive their sustenance from the water, as land plants
get theirs in part from the air, and the silica and lime thus ab-
sorbed is taken directly from solution; but the creatures which
live on these forms, and the carnivorous animals that feed on
them, may get their lime and silica at second hand by digesting
and assimilating that which the lower types take from solution.
Thus the solids built from solution into organic tests may go
through numberless changes before they come to rest on the
bottom.
Without pursuing the discussion of biological conditions favor-
able or unfavorable to deposition, and without entering upon the
question of coral formations, which are rarely of prominent inter-
est in stratified deposits, the writer wishes to consider only the
circumstances of limestone formation from organic remains, as :
‘that from chemical precipitates has been considered.
In discussing the solubility of shells in sea-water it has been
pointed out that the layer of organic matter which accumulates
at the sea bottom contains a solvent formed by the evolution of
carbonic acid in the process of decay. Through this layer all
substances must pass before they can become part of a lithified
stratum ; if they are plant tissue or flesh they will become more
or less oxidized; if they are calcareous tests they will be more
or less completely dissolved, and, if there be any chemically pre-
cipitated lime, arriving on the sea bottom it, too, would be dis-
solved in this menstruum. The earlier forms of dredge which
scooped into the sea bottom, brought up a mass of ooze, formed
of fine particles, burying organic forms. The later forms of
dredge, arranged to skim the surface of the bottom, bring up
*Op. cit., pp. 312-313.
CONDITIONS OF SEDIMENTARY DEPOSITION. 519
shells and organisms remarkably free from mud. Now it may
be conceived that the layer of mud on which the creatures live,
die, and with sunken organic remains decay, grades from the
fresh surface of recent accumulations downward into a much
more completely decayed and dissolved mass, and that this
rests upon a surface of limestone. In the upper part of this
unconsolidated stratum carbonic acid may most abundantly be
evolved; in its lowest part the more concentrated solution of
lime may accumulate. Then it is conceivable that lithifaction
by crystallization of the carbonate of lime from the more con-
centrated solution is constantly proceeding on the limestone
surface. If this conception be correct the formation of lime-
stone by organic means involves the re-solution and crystalliza-
tion of more or less of the calcite in the primary formation, and
only those organic forms can remain unchanged which resist the
solvent action. If they are delicate, as the trilobites’ branchia
from the Trenton limestones, described by Walcott, they give
evidence that they were rapidly buried and protected.
It is thought by some that limestones are evidences of organic
life at whatever period of sedimentary history they were deposited,
but it has here been shown that the source of all lime in the
sea is the land, and that, under conditions existing in certain
localities, both crystalline limestone and calcareous mud are now
forming chemically. It has also been shown that lime converted
into organic forms is subtracted from that which would other-
wise go to saturate the sea-water. If, then, in any early age of
the earth’s history, lime-using organisms were not present to
subtract and deposit lime from sea-water, and if the atmospheric
agencies worked then as now, the contributions from the land
must have continually added to the alkalinity of the sea until
chemical precipitation occurred. Such a process must have been
limited to seas rather than extended to oceans, because the con-
ditions of delivery of lime from the land were then, as now,
localized. With the development of marine life and the increased
demand for lime for organic use, and with the corresponding
deposition of organic limestone, the sea-water must have become
520 THE JOURNAL OF GEOLOGY.
less alkaline and the conditions of chemical precipitation must
have been still more restricted. In time it might occur that pe-
lagic organisms should demand so much lime for circulation from
the water to calcareous alge, to herbivorous and then to carni-
vorous forms, and so back into solution, that lime could escape
from solution by precipitation only under exceptional conditions.
If it be true that the oceanic oozes, the muds of the Caribbean,
the mud-flats of Florida, and similar calcareous deposits in differ-
ent seas the world over, be wholly organic, then marine life has
locked up more lime than the continents could concurrently sup-
ply, and the balance is now turned against chemical precipitation.
But it has not always been so.
BaILEY WILLIS.
TO DIELOR TAL.
In AN article on ‘‘ Englacial Drift,” in the July number of the
American Geologist, my friend, Mr. Warren Upham, referring to
my article in the first number of this Journal on the Englacial
Drift of the Mississippi Basin, takes exception to the impression
conveyed respecting his views in the matter of rising glacial cur-
rents. The present writer, he says, ‘“‘ several times speaks of the
opinions of writers who believe in the considerable volume of
the englacial drift, as if they supposed the glacial currents to
move gradually upward from the ground to the ice surface.
Such a supposition, however, seems to me quite untenable.
Instead, in my own writings and those of most, if not all, of
these authors, the exposure of the drift on the surface of the ice-
sheet near its border, whence much of it was washed away to
form the eskers, kames, and valley drift, is ascribed wholly to
the superficial melting of the ice sheet, which is called ablation.”
I very much regret to have given expression, or to have seemed
to have given expression, to the views of these writers in any
other terms than they would themselves have chosen, and |
cheerfully reproduce the corrective statement which Mr. Upham
makes. Until my attention was called to the matter, no other
interpretation of the views of these writers than that the supposed
rising glacial currents moved on gradually to the surface of the
ice occurred to me as possible, as no logical stopping place
short of that suggested itself. I do not see any other consistent
view now, but that does not affect the obligation to present
accurately the views actually held. I hope these writers will
credit me with attributing to them what seemed to be the most
logical aspect of the hypothesis entertained by them. The sup-
posed upward movement is attributed to differential motion
521
522 THE JOURNAL OF GEOLOGY.
between the successive layers of ice, as stated by Mr. Upham on_
pages 38-9 of the article referred to (quoted below). This dif-
ferential motion arises from friction at the bottom and extends
to the summit. It was natural, therefore, to take it for granted
that the supposed rising current extended as far as its postulated
cause. It was to be assumed, of course, that the current would
rise less rapidly in the upper part if the difference of movement
of successive ice layers were less there than below, but it would
seem that the rise must be supposed to continue a some vate
so long as the differential motion continued, 2z. ¢., until the sur-
face was reached. The accession of snow-fall within the zone of
accumulation would, to be sure, prevent erratics from reaching
the new surface thus continually formed, but it would not pre-
vent their reaching the surface in the zone of wastage. It is
this latter zone with which our problems of deposition and many
of our problems of derivation have chiefly to do. The career of
some erratics is wholly confined to it. It goes without saying
that ablation brings the surface down and is a factor in every ex-
posure within the zone of wastage, but this does not prevent the
erratics rising (by hypothesis) until they meet it. This conception
of rising currents met by a plane of ablation I supposed without
question to be that entertained by Mr. Upham and others. To
be sure, in a strict and complete statement under this view the ex-
posure of englacial erratics at the surface would be attributed to
the joint result of the upward movement and the downward melt-
ing, but the liberties of brief and convenient statement would
permit it to be referred to in terms of either factor,and I have inter-
preted the expressions of these writers on this basis. The cor-
rection does not, so far as I can see, in any serious way affect the
main question under discussion. If there were rising currents
bearing erratics to heights of 500 or 1000 feet above the base of
the ice the result in ultimate deposition would be essentially the
same as if the currents rose to the surface. If the rising currents
are a misinterpretation, it is immaterial whether they be sup-
posed to bear erratics to varying heights up to 500 or 1000 feet,
whence these erratics move forward parallel with the base of the
EDITORIALS. Rae
ice, or whether they be supposed to continue to rise (more and
-more slowly) till they meet the descending plane of ablation.
If currents rise by reason of differential movements to cer-
tain heights, but not beyond them, notwithstanding the extension
of the differential movements all the way up to the surface, a very
distinct statement of this limitation and of the dynamics invol-
ved, qualitative and quantitative, would be appropriate. Perhaps
such an explanation is intended in the following quotation from
Mr. Upham, which I introduce to give ampler expression to his
views, though I dissent from his interpretations of the crevasses
of the alpine glaciers and of the esker, Bird’s Hill, as well as
from his fundamental proposition.
“The conditions of the flowing ice which seem to me to have
been efficacious to carry drift upward into it from tracts of plane
or only moderately undulating contour, were the more rapid
onflow of the ice-sheet in its upper and central parts and even in
the portion near the ground but not in contact with it, than upon
the bed of the ice-sheet where its movement was much retarded
by friction. A very good analogy with the slowly rising cur-
rents which I believe to have existed in many portions of the
base of the ice-sheet is afforded by the edges of alpine glaciers,
where the crevasses extending diagonally up stream into the
glacier testify that the movement of its friction-hindered border
is from the side of the valley into the ice mass. But the arched
surface of the glacier and the great supply of its central current
prevent the drift so worn off and borne away from being carried
into the axial portion of the ice stream. Similarly the steady
accession to the mass of the ice-sheet over any place by onflow
from its thicker central part and by the accumulating snowfall
forbade the drift of the upwardly moving basal current from
being carried far into the ice in comparison with its total thick-
ness. The evidence of the esker called Bird’s Hill, near Winni-
peg, Manitoba, shows that much englacial drift had there been
uplifted from a nearly level country to a height of more than 500
524 DEE VOOLINALV OF NGEOLO GN.
feet in the ice-sheet.t Probably some of the englacial drift there
was as high as 1,000 feet or more in the ice, but doubtless a
larger part was below than above the altitude of 500 feet; and
this was on an area where the ice-sheet had attained probably a
thickness of 5,000 or 6,000 feet, its lower fifth or sixth part bear-
ing considerable enclosed drift. In like manner the outer por-
tions of the ice-sheet, where its thickness was less, had probably at
its time of culmination no englacial drift above its lower sixth or
fourth or third part. Whatever boulders and other drift became
incorporated in the higher portion of the zone reached by the
currents flowing upward would be thence carried forward in some
regions, as from the Huronian and Laurentian areas north of Lake
Huron to the boulder belts in Illinois, Indiana and Ohio, de-
scribed by Chamberlin? without intermixture with other englac-
ial drift brought into the ice by less powerful currents on all the
intervening extent, which in the case mentioned is about five
hundred miles.” 3
DCs
‘Geol. and Nat. Hist. Survey of Canada, Annual Report, new series, vol. iv., for |
1888-89, pages 36-42E.
2 Boulder Belts distinguished from Boulder Trains—their Origin and Signifi-
cance,’ Bulletin, G. S. A., vol. i, pp. 27-31. ‘‘ The Nature of the Englacial Drift of the
Mississippi Basin,” Journal of Geology, vol. i, pp. 47-60.
3The American Geologist, vol. xii, No. 1, July, 1893, pp. 38-39.
REVIEWS.
Correlation Essays, Archean and Algonkian. Bulletin of the U. S.
Geological Survey, No. 86. Pp. 549, 12 plates. By CHARLES
RICHARD VAN HIsE.
In order of publication, this is the seventh of the correlation essays
originally planned by the survey for the International Geological Con-
gress of 1891. If the long delay in the appearance of the present
essay is in any measure responsible for its excellence, no one will regret
that it did not appear ontime. This is not the first piece of good work
which Professor Van Hise has done; but he has done nothing which
has been of greater utility to the geological world than the present vol-
ume will prove to be.
In no department of geology has there been more rapid progress
during the last decade than in the department in which Professor Van
Hise is a specialist. In no department is it more difficult for those
who are not specialists to follow current progress. But so successfully
has Professor Van Hise written his essay that the reader will have little
difficulty in knowing the present status of pre-Cambrian geology in
America. He may know definitely what is definitely known, and he
may know definitely what is not known. More than this, he may
know definitely the limitations and imperfections of facts and_princi-
ples which are but partially worked out, without finding himself con-
fused between fact and possible fact, or between established principles
and unverified hypotheses. Consciously or unconsciously, the author has
given definite shape to the uncertainties and indefinitenesses of his sub-
ject, and in so doing has rendered an invaluable service to students.
A mere summary of what has been done in the various areas of
pre-Cambrian rocks would be valuable. But the present essay does
much more. The author is personally familiar with much of the ground
brought under review in the volume, and he has given, always without
a suggestion of dogmatism, what every reader is glad to have, his
own opinion concerning the interpretations to be placed on the phe-
525
526 THE JOURNAL OF GEOLOGY.
nomena of each of the regions with which he is familiar, together
with the reasons therefor. ‘The failure to summarize and interpret the
summaries of the literature reviewed has lessened the value of some of
the essays of this series.
The plan of the volume is simple. It consists of, first, a digest of
all the papers on the pre-Cambrian geology of North America which
had appeared at the time the manuscript left the author’s hands; sec-
ond, a discussion of the literature ; and, third, a discussion of the gen-
eral principles involved in the study of pre- Cambrian rocks, together
with a statement of the results which have already been attained in
America in the application of these principles.
The digests of the literatures are grouped on a geographical basis.
The digest of all publications bearing on the pre-Cambrian geology of
the original Laurentian and Huronian areas constitute one chapter,
and the digests of the literature of the Lake Superior region, of the
great northern areaof Eastern Canada and Newfoundland, of the isolated
areas in the Mississippi Valley, of the Cordilleras, and of the Eastern
United States, constitute each a separate chapter. Within each area
the digests are arranged chronologically. At the close of each chapter,
or in some cases at the close of their subdivisions, are summaries of the
results thus far attained in the respective areas. In all cases the digests
appear to be as nearly absolutely impartial as it is possible for human
work tobe. The total number of papers summarized is between 700
and 800. Many of them are papers of considerable length, some of
them being elaborate reports. When it is remembered that these
papers are not roughly abstracted, but that carefully considered digests
are presented, the amount of labor involved in the preparation of the
bulletin will be apparent.
It is the final chapter which, together with the maps, will attract
most attention. This chapter gives a concise outline history of the
development of pre-Cambrian geology in America, and a clear
exposition of its present status. Professor Van Hise concludes that it
may be accepted as demonstrated that in North America there is an
intricate system of granites and gneisses and crystalline schists, which
represent the oldest rocks of the continent, and that this system under-
lies all known sedimentary rocks and their derivatives, and that if it ever
contained sedimentary materials of any sort, all evidence of their
existence has been obliterated.
It is to this system of rocks that the name Archean is restricted.
REVIEWS. B27,
The minerals composing these rocks, wherever found, generally agree
in showing evidence of extensive dynamic changes, as do also the rela-
tions of each sort of rock composing the system, to each other. So
closely do the rocks of this system resemble each other in different
regions, that Professor Van Hise says that a suite of specimens of
Archean rocks from any one of the regions examined by him, if not
labeled, “could by no possibility be asserted not to have come from
any other.” The system is a unit, both in its positive and negative
characters.
To the Archean system thus defined are referred the basement com-
plexes of Arizona, of the Wasatch Mountains, of certain ranges of
Nevada, of Southwest Montana, of Texas, of the Lake Superior region,
of the Hudson Bay region, probably the basement complex of New-
foundland, and much of the great area of Northern Canada, known as
Laurentian. The basal complexes of the Front range, and of the
Quartzite Mountains of Colorado, are referred to the Archean with less
confidence. Still other areas not yet definitely classified may prove to
be Archean in whole or in part.
With reference to the origin of the Archean, Professor Van Hise
inclines to a modification of the theory that the system represents a
part of the original crust of the earth. He believes that the Archean
rocks were originally igneous, and that they may include not only such
remnants of the pre-sedimentary crust as may exist, but those deeper
parts of the crust which became lithified in later times, and which have
reached the surface by denudations. He suggests that the banded and
contorted granite-gneiss which serves as a background for the Archean
may represent the rocks having such an origin, while the other parts of
the system may be subsequent eruptives, assignable to no other system,
and physically a part of the Archean.
The author does not overlook the fact that this suggestion con-
cerning the origin of the Archean may make the system include rocks
which crystallized below the outermost crust after sedimentation began,
and that the date of this lithification may therefore be Algonkian, or
even post-Algonkian. Their crystallization at such a date is not looked
upon as sufficient reason for excluding them from the Archean group.
It is manifestly impracticable to have an Algonkian system below the
Archean, representing crystallization or lithification synchronous with
the Algonkian sedimentation above.
This being the conception of the Archean, it is evident that strati-
528 THE JOURNAL OF GEOLOGY.
graphical methods are not applicable to it. The only division which
seems applicable is a bifold one, based on lithological characters and
relations, viz.: 1, the more schistose rocks, generally dark colored, and
2, the more massive rocks (granites and granite-gneisses), generally
light colored. To the latter class it is proposed to restrict the name
Laurentian. For the former class, the codrdinate name Mareniscan is
proposed, the term being derived from the name of a township (Mare-
nisco) in Michigan.
The necessity for a group between the Archean and Cambrian has
come to be generally recognized during the last decade. But to all
except those engaged in the study of pre-Cambrian rocks, the names
which have been used to designate this group, or parts of it, have
always been confusing, because of their multiplicity, their lack of defi-
nition, and the lack of uniformity in their use. ‘This bulletin makes
clear the nomenclature which has been adopted by the survey, and sets
forth the relation of the various names which have been used to desig-
nate parts of the post-Archean (as here used) and pre-Cambrian group.
Whether or not those not connected with the survey agree that the
nomenclature officially agreed upon is the best possible, it is to be
hoped that it may be uniformly adopted in the interest of intelligibil-
ity. It has the merit of simplicity and definiteness, and of avoiding
disputed questions, so far as this is possible. ;
To the post-Archean pre-Cambrian group is given the name
Agnotozoic, or, preferably, since its fossils are becoming known /yo-
ferozoic, a term coordinate with Archean, Paleozoic, ete. Since it is
impossible to divide this group into systems codrdinate with Cambrian,
Silurian, etc., which can be correlated with each other throughout the
various areas of Proterozoic rock, the term Algonkian is used for the
present as a single system term to cover the whole Proterozoic group.
In many areas the group is distinctly divisible into two or three sys-
tems comparable with the Cambrian, Silurian, etc. ‘Thus in the orig-
inal Huronian area there are probably two unconformable series of
rocks, the lower unconformable on the Archean, and the upper uncon-
formable below the Cambrian. These may be correlated with some
degree of confidence with the Lower and Upper Huronian of the
Lake Superior region. But here a third series, the Keweenawan, inter-
venes between the Upper Huronian and the Cambrian, and is uncon-
formable with both. In the Grand Cafion region again, three series
are recognized. But their relation to the three series of the Lake
REVIEWS, 529
Superior region is not known. The same is true of other regions.
For this reason, the various terms, Huronian, Keweenawan, Vishnu,
Chuar, etc., which have been used to designate definite parts of the
group, will still be retained, for in the absence of criteria for the satis-
factory correlation of the subdivisions of the group in the various
regions where they occur, these parts must continue to bear local
names.
The group is so extensive as to be comparable in thickness to
the Paleozoic, Mesozoic and Cenozoic combined, and inferentially
to represent an equal lapse of time. It contains great systems, sepa-
rated by great unconformities. Concerning the two unconformities in
the systems in the Lake Superior region, those between the Lower and
Upper Huronian and between the latter and the Keweenawan, Pro-
fessor Van Hise says: ‘‘Each represents an interval of time suffi-
ciently long to raise the land above the sea, to fold the rocks, to carry
away thousands of feet of sediments, and to depress the land again
below the sea. That is, each represents an amount of time which is
perhaps as long as any of the periods of depositions themselves.” In
parts of the region the Lower Huronian is known to be unconform-
able on the Archean. In other parts the relations are unknown.
This statement of the case gives some idea of the thickness of the
group, as well as of its complexity and importance.
The delimitation of the Algonkian is theoretically easy, after the
definitions of the Archean and Cambrian. It includes all pre-Cam-
brian sedimentary rocks, and their igneous equivalents. Although a
great unconformity generally separates the two groups, helping to
render their distinction clear, it is not always easy of recognition.
Locally parts of the Algonkian have undergone such profound meta-
morphism at the hands of dynamic forces which affected the Archean
as well, that they seem to be structurally one. In such cases it is
believed that the apparent conformity is in reality apparent only, the
original structural relations being obscured or even obliterated by
the structures superinduced by dynamic forces on both series involved.
Even where there is a common structure in rocks regarded as Archean
and Algonkian, there is sometimes inherent evidence that one part of
the rocks concerned is clastic, while similar evidence is wanting in the
other.
Not the least instructive part of the volume is the discussion of the
principles applicable to Algonkian stratigraphy. It would be useless
530 THE JOURNAL OF GEOLOGY.
to attempt to summarize this discussion, since it is as brief as is con-
sistent with adequacy, in its original form. Suffice it to say that while,
as applied to Paleozoic rocks, the value of lithological characters and
structural relations are well understood, they have a somewhat differ-
ent meaning And a greater relative value when applied to the pre-
Cambrian formations. At the same time this application is more
difficult.
One of the most valuable parts of the volume consists of the twelve
maps, covering most of the areas where pre-Cambrian rocks are known
or suspected. Nowhere else does Professor Van Hise succeed better
in making the indefiniteness of our knowledge definite, than on the
maps. On but two of the twelve maps does he rep;esent Archean
rocks, viz., on the maps covering the original Huronian area and its sur-
roundings, and on the map of the Lake Superior region. Within the
United States, Archean rocks are mapped in but three states — Minne-
sota, Wisconsin and Michigan. This does not mean that Archean
rocks do not exist elsewhere, or that they are not known elsewhere,
but that their areas elsewhere, so far as covered by the maps, have not
been defined. Some of the areas which we have been accustomed to
see represented as Archean on maps made before the Algonkian was
differentiated, are now represented as ‘“‘unclassified pre-Cambrian.”
Of this the Adirondack region may serve as an example. The maps
tell us only that the rocks of this region may be Algonkian, or Archean,
or both. In the text Professor Van Hise’s opinion concerning the
area may be found. This is to the effect that the Algonkian is cer-
tainly represented in the region, and Archean possibly, but that
existing knowledge on the point is not sufficiently definite for carto-
graphic representation. Other areas which have been mapped as
Archean are represented simply as ‘unclassified partly or wholly
crystalline rocks.” Of the areas thus represented, the whole of the
crystalline schist belt of the Appalachian region may serve as an exam-
ple. The author’s map does not even assert that these rocks, or any
part of them, are pre-Cambrian. Here again we find the author’s
opinion in the text, where it is indicated that parts of this area are
pre-Cambrian, while other extensive portions may, or may not be.
Such pre-Cambrian areas as are known are not defined, and therefore
cannot be represented on the maps.
Algonkian rocks find definite representation in more regions than
the Archean. They appear upon the maps in Arizona, New Mexico,
REVIEWS. 531
Utah, South Dakota, Minnesota, Iowa, Wisconsin, and Michigan.
They are known, but their areas not defined, in various other localities.
The summaries of the several chapters, or their sections, the final
chapter, and the maps, should serve as a text-book on -pre-Cambrian
- geology for all advanced students in our universities. Not only will
the best information available be thus put into their hands, but the
whole treatment of the subject is such as give an intelligent insight into
the methods of geology, and into the methods of science as well.
ROLLIN D. SALiIspuRY.
ANALYTICAL ABSTRACTS OF CURRENT
LITERATURE.
SUMMARY OF CURRENT PRE-CAMBRIAN NORTH AMERICAN
LITERATURE.*
Cross! describes a series of hornblendic, micaceous and chloritic schists,
on the eastern side of the Arkansas river, near Salida, Col. In places these
grade into massive rocks. They are cut by granitic and pegmatitic veins, as
well as by dykes of porphyry. A detailed microscopical study leads to the
conclusion that the rocks are a metamorphosed volcanic series. The whole
constitutes a part of a single anticline. The schists are unconformably below
the Silurian, and as the known Cambrian in Colorado is a thin series of
quartzites and shales conformable with the Silurian, the Salida schists are
considered as pre-Cambrian. The relations of the schists to the Archean
complex are not exposed, but they are probably a continuation of the
hornblende-schists of Marshall Pass. Greenish schists are found at Tin Cup
Pass, and near the town of Tin Cup is a highly crystalline marble inter-
bedded with the green schists, and fine grained gneissoid rocks, showing that
metamorphosed sedimentary rocks do exist among the crystalline schists of
the Sawatch Range. Taking into account all the facts it is thought that the
schists and massive rocks of the Salida section probably ‘represent a great
series of surface lavas, erupted in Algonkian time.
Smyth (C. H.)? describes the rocks near Gouverneur, New York, as con-
sisting of gneiss, granite, limestone, and sandstone, with small amounts of
associated schists. The gneiss is the oldest rock of the region, underlying
the other formations. It sometimes grades into a true granite, the passage
being gradual. The two are regarded as different phases of the same rock,
either the granite being an unchanged remnant of a Plutonic mass from
which the gneiss is derived, or the result of fusion of the gneiss. Evidence
of unconformity between the beds of the limestone and the foliation of the
* Continued from page 314.
™Series of Peculiar Schists near Salida, Col., by Whitman Cross. In Proceedings
of Col. Scientific Soc., Jan., 1893, pp. I-10.
2A Geological Reconnaissance in the vicinity of Gouverneur, by C. H. Smyth, Jr.
In Transactions N. Y. Academy of Sciences, vol. xii., April, 1893, pp. 97-108.
532
ANALVTICAL ABSTRACTS. 533
gneiss was found in two localities, and was indicated in several others; there
is no evidence of irruptive contacts between the gneiss and limestone; the
gneiss shows no evidence of sedimentary origin; therefore, the simplest
hypothesis, but requiring more proof, is that the gneiss is ah eroded meta-
morphosed plutonic rock, upon which the limestone was deposited. The
marble is coarsely crystalline, and in age is next to the gneiss. Near the
base of the limestone, and interbedded with it, are peculiar schistose rocks,
which, while completely crystalline and resembling igneous rocks in composi-
tion, are indicated by their field relations to be of sedimentary origin. Near
Gouverneur an outcrop of limestone contains abundant fragments of black
schist, scattered through the limestone in a most irregular manner, and
making up, perhaps, one-third of the rock. This and other outcrops show
that the schist fragments are remains of once continuous schist layers, which
have been completely shattered in the course of metamorphism, since between
the continuous belts of schist and the Gouverneur locality there is every
possible gradation. While the schists show the effects of foldings, contor-
tions, stretchings and shattering, the limestone shows no traces of it, it
appearing to have been a plastic mass in which the schists moved with con-
siderable freedom. The conspicuous result of metamorphism in the lime-
stone is crystallization. In the limestones are also pegmatitic veins, which
have been much shattered by the dynamic action, reducing them to small
lumps of quartz and feldspar, scattered through the limestone. So far as
observed the pegmatite yields to strain only by fracturing, not showing pre-
liminary contortions, so general in the schistose layers.
In the southern part of the area examined is a granite, not grading into
gneiss, and which breaks through the limestone, causing great disturbance in
‘strike and dip, enclosing masses of the rock many feet in diameter, and
metamorphosing this rock to some extent. The sandstone at Gouverneur was
found in direct contact with the limestone. Here it appears that the lime-
stone surface has been subjected to erosion before the sandstone was deposited
upon it. In confirmation of this are seen narrow irregular cracks extending
several feet into the limestone, which have been filled with sandstone. The
limestone was evidently completely lithified when the sandstone was deposited
and sifted into it, and this implies discordance. This unconformity proves
that the limestone is older than the upper Cambrian, the data being wanting
for any more definite determination of its age. The metamorphism of the
rocks of the limestone- bearing series occurred before upper Cambrian time,
but the sandstone is metamorphosed, and this metamorphism must therefore
belong to post-Potsdam time.
Comments.—The inquiry rises whether the second metamorphism spoken
of, that of the sandstone, is produced merely by interstitial cementation, or is
dynamic metamorphism. If the first is found to be the explanation, so far as
534 THE JOURNAL OF GEOLOGY.
the paper gives any evidence, all of the igneous activity and dynamic
metamorphism are pre-Potsdam.
* Wadsworth gives a sketch of the iron, gold and copper districts of Michi-
gan. The Azoic or Archean rocks are divided from the base upward into Cas-
cade, Republic and Holyoke formations. These divisions are placed in order
as equivalent to the fundamental complex, lower Marquette series and upper
Marquette series of Van Hise. They are unconformable and represent three
different geological ages. The Keweenawan is divided into two divisions,
both of which are placed in the Cambrian ; the Lower Keweenawan, 25,000 ft.
of interbedded conglomerates and lava flows, with some intrusives; Upper
Keweenawan, 12,000 feet of sandstones and shales, not separable from the
Potsdam or Eastern sandstone.
The Azoic or Archean system consists of rocks formed (1) by mechanical
means, (2) by eruptive agencies, (3) by chemical action.
The Cascade, or oldest formation of sedimentary and eruptive rocks, con-
sists, commencing with the oldest, of gneissoid granites or gneiss, basic
eruptives and schists, jaspilites and associated iron ores, and granites, although
the above arrangement may be considered no more than a hypothesis, and it
is probable that the jaspilites and iron ores will be found to belong to the
Republic formation. It is also probable that the Cascade formation itself
will prove to be composed of two or more distinct geological formations, as
shown by the fact that the chief rock of the Huron Mountains appears to be
a gneissoid granite, rather than a true sedimentary gneiss. True sedimentary
gneisses are found in the Huron Bay and Cascade districts. In the former
area they contain fragments that closely resemble the gneissoid granites, and
thus they appear to be formed from the debris of those rocks. If, however,
the gneissoid granites are metamorphosed eruptive rocks, and not true
gneisses (which are restricted to metamorphosed sedimentary rocks), this fact
proves only that the gneisses are younget in order of time, but not of neces-
sity of younger geological age. Similar statements apply to the breaks
between the Cascade and Republic formations, and the break between the
Republic and Holyoke formations. In the Huron Bay, Menominee and other
districts the Cascade formation holds intrusive granites. Amphibole-schists
are also found intrusive in the gneisses in the Cascade area. In the Mar-
quette area the amphibole schists are cut by felsite or quartz-porphyry.
Much of the granite and felsite appear to have been erupted during the
time of the Cascade formation, and perhaps even later. On the Cascade
range hornblende-gneiss cuts the country rock. These dykes are cut by
tA Sketch of the Geology of the Iron, Gold and Copper Districts of Michigan,
M. E. Wadsworth, Rep. State Board Geol. Sur., Michigan, 1891-2; pp. 75-174;
Lansing, 1893. Also, see Annual Reports 1888-1892, ibid., pp. 38-73.
ANALVIICAL ABSTRACTS. 535
other dykes containing crystals of feldspar, while both are cut by gray
granite, that is in turn cut by red granite.
The Republic formation, commencing with the oldest division, is divided _
roughly as follows: Conglomerate-breccia and conglomerate-schist ; quart-
zite; dolomite; jaspilite and iron ore; argillite and schist; granite and
felsite; diabase; diorite and porodite; porphyrite. At the base of the
Republic formation is a series of conglomerates and conglomerate-schists,
which pass into hydrous mica-schists. Near Palmer, the coarse conglomerate
rests on the gneiss to the south, and is overlaid to the north by quartzite,
fragmental jaspilite and quartz-schist. The dip is about 40° northward.
The conglomerate contains numerous pebbles of gneiss, as well as some of
- granite, diorite, schist and quartz veins. Near the Volunteer mine quartzite
immediately overlies the basal conglomerate, and in other places reposes
directly on the Cascade formation.
The quartzite in the Menominee district, running from Sturgeon river
along Pine river to Metropolitan, is thought to belong to the base of the
Republic formation, since it is found at various places close to the gneiss and
granite, dipping away from them, and is cut by dykes of granite in Sec. 12,
T. 41 N., R. 30 W. The dolomite occupies a low horizon, either interbedded
with the quartzite or occupying its place. The fundamental ore and jaspilite
appears to belong, stratigraphically, to the Republic formation. The most of
the jaspilite of the formation is of detrital origin, being originally conglomer-
ates, breccias, sands, muds, which have been subsequently chemically acted
upon by percolating waters, since in the Cascade range the jaspilite and ore
form layers which are frequently interlaminated with quartzite. The jaspilite
of Negaunee and Ishpeming has failed to reveal any evidence that it is
sedimentary, although the associated argillite and schist are in part at least
clearly sedimentary. The argillite and schists are directly associated with
the jaspilite and iron ore. In places they grade up into the fragmental
jaspilite, and in other places are interbedded with it. They also succeed
the latter rocks and overlie them. These argillites and schists are older
than the diorites of the district, and are cut by them.
The Holyoke formation has the following succession, as far as known,
commencing with the base: Conglomerate breccia and conglomerate schist ;
quartzite; dolomite; argillite; graywacke and schist; granite and felsite;
diabase, diorite and porodite; peridotite, serpentine and dolomite; melaphyr
or picrite; diabase and melaphyr. The conglomerate at the base of the
Holyoke contains granitic material, as well as fragments from the jaspilite.
In many places the unconformity between the Republic and Holyoke forma-
tions is most marked, being seen at many of the mines. In many places, also,
the Holyoke formation overlaps the Republic, and is in contact with the
granite and gneiss of the Cascade. Associated with the Holyoke conglom-
536 LTTE fOOLINATE VO F AGH OTE OG NA
erate is a quartzite which includes the Mt. Mesnard and Teal Lake quartzites.
In See: 20, 1. 47 N., R: 26 W., and Secs: 8.andi1o;, Dayo IN; Raz Waemnear
Silver Lake and in other places, sediments of the Holyoke formation have
sifted down into the fissures and joints of the preéxisting rocks, when they
have a dyke-like character. For such formations the term ‘“clasolite”’ is
proposed. The dolomite of Mt. Mesnard and thence to Goose Lake, while
lithologically, like that placed in the Republic formation, is doubtfully referred
to the Holyoke. Argillite, graywacke and mica-schist occur extensively
in the Holyoke, constituting the upper horizon. It is doubtful whether any
granite or felsite of Holyoke age exists in the Marquette district.
Diabase, diorite, porodite, and peridotite occur abundantly, belonging
both to the Republic and Holyoke formations. According to Mr. Seaman,
diabase dykes of the Gogebic area are probably the same as those that cut
the overlying sandstones of the Keweenawan, from which it is concluded that
the Keweenawan lava flows are the effusive equivalents of the Holyoke dia-
base dykes.
The soft hematites of the region are produced by secondary enrichment
at places where the water could best act, being at points of fracturing or in
basins. The silica of the lean material has been leached out, and in its
place iron oxide substituted. Gold and silver veins are discussed, and a
classification of ore deposits given.
The Eastern or Potsdam sandstone rests unconformably on the Azoic.
This includes the unaltered horizontal sandstone, which is free from dykes of
eruptive material, and the Keweenawan, which consists of lava flows alter-
nating with sandstones and conglomerates, largely derived from the former.
Above, and conformably with the Eastern sandstone, near L’Anse, is lime-
stone of Silurian age, as shown by its fossil contents. On Keweenaw Point
the Eastern sandstone dips toward, and passes under, the interstratified sand-
stones and lavas of the Keweenawan. At or near the contact is a fault.
However, at Douglas, Houghton and Hungarian rivers, it is thought not to be
at the contact, and consequently that the Eastern sandstone underlies the
Keweenawan lava, but the Eastern sandstone may contain two or more sand-
stones of different ages, which may perhaps be considered as the most proba-
ble explanation of all the evidence. In Sec. 13, T. 46 N., R. 41 W., on the
South Trap range, a nearly horizontal, soft, friable micaceous sandstone is
found near the interbedded Keweenawan melaphyr and indurated sandstone.
This soft sandstone contains numerous spherical spots very common in the
Eastern sandstone, but not found in the Keweenawan. In the soft sandstone
are found pebbles and large angular fragments of indurated sandstone, which
Mr. Seaman thinks could only have been derived from the adjacent indurated
sandstone. The rocks of the Trap range here exposed are believed by Mr.
Seaman to hold a position near the top of the Keweenawan series, and he
ANALVTICAL ABSTRACTS. 5a
concluded that the soft sandstone belongs to a distinct and later geological
age than the Trap range. 3
The character and origin of the copper deposits are discussed.
Comments.—The major structural conclusions independently reached by
the Michigan Geological Survey are nearly identical with those which have
been published by the officers of the United States Geological Survey. The
same may be said as to the origin of the iron ores. Upona few points there
is, however, a difference of opinion.
The unconformity which exists between the Lower Marquette and the
Basement Complex marks a distinct geological age, whether gneissoid granites
composing the latter are metamorphosed eruptives or metamorphosed sedi-
mentary rocks. It is true that a sedimentary formation resting upon an
eruptive, and deriving material from it, is no evidence of a geological break
if the eruptive is a surface rock and has not been altered before the overlying
formation was deposited. If, however, the eruptive is a deep-seated rock,
or has been so sheared and folded as to take on a schistose structure before
the deposition of the succeeding formation, and has consequently reached the
surface by erosion, the discordance may mark as great a geological break as
an unconformity between a metamorphosed sedimentary rock and an unaltered
overlying series.
That there is more than one geological period represented in the Cascade
formation seems unlikely, and in a later note by Dr. Wadsworth this idea is
apparently abandoned. If any gneisses of the Huron Mountain prove to be
unconformably upon, and to have derived material from, an older gneissoid
granite series, it is probable that this new series will be found to be equivalent
to the Lower Marquette or Upper Marquette series rather than to belong to
the Cascade formation.
Jaspillite and ore are tentatively placed as one of the kinds belonging to the
Cascade formation or Basement Complex, although the major portion of them
are placed in the higher series. No large areas of this rock yet discovered
would be here placed by the reviewer. The jaspillite of Ishpeming and
Negaunee doubtfully referred to the Cascade is believed to be a sedimentary
deposit of the same age as similar rocks of the Lower Marquette series.
That the jasper near the base of the iron - bearing formation at Cascade is
interlaminated with layers of fragmental material is not sufficient evidence
that the jasper is or has been derived froma mechanical sediment. The
inferior formation of the lower Huronian is usually, if not always, a clastic
deposit, resting as it does unconformably upon an earlier series of granites,
gneisses and schists. This fragmental formation usually grades up into the non-
fragmental formation of the iron- bearing member, and before continuous
pure non - clastic sediments are reached there are often several alternations of
the two kinds of deposits. Such occurrences are exactly analogous to the
538 FHE JOURNAL OF GEOLOGY.
interlaminations of limestone with shale or sandstone at the transition horizon
which frequently occurs when a limestone formation rests upon a sandstone
formation.
As to the age of the Keweenawan, this series is placed by Dr. Wadsworth
as a lower part of the Potsdam, but is regarded by the reviewer as resting
‘unconformably below the Potsdam, and as belonging to a different geological
period. This question is one of great complexity, which can not here
be discussed in detail. However, Dr. Wadsworth refers the Keweenawan
so doubtfully to the Potsdam that the difference can hardly be said to be a serious
one. Thestatement that the most probable explanation of all the phenomena
at Keweenaw Point is that the Eastern sandstone is of different ages can
have but one meaning—that a part of this so-called Eastern sandstone
belongs to the Potsdam, and this Potsdam is later than, and unconformably
upon, the Keweenaw series, which latter includes another part of the Eastern
sandstone. Put in another way, Dr. Wadsworth extends the term Eastern
sandstone to cover all of the sandstone exposed until the Traps are reached.
That is, the break between the Potsdam and Keweenawan is in places a short
distance away from the Traps. This admits the difference in geological age
between the main area of Potsdam sandstone and the Keweenawan, and
merely shifts the boundary line between the two a short distance. It is nota-
ble that the most important new evidence presented upon the question is that
obtained by Mr. Seaman, Dr. Wadsworth’s assistant. Near the South Range
he finds outcrops which he regards as Eastern sandstone, holding indurated
fragments derived from adjacent ledges of upper Keweenawan sandstones,
and hence believes the Eastern sandstone to represent a later geological age.
It appears to the writer very doubtful whether the large number of mem-
bers given for the Republic and Holyoke series will be found to be gen-
eral for the Lower Huronian and Upper Huronian on the south shore of Lake
Sueprior, although each may be found at some locality.
Wadsworth’ states that recent work renders it probable that the Azoic or
Archean of Northern Michigan is divisible into five unconformable forma-
tions. The tentative arrangement, commencing with the oldest, with the par-
allel formations, as determined by the United States Geological Survey, is as
follows :
MICHIGAN GEOL. SURVEY. U. S. GEOL. SURVEY.
Cascade Formation. Fundamental Complex.
Republic Formation }
Mesnard Formation | Lower Marquette series.
Holyoke Formation /
Negaunee Formation | Upper Marquette series.
"Subdivisions of the Azoic or Archean in Northern Michigan,” by M. E. Wadsworth.
In Am. Jour. of Sci., vol. xlv., No. 265, Jan., 1893, pp. 72, 73.
ANALYTICAL ABSTRACTS. 539
Comments.—The suggestion of the two additional unconformities in the
Huronian of the Marquette district is so tentative that no criticism of it is
necessary. The suggestion implies that Dr. Wadsworth thinks this outcome
the most probable one. It appears to the writer, however, that it is far more
probable that the true explanation is that there are only three unconformable
pre- Keweenawan series. The additional unconformities are probably sug-
gested by the considerable local variation in the character of both the Lower
Huronian and Upper Huronian series, so that in different parts of the district
the same series has very different aspects.
Lane! holds that certain of the ore bodies of the Marquette district are
produced by abstracting iron oxide from amphibolites and depositing this
material at other places. The water is regarded as upward moving, hence
the ore bodies rest upon the diorites as foot walls. It is not denied that in
other places the iron is derived froma carbonate, or that silicia is replaced by
the iron oxide. At the Volunteer mine the ore seems in part to have replaced
the sandstone.
Bell reports on the Sudbury mining district :? The rocks are divided into
three groups, in ascending order: (1) A gneiss and hornblende - granite
series— Laurentian. (2) A series comprising quartzites, massive graywackes,
often holding rounded and angular fragments; slaty graywackes, with and
without included fragments; drab and dark- gray argillites and clay - slates ;
dioritic, hornblendic, sericitic, felsitic, micaceous and other schists; and
occasionally dolomites, together with large included masses or areas of pyri-
tiferous greenstones. This group constitutes the ordinary Huronian of the .
district. (3) A division consisting ofa thick band of dark-colored silicious
volcanic breccia and black slate (generally coarse), overlaid by drab and dark-
gray argillaceous and nearly black, gritty sandstones and shaly bands. The
breccia is underlaid in places by quartzite conglomerate. (4) In addition to
these, dikes of diabase and gabbro cut through all the foregoing, and are,
therefore, newer than any of them, although they may not belong to a later
geological period.
Flanking the Huronian rocks on the southeast is gneiss, and on the north-
west a mixture of gneissand hornblende- granite. ‘The first of these rocks is
of the characteristic Laurentian type, but the hornblende- granite and quartz -
syenite on the northwest are not always characteristic of the Laurentian.
These rocks, however, pass into the gneiss in sucha way, and are mingled with
* Microscopic characters of Rocks and Minerals.” A.C.Lane. Rep. State Board
Geol. Sur., Mich., for 1891-2, Lansing, 1892, pp. 176-183.
2 Report on the Sudbury Mining District, by Robert Bell. Annual Rep. Geol. &
Nat. Hist. Sur. of Canada for 1889-90. Vol. vy, Part F, p.95, with a geological map.
540 THE JOURNAL OF GEOLOGY.
them both on a large and small scale, that it was impossible to separate them.
Within the Huronian trough, and parallel with it, is also a tongue of gneiss
and hornblende - granite two or three miles wide and thirty-nine miles long.
The Huronian division forms a part of the great Huronian belt, extending
from Lake Superior and Lake Huron nearly to Lake Mittassini. The bedding
of the Huronian is usually nearly vertical, or stands at high angles. Occas-
ionally the rocks have been sheared by pressure. Graywacke- conglomerate,
in places full of rounded pebbles of gray quartz -syenite, is found on the Blue
River branch of the Spanish River, Lot 2, Con. III. In the township of
Hyman is an Augen-gneiss which is evidently a metamorphorsed clastic, as it
forms a part of the quartzite and graywacke series. The line of junction
between the Laurentian and Huronian is unusually straight. West of Lake
Wahnapitae, along the contact, there is evidence of great disturbance and
crushing, the rocks of the two series being much broken up and intermixed.
It is not improbable that at the junction line is a considerable fault.
The third division is less altered, and is in a distinct basin running from
the township of Trill northeastward to near the South Bay of Lake Wahna-
pitae, a distance of 36 miles, with a breadth of 8 miles in its central portion.
These rocks are perhaps unconformable to the older Huronian rocks on which
they rest, and may be Upper Huronian, or possibly lower Cambrian.
Along Onaping Lake and River, and along Straight Lake, are Huronian
outliers. The principal kinds of rocks in the first basin are slate conglomerates,
with well-rounded pebbles and boulders, mostly of binary granite, quartz,
quartzite and schists; and coarse arenaceous or graywacke conglomerate,
together with some pale-pink quartzites and blueish and greenish - gray felsites,
argillites and slates. The principal rocks of the second basin are graywacke-
schists, quartzites, quartzite or graywacke - conglomerates, green schists, hard
sandstones, greenstones, and some dolomites. In the conglomerates are peb-
bles of graywacke and hornblende-granites like the prevailing varieties found
in situ in the region, black slates and black and white quartz. On Lot 4, Con.
III, Moncrieff, is the junction of the Laurentian red hornblende - granite and
the graywacke.
It is concluded that the Huronian rocks of the Sudbury district are largely
of volcanic nature, although many of them have been rearranged by water;
hence they may be termed pyroclastic. The graywackes consist of granite
debris more or less comminuted by the modifying action of water. Under
this name is included many varieties of rocks, ranging from those which
approach quartzites to others approaching argillites. The largest fragments
are usually of red or gray aplite. As a general rule, the different divi-
sions of the Huronian rocks do not maintain their thickness very far on the
strike, but diminish more or less rapidly, their place at the same time being
filled by a corresponding thickening of other members of the series.
TAIN ALLY MCAT AB Sel CDSs 541
The trappean rocks of the district consist of (1) extensive masses, together
with many of smaller size, incorporated with the other Huronian rocks, and
probably contemporaneous with them ; and (2) dikes which cut through all the
members of the series. There are nearly fifty areas of diorite, two principal
belts of diabase, and a belt of slaty, greenish diorite, which in places becomes
brecciated, and includes fragments, from large boulders down to small peb-
bles, consisting principally of quartzites, granites, and syenites.
Very numerous details are given, which cannot be summarized.
Comments.— The conclusion of Bell, that the Huronian is divisible into
two divisions which are probably unconformable, corresponds with the more
recent conclusions of those who have studied the Huronian of the Lake Supe-
rior region and the original Huronian of the north shore of Lake Huron. The
area reported upon being a continuation of the Lake Huron Huronian, it is not
surprising to find the dual character of this series continue.
No light is given upon the character of the floor upon which the earliest
sedimentary rocks must have been deposited. That at several places are
found water- deposited conglomerate which bear well-worn pebbles and
boulders of granite, syenite, etc., which in one case are said to be exactly like
the granite found in situ, seems conclusive evidence that granite and
syenite existed in the region in a consolidated condition before the Huronian
members containing this detritus were laid down. A part of these conglom-
erates clearly belong to Bell’s older division of the Huronian, but this series is
not divided into formations, consequently we have no information as to
whether or not these conglomerates are at the bottom of the series.
Williams, ? gives microscopical notes on various rocks from the Sud-
bury district. The sedimentary rocks are found to include those which are
plainly clastic, those which are clastic but partially re-crystallized, and those
which are highly crystalline, but probably derived from clastics. In the
last division are placed felsite, gneiss-conglomerate, and gneiss. The erup-
tives, including various acid and basic deep-seated and surface rocks, also
show extensive metamorphism and re-crystallization. Placed among the
highly crystalline rock, probably derived from the clastics, are certain felsites,
gneiss - conglomerates, and gneisses. Certain granites, gneisses and schists
are of uncertain origin, but give no indication of clastic derivation.
C. R. Van HIsE.
2“Notes on the Microscopical Character of Rocks from the Sudbury Mining Dis-
trict, Canada,” by George H. Williams. Annual Rep. Geol. & Nat. Hist. Sur. of Can-
ada for 1889-90, vol. V; Part F, Appendix I, pp. 55-82.
THE
MOURNAL OF CEOLOCY
SHEPTEMBER-OCTORERK, 1503.
THEORIES OF THE ORIGIN OF MOUNTAIN RANGES.
MounTAins are the focal points of geological interest. In
their complex structure are contained all kinds of rocks, sedi-
mentary, eruptive and metamorphic; and in their formation are
engaged all geological forces in their greatest intensity. They
are the culminating points, the theatres of greatest activity of all
geological agencies; igneous agencies in their formation, aqueous
agencies by sedimentation in their preparation, and by erosion in
their subsequent sculpture. Their discussion, therefore, is a
summation of all the principles of structural and dynamical
geology. But they are equally important in historical geology,
for the birth of mountains marks the times of great revolutions
in the history of the earth, and therefore determine the primary
divisions of geological time. Evidently therefore the theory of
mountains lies at the very basis of theoretic geology, and a true
theory must throw abundant light on many of the most difficult
problems of our science.
But if this is the most important, it is also the most difficult
of all geological questions. My object now is to give, as briefly
as possible, the present condition of science on this subject. But
in all complex subjects there is a region of comparative certainty
and a region of uncertainty; a region of light and a region of
twilight. My farther object, therefore, will be to separate
sharply these two regions from one another, and thus to clear
the ground, narrow the field of discussion and direct the course
of profitable investigation.
VoL. I., No. 5. 543
544 THE JOURNAE Of GEOLOGY,
But first of all I must define my subject. A mountain range
is a single mountain individual—born at one time (monogenetic)
7.¢., the result of one—though it may be a prolonged—earth-effort ;
as contra-distinguished on the one hand from a mountain system
which is a family of mountain ranges born at different times
(polygenetic) in the same general region; and on the other from
ridges and peaks which are subordinate parts—limbs and organs
—of such a mountain individual. Now a theory of mountains is
essentially a theory of. mountain ranges, as thus defined. In all
that follows, therefore, on the subject of mountain structure and
origin, we refer to mountain ranges.
STRUCTURE OF MOUNTAINS.
The origin of mountains is revealed in their structure. We
must, therefore, give briefly those fundamental points of structure
on which every true theory of origin must be founded.
1. Thickness of Mountain Sediments.—The enormous thickness
of mountain strata is well known, but it is impossible to over-
state its fundamental importance. We therefore give some strik-
ing examples. The Paleozoic rocks involved in the folded struc-
ture of the Appalachian, according to Hall, are about 40,000 feet
thick. The Palzozoics and the Mesozoics in the Wasatch, accord-
ing to King, are about 50,000 feet thick. The Cretaceous alone,
in the Coast Range of California near the Bay of San Francisco,
according to Whitney, are 20,000, and in Shasta county, accord-
ing to Diller, are 30,000 feet thick. The Mesozoics and Ter-
tiaries of the Alps, according to Alpine geologists, are 50,000
feet.1 The upper Palaeozoic and Mesozoic of the Uinta, accord-
ing to Powell, are 30,000 feet. These are conspicuous examples,
but the same is true of all mountains.
It might be objected that these numbers express the general
thickness of the stratified crust everywhere—only that in moun-
tains the strata are turned up and their thickness exposed by
erosion. But this is not true. For in many cases the strata may
be traced away from the mountain; and in such cases they always
thin out as distance increases. For example, the 40,000 feet of
‘Jupp: Volcanoes, p. 295.
ORIGIN OF MOUNTAIN RANGES. 545
Appalachian Paleozoics thin out going west until at the Missis-
sippi river they are only 2000 to 4000 feet. The Paleozoics which
in the Wasatch are 30,000 feet thin out eastward until they are
only 1000 feet on the plains. It follows then that mountains are
lines of exceptionally thick sediments.
2. Coarseness of Mountain Sediments —Mountains are composed
mainly of grits, sandstones, and shales, z.e., of mechanical sedi-
ments, and most conspicuously so along their axial regions. As
we go from this region, sometimes in either direction, but espe-
cially in one direction, the strata become finer and finer; sand-
stones giving way to shales and shales to limestones, 7.¢., mechan-
ical to organic sediments. This is conspicuously true of the
Appalachian; in so many ways a typical mountain. As we pass
from the eastern ridge westward, grits and sandstones are replaced
by shales and these by limestones. Therefore mountains are also
lines of exceptionally coarse sediments.
3. Lolded Structure of Mountains—The folded structure of
mountains is perhaps the most universal, and certainly the most
significant, of all their features. But there is great variety in the
degree and complexity of the foldings. Sometimes the mountain
rises as one great fold. The Uinta is an example of this. Some-
times and oftener there are several open folds, like waves of the
sea. The Jura isa good example of this. Sometimes and often-
est of all, there are many closely appressed folds. This is the case
in the Coast Range of California, in the Appalachian, in the Alps,
and probably in the Sierra. The Appalachian may be taken
again as the type. In this range the folds are most numerous
and most closely appressed in the axial region, and open out and
die away in gentle waves as we go westward. Finally, some-
times in extreme cases, as in the Alps, the Pyrenees and probably
the Sierra, the strata of the lateral slopes are thrust in under the
central and higher parts, so that the strata of these central parts
are overfolded outwards on one or both sides. This is the Fan-
structure, so marked in the Alps and Pyrenees, where the under-
thrust and overfold are on both sides, but found also in the
Appaiachian and Sierra, where they are on one side only.
546 THE JOURNAL OF GEOLOGY.
Amount of Folding —F¥olded structure implies, of course, an
alternation of anticlines and synclines. The number of these
varies with the intensity of the folding. In the Coast Range
there are apparently four or five anticlines and corresponding
synclines. In the Sierra they cannot be counted, but there must
be very many so closely appressed that the strata seem to be a
continuous series dipping all in the same direction, 2.¢., steeply
toward the axis, for at least 30 miles. They cannot form a_
single series, for this would make an incredible thickness. It
must be a series repeated several times by extreme folding ; how
many, it is impossible now to say. In the Appalachian, accord-
ing to Claypole’, there are about Ig anticlines and synclines in
65 miles and in one part—Cumberland valley—there are eight in
16 miles. In the Vaudoise Alps, according to Renevier, there
are at least seven’, and in Savoy as many as 153. In many cases the
foldings are so extreme that the strata first rise as folds, then are
pushed over beyond the base as overfolds, and finally broken at
the crest and upper limb of the fold is pushed over the lower limb
many miles horizontally. In the Highlands of Scotland, accord-
ing to Peach‘, by overthrust, the Archean is brought over the
Silurian and overrides it for ten miles. In the Rocky Moun-
tains of Canada, according to McConnell’, the Cambrian is
brought over the Cretaceous and overrides it for seven miles.
In the Appalachian of Georgia, according to Hayes’, by over-
thrust, the Cambrian is made to override the Carboniferous for
eleven miles.
4. Cleavage Structure —Closely connected with the last, and
having a similar significance, viz., lateral squeezing and mashing,
is another structure—cleavage. This structure is often asso-
tAm’n Nat’st, Vol. 19, p. 257 and seq.
2 Archives des Science, Vol. 59, p. 5, 1877.
3 Archives, Vol. 28, p. 608, 1892, and 25, p. 271, 1893.
4Nature, Vol. 31, p. 29, 1884.
5 Geol. Surv. Can. 1886, Rep. D. p. 33.
© Bull. Geol. Soc. Am. Vol. 2, p. 141.
ORIGIN OF MOUNTAIN RANGES. 547
ciated with folding and both with mountain ranges. It is not so
universal as folding only because all kinds of strata are not
equally affected by it; being well exhibited only in fine shales.
It is important to observe that in slaty cleavage the sévzke of the
cleavage planes is the same as that of the strata, and both the
same as the trend of the mountain; and that the ap of the cleav-
age planes is nearly or quite vertical. Whole mountains are thus
cleavable from top to bottom.
5. Gramte or Metamorphic Axis—Some mountains are made
up wholly of folded strata. This is the case with the Appalachian,
the Coast Range, and the Jura. But most great mountains consist
of a granitic or metamorphic axis with stratified flanks. This is
conspicuously the case with the Sierra, the Alps, and most other
great mountains. So general is this, that the typical structure
of ranges may be said to be——a granitic axis forming the crest,
and stratified rocks, more or less folded, outcropping on the
slopes. This very characteristic structure ought to be explained
by a true theory of origin.
6. Asymmetric Form—Mountains are not usually symmetric,
with crest in the middle and slopes equal on the two sides. On
the contrary they usually have a long slope on one side anda
steeper, often a very abrupt, slope on the other. The crest or
axis is not in the middle but nearer to one side. The earth-wave
seems ready to break and often does break with a great fault on
the steeper side. The Uinta is perhaps the simplest example.
This range rises as a single great fold, but steeper on the north
side where there is a fracture and fault of 20,000 feet vertical.
Of course in this as in all cases the original fault-cliff has
crumbled down to a steep slope, or even been destroyed entirely.
The Sierra and Wasatch are remarkable examples of asymmetry.
The Sierra rises on the west side from the San Joaquin plains
near sea level by a gentle slope fifty to sixty miles long, reaches
its crest near 15,000 feet high and then plunges down by a slope
so steep, that the desert plains on the east, 4,000 to 5,000 feet
above sea level is reached in six to ten miles. There is
on this side a fault-cliff nearly 11,000 feet high. The Wasatch
548 THE JOURNAL OF GEOLOGY.
has a similar form, except that the fault-cliff looks westward
instead of eastward. It is true that the extreme asymmetry of
these two mountains was given them long after their origin and
by a different process to be presently described. “But even
before this last movement they were probably asymmetric, though
in a less degree. The Appalachian is perhaps here again a typi-
cal mountain. Its long slope is to the west and its crest close to
the eastern limit. The Alps, the Appenines, the Carpathians,
and the Caucasus, according to Suess, are foreign examples of the
same form.
There are many other interesting points of structure that
might be mentioned, but they are less significant of mode of
origin and therefore omitted in this rapid sketch.
ANOTHER TYPE OF MOUNTAINS.
I have given the main characteristics of mountains of the
usual type, of which the Appalachian, the Coast Range, the Alps
and Pyrenees may be taken as good examples. But there is
another type, different in structure and in mode of origin, to
which attention, I believe, was first called by Gilbert. It is
doubtful if they are found anywhere except in the Basin and
Plateau regions, and therefore the type may be called the Basin
region type. The Basin and Plateau regions are broken by
north and south fissures into great crust-blocks which by gravi-
tative readjustment have been tilted, z.e., one side heaved up and
the other side dropped down, so as to form a series of north and
south ridges and valleys. Each ridge rises by a long slope on
one side to a crest and then drops by a steep fault-cliff on the _
other. The ridges therefore are extremely asymmetric but the
asymmetry is produced in a different way from that of the usual
type. In a word, these mountains seem to be the result of a ser-
ies of enormous parallel faults. Such faults are common every-
where, but do not usually give rise to any inequalities which may
be dignified by the term mountain: or if so at one time, have
since been levelled by erosion. But those in the Basin region
are on so grand a scale and so recent in time, that they form
ORIGIN OF MOUNTAIN RANGES. 549
very conspicuous orographic features. I have sometimes doubted
whether they should be called ranges at all; but when we reflect
that at least 10,000 féet of the height of the Sierra is due to
normal faulting, it seems impossible to withhold the term. Thus
mountains may be divided into two types, viz., mountains formed
by folding of strata and mountains formed by tilting of crust-
blocks. The structure of the one is anficlinal or aiclinal, of the
other monoclinal. The Sierra probably belongs to both types.
It was formed at the énd of the Jurassic as a mountain of the
first type, but the whole Sierra block was tilted up on its eastern
side without folding, at the end of the Tertiary, and it then
became also a mountain of the second type.
A complete theory must explain this type also; but since
from its exceptional character it must be regarded as of subor-
dinate importance, we shall be compelled to confine our discussion
to mountains of the usual type.
EXPLANATION OF THE PRECEDING PHENOMENA.
In all cases of complex phenomena there have been many
theories, becoming successively more and more comprehensive.
The citadel of truth is not usually taken at once by storm, but
only by very gradual approaches. First comes the collection of
carefully observed facts. But bare facts are not science. They
are only the raw material of science. Next comes the grouping
of these facts by laws more or less general. This is the beginning
of true science. Every such grouping or reducing to law isa
scientific explanation, and therefore in some sense a theory. At
first the grouping includes only a few facts. The explanation or
theory lies so close to the facts as to be scarcely distinguishable
from them. It is a mere corollary or necessary inference. It is
modest, narrow, but also in the same proportion certain. Then
the group of explained facts becomes wider and wider, the laws
more and more general, and the theory more daring (but in the
same proportion also perhaps more doubtful): until it may at last
include the Cosmos itself in its boundless but shadowy embrace.
Now in this gradual approach toward perfect knowledge, there
550 THE JOORNALVORAGEROLOGY:
are two very distinct stages. The one consists of explanation
of the immediate phenomena in hand. This gives the laws of
the phenomena, and may be called the Formal Theory. The
other explains the cause of these laws, and may be called the
Causal or Physical Theory. All science passes through these two
stages. For example: Until Kepler, the phenomena of Planetary
motion were a mere chaotic mass of observed facts without
uniting law. Kepler reduced this chaos to order by the dis-
covery of the three great laws which go by his name. This is
the formal theory of Planetary motion. But still there remained
the question, why do planets move according to these beautiful
laws? Newton explained this by the law of gravitation. This is
the causal or physical theory.
But this is so important a distinction that I must illustrate by
examples taken from geological sclence. All the phenomena of
slaty cleavage are completely explained by supposing the whole
rocky mass to have been mashed together horizontally and
extended vertically. Thisis the Formal theory and may be regarded
as certain. But still the question remains: How does mashing
produce easy splitting in certain directions? The solution of this
question is the Physical theory, and is perhaps a little more doubt-
ful, though I think satisfactorily answered by Tyndall. But still
there remains a deeper and more doubtful ‘question, Whence
is derived the mashing force? Is it general interior contraction,
as some think, or is it local expansion as others think. A perfect
theory must answer all these questions. Take another example:
All the phenomena of the drift are well explained by the former
existence of an ice sheet moving southward by laws of glacial
motion, scoring, polishing, and depositing in its course. This is
the Formal theory. But still the question remains, What was the
cause of the ice sheet? Was it due to northern elevation, or to
Aphelian winter concurring with great eccentricity of the earth’s
orbit? And if due to northern elevation, what was the cause of
that elevation? A perfect theory must answer all these ques-
tions. Take one more example: All the phenomena of earth-
quakes are completely explained by the emergence on the surface
=.
ORIGIN OF MOUNTAIN RANGES. 551
and a spreading there from a centre, of a series of elastic earth-
waves. This isthe Formal theory. It explains the immediate facts
observed here on the surface, but no more. But still remains the
question, What is the cause, deep down below, of the concussion
which determined the series of earth-waves. This, the physical
theory, is far more doubtful. Or the theory may be made still
deeper and proportionately more doubtful. If our theory of the
cause of the interior concussion be the formation of a fissure or
readjustment of a fault, as seems in many cases probable, there
would still remain the question of the cause of great fissures and
of their subsequent readjustment by slipping. This is probably
as far as geological theory would go: for although cosmogony
may go still farther, the interior heat of the earth is usually the
final term of strictly geological theories.
I have made this long detour because I wish to keep clear in
the mind these two stages of theorizing in the case of Mountain
Origin. The formal theory is already well advanced toward a
satisfactory condition ; the physical theory is still in a very
chaotic state. But these two kinds of theories have been often
confounded with one another in the popular and even in the
scientific mind and the chaotic state of the latter has been car-
ried over and credited to the former also; so that many seem to
think that the whole subject of mountain-origin is yet wholly in
air and without any solid the foundation.
I. FORMAL THEORY.
A true formal theory, keeping close to the immediate facts
in hand, must pass gradually from necessary inferences from
smaller groups, to a wider theory which shall explain them all.
Inferences from 1 and 2,1. ¢., Thickness and Coarseness of Sedi-
ments.—The thickness of mountain sediments, as we have seen, is
greatest along the axis and grows less as we pass away from that
line. Now where do we find lines of very thick sediments form-
ing at the present time? The answer is: On sea bottoms
closely bordering continents. The whole washings of continents
accumulate very abundantly along shore lines and thin out sea-
552 LTE JOURNAL OF (GROLOGY:
ward. Mountains were therefore born of sea-margin deposits.
This view is entirely confirmed by the character of mountain
sediments. We have seen that these are coarsest near the crest,
becoming finer and then changing into limestones as we pass
farther and farther away from the crest. Now this is exactly
what we find in off-shore deposits. They are coarse sands and
shingle near shore, and then become progressively finer seaward,
until in open sea beyond the reach of even the finest mechanical
sediments, they are replaced by organic sediments which form
limestones. It seems evident, therefore, that the place of a
mountain-range before mountain-birth was a marginal sea-
bottom receiving abundant sediment from a contiguous conti-
nental land-mass. This explains at once the usual position of
mountains on the borders of continents. Here, then, is one
important point gained.
But such enormous thickness as we often find would be
impossible unless the conditions of sedimentation on the same
spot were continually renewed by pari passuw subsidence of the
sea-bottom. And we do indeed find abundant evidence of such
pari passu subsidence, not only at the present time in places
where abundant sediments are depositing, but-also in the strata
of all mountain ranges. In the 40,000 feet thickness of Appa-
lachian strata nearly every stratum gives evidence by its fossils,
of shallow water, and often by shore marks of all kinds, of very
shallow water. Therefore the place of mountains while in prepa-
ration, in embryo, before birth, was gradually subsiding, as if borne
down by the weight of the accumulating sediments, and continued
thus to subside until the moment of birth, when of course a con-
trary movement commenced. The earth’s crust on which the
sediments accumulated was bent into a great trough, or what
Dana calls a Geo-Syncline. This is another important poined
gained.
But let us follow out our logic. If the earth’s crust yields
under increasing weight of accumulating sediments, then ought
it also to rise under the. decreasing weight of eroded land sur-
faces. If it sinks by loading it ought also to rise by unloading.
ORIGIN OF MOUNTAIN RANGES. 553
And such indeed seems to have been the fact. For if all the
strata which have been removed from existing plateaus and
mountains were restored, it would make an incredible height of
land. At least 10,000 to 12,000 feet have been carried away by
erosion from the Colorado Plateau region and yet 8,000 feet
remain. At least 30,000 feet have been worn away from the
Uinta Mountains and yet 10,000 feet remain. Evidently there
has been a rise part passu with the lightening by erosion.
May we not then safely generalize? May we not conclude
with Dutton that the earth in its general form and in its greater
inequalities is in a state of gravitative equilibrium —that the
earth is oblate spheroid, only because this is the form of gravi-
tative equilibrium of a rotating body; that ocean basins and
continental protuberances exist, only because the materials
underlying the former are denser, and underlying the latter
lighter than the average. It is true that the spheroid form of
the earth and the sinking and rising of the crust by load-
ing and unloading may be explained on the supposition
that the tearth is) liquid) beneath sa /thim verust, but to) this
view there are three fatal objections. 1. The cosmic behavior
of the earth is that of a rigid solid. This I believe to have been
demonstrated. 2. The existence of the present great inequali-
ties of the earth would be impossible, except under the most
improbable conditions. For example, if the earth be fluid then
the crust must rest asa floating body. But if so, then, by the
laws of floatation, for every continental protuberance on the
upper side there must be a corresponding protuberance in
reverse on the other side of the crust, and for every great pla-
teau or mountain range there must be a corresponding plateau
or mountain range in reverse. And taking the difference of
specific gravity of the floating crust and the supporting liquid
to be as great as that between ice and water, these reverse ine-
qualities must be ten times as great as those at surface! Can we
accept so violent an hypothesis? But (3) repeated experiments,
especially very recent ones by Carl Barus," prove that rocks
* Am. Journal, vol. 45, p. I., 1893.
554 LTE Afi OWLS AL AOTMNGTE OL O GN
increase very notably in density in the act of solidification, so
that a solid crust would undoubtedly break up and sink in a>
liquid of the same material. But how then are we to explain
gravitative equilibrium in the case of a rigidly solid globe. I
answer, by two suppositions. 1. That the earth, though rigid
as glass or even Steel, to rapidly acting force, yet yields vescously
to heavy pressuse over large areas and acting for a long time. A
solid globe of glass six feet in diameter will very perceptibly
change form under its own weight. How much more the earth
under its own gravity. This completely explains the oblateness
of the earth even if solid throughout and had never been liquid at
all. The earth, though rigid, behaves like a very stiffly viscous
body ; like, for example, the ice of glaciers though very much
more stiffly viscous. This viscosity would not at all interfere
with its rigidity under the tide-generating influences of the sun
and moon — for these are far too rapidly acting.
2. The second supposition necessary is, that the earth is nor
absolutely homogeneous either in density, or in conductivity for
heat, that in secular cooling and contraction the denser and more
conductive areas, cooling and contracting faster, went down and
became the ocean basins, while the lighter and less conductive
areas were left as the more prominent land surfaces. And thus
to-day the ocean basins are in gravitative equilibrium with the
continental areas, because in proportion as oceanic radii are
shorter are the materials also denser; and in proportion as the con-
tinental radii are /onger, are the materials also specifically Aghter.
This condition of gravitative equilibrium Dutton calls /sos¢asy.
Thus then the great inequalities of the earth, constituting
ocean basins and continental surfaces, are the result of unequal
radial descent of the earth's surface by contraction in its secular
cooling. This is by far the most satisfactory theory of these
greatest inequalities.
In thus following the phenomena of Isostasy to their logical
conclusion, we seem to have gone beyond the limits of our sub-
ject, which is the ¢heory of mountains: but the close connection
which probably exists between the cause of continents and the
ORIGIN OF MOUNTAIN RANGES. 555
cause of mountains justifies the digression, if such it may be
called.
Inferences from 3 and 4, Folding and Cleavage.—Still adher-
ing closely to observed facts, there are some necessary inferences
from folded structure and cleavage. These structures are indis-
putable proofs that mountain strata have been subjected to enor-
mous /ateral pressure at right angles to the trend of the axis, by
which the whole mass has been mashed together horizontally.
But such horizontal mashing must of necessity produce corre-
sponding up-swelling along the line of yielding. In a word, it is
evident that mountains have been uplifted largely, at least, if not
wholly, by horizontal mashing. The only question that remains
is, Is lateral mashing alone sufficient to produce the highest
mountains? Let us see.
The amount of uplift in such cases would depend on two
things, viz., the thickness of the strata and the amount of mash-
ing. Now, as already shown, mountain sediments are 30,000,
40,000 and even 50,000 feet thick. The amount of mashing in
many mountains is almost incredible. In the Appalachian it is
so extreme that in one place, according to Claypole, ninety-six
miles of the original sediments have been crowded into sixteen
miles, and the shortening of the whole Appalachian breadth is
estimated as eighty-eight miles.‘ In the Alps the shortening is
estimated by Heim at seventy-two miles or one-half the original
breadth of the sediments. Ina word, we may without exaggera-
tion say that, in great mountains, the original space is to the
folded space as two to one, or even three to one. Now a crush-
ing of 30,000 feet of sediments into one-half their original space
would double their thickness, which is equivalent to a clear ele-
vation of 30,000 feet. But strata are 40,000 and even 50,000
feet thick. Evidently then this method alone is sufficient to
account for the highest mountains in the world, even allowing
for the enormous erosion which they have suffered.
The same is equally shown by the phenomena of slaty cleav-
tAmn. Natst. Vol. 19, p. 257.
?HeEIM: Archives des Sciences, Vol. 64, p. 120, 1878.
556 THE JOURNAL OF GEOLOGY.
age so often associated with folded structure. Slaty cleavage, as
has been demonstrated by experiment, as well as by field observa-
tion, is produced by a mashing together of the whole rocky mass
in a direction at right angles to the cleavage plane and a corre-
sponding extension in the direction of the ap of these planes.
Now since the cleavage dip is usually nearly or quite vertical,
this means a mashing together /orizontally and a proportionate
extension vertically. The amount of mashing together horizon-
tally and extension vertically has been in many cases somewhat
accurately estimated. In this case also, as in folding, we have
evidence of a mashing of two or even three into one and a
corresponding extension vertically of one into two or even three.
This amount of extension affecting thick strata is sufficient to
account for the highest mountains in the world without resorting
to any hypothetical force pushing upward from beneath.
There seems therefore to be no reasonable doubt that smoun-
tains are formed wholly by lateral crushing with proportionate up-
swelling. This is a very important point gained. Let us hold it
fast. This brings me naturally to the next point.
Inferences from 5 and 6, Gramtic Axis and Asymmetric Form. —
A granitic or metamorphic axis is a very general, though nota
universal, characteristic of mountains. The old idea (still held
by some) was that fused matter was pushed up through and
appeared above, the parted strata along the crest as the granite
axis, lifting the strata, as it were, on its shoulders to form the
slopes. But it must be observed that the axis is often only
metamorphic, not granitic, and moreover that some mountains
are composed wholly of folded strata alone. If, therefore, we
regard granite as often only the last term of metamorphism, we
may more properly speak of the axis of mountains as metamor-
phic. If so, then it is not necessary to suppose any vertical
uprising of fused matter by volcanic forces at all. On the con-
trary, we would explain the axis thus :
It is evident that accumulating sediments must cause corre-
sponding rise of the interior heat of earth toward the surface so
as to invade the lower parts of the sediments and their included
ORIGIN OF MOUNTAIN RANGES. BS
water. Now it is well known from the experiments of Daubreé
and others, that in the presence of water, even in small quanti-
ties, rocks become softened and even hydrothermally fused at
the very moderate temperature of 400° to 800° F.~ It is certain
then that such thickness of sediments as we know accumulated in
preparation for mountain birth, must have been softened to a
degree proportionate to the thickness, and therefore perhaps semi-
fused or even fused in their lower parts along the line of ‘thickest
deposit, and therefore of greatest subsequent elevation. On
cooling after elevation, this sub-mountain fused or semifused
matter would form a granitic or metamorphic core beneath the
highest part. The appearance of this core as an axis along the
crest is the result not of up-thrust but of swbsequent erosion greatest
along this line.
And this, initsturn, furnishes a key tothe location of mountains
along lines of thick sediments. For not only the lower parts of
such sediments but also the sea-floor on which they are laid down
would be hydrothermally softened or even fused. Thus would
be determined a line of weakness, and therefore a line of yielding
to lateral thrust, and therefore also a line of crushing, folding, and
upheaval. The folding and the upswelling and the metamorphism
would be greatest along the line of thickest sediments and become
less as we pass away from that line., In extreme cases, however,
the firmer lateral portions might be jammed in under the softer
central portions, on one or both sides, and give rise to the Fan-
structure character of complexly folded mountains. Or again, in
such cases the folds might be pushed clean over and broken at
the bend, and then the upper limb slidden over the lower limb
even for miles, forming the wonderful thrust-planes of the Alps,
the Appalachian and the Rocky Mountains, already described.
Thus the phenomena under (5) is completely explained.
But mountains are usually asymmetric, the crest being on one
side. This is explained as follows: Sedimentary accumulations
along shore lines are thickest zear shore (though not af shore) and
thin out slowly seaward. The cilinder-lens formed by sedimen-
tation is not symmetric, its thickest part being near one side, and
4
558 THE JOURNAL OF GEOLOGY.
that the shore side. This thickest line, as we have seen, becomes
the crest, which therefore is asymmetrically placed on the land-
side or side from which the sediments were derived. The over-
folding on the contrary is to the sea-ward.
SUMMARY STATEMENT OF THE FORMAL THEORY.
We may therefore group all these inferences and sum up our
view of the mode of mountain formation thus:
1. Mountain ranges, while in preparation for future birth,
were marginal sea-bottoms receiving abundant sediment from an
adjacent land-mass and slowly subsiding under the increasing
weight. 2. They were at first formed, and continued for a time
to grow, by /ateral pressure crushing and folding the strata together
horizontally and swelling them up vertically along a certain line
of easiest yielding. 3. That this line of easiest yielding is deter-
mined by the hydrothermal softening of the earth’s crust along
the line of thickest sedimentation. 4. That this line, by soften-
ing, becomes also the line of greatest metamorphism; and by
yielding, the line of greatest folding and greatest elevation. But
(5) when the softening is very great sometimes the harder lateral
strata are jammed in under the crest, giving rise to Fan-structure,
in which case the most complex foldings may be near but not at
the crest. Finally (6) the mountains thus formed will be asym-
metric because the sedimentary cilinder-lenses from which they
originated were asymmetric.
SOME EXAMPLES ILLUSTRATING.
It is hardly necessary to enforce these views by illustrative
examples. They at once arise in the mind of every geologist.
But there are those in this audience who are not geologists. I
therefore select a few examples among our own mountains.
1. Appalachian. It is well known that during the whole
Palaeozoic, the region now occupied by the Appalachian was the
eastern marginal bottom of the great interior Paleozoic Sea,
receiving abundant sediments from an eastern land mass of
Archean rocks, which then extended far beyond the present limits
of the continent and whose western coast-line was a little tothe east
ORIGIN OF MOUNTAIN RANGES. 559
of the present Appalachian crest. The sediments along this mar-
ginal sea-bottom increased in thickness during Cambrian, Silurian,
Devonian and Carboniferous (with some changes of Physical
Geography, but without greatly changing the line of sedimenta-
tion) until 40,000 feet thickness was reached. Such thickness, of
course, could not be attained without pari passu subsidence. We
have additional evidence of this in shallow water fossils and even
shore marks at many levels in the series. At the end of the coal
period, when 40,000 feet had accumulated, the increasing softening
along the line caused it finally to yield to horizontal thrust; the
whole mass of strata was crumpled together and swelled up along
the line of sedimentation and the Appalachian Range was born.
The same forces which caused its birth continued to cause its
growth for a long time. Subsequent erosion has sculptured it into
its present form, but as not exposed its granite core. The crest ison
the east or landward side, as we should expect, and the overfolds
are to the west or toward the sea of that time. This is perhaps
the most typical example we have.
2. Sterra.—lf it were not for a subsequent movement so late
as the beginning of the Quaternary, which greatly modified its
form, the Sierra too would beatypical range. During the whole
Paleozoic and the greater part of the Mesozoic the place now
occupied by the Sierra was the eastern marginal bottom of the
Pacific, receiving sediments from a continental land-mass in the
present Basin region. The shore line changed somewhat at the
end of the Paleozoic, but the Sierra region maintained a sea
bottom position. At the end of the Jura, when an enormous
thickness had accumulated, the increasing softening of the crust
determined a yielding to lateral thrust and consequent formation
of the range. Subsequent erosion has completely removed the
strata from the crest and exposed the granitic core as an axis*.
This axis is here also on the landward side, and the overfolds are
*Sierra granite is not Archzean as has been asserted by some, nor does it all ante-
date the birth of the range. This is proved (1) by the gradation traceable between
slates.and granites, and (2) by the fact stated by Whitney, by Fairbanks, and ay Diller
—that the granite in many places penetrates the slate as veins.
560 THE JOURNAL (OF (GEOLOGY:
to the seaward as in the Appalachian. The erosion of the Cre-
taceous and Tertiary times probably cut down the Sierra to very
moderate proportions and reduced it to an almost senile condi-
tion. At the end of the Tertiary a great fault and bodily uplift
of the whole Sierra block on its east side transferred its crest to
the extreme eastern margin, greatly increasing its height and
rejuvenating its erosive vigor.
3. Coast Range.—The formation of the Sierra transferred the
coast line westward of that range and the present place of Coast
Range became marginal sea-bottom, receiving sediment from a
now greatly increased land-mass. This continued until the end
of the Miocene when the Coast Range was similarly formed.
We might multiply examples, but these are deemed sufficient
to illustrate the principles.
MINOR PHENOMENA.
We have given only the most fundamental phenomena, z.e.,
those which reveal the mode of origin, and upon which, there-
fore, a true theory must be founded. But all other minor phe-
nomena associated with mountains are well explained by the view
above presented and their explanation confirms the view. For
example:
1. Eruptive Phenomena.—We have seen that beneath a moun-
tain, before and at the time of its formation, there is a deep-seated
core of liquid or semiliquid matter. Also it is evident that the
strong foldings of the strata in the act of mountain formation
must produce fissures parallel to the folds and to the mountain
axis, and that these fissures may reach down to the submountain
liquid matter. In the act of mountain formation, therefore, the
submountain liquid must be squeezed into the fissures forming
dikes, or through the fissures and poured out on the surface as
great lava floods, covering sometimes thousands of square miles.
In most cases subsequent erosion has swept these overflows clean
away leaving only their roots as intersecting dikes. Only the
most recent still remain. On these great fissure-eruption lava-
fields, ordinary volcanic or crater eruptions continue. for ages
ORIGIN OF MOUNTAIN RANGES. 561
after the mountain formation ceases. In these, however, mate-
rials are ejected not by mountain-making forces, but by the elastic
force of vapor from percolating waters. All these eruptive
phenomena are, therefore, associated with mountain ranges.
2. Faults—In folding, and especially overfolding, the strata
are, of course, often broken and the upper wall of the fissure is
pushed over the lower wall by horizontal thrust often thousands
of feet, forming reverse faults and so-called thrust planes. Hence
this style of faults are everywhere associated with strongly folded
rocks, and, therefore, with mountains, and are indisputable evi-
dence of horizontal crushing. In other places than mountains,
and in horizontal or gently folded rocks, the other style of faults,
2. é., normal faults, are more common.
3. Mineral Veins.—The filling of fissures at the moment of
formation with fused matter constitute dikes; but if not so filled,
they are afterwards filled by a slow process of deposit from cir-
culating waters and then they form mineral veins. These, there-
fore, are also common in mountains.
4. Earthquakes—Again, the immense dislocations of strata
which we find in faults did not occur all at once, but slowly
through great lapse of time; and yet on the other hand not by
uniform slipping, but by jerks, a little at atime. Every such
readjustment of the walls of a fissure, whether by increasing
lateral pressure (reverse faults) or by gravity (normal faults),
gives rise to an earthquake. Earthquakes, therefore, although
not confined to, are most. common in mountain regions, espe-
cially if the mountains are still growing.
Thus, leaving out the monoclinal type which seems to belong
to different category, all the phenomena, major and minor, of
structure and of occurrences connected with mountains, are
well explained by the theory of /ateral pressure acting on lines of
thick sediments accumulated on marginal sea-bottoms and
softened by invasion of interior heat. This view is therefore
satisfactory as faras it goes, and brings order out of the chaos of
mountain phenomena. It has successfully directed geological
investigation in the past and will continue to do so in the future.
562 THE JOURNAL OF GEOLOGY.
But there still remains the question: ‘‘What is the cause of
the lateral pressure?” The answer to this question constitutes the
physical theory. :
Thus far I suppose there is little difference of opinion. I
have only tried to put in clear condensed form what most geolo-
gists hold. But henceforward there are the most widely diverse
views and even the wildest speculations. But let us not imag-
ine, on that account that we have made no progress in the
science of mountain-origin. The formal theory already given is
really for the geologist by far the most important part of the
theory of mountain-origin. For I insist that for the geologist
formal theories are usually more important than physical theories
of geological phenomena. That slaty cleavage is the result of a
mashing of strata by a force at right angles to the cleavage-
planes, is of capital importance to the geologist, for it is a
guide to all his investigations. To what property of matter
this structure is due is of less importance to him, though of
prime importance to the physicist. That the phenomena of the
drift is due to the former existence of a moving ice-sheet is the
one thing most important to the geologist, guiding all his inves-
tigations. Whether this ice-sheet was caused by geographical or
astronomical changes is a question of wider but of less direct
interest to him. Soin the case of mountain ranges, the most
important part of the theory is their, origin by lateral pressure
under the conditions givenabove. The cause of the lateral pres-
sure, though still of extreme interest, is certainly of less immedi-
ate importance in guiding investigations.
PHYSICAL THEORIES.
The most obvious view of the cause of lateral pressure refers
it to the zntertor contraction of the earth. This may be called the
‘“‘ CONTRACTIONAL THEORY.”
This theory is so well known that I will give it only in very
brief outline. It assumes that the earth was once an incandescent
liquid and has cooled and solidified to its present condition. At
first it cooled most rapidly at the surface and must have fissured
ORIGIN OF MOUNTAIN RANGES. 563
by tension. But there would inevitably come a time when the
surface being substantially cool and moreover receiving heat also
from the sun, its temperature would be fixed or nearly so, while
the incandescent interior would be still cooling and contracting.
Such has probably been the case ever since the commencement
of the recorded history of the earth. The hot interior now
cooling and contracting more rapidly than the cool crust, the
latter following down the ever shrinking nucleus would be thrust
upon itself by lateral pressure with a force which is simply
irresistible. If the crust were ten times, yea one hundred times
more rigid than it is, it must yield. It does yield along the lines
of greatest weakness, z. ¢., along marginal sea-bottoms as already
explained. As a first attempt at a physical theory, it seems
reasonable, and therefore, until recently, has been generally
accepted. :
OBJECTIONS TO THE CONTRACTIONAL THEORY.
It is well known that American geologists have taken a very
prominent part in the study of mountain structure and mountain
origin. So much so indeed that the /ateral pressure theory in the
form given above and interior contraction as its cause, have some-
times been called the ‘American theory.” It is also well known
that my name, among others, especially Dana’s, has been associ-
ated with this view. All I claim is to have put the whole subject,
especially the formal theory, in a clearer light and more consist-
ent form.* The formal theory I regard as a permanent acquisi-
tion. The contractional theory may not be so. It is natural,
from my long association with it, that I should be reluctant to
give it up. But I am sure that I am willing to do so if a better
can be offered. We all dearly love our own intellectual child-
ren, especially if born of much labor and thought; but I am sure
that I am willing, like Jephtha of old, to sacrifice, if need be, this
my fairest daughter on the sacred altar of Truth. Objections have
recently come thick and fast from many directions. Some of these
*“ Theory of the Formation of the Great Features of the Earth’s Surface.” Am.
Journal, Vol. 4, pp. 345 and 460, 1872, and also “Structure and Origin of Mountains,”
Vol. 16, p. 95, 1878.
564 THE JOURNAL OF GEOLOGY.
I believe can be removed ; but others perhaps cannot in the pres-
ent condition of science, and may indeed eventually prove fatal.
Time alone can show. I state briefly some of these objections.
1. Mathematical physicists assure us that on any reasonable
premises of initial temperature and rate of cooling of the earth,
the amount of lateral thrust produced by iuterior contraction
would be wholly insufficient to account for the enormous fold-
ings... Let us admit—surely a large admission—that this is.
so. But this conclusion rests on the supposition that the whole
cause of interior contraction is cooling. There may be other
causes of contraction. If cooling be insufficient, our first duty is
to look for other causes. Osmund Fisher has thrown out the
suggestion (a suggestion by the way highly commended by
Herschel) that the enormous quantity of water vapors ejected
by volcanoes and the probable cause of eruptions is not meteoric
in origin as generally supposed, but is original and constituent
water occluded in the interior Magma.? Tschermak has con-
nected this escape of constituent water from the earth with the
gaseous explosions of the sun3 Is it not barely possible
that we may have in this an additional cause of contrac-
tion, more powerfully operative in early times but still continuing ?
See the large quantity of water occluded in fused lavas to be
“spit out’ in an act of solidification! But much still remains in
volcanic glass which by refusion intumesces into lightest froth.
Here then, is a second possible cause of contraction. If these
two be still insufficient, we must look for still other causes before
rejecting the theory.
2. Again: Dutton* has shown that ina v7gid earth it is impossi-
ble that the effects of interior contraction should be concentrated
along certain lines so as to form mountain ranges, because this
would require a shearing of the crust on the interior. The yield-
™Cam. Phil. Trans. Vol. XII., Part II.,. Dec. 1873.
?Cambridge Phil. Trans. Vol. XII., Part Il., Feb. 1875. Physics of the Earth’s
Crust, p. 87.
3Geol, Mag. Vol. IV., p. 569, 1877.
4Am. Jour. Vol. VIII., p. 13, 1874. Penn. Monthly, May, 1876.
ORIGIN OF MOUNTAIN RANGES. 565
ing according to him would be evenly distributed everywhere and
therefore imperceptible anywhere. This is probably true, and
therefore a valid objection in the case of an earth equally rigid in
every part. But if there be a sub-crust layer of liquid or semi-
liquid or viscous, or even more movable or more unstable matter,
either universal or over large areas, as there are many reasons to
think, then the objection falls to the ground. For in that case
there would be no reason why the effects of general contraction
should not be concentrated on weakest lines as we have sup-
posed.
3. But again: it has been objected that the lines of yielding
to interior contraction ought not to run in definite directions for
long distances, but irregularly in a@// directions. I believe we may
find the answer to this objection in the principle of flow of solids
under very slow heavy pressure. The flow of the solid earth,
under pressure in many directions, might well be conceived as
being deflected to the direction of least resistance, 2. ¢., of easiest
yielding.
4. But again: it will be objected that the amount of circum-
ferential shortening necessary to produce the foldings of some
mountains is simply incredible; for it would disarrange the sta-
bility of the rotation of the earth itself. According to Claypole,
in the formation of the Appalachian range, the circumference of
the earth was shortened eighty-eight miles and in the formation
of the Alps seventy-two miles. Now this would make a decrease
of diameter of the earth of twenty-eight miles in the one case
and twenty-three in the other. This would undoubtedly
seriously quicken the rotation and shorten the day. This seems
indeed startling at first. But when we remember that the tidal
drag is all the time retarding the rotation and lengthening the
day and much more at one time than now, we should not shrink
from acceptance of a counteracting cause hastening the rotation
and shortening the day, and thus giving stability instead of
destroying it. We must not imagine that there would be any-
thing catastrophic in this readjustment of rotation. Mountains
are not formed in a day nor inathousand years. It requires
566 TELE i OORINALL OF GHOLOGN«
hundreds of thousands of years, or even millions of years—if
physicists allow us so much.
The objections thus far brought forward, though serious, are
by no means unanswerable. But there is one brought forward
very recently which we are not yet fully prepared to answer and
may possibly prove fatal.
5. Level of No Strain—Until recently the interior contraction
of the earth was considered only roughly and without analysis.
It was seen that the surface was already cool and its temperature
fixed while the interior was still hot and cooling; and therefore
that the exterior must be thrust upon itself and be crushed. But
the phenomena are really far more complex than at first appears.
It is necessary to distinguish between two kinds of contraction
to which the interior layers are subjected, viz., radial and circum-
ferential. If there were radial contraction only, then undoubt-
edly, every concentric shell as it descended into smaller space
would be crushed together laterally. But there is for all layers,
except the surface, also a circumferential contraction, and this
would have just the opposite effect, z.e., would tend to stretch
instead of crush. Therefore wherever the decrease of space by
descent is greater than the circumferential contraction, there will
be crush, and where the circumferential contraction is greater
than the decrease of space by descent, there will be tension and
tendency to crack. There would be no veal cracking, only
because incipient cracks would be mashed out or rather prevented
by superincumbent pressure. Where these two are equal to one
another, there will be no strain of any kind. There is a certain
depth at which this is the case. It is called the ‘level of no
strain.’ To Mellard Reade is due the credit of first calling atten-
tion to this important principle.
Let us analyze the principle more closely. It is admitted
that at the surface there is no contraction of any kind. It is also
calculated that contraction of all kinds cease at depth of 400
miles. It is believed farthermore that commencing 400 miles
below the surface and coming upward the contraction increases
very slowly from zero to a maximum at the depth of 70 miles
ORIGIN OF MOUNTAIN RANGES. 567
and then decreases again
more rapidly to zero at
the surface. This is shown
in diagram, Fig. 1. In this
figure the curve represents
the relative rate of con-
traction whether radial or
circumferential of the sev-
eral layers: We use it,
however, only to represent
ine llatwer, lor tim Com
sidering the radial con-
TAGHOIN, ite si) iaoye” Ne
relative rate of the sev-
eral layers that immedi-
ately, concensus.) but
their rate of radial descent.
Now this is a summation
series and therefore in-
creases to the very surface,
but at different rates of
increase. The law of in-
crease of radial descent as
we come toward the sur-
face is shown in diagram,
Fig. 2* in which the rate
of increase is greatest at
seventy miles, just where
the curve changes from
concavity to convexity.
If now we superpose these
two diagrams the depth @
at which the two curves,
tI have taken these figures
from Claypole, but modified this
one so as to make it a truer repre-
sentation of the law.
400+ Miles
Fic. 1. s s=Surface; a 6=depth along radius; a@ + 6=
curve of contraction.
a Cc
s—
400+ Miles
t
Fic. 2. ¢ 6=curve of radial descent.
a Cc
400+6 Miles
Fic. 3. @ d=level of no strain.
568 TTE JOURNAL OF (GEOLOGY.
viz., that of circumferential contraction and that of radial descent,
intersect, is the level of no strain.
Now laborious calculations have been made by Dayison, Dar-
win and Fisher to determine the depth of this level of no strain.
All make it very superficial. Davison, taking an initial tempera-
ture of 7000° F., makes it five miles below the surface. Fisher,
on the same data, only two miles, and with an initial tempera-
ture of 4000° only 0.7 of a mile. It is easy to see that if this be
true, the amount of lateral thrust must be small indeed.
Now undoubtedly there is a true principle here which must
not hereafter be neglected, but it is almost needless to say that
these quantitative results are in the last degree uncertain. The
calculations are, of course, based on certain premises. These are
a uniform initial temperature of say 7000° F., a time of cooling,
say 100 or 200 millions of years, and a certain rate of cooling
under assumed conditions. The depth of the level of no strain
increases with the time and is still going downward. In a word,
ina question so complex both mathematically and physically and
in which the data are so very uncertain, every cautious geologist,
while freely admitting the soundness of the principle, will
withhold assent to the conclusions. Huxley has reminded us
that the mathematical mill, though a very good mill, cannot
make wholesome flour without good wheat. It grinds indiffer-
ently whatever is fed to it. It has been known to grind peas
cods ere now. It may be doing so again in this case. Let us
wait.
But besides withholding assent and waiting for more light, I
may add that these calculations, of course, go on the supposition
that the whole contraction of the earth is due to loss of heat;
but as we have already said, it may be due also to loss of consti-
tuent water. This would put an entirely different aspect on the
subject.
ALTERNATIVE PHYSICAL THEORIES.
I have given the objections to the contractional theory frankly
and I think fairly. They are undoubtedly serious. Let us see
what has been offered it its place.
ORIGIN OF MOUNTAIN RANGES. 569
I. READE’S EXPANSION THEORY.
This, the most prominent among alternative theories, was first
brought forward in Mr. Reade’s book on ‘Origin of Mountain
Ranges.” Although I have carefully read all that Mr. Reade
has written on the subject, I find it difficult to get a clear idea of
his views. But, as I understand it, it is in outline as follows: (1)
Accumulation of sediments off shore and isostatic subsidence of
the same. (2) Rise of isogeotherms and heating of the whole
mass of sediments and of the underlying crust in proportion to
the thickness of the sediments. (3) Eapansion of the whole
mass in proportion to the rise of temperature. If there were no
resistance, this expansion would be in all directions (cubic expan-
sion). (4) Butsince the containing earth will not yield to expan-
sion laterally, this lateral expansion is satisfied by folding, and this
in turn produces vertical upswelling. Thus thewhole cubic expansion
is converted into vertical expansion, which is therefore three times as
great as the linear expansion in any one direction. (5) Eleva-
tion would of course anyhow be greatest along the line of thickest
sediment; but this by itself would not be sufficient to produce a
mountain. (6) But farther—and here the theory is more obscure
—there is a concentration of the effects of expansion, along a
comparatively narrow line of thickest sediment, by a flow of the
hydrothermally plastic or even liquid mass beneath, éoward this
central line and then wpward through the parted strata, folding
these back on either side and appearing at the crest as the gran-
itic or metamorphic axis. (7) In his latest utterances he seems
to adopt the view of Reyer, viz., that the uplifted strata slide
back down the slope, producing the enormous crumpling so often
found, and exposing a wider area of granite axis. (8) From the
same liquid mass which lifts the mountain, come also the great
fissure eruptions and the volcanoes.
Mr. Reade makes many experiments to determine the linear
expansion of rocks, and he thinks that these experiments show
that when cubic expansion is converted into vertical expansion |
and this again concentrated along a line one-fourth to one-fifth
the whole breadth of the expanding mass, it would explain the
570 THE JOURNAL OF GEOLOGY.
elevation of the highest mountains. But still he seems uncertain
if it be enough. In fact, he declares that if it were not for another
factor yet unmentioned, he probably would never have brought
forward the theory at all.
(9) This factor is recurrency of the cause and accumulation of
the effects. And here the previous obscurity becomes intensified.
I have read and re-read this part without being able wholly to
understand him. He seems to think that when expansion had _
produced elevation, the mountain thus formed would not come
down again by cooling and contraction; but on the contrary would
wedge up by normal faulting and set in its elevated position. After-
ward, by new accumulation of heat, another elevation and setting
would take place and the mountain grow higher, and so on inde-
finitely, or until the store of heat is exhausted. Therefore he
characterizes his theory as that of ‘Alternate expansion and con-
J
traction,” or again as that of “ Cumulative recurrent expansion.”
Such is a very brief, perhaps imperfect, but I hope fair out-
line. of Readeis’ theory: t7seems to me) that) there are watal
objections to it. These I now state.
Objections —1. The first is znadequacy to account for the
enormous foldings of the mountains especially when there is no
granite axis to fold back the strata. It is true that Mr. Reade
makes comparison between his own and the contractional theory
in this regard, and seems to show the much greater effectiveness
of his own. This may be true if we accept his premises and com-
pare egual areas in the two cases. But the contractional theory
draws from the whole circumference of the earth and accumulates the
effects on one line, while in Reade’s theory the expansion is, of
course, very docad.
2. But the fatal objection is that brought forward by Davi-
son. It is this: sedimentation cannot, of course, increase the
sum of heat in the earth. Therefore the increased heat of the
sediments by rise of isogeotherms, must be taken from somewhere
else. Is it taken from below? Then the radius below must con-
tract as much as the sediments expand and therefore there will
be no elevation. Is it taken from the containing sides? Then
ORIGIN OF MOUNTAIN RANGES. 571
the sides must lose as much as the sediments gain, and therefore
must contract and make room for the lateral expansion, and
therefore there would be no folding and no elevation. I do not
see any escape from this objection. =
Thus it seems that Reade’s theory cannot be accepted as a
substitute. Is there any other ?
II. DUTTON’S ISOSTATIC THEORY."
Binkvorn’s discussion of isostasy is admirable, but his applica-
tion of it to the origin of mountains is weak. The outline is as
follows:
Suppose a bold coast line, powerful erosion and abundant
sedimentation. The coast rises by unloading and the marginal
sea-bottom sinks by loading. Now if isostasy is perfect, there
will be no tendency to mountain formation. But suppose a pil-
ing up of sediments, but—on account of earth rigidity—without
immediate compensatory sinking, and a cutting down of coast
land without compensatory rising. Then chere would be an tsostatic
slope toward the land. And the accumulated and softened sedi-
ments would shde landward, crumpling the strata and swelling them
up into a mountain range.
The fatal objection to this view is that complete isostasy is
necessary to renew the conditions of continued sedimentation and
therefore to make thick sediments, otherwise the sediments
quickly rise to sea-level and stop the process of sedimentation at
that place. But it is precisely a want of complete isostasy which
is necessary to make an isostatic slope landward. Dutton refers
to Herschel as having suggested a similar cause of strata crump-
ling and slaty cleavage*; but the principles involved in the two
cases are almost exactly opposite. Herschel supposes sediments
to slide down steep natural slopes of sea-bottoms and therefore
seaward. Dutton supposed sediments to slide wf natural, though
down isostatic slopes, /andward. Werschel’s is a theory of strata-
«Phil. Soc. of Washington, Bull. Vol. XI, pp. 51-64, 1889.
?Phil. Mag., Vol. 12, 197, 1856.
572 TE, JOURNAL OF (GEOLOGY.
crumpling and slaty cleavage; Dutton’s a theory of mountain
formation.
There has been no attempt to carry this idea of Dutton’s to
quantitative detail. It was probably thrown out as a suggestion
in mere despair of any other explanation, for he had already
repudiated the contractional theory. But the least reflection is
sufficient to convince that such slight want of complete isostatic
equilibrium as may sometimes occur would be utterly inadequate
to produce such effects. . :
III. REYER’S GLIDING THEORY.*
Prof. Reyer has recently put forward certain views fortified
by abundant experiments on plastic materials. His idea in brief
seems to be this: Strata are lifted and finally broken through by
up-rising fused or semi-fused matters and these appear above as
the granitic axis. As the axis rises, the strata are carried upward
on its shoulders, until when the slope is sufficiently steep the strata
slide downward crumpling themselves into complex folds and expos-
ing the granitic axis in width proportioned to the amount of
sliding.
No doubt there is much value in these experiments of Reyer,
and possibly such gliding does indeed sometimes take place in
mountain strata and some foldings may be thus accounted for.
But the great objections to this view are (1) that there is no
adequate cause given for the granitic uplift, and (2) that it utterly
fails to account for the complex foldings of such mountains as
the Appalachian and Coast Range where there ts no granite axis at
all. Reade, indeed, holds that the Piedmont region is the granite
axis of the Appalachian, and that the original strata of the east-
ern slope are now buried beneath the sea. But American geol-
ogists are unanimous in the belief that the shore line of the great
interior Paleozoic sea was but a little east of the Appalachian
crest and the sea washed against land of Archean rocks extend-
ing eastward from that line.
tNature, Vol. 46, p. 224, 1892, and Vol. 47, p. 81, 1892.
ORIGIN OF MOUNTAIN RANGES. BAS)
CONCLUSION.
After this rapid discussion of alternative theories in which we
have found them all untenable, we return again to the contrac-
tional theory, not indeed with our old confidence, but with the
conviction that it is even yet the best working hypothesis we
have. JosePpH Lr Conre.
ON THE MIGRATION OF MATERIAL DURING THE
METAMORPHISM OF ROCK-MASSES.
Tue researches of numerous geologists during the last two
decades have placed at our disposal a large amount of informa-
tion respecting the metamorphism of rocks, and from the facts
thus collected we are now ina position to draw conclusions which -
we may expect to have a wide application. The important
changes that affect the character of rock-masses divide roughly
into two classes.
First, there are those dependent on meteoric agencies. These
changes, though not necessarily superficial in the ordinary sense,
are due in the first place to the action of circulating waters in
communication with the atmosphere, and as a rule they involve
the addition or subtraction of various ingredients or the transfer-
ence of material from one place to another. The ordinary
“weathering” effects illustrate the removal of alkalies and silica,
the addition of water, oxygen, carbonic acid, etc. We must also
include the processes which have given rise to many crystalline
limestones and quartzites, serpentine-rocks, dolomites, iron-
stones, and jaspers, and even (as appears from Van Hise’s
researches in the Penokee region ) some mica-schists and fine-
grained gneisses. The characteristic of almost all these trans-
formations is that they are metasomatic as well as metamorphic.
Secondly, we have those transformations more usually under-
stood by the term metamorphism : viz., dynamic metamorphism,
due to. high pressure operating upon rock-masses, and thermal
metamorphism, due to high temperature, whether produced by
an intrusion or by the mechanical generation of heat. In these
various cases of metamorphism proper, metasomatism is rather
the exception than the rule. I shall deal here with thermal meta-
morphism only, and shall draw my data chiefly from the rocks
surrounding the large igneous intrusions of the English Lake
District, investigated by Mr. Marr and myself, but the conclusions
are confirmed in other areas.
574
METAMORPHISM OF ROCK-MASSES. 575
Metasomatic changes are known to take place during thermal
metamorphism as regards the vo/atile constituents of the rocks
affected. A (usually partial) loss of water and the elimination
(under proper conditions) of carbonic acid from carbonates are
instances of this; a more special case is the accession of boric
and hydrofluoric acids near the contact of metamorphosed rocks
with certain acid intrusives. Several observers have recorded a
transference of other materials (silica and soda) from an invad-
ing igneous magma to the neighboring rocks, but such a phe-
nomenon seems to be of uncommon occurrence, and to be con-
fined to the immediate vicinity of the contact. Apart from the
exceptions noted, there is every reason to believe that thermal
metamorphism involves no alteration in the bulk-analysis of the
rocks affected. Whatever part water may play in the various
chemical changes that are set up, it does not (as in atmospheric
metamorphism) act as a medium to transfer material to or from
the rocks in question.
I believe that we can go further, and assert that within the
mass of a rock undergoing thermal metamorphism any transfer-
ence of material (other than volatile substances) is confined to
extremely narrow limits, and consequently that, for a given tem-
perature of metamorphism, the mineral formed at any point
depends only on the chemical composition of the rock-mass
within a certain very small distance around that point. I[llustra-
tions of this principle, as stated in the latter form, are familiar to
all who have studied cases of ‘‘contact metamorphism” :' they
are very striking when some of the constituent substances of the
original rock were, by weathering or otherwise, locally aggregated
prior to metamorphism. By studying such cases we can not only
verify the principle here laid down, but also arrive at an estimate
of the actual limits within which interchange of material has taken
place.
An excellent test-case is afforded by rocks containing calcite.
It is well known that impure calcareous rocks are readily meta-
morphosed by heat into rocks rich in lime-silicates, with total
*Compare Bull. Geol. Soc. Amer. (1891) vol. iii., pp. 16-22.
576 THE JOURNAL OF GEOLOGY.
elimination of the carbonic acid, while pure limestones or dolo-
mites, under the same conditions, merely recrystallize without
chemical change. In other words, the carbonates are decom-
posed in thermal metamorphism only in the presence of silica in
some available form to take the place of the carbonic acid.
Interesting illustrations of this are given by some of the rocks
which have come under our notice.’ The Strap granite in West-
moreland metamorphoses certain basic lavas containing amygdules
of various dimensions, many of which were occupied, prior to the
metamorphism, by calcite. Near the granite the smallest of
these calcite-amygdules are converted into various silicates rich
in lime, the silica having been derived from decomposition-pro-
ducts lining the original vesicles or from the immediately adja-
cent portion of the rock. In the larger metamorphosed amyg-
dules, on the other hand, only the outer layers are transformed
into lime-silicates, the interior still consisting of calcite; which,
however, has recrystallized during the metamorphism, as is
proved by its moulding the silicates and being penetrated by
needles of actinolite, etc. Analogous appearances characterize
veins and lenticles of calcite in shales and the converse case of
argillaceous nodules imbedded in pure limestones and dolomites.
The conclusion is that carbonic acid is displaced from the calcite
only when there is in the immediate neighborhood either free
silica or some substance capable of furnishing silica. Where cal-
cite and quartz have recrystallized side by side in a meta-
morphosed rock, they are always separated by some one or more
lime-bearing silicates, but their distance apart may be very small,
and we deduce that the migration of silica to take the place of
carbonic acid has been restricted to extremely narrow limits. In
some highly altered rocks the distance is not more than one-
twentieth of an inch.
The limit of migration of material no doubt increases with
the temperature of metamorphism. This is well illustrated by
some calcareous ashes or tuffs. Ata considerable distance—say
a thousand yards—from a large granite intrusion, the carbonic
* See especially Quart. Journ. Geol. Soc. (1893) vol. xlix., pp. 359-371.
METAMORPHISM OF ROCK-MASSES. 577
acid is entirely expelled only from very fine-grained mixtures
of calcareous and ashy materials: approaching the contact, the
complete decomposition of the calcite is found to extend to suc-
cessively coarser-grained rocks. Another line of inquiry is
offered by the texture of the metamorphosed rocks themselves,
of whatever lithological nature, in a district of metamorphism
surrounding a large igneous intrusion, The size of the individual
crystals of secondary minerals increases towards the contact with
the intrusive rock: this may be taken to indicate that the migra-
tion of material within the mass of a rock undergoing meta-
morphism has more latitude when the temperature is higher.
For various reasons, however, it would be unsafe to found numeri-
cal results upon such observations. The crystals of certain meta-
morphic minerals attain to considerable dimensions by virtue of
their power of enclosing a large amount of foreign material ;
others, again, can apparently push aside solid impurities to make
room for their own growth. The texture of the metamorphic
rocks examined is still, however, in general accord with the con-
clusions reached by other methods of inquiry.
The question naturally arises whether the limit of migration
of material is the same for different substances. On this point
we have but little information. Among the various types of
“spotted” rocks described in aureoles of metamorphism is one in
which the spots are simply spaces free from the secondary brown
mica abundant in the general mass of the metamorphosed rock.
Since the iron compounds in the rock must originally have had
a generally uniform distribution, the phenomena of the spots
indicate a movement of ferrous oxide, and the radius of the spots
gives a measure of the extreme limit of such movement. In the
cases examined this is about one-twentieth of an inch, and we
may infer that the greatest distance of migration of ferrous oxide
has been about the same as that of silica at a similar tempera-
ture.
Not to insist unduly upon precise estimates, these and similar
observations certainly tend to show that in thermal meta-
morphism no interchange of material takes place except between
578 THE JOURNAL OF GEOLOGY.
closely adjacent points. The law that, apart from volatile con-
stituents, the total chemical composition remains unchanged is
true not only of the rocks in bulk, but of any individual cubic
inch of the rocks. This might be followed out into various
corollaries, of which I note only one, viz., that the greatest variety
of metamorphic minerals is to be found in rocks which were the
most heterogeneous prior to metamorphism. Such rocks are
breccias and fault-breccias, etc., and especially basic igneous
rocks more or less weathered before being metamorphosed.
ALFRED HARKER.
CAMBRIDGE, ENGLAND.
THE CORDILLERAN MESOZOIC REVOLUTION.
CERTAIN features connected with the occurrence of plutonic
rocks on the western side of America suggest hypotheses which
have an important bearing upon our general conceptions of the
structural development of the continent. These features are but
imperfectly and very partially recorded thus far in geological
literature, owing to the vastness of the field and the meagre
amount of investigation which has been devoted to it. Yet
enough facts have been accumulated to have impressed the writer
that they point to generalizations which have not yet been fully
presented for the consideration of students of continental
problems. To formulate these generalizations is the object of
this brief note. It is not the purpose of the writer to add to the
record of facts so much as to connote the more important of
them and to suggest their cumulative significance.
The researches of Richardsont and Dawson’ on the coast and
islands of British Columbia have shown that the Cretaceous rocks
of that region, ranging from the Azcel/a bearing horizon ( Neoco-
mian) to the Chico, repose upon a profoundly eroded complex
of granite and metamorphic rocks. The disturbances which have
affected these Cretaceous strata since their deposition have been
of a local rather than of a regional character. They lie upon the
old basement usually in but little disturbed attitudes, or are
inclined at low angles, though occasionally they are faulted or
sharply folded along certain lines of post-Cretaceous movement.
The same condition seems to generally characterize the more ele-
vated early Cretaceous rock of the British Columbian interior
along the cafion of the Fraser river. Jurassic rocks have been
described from British Columbia, but the Geological Survey of
Canada has since come to the conclusion that these rocks are
*Reports of Progress, Geol. Survey of Canada, 1871-2, 1872-3, 1873-4, 1874-5,
1876-7.
?Report of Progress, Geol. Survey of Canada, 1878-9. Annual Report (New
Series) Vol. II., 1886. Geol. Survey of Canada, Report B.
579
580 TTP JOURNAL ORNGIOLOGN:
-Cretaceous.’ If the Jurassic exists on the west coast of British
Columbia, it must occupy very limited areas or be involved in
the pre-Cretaceous metamorphic complex. The fossils collected
in the less altered portions of this complex by Richardson and
Dawson, show the presence of Triassic and Carboniferous for-
mations, but no undoubted Jurassic forms have yet been detected.
It therefore seems that the erosion to which the region was sub-
jected prior to the deposition of the Cretaceous was effected in
Jurassic time. As Dawson has shown,’ this erosion was of longer
duration in the southern part of the province than in the north-
ern, and the transgression of the Cretaceous sedimentation was
from north to south.
The further studies of Dawson upon the pre-Cretaceous com-
plex of granite and metamorphics have been fruitful of most
interesting and important results. Prior to his researches the
granite (and granite-gneisses) of the region were generally
regarded as the equivalent of the Laurentian of the east. It
was shown,? however, by him that the basement upon which the
now metamorphic sedimentary and volcanic strata of the Van-
couver series (Triassic, with probably some Carboniferous), was
deposited is non-existent, and has been replaced by an immense
mass of intrusive granite, which has absorbed by fusion all rocks
below the present remnants of the Vancouver series, and has
invaded the latter after the manner of an irruptive magma. This
post-Triassic granitic batholite is of enormous dimensions. In
the fall of 1890 the writer had an opportunity of examining it
cursorily for a distance in a straight line of over five hundred
miles, in and out of the fiords of the coast from Burrard Inlet to
Alaska; and the granite is known to extend far northward into
that territory. Its width may be placed at from sixty to one
"Sketch of the Geology of British Columbia, by G. M. Dawson, Geol. Mag., April
and May, 1881.
? Am. Jour. Sci., Vol. xxxix., March, 1890.
3 Annual Report (New Series), Vol. ii., 1886, Geol. Survey of Canada, Report B,
pp. 10-13.
COKDILEERAN MESOZOIC KEVOLYU TION. 581
hundred miles. In the portion examined there are several masses
or belts of schistose metamorphic rocks which have been sunk
down into the granite, but they form a small proportion of the
entire complex. The granite varies somewhat in_ mineralogical
composition, texture, and structure, and is often distinctly gneissic
locally. In places it is essentially hornblendic, in others it is
micaceous. Notwithstanding these variations, which are com-
mon in most large granite masses, the granite seems to be a unit
throughout, and the mass is certainly a very important factor in
the epeirogeny of the west coast of America. Even should it be
discovered by the closer scrutiny which science will certainly
demand, that there are portions of an older granite terrane to be
discriminated from the general mass, the conclusion will not be
invalidated, that in the interval between the deposition of Trias-
sic strata and the deposition of lower Cretaceous, the earth’s
crust was in this region invaded by an immense batholitic magma,
hundreds of miles in extent, which absorbed a large part of the
pre-Triassic basement, as well as a portion of the Triassic rocks
themselves. This invasion of the crust by the British Colum-
bian batholite seems to have conditioned a general and_pro-
nounced elevation of the coast. For the erosion which intervened
before the deposition of the Cretaceous was possessed of a vigor
only born of lofty mountains, removing the upper crust and cut-
ting down deep into the congealed granite. The Cretaceous
rocks were littoral deposits at the base of these lofty mountains.
Thus was a great revolution wrought in the geology and physi-
ography of the west coast of British Columbia in the interval
between the Triassic and Cretaceous times.
Little is definitely known of the geology of the Olympic
Mountains, but it is probable that the conditions which prevail
on Vancouver Island, which is the northern extension of the
range, hold good here, the Cretaceous rocks of the coast repos-
ing upon the lower flanks of mountains which consist of a com-
plex of granite and metamorphic rocks. These mountains are
probably the least known portion of the United States, and they
are mentioned here simply to indicate that important evidence
582 THE JOCRNAL OF (GLHOLOGY-
bearing upon the phenomena here discussed is likely to be found
in that region.
In southern Oregon,.on the line of the Southern Pacific Rail-
way, the writer has on several occasions observed the eruptive
contact of an extensive granite mass against sedimentary strata
which have been mapped as ‘“‘ Auriferous slates,’ which are prob-
ably early Mesozoic or Carboniferous in age. The intrusion of
the granite into the sedimentary rocks is unquestionable, the
relations being well exhibited in the excellent exposures afforded
by the railway cuttings.
In California the statements of Whitney* and the more recent
writings of the geologists of the U.S. Geological Survey, Diller,
Becker, Turner, and Lindgren, and of Mr. H. W. Fairbanks,
seem to leave no room for doubt that a great part, probably the
greater part, of the granitoid rocks of the Sierra Nevada is of ©
Mesozoic age, and has invaded the now more or less altered sedi-
mentary and volcanic rocks known as the ‘Auriferous slates,”
which range in age from the Silurian up to the Jurassic.
Here again we have clearly to deal with a granitic batholite
which must, by absorption or otherwise, have replaced a large
portion of the preéxisting lower rocks in the region affected.
From the facts recorded by able and critical observers, this
conclusion holds, notwithstanding the probability that there may
also be remnants of an older granite to be discriminated from
the Mesozoic mass. In the southern Sierra, as Becker has, with
wise caution, pointed out, we approach the region of Archean
granite known in the Grand Cajfion section. It would therefore
be not at all remarkable to find these more ancient granites
involved with the newer in the Sierra Nevada. But their presence
could not affect the important fact of an invasion of the crust
during middle Mesozoic time by an immense granitic batholite,
which invasion without doubt had much to do with the meta-
morphism of the strata which survived the upward progress of
the magma into the crust.
Here again the development of the batholite seems to have
"Geology of California, Vol. I. Auriferous Gravels.
CORDILLERAN MESOZOIC REVOLUTION. 5383
conditioned the uplift and wide-spread disturbance which is
-freely recognized in geological literature as having occurred at
the close of the Jurassic. Again we have, as in British Colum-
bia, a wonderful dissolving of the ancient status quo, a revolution
of no mean import, whether regarded merely as an historical
event or in its bearing upon the general principles of epeirogeny.
The important feature which distinguishes the group of facts
observed in the Sierra Nevada from those in British Columbia is
that in the former we have the Jurassic a part of the great
assemblage of rocks invaded by the granite while in British
Columbia these rocks are not known to exist. This difference,
taken together with the probable fact that the pre-Cretaceous
denudation of the Sierra was less profound than that of British
Columbia, suggests a progressive development of the batholitic
condition from north to south, so that the disturbance was felt
somewhat later in California, although it was part, doubtless, of
the same great subcrustal process.
In the Coast Ranges of California we have much less precise
information than in the case of the Sierra Nevada. Analogous
conditions seem to be indicated by the information at hand.
There are areas of granite and metamorphic rocks which have
been subject to great denudation prior to the deposition of the
@retaceous. " No rocks’ of ‘older’ age ‘than C@retaceous are
known to rest upon the worn surface of this complex.
Carboniferous fossils have recently been found by Mr. Fair-
banks in the Santa Ana Range*™ in a series of rocks into which
the granite of the region has been injected. The same geologist
informs us of the intrusion of the granite of the Gavilan
Range? into the Coast Range metamorphics, and of similar
relations in the Trinity Mountains in the Northern part of the
state. The writer, also, has observed that the granite of the
Santa Cruz Range is intrusive in the limestone of the metamorphic
complex. Mr. Fairbanks is of the opinion that generally the
= Nn, Geologist, vol. xi., Feb., 1893.
? Loc. cit.
3 Am. Geologist, March, 1892.
584 THE JOURNAL OF GEOLOGY.
granite of the Coast Ranges is the equivalent of that of the
Sierra, but direct evidence, of its) intrusion. into driassie or
Jurassic strata has not yet been adduced. All that can safely be
asserted at present, in the opinion of the writer, is that in the
Coast Ranges there is a pre-Cretaceous complex of granite and
metamorphic rocks analogous to that of the Sierra Nevada; and
that there is no evidence yet recorded which is adverse to Mr.
Fairbank’s correlation of the granites of the two regions.
In Mexico the official map shows conditions which resemble
those of the Sierra Nevada. Emerging from beneath the
volcanic sheets, or the mantles of Tertiary or Quaternary form-
ations there are, along the western side of the Republic,
numerous masses of granite rocks with associated metamorphics.
In these metamorphic rocks are occasional patches of Jurassic
and Triassic, conservatively limited in the mapping doubtless to
the actual areas where fossils have been found to so determine
their age. These small patches of known Jurassic and Triassic
age are suggestive of the proximate limit in age of the meta-
morphic series, and yielding to analogy we may be allowed to
suppose that the granite bears a relation to the Mexican meta-
morphics similar to that exhibited in the Sierra Nevada of
California.
In South America Steinmann’ calls attention to the import-
ant fact of the invasion of the Mesozoic strata of the Cordillera
by truly granitic and dioritic rocks. Karsten,? also, informs us
that in Columbia, Venezuela and Ecuador the Jurassic are the
oldest sedimentary rocks, but have been found at only one
locality, while the Cretaceous and Tertiary are abundantly
developed; and that the underlying basement upon which the
Cretaceous rests is largely granitic. Putting Steinmann’s and
Karsten’s information together we seem clearly to have the
conditions of British Columbia and California repeated as to the
development of a granitic batholite in the Cordilleran belt in pre-
*Am. Naturalist, Oct. 1891.
Geologie de ’Ancienne Colombie Bolivarienne, Nouvelle Grenada et Ecuador,
par Hermann Karsten, Berlin.
CORDILLERAN MESOZOIC REVOLUTION. 585
Cretaceous Mesozoic time, followed by continental uplift and
great denudation.
From the facts above cited certain conclusions seem to be
warranted which may be presented in the form of hypotheses
for future examination:
(1) The pre-Cretaceous Mesozoic revolution which has been
freely recognized by nearly all Californian geologists was not
limited to the western United States, but affected the entire
extent of the Cordilleran belt from Alaska to South America.
(2) It is not clear that the revolution was strictly syn-
chronous in all portions of the Cordilleran belt which have been
affected. It may have been progressive, and have extended
through the time from the close of the Triassic to the close of
the Jurassic so as to obliterate the Jurassic seas earlier in some
regions than in others.
(3) An essential feature of the revolution was the develop-
ment of batholitic magmas which invaded the crust, replaced
large portions of it, and eventually congealed as plutonic rock
of a prevailingly rather acid character.
(4) The development of the batholite, or batholites, was
followed or accompanied by continental uplift.
(5) The complex of invading granite and consequent meta-
morphics is analogous to that of the Archzan and indicates that
the conditions which are commonly recognized as Archean are
not peculiar to rocks of that age.
By way of addendum to this brief note it should be remarked
that the irruption of granite in South America did not wholly
cease with the Mesozoic revolution. Farther south than the
countries which have been mentioned, in the Cordillera of the
Argentine Republic, Stelzner has shown that this phase of
crustal development continued through into the Tertiary. After
a narration and discussion of his facts he formulates the follow-
ing conclusion :
“So mit bleibt denn nur noch die Annahme utbrig, dass die
als Granite, Syenite und Diorite zu bezeichnenden Andengesteine
eruptive Gebilde sind, die theils nach der Jura- und Kreidezeit,
586 THE JOURNAL OF GEOLOGY.
z. Th. sogar erst nach der in der Tertiarzeit erfolgten Ablagerung
der buntscheckigen Andesittuffe im gluthflissigen Zustande
emporgestiegen sind und diejenigen Lagerungsverhdaltnisse ein-
genommen haben, unter welchen wir sie heute beobachten
yy
k6nnen.
ANDREW C. Lawson.
BERKELEY, July 15, 1893.
‘Beitrage zur Geol. und Palaeont. der Argentinischen Republic, I. Geol. Theil, —
p. 207.
DHE BASIC MASSIVE ROCKS OR, Tih wAKE
SUPERIOR REGION.
Ill. SKETCH OF THE PRESENT STATE OF KNOWLEDGE CONCERN-
ING THE BASIC MASSIVE ROCKS OF THE LAKE
SUPERIOR REGION.!
Wirnour attempting to distinguish critically between the
different types of the basic rocks occurring in the Lake Superior
region, it will be sufficient for the present to call attention to
some of the work done on them, more especially with reference
to their microscopical examination. It will not be necessary to
refer to all of the articles in which the “traps” of the region
have been more or less briefly mentioned, as it will serve our
present purpose to allude only to the most important papers on
the subject, and to outline, where advisable, the descriptions of
the most important rocks as given by various authors. Professor
Irving? has discussed the theories held by some of the writers
with respect to the origin of the traps, but since these, when they
differ from the generally accepted theory of an igneous origin
for the rocks in question, are found to be opposed to the facts
observed, it would be unprofitable to discuss them further. There
can be no doubt but that all of the basic, massive rocks found in
dykes and beds in the Lake Superior region are truly igneous.
Douglass Houghton? first called attention to the wide-spread
occurrence of traps around Lake Superior in his Fourth Annual
Report as Geologist of Michigan. He identified knobs, dykes
and flows of trap, but was unable to distinguish between the
numerous varieties of the rock. His observations related prin-
cipally to the traps in the Archean and Keweenawan areas in
Michigan.
* This Journal, Vol. I., p. 433.
?The Copper-Bearing Rocks of Lake Superior. Monographs U. S. Geological
Survey, Vol. V., p. 7.
3Dated 1841. Reprint in Memoir of Douglass Houghton, by Alvah Bradish,
Detroit, 1889, pp. 167-168, and 176-182.
587
588 THE JOURNAL OF GEOLOGY.
Following Houghton, Messrs. Foster and Whitney* made an
examination of the copper and iron regions of Michigan under
the direction of the United States government. In their report
on the copper lands, they described briefly the occurrences of
dykes and flows of traps in the copper-bearing rocks of the south
shore of the lake. Among them they distinguished compact,
amygdaloidal, porphyritic, epidotic and brecciated varieties (pp.
69 and 70). In Part II. of the report, in their description of the
iron region, they refer to the large dykes in the Animikie rocks
on the north shore of the lake (pp. 12-13), and to the dykes of
diabase cutting the Archean schists in the neighborhood of Mar-
quette, Michigan (pp. 18 and 39). They also gave a recapitula-
tion of the characteristics of the traps of the entire region (pp.
85-94), with their chemical and mineralogical composition.
At about the same time that Messrs. Foster and Whitney were
engaged in their survey of the copper and iron rocks, Dr. D. D.
Owen,’ with his assistants, was employed in making a geological
reconnoissance of the states of Wisconsin, lowa, and Minnesota.
Messrs. D. D. Owen, J. G. Norwood, B. F. Shumard, Col. Whit-
tlesey, and Major R. Owen examined a much larger area than did
Messrs. Foster and Whitney, and were therefore not able to give
as much detailed description of the rocks observed as the last
named geologists succeeded in doing. They, however, mention
the occurrence of sheet and dyke gabbros in Wisconsin, and of
dyke gabbros in the Animikie of Minnesota.
Following these geologists came many others who examined
the Lake Superior region in more or less detail, but added little
to the knowledge of the trap rocks of the district, until, in 1871,
Professor R. Pumpelly’ published a paper on ‘‘The Paragenesis
and Derivation of Copper and its Associates on Lake Superior,”
in which he described the melaphyres and other basic rocks asso-
ciated with the copper on Keweenaw Point. After Pumpelly a
number of geologists visited the region, but they devoted their
‘Report on the Geology and Topography of a Portion of the Lake Superior Land
District, Part I. Washington, 1850. Part II., Washington, 1851.
?Report of a Geological Survey of Wisconsin, Iowa, and Minnesota. By D. D.
Owen. Philadelphia, 1852, pp. 142-164, 285, 304-306, 342-417.
3 Am. Jour. Sci. (3) II., 1871, p. 188.
LEU, THAVSIUC WS SH VAD IKONS, SE INGs 589
time principally to the discovery of the relations existing between
the several rocks, and made no efforts to divide these into their
varieties.
With the establishment of the surveys of Minnesota,
Michigan, and Wisconsin, however, an attempt was made to
classify with scientific accuracy the basic rocks of these three
states. Kloos* had already discovered the gabbro of Duluth
and had identified a melaphyre from the same place, but had
made no very exact determination of either. Among the geol-
ogists on the Michigan and Wisconsin surveys, Messrs. Julien,
Wright, Wichman, Pumpelly and Irving examined microscopi-
cally the rocks of the Huronian and the Keweenawan series of
Wisconsin, and of the Archean, Huronian and Keweenawan of
Michigan, and among the descriptions of these rocks which they
give may be found very exact accounts of the characteristics of
the diabases, gabbros and other basic eruptives of the region.
Messrs an os )ulienzvand: CEs W ried as teary as 1373,
mentioned quite fully the greenstones and traps of the Archean
and of the iron-bearing formations in Michigan. The former
writer identified many massive and schistose rocks to which he
gave the name of diorite, since he found in them hornblende, but
no augite. Mr. Wright likewise discovered hornblende rocks
which he evidently regarded as original, since he calls them all
diorites. Mr. Wright’s determinations are the first ones based
upon microscopical observations of Lake Superior rocks. Messrs.
Brooks* and Pumpelly® contented themselves with macroscopic
examinations of the basic rocks of the iron and copper-bearing
series in this state, and in this way distinguished diorites,
melaphyres and amygdaloids, while Mr. Marvine® divided the
"J. H. Kioos: Geologische Notizen aus Minnesota. Zeits. d. deutsch. geol.
Gesell. XXIII., 1871, p. 417. Trans. by N. H. Winchell, roth Ann. Rep. Geol. and
Nat. Hist. Survey of Minnesota, for 1881, p. 193.
2A. A.JULIEN: Geological Survey of Michigan, Vol. II., 1873, Appendix A, p. 41.
3C. E. WRIGHT: Ib. Appendix C, p. 213-231.
4T. B. BRooKs: Geological Survey of Michigan, Vol. I., 1873; Part I., Iron-Bear-
ing Rocks, pp. 99-104.
5R. PUMPELLY: Part IL., Copper District, Ib. pp. 7-16.
6A. R. MarvINE: Part IL., Copper District, Ib. pp. 95-116.
590 THE JOURNAL OF GEOLOGY.
rocks of the Eagle River section of Keweenaw Point into green-
stone or fine-grained diorites, feldspathic traps or coarse grained
diorites, and traps, including the melaphyres and amygdaloids.
Before the publication of the reports of the Wisconsin survey,
Messrs. Streng and Kloos' communicated the results of their
examination of certain Keweenawan rocks occurring in Minnesota
and in Wisconsin about the head of Lake Superior. Streng, who
did the microscopical work of the investigation, recognized among
his specimens melaphyres, augite-diorites, quartz-diorites and a
hornblende-gabbro to which reference has already been made in
a former article.* Pumpelly3 also had devoted his attention to
the rocks of the copper series. Hestudied more particularly the
fine and coarse-grained diabases and melaphyres of Keweenaw
Point.
With the publication of Volume III. of the Geological Survey
of Wisconsin a more general classification of the Keweenawan
rocks of Northern Wisconsin and of Keweenaw Point in Michigan
was given by the same author. He distinguished among them
diabases, hornblende and orthoclase-gabbros, melaphyres, augite-
diorites and porphyrites, the characteristics of which will be
mentioned when the discussion of the diabases and gabbros of
Keweenawan age is taken up. Inthe same volume Irving described
the rocks of the Huronian of Wisconsin, among which he found
gabbros (p. 147), and those of the Keweenawan in the same state
(pp. 168 to 193). The hornblende-gabbros and the augite-diorites
of Pumpelly he regarded as altered gabbros and diabases, and not
as original hornblende rocks. Julien’ also gave a very excellent
account of the microscopic appearance of two olivine-diabases
‘A. STRENG and J. H. Kioos: Ueber die Krystallinischen Gesteine von Minne-
sota in Nord Amerika. Neues Jahrb. f. Min., etc., 1877, pp, 31, 113, 225.
? This Journal, Vol. I., p. 447.
3R. PUMPELLY: Metasomatic Development of the Copper-Bearing Rocks of
Lake Superior. Proc. Am. Acad. of Arts and Sciences, 1878, XIII., Part II., pp. 253-
309.
4 Geology of Wisconsin, III., 1880, p. 29.
5A, A. JULIEN: Microscopic Examination of Eleven Rocks from Ashland county
Wisconsin. Geol. of Wisconsin, III., 1880, p. 224.
TELE BA. SUC NEA S ST VE ROCKS, VLG, “591
from Ashland county, Wisconsin; and ‘Wichman* published a
classification of Huronian rocks based on their microscopical
examination. Wichman divided the massive basic.rocks into dia-
bases, coarse-diabases and diorites. The only other microscop-
ical work done in connection with the Wisconsin Survey is that by
the late C. E. Wright, published in the second volume of the
reports. Inthis Mr. Wright? mentioned the occurrence of a diorite
containing augite in the bed of Black river.
Further, Dr. Wadsworth,3 in his discussion as to the origin of
the jasper and iron-ores of the Marquette region describes briefly
the microscopic features of many of the intrusive knobs that are
sO prominent a feature in the topography of the district. These
are declared to consist largely of diabase and coarse basalt, both
massive and slightly schistose.
The investigation of the basic rocks of the region had by this
time been sufficiently exact, and the number of specimens exam-
ined was large enough to give an idea of the characters of the
commonest types occurring there, but these investigations had
been undertaken by so many different geologists that no exact
correlation between the various varieties discovered was possible.
No classification of these could be accomplished until some had
examined specimens from all the different localities and had com-
pared them with one another. This work was undertaken by
Professor Irving* in 1881,and was ably accomplished by him in the
course of two years. All publications referring to the lithology
of the Keweenawan and Huronian formations on both sides of
the lake were carefully reviewed, most of the specimens described
in them were examined, and the results of this study and exam-
ination, together with a great deal of new information gathered
‘A. WICHMAN: Microscopical Observations of the Iron-bearing (Huronian) Rocks
from the Region South of Lake Superior. Ib. p. 600.
2 CHARLES E. WRIGHT: Geol. of Wisconsin, II., 1878, p. 637.
3M. E. WADSworTH: Notes on the Geology of the Iron and Copper Districts of
Lake Superior. Bull. Mus. Comp. Zoology, 1881, Vol. VII., p. 36-49.
4R. D. InvinG: The Copper-bearing Rocks of Lake Superior. Monograph V.,
U.S. Geol. Survey, Washington, 1883.
592 THE JOURNAL OF GEOLOGY.
during a trip among the dykes and sheets of the north shore of
the lake, were incorporated in a monograph and published under
the auspices of the U. S. Geological Survey in 1883. -
The greater portion of the volume is concerned with the dis-
cussion of the Keweenawan rocks, but a brief synopsis of the
character of the Huronian Series is given (pp. 367-409 ), and in this
a few descriptions of Huronian basic eruptives are communicated.
A brief synopsis of Irving’s results will serve to give an idea of
the relations of the different basic rocks to each other, and at the
same time will serve as a basis for the present paper.
The original basic rocks of the Keweenawan, according to
Irving, embrace gabbros and diabases, an anorthite rock consist-
ing almost exclusively of anorthite, malaphyres and amy gdaloids.
The rocks described under the various names possess in general
the characteristics of the respective types as defined by Rosen-
busch in the first edition of his Massige Gesteine. The gabbros
are coarse-grained rocks with a dark-gray or black color in the
least coarse-grained varieties, and a light-gray color when the
plagioclastic ingredient becomes greatly predominant as is apt to
be the case in the coarser kinds. Their texture is highly crystalline,
and their specific gravity varies between 2.8 and 3.1. The fine-
grained basic rocks, whose ordinary type is diabase, make up rela-
tively thin flows, that are almost invariably furnished with vesic-
ular or amygdaloidal upper portions. Externally the diabases are
dark in shade, being black, purple, dark green or brown, according
as the rock has undergone more or less alteration. In texture
they vary from medium fine-grained to cryptocrystalline. The
coarser kinds grade into coarse-grained gabbros, but this grada-
tion has never been observed in any one bed.. Moreover, the
diabases have undergone a great deal more alteration than the
coarser gabbros, and are very strongly marked by their external
characteristics, both in their fresh and altered states. They there-
fore seem to Irving to deserve a special name; since they possess
the structure of diabases he calls them by this designation. The
olivine-free diabases of the ordinary type pass into still finer
grained kinds of a black or brown color. Some of these are
THE BASIC MASS ROCKS, IEC. 593
entirely aphanitic, and all kinds tend to a porphyritic develop-
ment, carrying as phenocrysts oligoclase and more rarely labra-
dorite and augite. Like the diabases mentioned above, the dia-
base-porphyrites are furnished with amygdaloidal upper portions.
In the few instances in which the olivine-bearing rocks have an
undifferentiated glassy base, they are called melaphyres, although
placed among the fine-grained diabases. |
The most of the basic rocks of the region are in the form of
interbedded sheets. Dykes are rare. When they occur, their
material appears to be diabase or diabase-porphyrite. It is rarely
coarse enough to be classed with the rocks called gabbro.
In the Huronian areas on the other hand, large dykes of
coarse-grained gabbros’ cut through the sedimentary beds, and
with these are intercalated thick beds of gabbro, and occasionally
a few thinner ones of diabase.
Since Irving’s general classification of the rocks in question a
few other publications have appeared in which the petrography
of small areas, and the descriptions of hand-specimens are treated.
Messrs. Herrick, Tight and Jones’ busied themselves during
one summer with a study of the rocks around Michipicoten Bay, an
arm of Lake Superior extending northeasterly into Canada. Their
paper contains but little with respect to the basic eruptives not
found in Irving’s monograph. Dr. Wadsworth? has examined
some of the specimens gathered by the Minnesota Survey and
has divided the basic rocks into peridotites, basalts, including
gabbros, diabases, melaphyres, diorites and norites, peridotites,
and rocks regarded as altered andesites. All of Dr. Wadsworth’s
descriptions are marked by exactness, but the conclusions based
upon them are rendered less valuable than they would have been
had Wadsworth himself not been compelled to depend upon others
TIt will be shown later that most of the rocks called gabbro by Irving and others,
are not gabbros, but are coarse-grained diabases.
2C. L. Herrick, W. G. TicHTr and H. Jonrs: Geology and Lithology of Michi-
picoten Bay. Bull. Scient. Lab. of Denison Univ., Vol. II., Part 2, 1887, p. 120.
3Dr. M. E. WapsworTH: Preliminary Description of the Peridotytes, Gabbros,
Diabases and Andesytes of Minnesota. Bull. No. 2, Geol. and Nat. Hist. Survey of
Minn., 1887.
594 THE JOURNAL OF GEOLOGY.
for a knowledge of the field relations of the specimens studied.
Messrs. Herrick, Clarke and Deming’ have also studied a few
specimens of the gabbro, both ordinary and orthoclastic varieties,
from Duluth, but they have added little to what was already known
concerning them, except the suggestion of the possible depend-
ence of the orthoclase-bearing varieties upon their environment
for the peculiar characteristics which they possess.
The Canadian geologists have likewise been engaged in a
study of the rocks on the north side cf Lake Superior. Many
allusions have been made to the massive sheets and dykes in the
Thunder Bay region, but no microscopical descriptions of them
have been published, with the exception of a few notes by the
present writer appended to a report by Mr. Ingall? on Mines
and Mining in the Thunder Bay Silver District. In this report
the relations of the large dykes and thick beds of diabase or
gabbro to the fragmental rocks of the Animikie series north of
the lake are carefully sketched, and the microscopic features of
the most important rocks are described. In the Appendix,3 a
few altered gabbros and diabases from both sheets and dykes are
very briefly characterized. The former of these have the general
peculiarities of the gabbro from the great dyke on Pigeon
Point, Minnesota, referred to by the writer+ in‘an article on
certain contact phenomena at this place, and described at greater
length5 in a bulletin of the U.S. Geological Survey. In the
first of these two papers, in addition to the reference to the
Pigeon Point dyke, a few remarks are made concerning the rela-
tions of Irving’s orthoclase-gabbros to the more common varie-
*C, L. Herrick, E.S. CLARKE and J. L. DEMING: Some American Norytes and
Gabbros. Am. Geol., June, 1888, p. 339.
2E. D. INGALL: Report on Mines and Mining on Lake Superior. Geol. and
Nat. Hist. Survey of Cannda. Montreal, 1888.
3W. S. BAyLey: Notes of Microscopical Examination of Rocks from the
Thunder Bay Silver District.
4W.S. BAYLEY: A Quartz-Keratophyre from Pigeon Point and Irving’s Augite-
Syenites. Am. Jour. Sci. XXXVII., 1889, p. 54.
5W.S. BAYLEY: The Igneous and other Rocks on Pigeon Point, Minnesota,
and their Contact Phenomena. Bull. No. 109, U.S. Geol. Survey, 1893.
THE BASIC MASSIVE ROCKS, ETC. 595
ties of the gabbro of the region, but no detailed descriptions of
these rocks, nor of the ordinary gabbros, whose modified forms
they are supposed to be, are given. Finally, Dr. A. C. Lawson*
has mentioned some of the characteristics of ceftain diabases
from dykes in the Archean rocks of the Rainy Lake region, in
which the gabbroitic as well as the diabasic structures are well
exhibited, the former toward the centers and the latter near the
sides of the masses.
The most comprehensive treatment of the ‘‘ greenstones ”
and ‘‘greenstone schists”’ of the Lake Superior region is that
by Dr. G. H. Williams? in his bulletin on the origin of the
green schist, supposed to underlie the Huronian in Michigan. In
this volume the author not only describes the petrographical
features of the schists with which he deals, but he likewise
describes in some detail the microscopical characteristics of the
diabases, diabase porphyrites, sdiorites, diorite porphyrites and
gabbros, associated with the schists, and from some of which the
latter have been derived.
Within the past three years a number of papers have
appeared in which reference is made to some of the special
features of a few of the coarse basic rocks, both north and
south of the lake, but no articles have been published that deal
with their general features. Fairbanks’ has communicated a
few notes on the diorites and gabbros in the province east of the
north side of Lake Superior. Irving and Van Hise* have given
a brief synopsis of the characteristics of the diabase dykes and
interbedded sheets in the Penokee iron series on the south side
tA.C. Lawson: Notes on Some Diabase Dykes of the Rainy Lake Region.
Proc. Can. Inst. for 1887, and Report on the Geology of the Rainy Lake Region. Pt.
F., Ann. Rep. Geol. and Nat. Hist. Survey of Can. for 1887-88, pp. 57-73 and 147-164.
2G. H. WILLIAMS: The Greenstone Schist Areas of the Menominee and Mar-
quette Region of Michigan. Bull. No. 62. U.S. Geol. Survey, 1890.
3H. W. FAIRBANKS: Notes on the Character of the Eruptive Rocks of the Lake
Huron Region. Amer Geologist, I. 1890, p. 162.
4R. D. Irvine and C. R. VAN HisE: The Penokee Iron-bearing Series of
Northern Wisconsin and Michigan. Monograph XIX., U. 5S. Geol. Survey, 1893.
Chap. VII., The Eruptives.
596 THE JOURNAL OF GEOLOGY.
of the lake, and of the gabbro, diabases, diorites, melaphyres
and porphyrites of the Keweenawan overlying the Penokee
series to the north, while Hall" has described a few hand speci-
mens of diabases and gabbros from the Archean of Central Wis-
consin.
Further, in a discussion as to the nature of the diabase sheets
interbedded with the Animikie slates and quartzites in Minne-
sota and Canada, which leads to the conclusion that the former
are subsequent intrusions between the clastic beds, Lawson?
gives a short generalized description of the petrographical char-
acteristics of these rocks, and in a second article? he treats of
the structure and composition of the anorthite rock of Irving, to
which he gives the name anorthosyte. Finally, the writer in two
articles refers to the coarse gabbro* of north-eastern Minne-
sota and to the peridotites and pyroxenites® associated with it
along its northern border.
W. S. BAYLEY.
'C. W. HALL: Notes of a Geological Excursion into Central Wisconsin. Bull.
Minn. Acad. Nat. Sciences, III., No. 2., p. 251.
2A.C. Lawson: The Laccolitic Sills of the Northwest Coast of Lake Superior.
Bull. No. 8, Geol. and Nat. Hist. Survey of Minnesota, p. 30.
3A.C. Lawson: The Anorthosytes of the Minnesota Coast of Lake Superior
bs ps2:
4W.S. BAYLEY: A Fibrous Intergrowth of Augite and Plagioclase, resembling a
Reaction-rim, in a Minnesota Gabbro. Amer. Jour. Science, XLII. 1892, p. 515.
5W.S.BAyLEy: Notes on the Petrography and Geology of the Akeley Lake
Region, in North-eastern Minnesota, 1892, p. 193.
A STUDY IN CONSANGUINITY OF ERUPTIVE
INQCIS:-
WITHOUT being distinctly formulated, the principle of con-
sanguinity recently enunciated by Prof. Iddings has, as a working
hypothesis, been the guide of studies made within the last few
years on a group of Brazilian eruptive rocks, and the means of
arriving at some interesting and, in part, novel results. The
method of study followed, partly by plan, partly from force of
circumstances, being the comparative study of a group of locali-
ties on the assumption of genetic relations between them, rather
than detailed work at single points, was similar to what would
be applied to the study of a sedimentary group. This method
has in this case proved of great advantage, and, as a contribution
to the subject of consanguinity, seems worthy of being put on
record.
In 1883, the writer, whose previous training had been almost
exclusively in the domains of paleontology and the distinctly
sedimentary formations, finding himself in a region of crystalline
and metamorphic rocks felt the need of acquainting himself with
modern petrographic methods. Working in complete isolation
without previous instruction in this branch, without material for
comparison and almost without literature, he was also without
the traditions of the science and preconceived ideas of the
relations of the different petrographic groups, and thus free to
follow out the lines of investigation suggested by their apparent
field relations.
In working over the material at hand in the National
Museum at Rio, attention was attracted to specimens of nephe-
line-syenite, or foyaite (using that term as a general title for the
holocrystalline nepheline-orthoclase rocks) and as one of the
localities, the peak of Tingua, was readily accessible from Rio
an attempt to determine its field relations was resolved upon.
This heavily wooded mountain proved a hard nut to erack. and
several excursions gave very slender results beyond the fact that
597
598 THE JOURNAL OF GEOLOGY.
with the predominant foyaite, phonolite and basaltic rocks, which
have since been named monchiquites by Prof. Rosenbusch,
occurred. These two last types, found only in loose blocks or in
small dykes in gneiss that was clearly older than the foyaite,
gave no idea of their relations to the latter rock except that at
one point a small dyke of phonolite containing polyhedral inclu-
sions of foyaite, like raisins in a pudding, was observed cutting
foyaite of the same type as the inclusions. An examination of
a series of railroad cuttings between the peak and the city
showed a plexus of phonolite and monchiquite dykes together
with a peculiar feldspathic rock of syenitic aspect, which, as
they did not extend to the city, were suggestive of a possible
genetic connection with the eruptive center of Tingua, or of some
other similar center in the vicinity.
The occurrence of phonolites, hitherto only known on Bra-
zilian soil on the volcanic island of Fernando de Noronha, sug-
gested a search for phonolitic centers of eruption. About this
time a chance collection made by a naval officer from the island
of Cabo Frio, 60 miles from Rio, came to hand. As it con=
tained specimens of both phonolite and foyaite, an excursion
was resolved upon, guided by the thought that a rocky island
on an open coast should give good exposures and thus perhaps
prove a better point than Tingua for the study of the problems
presented in this mountain. The island, from two to three
miles long and from one-fourth to one-half mile wide, was found
to give an almost continuous rock exposure about its entire
margin. About four-fifths of the island is composed of coarse
grained sodalite-bearing foyaite somewhat different from the
Tingua type, and like it cut by numerous dykes of phonolite.
The remainder consists of augite-syenite of two types, except a
small point which is distinctly tuffaceous and cut by innumerable
small dykes of a basaltic character. In one place dyke-like
masses and large boulder-like inclusions of a pyroxene-plagio-
clase rock of a gabbro type occur. The coast of the mainland,
distant half a mile more or less from the island, is entirely free
from rocks of a syenitic character,and is composed of gneiss cut
CONSANGUINITY OF ERUPTIVE ROCKS. 599
by numerous dykes of phonolite, monchiquite and augite-syenite
porphyry, as well as of diabase which, as it occurs everywhere in
the gneiss regions of Brazil, was not taken into account.
Although nothing definite on the field relations of these various
rocks could be made out, the idea suggested at Tingua of a pos-
sible genetic relation between foyaite, phonolite and monchiquite
was strengthened by this repetition of the association and mode
of occurrence, that is to say, of a central mass of foyaite with
apophyses of phonolite and monchiquite. Aside from this, the
association of foyaite with augite-syenite, with a plagioclase rock
and with tuff of a volcanic character, suggested other lines of
investigation not in accord with the usually received notions
regarding these rocks.
Before a second projected excursion to Cabo Frio could be
realized a chance specimen of foyaite from the Pogos de Caldas
in southern Minas appeared at the Rio Museum. As a railroad
was under construction in this region the idea at once presented
itself that, aside from a study of this district, possibly Tingua and
Cabo Frio might be studied more advantageously several hun-
dred miles away than at those points themselves. Instead,
therefore, of returning to Cabo Frio an excursion was made to
Pogos de Caldas where the expectations formed were more than
realized. About twelve kilometers of almost continuous rock
cutting up a steep mountain slope giving one of the finest and
most varied exposures of eruptive rocks in the world, was found.
Here immense masses of tuff are seen to be cut by both foyaite
and phonolite ; dykes and sheets of foyaite pass into phonolite at
their margins ; small masses of phonolite’ are seen included in
foyaite and wice versa masses of foyaite are included in phono-
lite. Considerable masses of a leucite rock, the first known from
South America, cut by and buried under phonolite and present-
ing tuffaceous facies also occur. Small stringers of augite-
syenite were noted in the tuffs and phonolite, and nests of
* The name phonolite is retained for these rocks since no petrographer, not know-
ing their association, would ever think of calling them anything else, although some, with
that knowledge, prefer to call them nepheline-syenite porphyries or tinguaites.
600 THE JOURNAL OF GEOLOGY.
decomposed crystals, at first taken for analcime, as well as
polyhedral inclusions similar to those of the phonolite of
Tingua were obtained. To complete the felicity of the excursion
a cutting at the foot of the mountain showed the eruptive rocks
to be in part, at least, contemporaneous with Carboniferous strata.
With the data here obtained a paper was prepared and pre-
sented to the Geological Society of London (Quart. Jour. 43,
1887) announcing the discovery and general distribution of
nepheline and leucite rocks in Brazil, and the general conclusion
that the Pogos de Caldas eruptive center is volcanic in the most
restricted sense of the term, that it is of Carboniferous age, and
that here foyaite and phonolite occur as different phases of the
same magma."
The attack on Tingua was now renewed with the expectation
that a diligent search would reveal something analogous to the
Caldas region. A trip to the top of the peak showed little of
interest beyond a dyke of phonolite cutting foyaite at the very
summit. An examination of the margins, well shown by the
cuttings of an extensive series of railroad\and pipe lines (for the
water supply of Rio) at the front, a river valley at the back and
roads over the ridge at both ends of the peak, showed that the
foyaite is limited to the massif and nowhere presents unequivo-
cally the character of dykes. Two cuttings, onea tunnel, through
a spur covered with foyaite boulders as if from the outcropping
of a dyke, is conclusive on this point, as only gneiss was found
wn situ. Vhe eruptive rocks are therefore placed like a plaster on
the top and slopes of a gneiss ridge in a manner exceedingly sug-
gestive of volcanic conditions. By forcing a way through the
dense forest into the crater-like valley of a stream coming from
the very heart of the mountain, the long-sought-for evidence of
fragmental eruptives and of extensive masses of phonolite in
* Subsequent explorations of the Caldas center proves it to be one of the grandest
volcanic masses of nepheline rocks known, measuring from fifteen to twenty miles in
diameter. Contrary to the first impression the foyaite masses are comparatively
insignificant, and the massif is composed essentially of phonolite and tuff with possibly
a large proportion of basic leucite rock. A large and important mass of augite-syenite
appears to form part of the same volcanic massif.
CONSANGUINITY OF ERUPTIVE ROCKS. 601
sheets rather than dykes was found. A complete analogy, as
regards the essentially volcanic character of the massif, with the
Caldas region was thus established with the addition of evidence
of a lava-flow-like character in the foyaite masses. (Quart. Jour.
REEVE, WSOm):
A chance fracture of a Caldas specimen showing obscurely an
appearance of dodecahedral faces on the external surface of the
singular polyhedral inclusions so characteristic of the two places,
suggested the search for partially decomposed material which by
cleaving around the inclusions would show their true form and
reveal the mystery of their origin. This search was rewarded
with the discovery of free masses of foyaite, like those of Magnet
Cove, Ark., having the external form of leucite. The presence of
such rock masses with crystalline outlines in both phonolite and
foyaite is another link in the chain of evidence of consanguinity
of foyaite, phonolite and leucite rocks, while the presence of
accessory plagioclase in some of these masses, taken in connection
with the occurrence already noted at Cabro Frio, suggests
another interesting line of investigation.
Meanwhile another series of studies presented in an unexpected
manner certain new and interesting phases of the problem. Work
had been commenced on a deposit of magnetic iron ore at Ipanema
in the state of Sao Paulo where, from the extreme decomposition
of the rocks and other unfavorable circumstances, but little could
at first be made out beyond the association of the ore with a
peculiar clay made up in large part of scales of hydrous mica.
An ore of similar character at Jacupiranga in the same state was
being investigated by Mr. Henry Bauer,a German mining engi-
neer, and the collections sent by him showed the presence at that
place of an undescribed type of holocrystalline nepheline-pyrox-
ene rock since denominated jacupirangite,’ which, by enrichment
in iron, passes to an iron ore, and, by secondary alteration of the
pyroxene, affords the same peculiar micaceous clay. Certain basic
tAm. Jour. of Science, XLI., 1891, p. 311. The same, or a very similar, type was
described simultaneously from Finland by Ramsay and Berghell with the name of
ijolith (Geologiska Foreningens i Stockholm Foérhandlingar, No. 137, 1891).
602 LL Vi OOLINALE TOT NGE OLOGN
eruptives in these collections suggested a comparison with the
Tingua and Cabo Frio monchiquites, and Mr. Bauer was requested
to search for the characteristic rocks of these places, specimens
being sent him for comparison. The return mail brought typical
specimens of foyaite, and with this indication of a new locality
for that rock, and in the hope of being able to study the Ipanema
ore deposit more advantageously at another place, an excursion
to Jacupiranga was resolved upon. Under the guidance of Mr.
Bauer, and aided by subsequent investigations by him and Dr.
Eugen Hussak, the district was found to consist essentially of
jacupirangite cut by dykes of foyaite with which is associated
phonolite, various types of augite-syenite and a micaceous pyrox-
ene-plagioclase rock in such a way that there is no escaping the
conclusion of a genetic relation between these various types.
Outlying dykes of the plagioclase rock assume in one place the
characters of a gabbro, in another, those ofateschenite. Among
the outlying dykes of the district are various types of basic
eruptives, including leucite-basanite, vosgesite and _ syenite-
porphyry whose relations to the eruptive center are less clear,
but which are also suspected to be genetically connected with
the nepheline-bearing types. Most interesting is a cryptocrys-
talline orthoclase-pyroxene rock passing to coarse grained augite-
syenite and presenting a tuffaceous facies clearly indicative of
volcanic action.
With the clues obtained at Jacupiranga the study of Ipanema
became comparatively easy. The jacupirangite type passing to
an iron ore was found as a dyke with the facies of a breccia at
the margin, traversing decomposed rock which is evidently iden-
tical with the compact augite-syenite of Jacupiranga. By dili-
gent search the latter was found in a sound condition and pre-
senting a variety of interesting phases, such as a passage to coarse
grained augite-syenite, tuffs identical with those of Jacupiranga
and, most interesting of all, a basic facies in which the orthoclase
is replaced by phosphate of lime in the form of apatite. A sin-
gular mode of occurrence, and one bearing directly on the ques-
tion of consanguinity, is that of micro and macroscopic inclusions,
GONSAMG CLNIING OF Take SP: LVR: OCLES: 603
or segregations, of both the feldspathic and phosphatic types of
augite-syenite in a phonolitic nephelinite, apparently without
feldspar. The bulk of the iron ore at this place occurs as rounded
nodular segregations associated with apatite in a decomposed rock
which was evidently coarse grained and micaceous. This was
evidently not jacupirangite, but apparently some peculiar type of
nepheline or augite-syenite. Except for the absence of black
garnets it apparently corresponds closely with the ore-bearing
MOC On Masa Cove; Adc, Glescmose! [oy tie lee IDs, jj. JF.
Willams. It may be noted in this connection that the same
character (absence of black garnet) distinguishes the jacupirangite
from the ijolith of Ramsay and Berghell. |
As in the Caldas region, there is at Ipanema evidence that
the eruptive action took place in the late Carboniferous or post-Car-
boniferous times. This coincidence of age at two of the localities
may perhaps justify the assumption (which cannot be directly
proven for lack at the other places of sedimentaries intermediate
between the very ancient and the very modern), that all of these
eruptive centers are substantially contemporaneous. Bearing on
this question of age, as also on that of consanguinity, is the fact
that in a region characterized by Devonian and probably also Car-
boniferous strata in Paraguay, Pohlmann has reported nepheline-
bearing basalt, and Dr. J. W. Evans has lately communicated
specimens of foyaite and augite-syenite from Pao de Assucar on
the Paraguay, proving that this mass, hitherto reputed to be
granitic, represents another eruptive center similar to those studied
in eastern Brazil.
The evidence of consanguinity of foyaite and phonolite con-
sists of an intimate association within limited areas at all of
the localities mentioned, except Ipanema, where neither type
has as yet been found in a condition to be positively
identified; of a direct passage to phonolite at the margins
of foyaite masses at Caldas; of inclusions of phonolite in
foyaite at the same place and conversely of inclusions, evi-
dently formed zw setu of foyaite in phonolite at Caldas and Tingua.
In this connection may be mentioned an inclusion of the type of
604 IVE OWN AIG ON (CIKOVKOC NA.
foyaite, described by Prof. Rosenbusch and Dr. G. H. Williams
from the phonolite massif of the island of Fernando de Noronha,
whose eruption is presumed to be of much later date than that of
the continental centers above described. Whatever may be the
explanation of the assumption of the leucite form, without the
substance of that mineral, by these inclusions at Caldas and
Tingua, this phenomenon may also be cited as an evidence of
consanguinity. Confirmatory evidence is afforded by the inti-_
mate association of typical leucite and nepheline rocks in the
Caldas massif, and perhaps also by the occurrence in Paraguay.
The evidence of consanguinity of the augite-syenite type with
those bearing nepheline is almost equally complete. At Tingua,
where there is an apparent lack of this type, a single large frag-
ment was found as an inclusion in foyaite. At Jacupiranga, a
direct passage by disappearance of nepheline, from foyaite to one
phase of augite-syenite could be traced, while other phases of the
same type were found associated with foyaite in the same dyke or
boss. Most interesting is the association of this typeat Jacupiranga
and Ipanema with nepheline rocks more basic than the foyaites and
phonolites, such as the jacupirangites and phonolitic nephelinites,
in the latter of which it occurs as an inclusion or segregation. In
this connection it is interesting to note the tendency, rare among
the orthoclase rocks, of this type to present olivine as an acces-
sory element.
Still more interesting, though less conclusive, are the indica-
tions of consanguinity of foyaite with a group of plagioclase rocks
hardly, if at all, distinguishable from those of entirely different
genetic relations. At Cabo Frio the appearance is certainly that
of segregations of a plagioclase rock in the midst of foyaite, though
farther investigation is desirable. At Jacupiranga the two types
not only occur in the same dyke or boss, but nepheline has
actually been observed as a rare accessory in the gabbro-like
rock. The appearance of plagioclase in the pseudo-leucite crys-
tals of Tingua bears on the same question, as does also the appear-
ance in a large collection of phonolite from Fernando de Noronha
of a single specimen of an andesite-like rock, which unfortunately
CON SAIN G CHINIIN. (OFF TTA VLD ARO OLES: 605
was not observed in time to be included in the material sent to
Dr. G. H. Williams for study. Apparently there is a group of
gabbro and diabase-like rocks whose genetic relations are with
the nepheline-bearing rocks rather than with the ordinary mem-
bers of the groups which they so closely resemble.
The peculiar and varied group of basic dyke rocks recently
denominated monchiquites by Prof. Rosenbusch, afford evidences
of consanguinity by their almost constant association, as apophy-
ses, with the nepheline-bearing eruptive centers to whose imme-
diate vicinity they appear to be limited. If certain decomposed
dykes at Caldas and Ipanema are correctly referred, this group
occurs at all the Brazilian localities. A single instance of a basic
segregration resembling this type has been observed in a dyke
of phonolite. The occurrence within the space of a few meters
in the Tingua phonolitic tuffs of three small dykes of this type,
of which two, standing alone, would be taken as representing
tephrite and limburgite is suggestive of another line of consan-
guinity. Equally suggestive is the occurrence of vosgesite in the
vicinity of the Jacupiranga center of eruption.
Finally the evidence of volcanic action in the presence of
fragmental eruptives found at all of the five localities in constant
association with types ordinarily regarded as plutonic, such as
augite-syenite, is exceedingly suggestive.
ORVILLE A. DERBY.
SAO PAULO, BRAZIL, Aug. 1, 1893.
LAE DISSPCLED VOLCANO, OF CRAN DADE aS Arse
WYOMING.*
THE writer in exploring the north-eastern corner of the
Yellowstone National Park and the country east of it came
upon evidences of a great volcano, which had been eroded in
such a manner as to expose the geological structure of its basal
portion.
The work was carried on as a part of the survey of this
region, under the charge of Mr. Arnold Hague of the U. S.
Geological Survey. The paper is an extract from a chapter in
the final report on the Yellowstone National Park in process of
completion, and the writer is indebted to Major J. W. Powell,
Director of the Survey, and to Mr. Hague, chief of the division,
for permission to present it at this time in anticipation of the
publication of the final report.
The area of volcanic rocks described is but a small portion
of the great belt of igneous material that forms the mountains of
the Absaroka range, lying along the eastern margin of the
Yellowstone Park.
The volcano of Crandall Basin is one of a chain of volcanic
centers situated along the northern and eastern border of the
Yellowstone Park, which are all distinguished by a greater or
less development of radiating dikes, and by a crystalline core
eroded to a variable extent.
The Paleozoic and Mesozoic strata, which formed an almost
continuous series to the coal-bearing Laramie, had been greatly
disturbed and almost completely eroded in places before the
volcanic ejectamenta in this vicinity were thrown upon them.
The period of their eruption is, therefore, post-Laramie, presum-
ably early Tertiary.
The first eruptions of andesite were followed by those of
basalt in great amounts, and these by others of andesite and
*Abstract of a paper read before the British Association for the Advancement of
Science, September, 1893.
606
DIS SHOCMID VOLCANO OF. GRANDALLE SBA SIN. 607
basalt like the first. This was succeeded by a period of
extensive erosion; reducing the country to nearly its present
form. Then came the eruption of a vast flood of_rhyolite con-
stituting the Park plateau, which was followed in this region by
smaller outbreaks of basalt. The last phase of volcanic activity
is found in the geysers and fumaroles which have rendered this
region famous.
The volcano of Crandall Basin consists chiefly of the first
series of basic andesites and basalts. The earlier acidic andesite,
which occurs beneath these rocks, appears to be the remnants of
eruptions from neighboring centers.
Nothing remains of the original outline of the volcano. The
district is now covered by systems of valleys and ridges of
mountain peaks that rise from two thousand to five thousand feet
above the valley bottoms. The geological structure of the
country, however, makes its original character evident.
The outlying portions of the district to the south, west, and
north consist of nearly horizontally bedded tuffs, and subaérial
breccias of basic andesite and basalt. With these are intercalated
some massive lava flows, which are scarce in the lower parts of
the breccia, but predominate in the highest parts, above an
altitude of ten thousand feet. Here they constitute the summits
of the highest peaks.
In contrast to the well-bedded breccias around the margin of
the district, the central portion consists of chaotic and orderless
accumulations of scoriaceous breccia with some massive flows.
These breccias carry larger fragments of rocks and exhibit
greater uniformity in petrographical character.
A still more noticeable feature of the central portion of the
district is the occurrence of dikes which form prominent walls,
and may be traced for long distances across the country. The
greater part of them are found to converge toward a center in
the highest ridge in the middle of the drainage basin of Crandall
creek. A small number converge toward a second center three
or four miles east of the first. In the southern part of the
district there are many dikes trending toward a center near the
608 THE JOURNAL OF GEOLOGY.
head of Sunlight Basin, about fifteen miles south of the Crandall
center.
_ The center toward which the Crandall dikes converge is a
large body of granular gabbro, grading into diorite. It is about
a mile wide, and consists of numerous intrusions penetrating one
another and extending out into the surrounding breccia, which is
highly indurated and metamorphosed in the immediate vicinity
of the core. Within the area of indurated breccia the dike rocks.
become coarse grained rapidly as they approach the gabbro core.
This was undoubtedly the central conduit of an ancient volcano,
the upper portion of which has been eroded away.
Upon comparing the geological structure of this region with
that of an active volcano, like Etna, it is apparent that the lava
flows which form the summits of the outlying peaks must have
been derived from lateral cones fed by dikes radiating from the
central conduit. And assuming that the volcano of Crandall
Basin was similar in type to that of Etna, an idea of its original
proportions is derived by constructing upon profile sections
through the Crandall cone the outline of Etna. If the erosion of
the summits of the highest peaks is neglected, the resulting
height of the ancient volcano above the limestone floor is esti-
mated at about thirteen thousand four hundred feet. This is
undoubtedly too low, and is well within the limits of present
active volcanoes. Erosion has removed at least ten thousand
feet from the summit of the mountain to the top of the high
central ridge in which the granular core is situated, and has cut
four thousand feet deeper into the valleys on either side. It has
prepared for study a dissected volcano, which, it is hoped, will in
time reveal some of the obscurer relationships existing between
various phases ot igneous rocks.
Petrological Features —Ilt will not be possible in an abstract to
do more than present, in the briefest manner, the more salient
features of the petrology of the rocks of this volcano. The
rocks are mostly the same as those in various parts of the
Yellowstone National Park, some of which have been described
in another place. The older acidic breccia consists of fragments
DISSECTED VOLCANO OF CRANDALL BASIN. 609
and dust of hornblende-mica-andesite, hornblende-andesite, and
hornblende-pyroxene-andesite. They are partly glassy and
partly holocrystalline. In some places they appear to pass into
the overlying breccia, but in others they have been eroded and
weathered before the latter were thrown over them.
The upper breccia, which constitutes the main mass of the
volcano, is basaltic as a whole. It consists of pyroxene-andesite
and basalt, the latter predominating in the upper part of the
accumulation. The massive flows, as far as investigated, are all
basalt. The composition varies constantly within narrow limits.
A greater part of these rocks contain glassy groundmass.
The rocks constituting the dikes exhibit more variation than
the breccias, though the majority of them are like the breccias in
composition and habit, being basalt. They are generally more
crystalline. A great many dike rocks resemble the basalts in
outward appearance, but have little or no olivine, and are more
crystalline. The absence of olivine from the more crystalline
forms of these rocks appears to be due to the conditions which
influenced the crystallization of the rocks and not to their chem-
ical composition. For in some cases what appear in hand speci-
mens to be decomposed olivines are found to be paramorphs
after this mineral, consisting of grains of augite, magnetite, and
biotite. As the rocks become more crystalline biotite becomes
an essential constituent; the porphyritical minerals lose their
sharpness of outline and assume some of the microscopical char-
acteristics which they possess in gabbro.
Within the core the coarest grained forms are gabbro. The
composition varies in different parts of one continuous rock mass,
and also between different intrusions within the core. The tran-
sition is from gabbro to diorite with biotite and quartz; and the
extreme variety is that form of granite called aplite; the range
in silica being from 51.81 to 71.62 per cent.
Fine grained, andesitic equivalents of diorite occur in dikes
outside of the core, but none of the most silicious varieties have
been found outside of it. From this it appears that toward the
end of volcanic activity near the core the composition of the
610 THE JOURNAL OF GEOLOGY.
magmas became more and more silicious, and the volume of the
lava erupted smaller. But this change in composition was not
uninterrupted, for there are evidences of the alternate eruption
of basic magmas as well. Dikes of more silicious rocks are trav-
ersed by later dikes of basic rocks. This has taken place both
within and outside of the core. Some of these basic rocks are
uncommonly low in silica for rocks of this region. They are all
found at some distance from the core, with one exception, which_
is an intrusion within the core. They are lamprophyric in the
sense used by Professor Rosenbusch, and approach more or less
closely typical camptonites, monchiquites, kersantites, and min-
ettes. They are connected with the basalts of the district by min-
eralogical and structural transitions.
These exceptionally basic rocks are the chemical complements
of the acidic ones in the core and appear to be among the latest
extrusions. While they agree with one another in having a low
percentage of silica, they differ in the relative abundance of mag-
nesia, lime and iron oxide on the one hand, and of alumina, soda
and potash on the other.
As already pointed out by the writer in another place, the
variability in composition of all of the volcanic rocks in this vol-
cano illustrates one mode of differentiation of a magma at a par-
ticular center of eruption. A comparison of the chemical and
mineral composition of the rocks of this district furnishes addi-
tinal evidence of the fact that magmas which are chemically
similar will crystallize into different groups of minerals according
to the conditions through which they pass. Thus chemically
similar magmas may form basalt under one set of conditions, and
gabbro under others; the first composed of plagioclase, augite,
olivine, magnetite and sometimes hypersthene; the second con-
sisting of plagioclase, augite, hypersthene and biotite, besides some
magnetite, orthoclase and quartz, with or without hornblende.
Minerals, then, which are primarily functions of the chemical
composition of rocks are also functions of the physical conditions
affecting crystallization. Some of the conditions under which
the molten magmas solidified within the dikes and core of the
DISSECTED VOLCANO OF CRANDALL BASIN. 611
volcano of Crandall basin, may be inferred from a consideration
of the geological structure of this ancient volcano. The magmas
which solidified within that portion of the core now exposed, and
those in dikes within a radius of two miles, must have occupied
positions at nearly the same distance beneath the surface of the
volcano, that is, at a depth of about 10,000 feet and over. The
one was as deep-seated or abysmal as the other, and yet their
degrees of crystallization range from glassy to coarsely granular.
The influence of pressure on the crystallization is not recog-
nizable either in the size of grain or the phase of crystallization,
Marked changes in the crystallization may be traced horizon-
tally in the immediate vicinity of the core. They are rapid near
the core, and are accompanied by the induration and metamor-
phism of the surrounding rocks. They are ina general measure
independent of the size of the rock-body, since narrow dikes
within the core are coasely crystalline, while much broader ones
in the surrounding breccias are very fine grained. It was, unques-
tionably, the differences in the temperature of the core rocks and of
the outlying breccias which affected the degree of crystallization.
The former must have been more highly heated than the
latter rocks, and the magmas solidifying within them cooled
much slower than those injected into the outlying parts of the vol-
cano. In this case the depth at which the magmas solidified
appears to have been of little moment in comparison with the
temperature of the rocks by which they were surrounded.
The core of gabbro and diorite with an intricate system of
veins of middle grained porphyritic rocks, and radiating dikes of
aphanitic and glassy lavas, encased in an accumulation of tuffs and
breccias with flows of massive lava, constitute an extinct or com-
pleted volcano. The central core consists of the magmas that
closed the conduit through which many of the eruptions
had reached the surface. In solidifying they became coarse
grained. The question naturally suggests itself, Are these coarse
grained rocks any less volcanic than those that reached the sur-
face? What part of a volcano is non-volcanic ?
JosEpH P. IppDINGs.
INKOUNES OUN Isls Jee) AUNID) ZING IDIEIIOSIIES Ole
Wess MOSSMSSUBe We EIEIaAY ZAIN ID) ah,
ORIGIN FOE) art ORI S:
THE recent closing down of the silver mines of Colorado and
other Western states means not only a lessening of the silver pro-
duction of the country, but also the shutting off of its greatest
source of lead supply. During the past few years over two-thirds
of the total yield of domestic lead has been from the argentiferous
lead ores of Colorado, Utah, Idaho, Montanaand Nevada. Unless
operations are resumed in the West, the demand must consequently
soon be concentrated upon the deposits of non-argentiferous
lead in the Mississippi Valley, which have been in the past the
sole important producers. A rise in the price of lead is to be
expected asa result, which, in turn, will lead to increase in exploit-
ation and development.
The question naturally arises, therefore, to what extent are
these Mississippi Valley deposits to be depended upon for future |
supply. They have been large and almost constant producers
in the past; will they continue to be such in the future? The
history of their development, which is in many respects remark-
able, lends color to the hope that such will be the case, especially
in Missouri. Lead mining was begun in that state as much as
170 years ago, and has continued almost uninterruptedly since.
Indeed, the first deposit worked, that of Mine La Motte, has up
to this year supplied large quantities of ore, the total value of its
product to date being in the neighborhood of $8,000,000. The
various bodies of ore have shown signs of exhaustion from time
to time, and the industry in the state has waned. About the year
1854 the condition was such that even so competent a judge as
Prof. J. D. Whitney* ventured the prediction that the supply was
nearly exhausted, and that the lead mining of Missouri was a
thing of the past. But ever after such depression, deeper exca-
vations have developed new bodies of untouched ores, wider explo-
* Metallic wealth of the United States, p. 419.
612
ILIB/AVO) ZAIN) AIMCO SQUPLAOISH HS JO IAC. 613
rations have revealed new fields, or improvements in mining and
metallurgical methods have made previously rejected ores avail-
able. Along with this, the utilization of the associated zinc ores
has led to the opening up of deposits which previously lay
untouched, enclosing often unexpected quantities of lead. Dur-
ing the past twenty years Missouri's production has reached large
proportions. The total amount mined during this period is fully
twice that of the preceding 150 years—a startling refutation of the
early adverse predictions. The output during recent years has
been only second to Colorado’s, and this year will probably
be first among the states of the Union; the total amount pro-
duced to date probably equals, if it does not exceed, that of any
other state.
Similar in some respects are the facts of zinc production. The
mining of these ores does not, however, date much more than twenty
years back, and hence the industry has not suffered much from
the vicissitudes of the early mining. The production grew rap-
idly from its beginning, and now ranks first in the country. The
total output up to the present time is nearly equal to the combined
total productions to date of all other states in the Union.
The showing for the Upper Mississippi or Wisconsin zinc and
lead area is not quite so good. Mining there dates hardly more
than 100 years back, and it was not on an active basis before
1823. The period of maximum work was about the year 1845,
and soon after this time Prof. Whitney seems to have been of
the opinion that its prospects were better than Missouri's, though
he predicted a continued decline. The utilization of the zinc
ores began about 1860, which tended to sustain the mining indus-
try and the production of lead, though on a much reduced scale.
In the early seventies the production of zinc was quite large and
something like a resuscitation of mining took place. During the
past thirteen years there has, however, been a general decline, and
recently little mining has been in progress. At the time of
maximum activity, in 1845, the production of lead was about
27,000 tons per annum; but that of zinc ore, in 1872, was only
22,000 tons. The total amount of lead produced to date is prob-
614 DLE OULINAE. OF NGHOLOG Ve
ably something over 650,000 tons, and of zinc ore only about
250,000 tons.
With such facts in mind it is of interest to note that the
deposits to which they relate are the subjects of renewed study
at the present time, and the prospect of increased demands upon
them, above referred to, makes the revival of: the discussions of
their origin and mode of deposition most timely.
At the recent meeting of the American Institute of Mining
Engineers, held as part of the International Engineering Con-
gress, three papers were presented bearing, in whole or in
part, upon the ores of the Mississippi Valley, and another, on
the Bertha zinc mine of Virginia, described an ore body belong-
ing essentially to the same class. These papers were by Messrs.
BF: Posepny*, W. P. Jenney.”, 5. FP. Emmons?, W. PR. Blakes vanc
W.. H. Case5, respectively.
_ The first of these papers, by Professor Posepny, is a descrip-
tion and discussion of ore deposits in general, in which he advo-
cates their deep-seated origin through the medium of hot solu-
tions derived from great depths. The second paper, by Dr.
Jenney, is an exposition of his views concerning the origin of
the Mississippi Valley ores, derived from his recent studies in
the region. He repudiates the explanation of lateral concentra-
tion advocated by Whitney and Chamberlin, and reverts to the
old ideas of Owen and Percival, that the ores have come from
below, thus harmonizing with Posepny. The other three papers
are principally descriptive, though Mr. Emmons quotes Dr.
Jenney’s conclusions as applied to the Mississippi Valley ores.
Posepny’s direct reference to the ores here discussed is brief.
He marshals few facts from the region itself in support of his
theory, but rather argues, in a negative way, that no great
obstacles exist there which would prevent its accceptance. Thus,
"The Genesis of Ore Deposits.
The Lead and Zinc Deposits of the Mississippi Valley.
3 Geological Distribution of the Useful Metals in the United States.
4The Mineral Deposits of Southwest Wisconsin.
5 The Bertha Zinc Mine.
IIE AID. ALINE D) ZAIN SOE IPO SITIES). JE IAC, 615
as positive evidence in Missouri, he states that while the deposits
away from the granite and porphyry “islands” of southeastern
Missouri consist chiefly of lead and zine ores, ‘‘other metals,
such as copper, cobalt and nickel occur as the Archean founda-
tion rocks are approached.” This circumstance, he states, is
‘“‘an indication that the source of the lead deposits also is to be
sought in depth.” Whatever may los tne value oF tog “nmelicas
tion,” the facts, as stated, do not hold generally, in the opinion
of the writer. Professor Posepny reasons, presumably, from
observations made at Mine La Motte, where such conditions
exist. At other places, however, these changes in composition
are not observed as the crystalline rocks are approached. At
Bonne Terre copper pyrite was found in the old wpper workings
containing about four per cent. of nickel and cobalt. It does
- not characterize the deeper ores. At Doe Run, a mine recently
opened, work is prosecuted along the old water-worn pre-Cam-
brian surface of the Archean granites, amid the very conglomer-
ate boulders, and very little copper pyrite with cobalt and nickel
is found. Again, at other localities in St. Genevieve, Franklin,
Crawford and other counties, copper ores occur remote from any
granite or porphyry outcrops, and well above the basal beds of
the Cambrian.
In the way of negative evidence, our author, in considering
the Wisconsin deposits, seems to think the absence of ores in
the great thicknesses of limestones and sandstones which under-
lie the productive horizons a by no means conclusive fact as
opposed to their deep-seated source, and suggests that the solu-
tion may have come up through a passage not yet exposed, and
even that fault fissures and eruptive dikes exist which have not
been discovered. From the fact that he refers in this connection
only to Whitney’s report of 1862, we conclude that he has not
had access to the later and more exhaustive works of Strong and
Chamberlin. Perhaps, with the full light conveyed by these
reports and accompanying maps, Professor Posepny might have
attached more importance to the objections raised. It is difficult
to conceive how such a passage for the solutions as he suggests
616 THE JOURNAL OF GEOLOGY.
could possibly exist without its presence having been revealed
and its course traced, with all the widespread mining and explor-
ing which has been conducted in this region during the past
seventy years. Neither can one see how the solutions could
traverse the intervening great thicknesses of water-soaked sand-
stone without becoming diffused, in great part at least. The fail-
ure to find such a passage and the absence of the ores in the beds
assumed to have been traversed, though evidence of a negative
character is so strong that it becomes of almost positive value
in support of the theory of lateral segregation.
Dr. Jenney, in support of his position, recognizes systems of
fault fissures in the ore districts of both south-western and
south-eastern Missouri, which cross each other in different direc-
tions; these, he considers, served as channels for the metal bear-
ing solutions, and the association of the fissures with the ore
bodies he adduces as evidence of such derivation. The deposits
of the south-western portion of the state occur almost exclusively
in the Mississippian or Lower Carboniferous limestone. Cross
fissures or fault fissures in the rocks, if they exist, are not very
apparent. The strata are undoubtedly very much shattered in
certain limited areas, and have been subjected to extensive subter-
ranean erosion and corrosion and great silicification. Of a sys-
tem of extensive or considerable faults, recent stratigraphic work
in this region has, however, revealed nothing.
In the Cambrian limestones of the eastern part of the state
the conditions are somewhat different. Crevices and fissures are
there plainly developed, and evidence of considerable faulting
is indubitable. In Franklin County such vertical crevices have
supphed large quantities of ore. In that portion of the south-
east to which reference is especially made, however, and which
has produced by far the bulk of the lead, the crevices, whether
marking faults or not, are of insignificant dimensions, and the
experience has been that they contained themselves little or no
ore. On the contrary, the great ore masses consist of galena
disseminated through a thickness of the country rock, often of
fifty feet or more. At Bonne Terre a tract 1300 feet long by 800
IL JaAID ZAIN’ LAINE IOYBIPOSH iS) 5 J2 TAC. 617
feet wide has been mined out of such diffused ore. The crevices
which traverse this ore body are frequently almost blind, and can
only be detected by the drip of roof water. These are such as
occur in almost any massive rock. Further, one of the most
important faults in this region, which traverses the country about
two miles north of Mine La Motte, with an apparent throw of
300 feet, is entirely unaccompanied by ore, though the adjacent
ground has been prospected with the diamond drill. Again, not
a single instance can be recalled by the writer, in those mines
which work to the very contact with the underlying granite,
where faulting crevices extend down into that rock. They pos-
sibly do so extend in some instances, but there is no positive
evidence adduceable that they then continue ore bearing. Apart
from this, however, the association of ore and crevices, of course,
does not denote by any means a deep-seated source for the ore.
Such crevices generally act both as channels controlling their
distribution, and as receptacles for their accumulation whatever
the source of the ores. Hence, a disturbed and creviced region,
which is in other respects adapted to the reception of ores, will
be their most natural habitat. Therefore the explanation of the
localization of the deposits based upon such conditions is equally
consistent with any of the common theories of ore derivation.
The same, it would seem, can be said concerning the observed
paragenesis of the minerals and the growth of crystals, in which
Dr. Jenney sees additional foundation for his conclusions. If
we accept the broader idea of lateral secretion, which does not
demand that a mineral shall be derived from the very rock to
which it is attached, but recognizes abundant flow along crevices
and through porous strata and a consequent free transfer of solu-
tions from place to place, all the phenomena find at least an
equally ready explanation. It is argued further, in this paper,
as against the lateral secretion theory, that the metallic contents
of the country rocks are insufficient to have supplied the ore
bodies. The grounds for this statement are only suggested ; but,
to the best of our knowledge, the fact yet remains to be proven.
Due allowance is not made for the many and various ways in
618 THE JOURNAL OF GEOLOGY.
which minute quantities of substances disseminated through vast
volumes of rock may be brought together.
In evidence of the post-Carboniferous age of the deposits
the statement occurs several times in Dr. Jenney’s paper, that the
ores occur in the Coal Measures. This, we think, should be
made with limitations. They are found in shales of that age in
Jasper county, and at a few other localities, but these shales are
in isolated patches, which occupy depressions in the older ore-_
bearing Mississippian rocks. The metallic contents of the coal
may, hence, be derived, by some secondary process of transfer,
from adjacent ore bodies. In any case, the Coal Measures in the
state, as a whole, are practically destitute of these ores, and they
can thus hardly be stated to occur in that formation, whether
their absence be due to their prior formation or to limitations in
their distribution determined by physical causes.
Dr. Jenney seeks further to find support for the hypothesis of
the deep-seated origin of the ores through analogy, in stratigraphy
and geologic history, with regions of the far West. This attempt
does not seem, in our judgment, to be successful. The last pro-
nounced regional disturbance of both the Ouachita and Ozark
uplifts was immediately after the Coal Measure. period. In
Arkansas this was accompanied by great flexing of the strata.
There is no evidence in the Ozark uplift of any intense disturb-
ance of post-Cretaceous date, or of the presence, even at great
depths, of flows of such igneous rocks as accompanied the uplift
and preceded the ore formation of the Rocky Mountains. As
already expressed, the Missouri ores cannot be properly con-
sidered to occur in the Coal Measures of the state. Did sucha
profound fissuring take place in post-Cretaceous times as Dr.
Jenney’s hypothesis requires, we should expect to find it extend-
ing into the body of the Coal Measures, accompanied by the ores.
At least faulting or other such exhibition of disturbance would
be found, which phenomena do not characterize these rocks.
Over and above these considerations affecting the quality
of the support of this theory, there still remain the positive
obstacles to be disposed of. The almost entire absence of the
EAD SANZ COE OSIIES lee: 619
precious metals in the Missouri ores is a fact which further weak-
ens the force of any analogy which may exist between their con-
ditions of deposition and those of the Rocky Mountain ores.
How are the objections raised by Whitney and Chamberlin, dis-
cussed in a previous paragraph, to be met; suchas the facts that
faults are practically absent from the region; that there is little
ore in the underlying Lower Magnesian beds and none in the
Potsdam and St. Peter’s sandstones; that no deep and continuous
crevices like true fissures are found; that no hydrostatic cause is
assigned for the ascension of the solutions from great depths.
How could the ores be carried across such thick pervious and
water-soaked strata as those of the Potsdam and St. Peter’s
formations ?
The generally accepted facts that the deeper-seated rocks are
richer in metallic constituents; that subterranean waters are of
high temperature and under great pressure, and consequently
are powerful solvents; that the relief of pressure and the diminu-
tion of temperature accompanying the ascent of such solutions
supply an abundant cause for the deposition of their metallic
burdens, are all good and enticing general reasons in favor of the
adoption of the theory of a deep source for a// of our metalliferous
deposits. Yet, on the other hand, we must recognize that some of
our ores, notably those of iron and manganese, cannot be assigned
such an origin. Why is it not possible, on general grounds, that
other ores should be gathered as are those of these two metals ? In
reply, it is manifest that we cannot rely entirely upon such gen-
eral principles, as they are at present understood; but must resort
to specific facts in connection with special cases. Few definite
facts relating to this Mississippian area have been adduced in these
recent papers which can stand as new reasons for believing in the
deep origin of the ores, an explanation long since offered by
Owen and Percival. Neither have we attempted to introduce
positive demonstration in opposition to it. The question seems
to be very much 2 statu quo, and, so long as it so remains, the
old objections hold good and must be done away with before a
change of opinion is warrantable. ARTHUR WINSLOW.
JEDIT OIRIDA IE.
Tue Lake Superior excursion, under the leadership of Profes-
sors Van Hise and Wadsworth, which preceded the scientific
meetings at Madison and Chicago, was participated in by a
goodly company of foreign and American geologists from whose
testimony we learn that it was unusually profitable and enjoyable.
It was thoroughly planned, even to minor details, and carried
into execution with remarkable precision, no time being wasted
by errors or by undue attention to trivial features. Brief lucid
explanations by the guides brought out the essential features of
the formations and greatly facilitated observation.
*
*
THE meeting of the Geological Society of America at Madison
was attended by somewhat larger numbers than usually gather at
a summer meeting. The following twenty papers were offered
and read in full or given in substance, with the exception of two,
whose authors were absent, and which were only read by title for
lack of time On the Study ot Fossil Plants, (by Sir a@)a \\ine
Dawson ; Ona New Species of Dichthys, Ona new Cladodus from
the Cleveland Shale, and On a Remarkable Fossil Jaw from the
Cleveland Shale, by E. W. Claypole; Origin of Pennsylvania
Anthracite, by J. J. Stevenson; The Magnesian Series of the
North-western ‘States, by C. W. Hall and F. W. Sardeson; On
the Succession in the Marquette Iron District of Michigan,
by C. R. Van Hise; Extra-morainic Drift in New Jersey, by G.
Frederick Wright; On the Limits of the Glaciated Area in New
Jersey, by A. A. Wright; South Mountain Glaciation, by Edward
H. Williams, Jr.; Terrestrial Subsidence South-east of the Amer-
ican Continent, by J. W. Spencer; Evidences of the Derivation
of Kames, Eskers, and Moraines of the North American Ice-
sheet, chiefly from its Englacial Drift, and The Succession of
Pleistocene Formations in the Mississippi and Nelson River
Basins, by Warren Upham; The Cenozoic History of Eastern Vir-
620
EE DIRORIAL: 621
ginia and Maryland, by N. H. Darton; Notes on the Geological
Exhibits of the World’s Fair, by G. H. Williams ; Dislocation of
the Strata of the Lead and Zinc Region of Wisconsin and their
Relation to the Mineral Deposits, with some observations upon the
Origin of the Ores, by W. P. Blake; Geology of the Sandhill
Region in the Carolinas, by J. A. Holmes; The Gravels of the
Glacier Bay in Alaska, by H. F.Reid; The Arkansas Coal
Measures in their Relation to the Pacific Carboniferous Province,
by James Perrin Smith; Glaciation of the White Mountains,
ING Jal, oxy (G5 Jats lative eos:
Professor Reid’s paper on the Gravels of Glacier Bay was
given the form of an illustrated evening lecture, and was found
entertaining and instructive by the popular audience as well as the
members of the society. By admirable photographic illustra-
tions he brought forth very clearly and impressively many of the
features of glacial action. It was peculiarly valuable as illustrat-
ing the behavior of alpine glaciers when they reach unusual mag-
nitude, and particularly when they approach the Piedmont type.
The paper of Sir J. Wm. Dawson does not admit of ready
synopsis. It needs to be read in full. Professor Claypole pre-
sented a number of interesting and apparently important facts
relative to fossil fishes from north-eastern Ohio.
One of the more notable papers was that of Professor Steven-
son, in which objections were urged against the current doctrine
of the origin of anthracite through metamorphic agencies con-
nected with heat and pressure. In lieu of this hypothesis, which
the author held to be untenable, an hypothesis was offered con
necting the origin of anthracite with the conditions of deposition.
Anything less than a full statement of the author’s view in his
own language would fail to do it justice.
The paper of Professor Hall and Mr. Sardeson, read by the
latter, endeavored to correlate, in much detail, the series of mag-
nesian limestones of the north-western states. The most notable
feature was the placing of the dividing horizon between the mid-
dle and the upper Cambrian considerably higher than has been
done by most previous writers, throwing the larger part of the
622 THE JOURNAL OF GEOLOGY.
light-colored sandstones that lie below the alternating series into
the middle rather than the upper division.
Professor Van Hise gave a lucid sketch of the succession of
deposits in the Marquette district and the grounds on which his
interpretation is based. The paper showed the steady progress
that is being made in the disentanglement of the gnarled structure
of that region.
The papers of the Professors Wright awakened special interest _
from their relation to previously controverted ground. Contrary
to their recent contention, they now extend the glaciated area
so as to include the localities of High Bridge and Pattenburg and
a considerable territory in the Triasic region essentially as main-
tained by Professor Salisbury before the Professors Wright took up
the special study of the matter, though this was not as distinctly
acknowledged as might have been desired. The discussion on
the part of Chamberlin and McGee took the congratulatory form
in view of the removal of one important point of difference and
the advance toward harmonious views. It was noted that the
points of difference were essentially reduced to two: The corre-
lation of the Trenton gravels and the age of the extra-morainic
drift relative to the moraine. In regard to this last it was pointed
out that an important contribution had been made, unwittingly
perhaps, to the presumption of great difference in the ages of the
two drifts, in the fact that the outer drift, especially at such local-
ities as High Bridge and Pattenburg, where it is thick, could not
be presumed to be of the same age and character as that of the
moraine and moraine-bordered drift, or its glacial origin would
not have been previously denied by the Messrs. Wright, and that
its age must be presumed to be very much greater or it could not
have been referred to a residuary origin, especially to residuary
derivation from formations which have disappeared from the
neighborhood, since the moraine and moraine-bordered till are
very distinctly characterized glacial formations of fresh aspect,
while residuary accumulations and residuary topography are inher-
ently expressions of age.
Dr. Spencer submitted a large mass of valuable data relative
EDITORIAL. 623
to submerged channels in the south-eastern part of the continent,
particularly the Antillean region, and urged these as evidences of
very great subsidence. The paper awakened considerable discus-
sion, the general tenor of which was the acceptaftce of the evi-
dence and of the inference of subsidence, with an expression of
doubt as to the time of its occurrence and its relations to other
geological events.
The paper of Mr. Upham was a fuller statement of the argu-
ments he has recently advanced in support of the derivation of
kames, eskers, and moraines chiefly from englacial drift. These,
and his views of the internal movement of the ice upon which
they are in some degree founded, were opposed by Reid on phys-
ical grounds and by others on observational grounds. It was
remarked that existing glaciers fail to show basally-rubbed mate-
rial on their surfaces, even on their low terminal slopes, at least
as a common fact. In his second paper, Mr. Upham urged a
somewhat simple and brief succession of Pleistocene formations.
The successive lines of moraines and the observed overlaps of
till were interpreted as signifying minor and relatively brief halts
and readvances of the ice. In the discussion, this position was
opposed as being inconsonant with the evidences of interglacial
intervals and of intervening erosions, oxidations and other changes
which the formations were thought to present.
The papers of Darton and Holmes on different but analogous
portions of the coastal region showed the very great advances
which have been made in the last few years in the analysis and
differentiation of the coastal formations, and the interesting
discussions they called forth showed, in some measure, the
important bearing these have upon the interpretation of the
Pleistocene and immediately Pre-Pleistocene histories of the glac-
iated region.
Professor W. P. Blake, while coinciding in general in the views
held by Whitney and by Chamberlin respecting lead and zinc depos-
its, urged the existence of a greater amount of dislocation than
they had recognized, and attributed to it greater influence in
the localization of the deposits. His views are intermediate
624 LAE JOURNAE OF GHOLOGY.
between those of the authors mentioned and those ‘recently
advanced by Mr. Jenney.
THE attendance upon the meeting of the American Associa-
tion was less than usual, but the interest and the character of the
papers compared favorably with those of other sessions. The
provisions made by the local committee were excellent, and the
hospitalities extended by the citizens of Madison were graceful
and generous. The exceptional beauties of the place and the
superb weather lent attractiveness to the occasion.
In the Geological Section, the following papers were offered,
and, with few exceptions, read in full or in substance: Gravels of
Glacier Bay, Alaska, with lantern illustrations, by H. F. Reid; Use
of the Name ‘‘Catskill,” by John J. Stevenson; Section across the
Coastal Plain Region in Southern North Carolina, by J. A. Holmes ;
Notes. on Further Observations of Temperature in the Deep Well
at Wheeling, W. Va., by William Hallock; Recent Investigations
in the Cretaceous Formation on Long Island, N. Y., by Arthur
Hollick ; Character of Folds in the Marquette Iron District, by C.
R. Van Hise; The Fossil Sharks of Ohio, by E. W. Claypole;
Hillsdale County Geology, by Horatio P. Parmelee; Exhibition
of Trilobites, showing Antenne and Legs, by Chas. D. Walcott ;
Remarks on the genus arthrophycus Hall, On the Value of Pseudo-
alge as Geological Guides, Studies in Problematic Organisms, and
The Genus Fucoides, by Joseph F. James; Northward Extension
of the Yellow Gravel in New Jersey, Staten Island, Long Island
and Eastward, by Arthur Hollick; Some Questions Respecting
Glacial Phenomena about Madison, by T. C. Chamberlin; Amount
of Glacial Erosion in the Finger Lake Region of New York, by D.
F. Lincoln; Ice-sheet on Newtonville Sandplain, by F. P. Gulli-
ver; Additional Facts Bearing on the Question of the Unity of the
Glacial Period, by G. Frederick Wright; Changes of Drainage in
Rock River Basin in Illinois, by Frank Leverett; Graphic Com-
parison of post-Columbia and post-Lafayette Erosion, by W J
McGee; An Illustration of the Effect of Stagnant Ice in Sussex
Co., N. J., and A Phase of Superficial Drift, by R. D. Salisbury ;
EDITORIALS. 625
_ Tertiary and Quarternary Stream Erosion of North America, by
Warren Upham; The Emergence of Springs, by T. C. Hopkins.
As the writer was unable to hear a considerable number of these
papers his notes must be confined to comparatively few of them.
The paper of Mr. Lincoln presented a very interesting sketch of
the quite remarkable evidences of glacial erosion and modifica-
tion of surface in the Finger Lake region of New York. He
showed, successfully we think, that the existing topography could
not have arisen in its present form through the agency of sub-
aérial degradation alone nor by the simple deposit of drift material
on a surface so produced, but that a very notable amount of
reshaping of the rock-surface was the result of glacial abrasion.
Mr. Frank Leverett made a quite important contribution to
the data bearing upon the stages and duration of the earlier gla-
cial epoch. He has recently discovered evidence that the Rock
River formerly flowed nearly due south from a point near Rock-
ford into the Green River basin, and presumably onward to the
great bend of the Illinois River, near Hennepin, where an old
deep channel exists. From this course the river was diverted to
its present south-westerly course by the earliest or at least one of
the earlier stages of the ice invasion of that region. Between
the time of this diversion and the stage at which the kettle
moraine was formed across the Rock River about forty miles to
the north, near Janesville, Wis., the river cut a trench in rock
across a succession of preglacial cols to maximum depths esti-
mated at 100 to 125. feet. Mr. Leverett made careful estimates
of the total amount of rock excavation and found it to amount
to one square mile 1100 feet deep. Stated in another form, this
equals a trench 100 feet deep, one mile wide and eleven miles
long, or one-half mile wide and twenty-two milesmlongn je Aicer,
the trench had been cut, the glacial wash from the outer edge of
the kettle moraine partially filled the trench as shown by rem-
nants of terraces still existing at different points along it. The
amount of this filling within the area of the above computation is
estimated as one square mile goo feet thick or ;°, of the amount
of rock excavation. Since the formation of these gravels the
626 RELIED JOURNAL OF GEOLOGY.
stream has only partially removed this partial filling of the
trench previously cut. The estimated amount of the material
so removed since the time of the formation of the kettle moraine
is one square mile 650 feet deep, or $3 as much as the rock
excavation. From this it appeared that the amount of erosion
in all post-glacial time (including the last of the glacial period),
although wrought upon incoherent gravels, is much less than the
amount of rock cutting accomplished between the time the river
was diverted and the formation of the kettle moraine.
In the introduction to his paper Professor G, Mrederek
Wright stated that the hypothesis of an ice dam at Cincinnati
appeared to be in a damaged condition, as an agency to account
tor the? high terraces, of ithe upper Ohio andisome jormts
tributaries, and that it was a part of the purpose of the paper to
repair the damage. It proved in the sequel, however, an effort
at emendation by substitution. The additional facts bearing
upon the unity of the glacial period cited in the paper related
chiefly to a considerable depth of glacial wash in the trench of
a tributary of the Beaver River near Homewood, Pa., just
outside but near the border of the glaciated region. Professor
Wright contended that the trough in which this glacial material
lies must have been eroded previous to its deposition. This
erosion he referred to pre-glacial times. The filling reaches
nearly or quite to the upper terrace plain on the north side of
the tributary, but does not appear on the terrace plain south of
the tributary. In the course of his paper, and notably in the
discussion following, Professor Wright advanced the hypothesis
that the rock shelves which constitute the base of the high
terraces of the upper Ohio, Allegheny and adjacent rivers, were
formed during a stage of base-levelling in Tertiary times, that
the narrower and deeper valley below the rock shelves (in round
numbers 300 feet deep) was cut in this base-plane during a
stage of elevation just preceding the glacial period, and that
this trench was filled up with glacial wash and glacio-natant
material to a height, at some points, as much as sixty feet above
the rock shelves. In the discussion it was pointed out that, to
EDITORIAL. 627
account for the fact that the trains of gravel that rise on the
outer face of the adjacent moraines run down through this
narrower deeper valley at low levels, it is necessary to suppose
that there was an interruption of glacial action and a period of
excavation during which the previously formed 300 feet or more
of glacial wash was very largely carried away, and that this means
a discontinuity of glacial action and an interglacial interval. The
hypothesis is, therefore, not a contribution to unity but to discon-
tinuity. The amount of excavation between the time of the sup-
posed first filling of the trench and the partial refilling at the time
of the formation of the adjacent terminal moraine was several
times greater than all that has taken place since the moraine was
formed. It signifies, therefore, a very notable interruption of
continuity and a reversal of action. It may be here added that,
logically, it also means the abandonment of the “fringe” theory
to account for the older drift, for the filling of the valleys for
so great distance and to so great depth means more than a
trivial stage of advance, and the excavation previous to the
formation of the moraine means more than a slight stage of
recession.
Mr. Leverett has examined the Homewood locality since the
meeting, and became satisfied that the partial filling of the trench
at that point took place contemporaneously with a moraine
which crossed the valley only a short distance above (some
miles outside the glacial boundary as mapped by Lewis and
Wright, and even some distance beyond the striz not long since
reported by Dr. Forshay, Mr. Leverett finding striation half a
mile farther down the valley). The characteristics of this
moraine seem to Mr. Leverett to indicate that it belongs to the
group formed during the later incursion. The shelf of rock
south of the tributary was not covered by the glacial wash of
this stage because the trench lacked about twenty feet of being
filled by the wash. Mr. Leverett found other remnants which
he regards as parts of the same glacial flood-deposit farther
down the Beaver, the surface rapidly descending as is the habit
of such moraine-headed terraces near their sources. The facts
628 DHE JOURNAL OF GEOLOGY.
here, therefore, appear to be essentially the same as on other
tributaries of the region which are crossed by the group of later
moraines, and which seem to indicate profound excavation
between the earlier and later drifts. .
The hypothesis advanced in the paper, while not new in
itself, having been among the multiple working hypotheses used
by one or more students of the region, though not so far as
known adopted by any one previously, is much more deserving of
serious consideration than its predecessor, the Cincinnati ice dam. |
It may have some elements of truth in it, z. ¢., a portion of the
excavation of the rock below the old base-plane may have pre-
ceded the incursion of the glacial wash and even the glacial
period. If this should prove true the effect will be to extend
the importance of the earlier glacial epoch and to reduce the
time necessarily attributed to the interglacial interval of excava-
tion. The glacial formations of the lower Ohio and adjacent
regions, however, seem to indicate a more complex hypothesis
than this, or any previously advanced, which shall take cognizance
of more than one glacial episode previous to the formation of the
well-developed terminal moraines.
ONE session of the Geological Section was adjourned to
permit members to listen to papers read before the Anthropo-
logical Section having a geological bearing. These were the
“Evidence of Glacial Man in America,” by G. Frederick Wright;
and “The Antiquity of “Man im America, by W 4) McGee:
The former consisted essentially of a restatement of the sup-
posed evidences of the existence of man contemporaneously
with the glacial period found in the terraces at Madisonville and
Newcomerstown in Ohio, and at Trenton, N. J. The latter con-
sisted essentially of a discussion of the character of evidence
required for the establishment of the antiquity of man.
Emphasis was especially laid upon the distinction between legal
evidence and scientific evidence.
In the first paper no new discoveries were announced nor
any additional data of note added to previous evidence. On
EDITORIAL. 629
the other hand, the localities of Little Falls, Minn., Medora,
Ind., and Loveland, Ohio, which have recently been urged as
offering evidence of glacial man, were passed in silence. The
paper referred constantly to the chipped stones as ‘paleolithic
implements,’ and ignored the recent issue raised by Professor
Holmes’ investigations which are thought by many to make it
probable that, whatever their geological age, the chipped stones
are rejects and failures incident to the process of neolithic man-
facture, and are therefore neither ‘“paleolithic” nor “implements”
in the proper sense of the terms. In the discussion, attention
was called to the significant omission of three out of six of the
localities which a year ago were urged as furnishing evidence of
glacial man. Attention was called to the Ohio exhibit in the
Anthropological Department of the Exposition in Chicago as
furnishing proof that the testimony relating to the Newcomers-
town locality cannot be accepted as having scientific value,
because the point marked upon the photographs of the exhibit
as being the location of the find cannot be rationally supposed
to be the actual locality. Considerable discussion also turned
upon the possibilities of intrusion, particularly through the
agency of the growth and decay of the roots of successive
generations of forests. It was urged that, allowing not more
than six thousand years since the close of the glacial period,
and allowing one hundred years for a generation of trees, sixty
generations may have grown in succession. In the process of
the growth of the large roots of the trees, the gravels and other
material were pressed laterally and to some extent upward by their
expansion, and on the decay of the roots the space they
occupied was refilled, presumably from above, in part at
least. In the case of trees which have tap roots the penetration
is deep, particularly on gravel terraces where the substratum is
porous and relatively dry and the ground-water far below the
surface.* It was urged that, in the refilling of the numerous tubes
formed by the growth and decay of the roots of so many genera-
tions of trees, opportunities would be afforded for the occasional
and sometimes deep penetration of relics that were originally
630 THLE JOOKNAL (OF GZOLOGM.
deposited at or near the surface. It was objected that the tubes
formed by roots would be closed in by lateral creep and not
from above. This, it may be here remarked, would depend
upon whether the lower part of the root decayed before the
upper part, or whether the decay proceeded from the surface
downward. It would also depend upon whether the exterior of
the roots rotted first or whether the bark resisted decay longest,
leaving the interior, at a certain stage, practically hollow. It
would appear that this subject has not received adequate atten-
tion, and that careful investigations respecting the growth and
decay of roots in such situations should be made, and the possi-
bilities of intrusion by means of them carefully determined.
Reference was also made to the possibilities of intrusion through |
the agency of a similar succession of generations of burrowing
animals. In view of the fact that in the paper under discussion
only about twenty flaked stones of artificial origin were insisted
upon as occurring deep within the gravels, the question of the
possibilities of intrusion assumes very considerable importance.
A certain amount of intrusion can fairly be claimed as probable.
The vital question is, Can it be presumed to account for all cases
not otherwise accounted for?
THE admirable address of the retiring President of the
American Association, Dr. LeConte, appears in this number of
the JouRNAL and needs no comment. We hope to publish Vice-
President Walcott’s address in our next number.
THE Woman’s Section of the Geological Congress at
Chicago, assembled on Monday, August 21, and held short
sessions throughout the week. The following is the list of
papers :
Methods of Teaching Geology, by Miss Mary Holmes, Ph.D.,
Rockford, Ill.; Physical Geology, by Miss Mary K. Andrews,
Belfast, Ireland; Chemical Geology, by Miss Louise Foster,
Boston, Mass.; Granites of Massachusetts and Their Origin, by
Mrs. Ella F. Boyd, Heyde' Park, Missi; Artistic! Geology, by
EDITORIAL. | 631
Mrs. S. Maxon-Cobb, Boulder, Colo.; The Geology of Ogle
County, by. Mrs. C. M. Winston, Chicago ; The Fossils of the
Upper Silurian, by Mrs. Ada D. Davidson, Oberlin, Ohio;
Crinoidea and Blastoidea of the Kinderhook Greup as found in
the Quarries near Marshalltown, Iowa, by Jennie McGowen,
A.M., M.D., Davenport, Iowa; The Evolution of the Brach-
iopoda, by Miss Agnes Crane, Brighton, England; The Mas-
todon in Northern Ohio; Post-Glacial or Pre-Glacial ? by Miss
Ellen Smith, Painesville, Ohio; Paleontology, by Miss Jane
Donald, Carlisle, England; Glacial Markings, by Miss Thomson,
Newcastle, England.
THE general session of the Geological Congress convened at
Chicago on August 24, immediately following the close of the
meeting of the American Association at Madison.
The Congress was welcomed felicitously by the President of
the Auxiliary, Charles C. Bonney, and briefly by the Chairman
of the Committee on Organization.
Dime wher Cs) Selwia ml wresided sovers the sinst wsession. lar0
fessor Joseph LeConte and Mr. Hjalmar Lundbohm, of Sweden,
over the second session; and Professor James Hall and Dr.
Groth, of Munich, over the third. The following papers were
presented :
Pre-Cambrian Rocks of Wales, Dr. Henry Hicks, London,
England; The Classification of the Rock Formations of Canada,
with Special Reference to the Paleozoic Era, by Henry M. Ami,
Geological Survey of Canada; The Cordilleran Mesozoic Revo-
lution by Dr. A. C. Lawson, University of California; The Oil
Shales of the Scottish Carboniferous. System, by Henry M.
Cadell, late of the Geological Survey of Scotland; Distribution
of Pre-Cambrian Volcanic Rocks along the Eastern Border of
the United States and Canada, by Professor George H. Williams,
Johns Hopkins University; Huronian versus Algonkian, by Dr.
A. R. C. Selwyn, Director Geological Survey of Canada; On
the Migration of Material during the Metamorphism of Rock
Masses, by Alfred Harker, St. John’s College, Cambridge, Eng-
632 TST fOOLINAL OF SG OLO GNE
land; Wave-like Progress of an Epeirogenic Uplift, by Warren
Upham, Geological Survey of Minnesota; Zur Nereiten Frage,
by Dr) HH: B2 Geimitz, Dresden;)) Genetic Classifications aim
Geology, by W J McGee, Bureau of Ethnology ; The Extent
and Lapse of Time Represented by Unconformities, by Pro-
fessor C. R. Van Hise, U. S. Geological Survey; Restoration of
Clidastes (illustrated), by Professor S. W. Williston, University
of Kansas; Glacial Succession in the British Isles and Northern
Europe, by Dr. James Geikie, Geological Survey of Scotland;
Glacial Succession in Sweden, by Hjalmar Lundbohm, Geolog-
ical Survey of Sweden; Glacial Succession in Switzerland, by
Dr. Albrecht Heim, Zurich; Glacial Succession in Norway, by
Dr. Andr M. Hansen, Geological Survey of Norway; The
Succession of the Glacial Deposits of Canada, by Dr. Robert
Bell, Canadian Geological Survey; Glacial Succession in the
United States, by Dr. T. C. Chamberlin, University of Chicago;
Pleistocene Climatic Changes, by Warren Upham, Geological
Survey of Minnesota; Evidences of the Diversity of the Older
Drift in North-western Illinois, by Frank Leverett, U. S. Geolog-
ical Survey. A paper on the General Geology of Venezuela, by
Dr. Adolph Ernst, was omitted on account of the illness of its
author; and two papers by Dr. O. A. Derby, entitled, On the
General Geology of Brazil, and On the Eruptive Phenomena of
Brazil, were omitted because their author did not arrive until
after the session. Four other papers announced were not read.
The latter part of the first session was devoted to a general
discussion of the question, Ave there any Natural Geological
Divisions of World-wide Extent? The latter part of the second
session was devoted to the question, What are the Principles and
Criteria to be observed in the Restoration of Ancient Geographic
Outlines? Vhe general question assigned for the third discussion,
What are the Principles and Criteria to be observed in the Correlation
of Glacial Formations in Opposite Hemispheres? was omitted to
give time for the discussion of the preceding glacial papers.
Several of the papers read will appear in this JoURNAL, and
some of the matters touched upon in the discussions may be the
EDITORIAL. 633
subjects of subsequent comment. About one hundred geologists
were in attendance, a number which, under all the circumstances,
was greater than was anticipated.
The afternoons of each day were devoted to the Exposition.
Superintendent F. J. V. Skiff, Chief of the Department of Mines
and Mining, and his associates, gave the members of the Con-
gress a very pleasant welcome on their initial visit and provided
special privileges of inspection that were heartily appreciated.
Ash CoA,
REVIEWS.
Lruptive Rocks from Montana. By WALDEMAR LINDGREN. Proc. Cal.
ENGENGlA SIGIS (SKI Ay WO 2. 1 SOO
A Sodatite-Syenite and other Rocks from Montana. By W. LINDGREN,
with yanaliyses * by Wome. Niriviii iis yA )/OUn Ci Violen ice
April 1893.
Acmite-Trachyte from the Crazy Mountains, Montana. By J. E. Wou¥r
and R.S. Tarr, Bull. Mus. Camp. Zoélogy, Harvard College.
Vol. 16, No. 12. (Geological Series, Vol. 2).
Contributions to our knowledge of the mineral and chemical com-
position as well as the relationships of the igneous rocks of particular
regions, however fragmentary, are of the greatest importance; espe-
cially when they relate to the vast areas of North America which remain
almost unknown to the petrologist. The exploration of the great belt
of country, one hundred miles wide, extending from California to Colo-
rado and Wyoming along the fortieth parallel of latitude, by the
geologists under Mr. Clarence King, constitutes the one great system-—
atic study of the volcanic rocks of any considerable area on this
continent. Less extensive investigations of smaller areas, isolated
from one another and often separated by long distances, have been
made from time to time, and to some extent have been published.
But a large part of the work already done has not yet been printed.
The facts so far brought to light show that the rocks of the Great
Basin and the Pacific coast differ as a whole from those occurring in
the eastern portion of the Rocky mountains and the region immedi-
ately east of it. This difference consists mainly in the greater abund-
ance of the alkali-bearing rock-making minerals in the rocks of the
latter region, caused by the relatively higher percentage of sodium or
potassium in the magmas from which they have been derived.*
The recent papers by Mr. Lindgren and by Messrs. Wolff and Tarr
illustrate this characteristic of the volcanic rocks of Montana along the
frontal ranges of the Rocky mountains. All of the rocks described
occur as intrusive bodies; laccolites, sheets, dikes or necks. ‘They
tJ. P. Ippincs: The Origin of Igneous Rocks. Bull. Phil. Soc. Washington, Vol.
12, pp. 138, 139, 184.
634
REVIEWS. 635
were erupted in early Tertiary or late Cretaceous time in most cases,
but their exact date is not known. Owing to extensive erosion the
extrusive forms of these rocks, if they ever reached the surface, have
been entirely removed.
Mr. Lindgren observes in the first paper cited that the rocks of
this region appear to be more varied in chemical composition than the
series usually found in the Great Basin; magmas rich in potassium
are frequent, crystallizing as trachytes ; often they are very basic, and
contain much sodium, resulting in the abundant separation of such
minerals as nepheline, sodalite and analcite.
The more or less acid rocks in the Little Belt mountains and at
various points in front of the main range, west of Fort Benton, con-
stitute dacites, hornblende-andesites, and diorites. Similar rocks also
occur in the Moccasin mountains. They vary much in structure
and composition, and form a natural group. The prevalent habit is
porphyritic, but there appears to be a continuous series of transitions
from porphyritic to fine granular rocks. The phenocrysts are feld-
spar and hornblende, and sometimes quartz and mica. ‘The porphy-
ritical feldspars are in part orthoclase in varying quantities, and there
is reason to believe that these rocks pass by gradual transitions into
trachytic and rhyolitic forms.
Those varieties free from phenocrysts of orthoclase and quartz
grade into medium grained diorite, analogous to Stelzner’s “‘ Anden-
diorit,’”’ which contain besides plagioclase, hornblende and biotite, a
little orthoclase and quartz as the last minerals to crystallize.
Of the more basic rocks, a part are syenites and trachytes, and a
part basalts. The syenites which form dikes consist principally of
orthoclase, plagioclase, biotite and a pyroxene, probably malacolite.
They are called augite-syenites. The syenite from near Dry Fork,
Little Belt mountains, contains, in addition to these minerals, allotrio-
morphic grains of an isotropic substance, probably sodalite. The rock
contains 5.50 per cent. of K2O,and 4.14 per cent.of NazO. The augite-
syenite from the Highwood mountains is coarsely granular, and con-
tains 5.66 per cent. of K2O and 7.88 per cent. of NazO. This
syenite is surrounded by trachytic and basaltic dikes; and in one case
a dike of syenite was seen cutting one of the basaltic dikes.
The syenite from Square Butte at the northern end of the High-
wood mountain is characterized by a noticeable percentage of sodalite
and analcite, and has been called sodalite-syenite. Its chief constit-
636 IER, SKOIRINATE (O12 (CLE OLDEN.
uents are orthoclase, albite and hornblende. The relative proportions
of the minerals has been estimated to be: orthoclase, 0.50; albite,
0.16; hornblende, 0.23; sodalite, 0.08; analcite, 0.03. The horn-
blende was analyzed and found to correspond to barkevikite. Mr.
Lindgren calls attention to the resemblance in chemical composition
between this rock and many nepheline-syenites, except for the rela-
tively higher percentage of K2O in the rock from Square Butte. He
also notices the striking similarity between the analysis of this rock
and those of certain leucitophyres from Rocca Monfina, and remarks
that under different conditions the same magma, now crystallizing as
a sodalite-syenite, might have produced a leucite-feldspar rock.
Trachytic rocks, with a great variety of habits, are abundant in
the Highwood mountains. The essential minerals are sanidine and
augite, with less prominent biotite. The augite is deep green, often
somewhat pleochroic, and evidently contains an admixture of the
eegirine molecule. It is very characteristic not only of the trachytes
but also of the basaltic dike rocks of this region. ‘These rocks form a
connected series, the members of which differ in the relative quanti-
ties of augite and sanidine composing them. At one end of the
series is a rock consisting almost wholly of feldspar, and at the other
end a dark basaltic rock with porphyritical augites and a groundmass
of sanidine and augite. In structure these rocks range from holocrys-
talline and granular to glassy. Some of the trachytes contain small
crystals of sodalite (?) inclosed in sanidine. In one form of the rocks
sanidine ceases to be the prominent phenocrysts and augite takes its
place, and olivine occurs in the groundmass, which consists of feld-
spar and colorless glass easily soluble in HCl. Associated with the
sodalite-syenite of Square Butte are dark colored basaltic rocks, which
occur in three sheets at the base of the butte. Surrounding the butte
there are numerous dikes apparently radiating from the central mass.
One of these basaltic sheets contains phenocrysts of augite, olivine,
brown mica, and white isometric crystals whose original character is
uncertain. The rock is considerably decomposed. Another of the
sheets is like analcite-basalt but is also decomposed. The third is
coarsely granular and approaches theralite in composition.
The rocks described as analcite-basalts occur in dikes and possibly
as necks in association with the rocks already described. They con-
sist of augite, olivine, magnetite, and a mineral, which from its form
and optical properties, and from its chemical composition appears to
REVIEWS, . 637
be analcite. Biotite is sometimes present in small quantities. From
the very fresh appearance of these rocks it seems probable that the
analcite is a primary crystallization from the molten magma. ‘The
groundiass of the rock consists of augite and small.crystals of anal-
cite with magnetite. Mr. Lindgren calls attention to the difficulty of
distinguishing glass, if present, from isotropic analcite.
In the Bear Paw mountains there are dikes of rocks related to those
just described and which correspond to the lamprophyres of Rosenbusch.
They are dark, fine grained, and porphyritic with phenocrysts of augite
and long flakes of brown mica. The groundmass consists mostly of
lath-shaped plagioclase, augite and mica. Some varieties with pheno-
crysts of olivine and augite, in a glassy groundmass without feldspar,
approach certain limburgites.
The paper by Messrs. Wolff and Tarr is confined to a description
of certain trachytic and syenitic rocks in the Crazy mountains. The
first notice of the interesting rocks of this locality was published by
Mr. Wolff in 1885, and he has since undertaken a much more exten-
sive investigation of the same group of rocks, which is not yet com-
pleted. The trachytes form dikes, sheets and laccolites in the northern
portion of the range, and are associated with theralite. Like the
theralites and some other rocks of this range, they are coarse grained,
almost granitic when in thick sheets, fine grained and porphyritic
in the smaller sheets, dikes, and apophyses. When occurring in the
latter forms the rocks have a trachytic habit, and are called acmite-
trachyte. The phenocrysts are glassy feldspar, augite and small
sodalites. Biotite is scarce. The feldspar is soda-microcline or
anorthoclase. The augite is pale green at the center, and becomes
dark green at the margin, where the optical characters are those of
aegirine, similar to that in the theralite. The groundmass consists
essentially of lath-shaped feldspar and acicular crystals of aegirine.
With the green aegirine a few brown needles of acmite occur. There
is a variable amount of interstitial matter between the feldspars of the
groundmass which is probably nepheline in part, and partly analcite,
derived from the alteration of the nepheline.
The coarse grained forms of the rock, or syenite, consist of the
same essential minerals as the trachytic varieties. Sodalite is rare in
the coarse rocks, and acmite is not always present. Chemical
analyses of these rocks are published, but the discussion of them is
postponed until the monograph of the whole group of rocks is pre-
638 THE JOURNAL OF GEOLOGY.
pared. The resemblance between certain features of the rocks of
Montana and those from Arkansas, described by J. Francis Williams,
is pointed out by each of the writers cited. The resemblance to the
lamprophyric rocks in the Absaroka range, Wyoming, east of the
Yellowstone National Park, is also noticed.
Some of the petrographical characteristics of the rocks of this
region are: The prevalence of orthoclase in many intermediate and
basic rocks, leading to the frequent occurrence of trachyte and syenite
and some forms of lamprophyre, as well as* its presence in prominent —
crystals in the andesites and porphyrites, and the frequent occurrence
of dark green augite and aegirine, and occasionally of acmite.
The difficulty of distinguishing colorless glass from isotropic anal-
cite, both of which may occur in certain varieties of lamprophyre,
makes it necessary to use the greatest care in determining the charac-
ter of the apparent base in these forms of rocks. It seems probable
to the reviewer that in some instances, in which an amorphous glass
has been described as forming the matrix of the microscopic crystals
in some lamprophyric dike rocks, it will be found that a definite
isotropic alkali mineral is present, and that the rock is holocrystalline
JosepH P. IDDINGs.
THE
TOURNAL OF CEOLOGY
OCTOBER-NOVEMBER, 1893.
ChOLOGIC MINE Sis eI INDICATED BY tii SE DIVE IN=
TARY ROCKS OF NORTH AMERICA*
INTRODUCTION.
OF ALL subjects of speculative geology few are more attractive
or more uncertain in positive results than geologic time. The
physicists have drawn the lines closer and closer until the geolo-
gist is told that he must bring his estimates of the age of the
earth within a limit of from ten to thirty millions of years. The
geologist masses his observations and replies that more time is
required, and suggests to the physicist that there may be an
error somewhere in his data or the method of his treatment.
The geologist realizes that geologic time cannot be reduced to
actual time in decades or centuries; there are too many par-
tially recognized or altogether unknown factors; but he can
approximate the relative position of certain formations, and by
comparison of their sediments, dimensions, and contained record
of life with estimated rates of denudation, sedimentation and
organic growth, form ageneral estimate of their relative time dura-
tion. It is my purpose to-day to take up the consideration of
the evidence afforded by the sedimentary rocks of our continen-
tal area, and largely of a distinct basin of sedimentation, with a
view of arriving, if possible, at an approximate time-period for
their deposition. Before so doing, I will briefly refer to a few
of the opinions that have been held by geologists on geologic
* Vice-Presidential address delivered before Section E, Am. Assc. Ady. Sci., Madi-
son, Wis., August 17, 1893.
WO dl, IN@s 47s 639
640 MVE J OOMNAUL U6 CSROILOG WZ.
time and the age of the earth. Soon after geology emerged
from its pre-systematic stage, in the latter part of the eighteenth
century, and assumed an independent position among the induc-
tive sciences speculations on the age of the earth began. Dr. James
Hutton, the founder of modern physical geology, and the prede-
cessor of Lyell, in advocating the uniformitarian theory, was the
first to argue that the rate of destruction of one land area was
the means of measuring the duration of others, and that the con-
tinents were formed of the ruins of pre-existing continents, but
that in our measurement of time such periods were of indefinite
duration.t It was not, however, until 1830, when Sir Charles
Lyell published the results of his profound and_ philosophic
studies of geologic phenomena, that the broad outlines of the
law of uniformity, as opposed to the doctrine of geologic catas-
trophes, was fairly established. This work rendered possible a
computation of the age of the earth on the principle that geo-
logic processes were the same in the past as at present. He
based his estimate of time on a rate of modification of species of
mollusca since the beginning of the ‘Cambrian period,” and
divided the geologic series into twelve periods, assigning 20,000,- |
000 years to each for a complete change in their species,—or
240,000,000 years in all. This estimate excluded the “ antece-
dent Laurentian formation.” ?
The hour at our disposal does not permit of mentioning at
length the views of other geologists. Dr. Charles Darwin
thought that 200,000,000 of years could hardly be considered
sufficient for the evolution of organic forms,3 and Rev. Samuel
Haughton assigned 1,280,000,000 of years to pre-Azoic time,
and remarked that the globe was habitable, in part at least, for a
longer period.4 Ata later date he estimated a minor limit to
«Theory of the Earth; or an Investigation of the Laws observable in the Composi-
tion, Dissolution, and Restoration of Land upon the Globe. Trans. Royal Soc. Edin-
burgh, Vol. I., 1788, pt. I, p. 304.
2 Principles of Geology, 1oth Ed., Vol. I., 1867, p. 301.
3 Origin of Species, American Ed., from 6th Eng. Ed., 1882, p. 286.
4Manual of Geology, 3rd Ed., 1871, p. Iot.
CEOLOGIOC HME, 641
geologic time of 200,000,000 of years.t Dr. James Croll esti-
mated 72,000,000 years for the time duration since the first
deposition of sedimentary rocks, while Sir Alfred R. Wallace
thought that 28,000,000 years would suffice.2~ Of the value
of this estimate he says: ‘It is not of course supposed that the
calculation here given makes any approach to accuracy, but it
is believed that it does indicate the order of magnitude of the
Lime requiccds 2) Dire MAlexander Winchell reduced) ceologic
time still more in his estimate of 3,000,000 years for the whole
incrusted age of the world.t Later writers, however, do not
accept this, as we find Sir Archibald Geikie concluding on the
basis of denudation and deposition that the sedimentary rocks
would have required 73,000,000 of years for their deposition, if
denudation was at the rate of one foot in 730 years; or of 680,-
000,000 of years if at the slower rate of one foot in 6,800 years.5
Mr. T. Mellard Reade adopted one foot in 3,000 years as the rate
of average denudation throughout geologic time, and obtained a
result of 95,c00,000 of years as the time that had elapsed
since the beginning of Cambrian time. M. A. de Lapparent
is one of the few European continental geologists that has
written on geologic time. On the basis of mechanical denuda-
tion and sedimentation he thinks that from 67,000,000 to
90,000,000 of years would suffice, at the present rate of sedi-
mentation for everything that has been produced since the
consolidation of the crust.7 The two most recent writers who
have taken their initial datum point or ‘‘geochrone” from
the consideration of late Cenozoic or Pleistocene phenomena
* Nature, Vol. 18, 1878, pp. 267-268.
? Stella Evolution and its Relations to Geological Time, 1889, pp. 48-49.
3Island Life, 2d. Ed., 1892, pp. 222-223.
4 World Life, or Comparative Geology. Chicago, 1883, p. 378.
5 Presidential Address; report of 62d meeting British Assoc. Ady. Sci., 1892, p. 21.
®©Measurement of Geological Time. Geol. Mag., Vol. 10, 1893, pp. 99-100.
7 De la mesure du temps parles phénoménes de sédimentation. Bull. Soc. Geol.
France, 3d ser., Vol. 18, 1890, pp. 351-355. La Destinée de la terre férme et durée
des temps geologiques. Revue des questions scientifiques, July, 1891. Pamphlet.
Bruxelles. Pp. 1-38.
642 THE JOURNAL OF GEOLOGY.
have differed materially in their results. Mr. W J McGee esti-
mated that the mean age of the earth is 15,000 million years,
and that 7,000 million had elapsed since the beginning of Paleo-
zoic time." In a subsequent note he modifies this conclusion and
gives as a mean estimate 6,000 million years, of which 2,400 mil-
lion have elapsed since the beginning of the Paleozoic. This is
based on a minimum estimate of the age of the earth of 10,000,-
ooo years anda maximum estimate of five million million (5,000,-
000,000,000) years.* Professor Warren Upham concludes that
Quartenary time comprises about 100,000 years. He applies
Professor Dana’s time-ratio, and finds on this basis that the
time needed for the earth’s stratified rocks and the unfold-
ing of its plant and animal life must be about 100 millions of
years.3
From the foregoing estimates of geologic time the only con-
clusion that can be drawn is that the earth is very old, and that
man’s occupation of it is but a day’s spanas compared with the
eons that have elapsed since the first consolidation of the rocks
with which the geologist is acquainted.
When I began the preparation of this paper it was my inten-
tion to carefully analyze the sedimentary rocks of the entire geo-
logical series as exposed upon the North American continent. I
soon found, however, that the time at my disposal would make
this impracticable, and I decided to take up the history of the
deposits that accumulated in Paleozoic time on the western side
of our continent, in an area that for convenience I shall call the
Cordilleran sea. This was chosen as (1) I was personally
acquainted with many of its typical sections; (2) there was a
broad and almost uninterrupted sedimentation during Paleozoic
time ; and (3) there is a prospect for cbtaining more satisfactory
data as a basis of calculation, since calcareous deposits are in
excess of those of mechanical origin.
We will now consider certain points in relation to the growth
t American Anthropologist, Vol. 5, 1892, p. 340.
2 Science, Vol. 21, 1893, p. 309.
3 Am. Jour. Sci., Vol. 45, 1893, pp. 217-218.
GEOLOGIC TIME. 643
or evolution of the North American continent, as the deposition
of mechanical sediments depends to a considerable extent on the
character of the adjoining land area, and chemical sedimentation
is also influenced by it. =
GROWTH OF THE CONTINENT.
The Algonkian sediments were deposited in interior and bor-
dering seas that filled the depressions and extended over the
margins of the American continent. From the great thickness
of mechanical sediments it was evidently a period of elevated
land and rapid denudation. With the close of Algonkian time
extensive orographic movements occurred that outlined the sub-
sequent development of the continent. _The lines of the Rocky
Mountain and Appalachian ranges were determined, and the great
basins of sedimentation west of them defined. Subsequent move-
ments have elevated the old and formed new sub-parallel ranges.
These movements were often of long duration and also separated
by great intervals of time, as is shown by the long-continued
base levels of erosion during which the great thickness of calcar-
eous deposits accumulated in the Cordilleran and Appalachian
seas. Since Algonkian time the growth of the continent has
been by the deposition of sediments in the bordering oceans and
interior seas and lakes within the limits of the continental pla-
teau; and it is considered that the relative position of the conti-
nental plateau and the deep sea have not materially changed
during that period. How much the deposits on the continental
border have increased its area is unknown, as at present they are
largely concealed beneath the waters of the ocean. During Paleo-
zoic time the two areas of greatest known accumulation were in
the Appalachian and Cordilleran seas, where 30,000 feet or
more of sediments were deposited. In the Cordilleran sea sed-
imentation was practically uninterrupted (except during a short
interval in middle Ordovician time) until towards the close of
Paleozoic time. In the northern Appalachian sea it continued
without any marked unconformity, from early Cambrian to
the close of Ordovician time, and, south of New York, with
644 LE JOORNALE OF (GEOLOGY:
relatively little interruption, until the close of Paleozoic time.
Certain minor disturbances occurred along the eastern bor-
der of the sea, but they were not of sufficient extent to affect
a general conclusion—which is, that the depression of the areas
of deposition within the continental platform continued without
reversal of the subsidence during Paleozoic time. During Cam-
brian, and it may be late Algonkian time, the extended interior
Mississippian region was practically leveled by denudation, the
eroded material being carried into the Cordilleran and Appala-
chian seas, and, probably, to a sea to the south.
The sedimentation of the Mississippian area in Paleozoic time,
between the Appalachian and the Cordilleran seas, was small as
compared to that which accumulated in the latter. In Devonian
time there does not appear to have been any sedimentation in the
western portion of it west of the 94th meridian and east of the
Cordilleran sea, and it was slight in the same interval in the
Appalachian sea south of the 37th parallel.t There is little if
any evidence in the sediments of Paleozoic time to show that
they were deposited in the deep, open ocean; on the contrary,
they were largely accumulated in partially enclosed seas or
mediterraneans and on the borders of the continental plateau.
The former is particularly true of the sedimentation of the Cor-
dilleranand Appalachian seas and the broad Mississippian sea.
The close of the prolonged period of Paleozic sedimen-
tation was brought about by what Dana has termed the
“Appalachian revolution.” The topography of the continent
was more or less changed, and the conditions of sedimentation
that followed were unlike those that preceded. This revolution
raised above the sea level a considerable portion of the Cor-
dilleran and the Appalachian sea-beds and also of the Mississip-
pian sea, east of the 96th meridian and north of the 34th parallel.
*The non-occurrence of Devonian sediment has not yet been fully explained. It
has been suggested that the sea beyond the reach of mechanical sedimentation was too
deep for the deposition of calcareous deposits. It is more probable that the sea was
shallow and an area of non-deposition, or that its bed was raised to form a low,
level land surface at a base level of erosion that was subjected to very slight degrada-
tion.
GEOLOGIC TIME. 645
In its effect it may be compared to the Algonkian revolution’
that preceded the deposition of the Paleozoic sediments.
With the opening of new conditions the sedimentation of
Mesozoic time began upon the Atlantic border and over large
areas of the western half of the continent with the deposit of
mechanical sediments—sands, silts, etc-—during Jura-Trias time.
They are of a character that naturally follows a period of dis-
turbance of pre-existing conditions, and the formation of new
basins of deposition with more or less elevated adjoining land
areas. At its close orographic movements affecting the posi-
tions of the beds occurred upon the Pacific and Atlantic coasts,
and also, to a more limited degree, throughout the Rocky moun-
tain region. This does not appear to have extended over the
plateau region or the central belt between the 97th and 1o5th
meridians.
The Cretaceous formations have their greatest development
between the g7th and 112th meridians in Mexico and the United
States, in a broad belt which extends from the boundary of the
latter to the northwest into the British Possessions as far as the
61st parallel. They were of a marine origin until towards the
close of the period when a prolonged orographic movement
elevated a large area of the continent above sea level, and locally
upturned the Cretaceous strata in the Rocky mountain area.
The shoaling of the sea was followed by the formation of great
inland lakes, in which fresh water deposits succeeded the marine
and estuarian sediments. Over the coastal regions they were of
marine origin throughout.
The Tertiary sediments deposited on the Cretaceous are
marine on the Atlantic, Gulf of Mexico, and Pacific coasts, and
of fresh-water origin in the Rocky mountain and Great Plains
areas—where they were deposited in the great inland lakes out-
lined in the previous period.
*The term revolution is used to describe the culmination of a long series of
phenomena that finally resulted in a distinctly marked epoch in the evolution of the
continent. The “Appalachian revolution” began far back in the Paleozoic, and
culminated in the later stages of the Carboniferous and the Algonkian revolution,
probably began far back in Algonkian time.
646 THE JOURNAL OF GEOLOGY.
GEOGRAPHIC CONDITIONS ACCOMPANYING THE DEPOSITION OF
PALEOZOIC SEDIMENTS IN THE CORDILLERAN SEA.
The assumed area of the Cordilleran or Paleo-Rocky mountain
sea includes over 400,000 square miles between the 35th and 55th
parallels. To the eastward during lower and middle Cambrian
time a land area is thought to have extended from east of the
111th meridian across the continent to the Paleo-Appalachian
sea. This land was depressed toward the close of middle Cam-
brian time, and the Mississippian sea expanded over the wide >
plateau-like interior region, from the Gulf of Mexico on the
south to the Lake Superior region on the north; westward it
penetrated among the mountain ridges between the 1o5th and
111th meridians, laying down the upper Cambrian deposits that
are now found in New Mexico, Arizona, eastern Utah, the west-
ern half of Colorado, Wyoming, Idaho and Montana, and still
farther north into Alberta and British Columbia. During Ordo-
vician, Silurian, Devonian, and Carboniferous time this entire
Mississippian region, except portions in Devonian time, appears
to have been covered by a relatively shallow sea that was co-ex-
tensive with the Appalachian sea and that communicated freely
with the Cordilleran sea. During this same age, however, the
Rocky mountain area of New Mexico, Colorado, Utah, Wyom-
ing and Montana formed a more or less well-defined boundary
of ridges and islands between the Cordilleran and the interior sea
up to the 49th parallel. To the north of the latter the condi-
tions appear to have been the same as on the eastern side of the
continent, where the Appalachian sea communicated freely with
the Mississippian sea. From the data that we now have I think
that the Paleozoic ( Mississippian ) sea extended at times over
nearly all of the area subsequently covered by the Cretaceous
and the later formations between the Gulf of Mexico and the
Arctic ocean. This belt is bounded almost continuously on the
east and west by Paleozoic rocks that extend from the Arctic
ocean to Mexico, and whether of Cambrian, Ordovician, Silurian
or Devonian age they carry essentially the same fauna through-
out their extent. In the outcrops of lower strata that rise up
GEOLOGIC TIME. 647
through this Cretaceous area, the Cambrian, Ordovician, and
Carboniferous rocks are found encircling the pre-Paleozoic rocks.
Instances in which the Archean rocks have been met with
immediately beneath the Cretaceous in borings-in Dakota and
Minnesota are along the eastern border of the area, next to the
Archean rocks,—where it is probable that the Cretaceous over-
laps the Paleozoic to the Archean.
The western side of the Cordilleran sea seems to have been
bounded by a land area that separated it from the Paleozoic sea,
which extended through central California and the Pacific border
of British Columbia and Vancouver’s Island. From the posi-
tions of the Carboniferous deposits of California at the present
time it appears that this land varied from 100 to 150 miles in
width and was practically continuous along the western side of
the Cordilleran sea. This view is further strengthened by the
fact that the Carboniferous fauna of California has certain char-
acteristics which are not found in the Carboniferous of the Cor-
dilleran area. Our knowledge of conditions north of the 55th
parallel is limited by the want of accurate geologic data. If
Cambrian and Carboniferous rocks were not deposited in the
Mackenzie river basin and also on the eastern side of the area
now covered by Cretaceous strata, the inference is that during
Cambrian and Carboniferous time there was a land area to the
east and north of the northern Cordilleran sea that may have
been tributary to the latter.
SOURCE OF SEDIMENTS DEPOSITED IN THE CORDILLERAN SEA.
The sediments deposited in every sea or lake are derived
from land areas either by mechanical or chemical denundation.
Mechanical denudation results from the action of the waves
and currents along the shore and the agency of rain, frost, snow,
ice, wind, heat, etc., on the land. Rain is the most important
factor, and the result depends mainly upon its amount and the
slope or the gradient of the land. The general average of
denudation for the surface of the land areas of the globe, now
usually accepted, is one foot in 3,000 years. This varies locally,
648 THE JOURNAL OF GEOLOGY.
according to Sir Archibald Geikie, from one foot in 750 years to
one foot in 6,000 years.‘ Of the rate of denudation during
Paleozoic time about the Cordilleran sea we know very little, but
I think that it was relatively rapid in early Cambrian time and
during the deposition of the arenaceous sediments of the
Ordovician and Carboniferous. The material forming the argil-
laceous shales of the Cambrian and Devonian was supplied to
the sea more slowly. These conclusions are sustained by the
slight change in the character of the faunas where interrupted —
by the sands and pebbles of the Ordovician and Carboniferous
and the marked change between the base and summit of the
argillaceous shales. As a whole I think we are justified in
assuming a minimum rate of mechanical denudation—of con-
siderably less than one foot in 1,000 years—for the area tribu-
tary to the Cordilleran sea.
Chemical denudation is the removal of material taken into
solution by water. Mr. T. Mellard Reade has discussed this
phase of denudation in an admirable manner.? He came to the
conclusion, from what was known of the volume of water dis-
charged into the ocean per year, the average amount of material
in chemical solution and the area of land surface drained by the
rivers, that an average of 100 tons of rocky matter is dissolved
per English square mile per annum. Of this he says: “If we
allot 50 tons to carbonate of lime, 20 tons to sulphate of lime,
7 to silica, 4 to carbonate of magnesia, 4 to sulphate of mag-
nesia, I to peroxide of iron, 8 to chloride of sodium, and 6 to
the alkaline carbonates and sulphates we shall probably be as
near the truth as present data will allow us to come.’’3 By the
use of the data given by Mr. John Murray, in a paper on the
total annual rainfall on the land of the globe, and the relation of
rainfall to the discharge of rivers,+ I obtain 113 tons as the total
‘Brit. Assoc. Ady. Sci., Sixty-second Meeting, 1893, p. 21.
2 Proc. Liverpool Geol. Soc., Vol. III., pt. 3, 1877, pp. 212-235. Chemical Denuda-
tion in Relation to Geological Time, 1879, pp. I-61.
3 Loc. cit., p. 229.
4Scottish Geol. Mag., Vol. III., 1887, pp. 65-77.
GEOLOGIC TIME. 649
amount of matter in solution discharged into the Atlantic basin
per annum from each square mile of area drained into it. Of
this 49 tons consist of carbonate of lime and 5.5 tons of sulphate
and phosphate of lime.* -
Mechanical Sediments.—With the geographic conditions
described as prevailing during Paleozoic time, the source of
mechanical sediments later than the Middle Cambrian must have
been from the broken area on the eastern side that extended
100 to 200 miles to the eastward and to a much greater extent
from the land along the western side of the sea. The enormous
deposit of from 10,000 to 20,000 feet of mechanical sediments
in early Cambrian time is explained by the assumption of
favorable topographic conditions of denudation following the
Algonkian revolution and the presence of a land area over the
interior portion of the continent, and also, in all probability,
between the western side of the Cordilleran sea and the western
border of the continent. During this period the conformable
pre-fossiliferous strata of the Cambrian accumulated and about
6,000 feet of the lower fossiliferous rocks as they occur in the
Eureka district of central Nevada. Following the depression of
the continent, which carried down the central area and also
introduced the upper Cambrian ( Mississippian) Sea into the
Rocky mountain area of Colorado, etc., there were deposited of
mechanical sediments in central Nevada:
Ordovician sands, - - - - - = 500 feet.
Devonian fine argillaceous muds, - - - 2.000% ss
Lower Carboniferous sands, - - - = 2 0@0
Upper Carboniferous conglomerate and sands, - - 2,000 “
7,500 “
making a total of 7,500 feet of mechanical sediments, the remain-
ing portion of the section (15,150 feet) being limestone.
The following table exhibits the relative thickness of
*Total amount removed in solution per annum by rivers, 762,587 tons per cubic
mile of river water. Total discharge of river water per annum into the Atlantic, 3,947
cubic miles. Area drained, 26,400,000 square miles. Amount of carbonate of lime
per annum, 326,710 tons per cubic mile of river water; of sulphate and phosphate of
lime, 37.274 tons.
650 THE JOURNAL OF GEOLOGY.
mechanical and chemical deposits in the Cordilleran sea after
the middle Cambrian subsidence :
Wasatch. Central Southwest Montana. Alberta.
Nevada. Nevada.
Mechanical Sediment, - - 10,000 7,500 2,500 1,000 4,600
Chemical Sediment, - - 10,400 15,150 13,000 4,000 15,000
IRB, oe SSS T 2 is g
If an average is taken of the mechanical sediment deposited
subsequent to the close of middle Cambrian time, it will be found
to be about 5,000 feet for the entire area, which, | think, does
away with any necessity to assume an additional hypothetical
land area for the source of the mechanical sediment. The fine
sand composing the quartzites and the silt forming the shales, as
well as the fine conglomerate of later deposits, were derived from
the adjoining land areas, and, in all probability, currents swept
through from the ocean to the south or north, distributing the
mud and sand contributed from the rivers and streams along the
shores.
Chemical Sediments.—The present supply of the carbonate of
lime, silica, etc., contained in sea-water is derived from waters
poured into the sea by rivers and streams. The Cordilleran sea
undoubtedly received a large contribution from the adjoining
land areas, but a considerable amount was possibly derived from
an oceanic current that circulated through it as the southern
equatorial current of the Atlantic now sweeps through the
Caribbean. From the vast deposits of carbonate of lime it
might be assumed, @ priori, that the waters of a Mississippi or
Amazon were poured into it, but there is not any evidence of
the existence of such a river, although the tributary area may
have been very large in Cambrian and Carboniferous time, if the
drainage of the country west of Hudson’s Bay was to the west-
ward.
Conditions of Deposition——With free communication into the
open ocean on the south, and probably on the north, during
most of Paleozoic time strong currents must have circulated
through the Cordilleran sea. The broad distribution of
GEOLOGIC TIME. 651
mechanical sediments of a uniform character clearly shows this
to have been the case, especially in pre-Silurian (Ordovician )
time. The present known distribution of the mechanical sedi-
ments indicate that they were mainly brought into the sea from
the west,’ although a vast amount was derived from the land
on the eastern side in pre-Ordovician time. They were quite
evenly distributed over the sea bed, except where local accu-
mulations of silt and sand occurred near the larger sources
of supply, or in the direction of powerful currents within the
Sadana
The conditions of the deposition of the carbonate of lime are
less clearly understood than those governing mechanical sedi-
ments, and I shall enter upon the discussion of them at consid-
erable length. There are three methods by which it usually is
considered that it may be deposited: 1. Agency of organisms ;
2. Chemical precipitation; 3. By mechanical methods.
It is the general opinion of geologists that limestone rocks
are the result almost entirely of the consolidation of lime
removed from the sea water through the agency of life, and that
they consist of the remains of foraminifera, crinoids, corals, etc.,
or their fragments, embedded in a more or less crystalline matrix
resulting from subsequent alteration of the original deposits.
This, however, has been seriously questioned. Sorby, in giving
his general conclusions of an extensive microscopic examination
of limestones, states that:
Even if it were possible to study in a detached state the finer
granular particles which constitute so large a part of many lime-
stone formations, it would usually be impossible to say whether
they had been derived from organisms which can decay down
into granules, or from other organisms which can only be worn
down into granules, or from ground-down older limestone, or, in
some cases, from carbonate of lime deposited chemically as gran-
tileSta wt at cee) heshape sand) character of the identifiable
fragments do, indeed, prove that much of this must have been
derived from the decayed and worn-down calcareous organisms ;
*Geol. Expl. Fortieth Parallel, Vol. I., 1878, p. 247.
652 THE JOURNAL OF GEOLOGY.
and very often we may reasonably zfer that the greater part, if
not the whole, was so derived; but, at the same time, it is impos-
sible to prove, from the structure of the rock, whether some or
how much was derived from limestones or earlier date, or was
deposited chemically, as some certainly must have been.
In their memoir on coral reefs and other carbonate of. lime
formations in modern seas, Messrs. Murray and Irvine show that
temperature of the water has a controlling influence upon the
abundance of species and individuals of lime-secreting organisms ;
high temperature is more favorable to abundant secretions of
carbonate of lime than high salinity.?
Taking the samples of deep sea deposits collected by the
Challenger as a guide, the average percentage of carbonate of
lime in the whole of the deposit covering the floor of the ocean
is 36.83 ; of this it is estimated that fully 90 per cent. is derived
from pelagic organisms that have fallen from the surface water, the
remainder of the carbonate of lime having been secreted by
organisms that laid on, or were attached to, the bottom. The
estimated area of the various kinds of deposits, the average
depth, and the average percentage of carbonate of lime to each
are shown in the following table:
TABLE showing the Estimated Area, Mean Depth, and Mean Percentage of CaCOs, of
the different Deposits.
: Area Mean depth} Mean per ct.
eposit: seunreeniee! in farhora! of CaCO.
( Red clay, 50,289,600 2727 6.70
Oceanic | Radiolarian ooze, 2,790,400 2804 4.01
Oozes and <~ Diatom ooze, 10,420,600 1477 22.96
Clays | Globigerina ooze, 47,752,500 1996 64.53
|. Pteropod ooze 887,100 1118 79.26
Memisenous \ ees and pa 3,219,800 710 86.41
Deposits / ther terrigenous depos-
its, blue mud, etc. 27,899,300 1016 19.20
Loe. cit., p. 82.
“We have little knowledge as to the thickness of these depos-
its, still such as we have goes to show that in these organic cal-
‘Quart. Jour. Geol. Soc. London, Vol. 35, 1879, pp. 61-92.
2 Proc. Roy. Soc, Edinburgh, Vol. 17, 1890, p. 81.
GEOLOGIC TIME. - 653
careous oozes and muds, we have a vast formation greatly exceed-
ing in bulk and extent the coral reefs of tropical seas; they are
most widely distributed in equatorial regions, but some patches
of Globigerina ooze are to be found even within the Arctic circle
in the course of the gulf stream.’’*
The percentage of carbonate of lime contained in deposits
accumulating at different depths, as obtained from 231 samples
collected by the Challenger, is shown in the following tabulation :
I4 cases under 500 fathoms, m. p. c. 86.04
Ti a6 si 500 to 1000 as 6s 66.86
mi i 1000 to 1500 a6 Bt sate 70.87
42 fic fe 1500 to 2000 as be 69.55
68 sf s 2000 to 2500 se of 46.73
65 ee 0G 2500 to 3000 ef as 17.36
8 ‘s 3000 to 3500° ag a 0.88
2 “ts as 3500 to 4000 og te 0.00
I ug ss 4000 uy aS trace.
The fourteen samples under 500 fathoms are chiefly coral
muds and sands, and the seven samples from 500 to 1000 fath-
oms contain a considerable quantity of mineral particles from
continents or volcanic islands. In all the depths greater than
1000 fathoms the carbonate of lime is mostly derived from the
shells of pelagic organisms that have fallen from the surface
waters, and it will be noticed that these wholly disappear from
the greater depths.”
By a series of experiments Messrs. Murray and Irvine found:
“That although sea water under certain conditions may take up
a considerable quantity of carbonate of lime in solution, yet it is
unable permanently to retain in solution more than is usually
found to be present in sea water, and it is owing to this that the
amount of carbonate of lime is so constantly low. The reaction
‘between organic matter and the sulphates present in sea water
(to which we have referred) tends also to keep the amount of
carbonate of lime in solution at about one-half (0.12 grms.) of
what it might contain (0.28 grms. per litre). This peculiarity
of sea water, in taking up a large amount of amorphous carbon-
™Loc. cit., pp. 82-83.
A ILOCs Cli, [Oo tevin
654 THE JOURNAL OF GEOLOGY.
ate of lime and throwing it out in the crystalline form, accounts
for the filling up of the interstices of massive coral with crystal-
line carbonate in coral islands and other calcareous formations,
so that all traces may ultimately be lost of the original organic
Structures:
The authors explain the disappearance of shells and lime
deposits in the greater depths of the ocean by their being dis-
solved by the carbonic acid in the water, which is present in larger
quantity at great depths and also is produced by the decompo-
sition of the animal matter of the shell and of the various organ-
isms living in the water and onthe bottom. They conclude that:
On the whole, however, the quantity of carbonate of lime
that is secreted by animals must exceed what is re-dissolved by
the action of sea water, and at the present time there is a vast
accumulation of the carbonate of lime going on inthe ocean. It
has been the same in the past, for with a few insignificant excep-
tions all the carbonate of lime in the geological series of rocks
has been secreted from sea water, and owes its origin to organ-
isms in the same way as the carbon of the carboniferous forma-
tions; the extent of these deposits appears to have increased
from the earliest down to the present geological period.’
In their report on deep sea deposits, collected by the Chal-
lenger Expedition, Messrs. Murray and Renard state that the
chemical products formed in situ on the floor of the ocean nearly
all originate in a sort of broth or ooze, in which the sea water is
but slowly renewed. Many of them appear to be formed at the
surface of the deposit—at the line separating the ooze from the
superincumbent water, where oxidation takes place. In the
deeper layers of the deposit a reduction of the higher oxides fre-
quently occurs, and at the surface of the mud or ooze there are
many living animals, as well as the dead remains of surface
plants and animals.
tLoc. cit., pp. 94-95.
2 Loc. cit., p. 100.
3 Report on the Scientific Results of the Voyage of M. M.S. Challenger. Deep-
Sea Deposits, 1891, p. 337.
GEOLOGIC TIME. 655
DESCRIPTION OF MAP.
On the’map the hypothetical areas of the Cordilleran, Mississippian and Appa-
lachian seas are clearly indicated. The land area west of the Cordilleran sea is
numbered No. 1. The Californian sea and the area of Paleozoic deposits of western
British Columbia No. 10. The northern extension of the Cordilleran sea (No. 9) is
continued as the Paleozoic-devonian sea to the Arctic ocean, The early Cambrian
land area (No. 2) east of the Cordilleran sea must have been more or less covered by
water during later Paleozoic time. The area now covered by Mesozoic deposits,
indicated by No. 3, was presumably covered by the westward and northward extension
of the Paleozoic-Mississippian sea. The area east of the Appalachian sea is indicated
by No. 4; and the supposed land barrier between the Hudson Bay and the Mississip-
pian sea by No. 6; it is not improbable that during Ordovician or Silurian time a sea
may have connected the two latter seas. The region to the south, indicated by No. 5,
is supposed to have been covered by the southward extension of the Appalachian, Mis-
sissippian and Cordilleran seas. It is now covered by deposits of Mesozoic and
Cenozoic seas.
A more detailed description of the map can be gained from the section on the
growth of the continent and on the geographic conditions accompanying the different
depositions of Paleozoic sediments in the Cordilleran sea.
656 THE JOURNAL OF GEOLOGY.
They also conclude that practically all the carbon of marine
organisms must ultimately be resolved into carbonic acid, the
quantity of that acid produced in this way must be enormous,
and cannot but exert a great solvent action not only on the dead
calcareous structure, but also on the minerals in the muds on the
floor of the ocean. Of the effect of this destructive action, they
say: ‘In all cases, however, calcareous structures of all kinds
are slowly removed from the bottom of the ocean on the death
of the organisms, unless rapidly covered up by the accumulating
deposits, and in this way protected to a certain extent from the
solvent action of the sea-water. It is evident from the Challen-
ger investigations that whole classes of animals with hard calcar-
eous shells and skeletons, remains of which one might suppose
would be preserved in modern deposits, are not there repre-
sented ; although they are now living in immense numbers in the
surface waters or on the deposits at the bottom in some regions,
yet all traces of them have been removed by solution. A similar
removal of calcareous organic structures has undoubtedly taken
place in the marine formations of past geologic ages.’
From the preceding statements it is evident that initially the
greater part of the carbonate of lime is taken from the sea water
by organic agency, but in the working over of this material in
the chemical laboratory at the bottom of the sea a considerable
portion is taken up by the sea water as amorphous carbonate of
lime and thrown out in the crystalline form to form the matrix
of the undissolved shells, etc.3
Mr. Bailey Willis has recently studied the question of the
deposition of carbonate of lime, and states that ‘chemists
describe two conditions under which bicarbonate of lime may be
decomposed into neutral carbonate and carbonic acid: Ist, by
diminution of the tension of the carbonic acid in the atmosphere ;
2nd, by agitation of the solution.”
tLoc. cit., p. 255.
2 Loc. cit., p. 277. In this connection I wish to ask the student to read Messrs.
Murray and Irvine’s remarks on pp. 97-99, Proc. Roy. Soc., Edinburgh, Vol. 17, 1890.
3Proc. Roy. Soc., Edinburgh, Vol. 17, 1890, pp. 94-95.
GEOLOGIC TIME. 657
‘Theoretically either one of three things may occur to the
neutral carbonate of lime, if it be thrown out of solution by
either one of these processes. The carbonate may be redis-
solved, deposited as a calcareous mud, or built-into organic
structure.’ He studied some recent limestone deposited in the
Everglades of southern Florida and found it to be formed of
fragments of shells embedded in calcite. Hestates that, ‘‘ Under
the microscope the unaltered structure of the organic fragments
is strikingly different from that of the coarse holocrystalline
matrix, in which it is apparent that the crystals developed in
place. Were this a limestone of some past geologic period it
would be concluded, on the evidence of the crystalline texture
of some parts of it, that it had been metamorphosed, and that the
organic remains now visible had escaped the process which
altered the matrix. But the observed conditions of its formation
preclude the hypothesis of secondary crystallization.”* Appar-
ently the crystalline matrix is one primary product, and the cal-
careous mud is another, which being precipitated in the solution
remains an incoherent sediment.
I think we may accept the conclusion that the deposition of
carbonate of lime is by both organic agency and chemical pre-
cipitation. It is not necessary to speak of deposition by mechan-
ical methods except in relation to the deposition of chemically
derived granules. This probably takes place, and may bea very
important factor in the formation of limestones in seas receiving
a large supply of calcium from the land. Calcareous conglom-
erates do not enter as a prominent deposit in the Cordilleran area.
There is no evidence in the marine, geologic formations of
this continent that they were deposited in the deep sea; on the
contrary they are unlike such deposits and bear positive evidence
of having been laid down in relatively shallow waters. Lime-
stones with ripple-marks and sun cracks occur, and beds of
ripple-marked sandstones alternate with shales and limestones.
The more massive limestones, however, appear to have accumu-
lated in deeper water. The conditions in the Cordilleran sea
tSee Mr. Willis’ article in Journal of Geology, Chicago, September, 1893.
658 THE JOURNAL OF GEOLOGY.
were, I think, more favorable for rapid deposition than in the
deep open ocean, but probably not as favorable as about coral
reefs and islands. The limestones, and often the contained fos-
sils, clearly indicate the presence of many of the same conditions
of deposition as described by the authors I have quoted. More
or less decomposed shells occur in nearly every limestone and a
large proportion of limestone ; especially the non-metamorphic
marbles clearly show that they were deposited under the influ-
ence of the agencies at work in the laboratory of the sea. Willis
states that this occurs in the shallow waters of the Everglades of
Florida, and there is no@ priori reason why it did not occur through-
out geologic time,—on the contrary, there is no doubt that it did.
Rate of deposit in former times——It has frequently been
assumed that in the earlier epochs the conditions were more favor-
able for rapid denudation, and in consequence thereof the trans-
portation and deposition of sediment was greater. Professor
Prestwich considers * that prior to the sedimentary rocks the land
surface consisted of crystalline or igneous rocks subject to rapid
decomposition owing to the composition of the atmosphere and
to their inherent tendency to decay. They must have yielded to
wear and removal with a facility unknown amongst mechanically
formed and detrital strata where erosion operates. He thus
accounts for one of the factors that gave the large dimensions
and thicknesses of the earlier formations. Mr. Wallace thinks
that geological change was probably greater in very remote
times,’ stating that all tellurac action increases as we go back
into the past time, and that all the forces that have brought
about geological phenomena were greater.3
Geology, Vol. 1, 1886, pp. 60-61.
2Island Life, 2nd Ed., 1892, pp. 223-224.
3Sir William Thompson (Lord Kelvin), inferred from his investigations upon the
cooling of the earth, that the general climate cannot be sensibly affected by conducted
heat at any time more than 10,000 years after the commencement of the superficial
solidification. Treatise on Natural Philosophy, Cambridge, 1883, Vol. 1, pt. 2, p.
478. Of the degree of the sun’s heat we know so little that conjectures in relation to
it have little force against the conditions indicated by the sedimentary, rocks and their
contained organic remains.
GEOLOGIC TIME. 659
Dr. Woodward says, on the opposite view, that in the earliest
geological periods each bed of sand, clay, limestone, etc., had
actually to be formed, and that later deposits had the older sedi-
mentary ones to furnish material, and, therefore, the newer
deposits were laid down more rapidly.t This does not impress
me strongly ; but from my experience among the Paleozoic rocks
I agree with Sir A. Geikie, that ‘‘We can see no proof whatever,
nor ever any evidence which suggests that on the whole the rate
of waste and sedimentation was more rapid during Mesozoic and
Paleozoic time than it is to-day.’
Professor Huxley, in his presidential address to the Geologi-
cal Society of London in 1870, treats of the distribution of
animals and says of his hypothesis that it ‘requires no supposi-
tion that the rate of change in organic life has been either greater
or less in ancient times than it is now; nor any assumption,
either physical or biological, which has not its justification in
analogous phenomena of existing nature.” 3
In the Grand Canon of the Colorado, Arizona, there are
11,950 feet of strata of Algonkian age extending unconformably
beneath the Cambrian. There is nothing in this section to indi-
cate that the conditions of deposition were unlike those of the
strata of Paleozoic and Mesozoic time. The sandstones, shales,
and limestones are identical in appearance and characteristics
with those of the latter epoch. The deposition of sulphate
of lime and gypsum occurred abundantly in the upper portions
of the series, and salt is collected by the Indians from the depos-
its formed by the saline waters issuing from the sandstone 8,000
feet below the summit of the series. The sandstone and shales
were deposited in thin, even laminz and layers, and the sun cracks
and ripple marks give evidence of slow, uniform deposition. In
the upper part of Chuar terrane there are 235 feet of limestone.
And in one of the layers of limestone, 2,700 feet below the sum-
mit of the Chuar terrane, I find abundant evidence of the pres-
tGeol. England and Wales, 2nd Ed., 1887, p. 23.
2 Rept. Sixty-second Meeting Brit. Assoc. Ady. Sci., 1892, p. 19.
3Quart. Jour. Geol. Soc., Vol. 26, 1870, p. lxii.
660 THE JOURNAL OF GEOLOGY.
ence of spiculea of sponges, and what appear to be worn frag-
ments of some small fossils. There is absolutely nothing to indi-
cate more rapid denudation and corresponding deposition in this
early pre-Cambrian series than we find in the Paleozoic, Mesozoic
or Cenozoic formations.
PALEOZOIC SEDIMENTS OF THE CORDILLERAN SEA. :
The great sections of sedimentary rocks in Arizona, Nevada,
Utah, Montana, and in Alberta, B. A., all bear evidence that the
sediments of which they are built up were deposited in a con-
nected and continuous sea that extended from the vicinity of the
34th parallel, on the south, to the Arctic ocean on the north.
Judging from the data now available, the width of this sea varied
from 300 miles in Nevada to 500 miles on the line of the 4oth
parallel, and, with interruptions by mountain ridges, to 250 miles
on the 49th parallel. It appears to have narrowed to the north
in Alberta, British Columbia. Roughly computed, it covered
south of the 55th parallel 400,000 square miles exclusive of any
extension westward into northern-central California and south-
western Oregon and to the eastward over the area subsequently
covered by the great interior Cretaceous sea. There is also an
addition that might be made to allow for the contraction of the
area by the later north-and-south faults and thrusts. Dr. G. M.
Dawson estimates that in the Alberta and British Columbia area
the width of the zone of the Paleozoic rocks has probably been
reduced one-half by the folding and faulting, or from 200 to 100
miles.* This area assumed for the Cordilleran sea is on this account
probably one-half less than it was before the Appalachian revolution.
The Wasatch section, on the eastern side of the area under
consideration, has 30,000 feet of strata, of which 10,400 feet are
limestone.? Further to the west, 250 miles W.S.W., at Eureka,
Nevada, there 30,000 feet of strata in the entire section, and of
this amount 19,000 feet are referred to limestone.3 In the Pahran-
agat range and vicinity, 200 miles south of the Eureka section,‘
* Bull. Geol. Soc. Am., Vol. 2, 1891, p. 176.
? Geol. Expl. Fortieth Parallel, Vol. 1, 1878, pp. 155-156.
3 Mon. U.S. Geol. Survey, Vol. 20, 1892, p. 178.
4 Loc. cit. pp. 186-200.
GEOLOGIC TIME. 661
the limestones of the Paleozoic measure over 13,000 feet ina
section of 13,500 feet. This section includes only 350 feet of the
upper beds of the lower quartzite series, which is upwards of
11,000 feet in thickness in the Schell Creek range of eastern
Nevada.*
On the eastern side of the area, in Montana, 300 miles north
of the Wasatch section of Utah, the deposit of Paleozoic sedi-
Ment is Mess pvolume yi Ay Ce Reales “section, gives 3,800
feet of limestone in 5,000 feet of strata.2, This does not include
the 6,000 feet or more of sediments that occur below the fossilif-
erous Cambrian. I believe that the Paleozoic section will be
found to be considerably thicker to the westward in Idaho.
Continuing to the north 450 miles, the sections measured by Mr.
R. G. McConnell, give 29,000 feet of Paleozoic strata, including
14,000 feet of limestone. Ina “‘ Note on the Geological Structure
of the Selkirk Range,” Dr. Geo. M. Dawson describes a section
containing upwards of 40,000 feet of mechanical sediments, which
he refers largely to the Cambrian‘.
The Paleozoic limestones extend to the north, on the line of
the eastern Rocky Mountains, to the Arctic ocean. In latitude
55 to 60° N. the Devonian limestones are over 2,500 feet in
thickness, and there other still lower Paleozoic rocks that have
not yet been studied in detail. The Devonian limestones extend
700 miles in the valley of the Mackenzie, from Great Slave
Lake to below Fort Good Hope.’ No Carboniferous limestones
have been described from this region.
Tabulating the sections south from the 55th parallel and
allowing for a great thinning out of the sediments in Idaho and
Montana, we obtain an approximate general average of 21,000
feet of strata, of which 6,000 feet are limestone over an area
estimated to include 400,000 square miles. Each square mile
*Geol. and Geog. Surveys West of tooth Merid., Vol. 3; Geology, 1875, p. 167.
? Author’s manuscript.
3 Geol. and Nat. Hist. Sur. Canada; Am. Rep., 1866, pp. 17, D-30 D.
4 Bull. Geo. Soc. Am. Vol. 2, 1891, p. 168.
5 Rept. Expl. Yukon and Mackenzie Rivers Basins, N. W. Terr. Geolo. & Nat.
Hist. Sur. Canada, Vol. 4 (1888—’89), 1890, pp. 13 D-18 D.
662 LGM JOWUINAVE QUE (GIBOULOG IZ,
includes 27,878,400 cubic feet of limestone for each foot in thick-
ness and 167,270,400,000 cubic feet for a thickness of 6,000 feet,
which, with an average of 12.5 cubic feet to ton, gives 13,381,-
632,000 tons of limestone and impurities per square mile. The
result of ten analyses of clear limestones within the central por-
tion of area gives an average of 76.5 per cent. of carbonate of
lime.t. Taking 75 per cent. as the proportion of pure carbonate
of lime (after deducting 50 per cent. to allow for arenaceous and
argillaceous material in partings of strata, etc.), there remain.
5,018,112,000 tons per square mile; multiplying this by 400,000
the result gives the number of tons of carbonate of lime that were
deposited in what we know of the Cordilleran sea in Paleozoic
time, or 2,007,244,800,000,000 tons, or two billion million tons in
round numbers.
The following mode of presentation of the above was sug-
gested by Mr. Willis:
«In order to proceed with a calculation of the period required to form this thickness
of 15,000 feet of mechanical sediment plus 6,000 feet of calcareous sediment, it is
necessary, Ist, to compute the cubic volumes of the sediments; 2d, to estimate the area
from which they were derived; and, 3d, to divide the cubic contents of the sediments
by this land area. The result thus obtained represents the depth of erosion required
to furnish the whole deposit, from which we may estimate the time under different
assumptions of the rate of erosion.
But if we express amounts in cubic feet or tons the figures pass all comprehension ;
therefore, to simplify the statement, it is well to use a mile-foot as the unit of volume,
that is, the volume of one mile square and one foot thick. (1 mile-foot=.79 Kilometre-
metres). This is equal to 223,000 tons, if 1214 cubic feet of limestone equal one ton.
Thus stated mechanical sediments covering 400,000 square miles and 15,000 feet
thick contain 6 billion mile-feet (4,740 million Kilometre-metres); and calcareous
sediments covering the same area and 6,000 feet thick correspond to 2 billion 4 hun-
dred million mile-feet (1,896 million Kilometre-metres). In the calcareous sediments
a liberal allowance of one-half may be made for arenaceous and argillaceous matter
in the limestone and partings, and analyses of ten clear limestones within the central
part of the area give a little more than 75 per cent. of carbonate of lime. Applying
these reductions we get 900 million mile feet (711 million Kilometre-metres) of pure
carbonate of lime.
DURATION OF PALEOZOIC TIME IN:THE CORDILLERAN AREA.
Estimates from Mechanical Sedimentation —The land area tribu-
tary to the Cordilleran sea was larger before the depression of
*Geol. Expl. Fortieth Par. Vol. 23; Mon. U.S. Geol. Survey, Vol. 20.
GEOLOGIC TIME. 663
the continent, towards the close of middle Cambrian time than
during subsequent Paleozoic time. It included a portion of the
region to the eastward and probably a belt of land extending
well towards the Pacific coast of the continental-plateau. The
interior (Mississippian) region, west of the goth meridian, proba-
bly drained into the sea to the south, forming a Cambrian Missis-
sippi river prior to middle Cambrian time. This limits the
Cambrian drainage into the Cordilleran sea to an area estimated
at 1,600,000 square miles. The average thickness of mechanical
sediments deposited before upper Cambrian time is estimated at
from 10,000 to 15,000 feet. Taking the minimum of 10,000
feet and the assumed drainage area of 1,600,000 square miles
and the rate of denudation at one foot in 1,000 years, it would
have required 2,500,000 years to carry to the sea and distribute
the 10,000 feet of sediment. This means the deposition of .048
of-an inch per year, which is very small if the supposed con-
ditions of denudation and transportation were as favorable as the
character and mode of occurrence of the sediments indicate. If
one-fourth of an inch per year is assumed as the rate of deposi-
tion, the 10,000 feet of sediment would have accumulated in
480,000 years or, in round numbers, in 500,000 years, which
increases the rate of denudation to one foot in 200 years."
CAMBRIAN MECHANICAL SEDIMENTS.
. . : Rate of deposition over sea area of
oPtg.of erosion overland area | Time in years for ero: | sooyoon equate miles for strata 10,00
yeas q 4 p ; feet thick,
I foot in 3,000 years, - - 7,500,000 I foot in 750 years, or .016 inch
per annum.
I foot in 1,000 years, - - 2,500,000 I foot in 250 years, or .048 inch
per annum.
I foot in 200 years - - - 500,000 I foot in 50 years, or .24 inch
per annum.
In view of the evidence of rapid accumulation contained in the strata themselves
the most rapid rate of deposition here stated, namely, .24 inch per annum, is con-
sidered as the most probable.
*By Mr. Willis’ method (azze, p. 662, foot note) the mechanical sediments of
the Paleozoic age for the area under consideration corresponds to 6 billion mile-feet.
664 THE JOURNAL OF GEOLOGY.
In dealing with the post-middle Cambrian mechanical sedi-
ments we have a somewhat different problem, but, as a whole,
rapid deposition is indicated. For instance, the Eureka quart-
zite of the upper Ordovician is a bed of sandstone, varying from
200 to 400 feet in thickness, distributed over a wide area,—per-
haps 50,000 square miles. It is made almost entirely of a white,
clean sand that was deposited in so short an interval that the
Trenton fauna in the limestone beneath it and in the limestones
above it is essentially the same. The sand appears to have been
swept rapidly into the sea and distributed by strong currents.
The same is true of the 3,000 feet of the lower Carboniferous
sand and the 2,000 feet in the upper portion of the Carboniferous,
while the shales of the upper Devonian accumulated more slowly.
In this connection we must bear in mind that during the long
periods in which the calcareous sediments forming the limestones
were being deposited, the tributary land areas were in all proba-
bility base-levels of erosion, and chemical denudation was pre-
paring a great supply of mechanical material that, on the raising
of the land, was rapidly swept into the sea and distributed. In
this manner the time period of actual mechanical denudation was
materially shortened, yet, on account of the manifestly slower
deposition of the Devonian shales, the rate of denudation should
be assumed as less than during Cambrian time.
In post-Cambrian time the area of the land surface was
materially reduced by subsidence, which did not, however, greatly
extend the Cordilleran sea, and it may fairly be estimated at
600,000 square miles. The depth of mechanical sediments
already estimated is 5,000 feet, and their volume at two billion
mile-feet. Dividing the volume by the area of erosion we get
3,300 feet as the depth of erosion required.
Again, applying different rates of erosion, with allowance for
slow progress of degradation during Devonian time, we have:
Of this total the greater part, namely, two-thirds or 4 billion mile-feet, are of Cam-
brian age. Dividing this volume by the land area just given, 1,600,000 square miles,
we get 2,500 feet as the depth of erosion during the formation of the Cambrian
mechanical sediments. Assuming different rates of erosion we may obtain times dif-
fering as follows:
CHOLOCTC WE: 665
POST-CAMBRIAN MECHANICAL SEDIMENTS.
Rate of erosion over land area Time required for re- Rate of deposition in sea of 400,000
of 600,000 square miles. moval of 3,300 feet. square miles, for 5,000 feet of strata.
I foot in 3,000 years, - - 9,900,000 years I foot in 1,980 years, or .006
inch per annum.
I foot in 1,000 years, - - 3,300,000 years 1 foot in 660 years, or .og inch
per annum.
I foot in 200 years, - - - 660,000 years I foot in 132 years, or .18 inch
per annum.
The rate of one foot in 200 years is assumed as the most
probable and 660,000 years as the time required for the removal
and deposition of the 5,000 feet of post-Cambrian mechanical
sediments.
There is one factor that may need to be taken into considera-
tion in estimating the time duration of the deposition of the
mechanical sediments of the Cambrian and pre-Cambrian of the
northern portion of the Cordilleran sea that would materially
lengthen the period. Dr. George M. Dawson describes the
Nisconlith series, especially in the Selkirk range of British
Columbia, as composed of “blackish argillite-schists and phyl-
lites, generally calcareous, with some beds of limestone and
quartzite, 15,000 feet. It is correlated with the Bow River
series, which contains, in the upper portion, the lower Cambrian
yy
fauna. The presence of these calcareous beds indicates a slower
rate of deposition than we have estimated for the lower portion
of the Cambrian series over the greater part of the Cordilleran
sea; but as yet the correlation with the sediments of the Cordil-
eran sea is not sufficiently well established to warrant our allow-
ing a greater time period to the Cambrian on this account.
Estimates from Chemical Sedimentation—We have estimated
that the Paleozoic sediments of the Cordilleran sea contain
2,007,244,800 million tons (goo million mile-feet) of carbonate
of lime, which was derived by organic or chemical agencies from
the sea water to which it was contributed by the land. If oceanic
circulation could be excluded from the problem we might pro-
tBull. Geol. Soc. Amer., Vol. II., 1891, p. 168.
666 LE JOURNAL OF NGHOLOGVE
ceed directly to estimate the time required to obtain this amount
of lime from the land area tributary to the Cordilleran sea. It
may be well to make such an estimate on the basis that the
area of denudation tributary to the Cordilleran sea in post-
middle Cambrian time had 600,000 square miles from which
30,000,000 tons of carbonate of lime and 12,000,000 tons
of sulphate of lime were derived per annum,’ if we assume
T. Mellard Reade’s rate of erosion—of 50 tons of carb-
onate of lime and 20 tons of sulphate of lime per square mile —
per annum. If all of the 42,000,000 tons (equal to 18.8 mile-
feet) per annum were deposited within the limits of the Cordil-
leran sea, it would have taken 47,790,000 years for the accum-
ulation of the carbonate of lime now estimated to have been
deposited in the Cordilleran sea. Such a result is manifestly
a maximum based on the consideration of one set of phenomena.
In addition, however, to this supply of calcium the geographic
conditions appear to have been favorable to the free circulation
of oceanic currents through the Cordilleran sea, and the tempera-
ture was favorable to extensive evaporation and to the develop-
ment of organic life, as shown by the occurrence of corals
in the middle and upper portions of the Paleozoic, from the
Mackenzie river basin on the north to southern Nevada on the
south. These conditions would reduce the time necessary for
the deposition of the carbonate line.
Ocean water of the present time contains in solution
151.025000 tons of solid matter per cubic mile, which is divided
among various salts. A comparison of the matter in the sea
and river water shows that the sea contains 3.85 parts of mag-
nesium to one of calcium, and river water contains three parts of
calcium to one of magnesium. The silica and alumina of the river
water disappears in sea water, while the sodium is accumulated.
It is from these considerations and the fact that limestones are
"Messrs. Murray and Renard consider that organisms have the power of secreting
the carbonate of lime from the sulphate of lime contained in the seawater by chemical
reaction. For an account of the chemical action that takes place in the sea water, see
report of the Deep-Sea Deposits of the Challenger Expedition.
GCEROLOGIE AMV: 667
so largely formed of carbonate of lime that I have taken the
latter as a basis for estimates upon the rate of chemical sedi-
mentation, an allowance being made for the presence of silica,
alumina and magnesium in the limestones. =
Rate of Deposition of Recent Deposits——Of the rate of depo-
sition in recent deposits Messrs. Murray and Renard state,
in their report on the deep-sea deposits, that: “It must be ad-
mitted that at the present time we have no definite knowl-
edge as to the absolute rate of accumulation of any deep-
sea deposit, although we have some information and some
indications as to the relative rate of accumulation of the different
types of deposits among themselves. The most rapid accumula-
tion appears to take place in the Terrigenous Deposits, and
especially in the Blue Muds, not far removed from the embouch-
ures of large rivers. Here no great time would seem to have
elapsed since the deposit was formed, so far at least as the
materials collected by the dredge, trawl, and sounding tube are
concerned.
“Around some coral reefs the accumulation must be rapid,
for, although pelagic species with calcareous shells may be
numerous in the surface waters, it is often impossible to detect
more than an occasional pelagic shell among the other calcareous
debris of the deposits.
“The Pelagic Deposits as a whole, having regard to the
nature and condition of their organic and mineralogical constit-
uents, evidently accumulate at a much slower rate than the
terrigenous deposits, in which the materials washed down from
the land play so large a part. The Pteropod and Globigerina
oozes of the tropical regions, being chiefly made up of the cal-
careous shells of a much larger number of tropical species, must
necessarily accumulate at greater rate than the Globigerina oozes
in extra-tropical areas or other organic oozes. Diatom ooze, being
composed of both calcareous and siliceous organisms, has, again,
a more rapid rate of deposition than the Radiolarian ooze, while
in a Red Clay there is a minimum rate of growth.” *
™Report on the scientific results of the voyage of H. M. S. Challenger; Deep-Sea
Deposits. 1891, pp. 411-412.
668 THE JOURNAL OF GEOLOGY.
Professor James D. Dana estimates that the rate of increase
of coral reef limestone formations, where all is most favorable,
does not exceed perhaps a sixteenth of an inch in a year, or five
feet in a thousand years. Of this he says, ‘‘ And yet such lime-
stones probably form at a more rapid rate than those made of
shells.”’?
Messrs. Murray and Irvine, in their valuable paper on coral
teefs and other carbonate of lime formations in modern seas, cal-
culate the total amount of calcium in the whole ocean to be
628,340,000 million tons; also they estimate that 925,866,500
tons of calcium are carried into the ocean from all the rivers of
the globe annually. At this rate it would take 680,000 years for
the river drainage from the land to carry down an amount of
calcium equal to that at present existing in solution in the whole
ocean. They, say further: “Again, taking the “Challlencens
deposits as a guide, the amount of calcium in these deposits, if
they be 22 feet thick, is equal to the total amount of calcium in
solution in the whole ocean at the present time. It follows from
this that, if the salinity of the ocean has remained the same as at
present during the whole of this period, then it has taken 680,000
years for the deposits of the above thickness, or containing
calcium in amount equal to that at present in solution in the
ocean, to have accumulated on the floor of the ocean.’’? Accord-
ing to this calculation the mean rate of accumulation over
existing: oceanic areas is 4g22>,. Or .000032 feet per annum.
Was the Deposition of Chemical Sediment More Rapid in Paleozoic
Time ?—It has been claimed that the quantity of lime poured into
the ocean in earlier times was greater than during the later epochs
of geological history,—this arising from the more rapid disin-
tegration of the Archean, crystalline and volcanic rocks. It is
undoubtedly a fact that the ocean was stocked in Archean and
Algonkian time with matter in solution that produced salinity,
but we have no evidence from chemical precipitation that more
* Corals and Coral Islands, 3rd Ed., 1890, pp. 396-397.
2 Proc. Royal Soc., Edinburgh, Vol. 17, 1890, p. 101.
GEOLOGIC TIME. 669
calcium was poured into it than could be retained in solution.
The Laurentian limestones are crystalline, but, as has been
shown, this texture is consistent with either chemical or organic
origin. The unaltered limestones in the Algonkian rocks of
the Colorado Canon section show traces of life in thin sections,
and they may be, to a great extent, of organic origin. There is
no evidence in the texture, bedding or composition of these
ancient limestones to indicate that they were deposited under
conditions of salinity or of supply differing materially from
those of the present, and I do not find that we have reason
to believe that the deposition of the carbonate of lime was
more rapid in the Paleozoic than during the Mesozoic and
Cenozoic times, even though the supply from the land may
have been greater. Where the conditions were favorable for the
deposition of lime, as in the Cretaceous sea of northern Mexico,
we find evidence of an immense accumulation of calcareous sedi-
ments. Of the amount of calcareous deposits in the seas outside
of the continental areas that are not open to our inspection, we
know nothing ; but judging from the deposition that is going on
to-day in the great oceans, the accumulation of calcareous sedi-
-ment has gone on in the past as steadily and uninterruptedly as
at present, subject to varying conditions of temperature, life,
depth of water, etc.
Area of Deposition in Paleozoic Time.—We have no proof
that the salinity of the sea or the amount of calcium con-
tained in it has varied from age to age since Algonkian
time. ‘If it has not, all of the calcium poured into the
ocean during 2,000,000 years would have about equaled the
amount now contained in the limestones of that area. We have,
however, to account for the calcium deposited in the interior
Mississippian sea and the seas over other portions of this conti-
nent and other continental areas, and on portions of the floor of
the ocean that are now accessible for observation. It is also to
be considered that the land areas subject to denudation in
Paleozoic time were, in all probability, of no larger extent than
at the present time.
670 Wels JKQOLINAUE (U2 (CIR OVL OG.
The area of dry land to-day is estimated to be 55,000,000
square miles, and of oceans 137,200,000 square miles."
Mr. T. Mellard Reade estimates the area of the Paleozoic
formations of Europe at 645,600 square miles in the total area of
3,720,500 square miles. His estimate of the Paleozoic area is of
that which is exposed at the present time, and does not include
that which is concealed beneath other formations. I think it
will be a minimum estimate to consider that an equal area is
covered by the later formations, which, with that exposed, would
give in round numbers 1,290,000 square miles,—or one-third
of the land area of Europe. In North America nearly one-half
of the total area was covered by the Paleozoic sea; in South
America it was considerably less; and we know too little of the |
Asiatic and African continents to place any estimate upon their
Paleozoic areas. I think, however,.if we take one-fourth of the
present land area as the territory covered by the Paleozoic seas
we shall be considerably within the actual amount, even if we
add to the surface of the continents the margins of the continen-
tal platforms now beneath the sea. Deducting the one-fourth
from the total land area, there remain 41,250,000 square miles as
the land area undergoing denudation during Paleozoic time. It
may be claimed that large areas in the archipelago region of the
Pacific and in the Arctic ocean may have been land areas at that
time. To meet this, 8,750,000 square miles may be added to the
41,250,000, giving a total of 50,000,000 square miles-as the land
area of Paleozoic time.
The estimated areas of the various deep sea deposits of
to-day, containing a large percentage of the carbonate of lime,
are as follows: Globigerina ooze, 49,520,000 square miles, mean
percentage of carbonate of lime, 64.53; Pteropod ooze, 400,000
square miles, percentage of carbonate of lime, 79.26; Coral mud
and sand, 2,556,000 square miles, mean percentage of carbonate
of lime, 86.41. In addition to this, Diatom ooze covers an area
of 10,880,000 square miles, with 22.96 percentage of carbonate
of lime; and the mean percentage of carbonate of lime in the
*Dr. JOHN MurRRAY: Scottish Geog. Mag., Vol. 4, 1888, p. 40.
GEOLOGIC TIME. 671
Blue Mud and other terrigenous deposits that cover 16,050,000
square miles is 19.20. If we consider only those deposits con-
taining over 64 per cent. of carbonate of lime, we have
52,500,000 square miles, over which there is at thé present time
a deposition of the carbonate of lime being made. We have
roughly estimated that in Paleozoic time the area of the Paleozoic
sea, in which deposits were being accumulated, was over 13,000,-
000 square miles. It does not appear that there is any good
reason to suspect that the area of deposition of the carbonate of
lime in the open ocean during Paleozoic time was not fully equal
to that of the present time. Adding this area of 52,500,000 to the
13,750,000, we have over 66,000,000 square miles as the probable
area in which calcium was being deposited in Paleozoic time.
Conditions favorable for a rapid deposition of the carbonate of
lime -—TYhe condition most favorable for the rapid accumulation
or deposition of the carbonate of lime through organic or
mechanical agency is warm water and a constant supply of
water through circulation by currents; this is shown by the
immense abundance of life where the margin of the continental
plateau is touched by the Gulf Stream. Another favorable con-
dition is the supply of carbonate of lime by river water directly
into the ocean in the vicinity where the deposition of lime is
going on either through organic or inorganic agencies. This is
well illustrated by the conditions produced by the Gulf Stream.
The oceanic currents, passing along the northeastern coast of
South America, sweep the waters of the Amazon through the
Caribbean sea into the Gulf of Mexico, where they meet the
vast volume of water coming from the Mississippi. These are
poured out through the narrow straits between Florida and Cuba
and carried northward over the sloping margin of the continental
plateau. Under such favorable conditions the deposit must be
much greater than in areas where there is little circulation and
the supply of calcium is limited to the average which is con-
tained insea water. If to the preceding there is added extensive
evaporation within a partially enclosed sea, the rate of deposition
of matter in solution will be largely increased.
7
672 THE JOURNAL OF GEOLOGY.
The area over which calcareous depositions was going on
during Paleozoic time we have estimated at 66,000,000 square
miles, which includes the areas of the seas over the. continental
platforms and those of the surrounding oceans. As the con-
ditions appear to have been more favorable for the deposition of
lime in the Cordilleran aud Appalachian seas, we will assume
that it was four times that of the open ocean.” With a land
area of 50,000,000 square miles (ate p. 670) and a rate of
chemical denudation of 70 tons per square mile per annum, the
total calcium contributed to the ocean per year during Paleozoic
time would be 3,500 million tons or 3.78 times as much as that
estimated for per annum at the present time, which is 925,866,-
500 tons (ante p. 668). This would have provided 50.7 tons for
deposition per annum per square mile in the 65,000,000 square
miles of ocean and seas and 202.8 tons for deposition per annum
per square mile in the 400,000 square miles of the Cordilleran and
600,000 square miles of similar seas. On this basis 81,120,000
tons (36.4 mile-feet) were contributed per annum from the
ocean water to the deposit in the Cordilleran sea ; adding to this
the 42,000,000 tons (18.8 mile-feet) contributed per annum by
the denudation of the surrounding area to the Cordilleran sea,
we have 128,120,000 tons (55.2 mile-feet) as the amount avail-
able for deposit per annum in the Cordilleran sea. At this rate
it would have required 16,300,000 years to have deposited the
2,007.244,800 million tons (900 million mile-feet) of calcium in
the Cordilleran sea ; adding to this the 1,200,000 years estimated
for the deposition of the mechanical sediments, we have a total
of 17,500,000 years as the duration of Paleozoic time.
In reviewing the preceding estimates we must consider that,
*Under the reduction of 50 per cent. for the interbedded and intermingled
mechanical sediments and 25 per cent. for other material than calcium deposited
from solution, the apparent amount of calcium deposited in the Cordilleran sea was
greatly reduced. If this same ratio of reduction is applied to other Paleozoic lime-
stone areas, I doubt if over 1,000,000 square miles will be found to ‘contain as large
an average amount of calcium per square mile as the Cordilleran area. On this
account 1,000,000 square miles is the area taken for the greater rate of deposition of
calcium during Paleozoic time.
GEOLOGIC TIME. 673
throughout, I have increased the various factors above those
usually accepted: thus, for mechanical sedimentation, one foot
in 200 years is used. If the usually accepted average of one
foot in 3,000 years is taken the time period must be increased
fifteenfold (21,000,000 years), or the area of denudation from
1,600,000 square miles to 24,000,000—or three times the present
area of the North American continent.
In the estimate for the amount of chemical denudation the
largest average is taken—7o tons of calcium per square mile per
annum—and the assumption made that all calcium derived from
the adjoining drainage was deposited within the Cordilleran sea.
Again, the total supply provided per annum to ocean waters of
Paleozoic time is taken as 3.78 times greater than the amount
annually contributed to ocean waters to-day; of this, four times
as much is assumed to have been taken out per annum per square
mile as was taken by the remaining area in which calcium was
being deposited.
The area of the Cordilleran sea is given as 400,000 square
miles, but it was probably 600,000, if not much more. It may be
claimed that the area tributary to the Cordilleran sea was greater
than I have estimated. The evidence, such as it is, is against
such a view. As a whole I think the estimate of 17,500,000 years
for the duration of Paleozoic time in the Cordilleran area is below
the minimum rather than above it.
If the estimated rate of the deposition of coral limestones—
five feet in 1,000 years—given by Prof. Jas. D. Dana is correct,
the 19,000 feet of Paleozoic limestone in central Nevada would
have required 3,800,000 years to have accumulated under the
most favorable local conditions surrounding a coral reef. With
the exception of large deposits of corals in Devonian rocks no
appearance of a coral reef is recorded in the Cordilleran area.
TIME-RATIOS OF GEOLOGIC PERIODS.
The time-ratio adopted by Prof. James D. Dana for the Paleo-
zoic, Mesozoic and Cenozoic periods is: 12, 3, and I, respect-
ively". Prof. Henry S. Williams applies the term geochronology,
t™Manual of Geology, 1875, p. 586.
674 \ THE JOURNAL OF GEOLOGY.
giving the standard time-unit used the name geochrone. The
geochrone used by him in obtaining a standard scale of geochron-
ology is the period represented by the Eocene. His time-scale
gives 15 for the Paleozoic; 3 for the Mesozoic; and 1 for the
Cenozoic, including the Quaternary and the Recent.
The Rev. Samuel Haughton obtained the following time-
ratios from the maximum thickness of strata as they occur in
Europe:
SCALE OF GEOLOGICAL TIME. ,
: From Theory of From Maximum
Period. Cooling Globe. Thickness of Strata.
Azoic - - - - - : 33.0 per cent. 34.3 per cent.
Paleozoic - - - - - - Aliso) ADAG WE a
Neozoic - - - - - - AO. DRED reir
Total - - - - - - 100.0 per cent. 100.0 per cent.
He draws from this the principle—‘ 7he proper relative meas-
uve of geological periods is the maximum thickness of the strata
formed during these periods.” *
In considering the time-ratios for the Paleozoic, Mesozoic,
and Cenozoic rocks of the North American continent, as given
by Dana and Williams, I think that a too small proportion has
been given to the Mesozoic and Cenozoic. In the Mesozoic of
the western-central area occur the coal deposits of the Laramie
series and the great development of limestone (from 10,000 to
20,000 feet) in the Cretaceous of Mexico. The limits of this
paper do not permit of a discussion of the available data bearing
upon geologic time-ratios ; but from a comparison of the Paleo-
zoic, Mesozoic, and Cenozoic strata and the geologic phenom-
ena accompanying their deposition, I would increase the com-
parative length of the Mesozoic and Cenozoic periods so that the
time-ratios would be: Paleozoic, 12; Mesozoic, 5; Cenozoic,
including Pleistocene, 2.
DURATION OF POST-ARCHEAN GEOLOGIC TIME.
Taking as a basis 17,500,000 years for Paleozoic time and
the time-ratios, 12, 5, and 2 for Paleozoic, Mesozoic, and Ceno-
t Journal of Geology, Chicago, Vol. I., 1893, pp. 294-295.
?Nature, Vol. 18, 1878, p. 268.
GEOLOGIC TIME. 675
zoic (including Pleistocene) respectively, the Mesozoic is given
a time duration of 7,240,000 years, the Cenozoic of 2,900,000
years, and the entire series of fossiliferous sedimentary rocks of
27,650,000 years. To this there is to be added- the period in
which all of the sediments were deposited between the basal
crystalline Archean complex and the base of the Paleozoic.
Notwithstanding the immense accumulation of mechanical sedi-
ments in this Algonkian time, with their great unconformities and
the great differentiation of life at the beginning of Paleozoic
time, Iam not willing with our present information to assign a
greater time period than that of the Paleozoic—or 17,500,000
years. Even this seems excessive. Adding to it the time period
of the fossiliferous sedimentary rocks, the result is 45,150,000
years for post-Archean time. Of the duration of Archean or
pre-Algonkian time, I have no estimate based on a study of
Archean strata to offer. If we assume Haughton’s estimate of
33 per cent. for the Azoic period and 67 per cent. for the sedi-
mentary rocks, Archean time would be represented by the period
of 22,250,000 years. In estimating for the Archean, Haughton
included a large series of strata that are now placed in the Algon-
kian of the Proterozoic of the United States Geological Survey ;
and I think that his estimate is more than one-half too large; if
so, ten million years would be a fair estimate, or rather conject-
ure, for Archean time.
Period. Time Duration.
Cenozoic, including Pleistocene - - 2,900,000 years
Mesozoic - - - - - - - 7,240,000
Paleozoic - - - - - - 7 AGOOLOOON TS =
Algonkian - - - - - = 7/,500000
Archean - - - - - - 10,000,000(?)*‘
It is easy to vary these results by assuming different values
for area and rate of denudation, the rate of deposition of carbon-
ate of lime, etc.; but there remains, after each attempt I have
made that was based on any reliable facts of thickness, extent
and character of strata, a result that does not pass below
25,000,000 to 30,000,000 years as a minimum and 60,000,000 to
676 THE JOURNAL OF GEOLOGY.
70,000,000 years as a maximum for post- Archean Geologic time.
I have not referred to the rate of development of life, as that is
virtually controlled by conditions of environment.
In conclusion, geologic time is of great but not of indefinite
duration. I believe that it can be measured by tens of millions,
but not by single millions or hundreds of millions of years.
CHARLES D. Wa tcotTrtT.
ON THE ORIGIN OF THE PENNSYEVANIA
ANTHRACITE.
Lone ago, H. D. Rogers showed that the coal regions of
Pennsylvania are divided into rudely longitudinal basins or
troughs. In passing over the state northwestwardly, one crosses
first the Archean area at the southeast, with its patches of
Newark or Triassic; then the Great Valley, extending almost
unbroken from the Hudson river to Alabama, and showing only
Cambrian and Silurian with occasional patches of Devonian and
Lower Carboniferous. Crossing the irregular northerly or north-
westerly boundary of the valley, he reaches what, for the pur-
pose of this discussion, may be termed the Anthracite Strip,
which extends to the Alleghanies; this contains the Cumberland
coal field of West Virginia and Maryland, the Broad Top field
of southern Pennsylvania, and, still further northeast, the
Southern, Middle and Northern Anthracite fields. The Bitu-
minous coal basins, of which Rogers recognized six, are beyond
the Alleghanies; the first, between the Alleghanies and Laurel
Hill, is well defined near the Maryland line, but becomes less so
northward, though it can be traced without difficulty into New
York; the second, with Chestnut Hill as its westerly boundary,
is the Ligonier Valley, which like the last can be followed into
New York; the third, wider than the second, is less defined at
the west, as its boundary on that side is an anticline passing
but a little way east from Pittsburgh and producing insignificant
topographical effects; the most important portion of the basin,
in this connection, is the first sub-basin, known as the Connells-
ville coke basin, which follows the westerly foot of Chestnut
Hill. The remaining bituminous basins, including the rest of
‘Abstract of a paper read before the Geological Society of America, August,
1893.
677
678 THE JOURNAL OF GEOLOGY.
Pennsylvania, northwestern West Virginia and eastern Ohio may
be regarded as one, their details being unimportant in so far as
the present study is concerned.
The trend of the anticlinal and synclinal axes is not N. N. E.
and S.S. W. throughout, for one of the great curves of the
Appalachian system is within Pennsylvania; the axis of the
First Bituminous basin, for example, follows an almost W. S. W.
direction until, in Clearfield county, midway in the state, its
course is changed to S.S.W.; any topographical map of
Pennsylvania illustrates the condition.
Interesting variations in the rate of dip are shown along a
line drawn from Pittsburgh, Pa., southeastwardly across the coal
area to the Cumberland field in Maryland, the contrast between
the terminal conditions being very great. At Pittsburgh, the
rate seldom exceeds one degree; in the Connellsville sub-basin it
varies from four or six degrees along the lower portion of the
trough to somewhat more than ten degrees on the side of
Chestnut Hill, the increase in rate thus far being quite regular.
No further increase is found in crossing the second and first
basins, the dip even on the easterly side of the Alleghanies
rarely exceeding twelve degrees. But the extent of disturbance
becomes markedly greater at once after the Anthracite Strip has
been reached, for there dips of 20, 40, 70 and 80 degrees are
seen.
The conditions observed along this line are not representative
of those throughout the coal area, for in all the basins, even in
those of the Anthracite Strip, the degree of disturbance eventu-
ally becomes less along the trend northwardly. The existence
of the anthracite fields themselves is due to a remarkable
decrease in violence of the disturbance, a dying away northward
of anticlines, permitting formation of broad synclines, which in
their turn act as do the canoe synclines of the bituminous areas,
which, rising, send the lower formations into the air. South-
wardly, the condition is markedly different; for though the
extent of disturbance, except in the Anthracite Strip, decreases
rapidly, the decrease is due to depression of anticlines and not,
ORIGIN OF THE PENNSYLVANIA ANTHRACITE. 679
as at the north, to the general elevation of the synclines and
their passage into the New York plateau.
Analyses of coal samples, taken from the Pittsburgh bed in
the several basins, show a progressive decrease in-the proportion
of volatile, combustible matter toward the east or southeast, a
fact which early attracted the attention of H. D. Rogers, and
which has possessed much interest for geologists ever since.
Analyses made for the Second Pennsylvania Survey prove the
same condition in the lower coals. Mr. Winslow’s studies of .
the Arkansas coals show a similar tendency to decrease in the
same direction; and Murchison discovered a like condition in
the Donetz anthracite field of southern Russia.
H. D. Rogers,* in 1842, announced to the Association of
American Geologists the law of gradation, as he understood it,
which involves ‘‘a progressive increase in the proportion of the
volatile matter, passing from a nearly total deficiency of it in
the driest anthracites to an ample abundance in the richest
caking coal.’ Finding, as he believed, that the volatile matter
in the coal augments westwardly, precisely as the flexures
diminish, he attributed the variation to the influence of steam
and other intensely heated gases escaping through crevices
necessarily produced during the permanent bending of the
strata. Under such conditions, the coal throughout the eastern
basins, the more disturbed, would discharge more or less of the
volatile constituents during the violent earthquake action,
whereas the more western beds, less disturbed, would be less
debituminized.
J. J. Stevenson,? in 1877, showed that the variations in
volatile exhibited by the Pittsburgh coal bed along the south-
east and northwest line bear no relation whatever to increase or
decrease of stratigraphical disturbance, and suggested that the
variations are due to difference of conditions under which the
coal was formed.
*RoGeRs: Reps. of the Ist, 2d and 3rd meetings of the Association of American
Geologists and Naturalists. 1843, pp. 470 et seq.
2STEVENSON: 2d Geol. Surv. of Penn., Rep. of Progress on the Fayette and
Westmoreland Dist. Pt. I. pp. 61, et seq.
680 THE JOURNAL OF GEOLOGY.
J. P. Lesley,* in 1879, offered some interesting suggestions.
If the anthracite be metamorphosed bituminous coal, the change
might be caused by exposure to comparatively high temperature
at a great depth below the surface. As the temperature increases
one degree Fahrenheit for each fifty feet, more or less, of
descent, the coal under cover of a great thickness of rock could
not fail to be deprived of its volatile matter. He compares the
composition of coal from the highest available bed in western
Pennsylvania with that from the lowest bed in the same region,
and finds less volatile in that from the lower bed. As all of
the Paleozoic rocks thicken eastwardly, there must have been a
much greater pile of Coal Measures in the anthracite region than
in the bituminous areas, though erosion has removed the proof.
Necessarily then the coals of the anthracite region should show
less volatile than do those of the bituminous area, where the
pile of rocks was less thick.
Professor Lesley suggests also that if one desire to explain
the origin of the anthracite by oxidation in preference to meta-
morphism, the conditions afford basis for such explanation,
since in the anthracite region the rocks are not only broken and —
shattered by the folding, but they are made up largely of sand
and gravel, so that the conditions are such as to favor percola-
tion of water, evaporation, and consequently oxidation; whereas,
in the undisturbed bituminous areas, clayey beds are in large
proportion and lute down the buried coals so as to prevent per-
colation and the rest.
There is no possible room for doubt that bituminous coal can
be converted into anthracite by heat. The Galisteo, Elk Moun-
tain and other localities within the United States, the Hesse
Cassel and New Zealand areas in foreign lands, prove beyond
dispute that, under proper conditions, contact with molten rocks
suffices for the conversion. But no question of such conversion
is at issue here, for in Pennsylvania no dikes occur near enough
to the anthracite areas, or large enough even if near enough, to
*LESLEY: In McCreath, 2d Geol. Surv. of Penn., 2d Rep. of Progress in the
Laboratory, etc. 1879, pp. 153, et seq.
ORIGIN OF THE PENNSYLVANIA ANTHRACITE. 681
produce by contact the extensive tracts of anthracite still
remaining in the state.
Professor Rogers’s explanation seems to have been based
throughout on a misunderstanding of the conditions. There is
no good reason for supposing that the Appalachian Revolution
was produced by violent disturbances such as those imagined
by Professor Rogers; on the contrary, there appear to be the
best of reasons for supposing the final folding to be but an
acceleration of the process which had gone on, perhaps not con-
tinuously, from a very early period. The slowness of the pro-
cess even at the close is suggested by the courses of the main
waterways. The fundamental error, however, respects the rela-
tion of dip and volatile. The dip along the line selected by
Professor Rogers, that from Pittsburgh to the Cumberland coal
field in Maryland, does indeed show great changes, but as already
stated they are not gradual. Let the condition be recalled. At
Pittsburgh, the dip is from %° to 1°; in the Coke basin, 30 miles
away, it is from 4°—6° at the lower portion of the trough, to
10°—12° higher up the side of the anticline ; in the Salisbury basin,
34 miles further, the dip is the same or less, there being practi-
cally no change in the interval from the Coke basin; and no
further change is found until one has passed the Alleghanies and
entered the Anthracite Strip, where a marvelous change is seen,
for the dip is sometimes vertical. Now despite all this, the
decrease in volatile, as shown by the Pittsburgh coal bed along
this line, is almost regular; thus at Pittsburgh, the average
analysis shows of volatile 40.7 per cent. (ash and water being
ignored in the calculation); at Connellsville, 33.8, a decrease of
6.9 in 30 miles with an increase of dip from 1° to say 8° ; at Salis-
bury, the volatile is only 23.3, a decrease in 34 miles of 10.5
with no change whatever in rate or type of folding; while in
the Cumberland basin, about 15 miles further, the volatile is
18.8, a decrease of only 4.5, despite the complete change in type
and remarkable increase in extent of disturbance; and this last
field is within the anthracite strip itself, is in proper position, along
the trend, to be the continuation of the Northern Anthracite field.
682 THE JOURNAL OF GEOLOGY.
Professor Rogers’s error in this matter prevented him from
observing that the volatile decreases northwardly along the
trend in the several basins even more notably than along the
line chosen by him. The hardest anthracite is not in the
Southern field, where the folding is most complicated, but in the
Eastern Middle. The Southern Anthracite field shows all grada-
tions from bituminous coal at its southern extremity to hard, dry
anthracite at its northerly end.
Professor Lesley’s suggestion that the Coai Measures attained
to much greater thickness in the anthracite region than in the
bituminous areas hardly accords with the facts as now known,
many of them published since he offered his suggestions. It is
altogether certain now that the lower three divisions of the Coal
Measures in Pennsylvania, the Pottsville, the Lower Coal Group
and the Lower Barren Group, do not show any variations which
would justify one in basing a theory upon them; and it is much
more than probable that the Upper Coal Group and the Permo-
Carboniferous attain their greatest thickness in the north central
portion of the Appalachian basin, and that they diminish in
thickness westwardly, northwardly and eastwardly from south-
western Pennsylvania, as abundantly appears from the measure-
ments made by I. C. White and by the writer in Pennsylvania,
Ohio and West Virginia. In any event, the thickness of the
mass in northeastern Pennsylvania was small in comparison with
the thickness of the series in Virginia, West Virginia and
Kentucky, on the southeastern edge of the Appalachian basin;
yet in those states the coal shows no tendency to be anthracite ;
that of the Imboden coal bed of Virginia and Kentucky, almost
at the base of the Lower Coal Group of Pennsylvania, is richly
bituminous.
Nor does the theory that anthracite is bituminous coal con-
verted by heat due to mechanical force, commend itself in this
connection. The crushed and polished coal of the Broad Top
field is bituminous, whereas the uncrushed coal of the Northern
field in the same strip is anthracite. The Quinnimont coal, in
the gently flexed New River district of West Virginia, has
ORIGIN OF THE PENNSYLVANIA ANTHRACITE. 683
practically the same amount of volatile as is found in the same
coal near Pocahontas, Virginia, close to the great fault of Abbs
valley.
But it is unnecessary to look to metamorphisnr for an expla-
nation of the Pennsylvania anthracite; at best, metamorphism is
an unsatisfactory explanation, because it is difficult to find evi-
dence that metamorphosing agencies have been in operation
there. One does not think of metamorphism when he finds in
the coal of a given bed a variation of five or ten per cent. of
volatile within short distances, or even when he finds, as in
Sullivan county of Pennsylvania, anthracite in one bench and
bituminous in another bench at the same opening.
As was shown long ago by Bischof and others, anthracite can
be produced simply by continuation of the process whereby
vegetable matter is converted into bituminous coal—by continued
formation of carburetted hydrogen until the hydrogen has been
removed. Professor Lesley’s ingenious suggestion that this can
go on more readily in the anthracite region than in the bituminous
areas, because of the difference in composition and condition of
the rocks, hardly suffices. If only the extremes of the series
were to be accounted for, and if all were confined to the anthra-
cite strip, it might be regarded as sufficient; but all gradations
from rich caking coal to anthracite occur in the First bituminous
basin, where the rocks are comparatively undisturbed and con-
sist largely of argillaceous shale. Moreover, in a single colliery
within the Southern Anthracite field, one bench of the Mammoth
bed yields a more than semi-bituminous coal, while from another
is obtained almost the driest of anthracite. But an equally
serious objection is, that the coal must have been converted
finally before complete entombment, so that the effect of the
pressure would be to remove water and to solidify the coal. The
hardening of the coal was complete in the Broad Top field before
the Appalachian revolution occurred, for in the final folding the
coal, as shown in some mines, was broken into lenticular and
polished fragments precisely like those of the Utica shale within
the disturbed valley east from the Anthracite Strip. The Lara-
684 THE JOURNAL OF GEHOLOG ¥.
mie coals on the western side of the great plains.in New Mexico,
Colorado and Wyoming can hardly have undergone any material
change since the final burial; otherwise the strange variations
in composition would be inexplicable, the difference in con-
dition as to character of rocks and degree of disturbance being
insufficient.
Twenty years ago the writer, while connected with the Ohio
Survey, reached the conclusion that the marsh, from which sprang
the several beds of the Upper Coal group, originated at the east;
two years later he was led to assert that the coal beds were
formed as fringes along the shore of the Appalachian basin. If
this be the true doctrine, there should be found in northeastern
Pennsylvania,
First. A vastly greater thickness of coal than in other por-
tions of the basin.
Second. A greater advance in the conversion of vegetable
matter into coal, owing to the longer period elapsing prior to
entombment.
As to the first condition, there can be no doubt. A compari- |
son of the several divisions of the Coal Measures as they appear
in the several basins of the state illustrates it well; but sucha
comparison would be tedious here, and only the Lower Coal
group of the Pennsylvania series is used (that lying between the
Pottsville conglomerate below and the Mahoning sandstone
above ).
In the Anthracite Strip this group shows in the several fields,
from south to north, as follows:
Cumberland Field, bituminous, - = =wennligw
Broad Top Field, bituminous, — - - - 14/-15'
Southern Anthracite, bituminous to anthracite, ne On OOw
Middle and Northern Anthracite, anthracite, - 40'-58'
The thicknesses in the Bituminous basins are:
First, = - - - = < 21 '—23)'
Second, = = - - - - 11@), — yo)
Fifth, z - “ = = 8'6"-13'4"
The thicknesses, as given for the Anthracite Strip, are those
ORIGIN OF THE PENNSYLVANIA ANTHRACITE. 685
of coal exclusive of slate and other partings, but those for the
Bituminous areas include the slates and other partings, so that
the actual amount of coal is less than the figures indicate. It is
sufficiently clear that the conditions favoring the= accumulation
of coal in beds continued longer without interruption in the
anthracite region than they did elsewhere within the Appalachian
basin; for the contrast is equally marked, when the anthracite
region is compared with the Virginias or Kentucky further south-
westward. The process of conversion also continued longer
without interruption, as the chemical analyses show." Thus, in
the Anthracite Strip, one finds:
Cumberland Field (only the Pittsburgh), 4.47— 4.78 Coal, 13’
Broad Top Field, - - - 3.26-— 4.64 Coal, 14’
Southern Anthracite Field,
Southern prong, - - 4.36-12.40 Coal, 18'—30'
Main Field, - - - 11.64-23.27 Coal, 30'—60'
Western Middle Field, - 19.87—24 Coal, 40'—58'
Eastern Middle Field, - - 25.53-30.35 Coal, 52'-53’
Northern Field, - - 19.37-19.92 Coal, 44'-53'
The anthracite analyses are commercial, samples chosen from
carload lots. Very much higher ratios are obtained by sampling
single benches.
The First and Second Bituminous basins show a similar
change along the line of trend, the amount of volatile decreasing
northwardly as one approaches the old shore line.* Thus, in the
First, the Clarion coal bed shows from 2.94 to 4.84 near the
Maryland line, but from 7.07 to 10.28 in Sullivan county, where
is its last exposure at the north. In the Second basin, the Upper
Freeport coal shows 2.26 to 2.85 near the Maryland border, but
3.96 to 4.48 at the last northerly exposure, in Lycoming county.
The variations in the Third and other basins are less, as one
«The figures here given are the ratios between the Fixed Carbon and the Volatile
Combustible, the ash and water being ignored; the more volatile, the smaller the
ratio.
Some curious variations, apparently contradictory of the statement here made,
occur in the analyses. These will be discussed and their interest shown by the writer
in a review of theories respecting the origin of coal beds, which is now in course of
preparation.
686 LTE VY OCLNAL OFAGBOLOGYAS
should expect, for according to the supposition, the conditions
at that distance from the old shore line should vary little any-
where.
So one finds,
First. A decided increase in thickness of coal eastward, or
better, northeastward toward the anthracite region, and a less
marked increase northward in the Bituminous basins.
Second. A decided decrease in volatile in the direction of
increased thickness of coal, the decrease being comparatively
gradual until near the anthracite fields.
Third. That this decrease is gradual even in the Anthracite
Strip from the Cumberland Field to the semi-bituminous coals of
the Southern Anthracite field, where the rapid increase in thick-
ness is accompanied by a rapid decrease in the volatile.
When, in 1877, the writer called the attention of his col-
leagues on the Pennsylvania Survey to the fact that the decrease
in volatile is wholly without relation to increase or decrease of
disturbance in the strata, he suggested that the variation was due
to difference in conditions under which the coal had been formed
in the several localities discussed—a sufficiently comprehensive
hypothesis, but yielding in this respect to some others of later
date. Now, however, there seems to be no good reason for any
such suggestion; all that was needed was longer exposure to the
process whereby ordinary bituminous coal was formed. In
origin, the anthracite coal of Pennsylvania differs in no wise from
the bituminous coal of other parts of the Appalachian basin;
but because the great marsh, from which sprang the many beds,
originated in the northeastern corner of the basin and extended
thence again and again on the advancing deltas formed by streams
descending from the Appalachian highlands, the time during
which the successive portions of the marsh would be exposed
would be less and less as the distance from the northeastern and
northern border of the basin increased, so that the extent of chemi-
cal change would decrease as the distance increased. It is, there-
fore, to be expected that in the northeastern corner, where the
deltas were formed quickly after subsidence was checked, and
ORIGIN OF THE PENNSVLVANIA ANTHRACITE. 687
beyond which they advanced slowly, as shown by changing type
of rocks, the chemical change should have been almost complete,
especially in the eastern Middle and the eastern extremity of the
Southern field, which occupy that part of the area in which the
coal marsh, in almost every instance, appears to have thrust itself
first upon the advancing delta.
It is quite possible that when detailed study of the anthracite
areas in Arkansas and Russia have been made, the same explana-
tion may be found applicable there also, and that the anthracite
will be found near the old shore line, whence the marsh advanced
as new land was formed. Joun J. STEVENSON,
THE BASIC MASSIVE ROCKS OF THE LAKE SUPERIOR
REGION.
Ill THE GREAT GABBRO MASS OF NORTH-EASTERN MINNESOTA.
A. Introduction.
As Has already been stated in an earlier paper,? the writer
purposes, as time and opportunity permit, to discuss the petro-
graphical and stratigraphical relationships of the basic rocks that
constitute such an important element in the geology of the coun-
try bordering Lake Superior. In the series of papers, of which
this is the first, the petrographical characteristics of the various
types of these rocks will be described, and the views held by
previous workers with respect to their geological relationships
will be outlined. Thus, it is hoped, a foundation will be laid for
a new and more thorough investigation of the field relations of
these rocks than has heretofore been possible. As the case now
stands, several of the geologists who have investigated the
eruptive rocks of this region have erred in confusing types of
entirely different origins, and have thereby introduced into the
literature errors of observation that have rendered a clear under-
standing of the Lake Superior geology almost impossible.
When practicable the laboratory and field study of rocks
should proceed together, each aiding the other in solving the
knotty problems that so often arise in their progress. The
laboratory study of the eruptives in the region under considera-
tion has been almost entirely neglected, and consequently the
field problems arising in connection with them have largely
remained unsolved. When the peculiarities of these rocks—
their composition and structure—become known, much light
will be thrown upon their nature, and it will then be time to
again review their field relations, when it is believed that many
t This Journal, Vol. L., pp. 433 and 587.
2 This Journal, Vol. I., p. 435.
688
LTE BASIC MASSIVE ROCKS, ETE. 689
of the difficulties now surrounding them will disappear. At
present the main results reached by the field-geologists who have
busied themselves with the rocks under discussion will be
referred to. They must pass unchallenged except in the few
cases where the microscopic evidence is directly at variance
with them; and when there is no field evidence directly substan-
tiating them. At some time in the near future it is hoped that
an opportunity will offer itself for a more detailed study of the
rocks in the field. Then it will be proper to criticise the conclu-
sions arrived at by previous workers, and to suggest new views as
to the position and relation of the eruptives with respect to the
rocks with which they are associated.
B. The Position of the Gabbro.
The great gabbro mass which is the subject of this paper has
been placed by Irving in the Keweenawan group, the separation
of which from the underlying Huronian slates and quartzites and
the overlying Cambrian sandstone, is due principally to the
investigations of Brooks, Pumpelly, Irving and Chamberlin.
The history of the discussion which has led to the recognition of
the great Keweenawan series it will not be necessary to outline,
as it is well given in the essays, whose authors have been named.*
The only detailed description of the series as a whole has
been given us by Irving,? who makes it ‘‘include only the suc-
tIt should be stated here that although the individuality of the copper-bearing
series of rocks is recognized by nearly all geologists who have worked in the Lake
Superior region, several have declined to regard it as a distinct series, equivalent to
the Huronian or the Cambrian. These geologists prefer to look upon it as belonging
with the latter group as its lower member. Dr. Wadsworth has long held this view,
and Prof. N. H. Winchell (8th Ann. Rept. Geol. and Nat. Hist. Survey of Minn., p. 22;
17th ibid., pp. 54-55) in one of his most recent reports sums up the work of the Min-
nesota Survey in this direction in the statement that the Keweenawan series is closely
linked with “the great gabbro flow,” to which reference will be made hereafter, and
that both are members of the Potsdam. In a later report (20th Ann. Rept. Geol. and
Nat. Hist. Survey of Minn., p. 3) the same writer discusses the age of the gabbro and
concludes that it is much older than the Potsdam, but he does not assert positively that
the Keeweenawan beds overlying it are pre-Cambrian.
?The Copper-Bearing Rocks of Lake Superior, R. D. Invinc: Monograph V., U.
S. Geol. Survey, Washington, 1883.
690 THE JOURNAL OF GEOLOGY.
cession of interbedded ‘traps,’ amygdaloids, felsitic porphyries,
porphyry-conglomerates, and sandstones, and the conformably
overlying thick sandstones, as typically developed in the region
of Keweenaw Point and Portage Lake on the south shore of
Lake Superior.”
Although no distinct line of division between them can be
pointed out, the beds of the series naturally fall into an upper
division made up wholly of detrital material, principally shales
and red sandstones, and a lower division consisting chiefly of a
succession of basic flows, layers of conglomerate and sandstone
and quite a large proportion of flows of acid eruptive rocks.
The thickness of the upper division is estimated at 15,000 feet at
its greatest, and that of the lower division at from 22,000 to
24,000 feet. .
The recent discovery that the central part of the Keweena-
wan is underlain unconformably by a great mass of anorthosite,
which along the middle portion of the Minnesota coast comes to
the surface in many places, suggests to Lawson? that the maxi-
mum thickness of the lower Keweenawan beds at this place must
be much less than Irving’s estimate. His own figures are only
about one-tenth those of Irving. VanHise3 in a review of Law-
son’s article takes exception to the author’s small estimate, and
prefers to accept Irving’s figures, until these are proven inaccu-
rate by careful detailed investigation of the problem in the field.
Since it is only in the lower division that eruptive rocks occur,
our attention will be confined entirely to this. It is not possible
to determine positively for the entire series the actual succession
of the subordinate members belonging in it, for this, in an erup-
tive series, may vary in different areas, but Irving believes that
the following ‘‘broad horizons” may be recognized: (x0) a suc-
cession of heavily bedded coarse-grained olivine and orthoclase
gabbros, forming the base of the series; (2) a series of olivine
diabases and diabase-porphyrites, occurring at the lower hori-
TIC. Ps 24: A
2 Geol. and Nat. Hist. Survey of Minn., Bull. No. 8, p. 21.
3Jour. of Geology, Vol. I., p. 312.
THE BASIC MASSIVE ROCKS, ETC. 691
zons, together with acid eruptives of all kinds common to the
group, as quartz-porphyries, quartzless-porphyries, and fine-
grained red granites; (3) olivine-free diabases and other basic
rocks with amygdaloidal upper and lower surfaces; and (4)
detrital beds, chiefly porphyry conglomerates and sandstones,
rare in the lower third of the series, but increasing in thickness
and frequency towards the top. These various subordinate
divisions have been separated into smaller sub-divisions, and
their sequence, where possible, has been carefully detailed, but
since a discussion of this classification is not necessary to our
present purpose it need not be entered upon.
The lowest of the divisions of rocks belonging in Irving’s
Keweenawan has been said to consist of a succession of heavily
bedded coarse-grained olivine and orthoclase gabbros. The best |
exhibition of these gabbros is found in north-eastern Minnesota,
where the area underlain by them occupies about 2100 miles of
the surface of the state, extending from the east line of Range 1,
E., to about the middle of Range 15, W. The general shape
of the area is crescentic with the concave side turned toward
Lake Superior and its convex side facing the north-west. In its
widest part the crescent measures about twenty-two miles from
south-east to north-west. The chord connecting its two horns is
about 125 miles in length. The eastern extremity forms a nar-
row point about three miles north-west of Greenwood Lake, from
which point the area extends westward, widening gradually until
it reaches its broadest expanse, and then gradually contracting
until it finally abuts against the north shore of St. Louis Bay
west of Duluth, where it appears as a band forming the shore
line for ten or twelve miles, beginning in the western portion of
the city of Duluth and ending four miles east of Fond du Lac.
A second’ area of basal gabbro is in the Bad River region in
Wisconsin. Here the rock forms a narrow belt about forty-eight
miles in length and from two to five miles in width, stretching
from the Gogogashugun river south-westward to near Numakagon
lake, in T. 43 N., R. 6 W., Wis.
™Cf. pl. XXII., Copper-Bearing Rocks.
La
692 ALLE OUOTINATENOP AG LD OLO GN
It was not until a few years since that an attempt was made
to discover the true relations of these gabbros to the surrounding
rocks. In his Copper-Bearing Rocks (p. 266) Prof. Irving
places them at the base of the Keweenawan group, at the same
time stating that ‘“‘There is no definite evidence of unconformity
between the gabbros and the slates of the Saint Louis River,”
regarded as Animikie. Ina later paper the same writer’ refers
to a coarse-grained, stratiform olivine-gabbro at the base of the
Keweenawan. ©
Though nowhere so stated, the olivine-gabbros had by this
time been separated by the author from the overlying ‘ortho-
be)
clase gabbros,” and had been placed by him at the very base of
the Keweenawan group, with the orthoclase-gabbros immediately
above them. In his article? on the classification of the early
Cambrian and pre-Cambrian formations, we have this description
of the position and nature of this great mass of rocks, ‘.
We find at the base of the series [Keweenawan] an immense
development of stratiform, fresh and often exceedingly coarse
olivine-gabbro, the individual layers of which, notwithstanding
their complete crystallization, very coarse grain, and lack of
amygdaloidal or dense upper surfaces, seem evidently to have
formed great flows at the surface of the region as it stood at the
time of their extrusion.”
No more explicit statements of his views concerning this
basal gabbro appear in any of Irving’s writings. A reference to
the geological map of north-eastern Minnesota accompanying the
paper last referred to, will, however, show that at this time (1886)
he believed the basal gabbro in Minnesota to rest unconformably
upon the Animikie, since the former is represented as cutting
transversely belts of St. Louis slates, the Mesabi granite and
schists of the Archean, and the eastern area of Animikie slates
along the boundary line between Minnesota and Canada, which
slates here strike nearly east and west.
Although in his maps the “gabbro flow” is represented as
* Am. Jour. Sci., 3d ser., vol. 34, 1887, pp. 204, 249.
2Seventh Ann. Rept. U.S. Geol. Survey, 1888, p. 419.
THE BASIC MASSIVE ROCKS, ETC. 693
belonging with the Keweenawan rocks, the Wisconsin mass was
nevertheless recognized by Irving as presenting “the appearance
of a certain sort of unconformity with the overlying beds. These
gabbros, which lie immediately upon the Huronian slates, form a
belt which tapers out rapidly at both ends, and seems to lie right
in the course of the diabase belts to the east and west, since these
belts, both westward toward Lake Numakagon, and eastward to-
ward the Montreal river, lie directly against the older rocks, with-
Out atily OF the coarse Sabbrocintervening, 449). “ihe great
extent of coarse gabbro in Minnesota seems to sustain somewhat
the same relations to more regularly bedded portions of the
Se@iesaas
The only other descriptions of this great gabbro mass are to
be found in the reports of the Minnesota survey. In the report
for 1887 Prof. N. H. Winchell? details a few of his observations
on the ‘‘great gabbro flood,” and surmises that the “flow” did
not escape through a single fissure. The structure of the rock is
reported as roughly columnar, with sometimes apparent indica-
tions ‘‘of the existence of imbricating layers having a gentle dip,
as if the fluid rock had swept over the country in successive
tides. . . . In texture the gabbro is characteristically coarse.
Sometimes some of the constituent minerals are half an inch in
diameter. From this they graduate down to an extreme degree
of fineness.”
From the macroscopic descriptions of other varieties of the
rock that follow it is evident that the writer is not dealing exclu-
sively with specimens taken from the great ‘‘gabbro flood”’ at the
base of the Keweenawan, for, as the sequel will show, this
is composed of a rock which, in its unaltered state, possesses a
remarkably uniform texture, and is so well characterized that any
departure from it is presumptive evidence that the rock exhibit-
ing the variation belongs not in the ‘basal flow,” but in some
one of the numerous smaller beds interstratified with the Animi-
*Copper-Bearing Rocks, p. 155.
?Geol. and Nat. Hist. Survey of Minnesota, 16th Ann. Rept. for 1887. St. Paul,
1888, pp. 360-362.
694 THE JOURNAL OF GEOLOGY.
kie and the Keweenawan strata at various horizons, or in some
one of the many dykes cutting these.
In the report’ of the following year, upon referring to the posi-
tion of the gabbro with respect to the other formations, Prof.
Winchell says ° = .) “In generalthe: sabbro lies one the
Animikie (Taconic) in Minnesota.’ At Chub (Akeley) lake,
however, it seems to be underlain by a bed of quartzite, regarded
as a lower member of the copper-bearing formation of the Pots-
dam (Keweenawan of Irving and Chamberlin) in the seventeenth —
report, but looked upon as Animikie and denominated the
Pewabic quartzite in the sixteenth report,? and described under
d
the field name ‘‘muscovado”’ in earlier reports.
In a more recent discussion? as to the age of the gabbro,
Prof. Winchell briefly summarizes his previous views on the sub-
ject, and concludes that the supposed quartzite underlying the
gabbro belongs near the bottom of the Animikie, and since the
eruptive rock is so closely associated with the fragmental one,
that the former must be of nearly the same age as the latter.*
This conclusion is based on the supposition that the rocks
immediately underlying the gabbro are fragmental quartzites that
have been altered by the eruptive for miles even from its contact
with them.> But this is probably not always the case. As the
writer® has shown in another place, some of the so-called quartz-
ites are very basic crystalline aggregates of pyroxene and oliv-
ine, and others are granulitic phases of the overlying gabbro.
Since they are portions of the gabbro they are of the same age
as this, and are not available as stratigraphical data for use in
determining the time relations of the great ‘‘flow”’ with respect
*r17th Ann. Rept. for 1888. St. Paul, 1891, p. 52.
216th Ann. Rept., pp. 82-87.
3The Iron Ores of Minnesota. Bull. Minn. Geol. Survey, No. 6, 1891, p. 125.
4Cf. also: 20th Ann. Report, p. 2.
5H.V. WINCHELL: Ib. p. 127.
© BayLEY W.S.: Notes on the Petrography and Geology of the Akeley Lake
Region in Northeastern Minnesota. 19th Ann. Rept. Minn. Survey. Minneapolis,
1892, p. 193 et seq.
LTE ASC NMA SSLVEE ROCESS a he 695
to the Animikie and the Keweenawan rocks. Some of the rocks,
called by Winchell Pewabic quartzite, are probably true Animikie
fragmentals, or metamorphosed phases of these, but even in this
case there is no proof that the gabbro immediatelysucceeds them
in point of age. The evidence would simply indicate that the
eruptive is younger than the Animikie. It would not fix its age
more definitely. The observations of Winchell would thus seem
to lead to the same conclusion as that reached by Irving in so
far as the latter supposed the gabbro to be post-Huronian.
Upon returning again to the problem as to the age of the
gabbro Winchell * attempts to fix this more definitely by assum-
ing the identity of this rock with the anorthosite, which is shown
by Lawson to be older than the bedded Keweenawan. But it is
impossible at present to assert with any degree of certainty, that
the two rocks are the same (although VanHise holds with Win-
chell that their equivalency is possible), for the one has not been
traced into the other, nor has the upper limit of the gabbro been
carefully studied. This great mass may be much older than the
lowermost beds of the Keweenawan series, but as yet there has
been cited no proof in favor of the view.
So far as the little evidence at hand enables us to judge, the
gabbro whose petrographical characteristics are discussed in this
article, forms a great mass of enormous extent above the Animikie
but below the interbedded flows and fragmentals of the Kewee-
nawan series in Minnesota. There are obscure indications that
the mass is a great layer composed of successive’ flows that fol-
lowed one another so rapidly as to give no opportunity for the
action of erosion processes or for deposition between them. If
this be so the lack of more apparent bedding is doubtless due to
the great thickness of the individual beds, as is also their coarse
grain. There are some things about the mass, however, that
suggest another origin for it. ‘‘The great coarseness of grain,
the perfection of the crystallization, the abrupt termination of the
belts, the complete want of structure, and the presence of inter-
secting areas of crystalline granitoid rocks—all suggest the
*Bull. No. 8. Geol. and Nat. Hist. Survey of Minn. p. xviii.
696 THE JOURNAL OF GEOLOGY.
possibility that we have here to do with masses which have
solidified at great depths. They certainly cannot, however, be
regarded as intrusive in the ordinary sense of the word; so that,
unless we regard them as great outflows, we should be forced to
look upon them as the now solidified reservoirs from which the
ordinary Keweenawan flows have come.”?
C. Petrographical Description of the Normal Phase of the Gabbro.
Up to the present time there has appeared no general petro-
graphic description of the great gabbro supposed to be at the
base of the Keweenawan, although both Irving and Wadsworth
have given detailed descriptions of hand specimens taken from
it. The former writer,? in his monograph on the copper-bearing
rocks, refers to the great mass at Duluth as consisting principally
of a coarse orthoclase gabbro, but including some orthoclase-free
gabbro. The rock is “massive and irregularly jointed, making
great ledges facing in different directions, and furnishing bare
rounded summits to the hills which it composes. ”
“ The prevalent type of the gabbro . . . is of a light gray color,
and very coarse-grained, single feldspar crystals sometimes reach-
ing even an inch or two in length. The augitic ingredient is
plainly in greatly subordinate quantity, and often on a fresh sur-
face its presence cannot be detected at all. On exposed surfaces,
however, the weathering generally brings it out, and then it can
be plainly seen to fill the spaces between the feldspars. Titanif-
erous magnetite is also often perceptible to the naked eye in large
particles. ”
“ Less commonly the grain is finer and the color darker, the
augitic ingredient at the same time becoming more plentiful. In
the thin section the predominant feldspar is seen to be a plagio-
clase belonging near the oligoclase end of the series. There appears
also to be a younger feldspar present, which has the character
of orthoclase and fills corners between the plagioclase crystals,
around whose contours it moulds itself sharply. Streng and
* Copper-Bearing Rocks, p. 144.
* Copper-Bearing Rocks, Mon. V., U. S. Geol. Survey, p. 266 and 269.
DLE MASE NLASSIVic ROCKS 2 LE, 697
Kloos* found 1.61 per cent of potash in the rock, which they
very properly regarded as belonging to orthoclase. The spaces
between the feldspars are filled with a diallage which is always
more or less altered to greenish uralite. The alteration in many
sections is carried beyond uralite to chlorite. The magnetite is
very large, abundant and titaniferous. Apatites of large size are
found in all sections. Biotite is not an uncommon accessory.
Olivine is absent from all sections.”
It is very evident that the writer is not describing by these
words the rock of the great ‘flow’ as he defined it in his later
papers, but that he is dealing exclusively with the orthoclase
gabbros, which were afterwards separated from the underlying
mass and given a position just above this.”
The only specimen of the true basal gabbro examined by
iinvine steame trom thre Cloquet tiver, imSec- 34, ©: 53) Ni Re 4
W.in Minnesota. This he characterizes as ‘A very fresh olivine- ,
gabbro. It is light gray in color, very coarse grained, and [is |
composed chiefly of very fresh plagioclase (anorthite). Quite
fresh diallage fills in the space between the feldspars. A few
large fresh olivines occur here and there in the section. Titanif-
erous magnetite is abundant, and large sized, and biotite occurs
in a few small scales.”
Dr. Wadsworth* made no attempt to describe the general
features of this great mass of rock. His descriptions are of hand
specimens furnished him for examination by the officers of the
Minnesota survey. Among them were several representatives of
the ‘‘ basal flow,’> but these were not studied with reference to
each other, except in regard to their alterations.
t Neues Jahrb. f. Min., etc., 1877, p. 113.
2 See ante, p. 692.
3 Copper-Bearing Rocks, p. 272, also p. 46.
4Geol. and Nat. Hist. Survey of Minnesota. Bull. No. 2.
5The specimens described by Dr. Wadsworth that are thought to belong to the
basal gabbro are the following: No. 696, p. 69; 706 and 702, p. 70; 773 and 713, p.
71; 699, 769 and 701, p. 72; 689 and 721, p. 75; 780, p. 85; 707, p. 87; 693, p. 88;
694, 704 and 703, p. 89; 787, p. 90; 715, 692 and 777, p. 91; 691, p. 92; 700, 714 and
698, p. 93; 705, p- 94; 514 and 513, p. 95; 697 and 776, p. 96; and 781, p. 97.
698 THE JOURNAL OF GEOLOGY.
It has already been intimated that the normal rock of the
great gabbro is so uniform in its general character that, after
studying carefully one of its hand specimens, others might
easily be identified among a collection of specimens of the basic
rocks of the Lake Superior region, without much danger of error.
Its description, therefore, is quite a simple matter. In its macro-
scopic aspect the normal rock is a medium to coarse-grained, gray,
granular aggregate of a very lustrous plagioclase and a black
augite. The plagioclase is usually more abundant than the darker —
mineral ; its dimensions are larger, andits contours more frequently
approximate to those of crystals. It is of a light gray color and
has a glassy lustre on fresh fractures, while on weathered surfaces
it is white and opaque. Twinning striations are visible on nearly
every grain. The augiteon the contrary is jet black. Its cleav-
age faces are rather small, and its contours never approach those
of crystals; they are occasionally triangular or wedge-shaped
when they have any definite form, but are usually very irregular
in outline. In some of the coarse-grained varieties of the rock
there is a rudely lamellar arrangement of both the augite and the
feldspaf, so that the mass possesses a platy structure. With this
exception the gabbro has the typical granitic texture, and is thus
easily distinguished from all the other so-called flow gabbros of
northeastern Minnesota and the region bordering on Lake Supe-
rior in which is more or less perfectly developed the diabasic
texture.
The principal varietal differences noted in the rock are due
solely to the proportions of feldspar, augite and olivine present
in it. When the pyroxene is in moderate quantity the appearance
of the specimen is as indicated above. Sometimes the feldspar
is largely in excess, and pyroxene has almost entirely disappeared.
Now the rock. has a lighter gray color, and the bright shining
black particles are lacking. Again olivine is the principal com-
ponent when the tint of the rock becomes dark green. The
structure in all cases, however, remains the same. The varieties
are merely local phases of the predominant rock for on all sides
they grade into one another by insensible transitions. The
TED EA SKC NDA SSUV LE: LO CLES PAC: 699
density of the varieties depends of course upon their composition ;
the larger the proportion of feldspar present the lower the specific
gravity. Of the three specimens whose densities were determined,
one (10440) was found to have a specific gravity of 2.8061,
another (8786) of 2.9475, and the third (8589) of 3.0636.
The sections of nearly all specimens taken from the interior of the
gabbro area, or from points at some little distance from its north-
ern edge are similar, in that they represent a very fresh rock,
whose structure is monotonous and whose composition is quite
simple. All contain magnetite, olivine, pyroxene and plagioclase
as primary constituents, and many have in addition as secondary
components, biotite, chlorite and quartz. The proportions of
secondary products present are never sufficiently large to affect
the characteristics of the rock as a whole, though they be abund-
ant enough to change materially its appearance in thin section.
The usual succession in the formation of the primary minerals is
as indicated, and in this respect does the gabbro of the mass
under discussion differ most essentially from the other ‘“gabbros”’
of the same and neighboring regions, for in all of the latter
rocks studied the pyroxene is younger than the plagioclase.
The feldspar is the most abundant of the essential compo-
nents, sometimes constituting, as it does, almost the entire section.
It is nearly always in large grains, whose contours are very
irregular in shape, and only very rarely resemble those of the
lath-shaped grains of diabasic plagioclase. The mineral is quite
fresh and is devoid of secondary inclusions, other than a few
flakes of kaolin and small flecks of some chloritic substance.
The characteristic acicular inclusions of gabbroitic feldspar are
sometimes absent from the plagioclase of the Minnesota rock,
but more frequently they are present in the usual forms. Small
areas of augite and little grains of biotite and magnetite are also
enclosed in the feldspar, and dust-like particles are scattered
everywhere throughout the grain. The inclusion of augite within
the plagioclase would seem to show that the latter mineral is
undoubtedly younger than the former; but certain triangular
areas of pyroxene between grains of plagioclase would point to_
700 LTE OOLNAESOLNGLOCOGNE =
the opposite conclusion. The amount of plagioclase in all por-
tions of the gabbro mass is so great that it must have occupied a
long period in its separation. It is probable that the augite
began to separate from the magma that yielded the rock some
time before the plagioclase, but that after the feldspar began to
crystallize the two minerals grew side by side until all the pyrox-
enic material of the magma had been extracted from it, when the
feldspar continued its growth unaccompanied by the formation
of pyroxene. Thus some of the plagioclase is older than some ;
of the augite, though the greater part is younger than the great
mass of this mineral.
All the plagioclase grains are traversed by broad twinning
lamellae, the maximum extinction on each side of whose compo-
sition plane is about 35°. In order to determine accurately the
nature of this plagioclase, the three specimens whose densities
are given, were powdered and their feldspars separated by the
Thoulet solution. Most of the mineral was precipitated when
the density of the solution was between 2.674 and 2.728, the
limits in the different cases being as follows: in specimen
8786 between 2.700 and 2.728; in 8589 between 2.700 and 2.711,
and in 10440 between 2.674 and 2.712. Asa small amount of
the plagioclase in each specimen was more or less altered, the
average of the above figures may be taken as representing the
average density of the plagioclase in the gabbro. The method is
justified in the fact that the optical properties of the powder in
all cases was exactly the same, and that its precipitation was not
in steps or stages, but was continuous between the limits men-
tioned. The mean density of the feldspar separated from the
three rocks was thus 2.701, which indicates avery basic labrador- ©
ite. In the feldspar of a specimen of the gabbro from the Clo-
quet river Irving* reports 52.40 per cent. of SiO,, while for the
most acid member of the bytownite series Tschermak ? calculates
49.1 per cent. of SiO,. The largest quantities of the powder in
the above three cases fell respectively at 2.700, 2.711 and 2.712.
te
™ Copper-Bearing Rocks, p. 439.
? Lehrb. d. Mineralogie, 2te Aufl. 1885, p. 439.
LTTE ASAD SAC TIVES SUVA, TG OE LES) LG LEG: 7O1
There can thus be no doubt that the feldspar throughout the
entire mass of the rock is practically of the same character, since
the three specimens tested were taken from three widely separ-
ated portions of the gabbro area, and each represents a distinct
type of the rock. No. 8786 is very rich in olivine, No. 8589
contains much augite and a large quantity of brown biotite, while
No. 10440 is very rich in feldspar and quite poor in pyroxene.
An analysis of the feldspar separated from No. 8786, and
partial analyses of the plagioclase from the other rocks were made
by Dr. W. H. Hillebrand. They are as follows:
8786 8589 10440a 10440b
SI OR Rey isaeye shesereus 51.89 52.18 47.59 46.92
EN OR oeco-a Oeaio's oe 29.68 29.20 30.97 31.51
WEsOm oocccscccca6 »32 ah 1.55% 1.29*
ie tO airs apotocm ae on 37 Nate
GCAO Rae seieneciae 12.62 11.18
IMIEXO) scocobcatcsoe 38
IK AO) 6 spines tee ado 50
INeaO Gnas Ge cedde 6 3.87
Isl 0). (it@O™)) cases .07
HO (above 100°). . 39
Total 100.09
Sp. Gr. 2.700 2.711 2.712 2.074
The figures under 8786 and 8589 correspond very closely with
those of a basic labradorite. Those under 10440a and 10440b
are abnormal, in that they indicate that the more basic portion
of the feldspar in this rock has a lower specific gravity than the
more acid one. The alumina in the four cases, however, corre-
sponds quite well with the proportion of this oxide in basic
labradorites. In Ab,An,, which Tschermak makes the dividing
line between labradorite and bytownite, the percentage of alumina
present is 32.8 per cent. Since the rock specimens from which
these feldspars were separated represent the only phases of the
gabbro that have retained the normal gabbro characteristics, it is
probable that the feldspars themselves represent the variations
within whose limits all of the feldspar in the great mass of the
‘rock may be found. A comparison of this plagioclase with that
of the very coarse diabase from the boss-like dike forming Pigeon
* All iron determined as Fe,Oz.
702 PAE JOURNAL OPLGEOLOGY:
Point, show it to be a little more acid than the latter, though not
enough so as to cause it to be placed in a position in the plagio-
clase scale far removed from that of the feldspar of the diabase*.
The corresponding figures for the two plagioclases are:
Sine WAI,@. 0 2Hes@s HeO CaO ~=—-Na,O
Gabbro 51.89 29.68 .69 12.62 3.87
Diabase 53-75 30.39 1.26 10.84 3.76
The augite is generally older than the plagioclase, although
the latter mineral seems sometimes to mould the contours of the
former one. The pyroxene occurs either in the interstices
between the labradorite grains, or as narrow rims around the
olivine, forming a mantle that surrounds these and separates them
from the feldspar (see Fig. 1).2 The mineral is very light
colored, sometimes being almost colorless, but it is usually tinged
Dee
Fic. 1. Section of the olivine-gabbro, exhibiting the tendency of the pyroxene to
include olivine grains. Section 1103. XX 20.
with pink. It is moreover possessed of a diallagic parting,
accentuated by dark decomposition products, the most abundant
of which are tiny, irregular black and brown dots. These are
scattered everywhere throughout the pyroxene, but are accumu-
lated most thickly in the neighborhood of the cleavage lines. In
some of the pyroxene pieces are the peculiar platy inclusions
* Bull. U. S. Geol. Survey, No. 109.
*Cf. M. E. WADsworTH, Bull. No. 2, Geol. and Nat. Hist. Survey of Minn., Pl. III.
Fig. 1. In this figure the author pictures a pyroxene and olivine bearing the same
relation to each other as the diallage and olivine shown in Fig. 1 of this paper.
WEN, ToC MILA S SOLID, I ONCVGS\, SD INC: 703
characteristic of gabbro diallage. These are often arranged in
straight lines crossing the parting planes. They are frequently
so crowded that the line of inclusions appears as a dark bar cross-
ing the diallage at various inclinations to the cleavage, as in the
most notable case (No. 8786), where the direction of the bar
cuts the prismatic cleavage at 21° and on the same side of it as
the extinction, which is 37° (see Fig. 2). Under polarized light
the diallage appears as though polysynthetically twinned. The
lamellae holding the inclusions polarize with a slightly different
Fic. 2. Inclusions in Augite. Section 8786. XX ca. 18.
color from that of the inclusion-free lamellae. Moreover, the
material in the immediate vicinity of the several inclusions seems
to be more changed from its original condition than portions of
the same lamellz at a greater distance from them. This would
indicate that the inclusions have absorbed some of the material
of the pyroxene in their growth, and consequently that they are
not original inclusions, as are those found by Williams* in the
Cortlandt peridotites and norites, but are secondary like those
discovered by Judd? in the peridotites and gabbros of the West-
ern Islands of Scotland.
Under high powers a second cleavage can be detected asa
series of fine lines perpendicular to the prismatic cleavage, in
sections parallel to the vertical axis. Along these cleavage lines
are disposed the inclusions with their long axes so arranged in
the direction of the lines as to suggest that the latter were planes
of easy solution—that the decomposition of the diallage first
took place along them, and then attacked the pyroxene on both
sides.
t Am. Jour. Sci., 3rd ser., vol. 31, 1886, p. 33; and vol. 33, 1887, p. 141.
2 Quart. Jour. Geol. Soc., London, vol. 41, 1885, p. 354.
704 THE JOURNAL OF GEOLOGY.
The only other alteration noticed in the diallage is along its
edges, where brown and green hornblendes are developed, and in
one case where the pyroxene is replaced in part by rosettes of
chlorite that polarize in bright blue tints. The very deep pink
color of some of the diallage plates may be due to incipient alter-
ation, as along with the change in color there is produced a finely
fibrous structure. The writer has searched earnestly for indica-
tions of enstatite*’ in the rock under consideration, but has
failed to discover any, though strongly pleochroic hypersthene
is present in large quantity in certain of its phases to be men-
tioned later. In one or two specimens of the normal gabbro
there is also a little hypersthene, but it is not finely fibrous, and
it occurs as very compact plates side by side with equally com-
pact and very fresh plates of diallage.
Much of the pyroxene, as has been said, is in the interstices
between the plagioclase and therefore is probably younger than
this constituent. It is, however, not in the ophitic areas charac-
teristic of diabasic pyroxene, but is usually in narrow stringers
between the feldspar grains, and between these and the olivine.
In some sections every grain of olivine is thus separated from
plagioclase (Fig. 1), while in other sections, where this is not
the case, the diallage is in too small quantity to serve this pur-
pose. Narrow rims of this mineral also exist around magnetite
and biotite, and they occur between these two minerals and oliv-
ine and a fibrous growth that surrounds them, especially the
olivine, in a manner resembling a reaction rim.
Attempts to isolate the diallage for analysis were not success-
ful, as it was found impracticable to free its powder from hyper-
sthene and the brown earthy decomposition products of olivine.
The last mentioned mineral is usually quite fresh, and in large
quantity, though in a few specimens it is represented by only an
occasional grain in the thin section. Since it was one of the first |
separations from the magma yielding the rock, it is always present
in more or less well defined idiomorphic grains. These are
*Cf. M. E. WaDsworTH: Nos. 787 and 692, pp. 90 and gi. Bull. No. 2 Minn.
Geol. Survey.
THE BASIC MASSIVE ROCKS, EDC. 705
transparent and almost colorless. In thick pieces a yellowish
green tinge may be noticed, but in thin slices no recognizable
tint may be detected. The inclusions are opaque dendritic par-
ticles, spongy magnetite, and secondary products;among which
may be mentioned yellowish serpentine, chlorite, and opaque and
yellowish-brown earthy substances. These may occasionally
entirely replace the original mineral, but more frequently they
occur only in the cleavage and other cracks in the fresh olivine,
or along its edges.
In most cases the olivine is so fresh that it was thought worth
while to have an analysis of it. This has been made by Mr.
Hillebrand, who had furnished him a powder consisting of beauti-
fully fresh olivine intermingled with a little diallage, the mixture
having been separated from rock No. 8589 by means of methy-
lene iodide. The olivine was isolated by digestion with hydro-
chloric acid, and the solution obtained was analyzed with this
result : 3
On WO, MMW On CrfOn ISO) Nin CoQ IW CeK@) Wile) Isl). dowevl
BS) — Wa .92 ie, BROT AS + 20 p .90 26.86 .31 100.25
The olivine is thus a hyalosiderite with Mg: Fe about 1% :1.
The small quantities of manganese and cobalt present in it are of
interest from the point of view of Sandberger,’ as affording
another indication that olivine is frequently that constituent of a
rock which is the source of the material for ore segregations. In
the present instance they are of little significance, however, since
so far as known the only ores occurring within the large areas cov-
ered by the basal gabbro are magnetite and ilmenite. At Copper
Lake, in Secs. 9 and 10, T. 64 N., R. 4 W., weathered masses of
the gabbro are stained with a green coating of malachite, and the
same* staining has been noticed at the contact of the Pigeon
Point gabbro with a red granophyric rock, where it has resulted
from the alteration of chalcopyrite, but in neither case is the
copper compound in sufficient quantity to constitute an ore.
‘Cf. J. F. Kemp: A Brief Review of the Literature of Ore Deposits. School of
Mines Quarterly, XI., No. 4, p. 366.
2 Bull. U. S. Geol. Survey, No. 109.
706 THE JOURNAL OF GEOLOGY.
The relation existing between the olivine and the diallage is
the most interesting of the phenomena presented by the rock.
It has already been stated that but very few olivine-grains are in
direct contact with feldspar. Around nearly all are narrow rims
of pyroxene. At first glance these appear to be a sort of reac-
tion rim between the two minerals, but a more careful study of
the sections disposes of this assumption, for the surrounding rim
frequently broadens out and merges into a well defined diallage
plate (Fig. 3). In consequence of the occurrence of the olivine
and augite in the manner described sections of the rock exhibit a
Fic. 3. Olivine partly surrounded by narrow rim of pyroxene, which is continuous
with large plate of same mineral. 8803. X ca. 18.
kind of concentric structure, with the rounded olivine grains sur-
rounded by a zone of diallage, and imbedded in a mass of
plagioclase. Perhaps the most perfect exhibition of this associa-
tion of the three minerals is shown in the section of rock No. 1103
from the Cloquet River, where the augite is in such large quantity
as to completely envelop the olivine (see Fig. 1).
When the pyroxene is in smaller quantity the rim is much
narrower, and in many cases is in its turn separated from the
plagioclase by a fibrous growth between the last named mineral
and itself. This fibrous growth imitates in great perfection many
of the reaction rims described by various investigators * as exist-
t TORNEBOHM: Neues Jahrb. f. Min., etc. 1877, pp. 267 and 384. A. A. JULIEN:
Geology of Wisconsin, vol. 3, p.235, Pl. 22. F. BECKE: Min. u. Petrog. Mitth. 1882,
TLE BA SUC MAS SEVLE ROGCTES, = 211. HOE
ing between olivine and plagioclase in many basic rocks. It
usually consists of very fine fibres extending perpendicularly
from the bounding surfaces of the diallage rim, or when this is
lacking, from the peripheries of the olivine grains. In a few in-
stances the fibres form radial groups, centering at points on the
exterior of the surrounded mineral. The growth is especially
noticeable in the vicinity of the olivine, but it is occasionally
also found bordering magnetite grains (Fig. 4) and flakes of
biotite. The fact that the fibres are not confined to the borders
Fic. 4. Fibrous intergrowth around magnetite (?) Between the latter mineral and the
fibrous rim can be seen a narrow zone of diallage. Section 10439. X 20.
of olivine, but are found as well around magnetite, biotite,? and
outside of the diallage rims around olivine grains, is presumptive
evidence that the growth is not of reactionary origin.
Between crossed nicols portions of the fibrous zone polarize
brilliantly, while other portions have the pale blue tint of thin
feldspar. Under very high powers the individual fibres are dis-
covered to be discontinuous. They branch, fork and bend ina
fantastic manner, and sometimes stop abruptly, while new fibres
begin their courses some distance beyond and continue to the edge
iv., pp. 330, 350, 450. G. H. WiLiiAMs: Bull. U.S. Geol. Survey, No. 28,p. 52. M.
SCHUSTER: Neues Jahrb. f. Min. etc., B. B. v. p. 451. TEALL: Mineralogical Maga-
zine, Oct. 1888, p. 116. LAcRroIx: Bull. Soc. France d. Min., 1889, xii., p. 83.
2The biotite is probably secondary so that the occurrence of the fibrous rim
around it is of little importance as an aid in determining its nature.
708 THE JOURNAL OF GEOLOGY.
of the rim. It is impossible to determine the character of the fibres
in the finest rims, but in those in which the structure is coarser, it is
learned that two components are present. One is possessed of a
high index of refraction, and strong double refraction, and this
appears to be continuous with the diallage of the narrow zones
interposed between the fibrous growth and the surrounded
olivine. The other component penetrates between the pyroxene
fibres, and has club-shaped ends. Occasionally the twinning
bars of plagioclase may be detected in it, and hence it is assumed
to be a triclinic feldspar. The fibrous rim is thus an intergrowth
of plagioclase and augite, both of which minerals are.normal con-
stituents of the gabbro. In the fibrous rims they have evidently
crystallized contemporaneously, whereas in the main body of the
rock the main portion of the diallage preceded the plagioclase in
its separation from the magma. There is no necessity for
regarding the intergrowths as in any way connected with reac-
tionary processes, while there is abundant reason for believing
them to be due solely to the tendency of simultaneously crystal-
lizing minerals to mutually interpenetrate each other. This
tendency is well recognized as existing to a marked degree
between quartz and orthoclase, whereby granophyre is formed,
and to a less extent between various other minerals. Micropeg-
matitic intergrowths between hornblende and feldspar, for
instance, have been described by Lévy,’ Camerlander? and La-
croix,3 between hornblende and quartz by Kalkowsky,*+ between
garnet and feldspar by Becke,’ and between garnet and quartz
by Lacroix (l.c.,p. 317,) between diopside and quartz by Lévy,°
and between various monoclinic pyroxenes and plagioclase by
Beckes@ic.), Camerlander (1. c.), Lacroix (1), c)) pp. 3enand
318), and Lévy.?7, In the Minnesota rock the diallage in many
* Bull. Soc. Min. d. Fr., 1878, p. 41.
2 Ref. Neues Jahrb. f. Min., etc., 1888, II., p. 52.
3 Bull. Soc. Franc. d. Min., 1889, XII., p. 319.
4 Gneissformation, des Enlengebirges, p. 41.
5 Min. u. Petrog. Mitth. 1878, p. 406.
© Bull. des Serv. d. 1. Carte geol. d. 1. France, No. 9, 1890, p. 7.
7Ib. p. 7.
TTL VAST Cs VAS SIMA, AAO). CLES a LENG, 709
instances sends out tongue-like processes that penetrate far into
the plagioclase in which the pyroxene is imbedded (see Fig. 5),
so that there can be no doubt that the conditions were favorable
to the formation of intergrowths between these two minerals
during the period when they were separating from the rock
magma. The only essential differences between the fibrous
Fic. 5. Diallage plate and olivine grain in plagioclase. The augite in the bend
extends out into the feldspar, giving rise to an intergrowth, very like that of the
fibrous rim. 8803. X ca. 20.
intergrowthe and that illustrated in this figure are, first, the finer
structure of the former, and second, its occurrence around the older
components of the rock. Neither of these differences is impor-
tant, however. Only the second needs a moment’s consideration.
The position of the fibrous growth around the olivine and
other minerals is due not necessarily to the fondness of the inter-
growth for this place, but simply to the fact that the diallage,
during the earlier stages of its growth, fastened itself to the solid
particles in its vicinity and coated them with an envelope of its
material. Continuing its growth it formed the encircling rims of
this material that are so characteristic of many specimens of the
gabbro, and, when the feldspar began to separate it formed with
this the granophyric intergrowth. Since the position of the dial-
lage had already become fixed, the intergrowth naturally was
compelled to occupy a place just without this and around the
minerals which the diallage had already partially or entirely
encircled. Though a fibrous intergrowth of pyroxene and plagio-
clase with the aspect of a reaction rim surrounding the older min-
erals of a rock is a rare phenomenon, it is not a unique one, for
‘For fuller description of the intergrowth, see author’s paper in Am. Jour. Sci.
XLIII., 1892, p. 515.
710 THE JOURNAL OF GEOLOGY.
Camerlander,’ in 1887, described a similar intergrowth of these
two minerals around the garnets of a contact rock from Prachatitz,
in the Bohemian Forest, and mentioned that it strongly resembied
the kelyphite rims around garnets in serpentine.’
Biotite is present in many sections of the gabbro, though not
in all. It not only occurs in the neighborhood of magnetite,
where this mineral is in contact with plagioclase, but it is some-
times found imbedded in the feldspar and augite, and at other
times it forms a mosaic with decomposed diallage. In basal sec-
tions it is reddish brown, and in longitudinal sections is light
yellow normal to the cleavage, and dark brownish-green, almost
opaque, parallel to this structural feature. Inall cases it is prob-
ably secondary, for, even when it apparently occurs alone, a very
close inspection of its sections will often reveal remnants of mag-
netite grains imbedded in it. This form of the mineral is evidently
a reaction product between the magnetite and the plagioclase by
which it is surrounded. The remainder of the mica is probably
derived mainly from diallage, since when this mineral is perfectly
fresh biotite is absent from the rock, and when the pyroxene has
undergone any kind of decomposition, little flakes of biotite are
intimately intermingled with its undoubted alteration products. °
In the broad pieces of diallage in which the dark platy inclusions
are so common, little flakes and tiny needles of biotite are fre-
quently discovered lining the cleavage cracks, so that such pieces
not uncommonly are crossed by two sets of inclusions cutting
each other at some acute angle, one set comprising the gabbroitic
kinds already described, and the other set the biotite plates along
the cleavage cracks.
Magnetite is widespread throughout the rock, but it is not
abundant in most sections. It is in small grains, and in tolerably
large areas that are broadly rod-shaped or very irregular in out-
line. In most cases it occurs between neighboring plagioclase
tJahrb. d. K. K. geol. Reichsanst, 37, 1887, p. 117.
? The writer is informed by Dr. J. J. Sederholm that intergrowths similar to those
occurring in this Minnesota rock are common in Norwegian gabbros and in one from
Ylivilska, in Finland. In his university lectures Professor Brogger calls them “ coron-
ICES sz
WEED, eA SIG WMA SSSI, AR OCIGS V3 IRC Fin
grains, but sometimes it is included within them. The larger part
of the mineral is undoubtedly primary, while a smaller portion is
probably secondary. By its alteration it gives rise to biotite, as
mentioned above, through reactions set up between it and the
contiguous plagioclase, so that often a grain of the magnetite is
entirely surrounded by a true reaction rim composed entirely of
biotite. Leucoxene decomposition products were not once
observed.
Nowhere in the normal gabbro does the magnetite occur in
sufficient amount to constitute an ore, but in certain phases of
the rock that have lost entirely the gabbro characteristics, it is
known to exist in great quantities. Prof. Winchell* describes
these ores in detail and gives analyses of them; but most of the
titaniferous magnetites of this author’s gabbro-titanic-iron group
do not occur in the normal rock of his basal mass. They are
found either in its peculiar phases to be described later, or in the
Animikie and Keweenawan coarse-grained diabases, whose mag-
netite is always highly titaniferous, and in which there is always
an abundance of leucoxene. Only a few qualitative tests have
been made on the magnetite separated from the gabbro, but |
they all agree in showing no trace of titanium. If, upon further
investigation, it is found that an absence of titanium from the
magnetite of the basal gabbro is characteristic for the rock, an
important difference will have been discovered as existing between
it and the rocks of the interleaved flows of nearly similar compo-
sition in the underlying and overlying series.
The only other original component seen in any sections is
apatite. This is in the usual form, as colorless, acicular crystals
imbedded in feldspar, and in the various alteration products of
the diallage and olivine. It is present only in very small quantity.
Quartz is rare as a secondary substance, mingled with other
secondary products in the most altered phases of the rock. Inone
section (No. 8796) it is filled with tiny, opaque, acicular inclusions.
In order to learn something of the limits through which the
rock varies in its chemical composition two specimens were
*Bull. No. 6. Minn. Geol. Survey, p. 117 and 125.
712 THE JOURNAL OF GEOLOGY.
analyzed by Dr. H. N. Stokes of the laboratory of the U.S.
Geological Survey. No. 8589 contains a large proportion of
diallage and olivine, while No. 8786 is more nearly of the average
composition of the entire mass.
8589 8786
SiO, - - - - - 45.66 46.45
TiO, - - - - - 92 1.19
12 KOR - - - - - 05 02
Al,O, Sih - - - - 16.44 21.30
GirxO- - - - - - tr.
FeO - - - - - 13.90 9.57
Fe,O, - - - - - -66 aot
NiO - - - - - .16 .04 ;
MnO - - - - - tr. tr.
CaO - - - - 7R22 9.83
MgO - - - - - 11.57 7.90
K,O - - - - - 41 34
Na,O - - - - - 25r3 2.14
HO at 105° - - - - .07 14
H.0O above 105° - - - 83 1.02
Total, 100.03 100.75
The larger percentages of Al,O, and of CaO in 8786 as
compared with 8589, and the smaller percentages of FeO
and MgO, substantiate the results of the microscopical study.
An increase in the proportions of Al,O, and CaO indicates
an increase in labradorite, and a decrease in FeO and MgO,
a decrease in the iron-bearing minerals olivine and diallage.
The variations are somewhat larger than was to be expected
in a rock so uniform in structure and so monotonous in
composition as that of this great mass, but they are easily
accounted for by the local accumulation of certain of its heavier
constituents. So far as known there are no “schlieren” in the
normal rock nor any other evidences of a differentiation (‘« spal-
tung”) of its magma before cooling, so that the variations in
mineralogical and chemical composition must be looked upon as
due purely to accidental causes. Moreover, the differences are
not great enough to effect any material impression upon the
rock as a whole. Its characteristics are practically identical
throughout an area of several thousands of square miles, and are
LTE WB ASLO WA SST Vil TO CESS), 7 1G. 713
quite different from those of the comparatively thin flows
between the sedimentary layers of the Keweenawan.
Prof. Winchell, in his bulletin on The Iron Ores of Minnesota,
asserts* that the ‘‘gabbro is found associated with red syenite,
quartz-porphyry and various sedimentary rocks in northeastern
Minnesota, and, indeed, it passes through unimportant petro-
graphic changes into the well known ‘traps’ of the cupriferous
formation, from which it has not yet been possible to separate it
by any important lithologic or stratigraphic distinctions.” But
since Prof. Winchell has included within his gabbro the rocks of
Bellissima Lake, Carlton’s Peak and the feldspar masses enclosed
in the dark trap of Beaver Bay, it is plain that he does not con-
fine his remark to the rock to which the writer is now limiting his
attention, viz., the great coarse gabbro which Irving described
as the great basal flow of the Keweenawan. This rock, as has
been shown, by a study of specimens taken from very many dif-
erent localities (see list of specimens studied, p. 714) within the
area underlain by it, is so very uniform in its characteristic
features that no difficulty is experienced in distinguishing its thin
sections from those of any other rock in Minnesota north of
Lake Superior.
Summary.—The microscopical study of the gabbro of
5)
- Irving’s ‘‘ basal flow” at the bottom of the Keweenawan in Min-
nesota reveals a rock which is uniform in texture and composi-
tion throughout its entire extent. It is composed of magnetite,
olivine, diallage and labradorite as essential constituents, with a
little biotite and occasionally a very small quantity of quartz
as secondary components. Its structure, or better texture, is
typically granitic in that all of its comprising minerals are
hypidiomorphically developed, with the plagioclase younger than
the diallage. In this respect the rock is essentially different
from the so-called gabbros of the thick flows interbedded with
the clastic beds of the Animikie series and the Keweenawan
group in the same region, for in the latter, notwithstanding the
TET CiseDsy LOA.
714 THE JOURNAL OF GEOLOGY.
coarseness of their grain, the plagioclase is always older than the
diallage, and it always possesses in greater or less perfection the
lath-shaped sections characteristic of diabasic feldspar. This
being the case, it seems possible that the great gabbro of north-
eastern Minnesota is not a ‘‘flow’”’ or a ‘series of flows,” but is
the solidified reservoir * in which later flows originated or is a
batholitic mass, as Winchell? has latterly come to call it.
Further field work on the geological relationships of the mass
will probably show either that it is a batholite within the
Keweenawan series, well down toward its base, or that, like the
anorthosites of Lawson it is an eroded ‘“‘massive”’ upon the top of
which the later Keweenawan beds have been deposited.
List OF SPECIMENS OF NORMAL GABBROS STUDIED AND THEIR
LOCATIONS.
11031338) 4OO5Na) 200) We Sabin EComen Sec. 334) les aiiNe ue ecm vies
Minn.
6007 (1415) S. side Cross Lake, S. side Sec. 29-64-1 W.
(1416)
(1424)
6011 (1126) S.EY Sec. 21-64-3 W.
6013 (1127) N.W. side Copper Lake, Sec. 9-64—4 W.
6127 (1171) N.EY S.WY% Sec. 36-65-32 W.
6128 (1172) SEY S.WY Sec. 36-65-3 W.
6130 (3203) S.EY S.EY Sec. 36-65-3 W.
7025 (2091) 5S. shore Akeley Lake, Sec. 29—65-—4 W.
8589 (4025) S. shore of small lake in S.EY S.EY% Sec. 19-63-9 W.
8786 (3520) Near S.&% post of Sec. 35-61-12 W.
8788 (3528) N. shore Birch Lake, 200 paces E. of S.Y%post Sec. 24—
61-12 W.
8789 (3529) W. side Birch Lake, opposite N.E. arm of lake, Sec. 24—-
61-12 W.
8792 (3532) NW S.WY Sec. 9-62-10 W.
8793 (4259) N.WY S.EY Sec. 23-62-10 W.
8794 (3522) On Mishiwishiwi river, near centre Sec. 34—62-9 W.
Cf. ante, p. 696.
? Bull. No. 8, Geol. and Nat. Hist., Sur. of Minn. Preparatory note, P. xxiv. e¢ seg.
Wig JEAN SIO ALAS SWE, SEA OUCISGSy 8 JB ING: 715
8795 (3534) On Mishiwishiwi river, near centre of N¥% T. 61-7 W.
8796 (3848) On Mishiwishiwi river, about 2 miles E. of 8795.
8800 (3535) On Mishiwishiwi river, near S. side T. 62-8 W.
8803 (3537) SEY N.EY Sec. 7-63-8 W., 250 paces S. of S.E. point
of Snowbank Lake. =
8869 (4061) S.EY% Sec. 14-64—-7 W.
8896 (3856) N.WY Sec. 6-64-5 W.
10000 (3691)
10438 (5068) Half way down W. side Greenwood Lake, Sec. 29-64-2 E.
10439 (5069) Outlet Greenwood Lake, Sec. 33-64-2 E.
10440 (5013) Ca. S.EY Sec. 8-59-10 W.
10441 (5014) |
10442 (5015) | In order from S. to N. along a stream running from
10443 (5016) | asmall lake northward into Birch Lake. First speci-
10444 (5070) | men from about N. side of T. 59 R. 10 W.
10445 (5071) |
10537 (5160) SEY S.WY Sec. 33-65-5 W.
10538 (4985) S.EY%S.EY Sec. 32-65-5 W.
10539 (4986) S.WY S.EY Sec. 32-65-5 W. East end of portage
between lake Kabamitchikamak and small lake in Sec. 32—65~5
W.
10569 (5181) 1200 paces south N.W. corner Sec. 29—-65—4 W.
10570 (4995) 1500 paces S. of N.W. corner Sec. 29—-65—4 W.
10638 (5242) North of centre of Sec. 18-64-3 E.
SHOWING APPARENT REACTION RIMS.
6130 (3203), 7025 (2091), 8792 (3532), 8793 (4259), 8795 (3534), 8800
(3535), 8803 (3537), 10000 (3691), 10439 (5069), 10442 (5015),
10444 (5070).
NotEe.—The first number given in each case is the number of the specimen in the
collection of the Lake Superior Division of the U. S. Geol. Survey. The numbers in
parentheses are those of the corresponding thin sections.
W. S. BAyLey.
WATERVILLE, ME., July 1, 1893.
Correction.— In the reference (on page 591 of this Journal) to Dr. Wadsworth’s
work on the Intrusive Basic Rocks of the Marquette region, the date of the publication
of the “ Notes on the Geology of the Iron and Copper Districts of Lake Superior,”
is given as 1881. It should be 1880.
It is also stated on the same page that Wadsworth declared these rocks to consist
largely of diabase and coarse basalt, both massive and slightly schistose. It was, of
716 THE JOURNAL OF GEOLOGY.
course, not intended by the use of the word “slightly” to intimate that the author did
not recognize the true nature of the green-schists of the region. It is well known that
in the article referred to that he emphasized particularly the fact that the schists are
metamorphosed basic eruptives. He also showed that many of the rocks which still
preserve their diabasic and basaltic characters are nevertheless “slightly” schistose, and
it is this fact to which it was {desired by the writer to call especial attention. This
correction is made to prevent misapprehension of the writer’s attitude toward the val-
uable contributions of Dr. Wadsworth to our knowledge of the greenstone-schists of
the Lake Superior region. Vide also: Report of the State Board of Geological Sur-
veys for the years 1891 and 1892. Lansing, 1893. Pp. 124-125 and 133-141.
W. S. B:
ON Ene GEOLOGICAL STRUCTURE OF THE MOUNT
WASHINGTON MASS OF THE TACONIC RANGE.
(With Two Plates.)
Published with the permission of the Director of the United States
Geological Survey.
CONTENTS.
Introduction.
Topography.
Previous Work within the Area.
Conditions and Progress of the present Investigation.
Horizons Represented.
Their Lithological Character.
Canaan Limestone.
Riga Schist.
Egremont Limestone.
Everett Schist.
Explanation of Map, Areal Geology.
Method of constructing Sections.
Structure of the Mountain.
Variable Thickness of the Egremont Limestone.
Metamorphic Character of the Rocks as indicated by Microscopic Studies.
Summary and Conclusion.
1HAT portion of the Taconic Range which is known as Mount
Washington is both topographically and geologically a unit. It
covers an elongated elliptical area, about fifteen miles in length
and four and one-half miles in average breadth, lying in the states
of Massachusetts, Connecticut and New York. It occupies the
entire township of Mt. Washington, and portions of Sheffield
and Egremont in Massachusetts ; about one-third of Salisbury
in Connecticut; and portions of Northeast, Ancram, Copake and
Hillsdale in New York.
Topography.—The Mt. Washington mass is a double ridge
enclosing a summit plain. Mt. Everett, or the ‘‘Dome of the
717
718
Taconics” (2624 feet) lying in the
eastern ridge, is the highest peak and
one of the highest elevationsin Massa-
chusetts, while Bear Mountain (2355
feet) is the highest point of land in
the state of Connecticut. The main
summit plain is situated to the north-
ward of the center of the mass and has
an average altitude of about 1700 feet.
Corresponding with the elliptical out-
line of the mountain, this plain is
compressed at the north and south,
so that its length is about three miles
andits breadth two miles. Encircling
it is a line of peaks ranging from 1900
to 2000 feet in height. This encir-
cling wall of peaks is buttressed by
other peaks both to the northward
and southward, the southern side
being strengthened by a parallel belt
across the mountain, composed of
Mts. Gridley, Frissell and
Monument. Southward of this belt
of hills the elevated plateau recurs,
but without the rampart of peaks
which characterize it in the northern
Bear,
and more central area.
The Salisbury-Sheffield valley on
the east and the Copake. Hillsdale
valley on the west of the mass, con-
stitute a floor having an average alti-
tude of 700 feet, from which Mt.
Washington rises abruptly, the mean
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STRUCTURE OF THE MOUNT WASHINGTON MASS. 719
through which runs the Central New England and Western Rail-
road. On the northwest Mt. Washington is merged into the nar-
row ridge of the Taconics, which extends northward into Vermont.
The name Mt. Washington, however, applies properly to allio:
the range lying south of the South Egremont-Hillsdale turnpike.
The regular elliptical contour of the mass is broken on the north-
east by two deep embayments, the eastern one containing Fenton
Brook, and the western, which is knee-shaped, being occupied by
Sky Farm Brook. The regularity of contour is further interrupted
by an outjutting spur on the west side, known as Cook’s Hill.
South of the topographical break which limits the mountain in
the neighborhood of Ore Hill, the range of the Taconics pur-
sues a more interrupted course, the hills becoming smaller and
spreading out considerably.
Previous Work within the Area—As the aim of this paper is
mainly to deal with the problem of mountain structure, no men-
tion will be made of the part which the area has played in the
‘Taconic Controversy,’ except as structural facts may be brought
out by it. The boundary between the basement limestone and
the schistose rock of the mountain was roughly located by Hitch-
cock* for the northern portion, and by Percival®* for all but the-
extreme northern portion of the mountain. The former gives
(Plate 55 E of the work cited) a section across Mt. Washington,
in which the schist and limestone of the east base of Mt. Everett
are shown dipping at a steep angle east. Mather3 gives two sec-
tions across the Taconic Range in the vicinity of Mt. Washing-
ton. One of these (loc. cit. Pl. XIV, Fig. 1) is from Hillsdale,
N.Y.to Egremont, Mass., and passes a little to the north of Mt.
Washington; the other (Pl. XVI, Fig. 3) is from Hudson, N. Y.,
to the southwest corner of Canaan, Ct. The latter crosses the
mountain in a northwest-southeast direction and exhibits a syn-
clinal structure.+
*Geol. of Mass., EDWARD HircHcock, Amherst and Northampton, 1841, Frontis-
piece Map.
? Rept. on the Geol. of the State of Connecticut, J. H. PERCIVAL, New Haven, 1842,
Frontispiece Map.
3 Natural History of New York, pt. iv. Geology, pt. i. 1845.
4In his list of dip and strike observations MATHER includes several from the Mt.
Washington area (pp. 612-613).
720 THE JOURNAL OF GEOLOGY.
In 1864 James Hall and Sir William Logan* visited Mt. Wash- »
ington and described it as probably synclinal in structure.
The only investigator, however, who has made a detailed
study of the geological structure of the mountain is Professor J.
D. Dana, whose papers on the subject have appeared mainly in
the American Journal of Science. His first paper dealing with
the structure of Mt. Washington? appeared in October, 1873. It
contains asketch-map with dip and strike observations. On page
38 he states :
“Mt. Washington is a synclinal with lmestone below and slate
above.”
And on page 39:
“We thus find evidence of a very broad synclinal across the center of Mt. Wash-
ington. But just north, in Egremont, the structure is totally different; the ridges S and
T3 are the sources of very steep and comparatively narrow independent synclinals
with the axial plane inclined westward. * tS ES The synclinals S and T
become merged in one mass in Mt. Washington; and as the limestone does not
appear at the smmmit, the intermediate anticlinal in the mountain was only an anti-
clinal of slate. In other words, the synclinal of limestone beneath the mass of the
mountain was one great trough with breaks and incipient flexures; while to the north
these incipient ‘flexures became two defined synclinals, with the intermediate anti-
clinal—the synclinals being courses in the ridges S and T and the anticlinal that of
the limestone outcropping between; and then, farther north, there was formed the
Taconic synclinal T alone.”
In the same year there appeared in the Proceedings of the
American Association a paper entitled. “The Slates of the
Taconic Mountains of the age of the Hudson River or Cincin-
nati Group.4 In this paper Professor Dana states that limestone
dips west under slates along the east slope of Mt. Washington
for four miles, ‘‘that is, the whole eastern front.” He describes
* Paper read by T. STERRY HunrT before the Natural History Society of Montreal,
October 24, 1864. Reviewed in the American Journal of Science, 2d ser., Vol. xl, p. 96
(1865).
2On the Quartzite, Limestone and Associated Rocks of the vicinity of Great Bar-
rington, Berkshire county, Mass., J. D. Dana, American Journal of Science, 3d ser., vol.
Vi., Pp. 37.
3 The ridge S is that of Mts. Darby, Sterling and Whitbeck, and the ridge T that
of Mts. Prospect and Fray near the New York-Massachusetts state line. (Cf. map pl. i).
4J. D. Dana, Proc. A. A. A. S., 22d (Portland) meeting, 1873, pp. 27-29.
STRUCTURE OF THE MOUNT WASHINGTON MASS. 721
the mountain as composed of two close-pressed synclinals in the
Mt. Washington plateau with steep easterly inclined axes, and
that these synclinals are synclinals of slate riding over a single
synclinal of limestone. ° %
In 1877, in a paper entitled, ‘On the Relations of the Geology
of Vermont to that of Berkshire,’* he adds, referring to the
anticlinals of limestone between the three northern spurs of the
mountain :
“Tt has not been possible to follow these subordinate anticlinals southward,
because the limestone is not continued far in that direction, and the summit of the
mountain is under soil and cultivated farms. But yet the fact of flexure at the north
end is strong reason for believing that similar flexures, if not the same continued, char-
acterize the whole length from north to south of the mountain-mass, such a slate easily
flexing under uplifting lateral pressure. This is further sustained by observations
proving that other subordinate anticlinals exist on the western slope of the mountain,
in the vicinity of Copake Furnace. Close to the western foot there are two nearly par-
allel limestone areas, parallel to the axis of the range. The inner (or more eastern)
one is about a mile long, and the other about haif a mile. They are separated from
one another by a thin belt of hydromica slate, and the same slate exists on the other
sides. The dip of the beds of limestone and slate is to the eastward 50°, the strike
averaging N.15° E. (true). They are evidently registers of local folds—anticlinal and
synclinal, the former bringing up the limestone.”
In the paper ‘““On the Hudson River Age of the Taconic
Schists,’* Professor Dana has put on record new observations
showing the synclinal character of the mountain (1. c., p. 376)
and printed a map including a part of Mt. Washington (p. 379)3.
Another paper, ‘On the Southward Ending of a Great Syn-
clinal in the Taconic Range,’’¢ is specially devoted to a consider-
ation of the structure of Mt. Washington, and contains a map of
the southern portion of the mountain ona scale of eight-tenths
of an inch to the mile. Professor Dana’s earlier conclusions as
to the synclinal character of the mountain, had been largely drawn
from observations made in Massachusetts. The conclusion that
the synclinal character of the northern portion of the mountain
is continued to the southern extremity, he drew from the fact
*Am. Jour. Sci., 3rd ser., vol. xiv., pp. 262-263.
2 Am. Jour. Sci., 3d ser., vol. xvii., pp. 375-378 (May, 1879).
(3 Cf. also z6¢dem, Supplement to yol. 18, for dip and strike observations).
4 [bidem, vol. xxviii., p. 268 (Oct., 1884).
[2P THE JOURNAL OF GEOLOGY.
that a number of small limestone areas near Lakeville, in which
the strata are but gently inclined, are capped by a schist. This
schist he believed to be the same as the schist of the southern
extremity of the mountain. He says, speaking of these areas
(pe272)):
“Since the limestone is the underlying rock, they are all, if not monoclinal, as is
hardly possible, small overturned anticlinals, which have had their tops worn off so as
to show the limestone beneath.” » * eo * * * *
“The synclinal structure of the mountain is apparent also along portions of the
southern edge of the schist. At Ore Hill, one and a half miles west of Lakeville, the
schist overlies limestone.” :
On page 273 he says:
“The ore-pits that have been opened about the base of Mt. Washington, fourteen
in number, are situated near the junction of the limestone and schist, and in view of
the facts that have been mentioned, this means—wear where the limestone emerges from
beneath the schist.”
Referring to the dying out of the synclinal to the south of
the mountain, he says:
“ Again the pitch of the beds in the last three miles is southward in some parts,
instead of eastward or westward, showing a flattening out of portions of the synclinal
and subordinate anticlinals.”
“Tt thus appears that in the dying out of the synclinal, besides a flattening of por-
tions of the general synclinal and the introduction of southward dips, there was also a
multiplication of small subordinate flexures.”
“‘Farther there is a multiplication of ridges of schist in the limestone area.”
“Several such ridges, some quite small, are situated, as the map shows, south-
eastward of the mountain near the village of Salisbury; and others occur farther east.
They consist of the same mica schist as the mountain,—they have generally an easterly
dip, often a high dip; and the facts seem to show that most of them are syzclinal flex-
ures; that they occupy the troughs of local synclinals in the limestone; * * *
Most of them were, apparently, half-overturned troughs so pushed over westward that
the dip of the schist is generally eastward.” * * * * ES * *
The following is quoted from a paper*™ entitled ‘ Berkshire
Geology” (pp. 15-16) :
“The Mt. Washington schists lie in a trough very much like that of Greylock, but
one relatively shorter in its narrowed part and reversed in position. In the northern
half the trough is a very broad shallow one, while to the south the east side is pushed
up westward.”
t Berkshire Geology, by Prof. JAMES D. Dana. A paper read before the Berk-
shire Historical and Scientific Society of Pittsfield, Mass., February 5, 1885. Pitts-
field, 1886.
STRUCTURE OF THE MOUNT WASHINGTON MASS. 723
In Professsor Dana’s last series of papers’ on the Taconic
Area, he adds some strike and dip observations and prints a more
complete map of the area. In the second of the papers,” on
pages 439-442, he describes the variations in character of the
schist of Mt. Washington as showing a more intense degree of
metamorphism in the eastern portions, and in conclusion states
(p. 441): “The facts here reviewed relate, it should be remem-
bered, to a single stratum, that overlying the limestone.”
The several extracts above given will, I think, sufficiently
explain Professor Dana’s views regarding the structure of Mt.
Washington.
On the geological map of the Taconic area compiled by Mr.
C. D. Walcott,3 the Mt. Washington mass is indicated having the
same relations to the rocks of the adjoining areas as is shown on
Prof. Dana’s map.
Conditions and Progress of the Present Investigation —The writer
made a partial reconnaissance of Mt. Washington in the season
of 1889, but the mapping was largely done during the months of
July and August, 1891. He was assisted during the season of
1891 by Mr. Louis Kahlenberg, at present instructor in chemistry
in the University of Wisconsin. Mr. Kahlenberg has traced the
contact of schist and.limestone along the west base of the moun-
tain. The work has been in charge of Professor Raphael Pum-
pelly, then chief of the Archean Division of the U.S. Geological
Survey.
The reconnaissance of 1889 was made on the southeastern
flank of the mass and furnished only equivocal evidence concern-
ing the relations of the “Stockbridge” limestone of the valley
to the schist of the adjacent flank of the mountain. One of the
first results of the work of 1891 was the discovery of a calca-
tOn Taconic Rocks and Stratigraphy, with a Geological map of the Taconic
Region, J. D. Dana, Am. Jour. Sci., 1885 and 1887.
2 [bidem, 30 ser., vol. xxix., June, 1885.
3The Taconic System of Emmons, and the Use of the Name Taconic in Geologi-
cal Nomenclature, by CHas. D. WALcoTT, Am. Jour. Sci. vol. xxxv., pl. iii. (May,
1888).
724 | DHE JOURNAL OF GEOLOGY.
reous horizon occupying the central Mt. Washington plateau, and
the locating of its boundaries (cf. map). Observations were
then made a little to the north of Salisbury village which showed
conclusively that the schist of that vicinity is de/ow the limestone,
the structure of the mountain at that latitude being essentially
an anticlinal. On examining next the northern extremity of the
mountain, observations were quite as conclusive in proving that
the schist of Jug End is adove the valley limestone, and that the
section across the range at this latitude is essentially what Pro-
fessor Dana has described. This knowledge that we have to do
with two horizons of schist, the one lower and the other higher |
than the limestone of the Egremont valley, was soon followed by
the discovery of lithological differences between the different
beds, which have furnished the key to the structure. Topograph-
ical features soon suggested a course across the mountain through
which the limestone might pass and separate the upper schist of
the northern portion from the lower schist of the southern por-
tion. Through this path the calcareous horizon of the Egremont
valley, considerably modified it is true, has been carefully traced.
A large number of observations have been gathered from all parts
of the mountain mass. Each of the numerous peaks has been
ascended and as many data as practicable have been collected. At
this time the southern portion of the mountain had not been
carefully studied. Later in studying the area lying to the east
and southeast of the mass of Mt. Washington, it was found that
the limestone of that section is divisible into two beds separated
by a schist, which is lithologically identical with the lower of the
two horizons of schist in Mt. Washington. The evidence sup-
porting this and the manner in which the areal relations are illu-
sive in the indications which they afford regarding stratigraphy,
will be set forth in a later paper. The lower of the two lime-
stone horizons was found to extend westward and disappear under
the schist of the south end of Mt. Washington. The schist over-
lying it, which so resembled the lower of the Mt. Washington
schists, was also traced along the northern border of the lime-
stone into the southern portion of Mt. Washington. The areal
STRUCTURE OF THE MOUNT WASHINGTON MASS. 725
relations in the vicinity of the ‘mountain are set forth on
Plate 111.
Florizons Represented—The Mt. Washington series thus con-
sists, not of two members as supposed by Dana, but of four, two
of which are calcareous. The calcareous beds alternate with the
schists, which have been shown to possess marked lithological
differences. The sequence of these beds is as follows: (a) a cal-
careous horizon which I designate the Canaan Dolomite from its
typical development at Canaan ; (b) the lower schist bed, which
I call the Azga Schist from Mt. Riga peak where it is perhaps
most typically developed; (c) a calcareous horizon, which I
designate the Egremont Limestone from its wide extent in the
Egremont valley (this limestone is much modified in all locali-
ties above the valley floor); and (d) the upper schist horizon,
to which I give the name Everett Schist since it assumes its max-
imum thickness within the area at Mt. Everett. It will be noticed
that this sequence corresponds with that which Dale has deter-
mined for the Greylock mass in northern Berkshire county.
Below are given in parallel columns for comparison the series of
Mt. Washington and Greylock :
Mt. Washington Series. Greylock Series (Dale).
1. Canaan Dolomite. 1. Stockbridge Limestone.
2. Riga Schist. 2. Berkshire Schist.
3. Egremont Limestone. 3. Bellows Pipe Limestone.
An Wverett Schist: 4. Greylock Schist.
These beds are probably Ordovician though the lower portion
of the Canaan Dolomite may, like the Stockbridge Limestone, be
Cambrian.? No fossils have as yet been found in the vicinity and
it is hoped that further search may reveal them. Walcott} has
*The Greylock Synclinorium, by T. NELSON DALE. Amer. Geologist, July, 1891,
pp- 1-7. Also given in detail in a forthcoming monograph of the U. S. Geological
Survey, by Professor RAPHAEL PUMPELLY.
?On the Lower Cambrian Age of the Stockbridge Limestone, by J. EL1IoT WoLFF,
Bull. Geol. Soc. Am., vol. ii. 1891. See also DALE, 22d., vol. iii, pp. 514-519.
3The Taconic System of Emmons, and the use of the Name Taconic in Geolog-
ical Nomenclature, by CHas. D. WaLcort, Am. Jour. Sci., vol. xxxv, pp. 237-242, 399-
401, March and May, 1888. (With map).
726 THE JOURNAL OF GEOLOGY.
found Ordovician fossils in the limestone belts some distance to
the north and Cambrian fossils at Stissing Mountain to the south-
west.
Lithological Character of Horizons —(a) Canaan Dolomite. This
bed seems to be very rich in magnesia, the rock being in some
cases at least a true dolomite. This is shown by a number of
analyses of it by Mr. J.S. Adam.* This rock appears at the sur-
face only in the extreme southeastern portion of the area here
considered, where it presents few features different from those
which are common to the Egremont Limestone. Farther to the
eastward, however, and particularly in the vicinity of Canaan, it
is often characterized by the presence of interesting metamorphic
minerals, the well known salite and tremolite of that locality.
Phlogopite also has in one or two instances been found. In its
upper layers, where it approaches the overlying Riga Schist, the
rock may become graphitic, as at Ore Hill. As it appears in the
vicinity of the mountain, however, the rock presents no charac-
ters which can be relied upon to distinguish it from the higher
Egremont Limestone, and the differentiation is based on strati-
graphy alone.
(6) Riga Schist.—This horizon is tolerably uniform in charac-
ter, the principal differences being in the presence and variable
size of the metamorphic mineral individuals. Strictly speaking
the rock is a gneiss, owing to the abundance of feldspar, but in
order to distinguish it from more feldspathic and more or less
granitoid gneisses lying east of the Housatonic River, it is best
to refer to it as a schist, which it most resembles in structure. It
almost invariably is porphyritic from the presence of lenticular
to spherical grains of an acid plagioclase. The base is usually
composed of feldspar, quartz, and a colorless mica (in part seri-
cite) and biotite. Considerable graphite often exists in this base
as does also ilmenite. Chlorite when present is usually in small
amount. Garnets, staurolite, ottrelite, and biotite, as well as
plagioclase, are developed at many localities. On the summit
of the Lion’s Head the rock contains garnets (rhombic dodeca-
*See Am. Jour. Sci., vol. xlv. p. 404, foot note.
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STRUCTURE OF THE MOUNT WASHINGTON MASS. 727
hedra) over a centimetre in diameter, and staurolites (usually
inclined-cross twins) a centimetre or more in length. Tourma-
line occurs only in minute crystals, much less widely distributed
than any of the other metamorphic minerals “except ottrelite.
Some of the localities where macroscopic garnets and staurolites
were found in the rock have been indicated on the map—small
black circles and crosses standing for the two minerals respec-
tively.
(c) Egremont Limestone.— This horizon as developed in the
valley near the base of the mountain, is a white to gray crystal-
line limestone, which is often quite pure but for small scales of
colorless mica and grains of pyrite. Locally it contains thin
quartzitic or schistose layers. Generally it passes upward into
the Everett Schist of the flanks of the mountain through a graph-
itic layer of variable thickness, and a similar graphitic rock is
also to be found at its lower contact with the Riga Schist. As
met with in the summit plains, the limestone appears under two
modifications which grade insensibly into one another. They
are (1) a very micaceous limestone or calcareous mica schist ;
and (2) a graphite schist, often, though not always, calcareous.
The first mentioned modification is to be found only in the cen-
tral portions of the northern summit plain, where the larger
streams have cut through the thick drift deposits. It is richest
in calcite at two localities, one of which is in the bed of Wright
Brook about midway between its confluence with Ashley Hill
Brook and the north and south road to the east, and the other is
in the bed of City Brook. This rock also occurs in the small
brook near the house of H. F. Keith, in the bed of Huckleberry
Brook, and at several localities on the Ashley Hill road between
Huckleberry and Wright Brooks. It always contains a silvery
mica, graphite and pyrite.
In the northern summit plain graphitic schist (here generally
calcareous) forms a border separating the micaceous limestone
from the Everett Schist which surrounds it. According as it
occurs nearer the limestone, it is the more calcareous. In the
lower course of Wright Brook it contains layers of calcite over a
TOG THE JOURNAL OF GEOLOGY.
centimetre in thickness, while on the road encircling the west
flank of Mt. Everett it hardly effervesces at all with acid. At
localities south of the central plain the rock only rarely exhibits
effervescence with acid. The graphite schist differs from the
limestone not only in the large proportion of graphite and the
correspondingly small amount of calcite which compose it, but
its least calcareous varieties contain also much feldspar and quartz.
Garnets and tourmaline have each been found in one specimen,
the first near the lower, and the second near the upper schist con-
Natacr
(a) Everett Schist.—The rock of this horizon is not in all
cases to be easily distinguished from the Riga Schist. Like that
rock it is porphyritic from lenticular feldspar grains, but these
feldspars are much more abundant and more constant, and the
base is generally more chloritic or sericitic. Ottrelite is found
sparingly at some localities. The most striking lithological dif-
ference from the Riga Schist, however, exists in the entire absence
of macroscopic garnets and staurolites from this horizon, not an
individual of either species having been found within the entire
length and breadth of the area of this horizon exposed, though
they have been carefully sought at each locality. The beds
seem to become more sericitic along the northwestern foot of the
mountain. A phase of the rock which is more characteristic of
the southeastern portions of the area is very chloritic with mag-
netite octahedra sometimes as large a pea. Chloritic phases of
the rock also appear in the extreme northern areas.
Explanation of Map, Areal Geology.t— The eastern and south-
ern portions of the map are based on the Sheffield and Cornwall
sheets of the topographical map of Massachusetts and Connecti-
cut by the U. S Geological Survey, and the portion of the map
lying in New York State is compiled from older road maps. The
manner in which the Egremont Limestone crosses the mountain
separating the Everett and Riga Schist horizons, may well be
emphasized by special description. On the eastern side the
course of the calcareous horizon as it gains the summit plain is
tSee Plate III.
STRUCTURE OF THE MOUNT WASHINGTON MASS. 729
suggested by topography. The series of sections in Figure 2
will show this in some measure.’
Beginning with Mt. Everett, we find that it presents a uni-
formly steep eastern slope of Everett Schist, the limestone being
in contact near the Undermountain Road. Where the slope of
Mt. Race begins a little farther south, an abrupt recession occurs
in the face of the range, which extends west to the foot of steep
cliffs and south to the road north of Sage’s Ravine. Into and
Fic. 2. Series of sections from the east flank of Mt. Washington, showing how the
limestone of the valley gains the summit plain.
along this “bench” runs the Egremont Limestone. Proceeding
southward from the north end of this ‘‘bench,” a tongue of schist
is met lying within the hmestone, about midway between the
cliffs and the road, and forming a backbone, the slope immedi-
ately west being very gradual while that to the east is tolerably
steep. This tongue of schist broadens to the southward, narrow-
ing that belt of limestone which lies to the west of it. As this
limestone belt becomes narrowed toward the south, it ascends the
mountain, losing as it does so most of its calcite and developing
into a black graphitic schist. This reaches the altitude of the
summit plain about one-eighth of a mile north of Bear Rock
730 THE JOURNAL OF GEOLOGY.
Falls. From there it is traced with some difficulty along the
_ road to Sage’s Ravine, between garnetiferous schists on the east
and Everett Schists on the west. The garnets of the eastern
schist belt were found to extend northward into the contracted
part of the tongue of schist. Immediately north of Sage’s
Ravine the graphitic rock is distinctly calcareous. West of this
point the garnetiferous rock occupies the bed of Sage’s Ravine
as shown on the map and in sections, while the Everett Schists
occur on the road above. To the south of Sage’s Ravine and at
the altitude of the summit plain, opens a wide bench fully a quar-
ter of a mile in width with the Everett Schists rising abruptly
from its western edge in Mt. Bear. To the east of it are thin
caps of Everett Schist, then small outcrops of graphitic schists,
alternating for a short distance with garnetiferous and staurolitic
schists, and finally the latter occurs alone, clearly showing that
in the bench and for some distance east of it, the thin bed of
graphitic schist lies at the surface. These relations are exhibited
in section G’ of Fig. 2. Still farther south this bench is extended
into a broad swampy tract on the two sides of which the two
schist horizons are shown in outcrops, the garnetiferous rock
being on the east and the other schist on the west. This swampy
plain outlining the area occupied by the graphitic belt, crosses
the north and south Mt. Riga road just north of Mt. Riga (Bald
Peak), its northern and southern limits being marked by sharp
turns in the road and abrupt rises in the land, as well as by out-
crops of the two schist horizons. In the almost continuous areas
of exposures in the vicinity of the Mt. Riga Lakes, its course is
carved out sharply though the rock is not foundin outcrop. Be-
yond South Pond the belt narrows and begins to be followed with
difficulty. The graphitic rock has been found in outcrop in the
bed of a stream flowing toward Mt. Riga Station. Farther down
this stream is joined by another from the east flank of Mt. Thorpe,
containing likewise a belt of graphitic schists (here calcareous)
in contact with garnetiferous rock on the west. This belt of
graphitic rock is soon cut off to the south, but it is found to join
the ,main valley through a depression of the ridge to the north-
STRUCTURE OF THE MOUNT WASHINGTON MASS. 731
east of Mt. Thorpe, whence it continues northward as a transi-
tional zone between the valley limestone and the Everett Schist.
The rock of Mt. Thorpe is filled with garnets, and the area of
schist east of the easterly branch of the streant has also abund-
ant garnets, though they have only been found at some distance
from the graphitic rock. Between the two forks of this stream,
the upper schist rests as in a saddle, its southern termination
being a small triangular hill. The southeastern portion of the map,
which exhibits areal and structural features of much interest,
will receive fuller treatment in another paper, which will deal
with the structure of the area to the southeast of Mt. Washington.
Method of Constructing Sections —The lines of sections have
been made as nearly as possible perpendicular to the strike of
the strata. The strike has been obtained either by actual
measurement with the compass at the locality, or from the direc-
tions of the boundaries of horizons. The curvings of the sec-
tion lines must therefore indicate, either that the crest or trough
lines are inclined (pitch) or that the flexures are of variable
width. To the southward of section E the average pitch is
found to be northward, as shown by the areal relations, and as
indicated in the steep southern and gradual northern slopes of
thie) kions beadwuc aloe the nonthiomsections By the convexity
of the section lines towards the south is explained both by
southerly pitch and by a greater compression of the flexures in
the northern portion. Southerly pitch is suggested by the topo-
graphy of Mts. Everett and Undine, as well as by the pitching
trough and crest lines of coarse corrugations on the slope that
rises at the south end of Guilder Hollow (cf. reference to Dale
below). These facts when taken in connection with the sections
(Plate IV), show the mountain to have a general basin structure.
The determination of the dip is made with great difficulty
within the area studied, since the lamination indicative of the
plane of bedding is often obscured or even obliterated by subse-
* For the detection of pitch by the contour of an elevation I am indebted to Pro-
fessor Pumpelly for suggestions. He was, I think, the first to discover that these con-
tours betray in an important manner the inclination of the trough and crest lines of
folds.
732 LAE JOURNAL OF (GHOLOGY:
quently induced cleavage structure. In this particular the prob- |
lems have been essentially those which were encountered in the
Greylock area, and similar criteria have been made use of to
distinguish the planes of stratification.t Hence with the excep-
tion of those localities where contacts of the different rocks
are exposed, dip observations have been possible at only a few
localities where definite plications could be made out.
In the absence of dip observations, the sequence being
known, many structural facts have been deduced from the areal
relations of the several horizons.. Next in importance as a
method of determining structure is the interpretation of topo-
graphical features. It is by application of all of these methods,
whose relative importance is expressed by the order in which
they have been mentioned, that the sections have been con-
structed.
The longitudinal section (Fig. 3) which passes through the
mountain in a general north and south direction, nearly at right
angles to the cross sections just described, is constructed to show ~
how the northerly pitch of the southern portion of the mountain
carries the Canaan Dolomite and the Riga Schist so low that
they do not appear again to the northward, for although the
pitch in the northern part of the area is southerly, it is not suffi-
cient to entirely counteract the very considerable northerly pitch
of the southern portions of the mass.
Structure of the Mountain—The sections show that the south-
ern portion of the mountain is a geo-anticlinal in the Riga
_Schist, probably with moderate minor folds tolerably symme-
trical. Within the core of this anticlinal is the Canaan Dolomite,
which appears from under the schist.to the southeast of the
« An extensive study of the subject of secondary cleavage as it is met with in the
Greylock area, has been made by Mr. T. Nelson Dale, and will appear in full ina
monograph by Professor Pumpelly on the Geology of the Green Mountains. A sum-
mary of his observations and conclusions is contained in the American Geologist for
July, 1891. Mr. Dale has also published a paper entitled, “On Plicated Cleavage-
Foliation,” in the American Journal of Science for April, 1892. As the writer
assisted Mr. Dale during a portion of the field investigation, he became familiar with
the structures there exhibited, as he did later also in independent work in the northern
stretch of the Taconic Range west-of Williamstown.
- “
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se Riga Schist.
2 SB Egremont Limestone
Mt. Sterling JugEnd = 25 Bverett Schist-
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STRUCTURE OF THE MOUNT WASHINGTON MASS.
mountain mass. Proceeding northward, one of the
minor synclinals in the western limb of the anticlinorium
increases in depth and width by a northerly pitch of
its trough line, so as to show at the surface, first, the
Egremont Limestone, and then more and more of the
Everett Schist. The eastern limb of the anticlinal has,
in consequence, been narrowed, then compressed and
overturned, until east of Mt. Race its axis" inclines
westward about 35 degrees. The northerly pitch of
its crest line carries it continually deeper, until finally
it disappears beneath the limestone on the east flank
of Mt. Race (cf. Fig. 1). By this process the anti-
clinorium of the southern portion has been developed
in the central portion into a compound fold consisting
of two deeply corrugated synclinals (eastern and
western schist ridges ) and a central corrugated antici-
lina, which brings the limestone to the surface in the
central plain. Proceeding northward still, the flexures
sharpen and deepen and become reversed, much as
Professor Dana has described. This narrowing of the
folds contracts the mountain at its north end, and the
succeeding southerly pitching crest and trough lines
bring the limestone higher and higher until the over-
lying schist disappears altogether. To facilitate the
comparison of the flexures, Fig. 4 is introduced, the
curves being those of the contact of the Egremont
Limestone and the Everett Schist as developed in the
series of sections. The map, as well as the sections,
show that the small schist ridges in the limestone near
Salisbury are mainly infolded Riga Schist with the
axes of the folds inclined eastward.
Variable Thickness ‘of the Egremont Limestone.—
The upper limestone of Mt. Washington forms the
tIn this paper the term “axis” is used for the axial-plane bisecting
a flexure, and never for the crest line or trough line. Cf. MARGERIE ET
Heim, Les dislocations de I’ écorce terrestre. Ziirich, 1888, p. 53. ,
fe Si
‘UOISUIYSeAA “JI Shor} worjses yeurpnqyisuoT
733
734 THE JOURNAL OF GEOLOGY.
western part of the great belt which Professor Dana has mapped
in this section of Berkshire county. While it has not been found
possible to accurately measure its thickness, it may be safely
stated that the thickness never exceeds 600 to 800 feet, and that
the beds thin out toward the south end of the mountain. They
Fic. 4. Series of curves showing the probable form of the flexures in the rocks
of Mt. Washington.
also thin out toward the center of the mass from either side.
The minimum thickness in the southern portion of the area is
probably something less than 100 feet. The general truth of
this statement is borne out by an examination of the map and
sections (Sage’s Ravine, Bear Rock Falls, etc.) As the lime-
stones do not again appear on the southeast flank of the Corn-
wall-Sharon core of older rocks, it is probable this horizon never
STRUCTURE OF THE MOUNT WASHINGTON MASS. 735
extended much beyond its present limit in a southerly direction.
As the bed thins out it becomes more graphitic, indicating also
that the conditions attending its formation had here some
peculiar local characters. -
Metamorphic Character of the Rocks as Indicated by Microscopic
Studies —The microscopic examination of thin sections of rocks
from Mt. Washington shows clearly that they are strongly meta-
morphosed clastics. Evidence has been deduced from the
secondary growths of feldspars, garnets,and tourmalines, as well
as from the relations of the different metamorphic minerals to
one another, to show that the orographic forces to which these
minerals owe their development, operated in several more or less
distinct periods."
Summary and Conclusions— What has been set forth in the
preceding pages agrees well with Professor Dana’s views so far
as the northern portion of the area is concerned. In the south-
ern and central portions, however, where the areal and structural
relations are more obscure, I have arrived at very different con-
clusions. This has been due, not to the discovery of errors in
Professor Dana’s observations, which have been in the main con-
firmed, but to the collection of a larger number of observations and
to the application of some structural principles which were not
made use of in his study. A glance at the map will show how per-
fectly the belt of Egremont Limestone which crosses the southern
portion of the mountain, is concealed where it meets the valleys.
This belt, the discovery of which furnished a key to the struct-
ure, is not at first apparent to the geologist, because at its ends
the boundaries of the Riga Schist coincide closely in direction
with and form an extension of the boundaries of the Everett
Schist.
To summarize briefly the results which have been discussed
in the foregoing, the Mt. Washington series consists of four
members, which in order of age are as follows: 1) Canaan
Dolomite, 2) Riga Schist, 3) Egremont Limestone, and, 4)
Phases in the Metamorphism of the Schists of Southern Berkshire: Wm. H.
Hosss. Bull. Geol. Soc. Am., vol. iv., pp. 167-178, pl. 3.
736 THE JOURNAL OF GEOLOGY.
Everett Schist. A somewhat striking lithological distinction,
which has been valuable for purposes of identification, is found
to separate the two schist horizons, the Everett Schist being
entirely free from garnet and staurolite, while the Riga Schist
usually (though not always) contains macroscopic crystals of
one or both of them. The older rocks are found in the southern
portion of the area, a general northerly pitch carrying them
successively below the surface as we proceed northward, until at
the north end of the mountain we find the upper two members
of the series only.
The structure of the mass may be summarized by stating that
the beds have been thrown into corrugated folds which seem
to have moderate, tolerably symmetrical corrugations at the
south end of the mountain, but these corrugations deepen and
become frequently overturned as we proceed northward. In the
eastern portion of the area the axes of the reversed folds is gen-
erally westward. At the extreme south, the structure is a geo-
anticlinal, but this develops in the central and northern parts of
the area into a geo-synclinal owing to the continued dispropor-
tionate deepening and widening of one of its minor western
corrugations. The general pitch of the beds is north. A less
important southerly pitch which characterizes the northern
portion of the area, in combination with the general synclinal
structure in cross sections, gives to all the mountain except its
extreme southern portion a basin-like character. The rocks are
throughout strongly metamorphosed clastics, the orographic
disturbances to which they owe their marked crystalline character
and porphyritic crystals having operated in several distinct
periods. The Egremont Limestone shows a marked diminution
in thickness as we proceed southward in the area until it almost
disappears. Throughout the mountain plain it is greatly modi-
fied, being either a micaceous limestone or calcareous mica schist,
or a graphitic schist. The graphitic rock is most developed near
the schist contacts and in the southern portion is the only repre-
sentative of the limestone.
Wn. H. Hoses.
UNIVERSITY OF WISCONSIN, MADISON, WIS.
VODIEO RTA L.
AT THE recent meeting of the British Association for the
Advancement of Science in Nottingham, the section devoted to
geology was perhaps the busiest department of the association.
Contributions covering nearly all phases of the science crowded
the time allotted to the reading of papers. Among them petrol-
ogy held a prominent position, owing to the eminent character
of the president of the section, and to his successful labors in
this branch of geology. Mr. Teall based his presidential address
upon the data furnished by petrological research, which, to his
thinking, lend additional strength to the uniformitarian doctrines
of Hutton. By a variety of illustrations he showed the identity
of ancient and modern rocks, whether sedimentary, igneous, or
metamorphic, and inferred a similarity of physical conditions
attending their formation. He emphasized the high degree of
differentiation of organic life at the time when the first Cambrian
strata were deposited, and maintained that the crystalline schists
of earlier age, so far as we have yet become acquainted with
them, do not contain the records of the early stages of the
planets’ history. They can not be considered to represent the
primitive crust of the earth. His testimony as to the identity of
the volcanic lavas erupted in Paleozoic and Tertiary times in
Great Britain, both as regards their structure and composition,
allowance being made for subsequent alteration, is signi-
ficant. It shows that in this region, through a long succession of
ages, the groups of rock magmas developed in different periods
of volcanic activity have been similar, and that the essential
character of the petrographical province did not change.
Sir Archibald Geikie’s paper, ‘On Structures in Eruptive
Bosses which Resemble those of Ancient Gneisses,’’ wasa valuable
737
738 JOORNAL OF GEOLOGY.
contribution to the study of gneissic structure, since it showed the
possibility of a part, at least, of the banding in these rocks being
due to a primary banding of igneous masses through some pro-
cess of segregation or through differentiation of the magma into
layers. A parallel banding of igneous rocks in the neighborhood
of a plane of contact has been known, but its magnitude is
generally inconsiderable. The structure in the gabbro on the
Isle of Skye, however, which was described by Geikie, is on a
large scale, and without apparent relation to a plane of contact.
No attempt was made to suggest a cause for such a mode of
segregation, since the study of the locality where it is best
developed is not yet completed.
Prof. Brogger’s paper, ‘“‘On the Genetic Relations of the Basic
Eruptive Rocks of Gran, Christiania Region,” presented an array
of facts with regard to the differentiation of rock magmas. By
means of chemical analyses and field observations he showed that
basic magmas of like composition in neighboring localities had
separated into pairs of magmas, which were quite unlike one
another chemically ; producing dissimilar pairs of rocks. This
proves that a given magma may differentiate in more than one
manner, according to circumstances. The entire paper is to
appear in the Quarterly Journal of the Geological Society.
Mr. Harker discussed the question of magmatic concentra-
tion, or differentiation, with reference to its probable cause, and
pointed out what seemed to him obstacles to the application
of Soret’s principle. He suggested that’ a more probable
explanation would be found in Berthelot’s principle, or that of
maximum dissipativity. The applicability of Soret’s principle to
the differentiation of magmas is also assailed by Prof. Backstré6m
in an article to appear in the next number of this JouRNAL, and the
principle of liquation advocated. While it is quite probable that
all of the phenomena of segregation and differentiation may not
be accounted for by one law of diffusion dependent on osmotic
pressure, and while this law finds its most perfect realization in
the most dilute solutions, and while certain separations of rock
magma may take place near the point of saturation, still it can
ED ERORIA 730
not be denied that rock magmas at times are known to attain
extreme liquidity. Moreover, there must undoubtedly be a num-
ber of different physical causes at work conjointly, each of which
may preponderate under favorable conditions, so that it is quite
probable that no single process will be found adequate to explain
all the phenomena in question.
It is interesting to observe that, while the majority of petrolo-
gists are engaged in studying the evidences of differentiation of
molten rock magmas, the theory of magmatic synthesis proposed
by Bunsen is not being wholly neglected. From the nature of a
portion of the evidence it is possible to frame diametrically
opposite hypotheses, but when all of the conditions are taken
into account it would seem that but one of the hypotheses can
have a general or far-reaching application. Prof. Sollas’s paper,
“On the Origin of Intermediate Varieties of Igneous Rocks by
Intrusion and Admixture, as Observed at Barnavave, Carlingford,”
demonstrated how intimately the material of an acid molten
magma may penetrate the interstices of a highly fractured rock,
in this case basic; the delicate veins thinning to almost micro-
scopic dimensions. Instances of this kind are well known. The
assumption, however, that this process has taken place to a very
considerable extent, and has produced bodies of rock of inter-
mediate composition, seems to ignore the probable physical con-
ditions under which rock magmas are irrupted, and also the
geological probabilities of such things happening. Thus there
may be no defect in the logic of the assumption as an abstract
idea, but there may be little or no probability of its ever taking
place to a considerable extent in nature.
Other petrological papers were presented by Prof. Sollas, Mr.
Watts, Dr. Johnston-Lavis, and an interesting account of the vol-
canic phenomena of Japan was given by Prof. Milne, and
illustrated by lantern slides. It cannot be out of place, for one
who has been fortunate enough to have been a guest of the
Association, to express a high appreciation of the honor, as well
as of the generous social hospitality which has become a distin-
guishing characteristic of these meetings. isn
UR IE VALE IAS:
Correlation Papers. The Newark System. By IsRarL Cook RUSSELL. |
Bulletin 85, U. S. Geological Survey. Washington, 1892.
Tuis Bulletin adds another number to the list of invaluable correl-
ation papers, prepared especially for the Geological Survey, but of the
greatest service to all professional geologists and advanced students
alike. Prof. Russell’s paper is of exceptional completeness from the
bibliographical side; its index is a marvel of minute reference; every
author’s name is followed by a complete list of his writings, the more
important ones being analyzed; every locality noticed in any paper is
indexed separately, with reference to the place of its mention; occur-
rences of sandstone, shale, conglomerate and trap are catalogued under
these headings. Immediate reference may thus be made to any desired
item concerning the Newark system, excepting the fossils, which, for
some reason, are not indexed under their names, but only through the
authors who have described them.
The chief headings of the text are: Nomenclature, area, lithology
and stratigraphy, conditions of deposition, life records, associated
igneous rocks, deformation, former extent, correlation and summary.
A good number of maps serve to guide the reader to the easy under-
standing of the several areas into which the formation is divided. I
can only comment on a few of these subjects.
Professor Russell has done good service in the fourth headings in
showing the incompleteness of the evidence on which glacial action has
been argued as an agency in the deposition of the formation. Near
the margin of several of the Newark areas, heavy conglomerates, con-
taining boulders up to four or five feet in diameter, are known at vari-
ous localities; and although none of these deposits are unstratified,
they have frequently been appealed to as evidence of glacial action.
But none of the boulders are scratched or notably angular; all of them
are, as far as known, deposited near the shore of their time; all of them
are systematically interbedded with ordinary aqueous deposits. Cer-
740
REVIEWS. 741
tainly they are not unaltered glacial deposits; and to assume that they
are derived from such is to imply that no agency but glaciers is com-
petent to move boulders of several feet in diameter. Russell refers to
the occurrence of large angular rock masses on the-alluvial fans of the
arid regions at a distance of two or three miles from their source, to
show that the movement of large boulders may take place under sub-
aérial conditions ; he cites the absence of ice-borne boulders among
the finer strata of the Newark deposits; and he argues a relatively
warm, not a cold climate, from the prevailingly red color of the for-
mation and from the character of the fossils. Emerson has detected
large boulders in certain basal beds of the sandstonesin Northern Mas-
sachusetts, demonstrably close to their source, and not in the least
indicative of glacial transportation. Indeed, to conclude that glacial
action occurred at sea level during the period of Newark deposition
simply from the coarse nature of certain marginal conglomerates, is to
adopt an open alternative instead of a closed demonstration as a guide
to belief.
Another line of evidence may be introduced against Fountaine’s
argument that the Newark conglomerates of Virginia were derived from
glaciers which descended from the Appalachian mountains of that time.
Local glaciers could originate in that latitude only on lofty mountains,
from which they might descend to sea level, much as those of New
Zealand do now. But the evidence gathered from the outline of the
under border of the Newark areas does not at all favor the idea that
they closely adjoined lofty mountains. If such had been the form of
the surface whose submergence allowed the accumulation of the Newark
sediments, their under border must have been extremely irregular;
the Newark waters must have rounded many a bold promontory and
penetrated many a deep bay. ‘The basal sediments accumulated along
sO sinuous a water margin should now show some indication of these
promontories and bays. They should be distributed much in the way
that the Permian breccias of Wales lie around their once buried and
now resurrected mountains, and thus show their origin on an
extremely irregular coast. But as far as the basal beds of the Newark
system have been studied out, they do not indicate that the surface on
which they lie possessed any great relief at the time of their deposition.
Whatever deformation it had previously suffered, whatever mountain-
ous heights this deformation produced, the action of erosion had in
pre-Newark time carried away enough material to some unknown goal
742 JOURNAL OF GEOLOGY.
to leave a surface of only moderate inequality; by no means of such
inequality as would gather snow fields on its higher levels, and shed
long glaciers down its valleys into the Piedmont seas.
The prevailing red color of the Newark strata is also adduced by
Russell as indicative of a relatively warm climate, as contrasted to a
glacial climate. ‘To this might be added that the slow subaérial decay,
from which red soils and sediments seem to be derived, is inconsistent
with the conditions of decay on lofty mountains, from which the
detritus is shed rapidly, leaving a relatively large surface of bare rocks ;
while it is accordant with the idea of a well denuded region, from
which further denudation carries material slowly.
In examining the structural relations of the igneous rocks, it is
noticeable that little success has as yet attended the efforts of observers
southwest of the Delaware to distinguish between the intrusive and
extrusive origin of their trap sheets. It would seem from this that the
scouring of the decayed surface of the Newark belts by Pleistocene
glacial action has been an advantage to the geologist of to-day in New
Jersey, Connecticut and Massachusetts; but an advantage that is fre-
quently offset by the sheets of drift which obscure or conceal so
many of the weaker strata in the Connecticut valley. I believe that
Connecticut alone has yielded a greater number of localities where the
contact of the sandstones on the trap sheets can be actually seen, and
from which good hand specimens can be secured, than all the areas
beyond the Hudson. It may be noted that the map of the New York-
Virginia Newark area, compiled by Russell from such data as he could
gather together, does not give a correct impression of the crescentic trap
ridges of eastern Pennsylvania. I have only examined a small part of
that district, but from what was seen and from the topographic maps
of the Perkiomen drainage area, surveyed by the Philadelphia water
commissioners for a proposed new water supply, I think that an accu-
rate geological map of the district will disclose a more systematic
arrangement of forms than now appears.*
The deformation of the Newark areas has been a subject for much
discussion already, and it will doubtless furnish as much more in the
future. Before it can be successfully deciphered, the stratigraphic suc-
cession of the system must be made out; and that has not been gener-
ally done, as may be seen from Russell’s chapter on lithology and
tSince writing the above, I have seen the new geological map of Pennsylvania,
on which the curved trap sheets are clearly shown.
REVIEWS. 743
stratigraphy; in which the various kinds of rocks are enumerated, but
in which their succession and thickness is not stated. The difficulty of
the problem lies in the monotony of the strata, and in the doubt in
many cases as the origin of the trap sheets. Whatever success has yet
been gained in solving this problem, it has come chiefly through the
aid given by the old lava flows, and only secondarily through ordinary
stratigraphic methods. In Pennsylvania and further south, no com-
plete stratigraphic correlations have yet been established; mainly, as
has has been stated above, because the trap sheets there are not yet well
deciphered. In New Jersey the discrimination between intrusive and
extrusive sheets has been well accomplished, but doubt is felt as to
the location of fault lines by which they are dislocated, this doubt
resulting from the uncertainty as to the reappearance of identical sand-
stone strata or trap flows. It is only in the Connecticut valley that
the variety of trap sheets and associated sedimentary beds is such as to
make the demonstration of faults complete. Here, over a considera-
ble share of the area, the stratigraphic succession is made out with much
certainty; and the lines of dislocation are determined with sufficient
precision. At the same time certain fossiliferous beds, rare in the for-
mation as a whole, and therefore of all the more value in defining hori-
zons, have been traced for thirty or more miles inland from Long Island
Sound; and their dislocations agreeably confirm the conclusions pre-
viously reached as to the faulting of the trap sheets.
Like so many other features of this peculiar system of rocks, its
style of deformation isexceptional. It is nowhere folded in the ordi-
nary manner; where curvature of bedding appears, it is of such char-
acter as to give crescentic outlines to the beveled edges of the strata
now visible. ‘The formation is, as a rule, tilted over to a rather regu-
lar monoclinal attitude; but while the earlier conceptions of its struc-
ture implied that the monocline was practically uninterrupted, the later
studies show it to be complicated by numerous faults, traversing the
mass in various directions, and as a rule systematically arranged,
although the control of the system is obscure. One thing is clear: the
faults penetrate the crystalline foundation on which the Newark beds
lie; they are not dislocations within the Newark beds alone; indeed, it
almost seems fair to say that the dislocating forces were indifferent to
the cover of Newark beds, and that their action was chiefly expended
on a much deeper mass of rocks
The original extent of the Newark areas has been much discussed,
744 JOURNAL OF GEOLOGY.
and Mr. Russell, some years ago, espoused the idea that their present
surface was a comparatively small part of their original basins. This
matter is essentially indeterminate at present; but the valid evidence
of great post-Newark erosion disposes me to accept almost any measure
of former extension of the system that may be required by reasonable
argument. At first, the mind halts before the supposition that vast
masses have been uplifted and worn away in the ages since the date of
the Newark deposition, but the evidence of vast denudation in that
interval is now so complete that it no longer seems warrantable to
withhold belief in the ‘‘broad terrane hypothesis,” either from its
extravagant erosion of rock masses, or from an apparent insufficiency
of time for such extravagance.
On the other hand, while it seems likely that there was some con-
nection between the several separate Newark areas, because their fauna
and flora are so similar, it does not seem necessary to conclude that all the
space between the Connecticut and the New Jersey areas was once over-
spread by Newark strata. It may have been. ‘There was time enough
during the Newark deposition to furnish material for such a cover;
and there has been time enough since then to wear it away; but still
there is no direct evidence that it existed. The original boundaries
of the formation are very vaguely defined.
Noticing that a greater definiteness of results has been gained in
the Connecticut valley than in the other Newark areas, it is evident
that the physical conditions of origin of the trap sheets in the south-
ern areas deserve the closest scrutiny. If they prove to be intrusive
sheets, they are of little structural value. But if they are proved to be
extrusive, they may then be treated as conformable members of the
stratified series, and thus a key to the general attitude of the system is
gained. After this step, the detection of sequences of strata, includ-
ing extrusive trap sheets with the aqueous sediments, is of next import-
ance, as by this means faults may be located, and thus some advance ©
made in the general reconstruction of the formation.
But even where best studied out, it is likely that the cross sections
by which underground structure is represented are hardly more than
parodies on the facts; so insufficient are the opportunities for the dis-
covery of deep internal structures. A close knowledge of the system
seems beyond reasonable expectation.
WM: Dawits:
HARVARD COLLEGE, November, 1893.
REVIEWS. 745
Text-book of Comparative Geology. By E. Kayser, Ph.D. Translated
and edited by Puitip Lake. Pp. xii, 426. Swan, Sonnenschein
& Co., London. (Macmillan).
The translation of Dr. Kayser’s book is a welcome addition to the
literature of geology in English. Its title is fairly definitive. It is an
attempt to bring together, or to set in their proper relations, the
results of geological investigation conducted in the various parts of
the world. The volume is too brief to allow this to be carried out in
great detail. The abbreviation has been effected in part by the omis-
sion, or by no more than the merest mention, of results reached in
extra-European countries. ‘This is particularly true with that part of
the volume which deals with the post-Paleozoic formations. While at
first thought this might seem to detract from the value of the volume
for American students, we think on the whole it is an advantage
instead, if omissions were necessary. Data concerning American
geology are more easily accessible to American students than data
concerning European geology, which this volume measurably supplies.
The volume will find its chief use in America as a convenient refer-
ence book of European geology, and as such it should be widely dis-
tributed. Its abundance of tables, showing the relations of the sub-
divisions of the various systems in different countries, so far as they
are made out, are especially convenient for general reference.
At several points in the volume there is a noticeable tendency to
make unqualified statements where qualified statements would seem to
us better. A case in point is the unqualified denial of the organic
character of the Eozoon. It is true in most cases, where positive
conclusions are asserted, that they represent the best conclusions of
the present day, but in some cases they seem to us to represent prob-
able or qualified or tentative conclusions, not demonstrated or abso-
lute or final ones.
All pre-Cambrian rocks are represented as Archean, though the
length of Archean time is stated to be so great that the beginning of
the Cambrian “‘ may be considered as comparatively a recent event.”
In spite of this recognition of the importance of the Archean, but
fourteen pages are devoted to its consideration. Although different
systems are not recognized in the pre-Cambrian rocks, the diversity
of origin of different parts of the group is distinctly recognized. The
author is inclined to attach less weight to the existence of limestone
and graphite in the Archean rocks, as indications of life, than would
740 FOSKNATS ORANGE OL OG Nz
most geologists. He thinks that the strongest evidence for the exist-
ence of life in pre-Cambrian time is the high organization of the
Cambrian fauna. While geologists will be ready to assent to the
~strength of this last argument, they will hardly be ready to regard
it as the only strong reason for belief in pre-Cambrian life. To the
very considerable number of fossil forms already found in pre-Cam-
brian rocks no reference is made.
The important question of the origin of the Archean is rather
briefly dismissed. The discussion touching this question is much less ~
full and much less satisfactory than that of Prof. Van Hise, recently
published.* Indeed, had Prof. Van Hise’s discussion been pub-
lished before Dr. Kayser’s treatise, the latter author might have found
a way out of some of the difficulties which seem to lie in his mind con-
cerning the origin of the Archean.
An excellent feature of the book is the prefacing of the discussion
of each system by a short account of the origin and history of its
differentiation from underlying and overlying systems. Each system
is discussed under the general heads of — 1) Distribution and devel-
opment; 2) Paleontology. Under the first head, it could have been
wished that the structural relations of the systems had been more
uniformly and sharply brought out. Such clear statements as that
concerning the North American Devonian system, that it rests ‘‘con-
formably and without break on the Silurian, and is covered conforma-
bly by the Carboniferous” (page 111), are not always to be found.
Where knowledge does not permit such positive statements, definite
statements representing the degree of present knowledge would have
been welcome. So, too, the relations of faunal and stratigraphical
breaks are not always so clearly set forth as could have been desired
in a text-book.
In the discussion of the Permian system, Dr. Kayser brings out
the fact of wide-spread conglomerate formations (India, Victoria, Bra-
zil, South Africa) in tropical latitudes and the southern hemisphere,
which sometimes contain polished and striated stones very like those
of glacial formations of later date. In Africa the Dwyka conglomer-
ate rests on rock, the upper surface of which is smoothed and striated
like rock beneath the modern glacial drift. Dr. Kayser indicates that
the belief that these Permian conglomerate beds are of glacial origin
has gradually gained ground. ‘The flora succeeding the conglomer-
‘Bulletin of the U. S. Geol. Survey, No. 86.
REVIEWS. 747
ate in Africa, South Asia and Australia is characterized by Mesozoic
types. This change is believed by many to have been brought about
by the cold climate which was the determining cause of the conglom-
erate beds. Blanford and Waagen go further and cennect the decline
of the marine Paleozoic types with the cold climate of the end of the
Paleozoic.
In the discussion of the Mesozoic and Neozoic there is scarcely any
reference to American geology. In connection with the discussion of
Pleistocene geology, two glacial epochs are recognized. ‘The author
inclines to the eolian hypothesis for the origin of loess.
Both the physical and paleontological phases of the subjects dis-
cussed in the volume are illustrated by numerous figures, the former
rather less fully than the latter. A series of maps, showing the distri-
bution and relations of the systems described, would have enhanced
the value of the volume which is still great without them.
ROLLIN D. SALISBURY.
Lowa Geological Survey. Vol. 1. First Annual Report, 1892. SAMUEL
CALVIN, State Geologist, Des Moines, 1893. 8vo, 472 pp., ro
plates and 26 figures.
In addition to brief administrative reports, the first report of
Iowa’s third survey contains papers by S. Calvin, C. R. Keyes, Assistant
State Geologist, S. W. Beyer, H. F. Bain and G. L. Houser.
The introductory paper by Mr. Keyes, on the Geological Formations
of lowa, isa summary of present knowledge of the various formations
occurring within the limits of the state. The writer has availed him-
self of the various studies made of these rocks in recent years, and the
result is shown in an improved classification over that of preceding
surveys. While all the formations have come under careful study, the
most notable progress is shown to have been made in the classification
of the Devonian, the Carboniferous and the Cretaceous.
Investigations in northwestern Iowa have brought to light the
presence of undoubted eruptive rocks at no great depth below the
surface. In Mr. Beyer’s paper are given the details relating to the
discovery of typical quartz-prophyry, interbedded with sandstone
and gravel, in a deep well at Hull, lowa. The discovery by Culver
and Hobbs of eruptive rock within the Sioux quartzite in southeastern
748 JOURNAL OF GEOLOGY.
Dakota is referred to, and, following Hall, White, and Irving, the con-_
clusion is drawn that the Sioux quartzite is the oldest formation in the
state. Some familiar names have disappeared from the geological
section, and their places are assumed by newer but more appropriate
terms, as, for example, Oneota for Lower Magnesian, St. Croix for
Potsdam, while Hamilton is represented by four names applied to as
many subdivisions. The term Augusta is given to the terranes includ-
ing the Warsaw, Keokuk and Burlington, in place of William’s term
Osage which is discarded as inapplicable. The Warsaw beds of Hall
are here included with the Keokuk, and the term Warsaw dropped. An
error occurs in the definition of the St. Louis limestone on page 72,
where it is asserted that the brecciated limestone constitutes the base
of the beds in Iowa. This is the case only along the extreme margin of
the beds. Seaward from the old shore line, as shown along the Des
Moines in Van Buren county, the basal member consists of a brown,
magnesian limestone in fairly regular, more or less undulating beds.
The texture is sometimes nodular and sandy. In thickness the forma-
tion varies from five to fifteen feet or more.
The structure of the coal measures is treated in considerable
detail, and emphasis is given to conclusions based largely upon Mr.
Keyes’ investigations in Iowa. These rocks are included in two stages,
the lower or Des Moines, and the upper or Missouri formation,
White’s middle division being discarded. These are not considered
two distinct formations in the sense that the lower was deposited prior
to the laying down of the upper—the view commonly entertained—
but the two were formed contemporaneously, the former as a marginal
or shore formation, and the latter as its deep or open sea correlative.
The view here advanced seems to be a modification of that held by
Winslow. The conditions of deposition were evidently those of a
slowly sinking shore, and the marginal deposits practically underlie
the open sea formation though not necessarily much older ; hence the
terms lower and upper are retained, though emphasis is given to
their general contemporaneity. The summary of Professor Calvin’s
researches on the Devonian and Cretaceous rocks shows a marked
advance in the knowledge of these formations.
The classification of Iowa rocks, given by the different surveys, is
here presented for comparison:
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eSgr ‘LYOdad S,1TIVH
ras Os JOURNAL OF GEOLOGY.
Other papers by Mr. Keyes are: “Annotated Catalogue of
Minerals,” and ‘“ Bibliography of Iowa Geology.”
Professor Calvin’s paper is devoted to the Cretaceous deposits of
Plymouth and Woodbury counties. In the region studied these beds are
found to be sharply divisible lithologically into two divisions, a lower
consisting of soft sandstones, with bands of hard ferruginous concre-
tionary nodules, and variegated, often parti-colored clays, the latter
greatly predominating and resting upon these a white or yellowish
chalk, somewhat indurated in places into a soft fissile limestone. The
first is White’s Woodbury sandstones and shales, and the second is his
Inoceramus beds. Following Meek and Hayden, Professor Calvin
makes a threefold division of the beds, by drawing a somewhat
arbitrary line about forty feet below the base of the Inoceramus beds.
The lowest division contains impressions of leaves and a meagre
brackish water fauna. This he correlates with the Dakota group. The
second or middle division of dark colored calcareous shales, containing
marine mollusks, associated with the vertebra and teeth of bony fishes,
and the skeletons of marine saurians, is the Fort Benton group of
Meek and Hayden. The upper or Inoceramus beds represent the
Niobrara of the same authors. During this epoch the Cretaceous sea
had its farthest eastward extension, probably reaching as far as the
Mississippi river in northeastern Iowa.
Mr. Beyer’s paper is entitled Ancient Lava Flows in the Strata of
Northwestern Iowa, and relates to the discovery in a well at Hull,
Sioux county, of typical quartz porphyry at a depth of 755 feet.
Microscopical study shows it to have a pronounced flow structure, while
the quartz crystals show the effects of magmatic corrosion, and, in
some cases, fracturing with discordant orientation of the fragments,
from which it is inferred that the magma was semi-viscous and under
great pressure when the flow took place. In the drilling, the eruptive
rock was found to alternate with sandy strata, showing evidence of
metamorphism down to 1,200 feet. ‘Two hypotheses are advanced to
account for the flows: (1) That they took place in Paleozoic times,
perhaps Carboniferous, the lava being periodically poured out over
the old sea bottoms ; and (2) that the whole series of flows was con-
temporaneous, and in point of time post-Carboniferous. In this case
the intercalations may be regarded as intrusive sheets, following the
lines of least resistance and forcing themselves between the strata.
Most probability seems to attach to the latter view.
REVIEWS. 751
Mr. Bain’s paper deals with the distribution and relations of the
St. Louis limestone in Mahaska county, where it is shown to have the
same irregularity as to thickness and structure as it presents generally
in Iowa. ‘To explain the irregularity in the surface-of this formation,
appeal is made to erosion during Kaskaskia time, when Iowa was a
land surface. This would imply a considerable elevation in order to
produce the carving, a conclusion not wholly free from doubt. In
some localities a sandstone, treated as presumably belonging to the
coal measures, rests upon the limestone.
The remaining paper, by Mr. Houser, is devoted to a discussion of
some lime-burning dolomites, and dolomitic building stones from the
Niagara.
C. H. Gorpon.
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612 17th St., N. W., Washington, D. C.
THE
(OU TRIN AE OF GEOLOGY
NOVEMBER-DECBMBER, 1803.
Was, SULPPOSIEID) GILACIUATUKORN Ol Us WAVZIDE
THE inquiries I have received from time to time regarding
the supposed glaciation of Brazil in Pleistocene times, the doubts
sometimes expressed regarding it, and the occasional appeals
made to it,? induce me to state briefly what I know about the
matter.
Strangely enough the errors of Agassiz, Hartt and Belt regard-
ing glaciation in Brazil have been turned to account both by those
who have theories that need the support they think the glacia-
tion of Brazil would give them, and also by those who seek by
means of these errors to throw discredit on the subject of glacial
geology.
I believe the case has been generally dropped by geologists
as not proven, but I am confident that no one wishes to ignore
the evidence ‘‘merely because it runs counter to all his precon-
ceived opinions.’
EARLY VIEWS OF AGASSIZ AND HARTT.
When Professor Louis Agassiz made his trip to Brazil in
1865, on board the steamer going out he gave a series of
t Advance quotations are made from this article by Dr. Alfred R. Wallace in
Nature, Vol. 48, No. 1251, Oct. 19, 1893, 589-590.
°*The Glacial Nightmare and the Flood, by Sir HENRy H. Howortu, London,
1893. MARSDEN MANSON, in the Trans. of the Geol. Soc. of Australasia, I., pt. VL.,
155-170, and in the Trans. of the Tech. Soc. of the Pacific Coast, VIII., No. 2, Ig.
Geological and Solar Climates; their Causes and Variations, by MARSDEN MANSON,
University of California, May, 1893. Ragnarok, by Ignatius DONELLY.
3 WALLACE: Nature, Vol. II., 1880, 511.
Viole. INOS 8: 753
754 THE JOURNAL OF GEOLOGY.
lectures in which he suggested to his assistants the possibility
of the South American continent having been glaciated, and
reminded them that this was one of the important subjects for
their investigation.* ;
I subsequently learned from Professor Hartt, who was one
of the assistants, that these lectures prepared them to be con-
vinced that glaciation had taken place in Brazil, though he him-
self was rather inclined to believe otherwise.
Mrs. Agassiz’s book shows throughout how Professor Agassiz
found on every hand, from the time he landed in Brazil till he
left there, what he regarded as evidences of glacial action.
In the mountains about Rio de Janeiro he found erratic boulders
(pp. 86 e¢ seg.); at Ereré, in the Amazon valley, he found ‘the
only genuine erratic boulders I have seen in the whole length
of the Amazon valley,” (p. AIS )) 8 he declared that ‘il n’y a pas
trace des terrains tertiaires’? in that region, while the horizontal
sediments of that valley he explained as silts thrown down in
cold glacial waters behind a vast terminal moraine that stretched
across the mouth of the valley (p. 426), and of which the
island of Marajo was supposed to be a remnant; the table-topped—
hills he explained as the remnants of sediments left when this
great dam broke, and the waters swept the greater part of the
beds out to sea.
The lateral moraine on the south side of this great glacier
he expected to find in the interior of Ceara (p. 447-8); he went
to Ceara, and found at Pacatuba, near the coast, what he regarded
as glacial phenomena ‘‘as legible as any of the valleys of Maine,
tA Journey to Brazil, by Professor and Mrs. Louis AGassiz, Boston, 1868,
15. In Mrs. Acassiz’s Life and Correspondence of Louis Agassiz, Boston, 1886, IL.,
633, it is further stated that Agassiz was confirmed “in his preconceived belief that
the glacial period could not have been less than cosmic in its influence.”
2Bul. de la Soc. Géologique de France, XXIV., 110. In a letter to Elie de Beau-
mont, he speaks of these beds as loess, but he gives no specific explanation of their
formation. Comptes Rendus de l’Acad. des Sciences, 1867, 1269. Professor Agassiz
first published his paper on the Physical History of the Amazon valley in the Atlantic
Monthly for July and August, 1866; it was also published subsequently in his
Geological Sketches, sec. ser. Boston, 1886. II., 153 e¢ seg., and in the Journey to
Brazil.
SUPPOSED GLACIATION OF BRAZIL. 755
or in those of the valleys of Cumberland in England” (pp. 456,
463).
Naturally enough these views were received in the scientific
world with incredulity. As Mr. Wallace remarks, “Prof. Agassiz
was thought to be glacier-mad,’ but his earlier observations on
glaciers had been received with quite as much doubt,’ so that the
doubts have nothing to do with the. case one way or the other.
Professor Chas. Fred. Hartt states in his book3 that he was
at first very skeptical about Brazilian glaciation, but that he was
finally obliged to yield to the evidence collected by himself, and
to confess that Agassiz was right.
It should perhaps be mentioned here, that there is a general
impression that when Hartt wrote his book on the geology of
Brazil, he had spent several years, and traveled widely in that
country, and that the conclusions given by him are the results of
all his Brazilian work. This is far from being the case. When
he wrote the Geology and Physical Geography of Brazil, he
had spent only a year and a half in that country; on his first trip
he arrived at Rio de Janeiro, April 23, 1865, and left it on July
of the following year;+ on his second trip, he reached Para,
July 11, 1867,5 and returned from Rio in September of that
year,° making in all not more than eighteen months spent in
that country up to the time his book went to press. The belief
in the glaciation of Brazil, as there expressed, is therefore based
upon his earliest and least trustworthy work in that region.
Hartt fully recognized this afterwards, and I have often heard
him say, ‘I wish I had known as much about geology when I
wrote that book as I know now.”
He subsequently made several trips to Brazil; in one to the
* Nature, II., 511. LyYyELvw’s Principles of Geology, New York, 1889, 1, 466.
*Bul. de la Soc. Géol. de France, 1867-8, XXV., 685.
3 Geology and Physical Geography of Brazil, Boston, 1873, 29.
4 Agassiz, Journey, 46 and 540.
5 American Naturalist, I., 648.
° Geology and Physical Geography, 201.
756 LEME SOOKINAUL (ONE (GIZOILOG VA
Amazon valley he examined the table-topped hills* which
Agassiz had referred to glacial action, and the boulders he had
called “the only genuine erratic boulders” he had seen in the
Amazon valley. Already, in 1867, Professor James Orton, who
scouts the idea of the glaciation of the Amazonas, had discov-
ered at Pebas, in the supposed glacial sediments, ‘‘marine or
perhaps rather brackish water Tertiary fossils.’’?
In 1871 Hartt found the supposed erratics of the Amazon val-
ley to be boulders of decomposition derived from trap dikes near |
at hand, and stated that he ‘did not see, either at Ereré or in any
part of the Amazonas, anything that would suggest glaciation.’
He still clung, however, to the idea that the highland of Brazil
to the south had been glaciated.4
Unfortunately Hartt has left no further record of his later
views upon this’ subject, but that his views underwent a
radical change I know as positively as one can know the
opinions of another person. I went with him to Brazil in
1874, was with him in his work there until his death in 1877, and
remained yet five years later—in all eight years in that country.
Under his direction I did more or less work in the mountains
about Rio de Janeiro for the purpose of sifting the evidence of
glaciation in that region, and I am glad to say, in justice to the
memory and scientific spirit of my former chief and friend,
that long before his death he had entirely abandoned the theory
of the glaciation of Brazil, whether general or local, and that the
subject had ceased to receive further attention, even as a working
hypothesis. So much for Hartt’s opinions.
‘Bulletin of the Buffalo Soc. of Natural History, 1874, 201.
?On the Valley of the Amazon, by JAMES ORTON, Proc. Am. Assoc. Ady. Sci., 1869,
XVIII., 195-9; On the Evidence of a Glacial Epoch at the Equator, by JAMES ORTON,
The Annals and Magazine of Natural History, 1871, VIII., 297-305.
The Andes and the Amazon, by JAMES ORTON, N. Y., 1876, 282, 560. The fossils
collected by Orton are described in the Amer. Jour. Conchology, IV., 197, and VL., 192.
Others. are described from similar places in the Quar. Jour. Geol. Soc., XXXV., 76-88,
and 763 ez seq.
3 Amer. Jour. Sci., 1871, 295.
4Ann. Rep. of the Amer. Geographical Soc. of N. Y., for the year 1870-1, 252.
SUPPOSED GLACIATION OF BRAZIL. Thi
Thomas Belt, the author of The Naturalist in Nicaragua, says
in that volume’ that though no ice marks are visible he has seen
‘‘near Pernambuco, and in the Province of Maranham, in Brazil,
a great drift deposit that I believe to be of glacial origin.”
I have seen and studied the deposits to which Belt refers ;
my opinion is that while they bear a certain resemblance to
glacial drift they are entirely devoid of positive evidence of
glacial origin. The method of their formation is explained in
another part of this paper.’
AGASSIZ’S CHANGE OF VIEWS.
It is appropriate that I here quote from Professor N. S. Sha-
ler, a former pupil of Professor Agassiz :3
“There has been a good deal of discussion concerning the former exist-
ence of glaciers in the valley of the Amazon. Agassiz, to whom we owe the
first suggestion of the value of glaciation as a great geological agent, at one
time thought it likely that the valley of this great river had been the seat
of a glacier that poured its ice from the Andes nearly down to the sea. This,
which was hardly more thana suggestion put forth for the discussion of geological
students, was, I believe, practically abandoned by this illustrious naturalist
before his death, (In this assertion I have embodied the results of several
remarks by my late master on this subject made during the last two years of
his life. It is satisfactory to know that the only considerable mistake he made
in the matter of glaciation was corrected by his own reflections on the subject.
N.S. S.) and has been found to be an essentially mistaken view. The late
Professor Hartt, geologist of Brazil, at one time thought some of the debris in the
mountain districts near Rio de Janeiro was of glacial origin, but this sugges-
tion has never been submitted to discussion, and can have no weight against
the other evidence of a negative kind that goes to show that glaciation, save in
higher mountain countries, has never extended into the intertropical regions.”
* The Naturalist in Nicaragua, by Thomas Belt, F.G.S., 2d ed. London, 1888, 265.
2 It has been asked how I reconcile Belt’s statements regarding glaciation in Nica-
ragua with my inability to find trustworthy evidence of glaciation at a similar south
latitude. I don’t try to reconcile them; I am simply dealing with the facts as 1 know
them in Brazil. I have never seen the Nicaraguan deposits, but I can’t avoid suspect-
ing that they will turn out like the Brazilian ones, J. Crawford’s moraines and
“moutonnéd ridges” to the contrary notwithstanding. (Proc. Amer. Assoc, Ady. Sci.,
XL., 265, and Science, XXII., No. 263, p. 270).
3Glaciers, by N. S. SHALER and W. M. Davis, Boston, 1881, 47.
758 THE JOURNAL OF GEOLOGY.
In 1872 Agassiz went through the Straits of Magellan in
charge of the natural history work of the Hassler Expedition.
On that voyage he touched at Montevideo and at many points
south of that place, through the straits, and along the west coast.
The letters written by him on this trip suggest very strongly, if
they do not conclusively show, that he had at this time already
abandoned the idea that Brazil had been glaciated. Speaking of
certain boulders seen by him on the Cerro at Montevideo, Mrs. |
Agassiz observes’ that ‘As these were the most northern erratics
and glaciated surfaces reported in the southern hemisphere,” etc.
From this it appears that he no longer regarded the Brazilian
boulders as erratics.
After Agassiz had examined the glacial phenomena of the
Straits of Magellan and of the southern part of the continent, he
sent a report to the Superintendent of the U. S. Coast Survey,
dated at Concepcion Bay, June 1, 1872.”. This article also bears
evidence that he no longer regarded Brazil as having been glaciated.
In one place he says,3? ‘1 am prepared to maintain that the whole
southern extremity of the American continent has been uniformly
moulded by a continuous sheet of ice.” The italicsare mine. In
the next paragraph he says, ‘‘The first unquestionable voches
moutonnées | saw were upon the nearest coast opposite Cape
Froward.” Again he says (p. 271): ‘‘The equatorial limit of
this ice sheet both in the northern and the southern hemisphere
is part of the problem upon which we have thus far fewest facts
in our possession. In South America I have now traced the
facts from the southernmost point of the continent uninterruptedly to 37°
S. latitude on the Atlantic as well as the Pacific coast.” Again
*Louis Agassiz, his Life and Correspondence, Boston, 1886, II., 712. Rep. U.S.
Coast and Geodetic Survey for 1872, 215. Nature, 1872, VI.,€9. Evidently Burmeister
does not regard the boulders cited as glacial, for he uses the expression, “‘ phénoménes
de glaciers chez nous, et dont nous n’avons nulle part la preuve.” République Argen-
tine, II., 214, also 392, 393. ‘The same blocks are described by Darwin in his Geolog-
ical Observations, 432. He does not seem to regard them as erratics.
? Published in the New York Tribune of June 26, 1872, and reproduced in Nature
1872, VI., 216, 229 and 260.
3 Nature, 1872, VI., 230.
SOUOPPOSED GLACIATION OF BRAZIL. 759
(p. 272) he speaks of having traced. the palpable evidence of
glaciation ‘from Montevideo on the Atlantic to Talcahuano on
the Pacific coast.’ Speaking of evidence at Concepcion Bay he
says also (p. 272) ‘Think of it! A characteristic surface indicat-
ing glacial action in latitude 37° S. at the level of the sea!”
These quotations show as plainly as anything short of a pos-
itive statement can that Agassiz in 1872 no longer considered as
trustworthy what he had formerly regarded as the evidences of
glaciation in Brazil. For if he still believed ina glacier under
the equator itself, why should he tell us with exclamation points
_to think of a glacier thirty-seven degrees nearer the pole ?
BASIS OF THE THEORY.
I should be glad to leave the matter with these statements of
the changes of views on the part of both advocates of the glacia-
tion of Brazil, but persons who have theories based to a greater
or less extent on the glaciation of the tropics are very reluctant
to believe, in the face of the many positive statements of both
Agassiz and Hartt, and of the apparently trustworthy evidence
adduced by them, that the first impressions of those excellent
observers, both of whom were thoroughly familiar with glacial
phenomena in the north, were altogether wrong. It is not possi-
ble, neither is it necessary, to take up here the individual cases
spoken of by Agassiz and Hartt as evidence of glacial action.
Very nearly all the materials referred by them to the drift fall
under two principal heads:
First, the so-called erratic boulders, often imbedded in what
was considered boulder-clay.
Second, transported, water-worn materials.
ORIGIN OF THE BOULDERS.
The boulders believed to be erratics are not erratics in the
sense implied, though they are not always in place. The first
and most common are boulders of decomposition, either rounded
or subangular, left by the decay of granite or gneiss. Some-
times they are imbedded in residuary, and consequently unstrati-
THE JOURNAL OF GEOLOGY.
760
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Ory Jo Avg oy} Jo souvryUy oy} Je yeag ayuRID v ‘JeoT IewsnS Io monssy,p org ‘I ‘og
IUPPOSED GLACIATION OF BRAZIL. 701
fied- clays, formed by the decomposition in place of the
surrounding rock. And everyone has heard of the great depth
to which rocks are decomposed in Brazil.t The_true origin of
these boulders and the accompanying clays is often more or less
obscured by the “creep” of the materials, or, in hilly districts,
by land-slides, great or small, that throw the whole mass into a
confusion closely resembling that so common in the true glacial
boulder-clays. In this connection too much stress can scarely
be placed upon the matter of land-slides ; they are very common
in the hilly portions of Brazil, and, aside from profound striations
and faceting, produce phenomena that, on a small scale, resem-
ble glacial tillin a very striking manner. The fact that the
boulders are of various sizes, sometimes from ten to twenty feet
in diameter, and have mingled with them quartz fragments
derived from the veins that traverse the crystalline rocks from
which they are derived, adds to the resemblance of these mate-
rials to certain glacial products. Such boulders, however, are by
no means confined to the vicinity of Rio de Janeiro, but are com-
mon throughout Brazil wherever there are granites or gneisses.
They have been seen by the writer in the Amazon valley (Ara-
guary River) in the interior of Pernambuco,? Parahyba do Norte,
Alagoas, Sergipe, Bahia, Rio de Janeiro, Minas Geraes, Sao Paulo,
Parana, and Matto Grosso.
The positions in which such boulders are often found are
worthy of note, though one who felt disposed to regard them as
transported blocks would probably not consider their positions
as inconsistent with the glacial theory of their orgin. They are
abundant about the bases of granite hills and mountains where
they have been formed by the exfoliation of the great blocks
and slabs produced by the secular decay of the hills and moun-
tains. There are hundreds of rude boulders at the southeast base
*DARWIN: Geological Observations, 427; Liais: Climats, Géologie, etc., 2;
Pissis: Men. Hist. Inst. de France, X., 538; DERBY: Amer. Jour. Sci., 3d Ser.,
XXVII., 138; Mitus: Amer. Geologist, III., 351.
2In the American Naturalist, 1884, XVIII., 1189, I have given a sketch of some
boulders found in the state of Pernambuco; see also p. 1187 of that vol.
THE JOURNAL OF GEOLOGY.
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ee
SUPPOSED GEA CIATION OF eBicA Aide. FOP
of the Sugar Loaf at the entrance to the harbor of Rio, at the
east base of the Corcovado, and about every such mountain in
the vicinity of Rio de Janeiro. They" rest on the summits and
margins of the high, sharp mountain peaks; on the top of the
Sugar Loaf at the entrance of the Rio harbor, for example, there
are several such boulders, one of which is thirty feet in diame-
ter; the top of the Gavea, the flat-topped mountain southwest of
Rio, has hundreds of boulders on itssummits. Agassiz mentions
such boulders on the edge of rock basins (Journey, 493). He
‘was at a loss how to explain how loose masses of rock, descend-
ing from the heights above should be caught in the edges of
these basins, instead of rolling to the bottom.” The fact is that
the blocks referred to originated, not in the heights above, but
just where they now lie, as is shown beyond question by occa-
sional quartz veins passing from the boulders into the rocks upon
which they rest.”
In some of the shallow parts of the Bay of Rio de Janeiro
what were once small islands have had the residuary soils
removed and great nests of such boulders project from the water.
On the island of Paqueta in the bay are some beautiful examples
of such boulders lying in the water’s edge. I am fortunately
able to give an illustration showing the Paqueta boulders which
may be taken as a type of those found in and about the Bay of
Rio de Janeiro.
The second method by which these boulders have been
‘Sometimes boulders accumulate on one side of a hill or peak and not on the
opposite side. This is well illustrated in the case of the Sugar Loaf. On the side
facing the ocean there are thousands of boulders, many of them of enormous size, while
on the opposite side where there is less surf there are but few. The reason for this
difference is that there is a large dike-like ledge of hard rock exposed on the seaward
side of the peak. This ledge does not appear on the opposite side where the mass is
softer and weathers away evenly without leaving good boulder-forming fragments
about the base. The ledge referred to is shown in the accompanying illustration.
?In SHALER and Davis’ Glaciers, plate XXIL., is given an example of boulders of
decomposition in Central India. Exactly similar cases are common in the granitic
and gneissic areas of Brazil.
3See also BURMEISTER’S Reise nach Brasilien, Berlin, 1852, 111, 112.
704 TAD f[OURNAL ORG HOLOGEN:
formed is quite similar to the first, but instead of being cores of
granite or gneiss, they have been derived bythe same process of
exfoliation and decomposition from the angular -blocks into
which the dikes of diorite, diabase, or other dark colored rocks
break up. Their color marks them as quite different from the
surrounding granites, and the dikes themselves are almost invaria-
bly concealed. Moreover, these dikes not infrequently contain
inclusions of still different rocks and we thus occasionally have
boulders of various kinds of rocks mingled together. The resi-
duary clays derived from the decomposition of these dikes are
somewhat different in color from those yielded by the granites,
y
so that when ‘‘creep”’ or land-slides add their confusion to the
original relations of the rocks, the resemblance to true glacial
boulder-clays is pretty strong. The chance of discovering the
source of these boulders is further decreased by the depth to
which the mass of the rock has decayed, and by the impenetra-
ble jungles that cover the whole country and so effectually limit
the range of one’s observation. Dikes such as these last men-
tioned are not uncommon in the mountains of Rio de Janeiro.
Indeed what have generally been regarded as the very best evi-
dences of Brazilian glaciation,’ some of the boulders near the Eng-
lish hotel in Tijuca, fall under this head, though some of them
are of gneiss. ‘The fact is that the great mountain masses about
Rio are of granite or gneiss, while some of the boulders come
from dikes or other dark-colored rock high on their sides, dikes
which were not visited by Agassiz or Hartt.2 There is a good
example of a dike breaking up in boulders at the gap through
which the road passes from the Jardim Botanico to the Gavea
near the City of Rio. At this place the ground is covered to a
A Journey to Brazil, 86 e¢ seg. AGASSIZ: Geological Sketches, Boston, 1885,
Il., 155 e¢ seg. Harrt’s Geol. and Phys. Geog. of Brazil, 24-30.
? Darwin mentions boulders and dikes seen at Rio de Janeiro, (Geological Obser-
vations, pt. II., ch. XIII., 425; also Trans. Geol. Soc. London, 2d Series, 1842, VI., 427,
note). Professor O. A. Derby sent Rosenbusch specimens of diabase from twelve
dikes in the neighborhood of Rio de Janeiro, varying from twenty centimetres to sev-
eral metres in thickness. See Dr. E. O.*°Hovey’s descriptions of these rocks in
Tschermak’s Min. u. Petrog. Mittheilungen, 1893, XIII., 211-218.
SUPPOSED GLACIATION OF BRAZIL. 765
depth of fifteen feet or more with clays. through which are min-
gled boulders of diorite and granite and fragments of quartz.
Further east, at a lower level, some of the clays have been washed
over and contain subangular fragments of quartz, some of them
two feet in diameter, many of which are somewhat water-worn.
It is perhaps worth mentioning that these water-worn quartz
fragments imbedded in clays were regarded by Hartt as the best
evidence of glaciation. They were finally eliminated as such
evidence near the end of a rainy season by my finding a land-
slide filling up a small ravine in which the bed of the stream had
been strewn with similar quartz fragments, and the whole buried
beneath a slide of crumpled clays. A highly instructive lesson
can be had on the subject of boulders and clays, their origin and
relations to the so-called drift of Brazil from Professor Derby’s
paper on nephelene rocks in Brazil. Anyone reading that
article can readily fancy how Professor Agassiz, in a flying trip
across Sao Paulo and Minas, would have interpreted these clays
and boulders of different kinds and different colors.
In regard to the so-called erratics I should mention also the
opinion of another observer and writer upon Brazilian geology.
Emmanuel Liais, formerly director of the Imperial Observatory at
Rio de Janeiro, is very positive that there are no evidences what-
ever of glaciation in Brazil. Of the boulders supposed to be
erratics, he says :°
“These boulders though numerous are always in the immediate neighbor-
hood of the veins from which they are derived.... . Though presenting
sometimes the appearance of erratics by their abundance and rectilinear
arrangement, they are not transported boulders, and have nothing in common
‘with erratic phenomena. ... . I have not been able to find any signs of the
existence of a boulder that can be regarded as erratic and coming from a
region distant from the one where it is found. In the vicinity of these isolated
boulders one always finds dikes, veins or simply masses or boulders of the
same material intercalated with the terrain in place.”
He speaks of the occurrence of dikes of diorite from which
many of the boulders cited by Agassiz have been derived. More
t Quar. Jour. Geol. Soc., 1887, XLIII., 457-473.
72
2Climats, Géologie, etc., du Brésil, Paris, 1872, 18.
766 THE JOURNAL: OF (GEOLOGY.
o
than a score of statements of a similar nature may be cited from
Liais’ book. .
Count de la Hure has also pointed out how diorite breaks up
into boulders, and cites in evidence some of the very cuts on the
Pedro II. Railway which Agassiz and Hartt refer to the drift.
Saldanha da Gama in speaking of the exfoliation and decom-
position of granite rocks described by Count de la Hure and
Capanema says :*
“This and many other facts gathered by the Brazilian naturalist in his
observations on diorite and other rocks of that class led the eminent Swiss
geologist to point out that the study of the drift in Brazil will not be well
understood so long as one hasn’t a thorough knowledge of the decomposition
of the rocks.”
He also refers to the fact that these phenomena may be
observed in several of the Brazilian provinces.
The two kinds of boulders above mentioned are common in
the regions of crystalline rocks ; a third kind is found in those
parts of eastern Brazil that are covered, or were formerly covered,
by Tertiary sediments, namely in the State of Bahia, and thence
northward to the Amazon valley. These Tertiary deposits con-
tain beds of sandstone that are sometimes locally changed upon
exposure to the hardest kind of quartzite. Most of the
associated beds are friable and easily eroded, so that when the
surrounding strata have been removed there are left behind a few
blocks of quartzite, varying in size from a foot to four feet in
diameter. These boulders are so unlike the rocks from which
they have been derived and by which they are surrounded, that
unless one has given special attention to the study of Tertiary
sediments in that region he is liable to be much puzzled and even
misled by them. ’
ORIGIN OF THE WATER-WORN MATERIALS.
The second class of evidences by which Agassiz and Hartt
were misled consisted of transported, water-worn materials.
t Revista do Instituto Historico do Brazil, 1866, XXIX., 421 ef seg.
2 See BRANNER’S Cretaceous and Tertiary Geology of the Sergipe-Alagéas Basin
of Brazil. Trans. Amer. Phil. Soc., XVI, 1889, 419-421.
SUPPOSED GLACIATION OF BRAZIL. 767
These materials are made up of boulders, cobbles, and gravels,
sometimes assorted and sometimes having sand and clay mixed
with them, and are spread far and wide, though irregularly, over
all the Tertiary and Cretaceous area bordering the ocean, and
extend for a long distance into the interior, and far beyond the
borders of the Tertiary deposits. They were regarded by the
writers in question as analogous to the water-worn materials so
common in the northern drift. Had these materials been of
glacial origin it is not unreasonable to expect that striated
pebbles would have been found among them occasionally, but,
as a matter of fact, no such marks have ever been found, though
I have made the most diligent search for them. That the striae
have been obliterated by weathering agencies is out of the
question, because the preservation of the water-worn and pitted
faces of the pebbles shows plainly enough that striated faces
would have been preserved equally well had they ever existed.
The origin of these water-worn materials has already been
explained elsewhere, and from that article the following quota-
tion) 1s made = |
“This formation is spread over the hills and valleys of the Sergipe-
Alagoas basin and over the adjacent country in the form of a thin coating of
cobblestones, pebbles and sand, sometimes loose and sometimes cemented
into a pudding-stone as much as ten feet in thickness, and, when exposed,
stained black by manganese. It caps the summit of the tertiary plateaux or
their outliers, and it is frequently strewn along down the sides of hills and
accumulated in the valleys. It is not confined to the geographic limits of the
Cretaceous or Tertiary, but is found further inland and far beyond the present
limits of these formations. It is everywhere more or less irregular in thick-
ness, and nowhere can it be said to be universal or continuous. The writer
has seen this material throughout Sergipe and Alagoas, in Parahyba, and as
far inland as the head waters of the Rio Ipanema in the interior of the pro-
vince of Pernambuco, where there is no remnant of stratified Tertiary beds.
Between the lower Rio Sao Francisco and the frontier of the province of
Alagoas, and indeed in many parts of the province of Pernambuco, this water-
worn material is found mingled in bogs with the remains of extinct, gigantic
mammals.
One of the marked characteristics of this post-tertiary formation is that it
is much coarser inland, and grows finer as the coast is approached. The
trans, Amer. Phil. Soc., 1889, XVI., 421.
768 THE JOURNAL OF GEOLOGY.
explanation of this water-worn material seems to be that the Tertiary period
was closed by a depression along the present coast, which carried the beach
line far inland, or that it was already there. Then followed a gradual
emergence,’ during which the whole area now covered by this widely dis-
tributed water-worn material was passed gradually through the condition of a
beach, upon which the then loose, angular, surface rocks of the country were
rounded and worn into the boulders, cobbles and pebbles which we now find
scattered over this region. While the surf was beating upon and wearing the
hard crystalline and metamorphic rocks of the interior it was unable to pro-
duce any very marked effect upon the topography of the country, but when,
in the course of the land’s emergence, the soft, sandy and clayey beds of the
Tertiary were brought up within its reach, the work of land sculpture it was
able to do was enormously increased. During the emergence of these
Tertiary beds they were deeply eroded, and the mud which originally made
part of them was washed seaward, and the coarser materials were concentrated
upon the slowly receding beach. In some places these accumulations assume
unusual proportions, as if they had been brought together by the gradual
beating of waves along a beach, or had been reconcentrated by later streams.”’
GLACIAL TOPOGRAPHY.
Agassiz considered that the undulating outlines of the topo-
graphy about Rio de Janeiro were attributable to glacial action,’
though he recognizes the fact that nothing of glaciation was to
be learned from their appearance.3 A careful study of those
features, made with this suggestion in mind, shows that the
rounded hillsides have no uniformity in their arrangement, that
is, what would be s¢oss sides, judging from the topographic forms,
face now in one direction, and now in another, and that the out-
lines are simply those produced by ordinary decomposition and
erosion, though much influenced by structural features. Hlartt:s
opinion, as originally expressed in his book (ip: 33) was that the
forms of the hills were ‘due primarily to subaérial denudation.”
THE ABSENCE OF STRIA.
A bit of negative evidence of great importance against the
glacial hypothesis is the fact that nowhere has there been found
™ See also Pissis in Comptes Rendus de I’ Acad. des Sci., 1842, XIV., 1046.
2 Geological Sketches, II.,157. Bul. de la Soc. Géol. de France, 1867-8, XXV., 687.
3 Journey, pp. 69-70.
SUPPOSED GLACIATION OF: BRAZIL. 769
a single scratch either upon the rocks in place or upon a boulder,
cobble, or pebble, that could, by any legitimate stretch of the
imagination, be attributed to glacial action. And it is but just
to recall the fact that both Agassiz and Hartt recognized this as
the one piece of evidence, above all others, lacking for their
Brazilian glacial theory. How diligently Agassiz searched for
such evidence one can judge from the story of his journey as
told by Mrs. Agassiz and himself, and I know that Hartt left no
stone unturned and no locality unexplored that he thought might
afford him the long-sought striae. They both explained the
absence of such marks by supposing that they had been oblit-
erated by the decomposition of the rocks, and Agassiz believed
that in the Amazon region there were no rock surfaces exposed.’
But it cannot be considered credible that glacial striz should
have been preserved in Asia, Africa and Australia since Carboni-
ferous times,? but entirely obliterated in Brazil, both from the
bed rocks and from the conglomerates deposited in post-tertiary
times, or as has already been mentioned, that the pitted and
water-worn faces should have been preserved in these materials
while the ice marks should have been obliterated.
James E. Mills, a professional geologist and a former pupil
of Agassiz at Harvard, spent nearly two years in Brazil in the
states of Rio Grande do Sul, Rio de Janeiro, and Minas Geraes.
He expresses his views of the subject of glaciation in that
country as follows:3 ‘In those portions of Brazil which came
within my field of observation there is no glacial drift, and there
are no glaciated rock surfaces or glacial topography or other
signs of the existence of glaciers.”
Agassiz points out the weakness of his own theory regarding
Brazilian glaciation very nicely in his letter to Professor Pierce,
‘Journey, 426. There are plenty of rock surfaces in the Casaquiari region, on the
Araguary, the Tocantins, the Tapajos and in hundreds of other places away from the
immediate alluvial plain of the Amazon.
2 Geological Magazine, 1886, 492-495. For the literature of the subject see C. D.
WHITE in Amer. Geologist, May, 1889, 299-330.
3 American Geologist, III., 361.
770 LAE fOULINATE OF NG HOLOGN-
of Harvard, by saying: ‘But I have not yet seen a trace of glacial
action proper, if polished surfaces and scratches and furrows are
especially to be considered as such.’’*
BIOLOGICAL EVIDENCE.
Thus far I have confined myself to a statement of the tacts
that relate directly to glaciation. Aside from these a matter of
the utmost importance is the continuity of life from Tertiary
times down to the present, especially in the tropical and sub-
tropical parts of the earth. If glaciation had been cosmic, as
suggested by Agassiz—if it had taken place under the very
equator—then the reasoning of biologists regarding the origin
and distribution of the present life of the globe is about all at
fault. A reviewer of Hartt’s Geology of Brazil long ago called
attention to the fact that “the grand objection to the theory of
the former existence of a continental glacier in tropical America,
is the unbroken continuity of tropical life since the close of the
Tertiary period.”*? Mr. Wallace, in an earlier review, had already
called attention to the same point,3 while still another lays stress
upon the important fact that the plants found in the Amazonian
silts, supposed by Agassiz to be of glacial origin, are the remains
of tropical plants, and are not therefore comparable with the
Alpine plants growing beside existing glaciers in mountainous
regions.4
THE OPINIONS OF OBSERVERS.
The following are some of the opinions of geologists regard-
ing the phenomena regarded by Agassiz and Hartt as glacial.
These authors are quoted, not simply for the purpose of bring-
ing the weight of authority to bear on the subject, but because
they have all seen much of the geology of Brazil and are
competent to have opinions worthy of consideration. Darwin,
who visited Brazil in 1832 and saw something of these
tJourney in Brazil, 88.
2 American Naturalist, 1871, V., 36.
3 Nature, 1870, II., 511.
4The Geological Magazine, 1868, V., 458.
SOPPOSED GLACIATION OF BRAZIL, WAM
phenomena, stated that no true glacial boulders had been seen
in the inter-tropical regions.‘ The English botanist, George
Gardner, gives the correct explanation of the formation of the
soils about Rio.? Burmeister, who traveled extensively in Brazil,
is of the opinion that the facts appealed to by Agassiz in support of
his glacial hypothesis for Brazil are to be explained otherwise.3
Liais’ adverse opinion has already been cited. Dr. Guilherme S.
de Capanema, a Brazilian geologist, thoroughly disbelieves in the
theory of Brazilian glaciation. Professor James Orton’s papers
in which he controverts the glacial hypothesis in so far as it relates
to the Amazon valley have been cited, while Hartt himself recog-
nized the mistake of Agassiz in that region.5 Mr. James E.
Mills saw some of the best examples of the supposed glaciation
at Rio de Janeiro and spent more than a year in the highlands of
Brazil; his opinion regarding what he saw has already been
quoted. Professor Derby in speaking of the possibility of glacia-
ation omits all reference to the phenomena upon which Agassiz
and Hartt placed so much stress, namely, those in the mountains
about Rio, though to my knowledge, he is perfectly familiar with
those phenomena.°
tTrans. Geol. Soc. London, 1842, 2nd Ser. VI., 427.
2Jour. Roy. Hort. Soc., 1846, p. 191.
3 Description Physique de la République Argentine par Dr. H. Burmeister, Paris, ~
1876, I1., 393.
4Decomposicao dos penedos do Brazil, Rio de Janeiro, 1866; Revista do Instituto
Historico do Brazil, 1866, XXIX., 421.
5 Am. Jour. Sci., 1871, 295.
In the following references more or less doubt is expressed regarding the glacia-
tion of Brazil :
The Highlands of Brazil, by RicHARD F. Burton, London, 1869, I., 39, II., 218.
The Amazon and Madeira Rivers, by FRANZ KELLER, New York, 1874, 47. Fifteen
Thousand Miles on the Amazon, by BROWN and LIDSTONE, London, 1878, 42. Brazil,
the Amazon and the Coast, by HERBERT H. SmirH, New York, 1879, 634. Glaciers,
by SHALER and Davis, Boston, 1881, 47. A Geographia Physica do Brazil por J. E.
WAPPEUS, Rio de Janeiro, 1884, 55. Pre-historic America, by the MARQUIS DE
NADAILLAC, edited by W. H. DALL, London, 1885, 18, foot note. Report on Coffee
Culture, by C. F. VAN DELDEN LARENE, London, 1885, 24. Le Pays des Amazones
par F. J. de SanTA-ANA NERY, Paris, 1885, 36. A Year in Brazil, by H. C. DENT,
772 THE JOURNAL OF GEOLOGY.
I may sum up my own views with the statement that I did
not see, during eight years of travel and geological observations
that extended from the Amazon valley and the coast through
the highlands of Brazil and to the head waters of the Paraguay
and the Tapajos, a single phenomenon in the way of boulders,
gravels, clays, soils, surfaces or topography, that could be
attributed to glaciation. A glacial origin for certain gravels has
probably been suggested by Derby,’ because their origin is
somewhat obscure, but I am of the opinion that they admit of
the same explanation as the high river gravels of the south-
western United States, and that glaciation had nothing whatever
to do with them.’
Joun C. BRANNER.
London, 1886, 424. Three Thousand Miles through Brazil, by J. W. Wells, London,
1886, II, 373-4. Sparks from a Geologist’s Hammer, by ALEXANDER WINCHELL,
Chicago, 1887, 180. Notes of a Naturalist in South America, by JoHN BELL, London,
1887, 313-318 and 342. Darwinism, by ALFRED R. WALLACE, London, 1889, 370.
tWAPPEUS’ Geographia Physica do Brazil, p. 55.
2Tt may have some value as corroborating an opinion formed before studying the
geology of the Southern United States, that all the phenomena brought forward in sup-
port of the glaciation of Brazil are repeated in the Southern States, far south of what
geologists readily recognize as the utmost limits of glacial ice. In Arkansas for exam-
ple, boulders occur near Little Rock, of such shape, character, and distribution as to
strongly suggest a glacial boulder train, if the glaciation of the region were admissible,
or another explanation were not evidently the correct one. For an illustration of such
boulders see Annual Rep. Geol. Survey of Arkansas for 1890, II., 25.
CAUSES OF MAGMATIC DIFFERENTIATION.
In petrographical literature in recent years attention has
repeatedly been drawn to the fact, that igneous rocks, which are
closely connected geographically and in age, are also chemically
related to one another, showing a certain ‘consanguinity ’’—to
use Iddings’* very fitting expression—a relationship which makes
them form a distinct ‘‘ petrographical province” (Judd) when
compared with igneous rocks of other parts of the world. The
cause of this relationship has been sought in the supposition,
that all the different rocks of the ‘‘ petrographical province ”’
come from the differentiation of one common magma, originally
homogeneous.
As to the manner in which the differentiation took place,
opinions are divided. We may suppose that it took place during
the consolidation of the magma; in this way, a part of the
minerals crystallized out, then were mechanically accumulated
and finally reliquified. The differentiation of the original magma
into partial magmas could take place in this way, but, as far as I
can see, only on a small scale. A silicate magma during its
period of crystallization is certainly too viscous to permit of any
considerable diffusion. For example, in the reproduction of
rocks after the method of Fouqué and Lévy, in which process a
glass is first made having the desired composition, this glass may
be completely devitrified (fused), while it remains so viscous
that pieces of it neither change form nor adhere to one another.
Another theory, namely, that the differentiation has taken
place in the magma while quite fluid, possesses greater probability
and therefore more adherents. But concerning the details of the
method opinions differ. While certain petrographers apply the
™“ Origin of Igneous Rocks.” Bull. Phil. Soc.of Washington, 12. 89-214. (1892).
This paper contains an extensive bibliography of this subject, to which the reader is
referred.
773
774 Wied, SFOKINAIL, EF C/E OLOGY,
laws of dilute solutions to explain the differentiation of the
molten silicate magmas, others look upon the separation of the.
original magma into partial magmas as evidence of the incapacity
of the chemical compounds, constituting the original magma, to
dissolve one another completely at all states of temperature and
pressure. This latter theory is not as yet very much developed,
but has been considered by Durocher and Rosenbusch, whereas
the first theory, which consists essentially in the application of
what Teall has termed “Soret’s principle,” has been used by
several authors, in greatest detail by Vogt.
The principle known in petrographical literature as ‘“‘ Soret’s
principle” can be correctly formulated thus: ‘If in the same
dilute solution, the temperature is different in different places,
the concentration varies also and in such a manner, that, when
equilibrium is established in every point, it is universally propor-
tional to the absolute temperature —for, the osmotic pressure is
proportional to the absolute temperature, and if the pressure is
augmented in one place, part of the molecules must be driven
over to the place with less osmotic pressure, in order to maintain
the equilibrium. Here, as in the other applications of the laws
of gases to solutions, it must be remembered that these laws
apply rigidly only to very dilute solutions; concerning the
behavior of concentrated solutions we know very little, and
especially with reference to ‘‘ Soret’s principle.” Further, if two
or more substances are contained in the solution a difference of
temperature could not change the ve/ative concentration any more
than it could change the composition of a gas-mixture.* The
only thing that is altered is the proportion between the solvent
and the substance dissolved.
Consequently such definitions of ‘‘Soret’s principle” as ‘“‘The
compound or compounds with which the solution is nearly satu-
rated tend to accumulate in the colder parts,’? and ‘The most
*In very concentrated solutions it might happen that the osmotic pressure is a
different function of the temperature for the different substances in solution, and then
the relative concentration would be changed.
°TEALL: “ British Petrography,” 394. (London, 1888). ZIRKEL: “ Lehrbuch der
Petrographie,” Vol. I., 779. (Leipzig, 1893).
»
CAUSES OF MAGMATIC DIFFERENTIATION. 775
difficultly soluble compounds diffuse towards the plane of cool-
ing
solvent and the dissolved substance which is changed and this is
all—so far as we know at present. Consequently, in order that
one may use ‘‘Soret’s principle’ for the purposes of theoretical
7
are misconceptions. It is the proportion between the
petrography it is quite necessary to have the question settled :
what is ‘the solvent” and what “the thing dissolved ?”
Vogt? avoids this difficulty in the following way. He says:
‘Owing to chemical action certain ‘ liquid-molecules’ are individ-
ualized, which are preliminarily kept dissolved in the resting
magma, and which only by a subsequent lowering of temperature,
or pressure, are separated in the solid condition. The minerals
which crystallize first at every stage may consequently be con-
sidered originally ‘ dissolved’ in the remaining ‘ mother-liquor.’”
Here we find at first the supposition, that certain compounds are
“individualized 3 in preference to others, and consequently the
latter as not ‘‘individualized”’ form a sort of chaos. But this
remainder must certainly consist also of chemical compounds.
The author has perhaps thought that they should be dissociated,
but it must be remembered that the free ions cannot diffuse
independently of one another.
In the latter part of the quotation it is stated, that the sub-
stance which crystallizes out first when temperature sinks is to be
considered as dissolved in the solvent, which crystallizes at a still
lower temperature. But, in general, it is the solvent which
crystallizes out first when the temperature falls, and this crystal-
lization goes on until the ‘eutectic proportion” (Guthrie) is
reached, when both the substance dissolved and the solvent
crystallize simultaneously until the whole is solidified. If Vogt’s
reasoning is correct, the more a dilute solution of nitre is diluted
with water, so much the more should the water be regarded as
the substance dissolved.
™ “Tie am schwersten léslichen Verbindungen diffundiren nach der Abkiihlungsflache
hin.” BrOGGER: Zeitschr. f. Krystallographie 16, 85. (1890).
2 Geologiska Foreningens Foérhandlingar 13. 526. (Stockholm, 1891).
3 Or“ constituted” in the German edition, Zeitschr. f. prakt. Geol., 1893, 273.
776 THE JOURNAL OF GEOLOGY.
5)
Thus I have tried to show, that ‘“ Soret’s principle”? cannot be
applied to magmas, and consequently, if magmatic differentiation
were a process of molecular diffusion it could not be explained.
And it seems to me to be going too far to apply the laws of
dilute solutions to magmas before having attempted to consider
them simply as mixtures of liquids.
As an illustration of the conduct of two liquids when mixed,
let us take aniline and water. If they are mixed at ordinary
temperature, when equilibrium is established two layers are
formed, one containing I per cent. of aniline and gg water, the
other 98 aniline and 2 water.t But if they are mixed at 100° the
two layers formed will contain 4 aniline and 96 water, and g1
aniline and 9 water; at 150° the proportions are 14 aniline and
86 water, and 76 aniline and 24 water; at 160° they are 25 aniline,
75 water, and 68 aniline, 32 water, and at 166° the two layers
should have the same composition, being consequently identical.
Therefore, above 166° aniline and water mix in all proportions,
but delow this temperature the reciprocal dissolving capacity is
limited and generally a separation into two layers takes place,
the composition of which is a function of the temperature.
This seems to be common for all liquid-mixtures where no
chemical action takes place. For all such mixtures there exists
a temperature, above which they mix in all proportions. It is
true that this temperature is known only for a few combinations
of liquids, but it must be regarded as certain that it exists, and if
not below then at the critical temperature, because here the
capacity of mixing in all proportions is a general property of the
gases.
On the other hand, there are certain fluids, which at ordinary
temperature dissolve one another without limit, and for these the
temperature below which the dissolving capacity is limited is yet
to be determined, but in some cases this may not be reached
before the transition into the solid form takes place. For us the
principal question now is, can we assume that all the chemical
*The numbers given are obtained by interpolation in the curve of Alexejew in
WIEDEMANN’s Annalen 28, table 3. (1886).
CAUSES OF MAGMATIC DIFFERENTIATION. TAS
compounds forming the original rock magma are completely
soluble in one another? I think not.
We are told by Vogt* that silicates can be melted together
in all proportions. This may be true, but it dees not prove that
this mixture would not separate into layers of different compo-
sition, or at least become heterogeneous, if it were kept molten
for a sufficient time. The viscosity of molten glasses is very
great and consequently the separation must take time. Still
evidences of such separation—or “guation as we may call it,
following Durocher—in the manufacture of glass are not wanting.
It is well known to be very difficult to produce large pieces of
homogeneous glass, for example for optical purposes. Accord-
ing to Wagner’s Handbuch der chemischen Technologie? this
comes from the fact, “either that the individual compounds
formed during the melting process have not dissolved one
another or that they have separated from the mixture by a lower-
ing of the temperature’’; and further, ‘One will seldom find
large pieces of glass, which are completely free from this fault.’
But it is not necessary to leave the field of geology in order
to decide the question whether magmatic differentiation is a
diffusion, or a liquation, process. Let us select some examples
of differentiation, and examine them in the light of both theories.
I have chosen two, one on a small scale, the basic inclusions, and
one on a large scale, the great petrographical province of
Iceland.
By diffusion, according to ‘Soret’s principle,’ the basic
inclusions could never be thought to have been formed in situ
or approximately so—for, between them and the surrounding
magma there would be no difference in temperature, or at least
no difference sufficient to alter the osmotic pressure, which is
proportional to the absolute temperature, or enough to produce
t Zeitschr. f. prakt. Geol., 1893, 272.
2 13th edition, 720. (Leipzig, 1889).
3“ Entweder die einzelnen beim Schmelzprocesse entstandenen Verbindungen sich
gegenseitig nicht aufgelost, oder bei einem Nachlassen der Temperatur aus einem
Gemenge sich abgeschieden haben”; and further, ‘‘ Man wird selten gréssere Stiicke
von Glas finden, welche von diesem Fehler vollkommen frei wiren.”
778 LTTE J OOLINATE OF AGH OLOGN:
so radical a change in chemical composition. These inclusions
must, by this theory, be considered to be fragments of older
rocks, formed in this way. Still basic inclusions may be sup-
posed to have been formed by mechanical agglomeration, and no
doubt this has often been the case. But, in opposition to both
these theories, it is in many cases evident that the inclusions
were soft, and then the simplest view is that they were drops, or
portions, of a partial magma, which at the temperature, existing
immediately before crystallization, could no longer be held in
solution by the principal magma, but separated out,
The great petrographical province of Iceland is characterized
principally by enormous eruptions of plagioclase-basalts and
exceedingly subordinate eruptions of rhyolites, which, however,
are very numerous. No other eruptive rocks are known from
Iceland up to this time.*. If we considered the differentiation of
the primary magma, which here was very basic, as a diffusion-
d
phenomenon, according to ‘‘Soret’s principle,” it would be incom-
prehensible why the differentiation never stopped with the pro-
duction of an intermediate magma, and, moreover, this theory
would demand that every little rhyolite-emagma previous to the -
eruptions would have been surrounded by a broad zone, showing
all transitions to the basaltic magma. In both cases these inter-
mediate magmas should have been erupted at some time, but,
as already mentioned, we know a hundred eruptions of rhyolite
but not a single one of andesitic rocks. It therefore seems more
probable that these intermediate magmas never existed in the
petrographical province of Iceland, but that the acid partial
magmas were separated out directly from the basic original
magma, which by lowering temperature lost its homogeneity.
The conditions of temperature and pressure being different in
different places these acid partial magmas also became somewhat
different, but may all be classified as soda-rhyolites. The
chemical compounds, which constitute the silicate magmas—
and which are not necessarily identical with the rock-forming
* Refer to H. BACKsTROM: “ Beitrage zur Kenntniss der islandischen Liparite ” in
Geol. Foren. Forh. 13, 667. (Stockholm, 1891).
CAUSES OF MAGMATIC DIFFERENTIATION. 779
minerals—are naturally more than two, and therefore the liqua-
tion must become very complicated, being not only a function of
temperature but also dependent on the original proportions.
Therefore, in other places, where the original niagma had another
composition, relatively stable andesitic magmas might be formed,
but this was evidently not the case in Iceland.
Liquation is no doubt also a function of the pressure, but
experimental data are wanting. Still it may be considered as
probable that, if liquation would augment the volume of the
magma, then pressure would act the same as increase in tem-
perature, and inversely. The first is most frequently the case
with liquid-mixtures.
The purpose of this communication is to give to liquation
and not to diffusion its place as the working hypothesis, upon
which the theory of differentiation is to be constructed. How
far this theory may differ from the approximation to it, given by
Rosenbusch in his ‘ Kern”’-theory, the future will show.
In conclusion, I wish to express my best thanks to my
friend and colleague Dr. S. Arrhenius for much valuable infor-
mation furnished me in numerous discussions on this and other
subjects which lie on the border between petrology and physical
chemistry.
HELGE BAckKsTROM.
THE GEOLOGICAL STRUCTURE OF THE HOUSATONIC
VALLEY LYING EAST OF MOUNT WASHINGTON:
(With Plates V, VI, VIL.)
Published with the permission of the Director of the United States
Geological Survey.
CONTENTS.
Introduction.
The area studied.
Views of Percival and Dana regarding the area.
Lithological characters of the horizons.
Explanation of map.
Geological structure of the area. \
Structural features as shown in longitudinal sections.
Structural features as shown in transverse sections.
Structure of Tom’s Hill.
The great Housatonic Fault.
Metamorphism along the fault.
Thickness of the Egremont Limestone.
Conclusion.
In a former paper? I have discussed the geological struct-
ure of Mount Washington and shown that in that mass we have
to deal with a conformable series of beds embracing four distinct
lithological members. These members are: (1) a lower dolo-
mitic limestone—the Canaan Dolomite; (2) a lower schist
member containing usually abundant garnets and frequently also
staurolite—the Riga Schist ; (3) a calcareous member, in the
valley a marble but on the summit plain of the mountain and
along its base very micaceous and graphitic—the Egremont
Limestone ; and (4) a schist member very feldspathic and
*Part of areport of work done as Assistant Geologist in the Archean Division of
the U. S. Geological Survey, under the direction of Professor Raphael Pumpelly.
?On the Geological Structure of the Mount Washington Mass in the Taconic
Range. Journal of Geology, Vol. L, p. 717.
780
THE HOUSATONIC VALLEY. 781
usually either chloritic or sericitic, but always free from garnets
and staurolite—the Everett Schist.
The area studied—To the eastward of Mt. Washington,
at a distance of five or six miles, flows the Housatonic river, its
general course being like the crest-line of the mountain, nearly
south. To the northeastward of the mountain the intervening
area is a nearly level plain in which are extensive outcrops of the
Egremont Limestone, sometimes with thin intercalated mica-
ceous or quartzitic layers. This limestone belt extends almost to
the river at Great Barrington and Sheffield Plain. South of the
village of Sheffield, however, the level expanse of the plain is
broken by the occurrence along its eastern margin of low, sharp
ridges trending northeasterly to northwesterly, and increasing in
number as well as in height and breadth in going south. The
area covered by these ridges begins at Sheffield where two nar--
row ridges are separated by only a few hundred feet, and broad-
ens steadily in going southward, thus narrowing the belt of lime-
stone on its western border, and finally cutting it off near the
village of Salisbury by making connection with the southeastern
base of Mt. Washington. (Cf. Plate III. of Mt. Washington
paper). Corresponding with the increase in breadth which
characterizes the area in its southern portion, there is a marked
increase both in the height and the width of the individual
ridges. East of the Twin Lakes in Salisbury is Tom’s Hill,
which rises to a height of over 1,200 feet, while further south, to
the east of the village of Salisbury, is Barack M’Teth (1,300
feet), and Watawanchu Mountain (1,300 feet), and farther east
in about the latitude of Watawanchu Mountain is Mt. Pros-
pect’ (1,460). This tongue of alternating schist ridges so
sharply outlined, presents so much of unity in topographical and
geological features as to be eminently suited to separate treat-
ment. As the ridges are composed of the Riga and Everett
Schists, the area is closely connected geologically with Mt.
Washington. This paper is devoted to the consideration of
“To be distinguished from one of the northwest peaks of Mt. Washington which
bears the same name.
782 THE JOURNAL OF GEOLOGY.
the structure within this tongue-like area, which includes
between twenty and twenty-five square miles. The field work
was mainly done in 1888, though the southern portion of the
area was revisited in 1891, when the writer was assisted by Mr.
Louis Kahlenberg, and again in 1892 when he was assisted by
Mr. H. J. Harris. The work has been in charge of Professor
Pumpelly, then the head of the Archean Division of the U.S.
Geological Survey.
Views of Percival and Dana regarding the area—Though the >
map accompanying Percival’s report does not indicate the schist
areas within the area which is under consideration, he several
times mentions them in the text. One is surprised to find how
accurate were his observations and how correct his views regard-
ing the area, notwithstanding the limited facilities and unsatis-
factory condition of his survey. The following extracts from
his report* contain the more important statements which he
made having reference to this area.
“It (the limestone) is accompanied throughout with Mica Slate some-
times forming thin interposed beds, and at other times extensive ranges. The
Mica Slate, in the vicinity of the limestone, particularly when interposed in
thin layers in the beds of the latter, is very generally dark and plumbaginous,
but occasionally light gray, as in the more extended ranges. ‘These latter
usually occupy high narrow abrupt ridges, sometimes quite isolated, and at
other times in longer ranges, generally with an irregular outline.” (Pp.
126-127).
““A coarse dark Mica Slate, veined or knotted with quartz, and often
abounding in staurotides and garnets, occurs especially in the north part of
the ridge bounding, on the west, the valley south of Lime Rock village,
sabes Weare faye 27)
“The general surface of the valley, in the north part of Salisbury, in
Canaan, and in the adjoining part of Massachusetts, is low and level, but
traversed by ridges of Mica Slate, often high and abrupt, either isolated, or
in long continuous ranges, the latter generally presenting a distinctly curved
outline; 7 4(P.120);
“Between these two branches? extends a series of Mica Slate ridges, con-
tinued north from the ridge bounding the valley at Weed’s Quarry (KI1.) on
* Report on the Geology of Connecticut, by JAMES G., PERCIVAL, New Haven,
1842, pp. 124-130.
?Of the Housatonic Valley.
THE HOUSATONIC VALLEY. 783
the west, in a very undulating course, and marked by several transverse
depressions, to a high isolated summit,t adjoining the north line of the east of
the North Ponds? (Salisbury).” (P. 129).
In a paper read before the American Assoeiation in 18733
Professor J. D. Dana quotes Percival as stating that the mica
schist in which he found garnets in the township of Salisbury, is
below the ‘Stockbridge or Canaan Limestone,” but giving it as
his own view that the schist is the overlying rock. This observa-
tion of Percival has considerable interest, for though the “Stock-
bridge or Canaan Limestone ”’ has been shown to consist of two
members, one of which is below and the other above the Stauro-
lite-bearing rock, it is probable that Percival discovered a locality
at which the Riga Schist comes out from below the Egremont
Limestone.
On the map accompanying Professor Dana’s paper entitled
Taconic Rocks and Stratigraphy, a number of schist areas are
represented within the area here treated, which he correctly
described to be, in some cases at least, “isolated within the lime-
stone area, —as isolated as islands in a sea.’’> He mentions
eleven of them in Salisbury and eight in the part of Sheffield
township just north. He believed that there is but one schist
horizon, which overlies the limestone, and described three local-
ities, nearly or quite within the area studied, to sustain his views.
These are, (1) the hill three miles north of Gallows: Hill (locality
4, |. c., p. 213) where the schist “overlies the limestone”; (2)
Turnip Rock (locality 5, 1. c., p. 213) where schist overlies lime-
stone in a shallow synclinal; and (3) Tom’s Hill in Salisbury,
which is described asa very flat trough of schist toward the north,
but developing farther south into an overturned synclinal with
its axis dipping east (I. c., p. 214). The observations made by
tTom’s Hill.
2Twin Lakes.
3On Staurolite Crystals and Green Mountain Gneisses of the Silurian Age, by J.
D. Dana. Proc. A. A. A. S., 22d (Portland) Meeting, 1875, p. B25.
4 American Journal of Science, Vol. XXIX., June, 1885.
5 Amer. Jour. Sci., Vol. XXIX., March, 1885, p. 211.
784 THE JOURNAL OF GEOLOGY.
the writer accord with those of Professor Dana in the second
instance only, which relates to the upper or Everett schist mem-
ber. As will be fully shown below, the other mentioned locali-
ties have a much more complicated structure than was supposed
by Professor Dana.
LITHOLOGICAL CHARACTERS OF THE HORIZONS.
As has already been stated, the horizons outcropping within
this area all belong to the Mt. Washington series, viz.: The
Canaan Dolomite, the Riga Schist, the Egremont Limestone, and
the Everett Schist. The Canaan Dolmite seems to be for the
most part a dolomite or dolomitic limestone, with more or less
admixed quartz. A white pyroxene or salite is found to be com-
mon in it in the vicinity of Canaan, and in the belts extending
east and northeast from that point. It has also been found at
several localities in the vicinity of Lime Rock, but is only rarely
seen west and southwest of that place. Tremolite is also found
in this horizon, but as will be more fully explained beyond, this
is largely restricted to a zone bordering the Housatonic River on
the east. Masses of Canaanite are also found in this horizon,
and as neither pyroxene nor tremolite has been found in the
Egremont Limestone, their presence here is useful for purposes
of identification.
The Riga Schist within this area has the characters which
distinguish it on Mount Washington. In most of the ridges
where it occurs, garnets alone or garnets and staurolites have
been found in it. They are most abundant and of largest dimen-
sions in the ridge south of Twin Lakes Station, the ridge south
of Chapinville Station, in Tom’s Hill and Mile’s Hill, in Mt.
Prospect (south of the area here mapped), and in Barnard Mt.
and Johnny’s Mt.* near Sheffield.? The mica is often a silvery
* These minerals were described from this locality in 1824 by Dr. Chester Dewey.
Am. Journ. Sci., Vol. VIIL., p. 7.
* Professor Dana has specially mentioned them from many of these localities.
(l. c., p. 440). The increase in size of garnets and staurolite from Mt. Washington to
the Housatonic, as described by him, has not been confirmed by this study. The
largest that have been noted are from the south end of the ridge south of Chapinville
Station.
Jour, Geo, Vor. J, 1893.
ig
ALEGEND
SQ Quartzite
Bi NN Everett Schist
b
% : ESS 2|Tremolitic Limestone 49
along Fault Line
Strike and Dip
GEOLOGICAL MAP OF PORTIONS OF
SHEFFIELD, MASS. AND SALISBURY, CT.
One Mile
THE HOUSATONIC VALERY. 785
sericite and considerable graphite is sometimes associated
with it.
The Egremont Limestone resembles that found along the
east base of Mt. Washington, its principal impurities being mus-
covite and quartz. It contains locally important layers of cal-
careous mica schist. In the vicinity of Twin Lakes, two distinct
beds of the latter are made out, one immediately below the
Everett Schist—a transitional zone—and the other lower down
near the middle of the horizon. A third, less important and less
constant, zone forms a transition from the Riga Schist to the
Egremont Limestone. The upper of these layers forms the cap
of Babe’s Hill (northeast of Washining Lake). The middle
layer is also found in the same hill along the southwest base, and
the lowest layer may be seen above the Riga Schist at the first
road-corner northeast of Chapinville. Graphitic phases are found
as a transitional zone between this horizon and the overlying
Everett Schist in the northeastern part of the area, particularly
in areas 16 and 25.
The Everett Schist is not chloritic to any marked degree, as
is so often the case on Mt. Washington, but is frequently
sericitic, usually porphyritic from rounded eyes of feldspar, and
frequently passes downward into graphitic schist.
EXPLANATION OF MAP.
The map which accompanies this paper (Plate V.) is based
on the Sheffield and Cornwall sheets of the topographical atlas
ot the United States, by the U.S. Geological Survey, and is
drawn on the same scale—1I: 62,500, or one inch to the mile.
It overlaps by about one half mile the map which accompanies
the Mt. Washington paper. To bring as much of the area as
possible on the page, the narrow northern portion is placed in
one corner, its actual position being roughly indicated by the
positions of the Housatonic Railroad and the large marsh to the
west of it. Fig. 5 also extends the map some distance to the
south. The area covered by the Egremont Limestone is left
blank, while the Riga and Everett Schist areas are shaded, the
786 THE JOURNAL OF GEOLOGY.
former being the darker. The more important of the schist
areas have been given numbers from 1 to 38. An attempt has
been made to indicate the geological structure on the map by the
introduction of such of the important dip observations as the
scale of the map will allow, as well as small arrows which indicate
the inclination of the trough and crest-lines (pitch). The course
of an important fault is traced along the east bank of the Housa-
tonic River.
GEOLOGICAL STRUCTURE OF THE. AREA.
Since the beginning of the study of the Green Mountains by
the Archean Division of the Survey, Professor Pumpelly has
emphasized the necessity of making careful observations of the
pitch of flexures, in order to arrive at a complete knowledge of
the geological structure. Observations of this character have
furnished the key to the structure within the area here studied.
The crest lines of the folds show considerable and frequently
changing inclinations, but the beds have withstood the stress to
which they have been subjected in this direction without disloca-
tion, as there is no evidence of any cross faults. The disturb-
ance which came from the east, and which developed the flex-
ures, has been so great as to overturn most of them, so that their
axes dip east, and locally to cause a disruption with the produc-
tion of rather steep thrusts of small displacement. An important
dislocation has occurred along the course of the Housatonic
River, which has carried the Canaan Dolomite over the newer
beds exposed west of the river.
Structural features as shown tn longitudinal sections —A glance
at the map will show that all the important ridges, with the
exception of Barack M‘Teth, Turnip Rock, and the Bear’s Den,
are formed of ‘the Riga Schist. The fact ithat ‘these tnrdges
steadily increase in height in going southward, as well as the
tongue-shaped outline of the area, indicates that the general
pitch of the flexures is toward the north. This is in perfect
accord with the fact that the folds in the main part of the Mt.
Washington Mass have a northerly pitch. But although the
general pitch within the area now under consideration is north-
THE HOUSATONIC VALLEY. 737
erly, the local pitch” varies greatly both in degree
and direction, and is as frequently southerly as
northerly, as indicated by the arrows on the map.
At the south base of Tom’s Hill the southerly
pitch varies from 30° to 50°, and on the road
cutting across the north foot of Barack M‘Teth,
beautiful corrugations in the Everett Schist pitch
southward at as steep an angle as 50°. These
corrugations are unsymmetrical, the west limbs
ie | ve
UTH 3979} {
‘OTT
"I
being the shorter and steeper. The local varia-
tions in pitch are strikingly indicated on the map
by those ridges of schist which are arranged line-
arly in the direction of the prevailing strike, being
cut off from: one another by limestone. The
7
eel cares me:
ete 4
minor changes in pitch are further shown by
variations in width of the ridges. Thus we find
along the western margin of the area three marked
undulations in the crest-line of an anticlinal of
Riga Schist trending north-northeast. The north-
ernmost is essentially the double undulation of
Horse Hill and area No. 29, then follows the area
northeast of Chapinville (14), and the area south
of Chapinville Station (10). Fig. 1, which is a
longitudinal section along this line, shows besides
the three main undulations just mentioned, a num-
ber of secondary waves of more or less importance.
In Fig. 2 (A) these curves of the crest-line may
be better observed. The manner in which this
anticlinal ridge disappears near the southern limit
of the map is shown in Fig. 1 of Plate VII. The
Bae SN eS
;
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be
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a
‘Jao} porpuny say sjenbos your yyYysto-auo ‘oyeos yeoIeA $ apTuUt
auo sjenba your suo ‘ayes [eyUOZIOF] “YIOL, YOVIV 0} [IPT Vs10FY wos woos jeurpnqysuoyT
«The pitch at any given locality is determined, either (1) by
the direction in which the strike of the two limbs of a fold diverge
in a synclinal fold or converge in an anticlinal fold; or (2), by the
pitch of the plications in the schist. The harmony in direction and
degree of inclination between the pitch of plications and that of
the folds of which they are a part, was first suggested by Pro-
fessor Pumpelly, and proven in the Greylock area. (Cf. T. Nelson
Dale, Amer. Geologist, July, 1891).
#1
rel
CAD UL youszeg
788 LHE JOUORNATE OF (GEOLOGY.
ridge of Riga Schist is seen at A outlined from the surround-
ing Egremont Limestone by a dotted and dashed line. At
B and C are seen Turnip Rock and Barack M‘Teth, composed
of Everett Schist. Between A and C the average strikes in the
limestones are nearly east-west, and the dips (due entirely to
pitch) about 30° south. Approaching Turnip Rock the strikes
become northerly and the dips easterly, as the limestone mantles
around the ridge A.
A second elevated area of the Riga Schist having three
principal undulations in the direction of its prevailing strike,
Fic. 2. Diagrams illustrating some of the structural features of the area studied.
A; Flexures in crest-line of the western ridge of Riga Schist. B, Flexures in Tom’s
Hill and region to the west (from section F, Plate VI). C, Diagram showing the cor-
rugated character of some of the smaller schist knolls near Salisbury. D, The same
in section. E, Diagram showing the probable manner of development of small steep
thrusts in the sharply folded region southeast of TTom’s Hill, and in Horse and Peck’s
Hills.
corresponding with the three undulations of the western schist
anticlinal, is traced along the eastern margin of the district. The
northern of its three undulations brings to the surface in Peck’s
Hill, schist areas 26 and 19, and the accessory overturned and
ruptured fold of areas 22—24; while the central undulation brings
up in Miles Hill and Tom’s Hill schist areas 1 and 4, and the
southernmost undulation develops the extensive schist areas south
of Washining Lake (Area No. ©). - The schist of Peek’s; Hull
disappears south of the swamp on the north base of the eleva-
tion, but the narrower eastern fold reappears north of the swamp
in Johnny’s Mount and Barnard Mount, where it, too, soon disap-
jour) Grow Vos al 1803: PLATE VI.
pee ay &
EE
SECON tit ACCOMPANY
MAAFP.
Base is Sea Level,
Hor. Scale:lin.=1im.
Wert.Scale: Yin= 500 ft.
WW. de
LTE ALO SA RONG VATCEIEN 789
pears beneath the limestone as the most northerly outcrop of the
Riga Schist. The southern limit of the central crest of the eastern
undulation is at the south base of Tom’s Hill, where the schist
disappears through a southerly pitch varying from 35° to 50°,
allowing the Housatonic River to take at this point a south-south-
westerly- course after being carried to the eastward by the unyield-
ing schist mass of the hill. The minor undulations of the
crest-lines of flexures within the northern part of this eastern
ridge, are beautifully shown, not only by the areal relations and
by divergence of strike observations, but also by the pitch of the
plications (cf. arrows on map). Within the central undulation
(Miles Hill), the same feature is indicated in the small basins of
limestone which are entirely enclosed within the boundaries of
the Riga Schist. The triple undulation of the western ridge of
the district has a perfect parallel on the east. To the southwest
of Tom’s Hill just south of Washinee Lake appears an anticlinal
of schist, which continues to rise and broaden in going south.
The island in the lake is an anticlinal of the Egremont Limestone
where it mantles over the ridge of schist. From below the schist
anticlinal emerges the Canaan Dolomite near the southern margin
of the map. As would be expected, the caps of Everett Schist
which are found within the area studied, are widest opposite
where the ridges of Riga Schist disappear, z. e., where basins of
quaquaversal synclinals are formed by the coincidence of longi-
tudinal and transverse synclinals.
Structural Features as shown in transverse sections. —The
nature of the flexuring within the area studied is indicated in the
series of sections (cf. Plate VI). The types are the unsymmetrical
fold with shorter and steeper western limb, indicating an easterly
dipping axis, and the overturned or reversed fold with easterly
dipping axis less steep than the first. The western limb of the
sharper reversed folds has been ruptured, insome cases producing
rather steep thrusts of small displacement. The hade of these
faults is about 45°. The main flexures carry also subordinate sys-
tems of flexures. The areal geology of Horse Hill and Miles
Hill in particular, shows that these properly secondary foldings
790 IWZ0E GOIN, QUE (GAB OVLIOXG YZ,
are corrugated by a tertiary system of small flexures, and exami-
nation of the plications at localities usually reveals even a quar-
ternary system of minor foldings. Many of the small knolls
near Salisbury present a surface something like the half of a
muskmelon, except that a section, instead of resembling an epicy-
cloid, would be more like a sine curve developed on an arc (cf.
Fig. 2 (C). Figure 2 (D) illustrates this structure as seen in
the anticlinal ridge No. 6 south of Twin Lakes Station, and in a
number of small hills near Salisbury.
The Everett Schist occurs in caps or mantles which are for
the most part shallow, nearly symmetrical, synclinals, as exhibited
Fic. 3. View of Tom’s Hill from the northwest, showing the serrated contour
caused by the alternation of belts of schist and limestone. A, Tom’s Hill. B, North-
east foot of Miles Hill. C, Canaan Mt. D, Babe’s Hill.
in Turnip Rock (g), the cap on the southwest slope of Peck’s
Hill (27), and the Washining Lake Mantle (5), the latter being
a double synclinal, as shown by the anticlinal ridge which forms
the island in the lake.
Structure of Tom’s Hill—The doubled-peaked elevation east
of Washining Lake is a compound anticlinal of Riga Schist,
with two prominent crests appearing in Tom’s Hill and Miles
Hill respectively. These anticlinals, like most others in this
region, are pushed over to the westward. A number of subordi-
nate anticlinals, likewise compressed and overturned and here
probably ruptured, are indicated on the map along the northern
boundary of the Riga Schist by fingers of schist which protrude
JOURS GEO VOW. ln aoge Prate VII.
THE HOUSATONIC VALLEY. 791
into the limestone, as well as by the serrated contour of the ridge
when seen from the northwest (cf. Fig. 3). Between Tom’s
Hill and Miles Hill is a fold of Egremont Limestone over-
turned to the west and enclosing a core of the_Everett Schist.
The islands of limestone inclosed in the schist of the eastern
flank of Miles Hill, are the result of frequent alternations of
pitch in small reversed folds which for a short distance have
been ruptured. A stereogram showing the surface of the schist
before it had been cut away by erosion would here present the
characters of 'a choppy sea (cf. Fig. 2 E.) These long alter-
nating belts of schist and limestone on the southeast foot of the
hill northwest of the railroad bridge (V on map), are indicated
topographically by a series of low, sharp ridges which have
gradual east and steep west slopes (cf. Plate VII., Fig. 2).
Farther south, near the railroad bridge, the several schist ridges
become fused together and show more symmetrical undulations.
The dips are here uniformly east at angles varying from 30° to
50°, and the closeness with which the belts are crowded together
allows insufficient room for the full thickness of the Egremont
limestone of this vicinity. The indications therefore are that the
folds have here been so sharply compressed that the beds have
found relief in a slight dislocation or thrust, producing a struct-
ure. best illustrated in Fig. 2 (B), to which Suess has applied
the term Schuppenstruktur, and which I would term weather-
board structure. It is probable that both the throw and dis-
placement of these dislocations is very slight, being greatest
where the crest-lines show an anticlinal structure and least where
they show a synclinal structure. An attempt has been made to
show the nature of these dislocations as they are supposed to
occur on the southeast flank of Miles Hill (Fig. 2 E.) Owing
to the covering of earth in the valleys, the course of the fault is
not exposed. The only locality where the beginnings of such a
*EDUARD SUEss: Das Antlitz der Erde, Vol. L., p. 149.
Gosselet has used structure ecailleuse (Ann. soc. geol. du Nord, Vol. XIL., 1885, p.
197) for similar structures, and Margerie recommends structure imbriguée (Margerie
et Heim, Les dislocations de l’ecorce terrestre, Ziirich, 1888, p. 82).
792 THE JOURNAL OF GEOLOGY.
fault have been actually observed in the rock exposure, is on the
railroad a half mile southeast of the locality just described (S
on map). The nature of the flexuring at this point is made
Sections
on
Southeast of Toms Hill
in
SALISBURY
One Inch is 100 Feet
° 25° 50"
FIG. 4.
clear in Fig. 4, which shows sections in Riga Schist and Egre-
mont Limestone both northwest and southeast of the track,
developed on the plane of the track. At the point A, a sharp
overturned fold in the limestone shows unconformity with the
LATE THOM SAL OUNL ES VAALETE ae 793
underlying schist through a slight fault. The marked difference
between the sections north and south of the track is due to steep
southerly pitch.
The great Housatonic Fault—FEnough has been presented in
the Mt. Washington paper and in the present discussion, to show
that the limestone of this region is divisible into two horizons—
the Canaan Limestone or Dolomite, lower than the Riga Schist,
and the Egremont Limestone above that schist. Additional
evidence might be brought forward, if it were necessary, from
the region lying to the southward in the vicinity of Limerock.
As has also been stated, the Canaan Dolomite, particularly in the
vicinity of Canaan and in the valleys east and northeast of there
(Monterey, Mill River, Clayton, East Canaan), abounds in crys-
tals of white pyroxene, which has never as yet been found in
the Egremont Limestone. Hence this mineral has a certain value
for purposes of identification, comparable with that of the garnet
and staurolite of the Riga Schist. Masses of Canaanite also
occur in it though absent from the Egremont Limestone. Early
in this investigation, when the possibility of a differentiation of
the limestone was only suspected, this lithological peculiarity
was noted, but as the pyroxene-bearing limestone to the east-
ward did not seem to be separated from the pyroxene-free lime-
stone to the westward by any areal break, the question of
divisibility was left open. It was, however, observed that the
Housatonic river roughly outlined the westward extension of the
pyroxene-Canaanite rock to the north of the interstate boundary.
Another striking feature of this line is a ridge more or less pro-
nounced, having its course along the banks of the river. In the
southern half it follows the east bank of the river, but crosses it
at the small hill called the ‘‘ Cobble,” just northeast of Miles Hill,
and to the north of that point borders the west bank." This
ridge is composed of a rock which has not been found else--
where in the region. It is a dolomite abounding in tremolite
and containing layers of quartzite and quartzitic dolomite. Par-
*The southern portion of this ridge (that east of the river) is the ridge mentioned
as Canaanite on page 126 of Percival’s report.
794 THE JOURNAL OF GEOLOGY.
ticularly along its west margin the rock is found to be seamed
with vein quartz in every direction. These characters have not
been found outside of the ridge, which is rarely over a quarter of
a mile wide. The well known greenish tremolite of: Canaan is
from Maltby’s Quarry at the extreme south of this ridge. The
rock was provisionally designated the tremolitic quartzitic lime-
stone and its area was mapped. Sudden changes in the strike
and dip of the beds were found to be particularly common in
this ridge.
Now that the stratigraphy has been determined, there seems
to be no reason to doubt that this ridge marks the course of a
great reversed fault, which in its upthrown limb brings the
Canaan Dolomite against the newer beds in its western or under-
thrown limb. The development of tremolite is ascribed to the
profound shearing which has occurred along the fault plane, and
the ragged dolomite filled with quartz veins to fracturing or
crushing and recementing of the fragments by the silica of
waters which have percolated along the fractures—in other
words, it is a fault breccia. The ridge has survived as a topo-
graphical feature, because of the framework of quartzite and vein ~
quartz and the imbedded crystallized silicates in the dolomite.
The fault line may be followed by these characters from near
Sheffield village to Maltby’s Quarry, northwest of South Canaan,
a distance of about ten miles. To the northward it probably
connects with some of the faults of Vosburgh Hill, but its course
here has not been followed. To the south of Maltby’s Quarry
the fault is followed in the direction of the prevailing strike to
the northeast base of the Cobble,? which base it coincides with
for some distance. This, as will be more fully shown later when
that area is described, is indicated by the Cambrian Quartzite
being absent, the actual contact of gneiss and apparently over-
lying Canaan Dolomite being exposed. On the west base of
this narrow hill, the quartzite is present separating the gneiss and
dolomite, and it also runs around the north end of the hill to
* At South Canaan. This is not the Cobble already referred to and located on the
map (Cf. Plate V.)
WEE SLOUSAL ONT CY VATHEEN
stop abruptly at the northeast base.
195
The well known white
pyroxenes of Canaan come from the dolomite adjacent to the
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Fic. 5. Map and section of the vicinity of the Housatonic Fault, southwest of
Canaan village. Scale and legend the same as in Plate V.
fault line, on the road running immediately at the east base of
this hill, and are much the largest that have been found in the
796 THE JOURNAL OF GEOLOGY.
region. The fault probably extends a considerable distance
farther to the southward but its course has not yet been traced.
The northern course of the fault is indicated on the map.
Starting at the Maltby Quarry, where the surface rock on
both sides of the fault line is Canaan Dolomite, and going north-
ward, to the west of the fault line the generally northerly pitch
carries the beds lower and lower so that Egremont Limestone is
met before Sheffield is reached. On the east, however, no such
pitch exists, and Canaan Dolomite is the surface rock for the
entire distance. The Riga Schist has not been found in actual
outcrop abutting against the fault plane and separating the two
calcareous horizons, but this is explained by the absence of out-
crops along the river valley. The map and section in Fig. 5 are
introduced to indicate how the Riga Schist is believed to meet
the dolomite at the fault line. This map is drawn on the same
scale and has the same legend as Plate V. An examination of
Plate V. will show how the hard Riga Schist of Miles Hill has
‘caused a deflection of the Housatonic River to the eastward in
that vicinity. The important easterly deflection which exists in
the vicinity of the Canaan Camp Ground (cf. Fig. 5) is believed
to be caused in the same way. The low area between the river
and the road to the west of this bend is bare of outcrops, but
Riga Schist is encountered on the road and covers a considerable
area west of it. On the east of the river at this bend the tremo-
litic Canaan Limestone is encountered almost at the river’s bank.
There seems, therefore, reason for believing that in this vicinity
the fault follows the river and that the two rocks abut against
one another at the fault plane.
To the southward of the Maltby Quarry the fault is of a
somewhat exceptional character, since the prevailing northerly
pitch of the beds to the west of the fault line brings beds lower
than the dolomite (First Cambrian Quartzite and then Cambrian
Gneiss) to the surface in the Cobble. The upper limb of the
fold is no longer the overthrown limb, but it is forced to a lower
position. We have here, then, an example of a fault, which at
the north is a rather steep overthrust with Canaan Dolomite over
THE HOUSATONIC VALLEY. 797
Egremont Limestone, and at the south end a reversed fault with
the same rock over Cambrian Gneiss. It follows that the throw
varies most widely. At some fulcrum point, which must be near
the Maltby Quarry, this is practically mz. To the north of that
point, the western limb has been downthrown an amount which
steadily increases in going north, till in the vicinity of Sheffield
it can hardly be much less than a thousand feet. To the south-
ward of the Maltby Quarry, the western limb has been upthrown
and the amount of this upthrow at the Cobble must be several
hundred feet.
The occurrence of two very thin quartzite lenses, which
follow a line parallel with the fault line along “Silver Street” in
Sheffield (Ge Plate V.), is reason to believe that two secondary
faults there run parallel to the main fault.
Additional evidence of the main overthrust is the occurrence
of numerous very large boulder-like masses of the tremolitic
quartzitic dolomite, resting on the Riga Schist to the east of the
road on the northeast flank of Miles Hill. It might be argued
that they are of glacial origin, since the direction of glacial move-
ment in this section is favorable, but they could only have come
from a point just across the river, and such masses are not dis-
tributed over the area to the southwest. Such masses are, how-
ever, found in abundance along the eastern side of the overthrust
for almost its entire length, and it therefore seems most probable
that they are fracture blocks produced in the faulting, which
have rounded through weathering, and as degradation has gone
on, have settled down upon lower beds of the mother rock, and
to some extent also upon the Riga Schist west of the river.
This reversed fault presents some analogies with the over-
thrust faults of the southern Appalachians described by Hayes,*
and those in New York described by Darton’, but the fault plane
tThe Overthrust Faults of the Southern Appalachians, by C. W. Hayes. Bull.
Geol. Soc. Am., Vol. 2, pp. 141-154, pls. 2-3. Cf. also Willis and Hayes, Am. Jour.
Sci. (3) XLVI, pp. 257-268. Oct., 1893.
2 On two Overthrusts in New York, by N. H. Darron. Bull. Geol. Soc. Am., Vol. 4,
PP: 430-439.
798 LLLLES J OOLINATE NOL MCHA OLO GN
has here a steeper hade, so that the older dolomite has been car-
ried only a short distance over the newer beds. .
Metamorphism along the fault—Of considerable interest is the
recrystallization which has taken place along the fault plane. ‘Phe
tremolite of the Housatonic ridge, and the large pyroxene crys-
tals of the east base of the Cobble at South Canaan, must be
explained in this way. The ragged quartzitic dolomite rock
which characterizes the Housatonic ridge throughout its entire
extent and is not found elsewhere in the region, is believed to
owe its characters to a crushing along the fault and a recementing
of the fragments by a vein quartz—it is in other words, a fault
breccia.
In the vicinity of the great thrust planes of the Northwest
Highlands of Scotland, which have been so carefully studied by
Geikie, Peach and Horne, and their associates of the Geological
Survey of Scotland’, schistose structure and new minerals have
been developed by the shearing, micas, hornblende, actinolite
and garnet being produced in this way*. Another instance of
this sort is furnished by the overthrusts of the Rocky Mountains
along the line of the Northern Pacific Railway.3 These thrusts
have likewise produced metamorphism of the beds along the
thrust planes, argillaceous layers being made schistose and lime-
stones being whitened and cracked.
Thickness of the Egremont Limestone—In the Mt. Washington
paper, I have shown that the thickness of the Egremont Lime-
stone in the southern portion of the summit plain is less than
one hundred feet, and that a little farther south it probably dies out
altogether. In the northern portions of that area, where it
* The Crystalline Rocks of the Scottish Highlands, by ARCH. GEIKIE, B, N. PEACH,
and JOHN Horne. Nature, Vol. XXXLI., pp. 29-35, Nov., 1884.
Report on the Recent Work of the Geological Survey in the Northwest Highlands
of Scotland, Based on the Field Notes and Maps of Messrs. B. N. Peach, J. Horne, W.
Gunn, C. T. Clough, L. Huxman, and H. M. Cadell. Communicated by A. GEIKIE.
Quart. Jour. Geol., Soc., London, Vol. XLIV., pp. 378-441, 1888.
2Nature, Vol. XXXI, p. 35.
3 Report on the Geological Features of a Portion of the Rocky Mountains, by R. G.
McConnELL. Ann. Rep. Geol. Surv. Canada, (New Series) Vol. II., 1886, p. D34.
TRE LOG SARONUG, VATLETIY A 799
attains a greater thickness, no measurements could be made,
though it can safely be said that it does not exceed a few hun-
dred feet. The relations made out in the area now under consid-
eration, allow of a thickness which agrees well with that found in
Mt. Washington. A locality which illustrates this will be here
briefly mentioned, because the structure is so simple as to afford
reliable results. The locality is a knoll called Pine Hill, lying at
De
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Fic. 6. View of Pine Hill on the southeast flank of Tom’s Hill, seen from a point
to the west. A, Riga Schist. B, Pine Hill composed of Egremont Limestone. C,
Approximate position of cap of Everett Schist.
the southeast foot of Tom’s Hill south of the railroad. The dips
are low, due entirely to pitch, and the thickness of the limestone
less than 100 feet. (This locality is marked P on the map).
North of the track (A in Fig. 6) is seen the Riga Schist pitching
south at an angle of about 35°. Across the track and a little farther
east is Pine Hill (B), composed of a pure, white limestone dipping
conformably over the schist, and capped on its south slope by a
thin layer of the Everett Schist. The outcrops of this rock are
hidden in the view, but their approximate position is shown by C.
The thickness of the Riga Schist and the Canaan Dolomite have
800 THE JOURNAE OF GEOLOGY.
not been measured. The former probably has a thickness of much
less than a thousand feet. A locality where the Canaan Dolomite
appears below it in the core of a fold, is shown in Plate VIL,
ee 3F
Conclusions—Some of the results of this study may be sum-
med up in the following statements :
I. The district is geologically closely connected with Mt.
Washington, and contains the same horizons, viz: Canaan Dolo-
mite, Riga Schist, Egremont Limestone, and Everett Schist.
For the most part the same general lithological features charac-
terize these horizons as on Mt. Washington. Pyroxene is a charac-
teristic mineral in the lower but absent from the upper calcareous
member. Garnets and staurolites are abundant in the lower but
absent from the upper schist member. Locally important beds
of calcareous schist occur in the Egremont Limestone. The
Everett Schist differs from much of that of Mt. Washington in
being essentially non-chloritic. The Egremont Limestone has a
thickness of less than 100 feet in the southern part of the area.
I]. The tongue-like outline of the area containing schist
exposures is due to a general northerly pitch of the flexures to
the west of the Housatonic River, though the local pitch of these
flexures varies greatly and is as often south as north. Most of
the prominent ridges are anticlinals of the Riga Schist, the few
areas of Everett Schist being synclinals and largest where basins
are formed by a coincidence of longitudinal and transverse syn-
clinals. The schist areas exhibit an arrangement in four’ east
and west belts having each a width of about two miles, as the
result of four marked undulations in the crest lines of the flex-
ures. Particularly toward the north these belts are further sub-
divided by a secondary series of undulations a half mile or more
in width, and a tertiary series of yet smaller waves can in some
cases be made out at localities. These facts show that the area
has been subjected to compression in a north and south direction,
™(1) Bear’s Den, Barnard Mt., and Johnny’s Mt.; (2) Horse Hill, Peck’s Hill,
etc.; (3) Northern Chapinville area, Tom’s Hill, and Miles Hill; (4) Southern Cha-
pinville area, and area No. 6.
LAE LOTSA DONIC VALERY: 801
as well as in an east and west direction. The compression from
the north and south has produced no dislocation, as no transverse
faults have been discovered.
III. The rocks of this area have been very sharply folded.
The types of folds are the unsymmetrical, with short and steep
western and longer eastern limbs, and the overturned and sharply
compressed fold with an easterly dipping axis. Reduced and
ruptured underthrown limbs are not uncommon, but the evidence
is that the extent and the throw of these minor faults is very
slight. On the southeast flank of Tom’s Hill this has produced
the structure which Suess has called Schuppenstruktur. 1 would
suggest, as an English equivalent of this term, weather-board
structure.
IV. An important reversed fault, which has been termed the
Housatonic Fault, has a northerly course along the eastern
border of the area of schist ridges. Its course very nearly coin-
cides with that of the Housatonic River for a considerable dis-
tance. The fault is traced from near Sheffield village to beyond
South Canaan, a distance of about twelve miles. North of the
Maltby Quarry it has the characters of an overthrust which
increases in throw in going north, owing to the northerly pitch
of the beds to the west. This has carried the Canaan Dolomite
of the eastern or normal limb over the newer Egremont Lime-
stone and Everett, Schist of the western reversed limb. South
of the Maltby Quarry the western limb has been upthrown,
bringing Cambrian Quartzite and Gneiss against the dolomite.
The dolomite has been extensively crushed and metamorphosed
along the fault plane. Tremolite and white pyroxene have been
extensively developed in the vicinity of the fault plane, and
vein quartz has cemented the dolomite fragments together, pro-
ducing a fault breccia.
It is very probable that the rapid alternations of pitch which
characterize this area are not altogether unusual. It is only
rarely, however, that the areal relations shed so much light upon
the form of the crest lines and trough lines of folds. What
has been set forth will, I think, show that evidences of general
802 THE JOURNAL OF GEOLOGY.
pitch, to be reliable, must be based on observations made over a
considerable area. Wma. H. Hoses.
UNIVERSITY OF WISCONSIN,
MapIson, WIs.
EXPLANATION OF PLATES.
PLATE V.—Geological Map of portions of Sheffield, Mass., and Salisbury, Conn.,
based on the Sheffield and Cornwall sheets of the Topographical Map of the United
States by the U. S. Geological Survey. Scale 1: 62,500.
PLATE VI.—Series of Geological Sections to accompany Plate V. Their location
is indicated on the map (Plate V.) Horizontal Scale: one inch equals one mile.
Vertical Scale: one-eighth inch equals five hundred feet.
PLATE VII.—Fic. 1. View showing the southern termination of one of the longi-
tudinal undulations of the western schist anticlinal, as seen from the west. A, South-
ern limit of a ridge of Riga Schist (No. 10). B, Turnip Rock (Everett Schist). C,
Barack M‘Teth (Everett Schist). D, Knoll of Riga Schist. E, Tom’s Hill in the
distance. F, Ridge No. 6 (Riga Schist). The dotted and dashed line shows the
approximate boundary between the Riga Schist and the Egremont Limestone, and the
dotted line the approximate boundary between the Egremont Limestone and the
Everett Schist.
Fic. 2. View of schist ridges separated by belts of limestone at the southeast base
of Tom’s Hill near the railroad bridge. A, B, C, Schist ridges. D, Slope of Tom’s
Hill where a fourth schist belt is hidden in the trees.
Fic. 3. Canaan Dolomite occupying the core of an anticlinal of Riga Schist at
the south end of area No. 6. The view looks southeast. A, Outcrop of Riga Schist.
B, Canaan Dolomite. C, Riga Schist.
THE NEWTONVILLE SAND-PLAIN.
1. Lntroduction—During the past year the writer has studied
the Newtonville (Massachusetts) sand-plain under Professor
Davis, of Harvard University, and after studying the deposit as it
now exists, made a detailed map of the plain with its feeding esker.
Then a model of the region was made in clay on the scale of
1:4000. This clay model was photographed, and is here repro-
duced in half-tone, in Fig. 1, Newtonville Sand-plain. The con-
ditions of formation were then studied, and a second model con-
structed, showing a conjectural relation of deposits to the margin
of the New England ice-sheet at the time of its formation. A
photographic reproduction of this is given in Fig. 2, Ice-sheet
Restored.”
2. Making the models—The clay was built up in a solid mass
to the greatest required height, and the details of form were then
cut with graving tools. In making such models it is essential
that the foundation for the clay should be firm and not liable to
warp. Aslate slab, or a piece of heavy plate glass answers
the purpose well. While at work on the model it is important
to keep the clay moist. So a box lined with rubber cloth should
be provided, large enough to cover the clay without touching it,
and an inner layer of muslin put in to hold the water. When the
model is ready to have a plaster mold made, the edges should be
trimmed square, tapering slightly up from the slate so that the
mold will slip off easily, the surface oiled, boards placed an inch
and a half from the four sides, and liquid plaster poured over it.
After the plaster has set, it may be wedged up from the slate or
glass, and lifted from the clay. Then the plaster negativeshould
be carefully washed with a brush to remove all oil or clay stick-
*Teachers or others who desire copies of models, photographs, or lantern slides
can arrange for them by corresponding with the writer.
803
804 THE JOURNAL OF GEOLOGY,
ing to it, and when hardened with a thin solution of glue and
dried it is ready for the taking of a paper positive. This papzer-
maché model is a close representation of the original clay.
3. A late glacial deposit—A glance at the first model will
show the typical form of these delta deposits, the esker like an
arm, and the sand-plain like a hand with its finger lobes. The
esker rises in height as it approaches the head of the plain. The
top of the sand-plain slopes very gently downward from the head
to the top of the lobes, but the front slopes of the lobes are much
steeper, about twenty degrees.
The sand and gravel are so little disturbed that the deposit
cannot be pre-glacial. That the deposit was not made by marine
or fluviatile action is shown by the three following considerations.
First, an aqueous deposit of gravel, composed of fragments from
the crystalline high-lands between two and three miles to the north,
should have extended originally from its source outward ; but
the amount of denudation and transportation required to cut out
these delta deposits from a continuous sheet extending across the
Charles river to the crystalline highlands on the north, whence
a large part of the fragments come, would be greater than the
post-glacial denudation that has been measured elsewhere.
Second, the delta front and the even sloping delta-plain imply
standing water, and if this water level existed for so long a time
as would be required to form such an extensive deposit, we
should expect to find more evidence of its shore line in other
localities than now exists. Third, the constructional forms, cusps,
hollows, kettle-holes, at the head of the sand-plain are so marked
that one cannot believe them to be the product of erosion.
The kettle-holes and marshy depressions show that the plateau
tops did not extend much farther than at present.
The dwindling New England ice-sheet, whose existence is
proved by other facts, supplies all the conditions necessary for
the construction of such discontinuous deposits. The ice-sheet
could not have advanced over the plain after its deposition, for |
the sand and gravel would have been easily carried away. There
is no gullying of the sides of the sand-plain; therefore it was
805
IIL SAILING,
THE NEWTONVILLE SAND
806 THE JOURNAL OF GEOLOGY.
formed not so very long ago. But the gravel is evidently of glacial
origin, being of angular and subangular pebbles, of great variety
of material. The conclusion seems inevitable, therefore, that
these deltas were formed during the retreat of the ice-sheet.
4. Stagnant, melting ice.—In the retreat of the ice-sheet there
were parts at least which became too thin to move. As Professor
Davis has said : :
During this time it must have melted irregularly, presenting a very uneven,
ragged front, from which residual blocks may have been frequently isolated ;
and it must have endured longest in the valleys, where it was thickest, not
only by reason of its greater depth, but also because its surface there, where
motion had been fastest and longest maintained, must have been higher than
on the hills—this being homologous with the variation in the thickness of a
Swiss valley glacier from middle to sides.”*
It seems to me that we must consider the change to have
been gradual from a moving glacier to a stagnant one, and that
there may have been times of renewed activity with a forward
motion, even in the period of decline. Such forward motion may
have had some influence in shifting the course of esker rivers
and so have determined where the next sand-plain was to be built.
So far as I know, this point has not been worked out in the field.
Crevasses are formed as the ice moves, and change their posi-
tion according to the tensions in the mass of the glacier. When
the tension from motion has ceased, and the ice has become a
diminishing, drift-covered mass, the condition represented in
Fig. 2, we should not expect to find any crevasses remaining.
They would either have been closed by the forward motion of
the ice, or would have lost their distinctive character by the
excessive melting of their sides, while the water would have
washed detritus into them covering the underlying ice, and pre-
venting it from melting as fast as that on either side. Such
protection of the ice by detritus must have had great influence in
determining the surface forms of the stagnant ice-sheet, as is
shown in Professor Russell’s account of the sand cones and the
deposits in glacial lakelets.
* Bull. Geol. Soc. of Am., Vol. I., p. 196.
THE NEWTONVILLE SAND-PLAIN. 807
5. Comparison of models—Turning from Fig. 1, which shows
the deposits as they exist to-day, to Fig. 2, which shows the
theoretical conditions of formation, it will be seen that the north-
ern half is covered with ice, from which is issuing an esker river.
The ice in the second is represented as fitting into the inter-
cuspate hollows shown at the head of the sand-plain in the first
model, and is from one hundred to three hundred and fifty feet
thick. Toward the rock hills on the east and west it falls off, as
would be the case where the ground was higher. The ice has a
convex curving surface in front, with contours softened by melt-
ing, while on top it is approximately level with here and there
surface streams, moulins, and perhaps a little lake.
The three little knobs of older date than the sand-plain
standing near its front margin, can be seen in both models. The
till-covered hills of bed rock are also the same in the two, but in
the second the water stands higher up on their sides. The
second model being a trifle larger, a little more of them is shown
on the edges. The group of hummocky kames, shown to the
southwest of the sand-plain in the first model, is covered in the
second by the body of standing water into which the esker river
flowed.
6. Esker river.—Professor Chamberlin has given us the very
helpful distinction between “kame” and ‘“esker”’ (osar), from
the use of the words in Scotland and Ireland respectively. The
former is used by the Scotch for their irregular mounds and hil-
locks, so typically shown in that country, and which, if developed
at all in lines, have their axes at right angles to the direction of
ice flow; and the latter for the Irish ridges of sand and gravel,
beds of former glacial rivers, which have their axes parallel to
the lines of motion in the ice. This terminology is here followed.
In the first model the esker, a ridge of sand and gravel, fairly
stratified, may be traced from the middle of the northern end,
where it is some ten to twenty feet high, curving eastward and
then southward again, gently rising to some seventy feet above
the alluvial plain shown on the northwest corner of the model of
the sand-plain, and one hundred and thirty feet above mean tide.
808 THE JOURNAL OF GEOLOGY.
Then it falls ten feet, and, curving a little to the west, rises thirty
feet to where it reaches its greatest elevation, one hundred and
fifty feet above mean tide. This is also the elevation of the
front of the sand-plain. At this point it breaks up into several
more or less clearly defined branches, which distribute the sand
to build up the delta in the estuary.
These branches fall off in height towards the head of the sand-
plain, as is often seen in similar deposits elsewhere. As it has been
shown that the amount of post-glacial erosion has been small,
this depression must be due to conditions existing while the ice
was present. The first model shows a large kettle now occupied
by a pond which lies north of the sand-plain and east of the
esker. This depression, being filled with ice after the course of
the esker river was changed, must have had an outlet, and as the
main body of ice would have prevented the formation of an out-
let on the north, it seems reasonable to suppose that this water
quietly cut through a slight sag in the esker to the west. This
cutting would have continued until the ice-sheet had retreated
farther north, and the ice block in the kettle had melted, and its
depth would be governed by the amount of the lowering of the |
water in the estuary, caused by rising of the land.
Two branches from near the north end of the esker run into
cusps at the head of a second smaller sand-plain deposit, formed
when the ice-front had retreated some two thousand feet, and
while the ice remained at this second point there would have
been no outlet for the water to the north. The frontal lobes of
this second sand-plain are not at all typically developed.
7. Delta streams.—In front of the openings of the esker tun-
nels will be seen the depositing streams breaking up into many
branches, as Professor Russell has described them in Alaska’.
Some of them are represented as having already ceased to
flow to the edge of the delta, and are fast filling up; others
are pushing out their resulting lobes as far as they can reach;
while a third class are supplying detritus to those in front, and
are building up their channels to give themselves greater carry-
*See Malaspina Glacier, page 238.
THE NEWTONVILLE SAND-PLAIN.,
810 THE JOURNAL OF GEOLOGY.
ing power by increasing their slopes. The front lobes are too
strongly shown in the photograph, Fig. 2, as they were left to
show the limits of the delta. In the papier-maché copies, the
water completely covers the slopes of the lobes. ;
On this deposit, which is 4000 feet from east to west, and
2000 to 3000 feet from north to south, there is only one small ket-
tle-hole. This lack of kettle-holes, so abundant elsewhere, may
be taken as an indication that the ice-sheet was comparatively
continuous at this time. It evidently became more broken
immediately after the course of the esker stream was changed,
as there are several kettle-holes to the north of the sand-plain.
8. Superglacial streams.—These are represented on the model
as smaller than the main channels below, and more inconstant in
direction. Their development after the closing up of the cre-
vasses has been made the subject of special study, and its results
are shown on the model. Other conceptions of this surface will
no doubt occur to many, and any criticism or suggestion will be
gladly received. One of the processes that has been a promi-
nent factor in the determination of the form of the surface is
that described above, where the detritus in the bed of the stream
protects the underlying ice. Little accidents of melting and
washing would shift the course of these streams, so that the
arrangement of them upon the surface would not be shown by
any deposits to-day. As soon as one of these streams found an
opening through the ice, a moulin would be formed.
9. Moulins and kames.—I\n the second model I have made
moulins in the ice-sheet above the kames in the first model,
though I should not like to be understood as affirming that all
these kames were surely formed in this way. It is quite proba-
ble that further study would show facts pointing to several gen-
eses. Professor Chamberlin says, in speaking of the formation
of similar deposits :
‘No existing agency, by any extension of its magnitude, is at all compe-
tent to account for their localization. The formative agency, or combination
of agencies, must have produced, at once, local assortment and local heaping
of the assorted material, or, in other words, the assorting waters must have
THE NEWTONVILLE SAND-PLAIN. Sil
been confined and concentrated in their derivative action, and likewise con-
strained so as to heap their material into tumuli, whose location was deter-
mined by the constraining agency more than by any feature of the local
topography or other present condition.’”*
That some kames are moulin-kames seems to be undoubted,
and perhaps we may best picture to our minds their formation
by turning an hour-glass and watch the sand heap itself up. A
certain amount of stratification will take place in air, which would
be increased when the air is replaced by water.
10. Shore-line.—With the working hypothesis that this sand-
plain was formed in a body of standing water, I reached the con-
clusion that it was at the head of an estuary. With the existing
topography to the south it is almost impossible to conceive of
the water as having been enclosed. Such a pond would require
too many dams not now existing. If one accepts the delta front
as proof of a body of standing water, he seems forced to con-
clude, on looking over the ground, that the Newtonville sand-
plain was built in an arm of the sea. If so, the estuary must
have connected with the Atlantic along the present course of
the Charles river and through Mother brook to the Neponset.
It must have had a very temporary shore-line at any given level,
as there is hardly a trace of it now on the till-covered slopes,
except in one place on the east bank of the Charles river, about
a mile southeast of Newton Upper Falls where Dr. T. W. Harris
found a faint cliff, as if made by shore cutting, with a long,
gently shelving slope below it. In representing this shore-line
on the second model, I have tried to show no beach effect, but
to indicate that the land was but recently submerged, and that
the water conformed to the contour of the till-covered slopes.
11. Relation to other sand-plains—TVhe intimate connection
between the Newtonville sand-plain and the one immediately to
the north of it, branches of the same esker running to each, sug-
gests a connection of this bit of the history of our New England
ice-sheet with other portions. Were the Auburndale sand-plains
formed before or after the Newtonville? What other esker
tAm. Jour. of Sci., 1884, p. 381.
812 THE JOURNAL OF GEOLOGY.
rivers emptied into this estuary ? When should we expect to
find terraces on either side of a sand-plain, as at Pawtucket,
R. Ip Why are not sand-plains of more frequent occurrence
throughout the area covered by the ice-sheet ? These and many
other questions are suggested as we study the details of the ice’s
work. Their answers await the future study and research of
those local observers, who will make themselves familiar with
the geographic forms of their own regions.
Pe Gurenyere
REFERENCES.
Davis, WILLIAM M.—Structure and Origin of Glacial Sand-plains. Bull.
Geol. Soc. of Am., Vol. I., pp. 195-202.
Davis, WILLIAM M.—Subglacial Origin of Eskers. Proc. Boston Soc. of Nat.
Hist., Vol. XXV., 1892, pp. 477-499.
RUSSELL, I. C.—An Expedition to Mount St. Elias, Alaska. Nat. Geog. Mag.,
Vol. III., pp. 53-204.
RUSSELL, I. C.—Malaspina Glacier. Journalof Geology, Vol. I., No. 3, pp.
219-245.
CHAMBERLIN, T. C.—Hillocks of Angular Gravel and Disturbed stratifica-
tion. Amer. Jour. of Sci., Vol. XXVII., 1884, pp. 378-390. Contains
References.
CHAMBERLIN, T. C.—The Horizon of Drumlin, Osar and Kame Formation.
Jour. of Geol., Vol. I., No. 3, pp. 255-267.
WriGut, G. F.—The Ice Age in North America.
UpHAM, WARREN.—Upper Beaches and Deltas of Glacial Lake Agassiz.
Bull. 39, U. S. Geol. Surv.
THE STRUCTURES, ORIGIN, AND NOMENCLATURE
Qle INBUS, ACIUD) WOIIGAINIIC INOCIKS Ole Sw ial
MOUNTAIN.
THE identification of acid and basic volcanic rocks in the
South Mountain, Pennsylvania, has already been announced.*
This announcement has been further substantiated by detailed
petrographical study which it will be the purpose of a later com-
munication to discuss. The present discussion of these rocks
will be limited to the acid volcanics, and its object will be; a) to
show that the acid volcanics were originally identical with their
recent volcanic analogues; b) to further show that their present
differences are due to changes subsequent to solidification, chief
among which has been devitrification ; and c) to propose a name
for them that shall express these facts. The structures, which
will be described in the course of the paper, will be considered
a sufficient guarantee of the igneous origin of the rocks which
possess them, without further proof on that point.
Three distinct rock types have been recognized in the South
Mountain. (i) A silicious sedimentary formation, represented
by a quartzose conglomerate, a sandstone, anda compact quartz-
ite. This is rarely accompanied by an interbedded argillaceous
slate. The age of these sediments has been recently deter-
mined as lower-Cambrian by Mr. Walcott? from the discovery of
fossils in the interbedded slates. Underlying these Cambrian
sediments, but exposed by erosion for many square miles
(150-175), are two types of volcanic rocks, distinctly different
in chemical composition but affected by lke conditions of con-
tG. H. WiLiLiaMs: The Volcanic Rocks of South Mountain, in Pennsylvania and
Maryland. Am. Jour. Sc., XLIV., Dec., 1892, pp. 482-496, pl. I. The Scientific
American, Jan. 14, 1893.
2C. D. WatcoTtT: Notes on the Cambrian Rocks of Pennsylvania and Maryland
from the Susquehanna to the Potomac. Am. Jour. Sc., Vol. XLIV., Dec. 1892, p. 481.
813
814 LHE JOORNALEVOFNGEHOL OG Va
solidation and subsequent alterations. (2) In the northern part
of the range a brilliantly colored acid volcanic rock predomi-
nates. It is porphyritic or non-porphyritic, amygdaloidal or
compact. It is accompanied by pyroclastics and breccias. It
is sometimes sheared into a fissile slate or sericite schist. (3)
Toward the south and extendinginto Maryland a dark green
basic volcanic rock predominates. This is also amygdaloidal or
compact, accompanied by pyroclastics or breccias, and usually
rendered schistose by pressure.
The acid volcanics—While some of the acid volcanics are
typical quartz-porphyries, others possess a groundmass which,
although holocrystalline, contain the evidence of a distinctly dif-
ferent original character. It it this important portion of the acid
flow, which will be more particularly treated in what follows.
Certain conspicuous structures of the groundmass contain the
history of the rock and merit a detailed description.
Fluidal structure -—The fluidal structure, which is a familiar
one to all students of rhyolitic lavas, isa marked feature of these
pre-Cambrian volcanics. Delicate lines of flow are brought out
in great detail by weathering or are painted in brilliant colors in
the material washed by the mountain brooks. The microscope
shows globulites of magnetite, and hematite, and indefinite
opaque microlites following sinuous lines of flow, twisting around
the phenocrysts and imparting to them the appearance of eyes.
Microporkilitic structure*—TYhis name has been given to a
structure which is almost universally present in the acid and
more rarely in the basic volcanics of the South Mountain. It
consists in the presence in the groundmass of irregular quartz
areas enclosing micolites of lath-shaped feldspars or other min-
erals with independent optical orientation. This structure
between crossed nicols gives a pronounced mottled or patchy
appearance to the groundmass, an appearance which has not
infrequently been noted in volcanics of all ages. It has been
variously described, usually without being named, in quartz-
*G. H. WILLiaMs: On the Use of the Terms Poikilitic and Micropoikilitic in
Petrography. Jour. of Geol., Vol. I., No. 2, February—March, 1893, pp. 176-179.
ACID VOLCANIC ROCKS OF SOUTH MOUNTAIN. 815
porphyries, felsites, porphrites, peridotites, and rhyolites by
numerous writers.‘ This structure was also found in the pre-Cam-
brian felsite of Georgia,” and in felsites of the same age in the
neighborhood of Boston,3 and from Marblehead Neck, Mass.
While the term micropoikilitic is not restricted to a quartz-
feldspar intergrowth, in most of the occurrences described these
have been the component minerals. Inthe rocks under dis-
cussion the feldspathic material is often so abundant as not to
permit of the determination of the mineral character of the host.
In such cases, however, a clue to the nature of the cementing
material is found in its optical continuity with the porphyritical
quartz. The feldspar phenocrysts, on the other hand, do not
TR. D. Irvine: Monograph V., U.S. G. S., Copper-bearing Rocks of the Lake
Superior Region, pp. 99-100, Pl. XIII., Fig. 13-14, 1883.
G. H. WILLIAMS: Neues Jahrbuch fiir Min., etc. B. B. II. 1882, S. 607, Pl. XIL.,
Fig. 3. The Peridotites of the Courtland series. Am. Jour. Sc., Vol. XXX., p. 30, Vol.
XXXIIL., p. 139.
E. HawortH: A Contribution to the Archean Geology of Missouri, Am. Geol.,
1888, Vol. I., p. 368, Figs. 1 and 2, Pl. I.
WHITMAN Cross: On some Eruptive Rocks from Custer Co., Colorado. Proc.
Col. Sc. Soc., Vol. II., 1888, pp. 232, 242.
On a series of peculiar schists near Salida, Col. Proc. Col. Sc. Soc., Jan., 1893, p. 8.
J. P. Ipp1nes: The Eruptive Rocks of Electric Peak and Sepulchre Mountain,
Y.N.P. 12th Ann. Rep. U.S.G.S., pp. 589, 646.
WALDEMAR LINDGREN: A Sodalite Syenite and other Rocks from Montana.
Am. Jour. Sc. (3), Vol. XLV., April, 1893, p. 287.
J. S. DILLER: Mica-peridotite from Kentucky. Am. Jour. Sc. (3), Vol. XLIV.,
Oct., 1892, p. 287.
J. J. Harris TEALL: British Petrography, 1888, p. 337.
ALFRED HARKER: Bala Volcanic Series of Rocks, pp. 23, 53, 54.
A. C. BROGGER: Der Mineralien der Syenitpegmatitgange der siidnorwegischen
Augit- und Nephelinsyenit. Groth’s Zeitseh. fiir Krys., etc., Vol. XLV., p. 546.
Orro NORDENSKJOLD: Ziir Kentniss der s. g. Hailleflinta des Nordostlichen
Smalands. Bull. Geo. Ins. Upsala, No.1, Vol. I., 1893, p. 232.
? A section of this felsite, loaned by Professor Pirsson, possesses an interesting and
striking resemblance to the South Mountain acid volcanics, and indicates the south-
ward persistence of this rock type.
3 Thin sections of these felsites were kindly loaned by Mr. Diller. They have
many microscopic features in common with the South Mountain rocks, and like them
were first referred to a sedimentary origin. J. S. DILLER: Felsites and their asso-
ciated Rocks north of Boston. Proc. Bos. Soc. Nat. His., Vol. XX., Jan. 21, 1880.
Bull. Mus. Comp. Zo6l., Harvard College, whole series Vol. XII., Geol. series Vol. 1.
816 THE JOURNAL OF GEOLOGY.
affect the orientation of the cement. Where the rock is coarser
grained, as is the case in some of the basic volcanics, the charac-
ter of the cement can be directly tested and the material proved
to be quartz. :
While in some cases this structure is undoubtedly of primary
character, as Professor Iddings considers it to be in many
porphyrites, ina large class of rocks its secondary origin seems
equally plain, Dr. Irving, who very early described this struc-
ture in the acid lava flows of the Keweenawan series, thus speaks
of its origin. ‘‘Whether this secondary quartz may ever be
rather a result of devitrification than a truly secondary or alter-
ation-product I have no means of deciding, though it is certainly
the latter often, and I should suppose always. It surely can
have no connection with the original solidification of the rock.”
Observations made on the South Mountain rocks likewise point
to a secondary origin for these quartz areas. As the origin of
the structure is of importance in its bearing on the question of
the primary or secondary character of the crystalline ground-
mass, these observations will be briefly mentioned. In a speci-
men of basic lava from the railroad tunnel near Monterey the
outline of lath-shaped feldspars forming an ophitic structure,
which is undoubtedly original, is completely preserved. None
of the original constituents of the rock remain, however, unless
some of the titaniferous iron oxide is original. The rock con-
sists entirely of quartz, epidote, magnetite (or ilmenite), and
leucoxene. The quartz acts as a cement for the other minerals,
forming irregular interlocking areas which are quite similar to
the micropoikilitic areas of the acid rocks and which produce in
polarized light the familiar patchy effects. Fine cracks traversing
the rock, and parting the ferro-magnesian phenocrysts (now repre-
sented by epidote) are plainly prior to the quartz areas in which
they become invisible. There can be no question as to the
secondary character of the micropoikilitic structure in this case.
In the acid rocks the quartz areas are frequently more or less
oval and outlined by a microfluidal arrangement of globulites,
‘Opus cit., p. 100.
ACID VOLCANIC ROCKS OF SOUTH MOUNTAIN. 817
longulites and trichites of iron oxide. Zirkel figures and
describes a similar appearance in the rhyolites of the 4oth
parallel.* He speaks of faint granular lines ‘‘ which by their
fluidal running form a net with a multitude of-meshes of oval
shape.’’ The meshes are filled by one of two types of crystalli-
zation, the micro-felsitic or the spherulitic. The lines suggested
to Zirkel perlitic parting. In the ancient lavas of South Moun-
tain the meshes are filled by the micropoikilitic areas or by
spherulitic crystallization or by intermediate stages of altera-
tion, that is, spherulites more or less broken up into micro-
poikilitic areas. In the trichitic spherulites of the modern
rhyolites* there is an appearance similar to the micropoikilitic
mottling, caused by the breaking up of the radiating spherulitic
fibers into irregular areas which extinguish differently ; just such
an intermediate stage between the spherulitic and a completely
micropoikilitic crystallization as has been noted in the ancient
volcanics. These observations suggest that the micropoikilitic
structure represents recrystallized spherulitic growths when it is
not the direct results of infiltration and devitrification. In many
cases, the crystallization has undoubtedly never been spherulitic,
if however, the micropoikilitic structure has been shown to be
subsequent to spherulitic crystallization, that is, to the consolida-
tion of the rock in numerous instances in the acid volcanics,
selected from widely separated localities in the South Mountain,
the presumption favors the secondary origin of the micropoikilitic
structure wherever present in these rocks.
Spherulitic structure —Ywo sorts of spherulitic crystallization
are present in these rocks. They differ in no essential respect
but are unlike in appearance. The most numerous spherulites
are also the simplest and smallest. They are colorless micro-
scopic spheres, scarcely or not at all perceptible in ordinary light
but showing the usual distinct dark cross between nicols. Spheru-
tVol. VI., Geo. Exp. of the goth parallel, Fig. 1, Pl. VI., Fig. 1, Pl. VIII.
2Sections of material from the Rosita Hills, Colorado, and of the Obsidian Cliff,
Y.N.P., were kindly loaned the writer for comparative study by Dr. Cross and Pro-
fessor Iddings.
818 THE JOURNAL OF GEOLOGY.
lites, in every respect similar, have been described and figured
by Professor Iddings from the Yellowstone Park rhyolites.t
While it is not impossible that some of the colorless spherulites
are secondary, there is pretty good evidence that many, if not
all of them, are primary. These spherulites are embedded ina
base which suggests in every way a former glassy condition. In
ordinary light there is no appearance of crystallization except
the porphyritical. Traversing the groundmass are cracks which
occasionally cut directly through a spherulite. Between crossed
nicols the field breaks up into a holocrystalline quartz-feldspar
mosaic in which the cracks are lost. It seems fair to conclude
that the spherulitic crystallization was prior to the cracking, that
the granular crystallization is subsequent, and that the cracking
took place in an already solidified glass. In these facts we
again find obvious indications of a secondary crystallization. In
this case the process seems to have been one of devitrification.
The other class of spherulites corresponds to those figured by
Professor Iddings in Plate XVII.2. They are much larger than
those which have just been described ; the smallest being easily
discernible by the unaided eye, and the largest about the size of
a butternut. Hence they become a conspicuous feature of the
rock as exhibited in-the field. They are rarely altogether absent,
and in some localities are crowded so close together as to consti-
tute the major part of the rock mass. When without regularity
of arrangement, and when brought out in relief by weathering,
these spherulites give to the rock a superficial resemblance to a
conglomerate composed of rounded pebbles of uniform size and
shape. The rich greys, blues, purple and red of the spherulites
and matrix render this a conspicuous rock.
Spherulites become an even more striking feature of these
rocks when arranged in layers such as have been described in
the modern rhyolites of the Yellowstone National Park3 Ona
face of the rock normal to the layers, they appear as long
tOpus cit., Pl. XVIL., p. 276.
2 Opus cit. p. 277.
3 DDINGS: opus cit. p. 276, Pl. XVIII.
ACID VOLCANIC ROCKS OF SOUTH MOUNTAIN. 819
parallel bands simulating lines of bedding. Sometimes these
bands are 4 m.m. wide, at a nearly uniform distance apart and
of an indefinite length. In other cases they are very narrow,
dwindling into mere lines and dying out, to be replaced immedi-
ately by other lenticular bands. The rock cleaves readily
parallel to the planes of these bands, which have become planes
of weakness and solution, and the spherulites are entirely
replaced by secondary silica. This fact, imparting to the bands
an opaque white color, render them the more conspicuous in
contrast with the blues or reds of the rock surface.
The spherulites which remain unaltered show in the thin sec-
tion clear cut, circular, semicircular, and fan-shaped outlines, and
are colored purple or red by finely disseminated particles arranged
either radially or concentrically in threefold zones. Feldspar
phenocrysts often occupy the center of the radial growth. These
well preserved spherulites are associated with a groundmass
which preserves the characteristics of a glass in great perfection,
and which, in ordinary light, could readily be mistaken for a fresh
glassy lava. It bears the closest resemblance to the base of
some of the Colorado rhyolites. Delicate perlitic parting, which
because of its delicacy is usually obliterated, is here preserved in
wonderful detail. The presence of innumerable globulites accen-
tuates the perlitic and rhyolitic structures. With crossed nicols
the aspect of the groundmass completely alters. All glassy
structures disappear, to be replaced by granular quartz and
feldspar.
It is impossible by any description to carry the definiteness
of conviction as to the original glassy nature of the groundmass
which the character of such rock-sections justifies. To one who
has studied them in both ordinary and polarized light there can
be no question as to the secondary character of the holocrystal-
line groundmass. One cannot escape the conviction that the
rock originally consolidated as a spherulitic perlite, and has
become holocrystalline by a process of devitrification.
Associated with a groundmass, whose early glassy condition is
not so strongly marked, are the altered spherulites. Their spherical
820 LES, JOORNAL OF AGLOEOGM,
shape in the hand specimen and their sharply defined outline in
the thin section in ordinary light alone testify to their former
presence. With crossed nicols these boundaries become incon-
spicuous, and the field of the microscope shows only a uniform
quartz-feldspar mosaic. The crystallization within the spheru-
litic boundary is sometimes finer grained than that of the ground-
mass, or the micropoikilitic structure is present in the former
when absent from the latter, otherwise the spherulite is in no
way distinguished from the groundmass. In the case of the
chain spherulites the alteration is complete and universal. There
is, in ordinary light, an impressive similarity with the fresh chain
spherulites of the Yellowstone Obsidian. The same irregularly
scalloped outline, the same central chain of clear spherules. With
crossed nicols the close similarity vanishes, for in the ancient
rocks the radial growth has utterly disappeared. The clear
spherules are composed of finely granular quartz while the sin-
uous border is not to be distinguished from the quartz-feldspar
groundmass.
Axiolitic structure—Closely related genetically to the chain
spherulites, but unlike them in being linearly radial rather than
centrally, is the axiolitic formation.‘ These have been described
in rhyolites and occur somewhat sparingly in their ancient proto-
types of the South Mountain.
Rhyolitic structure —The sections in which the axiolites were
observed possess a holocrystalline character, but exhibit in
ordinary light flow and vesicular structures, together with string-
ers and shreds and curved patches of a brownish red color form-
ing what has been called a rhyolitic structure. This latter
structure, which has been figured and described by Rutley,?
Nordenskjéd,3 and Vallée-Poussin,s and on a macroscopic
tZIRKEL: opus cit. p. 167.
?RUTLEY: On the Microscopic Structure of Devitrified Rocks from Beddgelert -
and Snowden. Q.J. G.S., Vol. XXXVIL., 1881, p. 406, Fig. 1-2.
3 NORDENSKJOLD: opus cit., p. 5.
4VALLEE-PoussiIn: Les Anciennes Rhyolites dites Eurites de Grand-Manil.
Bull. de L’Acad Roy. de Belgique, 3d series, Tome 10, 1885, p. 271.
ACID VOLCANIC ROCKS OF SOUTH MOUNTAIN. 821
sealle by Irving,* is essentially nothing. else than a special phase
of the fluidal structure, a phase peculiar to flowage in lava consol-
idating with extreme rapidity, that is, in an acid glass. The
granular crystallization has developed with entire disregard to
these curved patches, shreds and stringers.
Lithophysal structure —Often the macroscopic features of the
South Mountain acid volcanics disclose their original character
more convincingly than does the microscope. Lithophysz are
one of the structures which are best revealed in the hand-
specimen, where they are brought out in delicate relief by
weathering. The rose-pink petals of the lithophyse in a paler
pink base produce quite as beautiful specimens of this glassy
structure as any rhyolite shows. The micro-pegmatitic structure
shows itself in microscopic pegmatoid groups of phenocrysts
such as are found in the Yellowstone rhyolites.?
Perhitic parting —That this structure is occasionally present in
the South Mountain rocks in great perfection has already been
noted. While its presence is a most reliable test of the former
character of the rock, its absence furnishes no evidence against
the previous glassy condition of the rock, both because many
recent rhyolites show no trace of that structure and because it is
most readily effaced by devitrification.
Amygdaloidal structure —In some localities the acid volcanics
are conspicuously amygdaloidal. The bright green amygdules
of epidote in a pale pink matrix render this rock strikingly
handsome. In a few instances? the vesicles, which, as seen
under the microscope, are bordered by a broad rim, like the
ground-mass in crystallization, but are separated from it by a
clear zone of silica and are darkened by an abundance of black
iron oxide, bear on the inner edge of this border spherulitic
growths. These are surrounded by a clear zone of silica while
the center of the vesicle is filled either with an opaque black
*IRVING: opus cit., pp. 312-313, Fig. 22.
2IDDINGS: opus cit., p. 275, Pl. XV., Fig. 5.
3In specimens from Racoon Creek at the east base of Piney Mountain, south of
Caledonia Furnace.
822 LTE OW TIN ALES OTING TSO [EO (GWA
oxide or with granular quartz. Crossed nicols show that the
spherulites are oriented optically with the surrounding silica, and
that the preservation of the radiate structure is due to the arrange-
ment of impurities. The appearance of these vesicles is very
like those figured by Professor Cole,* who explains their forma-
tion by a dual mode of growth—a growth from the groundmass
outward converging toward a center, as well as from the center.
Whatever may be the facts with reference to the Roche Rosse
Obsidians, it is not necessary to call into play an abnormal
method of crystallization to explain the phenomena observed in
the South Mountain rocks. The spherulites projecting into the
vesicles, with their bases sunk into its wall, were recognized by
Professor Iddings, who kindly examined the sections, as tridy-
mite spherulites, such as form on the walls of vesicular cavities
in all modern lavas.
Taxitic structure.—Still another structure which the South
Mountain rocks possess in common with rhyolites is what has
been called the taxitic. This consists in the intimate mingling
of two portions of the magma, which, from some cause (liqua-
tion), are slightly differentiated. The iron constituent, which
evidently separated out in the original glass, has been still
further crowded into bands and curved lines by the secondary
crystallization. The result is the production in some cases of
an irregular mottling: @faxifes; and in other cases of a more or
less complex network of interlacing bands following lines of flow:
eutaxites. This mottling and banding is rendered the more
striking by a marked contrast in color. The body of the rock
is light gray or pink, and the lines dark blue, gray or red,
according as the iron is more or less oxidized. When the iron
constituent is arranged in oval or spherical outlines, denoting the
former presence of spherulites, the rock may properly be termed
a spherotaxite.?
TGRENVILLE A. J. COLE and GERARD W. BUTLER: on the Lithophysze in the
Obsidian of the Roche Rosse, Lipari. Q. J. G.S., Vol. XLVIIL., p. 438.
? Note sur les Taxites et sur les Roches clastique Volcanique. Bul.de 1’ Soc. Belge.
d’Geo. et Tome V., 1893.
ACID VOLCANIC ROCKS OF SOUTH MOUNTAIN, 823
Trichitic structure—The universal presence of globulites,
trichites and microlites of black and red iron oxide, in flow
bands, or indifferently distributed, or in concentric zones around
spherulites and vesicles is worthy of mention as a further point
of resemblance to the modern rhyolite. Such trichites in similar
rocks have been described by various petrographers.* Such, in
brief, is the character of the evidence for the secondary nature
of some of the holocrystalline groundmass of the acid volcanics
of the South Mountain. It is not easy to present the proof so
that it shall carry the weight which justly belongs to it. Very
much depends upon effects which it is impossible to reproduce
by description, but which carry conviction to the student of
these rocks. The contrasting appearance of the sections in
ordinary and polarized light cannot be adequately reproduced.
The disappearance under crossed nicols of rhyolitic, perlitic,
spherulitic, and fluxion structures, so clearly indicated in ordinary
light, and their replacement by a homogeneous holocrystalline
mosaic is one of the strongest evidences of the secondary char-
acter of the crystallization. Nor are there lacking instances
where the subsequent nature of the crystallization is in other
ways distinctly proven, as in the replacement of radial crys-
tallization by the granular aggregate of quartz and feldspar,
which is homogeneous with a granular groundmass, as well as in
the character of the micropoikilitic structure. One or more of
the structures which have been described are invariably present
in the acid volcanics of certain localities. The occurtences,
where their structures are absent, show a genetic relationship in
the field to typical representatives of the modern rhyolite. 3
The writer considers that the acid lava flows in South
Mountain were, at the time of their consolidation, quite com-
parable to similar flows as they now appear in the Yellowstone
National Park. Certain portions of the flow, as in the case of
tS. ALLPORT: On certain ancient divitrified Pitchstones and Perlites from the
lower Silurian District of Shropshire. Q.J.G.S., Vol. XXXIIL., p. 449.
O. NORDENSKJOLD : opus cit.
R. D. IRVING: opus cit. p. 312.
824 THE JOURNAL OF GEOLOGY,
the Obsidian Cliff, were completely vitreous save for spherulitic
and lithophysal crystallization. In other localities the lava was
lithoidal, and in the central portion of thick flows holocrystalline.
In this way three types of acid volcanics would be developed—
rhyolites, lithoidal rhyolites, and quartz porphyries. Every grada-
tion between these types would accompany them. Thus, while
there are certain areas in the South Mountain, notably the
Bigham Copper Mine and Racoon Creek localities, which exhibit
typical ancient rhyolites, other regions display genuine quartz-
porphyries. While in the latter rocks, which constitute a large
part of the acid volcanics, the groundmass may have been, and
probably was, originally holocrystalline, as in some modern lavas ;
in the case of the former rocks, it is supposed that the ground-
mass was, at the time of consolidation, wholly or partly glassy.
The secondary character of some of the holocrystalline ground-
mass once conceded, and the indications of an original glassy
base recognized, it is easy to suppose that the former was devel-
oped from the latter by a process of devitrification.
That the process of crystallization does not necessarily cease
with the solidification of a rock is well known. That the crys-
tallizing forces are active in a glass as well as in a molten magma
has been proven by experiment.t. This action is exceedingly
sluggish, and requires, unless accelerated by heat and moisture,
an immense amount of time. Devitrification has been considered
the result only of dynamic action.? While dynamic action
undoubtedly accelerates the process of devitrification, if it does
not initiate it, devitrification may also take place independently
of dynamic action, as was the case in the famous example of the
old cathedral window-glass3 and the ancient devitrified glass
from Nineveh investigated by Sir David Brewster. The nature
* DAUBREE: Géologie Expérimentale, 1879, p. 158.
? VALLEE-PoussIN: Les Eurites quartzeuses (rhyolites anciennes) de Nivelles et
des Environs. Bull. Acad. Roy. Sc. Lett. et des Beaux Artes de Belg. 56 annue, 3d
series, Tome 13, No. 5, 1887, pp. 521-522.
3 Brit. Assoc. Rep., 1840.
4 Trans. Roy. Soc. Edin., Vols. XXXII, X XXIII.
ACID VOLCANIC ROCKS OF SOUTH MOUNTAIN. 825
of the process is in no way different from the process of crys-
tallization in a fluid magma, save in the rapidity of the action,
and is of both a physical and chemical character. It is not the
purpose of this paper to discuss the other evidences of meta-
_ morphism in the South Mountain rocks. There is ample proof
that both dynamic and statical metamorphism were wide spread.
While the former would, by shearing, obliterate the original
structures of a glassy rock and produce a slate, the latter might
be an important initiatory and accelerating factor in the process
of devitrification of the glassy rocks.
Nomenclature —The character of the acid rocks has been
briefly presented, and there remains to be considered a name or
names which shall be descriptive of them. While the possibility
of devitrification can hardly be doubted, the fact that a finely
crystalline aggregate of quartz and feldspar may also be the direct
product of consolidation from a molten magma is equally recog-
nized by the writer, and to the acid rocks possessing such a
groundmass the name quartz-porphryry is given. It is by no
means always possible to distinguish between a primary and sec-
ondary crystalline groundmass, hence no attempt is made to
draw a sharp line between the quartz-porphyries and the devitri-
fied rhyolites.
The typical ancient originally glassy acid volcanic should
be distinguished in some way by the name from the typical
ancient originally holocrystalline acid volcanic. Is there any
name now in use which does this? A great variety of terms has
been applied to the acid type of the older volcanic rocks. Under
the general group of quartz-porphyries, Rosenbusch classifies
them as muicrogranites, with a microgranitic groundmass, gvano-
phyres with a micropegmatic groundmass, felsophyres, with a micro-
felsitic base, and witrophyres (including pitchstones and pitchstone
porphyries), with a vitreous base. Foqué and Lévy use micro-
granitite, micropegmatite and porphyr petrosiliceuxas correspond-
ing terms. By British petrographers these acid rocks have been
termed hornstones, claystones, and claystone porphyries, felsites,
quartz-felsites, and felsites porphyries, agreeing in this respect
826 DHE JOURNAE- OF \GHOLOGN:
with the older German usage, when they have not followed
Rosenbusch. In America both German and English usage has
been followed with more or less confusing results. In the
nomenclature of the South Mountain rocks an effort has been
made to avoid such confusion and to use such a term or terms as
shall accurately describe them and all similar rocks. No one of
the terms mentioned succeed in doing this. Although, perhaps,
most nearly like the felsophyres, these South Mountain rocks
cannot be included under that term since they now possess a —
holocrystalline groundmass.
In so much as many of the English felsites have been shown
by Rutley, Allport, Cole, and Bonney to be devitrified obsidians
and pitchstones, and thus, like these American rocks, the repre-
sentatives of the glassy lavas of pre-Tertiary times, these pre-
Cambrian lavas of the South Mountain might with some
propriety be termed felsztes. Felsites, however, though useful as
a field name may well be objected to as an inaccurate petro-
graphical term. It was originally used to describe an acid base,
unresolvable to the naked eye, and at first supposed to be a sin-
gle mineral.t With the introduction of the microscope this
macro ‘ felsitic’’ base was resolved into the microgranitic, micro-
pegmatitic, and microfelsitic groundmass, the point of ignorance
being shifted from the felsitic base, macroscopically unresolv-
able to the microfelsitic base, which is microscopically unresolva-
ble. On the continent felsite has been practically replaced by
these terms. British and American petographers have retained
it as a field name for rocks formed of this macroscopically unre-
solvable base without phenocrysts or with inconspicuous pheno-
crysts. The South Mountain rocks are both without phenocrysts,
with inconspicuous phenocrysts, and with abundant and conspic-
uous phenocrysts. As this irregular distribution of the porphy-
ritical crystals may characterize a single lava flow, it does not
seem a sufficient ground for a separation of rock types.
‘GERHARD: Beitrage zur Geschichte des Weissteins des Felsit und anderer
verwandten Arten’” Abhandl. der k. Akad. der Wissensch. zu Berlin, 1814-1815.
s. 18-26. Naumann Lehrbuch der Geognosie Band 1, 2d ed. 1858,s. 597.
ACID VOLCANIC ROCKS OF SOUTH MOUNTAIN. 827
It is very generally recognized that structural features are not
conditioned by the geological age of rocks, but are, on the other
hand, a function of the conditions of consolidation. That the
conditions attending the consolidation of surface flows in pre-Ter-
tiary times do not differ from those attending the consolidation
of similar flows in post-Tertiary times has been illustrated by a
wide survey of pre-Tertiary and Tertiary rocks on the part of
Allport, Judd, Teall and others' With this recognition has come
the growing conviction among petrographers that mere age
should be eliminated asa factor in rock nomenclature.? While this
is true, it is felt, on the other hand, that there should be some
recognition in the rock name of the alteration which the rock
has undergone subsequent to its solidification. If, at the time of
its solidification, the rock presented the features of a rhyolite, as
it is believed much of the South Mountain acid lava did, but since
that time has become holocrystalline, both these facts, its orig-
inal character and its present alteration, should be recognized in
the name.
Such a result might be secured by the retention of such well
established names as rhyolite, obsidian, trachyte, etc., preceded
by a prefix which shall have such a designation as to indicate the -
altered character of the rock. The prepositions meta, epi and
apo, as prefixes, all indicate some sort of an alteration. Their
exact force has been thus defined by Professor Gildersleeve : meta
indicates change of any sort, the nature of the change not speci-
fied. This accords with the use of the prefix by Dana in such terms
as ‘‘metadiorite’’ and ‘‘metadiabase.’’ These terms have been
recently revived to designate rocks ‘‘now similar in mineralogical
tALLPORT: Address of the Pres. of the Geo. Sec. of the British A. A. A. S., 1873,
and many other writings by the same author.
Jupp: On the Gabbros, Dolerites and Basalts of Tertiary Age in Scotland and
Ireland. QO.J.G.S., Vol. XLII., 1886, pp.49-97.
TEALL: British Petrography, pp. 64-69.
2Reyer, Tietze, Reiser, Reusch (H. H.), and Suess support the statement that
age is not a just ground of distinction between eruptive rocks, and RKosenbusch consid-
ers that in no very distant future the separation of effusine rocks into an older and
a younger series will prove untenable.
$28 THE JOURNAL OF GEOLOGY.
composition and structure to certain igneous rocks, but derived
by metamorphism from something else. Epi signifies the pro-
duction of one mineral out of and upon another. This prefix has
yy
not been much used. We find it in such terms as epidiorite,
epigenetic hornblende. and epistilbite. dfo may properly be
used to indicate the derivation of one rock from another by some
specific alteration.
If, therefore, we decide to employ this prefix to indicate the
specific alteration known as devitrifiction (Antglasung) we may —
obtain, by compounding it with the name of the corresponding
glassy rocks, a set of useful and thoroughly descriptive terms,
like aporhyolite, apoperlite, apobsidian, etc., as to whose exact
meaning there can be no doubt. In accordance with this usage
it is proposed to call all the acid volcanic rocks, whose structures
prove them to have once been glassy, aporhyolites. While those
which have consolidated at a sufficient depth to secure a holo-
crystalline groundmass should be termed guarts-porphyries, whether
ancient or modern lavas. The writer realizes that the introduc-
tion of a new name into petrographical nomenclature is to be
deplored unless it can be shown that the name is formulated in
accordance with certain well defined principles. A good rock
name should express composition, original structure, and, as far
as possible, the process of alteration, if any, that the rock has
undergone. It is thought that aporhyolite and the suggested
series of similarly formed terms meet these requirements. They
are, therefore, adopted as preferable to any in present use.
Paleozoic and pre-Paleozoic acid volcanics have long been
studied on the Continent, Although their variation from the
modern type of acid volcanic, rather than their resemblance to
that type, has for the most part been emphasized by German and
French petrographers, there have not been wanting able advo-
cates of devitrification and of an original glassy base for the
ancient lavas. R. Ludwig (1861), and Vogalsang? (1867)
WHITMAN Cross: Ona Series of Peculiar Schists near Salida, Colorado. Proc.
Col. Sc. Soc., 1893, p. 6.
2 Philos. d. Geologie, 144, 153, 194.
ACID VOLCANIC ROCKS OF SOUTH MOUNTAIN. 8209
incline to the opinion that the groundmass of certain quartz-
prophyries is the result of the devitrification of a glassy lava.
The late Dr. K. A. Lossen* (1869), on comparing the spheru-
litic porphyries of the Harz Mountains with the obsidians of
Lipari, Mexico and Java, found the resemblance sufficiently
striking to lead him to declare that “the porphyry groundmass
was originally crystallized as glass, and became cryptocrystalline
through molecular rearrangement.” Later, Kalkowsky? (1874)
suggests devitrification through the chemical activity of water,
as the process by which the microfelsitic base of certain pitch-
stones and felsites was developed, and still later H. Otto Lang
(1877) described a macroscopically unindividualized base which
is similar microscopically to the devitrified base described by
Kalkowsky. Sauer (1889) considers the Dobritz porphyries as
the final alteration product of a pitchstone. C. Vogel comes to
the same conclusion as to the Umstadt porphyries in Hessen.
More recently Klockmann‘* (1890) describes the replace-
ment of the spherulitic crystallization in quartz-porphyries,
through secondary processes, by a fine grained aggregate of
quartz and feldspar. Osann5 (1891) describes incipient devit-
rification in perlite and other glassy rocks from Cabo de Gata.
Finally, Link (1892) considers that it is not impossible that the
fine grained groundmass of some rocks from America that are
closely related to mica-syenite-porphyries, was once glassy or at
least partially glassy. Many no less capable observers still hold
to an original difference between ancient and recent acid vol-
canics, and the possibility of devitrification and original simi-
larity is yet an open question in Germany.
*Beitrage zur Petrographie der Plutonischen Gestein Abh. der Berliner Akad.
1869, p. 85.
? Mikroskopische Untersuchungen von Felsiten und Pechsteinen Sachsens T. M.
P, M., 1874, pp. 31-58.
3 Heinr. OTro LANG: Grundriss der Gesteinskunde, 1877, p. 43.
4F. KLOCKMANN: Die Porphyre der Geol. d. s.g. Magdeburger unferandes m.
besonderes Beriisksichtigung d. auftretenden Eruptivgesteine Jahrbuch k. p. Geo.
Land. u. Bergakad. zu Berlin, 1890, vol. XI.
5 Z. Geol. Ges. 691, 716.
830 THE JOURNAL OF GEOLOGY.
In France, La Croix’ describes andesites from Martinique
in which the glass has altered into quartz spherulites and a
granular quartz aggregate. It is interesting to note that many
of the halleflinta of Sweden, which, like the South Mountain
volcanics, were once described as sedimentary, are proving to be
acid volcanics preserving the features of their modern equivalents.
Quite recently, glassy and rhyolitic structures in these rocks
have been observed and described by Otto Nordenskjéld.? In
Belgium Vallée-Poussin seems to be the only writer who has
brought out the resemblance between the eurites of that country
and modern rhyolites. He describes at some length structures
similar to those possessed by the aporhyolites of South Mountain.
A vacillating state of mind as to the matter of nomenclature is
indicated in the titles of his successive papers.3
In England the rhyolitic character of the ancient acid vol-
canics has been recognized and emphasized, and the idea of devi-_
trification is widely accepted. Allport, Cole, Bonney, Rutley and
Harker have accomplished most valuable work along this line.
Dr. Wadsworth‘ was the first American petrographer to advocate
the abandonment of age as a factor in rock classification ;
while at the same time he recognized devitrification as the pro-
cess which has been forming felsites out of rhyolites. What he
says is of interest in its anticipation of ideas now more gener-
ally accepted. ‘This devitrification gives rise in the older and
more altered rhyolites to the feldspar, quartz and microfelsitic
Comptes rendus, CXL, p. 71.
2 Opus cit.
3Les Anciennes Rhyolities dites Eurites de Grand-Manil. Bull. Acad. R. de
Belg., 3d series, Tome 10, 1885, pp. 253-315.
Les Eurites quartzeuses (rhyolite anciennes) de Nivelles et des Environs. Bull.
Acad. R. des Sc. et des Beaux-Artes de Belg. 56 annue, 3d series, Tome 13, No. 5, 1887.
4M. E. WApDsworTH: Notes on the Minerology and Petrography of Boston and
vicinity. Proc. Boston Soc. Nat. His., vol. XIX., May, 1877, p. 236.
On the Classification of Rocks. Bull. Mus. Comp. Zool., Harvard College, vol.
V., No. 13, June, 1879, p. 277.
ACID VOLCANIC ROCKS OF SOUTH MOUNTAIN. 831
(so-called) base that has so puzzled lithologists in the study of
the felsites. The rhyolites of all volcanic rocks preéminently
show lamination produced by flowing, a fact which is doubtless
due to their being so siliceous. This structure and their devitri-
fication enables us to trace a direct connection between the rhyo-
lites and felsites, which are simply the older and more altered
Gly OlibeS Hanan: 2. One of te best illustrations of this) ds
to be found on ilar tole head Neck, Mass., where at least two dis-
tinct flows of felsite occur, one cutting the other. They. show
the fluidal structure so characteristic of rhyolites,—a character
that has been mistaken for lines of sedimentation by geologists.
While the enclosed crystals of orthoclase have been taken for
Peblesweri) ue. aN \ nile sto themnakedseyerandaunder thc
microscope this rock shows the fluidal structure of a rhyolite, in
p- 1. it is seen that the base has been completely devitrified, a
process that is carried to a great extent in many known modern
thyolites.” No other American petrographer has so distinctly
advocated the identity of felsites and ancient rhyolites in spite
of the fact that many of our felsites illustrate it as unmistakably
as do the English felsites. Dr. Irving" in his description of the
Beaver Bay group of the Keweenaw series repeatedly calls atten-
attention to the resemblance between the ancient felsites’ and
quartz-porphyries and the modern rhyolites, although he does not
express an opinion as to their equivalence. The statement ‘that
the degree of crystallization developed in igneous rocks is mainly
dependent upon the conditions of heat and pressure under which
the mass has cooled and is independent of geological time”
made by Messrs. Hague and Iddings® expresses essentially the
position of American petrographers on this question.
Apparently in none of the felsites elsewhere described have the
varied structures of the modern rhyolite been more perfectly and
conspicuously preserved than in the aporhyolites of the South
Mountain.
Opus cit., pp. 312, 313, note 5, p. 436.
2 On the Development of Crystallization in the Igneous Rocks of Washoe, Nevada,
with Notes on the Geology of the District, Bul. 17 U.S. G. S. 1885, p. 4o.
832 THE JOURNAL OF GEOLOGY,
The subject discussed in this paper forms a part of a thesis,
on South Mountain, presented at the Johns Hopkins University.
The petrographical study was conducted in the petrographical
laboratory of that institution, under the immediate’ supervision
of Professor G. H. Williams, to whose valuable suggestions and
stimulating interest the writer is in every way indebted.
F. Bascom.
PETROGRAPHICAL DEPARTMENT,
STATE UNIVERSITY, COLUMBUS, OHIO.
SFODIES FOR SLUDENES
GENETIC RELATIONSHIPS AMONG IGNEOUS ROCKS.
Ir is desirable that the student of igneous rocks should
appreciate the fundamental relationships existing between various
kinds of igneous or eruptive rocks so far as they are understood
at the present time, in order that he may form a proper idea not
only of what an igneous rock actually is, but also of the uses
and limitations of the terms by which they are designated. So
it has been thought desirable to present, in an elementary form,
some of the data and opinions bearing upon the genesis of differ-
ent kinds of rock magmas. :
It can be shown that all eruptive rock masses, whether
emanating from volcanic vents at the surface of the earth or
found enclosed within such vents, or confined to fissures not
immediately connected with actual volcanoes, with the exception
of certain infrequent occurrences of sandstones, which have
been forced, while in a loose and incoherent state, into cracks—
it can be shown that all ordinary eruptive masses were in a com-
pletely molten or fused condition before solidifying into the
rocks they now are, and hence the terms eruptive and igneous
are practically synonymous.
The igneous mass or molten magma, as we know by observa-
tions at active volcanoes, may obtain a liquidity comparable
to that of water,’ which, of course, would obtain for different
temperatures in the case of magmas having different chemical
compositions; the less silicious magmas reaching this liquidity
at a somewhat lower temperature than the more silicious ones.
During the process of cooling, magmas become gradually more
tJAMES D, DANA: Characteristics of Volcanoes, etc. New York, 1891, p. 143.
833
834 THE JOURNAL OF GEOLOGY.
viscous, and crystallization generally takes place, but the two are
in a measure independent operations, and the viscosity may be
advanced so rapidly that crystallization is more or less completely
prevented and glassy rocks result. According to thé conditions
under which rock magmas cool solidification will be accompanied
by more or less complete crystallization. The size also of the
crystals will vary with the rate of cooling, and the general
texture of the rock will be affected. Different parts of one rock
magma may experience different conditions of cooling, and there
will result a variety of textures or structures within the mass.
It may be that the textural differences are sufficiently pronounced
to be given distinctive names, which become the terms by which
_ certain kinds of rocks are designated; for example, granite,
porphyry, pearlite, pumice, etc. There is then a relationship
between certain kinds of igneous rocks which exists because of
different conditions which have attended the solidification of
various portions of one body of magma, or of several magmas
alike in other respects. The significance of this relationship was
long ago appreciated by James D. Dana,* who maintained that
the textural differences among rocks were mainly due to the
physical conditions under which they consolidated ; an idea ably
advocated and corroborated by Judd,? and more recently sub-
stantiated by numerous observations in many localities.
Igneous rocks often differ from one another in mineral and
chemical composition; in fact, some kinds differ so widely from
one another in a mineralogical sense that they possess no mineral
in common. And most kinds contain the minerals which may
be common to them in quite diverse proportions, and associated
with various other species. Chemically they consist of the same
essential constituents in variable proportions, the variations being
within certain limits. But the proportions are so far from being
*United States Exploring Expedition during the years 1838-1842, under the com-
mand of Charles Wilkes, U.S. N., 4to. Philadelphia, 1849, Vol. 10, Geology, p.
372 et Seq.
2J. W.Jupp: On the Ancient Volcano of the District of Schemnitz, Hungary.
Quart. Jour. Geol. Soc., 8vo, Vol. 32, 1876, p. 292 ef seg.
GENETIC RELATIONSHIPS AMONG IGNEOUS ROCKS. 835
fixed for similar kinds of rocks that it would be almost impos-
sible to find two instances in which the proportions between the
essential ingredients were exactly the same. The independence
of many kinds of igneous rocks might seem at first thought to
be clearly established by these mineralogical and chemical
divergences. This apparent independence disappears when a
great number of rocks are investigated. It is found that few
rocks contain the same minerals in any given proportion, and
that the variable proportions of minerals produce varieties of
rocks which grade insensibly from one extreme of mineral com-
position into another. Intermediate varieties of rocks which
form transitions from one type, or distinct kind, to another have
been recognized for many years. But it is becoming more and
more evident that the so-called type-rocks are not more abund-
ant in nature than the intermediate forms. It is found that
particular kinds of rocks may preponderate in one region and
the intermediate varieties be subordinate, but that in other
localities the relations may be reversed, and the so-called transi-
tional forms may prevail.
The mineralogical gradation of one kind of rock into another
is indicated not only by the comparison of all known varieties of
igneous rocks, but more especially by the study of all the occur-
rences of such rocks in any region where they are abundant.
The absence of distinctive types, and the presence of all possible
varieties intermediate between the extremes is the most notice-
able characteristic. Moreover, the transitional variations are not
simply represented by slightly different bodies of rock, but they
may often be found to exist within one continuous rock mass.
Thus, a large body of rock may change in mineral composition
from one spot to another by the most gradual transitions, giving
rise to constitutional facies of the main mass. Again, it is found
that a large body of rock, which may be nearly homogeneous
throughout, exhibits certain mineralogical facies which are like
the main portion of some other rock-body in the same region;
so that the subordinate variety in one mass is the predominant
form in another.
836 THE JOURNAL OF GEOLOGY.
The ability of a rock magma to change in chemical composi-
tion in different parts, so as to crystallize into different mineral
combinations which correspond to mineralogically diverse rocks,
does not appear to be limited to small volumes of magma, but
shows itself on quite different scales; sometimes confined toa
narrow dike, at others acting throughout a large mass thousands
of feet in diameter. That which is seen to have taken place
within a comparatively limited volume of molten magma might
be reasonably assumed to be possible within much greater
volumes. Nevertheless it does not necessarily follow that it has
done so; conditions which may have brought about the change
in one case may not exist in another.
The probability that such changes have taken place in great
reservoirs of molten magma, and have brought about the chemi-
cal and mineralogical differences among igneous rocks, finds its
support in other evident relationships than those of facies and the
gradual transitions in mineral composition between the kinds of
rocks. The nature of this evidence is twofold and consists, first,
in the existence of associations of various kinds of igneous rocks
in volcanic regions; and second, in chemical and mineralogical
diversity between different associations of rocks, that is, between
groups of rocks belonging to different regions. The association
of various kinds of rocks in particular volcanic districts, and
their constant recurrence in company with one another in widely
distant parts of the world impressed itself upon the minds of
Scrope,’ Darwin? and Dana? in the first half of the present cen-
tury, and led them to the opinion that the various kinds of lavas
thus associated must have originated from some common source,
that is, from a common molten magma, by some process of
separation or differentiation.
Subsequently, as the chemical and mineralogical constitution
of rocks became more readily determinable, it was discovered
that there were chemical and mineralogical characteristics of
1G. P. SCROPE: Volcanos, 8vo, London, 1825.
2CHARLES DARWIN: Volcanic Islands, 8vo, London, 1844.
3 Loc. cit.
GENETIC RELATIONSHIPS AMONG IGNEOUS ROCKS. 837
whole groups or associations of rocks which distinguished them
from groups in other regions. This was noticed by Judd in
studying the volcanic rocks of Hungary and Bohemia, and was
afterwards clearly expressed by him in defining petrographical
provinces as districts ‘within which the rocks erupted during any
particular geological period present certain well-marked pecu-
liarities in mineralogical composition and microscopical structure,
serving at once to distinguish them from the rocks belonging to
the same general group, which were simultaneously erupted in
other petrographical provinces.
individuality of a petrographical province is found in the unusual
group of rocks described by Brégger,? from the region of Chris-
tiania. They are characterized by a high percentage of sodium
and a consequent abundance of alkali minerals. Brégger calls
attention to the remarkable fact that the greater part of the
rocks in this district are absolutely peculiar to the locality, or
IT
A striking illustration of the
nearly so, and have not yet been found in any other part of the
world. The association of special kinds of rocks in different
localities has also been pointed out by Rosenbusch,3 and urged
as evidence of a genetic relation between the rocks so grouped.
Certain chemical characteristics of special geographical
groups of rocks become apparent when all of the chemical
analyses are systematically compared and their variations plotted
graphically, as has been done by the writer for the rocks of
particular localities in the Yellowstone National Park, and for
those of Vesuvius and vicinity, and of Pantellaria. It is
observed in these cases that the relations of the alkalies to one
tJ. W. Jupp: On the Gabbros, Dolerites and Basalts of Tertiary Age in Scotland
and Ireland. Quart. Jour. Geol. Soc., Vol. 42, p. 54, 1886.
?W. C. BROGGER: Die Mineralien der Syenitpegmatitgange der Siidnorwegischen
augit- und nephelinsyenite. Zeitschr. fiir Kryst. u. Min., 8vo, Leipzig, 1890, Vol.
XVI., p. 83.
3H. RosENBUSCH: Microskopische Physiographie der massigen Gesteine, 8vo,
Stuttgart, 1886, pp. ix., 600, 628, 767, 795, 809, 810, 821. Also in Mineral. und
petrogr. Mitth. XI., 1890, p. 445.
4J. P. Ippincs: The Origin of Igneous Rocks. Phil. Soc. Washington, Bull.
Vol. XIL., 8vo, pp. 89-214, Pl. 2. Washington, 1892,
838 THE JOURNAL OF GEOLOGY.
another and to the other constituents is characteristic of the
rocks of each group. A genetic relationship is clearly indicated,
and it appears that the various rocks in each locality have been
derived from a general magma peculiar to the locality.
The distinguishing characteristics of the rocks of different
petrographical provinces which may be observed in their chemi-
cal composition also find expression in certain mineralogical
peculiarities. Thus the presence of a relatively high proportion
of potash will insure an abundance of potash-bearing minerals,
as at Vesuvius. The relatively high percentage of soda in the
rocks of Pantellaria, together with low alumina and relatively
high ferric oxide, determines the prevalence of alkali-feldspars
rich in soda, and of soda-bearing ferro-aluminous silicates,
znigmatite or cossyrite. The less prominent position of the
alkalies in the rocks of Electric Peak and Sepulchre Mountain,
and the relatively higher percentages of magnesia and iron oxide
leads to the very general presence of orthorhombic pyroxene in
these rocks, which is in contrast to the less magnesian and more
alkaline rocks of Central France and Germany. The abundance
of alkalies and general preponderance of soda in the rocks of the
Christiania district expresses itself in the abundance of the alkali-
feldspars and feldspathic minerals, and in the prevalence of
acmite- and riebecite-molecules in the pyroxenes and amphi-
boles.
From this it follows that certain rocks belong in particular
natural series or groups, and are absent from others, and that
two natural series of rocks, when arranged according to the per-
centages of silica, may grade through similar ranges of silica,
but may each embrace different kinds of rocks. Thus:
Silica Silica
Percentages. Yellowstone Park. Percentages. Vesuvius and Ischia.
48-53 Basalt. 40-55 Leucitophyre.
55-62 \ Pyroxene-andesite.
& Hornblende-andesite. 55-62 Trachyte.
64-68 { Hornblende-mica-andesite.
? Dacite.
70-75 Rhyolite. 69-71 Rhyolite.
In such series it happens that rocks bearing the same name
differ in certain mineralogical respects, and are really more
a“
GENETIC RELATIONSHIPS AMONG IGNEOUS ROCKS. 839
closely allied to the chemically nearest variety in their own
group than they are to the rock of the same name in another
group.
It must not be inferred from the facts just given that every
natural group of rocks has some peculiarity which distinguishes
it from every other group. There are many natural groups or
petrographical provinces, the rocks of which are identical in the
minutest detail with those of neighboring or distant regions.
And the limits or boundaries of such provinces are not sharply
drawn in nature. In some regions the transition from one prov-
ince to another appears abrupt, in others very gradual. Thus,
while certain provinces exhibit distinct mineral and chemical
characteristics, others appear to possess characters of several
provinces.
Recognizable chemical differences may exist between groups
of rocks within less than a hundred miles of one another, and
again broad general features may be persistent, or at least may
be prevalent, over vast areas of the globe. Within these areas,
of course, subordinate variations may exist... The most impres-
sive illustration of this law is furnished by the igneous rocks of
the two continents of North and South America. The great belt of
Cordilleras and parallel ranges stretching along the western side
of North America abound in igneous and volcanic rocks which
belong to a quite uniform petrographical province, extending from
British Columbia to Mexico and Central America. They are not
specially rich in alkalies, and are characterized by a very general
presence of the ferro-magnesia mineral, hypersthene ; local varia-
tions occur.. As the eastern portion of this mountain system is
approached from the west a gradual increase in alkalies is notice-
able, and rocks bearing nepheline, leucite and more frequent
alkali-feldspars make their appearance, containing alkali-bearing
ferro-magnesian minerals. These have already been described,
from Montana, Wyoming, Dakota, Colorado and Texas, and are
especially well developed in Arkansas. Similar eruptive rocks
have been found in the eastern portion of the continent, in New
Jersey, New England and Canada.
840 THE JOURNAL OF GEOLOGY,
In South America the great Cordilleran system of the Andes
presents a petrographical province identical, chemically and
mineralogically, with those of the North American Cordilleras, and
which appears to extend throughout its entire length. In the
eastern part of the continent and on the islands off its coast the
petrographical province is in turn identical in many respects with
the eastern province of North America; the correspondence being
most pronounced between the rocks from Brazil, described by
Derby*, and those from Arkansas described by J. Francis Wil-_
liams.?
The chemical and mineralogical qualities or peculiarities which
characterize the rocks of particular groups, and at the same
time serve to distinguish them from those of some other groups,
are like family traits of character, and suggest the intimate rela-
tionship and common origin of all of the igneous rocks of the
group. They prove conclusively that the varieties of rocks
occurring at a particular center of eruption, or ina volcanic dis-
trict, have been derived from some magma common to the dis-
trict by a process of differentiation similar to that which has
caused smaller bodies of molten magma to become chemically
heterogeneous and has produced mineralogical facies.
That the process which has produced the many kinds of igne-
ous rocks in any region, with all their transitions into one
another, was a process of differentiation of an originally homo-
geneous magma, and not the compounding of two or more dif-
ferent ones, is shown by the geological relationships between the
various bodies of rock belonging to a volcanic center; more
especially the order in which they have been erupted. A process
dependent upon any set of physical conditions, which continues
active for long periods of time must yield results that are to a
very considerable extent functions of time, that is, they must be
1Q, A. DERBY: On Nepheline Rocks in Brazil, with special reference to the Associa-
tion of Phonolite and Foyaite. Quart. Jour. Geol. Soc. 8vo, London, Aug., 1887.
Also The Tingua Mass. Jézd., May, 1891.
2J. FRANCIS WILLIAMS: The Igneous Rocks of Arkansas. Annual Report of the
Geological Survey of Arkansas for 1890. Little Rock, 1891.
GENETIC RELATIONSHIPS AMONG IGNEOUS ROCKS. 841
accumulative. Hence, if the process is one of synthesis or com-
mingling, the mixture should be the more complete the longer
the process has been in operation. On the other hand, if the
process is one of differentiation the separation should be the more
perfect as time goes on. The various bodies of rock occurring
in a large volcanic region have been erupted at widely different
times, and while belonging to a connected period of volcanic
activity may often represent the lapse of ages. Their genetic
relationship has been the result of some active principle coéx-
tensive with this vast time, and persistent or intermittent; the
effect in either case must be accumulative.
It is found in all regions carefully investigated that there is a
sequence in the eruption of different varieties of rocks which is
most characteristic. From the nature of the causes leading to
the extrusion of volcanic lavas, the irregularities of the conduits
through which they reach the surface and the probable diversity
in the physical conditions obtaining in different regions, it is to
be expected that the course of events will not be the same in all
cases, or constant in any one instance. Hence the sequence of
rocks will not be uniform for all regions, nor will it necessarily be
simple in any case. The sequence discovered by von Richthofen,?
when expressed in general terms, is of very wide application, and
is to the effect that the earliest eruptions are of rocks having an
average or intermediate composition, and that subsequent erup-
tions bring to the surface magmas of more and more diverse com-
position; the last eruptions producing the most diverse forms.
The transition from a magma of intermediate composition to
those of extremely divergent composition, is clearly the result
of a process of differentiation. ‘This correspondence between
the petrographical and the geological succession,” as Brégger?
remarks, ‘‘appears to prove conclusively a genetic connection
between successive eruptions.” The same conviction has been
expressed by Geikie, Teall and others. Evidences of the mixing
*F. von RICHTHOFEN: The Natural System of Volcanic Rocks, 4to. San Fran-
cisco, 1868.
2Loc. cit. p. 83.
842 LAE JOURNAL OF SGHOLOGY
of different rock magmas to form an intermediate modification
are exceedingly local, and appear to be confined to narrow limits
along the junction of one body of rock with another.
The genetic relationship between the various kinds of igne-
ous rocks belonging to a center of volcanic activity, which is
plainly indicated by their chemical, mineralogical and geological
relationships, is in the nature of a generic connection. They
have originated from some common magma or parent stock, and
to a very large extent are characterized by whatever distinguish-
ing peculiarity was characteristic of the parent magma. They
are in this sense consanguineous. _ The presumably homogen-
eous parent magma has become heterogeneous by some chemico-
physical process or processes, so that different portions of it
have different chemical constitutions. The differentiation un-
doubtedly takes place according to fixed laws and within limita-
tions affected by the original constitution of the magma, and
by the external controlling conditions or agencies. Further than
this we shall not venture in the present article. It will be
sufficient to consider some of the consequences of the general
principles of magmatic differentiation.
First. If differentiation is controlled by external agencies or
conditions, such as changes of temperature and pressure, which
depend largely on the environment of the magma, then the
results of differentiation should vary when the external conditions
vary. It is not to be expected, therefore, that similar magmas
will always yield the same results when differentiated, within
certain limits. They may have experienced quite different
physical conditions. The more uniform the conditions the more
concordant the results.
Second. Since the process of differentiation requires time,
is progressive, and, from geological evidence already alluded to,
often continues for ages, it follows that eruptions from a reser-
voir, where the process of differentiation is taking place, will draw
off magma whose constitution will depend on the phase of dif-
ferentiation attained by the parent magma. The phase will nat-
urally depend on the time at which the eruption takes place.
GENETIC RELATIONSHIPS AMONG IGNEOUS ROCKS. 843
Moreover, since the process of differentiation necessitates the
coéxistence of differently constituted derived magmas in various
parts of the parent body or reservoir, the kind of magma drawn
off at an eruption will also depend upon the portion of the
reservoir drawn from.
Third. If, in a given region of eruptive rocks, each body of
rock was the immediate solidification of the magma drawn
directly from one common reservoir, they would represent the
phases of differentiation in the parent magma at the time when
the eruptions took place. If, however, the magma drawn from
the reservoir did not solidify immediately, but remained in a
molten condition within the fissure or conduit, a still further
differentiation within this derived magma might take place
under conditions imposed by its new environment. In this
manner differentiation might proceed at quite different rates
and possibly with diverse results in the parent magma and
in the derived magma. Material, then, which, through sub-
sequent eruption, might come to a place where it could
solidify, might be derived from the parent magma or from
the derived magma, and would represent different phases
of differentiation. Either set of conditions of eruption may
exist in nature, and much more complex ones. The first may
very well be found in great fissure eruptions such as have taken
place in western America. The second are probably represented
by groups of volcanic vents. Both are simply modifications of
eruptive processes, and differ in no essential respect.
The genetic relationship of rocks belonging to one center of
eruption, or to one group of centers, or to one petographical
province, makes plain the fortuitous character of so-called rock
types ; the constitution of any rock mass depending primarily
upon the phase of differentiation, and on the portion of the
reservoir let out. It proves the fundamental character of the vari-
ability in composition of such rocks, both as between different
bodies of rock and also within the mass of one continuous body
in many cases. The degree of homogeneity in a rock body will
depend upon the relation of its volume to that of the reservoir
844 THE JOURNAL OF GEOLOGY.
from which it was drawn, and the conditions of differentiation
existing there, and, further, upon whether it has undergone sub-
sequent differentiation within itself.
The textural variations which were discussed in the first
part of this paper, and which may exist in diverse portions of
one rock body, or in different bodies of similar magmas, add still
further to the complexities in solidified magmas. Rock magmas
are thus known to vary frequently in chemical composition, min-
eral composition and texture. Names of rocks which are defined i
in terms of these three characters, can only apply to that
portion of a rock body exhibiting the characters specified.
Other parts of the mass will have different names, and to this
extent be different rocks. The student should therefore recog-
nize the difference in the idea conveyed by the term sacks
as ordinarily used, and that which is involved in the expression
rock-body, as a geological unit.
JosErH P. IppDINGs.
EE DITORIALS
THE December /orum contains an interesting article by Dr.
D. G. Brinton on “The Beginning of Man and the Age of the
Race.” It affords, incidentally, several suggestions of value to
geologists who are concerned in working out the problems which
relate to the fossil relics of man on this continent. Dr. Brinton
reasons that we have good grounds for locating man’s birthplace
only where mammals that are very near to him in physical prow-
ess and mental aptitude are known to have existed some fifty or
one hundred thousand years ago. This, he thinks, ‘‘at once
excludes a large portion of the earth’s surface, as the Arctic, Ant-
arctic, and colder temperate zones, the lofty plateaus of the world
and its inclement shores.’ ‘The whole of America must be
excluded, for it shows no signs of having been the home of the
higher mammals, that is, apes or monkeys without tails and with
thirty-two teeth.” By similar exclusions, the area of probable
origin of man is limited to Southern Asia, Southern Europe, and
Northern Africa. A fuller exposition of Dr. Brinton’s views was
given in his address before the American Association for the
Advancement of Science at Madison iast August.
Without giving unqualified assent to all the limitations urged
by Dr. Brinton, it would appear from the distribution of types
kindred to man in the Pliocene and Pleistocene periods, and from
the fact that the evolution of a naked animal from the hairy one
can reasonably be supposed to have taken place only ina very
warm climate, that primitive man, in the strict and proper sense
of the term, can scarcely be supposed to have been an inhabitant
of America. It is difficult to see how he could have reached
this continent while in his strictly primitive state by land migra-
tion (even if there were land connection in the Behring region)
845
846 THE JOURNAL OF GEOLOGY.
without traversing extensive cold and mountainous tracts quite
prohibitory to a strictly primitive naked man of tropical origin,
unless such transit were made in the early part of the Tertiary
era before the development of cold northern climates‘and before
the erection of the modern mountain systems. The early Ter-
tiary, however, was an era of submergence rather than of eleva-
tion and land connection, and the possibility of such migration
is extremely doubtful. Primitive man cannot well be supposed
to have gained access to America by water until he had learned -
the art of navigation, or, in other words, until he had reached a
somewhat advanced state of civilization. The strong presump-
tion is, therefore, that man came to America only after he had
attained toa stage of development much beyond the primitive one.
It would appear that he must have become possessed of the power
of protecting himself from the vicissitudes of climate and of
securing the means of living under adverse conditions, or else
had acquired the arts of navigation to an extent that would per-
mit him to cross from the one continent to the other in warm
latitudes.
As man’s full evolution did not, therefore, probably take
place on this continent, a complete series of relics of that evo-
lution cannot be looked for here. Hence a system of interpreta-
tion of fossil relics which is based upon a theory of complete
evolution here or which presumes the existence here of a com-
plete series of relics does not carry inherent force, but rather the
contrary. Itis more probable that the oldest fossil relics of man
on this continent represent, not a primitive, but some advanced
stage of evolution. There is no inherent reason for expecting
to find ‘‘paleolithic” or any other very primitive stage of culture
here, however well demonstrated that stage may be on the east-
ern continent. To establish the existence of that stage here,
unquestionable geological evidence, strong in itself and quite
independent of theoretical support, must be produced. The geo-
logical problem in America will be greatly clarified when it is
recognized that its solution must rest on strict stratigraphical and
paleontological grounds, and not on any parallelism with a
EDITORIALS. 847
theoretical evolution applicable only to the land of man’s origin.
The present stage of civilization is certainly not an immediate
derivative of the next preceding, but has been imposed. upon it
unconformably, so to speak, and disjunctively.- It is intrusive or
superposed, and not derivative. So it is probable that the pecu-
liar phases of the higher civilizations found in Central and South
America were intrusive and not derivative. It is, therefore, not
improbable that the entire succession of civilizations on the
American continent consists of a series of intrusions or super-
positions from the west and from the east, overlapping each
other unconformably and disjunctively. They can, therefore, be
worked out safely upon no theory ef genetic succession. Each
factor must be determined by means of its own inherent evi-
dence. CG.
Paar
PROFESSOR JAMES D. Dana has a short article in the Novem-
ber number of the American Journal of Science* touching upon
the recent discussion of the divisibility of the glacial period, in
which he draws forth generalizations on two important lines, viz.,
(1) the personal attitude of writers on the subject, and (2) the
difference between the glacial phenomena of New England and
of the upper Mississippi basin. These seem to us to lie in the
right direction, in the main, but in both cases to have somewhat
missed the truest lines of distinction and to have fallen short of
the most significant features. Professor Dana draws attention to
the divergent views of New England and of western glacialists,
and concludes that there must be some difference in the phe-
nomena of the tworegions to account for the differences of view.
This seems to us very true and very important. The difference
in the phenomena is, however, we think much more radical, and, at
the same time, much more simple than that suggested by Pro-
fessor Dana. It is, to our view, simply this: In New England
only the latest epoch of the glacial period is distinctly repre-
t New England and the Upper Mississippi Basin in the Glacial Period. Am. Jour,
Sci. III., Vol. XLVI., No. 275, Nov., 1893, pp. 327-330.
848 THE JOURNAL OF GEOLOGY.
sented. The earlier episodes (to use a term not in controversy )
may have representatives there in overridden and buried depos-
its, but, if so, they are obscure and have not been distinctly
delineated. Inthe West, on the other hand, a very considerable
series of episodes is well displayed. These embrace not only
those presented in New England, but a considerable series of
earlier ones not at all (distinctly) represented there. These
greatly prolong and diversify the glacial series. In our judg-
ment, it is not simply a doubling of that of New England, but a
much higher multiplication. The whole series cannot, there-
fore, be judged by the incomplete New England representa-
tives. All investigators, we think, or nearly all, agree that the
New England glacial deposits fall within a relatively brief epoch
and are not much (at least not very distinctly) differentiated.
We agree heartily with those who would refer the declared New
England drift to one epoch (reserving opinion, of course, regard-
ing remnants of overridden or obscure drift of earlier episodes).
New England is little better fitted to be a standard for the inter-
pretation of the whole glacial series than it is for the whole
Paleozoic series. In neither case is the series fully and dis-
tinctly represented, nor in either case is it typical. This is
implied significantly in the relative state of delineation of the
formations in the eastern and western sections. With a great
preponderance of workers and of skill, no historical divisions of
the glacial formations have yet been traced entirely across New
England, not even those of an episodal rank. In the interior, on
the other hand, something like a score of historical stages have
been delineated over broad areas. Lines of episodal delimita-
tion aggregating many thousands of miles have been mapped.
Any attempt, therefore, to revise the work of the interior by the
phenomena of New England is not likely to be more successful
than the revision of the Paleozoic series on a like basis.
In classifying personal opinions, a dividing line separating
the New England and the western workers is valuable and sig-
nificant. But a much more significant cleavage plane, we think,
may be found between those glacialists who have studied the
EDITORIALS. 849
later episodes (or the earlier episodes) exclusively and those
who have studied dot. To have studied the Hudson River beds,
east and west, is an inadequate preparation for deciding whether
they are to be placed in a separate epoch from-the Trenton beds
or not. Both the Hudson River beds and the Trenton beds
should be studied in regions where both are well displayed. So
of the drift deposits. Classified on the basis of the formational
distribution of critical studies, the true generalization falls easily
into form, viz., those who have studied the formations of one
epoch believe in one epoch; those who have studied the forma-
tions of more than one epoch, believe in more than one epoch.
The special individual opinion upon which Professor Dana
lays stress ceases to have significance, or rather has its signifi-
cance reversed, when it is observed that the studies on which it
is based (most admirable in extent and in quality) fall almost
exclusively within zones referred, by common consent, to a sin-
gle, late, relatively brief glacial epoch.
Respecting the reference of the differences between the drift
of the east and of the west to meteorological causes there is
room here only for inviting attention to the pregnant fact that
the greatest southward extension of the drift is found where the
present meteorological and topographical conditions are least
favorable. The drift of the interior reaches south of 38° latitude,
that of New England only a little south of 41°,a difference that
equals about three-fourths of the extent of New England in lati-
tude, exclusive of Maine. The inferiority of the drift of New
England in extent, in massiveness, and in serial development is
the feature that calls for explanation in adverse conditions rather
than the magnificent deployment of the glacial series on the
plains of the interior. TAGs.
REVIEWS.
i
RECENT CONTRIBUTIONS TO THE SUBJECT OF DYNAMOMETAMORPHISM
FROM THE ALPS.
A. Heim: Geologie der Hochalpen zwischen Reuss und Rhein. Bei-
trage zur geologischen Karte der Schweiz, Vol. XXV., 4°: Bern,
1891, pp. 503.
C. Schmidt: Beitrage zur Kenntniss der auftretenden Gesteine. ib.
Anhang, pp. 76.
L. Mitch: Beitrage zur Kenntniss des Verrucano. Erster Theil : Leip-
Zig, 1892, pp. 145.
M. P. Termier: Etude sur la Constitution géologique du Massif de la
Vanoise. Bull. des Services de la Carte géol. de France. No. 20,
Paris, 1891, pp. 147.
For many years both Huttonian (metamorphic) and Wernerian
(original deposition) principles have been advanced to explain the
crystalline schists of the Alps, as well as those of other regions.
Because of their youth these great mountains are in many ways pecu-
liarly fitted to throw light upon the difficult problems presented by
these rocks. Many of the most classic Alpine localities are now being
investigated by modern methods and are yielding welcome results
which tend to establish not merely the fact, but also the nature, cause
and processes of metamorphism.
Nowhere is this more true than in the region of vast earth-move-
ments which Professor Heim of Zurich, has made the scene of his life
work. As the result of his labors in this field, he was able to publish
in 1878 his monograph on the Tédi-Windgdlle group and _ the
accompanying essay on the Mechanism of Mountain-making—a work
which must certainly be regarded as epoch-making in suggesting the
clue to a satisfactory explanation of the problems of regional meta-
morphism. ‘This book Professor Heim now supplements with another
of almost equal size, which contains the explanatory and descriptive
text of the remainder of Sheet XIV of the Geological Survey of Switz-
850
REVIEWS. 851
erland. ‘This map, which was published ‘on a scale of 1: 100,000 in
1885, embraces the area between the St. Gotthard railway and the
Rhein, north of the great central (Tessin) massif which forms the
south flank of the Alps. Hence it includes the eastern portion of the
Aar and Gotthard massifs, with all the younger formations in their
most disturbed and implicated development. The thirteen years
which have elapsed since the appearance of the earlier work have so
greatly multiplied observations and stimulated thought that the stand-
point regarding the whole subject of dynamic metamorphism is seen
to be faradvanced. Nor has Professor Heim himself been instrumental
in any small way in bringing about this result. Aside from his own
detailed field work, his suggestions as to the efficacy of orographic
movement as a metamorphosing agent have been of profound and
world-wide influence. Hence we cannot be surprised that he should
have inspired enthusiastic students within the limits of his own special
field. Others have worked out under his direction many details upon
which some of his own broadest and most far-reaching generalizations
rest. Some of the best of these results appear almost simultaneously
with his latest work and form an integral portion of it. This is nota-
bly true of the special petrographic studies of both the eruptive and
sedimentary rocks of two important and much discussed horizons—the
Bundnerschiefer and the Verrucano—in both of which the processes
of dynamometamorphism can be made out clearly and precisely fol-
lowed.
More than one quarter of the Swiss atlas sheet XIV is occupied
by that diversified complex of phyllites and schists, called by Heim
the Bindnerschiefer. ‘Their stratigraphical relations are, on account of
the dislocations to which they have been subjected, often very obscure.
They have been variously interpreted by different observers, but as the
result of years of mature observation Professor Heim gives a full pre-
sentation of the facts, and now concludes that he must differ with
Bonney, Giimbel, Diener and others who have ascribed to them a
greater age, and agree with A. Escher v. d. Linth, Theobold and
Rolle who regard them as a united and continuous series belonging in
fhe main to the Lias. ‘Toward the east, where these schists have their
broadest and least disturbed development, they are comparatively little
altered, and consist of calcareous shales and phyllites, impure lime-
stones, sandstones, dolomitic and gypseous beds, interstratified with
green schists and serpentine which are shown by microscopical exam-
Ba THE JOURNAL OF GEOLOGY.
ination to be altered volcanic material in conformable layers. Farther
west, where these same rocks become tightly compressed between the
gneisses of the central massifs, they have become recrystallized in pro-
portion to the amount of their dislocation. ‘The study of the Bund-
nerschiefer,” says Heim, ‘‘was that which years ago first convinced me
of the possibility and reality of crystalline metamorphism being pro-
duced without the agency of eruptive contact, since I here for the
first time observed how a belemnitiferous calcareous argillite became
gradually more and more crystalline by the development of such
minerals as mica, garnet, hornblende, zoisite, etc., at first as indistinct
and imperfect nodules, and later as good crystals” (1. c., p. 52).* The
Biindnerschiefer, both in their less altered localities and in occasional
beds, which have been by chance saved from metamorphism, are quite
rich in Jurassic fossils.
About one-half of Professor C. Schmidt’s appendix to Professor
Heim’s monograph is devoted to the petrographical description of the
Biindnerschiefer, while the remainder treats of the crystalline rocks of
the Aar, Gotthard and Adula massifs. A few preliminary remarks on
the melaphyre of the Karpfstock supplement the author’s earlier com-
munications with reference to the eruptives occurring in the Glarner
double-fold.* | The rocks from the three crystalline massifs are mainly-
the characteristic Alpine gneiss-granites or protogine, with dioritic or
amphibolitic interpositions. Sericite- ottrelite- paragonite- zoisite-
glaucophane-schists and eclogites also occur. The Adula gneiss is
characterized by a green potash-mica (phengite) which is both uniaxial
and biaxial. The rocks of the Béndnerschiefer are described by
Schmidt under two principal heads: @) gray and black schists which
are more or less completely metamorphosed sediments; and 4), green
schists which are foliated and metamorphosed eruptive material.
Under the first division are mentioned schists with newly crystal-
lized chloritoid, zoisite, tourmaline, epidote, biotite, muscovite, quartz,
plagioclase and rutile. In some cases complete pseudomorphs of
zoisite after echinoid remains are to be found. Other more tightly
compressed beds at Nufenen, Val Piora, Lukmanier, Scopi, Ariolo,
and other localities are still more highly crystalline, containing dis-
thene, garnet, staurolite and similar minerals in abundance. ‘These
rocks have also been petrographically studied by Prof. U. Grubenmann.?
* Neues Jahrbuch fiir Min., etc., Beil. Bd. IV., p. 288, 1886. Ib., 1887, I1., p. 58.
?Mitth. Thurgauischen Naturf. Gesellsch., Heft. VIII., 1888.
REVIEWS, : 853
The second division or green schists include foliated gabbro, diabase,
variolite, serpentine and various pyroclastic deposits now filled with
new epidote, uralite, chlorite, saussurite and other secondary products.
They show many points of analogy with the greenstone schist areas of
the Marquette and Menominee districts on Lake Superior. Of more
than usual interest are Schmidt’s descriptions of the chloritic ferru-
ginous odlite of Callovien. This was once a glauconitic odlite of
Jurassic age, whose spherical particles have, by dynamometamorphism,
been flattened, while their iron has crystallized as magnetite and hema-
tite, and their glauconite changed to chlorite. The process of meta-
morphism in the Biindnerschists is summed up by Schmidt as follows:
“The first stage of the metamorphism of the sediments always con-
sists in the development of rutile microliths, as well as isolated and
usually skeleton crystals whose nature depends on the composition of
the metamorphosed material. These new phenocrysts gradually
increase both in number and size; they are always filled with
abundant inclusions of the groundmass whose sedimentary arrange-
ment is not destroyed within the newly formed phenocryst. Finally,
the clastic groundmass is transformed into an aggregate of crystal-
line minerals; and, where the metamorphism is most intense, the
contrast between new phenocrysts and groundmass is least distinct.”
(Us: Go [Do “yp ita))
As a result of both his own and Schmidt’s work, Heim concludes
(l. c. p. 488): 1) that all the demonstrable orographic disturbance,
and hence all the dynamometamorphism within his area, is post-
Eocene, and much of it post-Miocene; 2) that two sorts of meta-
morphism must be distinguished. The recent dynamic metamorphism
which was caused by, and hence was synchronous with orographic
movement ; and the much more ancient and probably still continuous
metamorphism due to heat, inoisture, and simple pressure without
motion, which he calls dagenefic metamorphism (statical metamorphism
of Judd). He contrasts the effects of mechanical metamorphism upon
highly crystalline and sedimentary rocks, in that the same cause
crushes the former into a finely granular schistose series, and recrys-
tallizes the latter by developing large phenocrysts within them. He
attributes these results in his particular Alpine region entirely to
dynamic action, since he can find no trace of’ eruptive material
which could have produced contact metamorphism in rocks of tertiary
age.
854 LTE, JOULNATS OPN GE OLOGY
The regret expressed by Professor Heim at the time of writing
his text that no one had been found to thoroughly investigate the
dynamic phenomena of the Verrucano seems about to be removed by
the work now being published by Dr. L. Milch of Breslau. He has
recently offered as his hadzlitationschrift the first part of his petro-
graphical study of the Verrucano rocks of Graubtinden, which deals
with the historical development of the knowledge of this formation
and the dynamic metamorphism of the eruptive rocks occurring in it.
The second part, to be published later, will treat of the metamorphosed —
sediments and chemical aspects of the whole subject. The basic carbon-
iferous eruptives of the region investigated are all melaphyres belong-
ing to the three types: olivine-weisselbergite, navite and tholeiite ;
in other words old basalts. Some of them are well preserved, and show
clearly the progressive effects of metamorphism with increasing
mechanical disturbance. Some of the rocks are massive and others
amygdaloidal, but the effect of the pressure is finally to destroy all of
their original characters and to produce from them chloritic, epidotic,
sericitic, or carbonate schists, which could just as well have originated
from sediments of the proper composition. The mechanical action
differentiates the originally homogeneous rock into portions of very
different mineralogical composition, which in the most squeezed parts
of a fold form fine parallel layers, but in the less compressed areas are
intimately interlaced. Thus the same orographic force, while it may
produce the same result from rocks genetically very distinct, can also,
on the other hand, produce highly diverse rocks from one and the
same mass.
The acid Carboniferous eruptives of the area studied are quartz-
porphyries, or old rhyolites. Some of these form an important part
of the pebbles in the Verrucano conglomerates, while others occur 77
situ as a contemporaneous part of this formation. The latter rocks
show many points of resemblance with the Windgaille porphyries, con-
sidered by Heim and Schmidt (N. J. B. BB. IV., 1886) as pre-Carbon-
iferous. Milch distinguishes two categories of metamorphic changes
exhibited by these acid eruptives. The first is mainly mechanicad,
consisting of crushing and granulation, and producing fine-grained,
jaspery schists; the second is mainly chemzca/, producing sericite
from the feldspathic constituents which forms interlacing mem-
branes. There is then here observable a complementary relation
between the mechanical and chemical work of dynamometamorphism,
REVIEWS. | 855:
like that pointed out by the present writer in the greenstone-schists
and associated rocks of Lake Superior. (Bull. U. S. Geol. Surv.,
No. 62).
Professor Termier of the Ecole des Mines at Saint-Etienne has given
in his essay on the constitution of the Vanois massif in Savoy, another
excellent contribution to our knowledge of the effects of orographic
movement in metamorphosing Alpine sediments of Caboniferous and
Triassic age. This is all the more welcome from France where
dynamometamorphism has been rather, slow to gain recognition, in
spite even of the convicting demonstrations by Gosselet in the Ard-
ennes. The schistes lustrés, which bound the Vanois massiv on the
east, considered by Lory as upper Triassic, are made by Termier pre-
Carboniferous. The principal horizons which have been studied with
reference to metamorphism are the Permian and Trias. The former is
represented mainly by quartzites and phyllites, altered and recrystall-
ized in proportion to the disturbance they have suffered. In the
phyllites rutile, sphene, tourmaline, garnet, zoisite, epidote, glauco-
phane, chloritoid, various micas and feldspars, and quartz have been
abundantly developed. Many interesting details and figures are given
to illustrate the development of these new minerals. Albite crystals
by their growth in the phyllite have sometimes displaced all, or only a
part of the original schist constituents, while in other cases they have
not disturbed their position at all. Various minerals are traced in
their gradual development from indistinct nodules to perfect crystals.
Only the metamorphism of sedimentary beds is considered, and the
general conclusion is reached that their alteration is independent of
eruptive action, and entirely conditioned by the heat produced by
orographic movements. This heat is supposed to have been very
gradually produced and very slowly dissipated. The author thinks
that a temperature of 200 to 250 C., continued through ages, would
suffice to crystallize new compounds like feldspar, quartz, carbonates,
tourmaline, chlorite, micas, ilmenite, rutile, etc., without affecting the
bulk composition of the rock. In exceptional cases an intenser move-
ment might give a temperature of 300 C., sufficient to produce amphi-
bole, which will appear as glaucophane, if, as in his Permian beds, the
original sediments are very rich in soda.
GEORGE H. WILLIAMS.
856 THE JOURNAL OF GEOLOGY.
Text Book of Geology : By SIR ARCHIBALD GEIKIE, F.R.S. Third edi-
tion, revised and enlarged. Pp. i-xvi, £147.
The preface to the third edition of this standard text-book states
that it has been entirely revised and in some portions recast and
re-written, so as to bring it abreast of the continuous advance of geo-
logical science.
A careful comparison of the third edition with the second indicates
that this claim is fully warranted. ‘The general plan of the volume is
unchanged, but there are few discussions in which modifications do-
not appear. In many places the changes consist of nothing more
than the addition or modification of a sentence or a paragraph. Even
these minor modifications and additions are of great value, since in
them are embodied many of the newer facts and ideas which recent
research has developed. Thus we find the newer estimates of the
average elevation of the continents ; new suggestions concerning the
age of the earth; the introduction of new descriptions of minerals of
petrographical importance, and the modification of some upon which
new light has been thrown by recent investigations ; the adoption of
Rosenbusch’s terms for certain rock structures ; the use of the word
megascopic in place of macroscopic ; a re-arrangement of rocks upon
a genetic basis, as sedimentary, massive or eruptive, and schistose or
metamorphic, and a better subdivision under these heads; throughout
the descriptions of rocks, additions and improvements incorporating
the more essential facts brought out in recent publications. The pos-
sibility of the metamorphic origin of some granites is minimized, and
the probability that the greater number of them are eruptive is empha-
sized ; the processes of metamorphism are elaborated, and the kinds of
mineralization of common occurrence are pointed out. We find,
too, new facts as to the amplitude of earthquake waves; the results
of the more recent mathematical calculations concerning the dis-
tortions of the sea level by the attractive influence of land eleva-
tions ; fuller statements as to the possibility of changes of sea level,
and concerning the causes of oscillations of the level of land and sea ;
the conclusions to which experiment has led concerning the effect of
hot water on the fusion temperature of rock ; new ideas concerning the
flow of rock as the result of crushing and pressure ; clear cut state-
ments growing out of recent discussions concerning the efficiency of
glacial erosion ; a multitude of facts at one point and another drawn
from the reports of the Challenger, and from the reports of other deep
REVIEWS, 857
sea exploring expeditions, as to sedimentation far out from land ; the
results of recent biological investigation touching the supply of lime
carbonate and silica from which animals and plants secure materials
for their shells ; a more explicit statement than the earlier edition con-
tained concerning the complexity of the glacial period ; a modification
of the classification of geological formations of North America, incor-
porating the ideas of the correlation essays of the United States Geo-
logical Survey, etc., etc. The additions and changes concerning these
topics fairly represent the character of the alterations to be found
throughout the volume. These new touches are sufficiently numerous
and suggestive to make the volume valuable, even to those already in
possession of the earlier edition.
At a number of points the changes have been much more consid-
erable. Thus twelve pages were devoted to the discussion of the Arch-
ean in the old edition, while thirty-seven pages are given to the pre-
Cambrian in the new. The general character of the changes at this
point were foreshadowed in an article by Sir Archibald in the first
number of this journal. Two groups of pre-Cambrian rocks are dis-
tinctly recognized, the lower consisting of gneisses and schists, and the
other of the pre-Cambrian sedimentaries and volcanics. The charac-
ter, the relations, and the genesis of these groups is briefly but com-
prehensively set forth. Concerning the first group the conclusion:
reached, as expressed in the author’s own words, is as follows :
“These rocks are in the main various forms of original eruptive
material, ranging from highly acid to highly basic; they form in gen-
eral a complex mass belonging to successive periods of extrusion ; some
of their coarse structures are probably dueto a process of segregation in
still fluid or mobile, probably molten, material consolidating below the
surface; their granulitized and schistose characters, and their folded
and crumpled structures point to subsequent intense crushing and
deformation ; their apparent alternation with limestone and other rocks,
which are probably of sedimentary origin, are deceptive, indicating no
real continuity of formation, but pointing to the intrusive nature of the
gneiss.”
Concerning the second group of pre-Cambrian rocks, the sediment-
ary and volcanic series, Sir. Archibald {takes the same position as in
the article already referred to* and essentially the same position as that
of Prof. Van Hise, already set forth in this journal’ and elsewhere. °
tThis Journal, Vol. I., p. 1.
2\VOllo Mos INO; 25 19s UABs
3 Bulletin 86, United States Geological Survey.
858 THE JOURNAL OF GHOLOGY.
The adoption of any general terminology for the pre-Cambrian
rocks is deprecated. In the author’s judgment, “ the term Laurentian
cannot henceforth have more than a local significance.”’ He further
indicates his belief that “there will be much less impediment to the
progress of investigation by the multiplication of local names than by
the attempt to force indentifications for which there is no satisfactory
basis. Each country will have its own terminology for pre-Cambrian
formations, until some way is discovered of correlating these formations
in different parts of the globe.” The great duration of the time inter- —
val represented by the pre-Cambrian sedimentaries and their great un-
conformities is distinctly recognized. Much fuller details are given in
this than in any earlier edition, concerning the development of the
pre-Cambriah in different parts of the world. On the whole, the
chapter on pre-Cambrian is much more satisfactory than in any other
existing text-book. Several other periods are much more fully dealt
with in this edition. This is especially true of the Silurian and Ter-
tiary. Various new figures of fossils are introduced, representing
important species of recent discovery.
In the section dealing with glacial geology, we notice that no dis-
tinction is made between the formations known in America as kames and
osars, and are a little surprised to find the statement concerning kames
(osars as we know them in America) that ‘no very satisfactory statement
of their mode of origin has yet been given.” Perhaps this may be true
in a restricted sense, since there is much discussion as to the exact
character of the streams which produce them, but that the formations
which we have come to call osars were produced chiefly by superglacial
or subglacial streams, does not seem to admit of serious question, so
far as America is concerned. We are also surprised to find the loess
placed in the recent or post-glacial series. This is not the correct
reference of most of the loess in the United States, for at various points
along the northern border of the very extensive loess covered area, as |
in Illinois and Iowa, the loess is frequently found beneath the till of
the later ice invasions. The eolian theory of the origin of the loess is
favored. ‘This seems to be by far the most satisfactory theory for the
Asiatic loess, and is finding much favor in connection with the loess of
Europe. It is doubtless the loess of these countries to which reference
is especially made. But the points urged in support of the eolian
theory are not all applicable to the American formation. For example,
“the thoroughly oxidized condition” of the iron content of the loess
REVIEWS. 859
cannot be urged in support of its eolian origin on this side of the
Atlantic. Where the loess of the United States is typically developed,
and has any considerable thickness, its iron content is not often thor-
oughly oxidized below a depth of four to six feet- The same is true
of the loess of some parts of Germany. So, too, it may be much more
troublesome to account for the presence of even a few aquatic shells in
an eolian deposit, than for the presence of many land shells in a water
deposit. The frequent inter-stratification of loess and sand at the base
of the formation, the occasional presence in the loess of stone quite
beyond the power of wind to transport, its general habit of following
river courses, the presence of aquatic shells, and its lack of oxidation
and leeching except for a short distance from the surface, are consider-
ations of sufficient weight to make it very doubtful if the larger part of -
the American loess can be due to the wind. On the other hand, we
believe that some (quantitatively a small part) of the loess of the
United States is unquestionably of eolian origin. It has long seemed
possible to the writer that formations may have been grouped together
under this name which have had very different origins at very different
times. This notion is emphasized in the volume before us, where the
adobe of the United States, two or three thousand feet thick, is referred
to as the loess, though this is not the formation commonly known as
loess, and can hardly be one with it in origin. Many new facts are
given concerning glaciation in regions where the work of the ice has
not, until recently, been known.
The incorporation of the great body of new facts and suggestions
throughout the volume has meant the digestion of a large body of
recent literature. Indeed, there appears to have been very little geo-
logical literature produced since the earlier edition of the work of
which the author has not made use, and to which we do not find ex-
plicit reference in the new edition.
ROLLIN D. SALISBURY.
Bodengestaltende Wirkungen der Eiszeit. Vortrag von DR. AuG. BOuM,
Privatdocent an der k. k. technischen Hochschule, Vienna.
The difficulty of finding satisfactory summaries of the physical
features of European countries makes such essays as the above espec-
ially welcome to the American student, particularly if he contemplates
a trip abroad. ‘The essay is one ofa series of lectures, published by
860 LL LO OLIN ATE OL: AGHAOLRO GNA
the Verein sur Verbreitung naturwissenschaftlicher Kenntnisse in Vienna,
now in its thirty-third year. The essays may be had separately, and a
table of contents of the thirtyodd volumes may be procured from the
publisher, Hélzel, for a nominal price ; from this one may select such
numbers as he wishes. Recent volumes contain articles by Suess,
Ueber die Structur Europas, from which the geological traveler may
gain a breadth of view that will greatly profit him ; by Penk, on Das
Oesterreichische Alpenvorland, and Die Donau (Danube), from which
more local views “may be gathered of equal value in closer studies.
Dr. Bohm’s essay is a well-argued presentation of the belief that even
the greater Swiss lakes, as well as nearly all the smaller ones, are the
result of glacial erosion. He justly emphasizes the moderate propor-
tion of depth to length in even the deepest of the marginal lakes ; and
the location of these lakes with respect to the greater glacier which
formerly emerged from the Alpine valleys on the Piedmont districts.
Even in those valleys where no marginal lakes now exist, as in the valleys
of the Lech, Inn, Salzach, and others, rivers emerging from the north-
eastern Alps, there have recently been lakes, but their basins are now
filled and drained by the active streams that traverse them. The high
level lakes, held in rock basins and enclosed by mountain cirques
(Karen), are with even more confidence ascribed to glacial action.
Many of the smaller lakes have been extinguished already since the
glacial period. In the Tyrol, no less than 118 lakes recorded on the
maps of the last century, are nowdrained. In this relation, the Alpine
valleys seemed to have advanced further towards recovery from the
glacial accident to which they have been subjected than the Norwegian
streams; for in Norway, many a river is still only a string of lakes.
It is notable that drumlins are not mentioned by Dr. Béhm as char-
acteristic products of glacial action ; hence we must infer that they are
seldom seen in Continental Europe. Wo. M. Davis.
ANALYTICAL ABSTRACTS OF “CURRENT
ILI RATNUURIE.
Conditions of Appalachian Faulting. By Baitey Wiis and C. WIt-
LARD Haves. (Amer. Jour. of Sci. Vol. XLVI., pp. 257-260).
The cross section of a great mass of sediments accumulated over a zone
parallel to the shore is that of a bi-convex lense. One edge rests against the
shore from which the mass at first thickens rapidly and then thins gradually
seaward. A broad shallow trough is thus formed by the deeper strata which
may be called an original syncline. The authors give data to show that pre-
vious to compression such original synclines of deposition existed in the
paleozoic strata of the Appalachians in Pennsylvania, east Tennessee, north-
west Georgia, Alabama and in other localities.
In the original synclines of the Appalachian province the steeper seaward
dip was northwestward and the gentler shoreward dip was southeastward.
If strata in such a position be subjected to sufficient compressive force, the
original syncline will be exaggerated and the steeper shorter arm will be
rotated as between the forces of a couple. If compression is continuous
long enough the beds may be overturned.
From this stepfold a thrust-fault may develop in either of three ways. The
pressure tending to exaggerate the fold is most efficiently transmitted by
the most massive stratum, and any condition which weakens this stratum may
lead toa fault. The three conditions under which this massive stratum
may be weakened are erosion, fracture, plastic flow; the second being the
most common in the Appalachian region, where the massive stratum seems
to have fractured, forming thrusting faults under loads of 2,800 to 11,000
pounds per square inch, but to have folded without breaking under loads of
11,000 to 34,000 pounds per square inch.
The authors discuss with the aid of diagrams the mechanics of repeated
parallel folds, and show that the parallel folds are later than that located by
the original syncline, and are consequent each upon the next preceding it in
time and position. In the Appalachians the compressing force was directed
both northwestward and southeastward. But when folding began there was a
movement from the force towards the resistance. This the authors conceive
to have been a superficial flow of a broad zone from northwest to southeast,
from the sea towards the land. Jals JIBS LS
861
862 THE JOURNAL OF GEOLOGY.
Ueber Geroll- Thonschiefer glacialen Ursprungs in Kulm des Franken-
waldes. By ERNST KaLKowsky in Jena (Zeitschrift der Deut-
schen geologischen Gessellschaft. XLV. Band. 1. Heft. Jan-
uar, Febuar und Marz, 1893, pp. 69-86.) ;
In the midst of the shales and greywackes of the Upper Kulm of Frank-
enwald, there is a peculiar sort of conglomerate (gev0//-thonschiefer). This
conglomerate is exposed at but few points. It is not certain that all the
exposures belong to one horizon, though nothing is known which forbids this
conclusion. The demarkation of the conglomerate from the underlying and |
overlying beds is sometimes, but not always, distinct. The conglomerate has
a known thickness at one point of at least 18 m. It is wholly unstratified, and
is made up of something like equal parts of clayey matter, and well-rounded
stones (gevd//en). The sand grains are conspicuously angular, while the larger
stones are as distinctly well-rounded. Inno case do the sandy or stony mate-
rials show any traces of arrangement suggestive of stratification.. The
stony material varies in size from pebbles to small boulders, the largest being
22 X29 X12 c.m. In connection with these limitations in size it must be
remembered that the exposures are very limited. While it is difficult to
determine the origin of the stony material in all cases, it does not seem
necessary to suppose that it is of very distant origin. The author considers
the various possibilities concerning the origin of this conglomerate, and con-
cludes that it is the work of rivers which were affected by floating ice. The
conglomerate is therefore an indication of cold climate in the adjacent
regions at the time of its formation. The author thinks that the Carbon-
iferous ice period, belief in which seems not to be without foundation, may be
brought into connection with the cold climate indicated by this conglomerate
bed in the upper Kulm. He further thinks that the cold climate of the Kulm
may have made itself felt over wide areas, since more or less extensive con-
glomerate beds of this age occur in widely separated parts of the German
Empire. IRDA S),
ACKNOWLEDGMENTS.
The following papers have been donated to the library of the Geological Depart-
ment of the University of Chicago, mainly by their authors:
ANDREA, A., AND C. A. TENNE.
—Ueber Hornblendekersantit und den Quarzmelaphyr von Albersweiler R—
Pf. 2 pp.—Zeit. d. Deut. geolog. Gesell., 1832.
BARROIS, CHARLES.
—Mémoire sur la Distribution des Graptolitesen France. 75-194 pp.—Extrait
des Annales de la Société Géologique du Nord, March 23, 1892.
BEACHLER, CHARLES S.
—Erosion of Small Basins in Northwestern Indiana during the ‘Time preceding *
the Pleistocene Period. 3 pp.—Am. Geol., Vol. XII, July, 1893.
BERGHELL, Hueco.
—Geologiska iakttagelser, hufondsakligast af qvartarfildningarna, langs Karel-
ska jernvagens tva forsta distrikt och Imtrabanan. 33 pp-, I map, 2 pl.—Fennia,
4, 5, Helsingfors, 1891.
—Geologiska iakttagelser langs Karelska jarnvagen. 18 pp-, I map, 1 pl.—
Fennia, 5, 2, Helsingfors, 1892.
—Huru bor Tammerfors-Kangasala asen uppfattas? 10 pp., I map.—Fennia,
5, 3, Helsingfors, 1892.
BELL, ROBERT, B.A.Sc., M.D., LL.D.
—The “Medicine-Man”; or Indian and Fskimo Notions of Medicine. 13 pp.
—Can. Med. and Surg. Jour., March-April, 1886.
—Eskimo of Hudson’s Strait (by F. F. Payne). 18 pp.—Extr. Proc. of Can.
Inst., 1889.
—Notes on Diseases among the Indians frequenting York Factory, Hudson’s
Bay (by Percy W. Mathews, M.R.C.S.E., M.R.C.P., Lond., Medical Officer to
Hudson’s Bay Company). 20 pp.
—KRemarks on the Distinctive Characters of the Canadian Spruces—Species of
Picea (by George Lawson, Ph.D., LL.D., F.R.S.C.) 12 pp.
—Report of the Hudson’s Bay Expedition of 1886 under the command of
Lieut. A. R. Gordon, R. N. 133 pp., 4 maps, 2 IIL.
—The Mineral Resources of the Hudson’s Bay Territories. 9 pp-—Trans. Am.
Inst. of Min. Eng., Pittsburgh Meeting, Feb. 1886.
—The Causes of the Fertility of the Land in the Canadian North-West Terri-
tories. 156-162 pp.—Trans. Roy. Soc. Can.
—The Geology and Economic Minerals of Hudson Bay and Northern Canada.
241-245 pp.—Trans. Roy. Soc. Can.
863
/
864 VOORNAL OPE GTEOLGOGNE
—Notes on the Birds of Hudson’s Bay. 49-54 pp.—Trans. Roy. Soc. Can.
—The Forests of Canada. 15 pp.—Record of Sci., Vol. II, No. 2, 1886.
—The Geographical Distribution of the Forest Trees of Canada. 21 pp., I
map.—Rep. of the Surv., 1880.
—The Huronian System in Canada. 13 pp.—Presidential Address, Roy. Soc.
" Can., May 22, 1888.
—The Petroleum Field of Ontario. 101-113 pp.—Trans. Roy. Soc. Can.
—Alexander Murray, F.G.S., F.R.S.C., C.M.G. 96 pp.—Can. Rec. of Sci.,
April, 1892.
—A Plea for Pioneers. 3 pp.
—Case of Progressive Pernicious Anemia. 12 pp.
—Charts showing the Mean, Monthly and Annual Temperatures of Hudson’s ©
Bay and Eastern Canada, Oct. 1885—Sept. 1886 (by Andrew R. Gordon). 14 pp.
—Forest Fires in Northern Canada. 7 pp.—Rep. Forestry Congress, Atlanta,
Dec. 6, 1889.
—Marble )sland and the North-West Coast of Hudson’s Bay. 15 pp.—Proc.
Can. Inst., Toronto.
—On Glacial Phenomena in Canada. 237-310 pp.—Bull. Geog. Soc. of Am.,
Vol. I.
—On Some Points in Reference to Ice Phenomena. 85-91 pp.—Trans. Roy.
Soc. of Can., Vol. IV, Sec. III, 1886.
—Report on the Geology of Manitoulin Island. 15 pp.—Report of Progress
of Geol. Surv. of Can., 1863-1866.
—The Geology of Sudbury District. 95 pp.—Report on Sudbury Mining Dis-
trict, 1888-1890.
—The Laurentian and Huronian Systems in the Region North of Lake Huron.
34 pp.—Report of the Bureau of Mines, Ont.
BLOMSTRAND, C. W.
—Om Monaziten Fran Ural. 26 pp.
BEYER, SAMUEL W.
—Ancient Lava Flows in the Strata of Northwestern Iowa, 165-160 pp.
Borm, MM. G.
—Extrait du Bulletin de la Société Géoligique de France. 403-414 pp.—3 sérié,
t. XV, p. séance du 7 mars. 1887.
Boone, RICHARD G.
—Results under an Elective System. Part I, 53-73 pp., Part II, 142-156 pp.—
N. Y. Ed. Rev.
BRIGHAM, ALBERT P.
—The Finger Lakes of New York. 21 pp.—Bull. Am. Geog. Soc., Vol. XXV.
No. 2, 1893.
Brown, H. Y. L.
—On Additional Silurian and Mesozoic Fossils from Central Australia (by R.
Etheridge, Jr.) 8 pp.—Geol. Sur. New South Wales.
CADELL, HENRY M., B.Sc., F.R.S.E.
—The Yellowstone Region and its Geysers. 16 pp., Ill., Sketch-map.—Read
at the Meetings of Soc., Edinburgh and Glasgow, March and April, 1892.—Scot.
Geog. Mag., May, 1892.
ACKNOWLEDGMENTS. 865
—SsSome Ancient Landmarks of Mid-Lothian. Ir pp., I map.—Scot. Geog.
Mag., June, 1893.
—The Occurrence of Plant Remains in Olivine Basalt in the Bo’ness Coalfield.
191-193 pp., I pl.—Trans. Roy. Soc. Edin., 1892, Vol. VI.
—Geology as a Branch of Technical Education. 209- pp., Ilustrated.—Lec-
ture at the Opening of the Class of Geology in the Heriot-Watt College, Edin.,
Novy. 4, 1887.
—The Breadalbane Mines (and J. S. Grant Wilson). 189-207 pp., 2 pl.—
Proc. Roy. Phys. Soc., Edin., Vol. VIII, 1884.
—A Visit to the Coal, Oil and Anthracite Districts of Pennsylvania, August,
1891. 24 pp.—Read before the Min. Inst. of Scot. Nov. 21, 1891.
—The Utilization of Waste Lands. 14 pp.—Scot. Geog. Mag., July, 1888.
—The Dumbartonshire Highlands. 11 pp., 1 map.—Scot. Geog. Mag., 1886.
—Experimental Researches in Mountain Building. 337-356 pp., Illustrated.
—Trans. Roy. Soc., Edin., Vol. XXXV, Part 7.
CLAYPOLE, E. W., B.A., D.Sc. (Lonp.), F.G.S.
—On the Structure of the American Pteraspidian, Paleeaspis. 542-561 pp.,
Ilustrated.—Quart. Jour. Geol. Soc., Lond., Vol. XLVIII, 1892.
—The Head of Dinichthys. 203-207 pp., Lllustrated.—Am. Geol., Vol. X
Oct. 1892.
Corr ED
—Descriptions of some Extinct Fishes previously unknown. 310-316 pp.—
Proc. Acad. Nat. Sci., Phila,, 1855.
CANAVARI, MARIO.
—Idrozoi titoniani della regione mediterranea appartenenti alla famiglia delle
Ellipsactinidi. 57 pp., 5 pl.—R. Comitato Geologico d’ Italia, Vol. IV, Parte
seconda.
CUSHING, H. P., AND E. WEINSCHENK.
—Zur genauen Kenntnis der Phonolithe des Hegaus. Separat-Abdruck aus
Tschermak’s Mineralogischen und Petrographischen Mittheilungen. 38 pp.
DENISON, CHARLES, A.M., M.D.
—Abnormal Intra-Thoracic Air-Pressures and their Treatment. 41 pp., Ilus-
trated.—Address at the Seventh Annual Meeting of the Am. Climatological
Assoc., Sept. 2, 1890.
EYERMAN, JOHN, F.Z.S., F.G.S.A.
—On a Collection of Tertiary Mammals from Southern France and Italy; with
brief descriptions thereof. 159-165 pp.—Am. Geol., Vol. XII, Sept. 1893.
FERRIER, W. F., B.A.Sc., F.G.S.
—Notes on the Microscopical Character of some Rocks from the Counties of
’
Quebec and Montmorency. 10 pp.
FAIRCHILD, HERMAN LE Roy.
—Proceedings of the Fourth Annual Meeting of the Geological Society of
America, held at Columbus, O., Dec. 29, 30,31, 1891. 454-541 pp., 3 pl.—Bull.
Geol. Soc. Am., Vol. III. 7
GANNETT, HENRY.
—The Movements of our Population. 44 pp., Ill—Nat. Geog. Mag., March
20, T8093.
— 866 JOWURNAT OF (GEOLOGY:
GRESLEY, W. S., F.G.S.
—On the Occurrence of Fossiliferous Hzematite Nodules in the Permian Brec- —
cias in Leicestershire. 24 pp., 1 pl.—Mid. Nat., 1886.
—The Occurrence of Variegated Coal-measures, Altered Iron-stones, etc., at
Swadlincote, Derbyshire. 115-117 pp.—Extr. Geol. Mag., Dec. IH, Vol. V, No.
3, 1888.
—Specimens from the Permian Breccia of Leicestershire, collected by W. S.
Gresley, Esq., F.G.S. (by Professor T. G. Bonney). 20 pp.—Mid. Nat., Vol. XV.,
Feb. and March, 1892.
—Re “Explosive Slickensides.” 572-573 pp.—Extr. Geol. Mag., Dec. III,
Vol. IV, No. 11.
—On a Modern Ferruginous Conglomerate upon Ashby Wolds, Leicestershire. —
11-12 pp.—Extr. Geol. Mag., Dec. III, Vol. III, No. 1, Jan. 1886.
—On the Occurrence of Boulders and Pebbles in the Coal Measures. 12 pp.,
Ill.—Trans. Manchester Geol. Soc.
—Notes on the Formation of Coal Seams. 8 pp.—Quart. Jour. Geol. Soc.,
Nov. 1887. j
—North American Geological Notes. 7 pp.—Trans. Manchester Geol. Soc.,
Part II, Vol. X XI.
—Formation of Coal-beds. 8 pp., Ill.—Mid. Nat., Feb. 1880.
—Boulders in a Coal-seam. 553-555 pp.—Geol. Mag., Dec. III, Vol. II, No.
12, Dec. 1885.
—A Typical Section, taken in Detail, of the ‘Main Coal” of the Moira, or
Western Division of the Leicestershire and South Derbyshire Coalfield. 15 pp.,
Ill.—Trans. Manchester Geol. Soc., March’8, 18092.
—A Fossil Tree at Clayton, Yorkshire. 229-232 pp., Illustrated.—Mid. Nat.,
Sept. 1886.
—A Hitherto Undescribed Phenomenon in Hematite. 219-223 pp., Illus-
trated.—Am. Geol., April, 1892.
—A Fossil Tree at Clayton, Yorkshire. 229-232 pp., Illustrated.—Mid. Nat.,
Sept. 1886.
HAZEN, HENryY A., A.M.
—The Reduction of Air-Pressure to sea level, at Elevated Stations West of
the Mississippi River. 42 pp., 20 Illustrated.—War Dep’t, 1882.
HINDE, GEORGE J., PH.D., F.G.S.
—A New Ordovician Sponge. 3 pp., ll.—Geol. Mag., Dec. III, Vol. X, No.
344, Feb., 1893.
—Notes on Radiolaria from the Lower Palaeozoic Rocks (Llandeilo-Caradoc) of
the South of Scotland. 40-59 pp., 2 pl.—Annals and Mag. Nat. Hist., July, 1890.
—Note on a Radiolarian Rock from Fanny Bay, Port Darwin, Australia. 221-
226 pp., I pl.—Quart. Jour. Geol. Soc., Vol. XLIX, May, 1893.
—QOn a Radiolarian Chart from Mullion Island (by Howard Fox, Esq., and J.
J. H. Teall, Esq.) 211-218 pp., 1 pl.—Quart. Jour. Geol. Soc., Vol. XLIX, May,
1893.
HENNIG, ANDERS.
—Studier ofver bryozverna i Sveriges Kritsystem. I Cheilostomata. 49 pp.,
2 pl.
ACKNOWLEDGMENTS. 867
HENNING, ERNST. f
—Agronomiskt-Vaxtfysiogwomiska Studier. 34 pp.
Lawson, ANDREW C.
—I. The Anorthosytes of the Minnesota Coast of Lake Superior. 24 pp.,
7 pl.—Bull. No. 8, Geol. and Nat. Hist. Surv. of Minn., II. The Laccolitic Sills
of the Northwest Coast of Lake Superior. 24 pp., Ilustrated.—Bull. No. 8, Geol.
and Nat. Hist. Sury. of Minn., with Prefatory Note on the Norian of the North-
west (by N. H. Winchell). 34 pp.—Bull. No.8, Geol. and Nat. Hist. Surv. of Minn.
LESQUEREUX, LEO.
—Recent Determinations of Fossil Plants from Kentucky, Louisiana, Oregon,
California, Alaska, Greenland, etc., with description of new species. 11-38 pp.,
12 pl.—Proc. U. S. Nat. Mus., 1888.
LINDGREN, WALDEMAR.
—Two Neocene Rivers of California. 258-298 pp.—Bull. Geol. Soc. Am., Vol.
TV, June, 1893.
LOw1L, Dr. FERDINAND,
—Uber Thalbildung. 136 pp.
LUNDBOHM, HJALMAR.
—Om Berggrunden i Vesternorrlands kusttrakter. 321-326 pp.
—QOm Granitindustrien 1 Utlandet Sarskildt Storbritannien. 61 pp., 1 pl.
—Geschiebe aus der Umgegend von Konigsberg in Ostpreussen.
—Verzeichniss einer Sammlung Ost und Westpreussischer Geschiebe. 84-92 pp.
—Engelska Byggnadsmaterial och Byggnadssatt samt de senares tillamplighet
i sverige. 46 pp., 3 pl. ;
Apatitforekomster 1 Gellivare Malmberg och Kringliggande Trakt. 48 pp., 3 pl.
—Apatitforekomster i Norrbottens Malmberg. 38 pp.
MILLER, 5. A.
—Description of New Species of Fossils. 9 pp., 4 pl.—Jour. Cin. Soc. Nat.
Hist., July, 1882.
PENFIELD, S. I.
—On Pentlandite from Sudbury, Ontario. 493-497 pp.—Am. Jour. Sci., Vol.
XLV, June, 1893.
—On Cookeite from Paris and Hebron, Maine. 393-399 pp.—Am. Jour. Sci.,
Vol. XLV, May, 1893.
PHINNEY, ARTHUR JOHN. :
—The Natural Gas Field of Indiana. 590-742 pp., 5 pl.—Extr. Eleventh An-
nual Report of the Director, 1889-1890.
PILLING, JAMES CONSTANTINE,
—Bibliography of the Athabascan Languages. 125 pp.—Bureau of Ethnology.
PIRSSON, L. V.
—Note on some Volcanic Rocks from Gough’s Island, South Atlantic. 380-
384 pp.—Am. Jour.’Sci., Vol. XLV, May, 1893.
—Datolite from Loughboro, Ontario. 101-102 pp.—Am. Jour: Sci., Vol. XLV,
Feb. 1893.
PITTIER, H.
—Annales del Instituto Fisico-Geographico y del Museo Nacional de Costa
Rica. Tome III.—1890. 162 pp.
868 JOURNAL ODGEOLOGY:
PROSSER, CHARLES S. é
—Quarterly Report of the Kansas State Board of Agriculture. 158 pp.
QUEREAU, EDMUND CHASE, PH.D.
A Study in Geology. 30 pp., 3 pl.—From Rep. Dep’t Nat. Hist. in the Col-
lege of Liberal Arts, Northwestern University, 1892.
—Vorlaufige Mitteilung tiber die Klippenregion von Iberg. 553-557 pp.—Zeits.
der Deutsch. geolog. Gesell. Sitzung in Strassburg, Aug. 1892. ~
REDWAY, JACQUES W.
—A Problem in River Hydrography. 31 pp.—Proc. Eng. Club. Phila.
—Climate and the Gulf Stream. 237—242.—Forum, Oct. 1890.
—The Influence of Rainfall on Commercial Development. 14 pp.—Proc. Eng. |
Club, Phila., Vol. IX, No. 4, Oct. 1892.
—The Physical Geography of the United States. 791-817.—Prepared for the
popular reprint of the Encyclopedia Britannica.
—Report on the Treatment of Tailings by the Lithrig System (by J.C. New-
berry). 18 pp., 4 pl.—Dep’t of Mines, Victoria.
RUTLEY, FRANK, F.G.S.
—Notes on Crystals of Manganite from Harzgerode. 2 pp.—Muin. nee Vol.
X, No. 45.
—On Composite Spherulites in Obsidian, from Hot Springs, near Little Lake,
California. 423-428 pp., 1 pl—Quart. Jour. Geol. Soc., Aug. 1890.
—On a Spherulitic and Perlitic Obsidian from Pilas, Mexico. 530-533 pp.,
1 pl.—Quart. Jour. Geol. Soc., Nov. 1891.
—On Fulgurites from Monte Viso. 60-66 pp., 1 pl.—Quart. Jour. Geol. Soc.,
Feb. 1889.
—On the Microscopic Structure of Devitrified Rocks from Beddgelbert and
Snowdon. 403-413 pp., 1 pl.—Quart. Jour. Geol. Soc., Aug. 1881.
—On Community of Structure in Rocks of Dissimilar Origin. 327-341 pp.—
Quart. Jour. Geol. Soc., May, 1879.
—The Dwindling and Disappearance of Limestones. 372-384 pp., I pl.—
Quart. Jour. Geol. Soc., Aug. 1893.
—The Microscopic Characters of the Vitreous Rocks of Montana, U. S. A.
391-402 pp., 1 pl.—Quart. Jour. Geol. Soc., Aug. 1881.
SALISBURY, ROLLIN D.
—Surface Geology. Report of Progress, 166 pp.—Geol. Sury. of N. J., 1892.
SHELDON, E, S.
—The Origin of the English Names of the Letters of the Alphabet. 66-87 pp.
Read at the Meeting of the Modern Language Conference of Harvard Univer-
sity, Dec. 15, 1890.
SHUMARD, GEORGE G.
—Artesian Water on the Llano Estacado. 9 pp.—Bull. No. 1, Geol. Surv. of
Texas.
~—Report and Analyses of Texas Sumach (by George H. Kalteyer). 77 pp.—
Bull. No. 1, Geol. Surv. of Texas.
SMITH, EUGENE ALLEN, PH.D.
—Sketch of the Geology of Alabama. 36 pp.
ACKNOWLEDGMENTS. 869
STEVENSON, JOHN J.
—John Strong Newberry. 15 pp.—Am.Geol., Vol. VI, July, 1893.
—Transactions of the Royal Society of South Australia. Vol. XIII, Part I,
June, 1890. Tenth Annual Report of the Trade and Gonommeres of Minneapolis for
the year ending December 31, 1892. =
—The American Geologist. Vol. XII, No. 4, Oct. 1893.
TYRRELL, JOSEPH B.
— Foraminifera and Radiolaria from the Cretaceous of Manitoba. 111-115 pp.
—Trans. Roy. Soc. Can., 1890.
U. S. DEPARTMENT OF AGRICULTURE.
—Report on the Forecasting of Thunder Storms during the Summer of 1892
(by N. B. Conger). 54 pp., 5 maps.—Bull. No. 9, Weather Bureau.
—Report of the First Annual Meeting of the American Association of State
Weather Services. 49 pp.——Bull. No. 7, Weather Bureau.
VopcEs, A. W.
—On the North American Species of the Genus Agnostus. 377-396 pp., 2 pl.—
Am. Geol., Vol. IX, June, 1892.
—A Monograph on the Genera Zethus, Cybele, Encrinurus and Cryptonymus.
35 PP- 4 pl.
WARD, LESTER F.
—The Palzontologic History of the Genus Platanus. 39-42 pp., 6 pl.—Proc.
U.S. Nat. Mus.
WHITTLE, CHARLES Livy.
An Ottrelite-bearing Phase of a Metamorphic Conglomerate in the Green
Mountains. 270-277 pp.—Am. Jour. Sci., Vol. XLIV, Oct. 1892.
WHITE, C. A., M.D.
—Remarks upon certain Carboniferous Fossils from Colorado, Arizona, Idaho,
Utah and Wyoming, and certain Cretaceous Corals from Colorado. 209-221 pp.—
Bull. of Suv., Vol. V, No. 2.
—Memoir of Amos Henry Worthen (1813-1888). 341-362 pp.—Read before
the Nat. Acad., 1893.
WHITEAVES, J. F., F.G.S.
—Hlustrations of the Fossil Fishes of the Devonian Rocks of Canada. Part I,
1OI-I10 pp., 4 pl.; Part I, 77-96 pp. 5 pl.—Trans. Roy. Soc. of Can., Vol. VI.
Sec. 4, 1888.
WILLIAMS, GEORGE H.
The Non-feldspathic Intrusive Rocks of Maryland and the Course of their
Alteration. 35-49 pp., Ill—Am. Geol., July, 1890.
—On the Serpentine (Peridotite) occurring in the Onondaga Salt-group at
Syracuse, N. Y. 137-145 pp.—Am. Jour. Sci., Vol. XXXIV, Aug. 1887.
—The Geology of Fernando de Noronha. Part I (by John C. Branner). 145-
161 pp., Ill.—Am. Jour. Sci., Vol. XXXVII, Feb. 1889. Part II, Petrography.
178-189 pp.—Am. Jour. Sci., Vol. XXXVII, Feb. 1880.
—Notes on some Eruptive Rocks from Alaska. 63-73 pp.—Nat. Geog. Mag.,
Vol. IV.
—Piedmontite and Scheelite from the ancient Rhyolite of South Mountain,
Pennsylvania. 50-57 pp.—Am. Jour. Sci., Vol. XLVI, July, 1893.
870 JOURNAL OF GEOLOGY.
—On the Hornblende of St. Laurence County, N. Y., and its Gliding Planes.
352-358 pp.—Am. Jour. Sci., Vol. XX XIX, May, 1890.
—Note on Some Remarkable Crystals of Pyroxene from Orange County, N. Y.
275-276.—Am. Jour. Sci., Vol. XXXIV., Oct. 1887.
—Celestite from Mineral County, West Virginia. 183-187 pp.—Am. Jour.
Sci., Vol. XXXIX, March, 1890.
—Colestin von Mineral County, West Virginia. 6 pp.—Zeit. fiir Krystallo-
graphie, etc., XVIII. Leipzig, Wilhelm Engelmann, 1890.
—Cause of the apparently Perfect Cleavage in American Sphene (Titanite).
486-490 pp.—-Am. Jour. Sci., Vol. XIX, June, 1885.
—Anglesite, Cerussite and Sulphur from the Mountain View Lead Mine, near _
Union Bridge, Carroll County, Md. 6 pp.—Johns Hopkins Univ. Cir., No. 87.
—On a Remarkable Crystal of Pyrite from Baltimore County, Md.—Johns
Hopkins Univ. Cir., No. 52, 1886.
—Syllabus of Lectures on Optical Crystallography. 6 pp.
—Note on Crystals of Metallic Cadmium. 273-276 pp.—Am. Chem. Jour.,
Vol. XIV, No. 4.
—On the Crystal Form of Metallic Zinc. 8 pp., 2 pl—Am. Chem. Jour., Vol.
Il, No. 4.
—Contributions to the Mineralogy of Maryland. 9 pp.—Johns Hopkins Uniy.
Cites INI@s 3/5.
—On the Possibility of Hemihedrism in the Monoclinic Crystal System, with
especial reference to the Hemihedrism of Pyroxene. 115-120 pp., Ill.—Am.
Jour. Sci., Vol. XX XVIII, Aug. 1889.
—Note on Quartz-Bearing Gabbro in Maryland (by Ulysses Sherman Grant).
4 pp.—Johns Hopkins Univ. Cir. No. 103.
—On a Petrographical Microscope of American Manufacture. 114-117 pp.
—Am. Jour. Sci., Vol. XX XV, Feb. 1888.
——A New Machine for Cutting and Grinding thin Sections of Rocks and
Minerals. 102-104 pp.—Am. Jour. Sci., Vol. XLV, Feb. 1893.
—The Volcanic Rocks of South Mountain in Pennsylvania and Maryland.
482-496 pp., I map, 1 pl.cAm. Jour. Sci., Vol. XLIV, Dec. 1892.
—Some Modern Aspects of Geology. 640-648 pp.—Pop. Sci. Monthly, Sept.
1889.
—The Geology of Washington and Vicinity \by W J McGee). 38-64 pp.—
Int. Cong. of Geol., fifth session, 1891.
—On the Use of the Terms Poikilitic and Micropoikilitic in Petrography. 176—
179 pp.—Jour. of Geol., Vol. I, No. 2, Feb.—March, 1893.
—Die Eruptivgesteine der Gegend von Triberg im Schwarzwald. 54 pp., 2 pl.
Baltimore American Institute of Mining Engineers. 139 pp., 3 maps.—Am.
Inst. Min. Eng., Baltimore Meeting, Feb. 1892.
—Contributions to the Geology of the Cortlandt Series, near Peekskill, N. Y.
259-269 pp., Ill.—Am. Jour. Sci., Vol. XXVIII, Oct. 1884.
—A Summary of Progress in Mineralogy and Petrography in 1885. 296-
1216 pp.—Am. Nat., 1866.
—QOn a New Plan proposed for future work upon the Geological map of the
Baltimore Region.—Abstr. from Balt. Nat. Club, May 18, 1887.
ACKNOWLEDGMENTS. 871
—Geology of Baltimore and Vicinity. Part I. Crystalline Rocks. 77-124 pp.,
imap. Part II. Sedimentary Rocks (by N.\H. Darton). 125-139 pp., 1 map.—
Extr. Guide Book of Balt., Feb., 1892.
—Modern Petrography. 35 pp.
—Geological and Petrographical Observations in Southern and Western Nor-
way. 551-553 pp.—-Bull. Geol. Soc. Am., Vol. I.
—Notes on the Eruptive Origin of the Syracuse Serpentine. 533-534 pp.—
Bull. Geol. Soc. Am., Vol. I.
—The Nickel and Copper Deposits of Sudbury District, Canada (by Robert
Bell). 125-137 pp.—Bull. Geol. Soc. Am., Vol. II,
—-On the Serpentine of Syracuse, N. Y. 232-233 pp.—Sci., Vol. IX, No. 214,
March 11, 1887.
—The Microscope and the Study of the Crystalline Schists. 2 pp.—Sci., Vol.
XXI, No. 518, Jan. 6, 1893.
—On a Geological Excursion iu the Northern pbpelachian Chain. 27-28 pp.—
Johns Hopkins Uniy. Cir., Vol. X, No. 84.
—Maps of the Territory included within the State of Maryland, especially the
vicinity of Baltimore. 37-45 pp.—Johns Hopkins Univ. Cir., Vol. XII, No. 103.
WINSLOW, ARTHUR.
—The Geology and Mineral Products of Missouri. 14 pp., Ill.
(further acknowledgments of pamphlets already received will be made in the next number.)
VN DES fo VOLGILE
Abbott, C. C. Recent Archzological Explorations in the Valley of the Dela-
Acknowledgments. - —— - > 5 5 ~ I0T, 209, 315, 423,
ware. (Abstract). - - - 2 2 E S
Adams, Frank D. On the Typical Laurentian Area of Canada. - -
ANALYTICAL ABSTRACTS OF CURRENT LITERATURE.
Andes.
A New Teniopteroid Fern and its Allies. David White. - -
The Age of the Earth. Clarence King. - - - -
The Age of the Earth. Warren Upham. - - pee
The Catskill Delta in the Post-Glacial Hudson Estuary. W. M. Davis.
The Climate of Europe during the Glacial Epoch. Clement Reid. -
Conditions of Appalachian Faulting. Bailey Willis and C. Willard
Hayes. - - - - - - - 3
Continental Problems. G. K. Gilbert. - - - -
The Correlation of Moraines with Raised Beaches of Lake Erie. Frank
Leverett. - - - - - - -
Deep Sea Sounding. A. S. Barker. - - - -
The Drainage of the Bernese Jura. A. F. Foerste. - - -
Geographic Development of the Eastern Part of the Mississippi Drainage
System. Louis G. Westgate. - - - - -
Geological Survey of Alabama. Bulletin 4. C. W. Hayes. - -
Measurement of Geological Time. ‘T. Mellard Reade. - -
Observations and Experiments on the Fluctuations in the Level and Rate
of Movement of Ground-water. F. H. King. - -
On a New Order of Gigantic Fossils. Edwin H. Barbour. - -
On the Glacial Period and the Earth Movement Hypothesis. James
‘Geikie. - - - - - - - -
Rainfall Types of the United States. Gen. A. W. Greeley. - -
Recent Archeological Explorations in the Valley of the Delaware.
Chas. C. Abbott. - - - - - - :
Studies in Structural Geology. Bailey Willis. - - =
Summary of Current Pre-Cambrian North American Literature, with
Comments. C. R. Van Hise. - - - 304,
The Sub-glacial Origin of Certain Eskers. W.M. Davis. - -
Ueber Geréll-Thonschiefer glacialen Ursprungs in Kulm des Franken-
waldes. Ernst Kalkowsky. - - - - - -
The Vertical Relief of the Globe. Hugh Robert Mill. - -
The Volcanic Rocks of the Andes. J. P. Iddings. - - -
Anthracite. On the Origin of Pennsylvania Anthracite. John J. Stevenson.
il
iv INDEX LO? VOLOME Tf,
Archean. On the Pre-Cambrian Rocks of Great Britain. Sir Archibald
Geikie. - - - - - - - - -
Backstrom, Helge. Causes of Magmatic Differentiation. - = =
Baraboo. Some Dynamic Phenomena shown by the Baraboo Quartzite Ranges
of Central Wisconsin. C. R. Van Hise. - - fies -
Barbour, Edwin H. On aNew Order of Gigantic Fossils. (Abstract). -
Barker, A.S. Deep-SeaSounding. (Abstract). - - :
Bascom, F. The Structures, Origin, and Nomenclature of the Acid Volcanic
Rocks of South Mountain. - - - 2 :
Basic Massive Rocks of the Lake Superior Region. W.S. Bayley. - = R9)
Bayley, W. S. Sketch of the Present State of Knowledge concerning the
Basic Massive Rocks of the Lake Superior Region. - - -
The Basic Massive Rocks of the Lake Superior Region. - BAL.
Branner, John C. ‘The Supposed Glaciation of Brazil. - - = :
Brazil. The Supposed Glaciation of Brazil. John C. Branner. - -
Canada. On the Typical Laurentian Area of Canada. Frank D. Adams.
Causes of Magmatic Differentiation. Helge Backstrom. - - -
Chamberlin, T. C. The Horizon of Drumlin, Osar, and Kame Formation.
The Nature of the Englacial Drift of the Mississippi Basin. is
Connecticut. Some Rivers of Connecticut. Henry B. Kummel. - -
The Geological Structure of the Housatonic Valley Lying East of Mount
Washington. Plates V, VI, VII. Wm. H. Hobbs. - - -
Consanguinity of Eruptive Rocks. Orville A. Derby. - - -
Contact between the Lower Huronian and the Underlying Granite in the Repub-
lic Trough, near Republic, Michigan. Henry L. Smyth. - -
Cordilleran Mesozoic Revolution. Andrew C. Lawson. - - -
Davis, Wm. M. Reviews,—Correlation Papers. The Newark System. ees
Russell. - - - = - - - -
Bodengestaltende Wirkungen der Eiszeit. Dr. Aug. Bohm. -
The Catskill Deltain the Post-Glacial Hudson Estuary. (Abstract).
The Sub-glacial Origin of Certain Eskers: (Abstract). - -
Derby, Orville A. A Study in Consanguinity of Eruptive Rocks. - -
Dissected Volcano of Crandall Basin, Wyoming. Joseph P. Iddings. -
Drumlins. The Horizon of Drumlin, Osar, and Kame Formation. T. C.
Chamberlin. — - . - - - - - -
EDITORIALS.
“The Beginning of Man and the Age of the Race.” T.C.C. - -
“Man and the Glacial Epoch.” R.D.5.. - - - -
EnglacialiDritti Leu. - - - - - -
Errors as to the Champlain Depression. T.C.C. - - =
Dhe GeclogicalvAtiasiotsthe. Ue SeGasuw Juba - - -
The Geological Congress of the World’s Congress Auxiliary. T.C. C.
“New England and the Upper Mississippi Basin in the Glacial Period.”
Ws Ge - - - - - - : -
Notes on the Meetings of the Geological Society of America, of the Ameri-
can Association at Madison, and of the Geographical Congress at
@hicaconen-1 GG: - - - - - - -
620
INDEX FO VOLUME S:
Nottingham Meeting of the British Association for the Advancement of
Sclences elmeeads : - nae = : 2
- Oscillations of the Earth’s Crust. T.C.C. - - - -
The Scope of the Journal of Geology. T.C.C. - - -
The Summer Meeting of the Geological Society of Anferica. T.C. C.
Englacial Drift. The Nature of the Englacial Drift of the Mississippi Basin.
T. C, Chamberlin. - - - - - - -
Europe. On the Glacial Succession in. James Geikie. Review by R. D.
Salisbury. - - - - - - - -
Foerste, A. E. The Drainage of the Jura. (Abstract). - = -
Geikie, Sir Archibald. On the Pre-Cambrian Rocks of Great Britain. =
Geikie, James. On the Glacial Period and the Earth Movement Hypothesis.
(Abstract). - - - - - - - -
On the Glacial Succession in Europe. Review by R. D. Salisbury. -
Genetic Relationships among Igneous Rocks. Studies for Students. J. P.
Iddings. - - - - - - -
Geological Time as Indicated by the Sedimentary Rocks of North America.
C. D. Walcott. - - - - - - - :
Geological Structures of the Mount Washington Mass of the Taconic Range.
Wm. H. Hobbs. - - - - - - -
Geology. As a Part of a College Curriculum. H.S. Williams. = -
Gilbert, G. Kk. Continental Problems. (Abstract). - : -
Glacial Succession in Ohio. Frank Leverett. - - - - -
Glacial Epochs. Distinct Glacial Epochs and the Criteria for their Recogni-
tion. Studies for Students. Rollin D. Salisbury. - -
Glacial Man. Are There Traces of Glacial Man in the Trenton Gravels ?
W.H. Holmes. - - - - ee - - -
Traces of Glacial Man in Ohio. Plate Il. W.H. Holmes. -
Glaciers. The Las Animas Glacier. George H. Stone. - - -
Malaspina Glacier. I.C. Russell. - - - - -
Gordon, C. H. Reviews:—lowa Geological Survey, Vol. I. Samuel Calvin.
Great Britain. On the Pre-Cambrian Rocks of. Sir Archibald Geikie. >
Greeley, Gen. A. W. Rainfall Types of the United States. ee =
Gulliver, F. P. The Newtonville Sand-Plain. - - -
Harker, Alfred. On the Migration of Material aliing the Mee nee of
Rock Masses. - - - - - - -
Hayes, C. W. Geological Survey of Alabama. Bulletin 4. (Abstract). -
(and Bailey Willis) Conditions of Appalachian Faulting. (Abstract).
Hobbs, Wm. H. On the Geological Structure of the Mount Washington Mass
of the Taconic Range. Plates III., IV. - - SNA -
The Geological Structure of the Housatonic Valley Lying East of Mount
Washington. — - - - - - - - -
Holmes, W. H. Are there Traces of Glacial Man in the Trenton Gravels ?
Traces of Glacial Man in Ohio. Plate II. - - - : -
Housatonic. Geological Structure of the Housatonic Valley Lying East of
Mount Washington. Plates V, VI, VII. Wm.H. Hobbs. - -
Iddings, Joseph P. A Dissected Volcano of Crandall Basin, Wyoming.
vi ; INDEX TO VOLUME I.
Iddings Joseph P. Genetic Relationships among Igneous Rocks. Studies for
Students. - - : = 5 - = As
Reviews :—Eruptive Rocks of Montana—Waldemar Lindgren. A Soda-
lite-Syenite and other Rocks from Montana—W. Lindgren. Acmite-
Trachyte from the Crazy Mountains, Montana—J. E. Wolff. - -
The Volcanic Rocks of the Andes. - - - - -
Iron. The Chemical Relation of Iron and Manganese in Sedimentary Rocks.
Rk. A. F. Penrose, Jr. - - - - 2 -
Kalkowsky, Ernest. Ueber Geroll- Thonschiefer glacialen Ursprungs in Kulm
des Frankenwaldes. (Abstract). - - = : =
Kames. The Horizon of Drumlin, Osar, and Kame Formation. T.C.Chamberlin.
King, Clarence. The Age of the Earth. (Abstract). - - -
King, F. H. Observations and Experiments on the Level and Rate of
Movement of Ground-water. (Abstract). - - - -
Knowlton, F. H. Reviews :—Cretaceous Fossil Plants from Minnesota. By
Leo Lesquereux. - - - - - - -
On the Organization of the Fossil Plants of the Coal-Measures. By
W. C. Williamson. - . . - - - =
Kummel, Henry B. Some Rivers of Connecticut. - : =
Lake Superior. An Historical Sketch of the Lake Superior Region to Cam-
brian Time. C. R. Van Hise. Plate I. - - - =
Sketch of the Present State of Knowledge concerning the Basic Mas-
sive Rocks of the Lake Superior Region. W. S. Bayley.
The Basic Massive Rocks of the Lake Superior Region. W.S. Bayley. 433, 6
Las Animas Glacier. George H. Stone. - - - - -
Laurentian. Geological History of the Laurentian Basin. Studies for Students.
Israel C. Russell. - - - - - - =
On the Typical Laurentian Area of Canada. Frank D. Adams. -
Lawson, Andrew C. The Cordilleran Mesozoic Revolution. - -
Lead. Notes on the Lead and Zine Deposits of the Mississippi Valley and the
Origin of the Ores. Arthur Winslow. - - - -
Le Conte, Joseph. Theory of the Origin of Mountain Ranges. - -
Leverett, Frank. The Correlation of Moraines with Raised Beaches of Lake
Erie. (Abstract). - - - - - - -
The Glacial Succession in Ohio. - - - - .
Maine. ‘The Osar Gravels of the Coast of Maine. Geo. H. Stone.
Malaspina Glacier. I. C. Russell. - - - - - -
Manganese. The Chemical Relation of Iron and Manganese in Sedimentary
Rocks. R. A. F. Penrose, Jr. - - - - -
A Pleistocene Manganese Deposit near Golconda, Nevada. R. A. F.
Penrose, Jr. - - - - - -
Melilite-Nepheline-Basalt and Nepheline-Basanite from Southern Texas. A.
Osann. - - - - - - -
Metamorphism. On the Migration of Material during the Metamorphism of
Rock Masses. Alfred Harker. - - - >
Migration of Material during the Metamorphism of Rock Masses. Alfred Harker.
INDEX TO VOLUME TI.
Mill, Hugh Robert. The Vertical Relief of the Globe. (Abstract). -
Mississippi. The Nature of the ge. Drift of the Mississippi Basin.
T. C. Chamberlin. - - - - -
Mountains. Theory of the Origin of Mountain Ranges. Joseph Le Conte. -
Mount Washington. On the Geological Structure of the Mount Washington
Mass of the Taconic Range. Wm. H.Hobbs.’ - - -
Newtonville Sand-Plain. F. P. Gulliver. - - - -
Notes on the State Exhibits in the Mines and Mining Building at the World’s
Columbian Exposition, Chicago. Kk. A. F. Penrose, Jr. = E
Ohio. The Glacial Succession in Ohio. Frank Leverett. - -
Traces of Glacial Man in Ohio. W.H. Holmes. Plate II. = =
Origin of Pennsylvania Anthracite. John J. Stevenson. : = =
Osann, A. Melilite-Nepheline-Basalt and Nepheline-Basanite from Southern
Texas. = : - 2 - = - -
Osars. The Horizon of Drumlin, Osar, and Kame Formation. T.C.Cham-
berlin. - - - - - - :
The Osar Gravels of the Coast of Maine. Geo. H. Stone. -
Penrose, R. A. F., Jr. The Chemical Relation of Iron and Manganese in Sedi-
mentary Rocks. = 2 - a - - -
A Pleistocene Manganese Deposit near Golconda, Nevada. -
Notes on the State Exhibits in the Mines and Mining Building at the
World’s Columbian Exposition, Chicago. - - - -
Review :—The Mineral Industry, its Statistics, Technology and Trade
in the United States and other Countries. Richard P. Rothwell. -
Pleistocene Manganese Deposit near Golconda, Nevada. Rk. A. F. Penrose, Jr.
Poikilitic. On the use of the Terms Poikilitic and aU aa in Petro-
graphy. G. H. Williams. - - - - -
Pre-Cambrian. An Historical Sketch of the Lake Superior Benign to Cam-
brian Time. C. R. VanHise. Plate I. - - - -
On the Pre-Cambrian Rocks of Great Britain. Sir Archibald Geikie.
Reade, T. Mellard. Measurement of Geological Time. (Abstract). -
Reid, Clement. The Climate of Europe during the Glacial Epoch. (Abstract).
REVIEWS:
Bodengestaltende Wirkungen der Eiszeit, Dr. Aug. Bohm; by Wm. M.
Davis. - - = = = = - = -
Correlation Essays, Archean and Algonkian, C. R. Van Hise; by R. D.
Salisbury. - - - - - = - -
Correlation Papers. The Newark System, Israel C. Russell; by Wm. M.
Davis. = - - ree - - - =
Cretaceous Fossil Plants from Minnesota, Leo Lesquereux; by F. H.
Knowlton. - - - - - - - -
Crystalline Rocks from the Andes; Untersuchungen an altkrystallinen
Schiefergesteinen aus dem Gebiete der argentinischen Republik, B.
Kiihn. Untersuchung argentinischen Pegmatite, etc., P. Sabersky.
Untersuchungen an argentinischen Graniten, etc., J. Romberg; by
George H. Williams. - - : - - -
Iowa Geological Survey, Vol. I., Samuel Calvin ; by C. H. Gordon. -
Vil
422
47
542
717
803
457
129
147
677
341
255
246
~s
aoe
“Ie
Vill INDEX TO VOLUME ‘7.
Eruptive Rocks of Montana, Waldemar Lindgren. A Sodalite-Syenite
and other Rocks from Montana, W. Lindgren. Acmite-Trachyte from
the Crazy Mountains, Montana, J. E. Wolff ; by Joseph P. Iddings. —-
The Mineral Industry, its Statistics, Technology and Trade in the United
State sand other Countries, Richard P. Rothwell; by R. A. F. Penrose, Jr.
Monographs of the United States Geological Survey. Vol. XVII. The
Flora of the Dakota Group, Leo Lesquereux ; by David White. -
On the Organization of the Fossil Plants of the Coal-Measures, W. C.
Williamson; by F. H. Knowlton. - - - - -
Recent Contributions to the Subject of Dynamometamorphism from the
Alps. A. Heim, C. Schmidt, L. Milch, M. P. Termier; by Geo. H.
Williams. - - - - - - - -
Text-book of Comparative Geology, E. Kayser; by R. D. Salisbury. — -
Text-Book of Geology. Sir Archibald Geikie; by R. D. Salisbury, -
Rivers. Some Rivers of Connecticut. Henry b. Kummel. - - -
Russell, Israel C. Geological History of the Laurentian Basin. Studies for
Students. - - - - . - - -
Malaspina Glacier. - - - - - - -
Salisbury, Rollin D. Distinct Glacial Epochs and the Criteria for their Recog-
nition. Studies for Students. - - - - -
Reviews :—On the Glacial Succession in Europe. James Geikie. -
Correlation Essays, Archean and Algonkian. C. R. Van Hise. -
Text-book of Comparative Geology. E. Kayser. - - -
Text-Book of Geology. Sir Archibald Geikie. - - -
Sand-Plain of Newtonville. F. P. Gulliver. - - - - -
Sedimentary Rocks. Geologic Time as Indicated by the Sedimentary Rocks of
North America. Chas. D. Walcott. - - - dat -
Sketch of the Present State of Knowledge concerning the Basic Massive Rocks
of the Lake Superior Region. W.S. Bayley. - - -
Smyth, H. L. A Contact between the Lower Huronian and the Underlying
Granite in the Republic Trough, near Republic, Michigan. — - -
South Mountain. The Structures, Origin, and Nomenclature of the Acid Vol-
canic Rocks of South Mountain. F. Bascom. - - - -
Stevenson, John J. On the Origin of the Pennsylvania Anthracite. -
Stone, Geo. H. The Las Animas Glacier. - - - . -
The Osar Gravels of the Coast of Maine. - - - -
STUDIES FOR STUDENTS :
Conditions of Sedimentary Deposition. Bailey Willis. - - -
Distinct Glacial Epochs and the Criteria for their Recognition, Rollin
D. Salisbury. - - - - - -
The Elements of the Geological Time-Scale. H.S. Williams. - -
Genetic Relationships among Igneous Rocks. J. P. Iddings. -
Geological History of the Laurentian Basin. Israel C. Russell. -
The Making of the Geological Time-Scale. H.S. Williams.
Time-Scale. The Elements of the Geological Time-Scale. Studies for Stu-
dents. H.S. Wiiliams. - - - - z -
634
414
300
303
850.
745
856
371
394
219
525
745
639
268
INDEX TO VOLUME TI.
The Making of the Geological Time-Scale. Studies for Students. H.S.
Williams. - = : S ‘ 2 : L
Trenton Gravels. Are there Traces of Glacial Man in the Trenton Gravels ?
W.H. Holmes. - - = = 2 2 5
Upham, Warren. The Age of the Earth. (Abstract). = - -
Van Hise, C. R. An Historical Sketch of the Lake Superior Region to Cam-
brian Time. Plate I. : - ees . :
Some Dynamic Phenomenon shown by the Baraboo Quartzite Ranges of
Central Wisconsin. Ae - - - - - -
Summary of Pre-Cambrian North American Literature. Abstract, with
comments. = - > = - c = 2{oy/l,
Volcanic Rocks. The Volcanic Rocks of the Andes. J. P. Iddings. - -
The Structures, Origin, and Nomenclature of the Acid Volcanic Rocks of
South Mountain. F. Bascom. - - - - - E
Walcott, C. D. Geologic Time, as Indicated by the Sedimentary Rocks of
North America. - - - - - - -
Westgate, Louis G. Geographic Development of the Eastern Part of the Mis-
sissippi Drainage System. (Abstract). - - - -
White, David. A New Tzniopteroid Fern and Its Allies. (Abstract). -
Review. Monographs of the United States Geological Survey, Vol.
XVII. The Flora of the Dakota Group, by Leo Lesquereaux. - -
Williams, G. H. On the Use of the Terms Poikilitic and Micropoikilitic in
Petrography. - - - - - - -
Reviews. Crystalline Rocks from the Andes. Reports of B. Kiihn,
P. Sabersky, J. Romberg. - - - - - -
Recent Contributions to the Subject of Dynamometamorphism from the
Alps. A. Heim, C. Schmidt, L. Milch, M. P. Termier. - -
Williams, H.S. Elements of the Geological Time-Scale. Studies for Stu-
dents. - - - - - - >
Geology as a Part of a College Curriculum. - - - -
Making of the Geological Time-Scale. Studies for Students. -
Willis, Bailey. Conditions of Sedimentary Deposition. Studies for Students.
Conditions of Appalachian Faulting (C. W. Hayes). (Abstract). -
Studies in Structural Geology. (Abstract). - - - .
Winslow, Arthur. Notes on the Lead and Zinc Deposits of the Mississippi
Valley and the Origin of the Ores. - - - - :
Wisconsin. Some Dynamic Phenomena Shown by the Baraboo Quartzite
Ranges of Central Wisconsin. C.R.Van Hise. - - -
Wyoming. A Dissected Volcano of Crandall Basin, Wyoming. Joseph P.
: Iddings. - - - - - = =
Zinc. Notes on the Lead and Zinc Deposits of the Mississippi Valley and the
Origin of the Ores. Arthur Winslow. - - - -
ix
180
15
203
113
347
532
164
813
639
420
419
300
176
411
580
283
38
180
476
861
96
612
347
606
612
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