W. Steadman (William Steadman) Aldis.

The American journal of science and arts online

. (page 49 of 59)
Online LibraryW. Steadman (William Steadman) AldisThe American journal of science and arts → online text (page 49 of 59)
Font size
QR-code for this ebook


The result is, a conviction that the facts which I have given
respecting the conglomerates, are only another phase of the phe-
nomena described by these eminent geologists. If the facts
they adduce prove the elongation and expansion of slate, lime-
stone and fossils, as is generally conceaed, although proved
mainly by the microscope, why should we think it strange that
the like effects may have been produced upon conglomerates, so
as to show themselves on a large scale, and to unaided vision?
The manner in which the veteran geologist, Scrope, supposes
gneiss and mica $chist may have been formed out of granite,
(which he has illustrated by figures, Phil, Magazine, vol. li, p.
19^), whatever we may think of the hypothesis, corresponds
very nearly with some of my suppositions, or rather facts, as
to the conversion of conglomerates into schists. And the
ideas of most of these writers as to the former plastic condition
of most of the rocks, correspond with those wnich I have ex-
pressed. K I am wrong, then, I have the consolation of being in
good company. •

Prof. Tyndall, in his recent work on the Alpine Glaciers, has
referred to an interesting specimen in London, analogous to the
conglomerates of Rhode Island and Vermont.

In the museum of the Government school of Mines, he says,
"we have a collection of quartz stones placed there by Mr.
Salter, and which have been subjected to enormous pressure, in
the neighborhood of a fault. These rigid pebbles, have in
some cases, been squeezed against each other so as to produce
a mutual flattening and indentation. Some of them have
yielded along planes passing through them, as if one half had
slidden over tae other; but the reattachment is very strong.
Some of the larger stones, moreover, which have endured pres-
sure at a particular point, are fissured radially around the point.
In short, the whole collection is a most instructive example of
the manner and extent to which some of the most rigid substancea
Aif. Jour. Scl— Second SsbieSt Vol. XXXI, No. 08.— Kjlt, 186L
51



Digitized by



Google



302 Review of the Progress of

in nature can yield on the application of a sufficient force. — {Ola*
ciers of the Alps^ p. 404, Amer. EA)

Though these specimens are not so definitely described as we
could wish, we presume they are conglomerates with flattened
quartz pebbles, like those in Ehode Island and Vermont. Our
objections to Prof. Ty ndall's hypothesis, which imputes the effect
wholly to the mechanical compression of solid quartz, are as
follows :

1. The compression of pure quartz pebbles, such as some of
those in Rhode Island, and most of those iu Vermont, would
break and crush them, nor have we any reason to suppose that
the fragments could be reconstructed so as to form hyalino
masses, without fissures. There is no fluid, as in ice, to produce
regelation ; nor could the particles be brought near enough for
molecular attraction, without being crushed into the finest pow-
der, by such a pressure as the facts show not to have been ex-
erted upon the conglomerates.

2. The compressing force has not been great enough to de-
stroy except partially, the form of the pebblea It has not
crushed but only moulded them, except that now and then, one
has been fractured. If it had been powerful enough to compress
and distort solid quartz and to reunite its particles, it must nave
destroyed all marlb of a mechanical origin in the pebbles.

3. There is evidence, as we have tried to show, in the prece-
ding discussion, that many of the pebbles, especially in the Ver-
mont rocks, have undergone a cnemical change ; that certain
silicates have been abstracted from them, leaving the excess of
silica in the form of quartz. This, of course, would require
such a degree of plasticity, as to enable water to permeate the
mass>

March dOth, 1861.



Abt. XXXV^ — On some points in American Geology; by T.
Stebry Hunt, F.RS., of the Oeological Survey of Canada.

The recent publication of two important volumes on Ameri-
can geology seems to afford a fitting occasion for reviewing some
questions connected with the progress of geological science, and
with the history of the older rock formations of North America.
The first of these works is the third volume of the Palaeontology
of New York by James Hall ; we shall not attempt the task of
noticing the continuation of this author's labors in the study of
organic remains, labors which have by common consent placed
him at the head of American palaeontologists, but we have to
call attention to the introduction to this third volume, where in
about a hundred pages Mr. Hall gives us a clear and admirable



Digitized by



Google



American Gfeology, by T. S. Hunt. 803

Bummary of the principal facts in the geology of the United
States and Canada, followed by some theoretical notions on the
formation of mountain chains, metamorphism and volcanic phe-
nomena, where these questions are discussed from a point of view
which we conceive to be of the greatest importance for the fu*
ture of geological science. A publication of this introduction
in a separate form, with some additions, would we think be most
acceptable to the scientific public.

The other work before us is Prof H. D. Hogers' elaborate re-
port on the geology of Pennsylvania, giving the results of the
Survey of that State for many years carried on under his direc-
tion, and embracing a minute description of those grand exhibi-
tions of structural geology, which have rendered that State clas-
sic ground for the student. The volumes are copiously illustra*
ted with maps, sections and figures of organic remains, and the
admirable studies on the coal fields of Pennsylvania and Great
Britain add much to its value.

The oldest series of rocks known in America is that which
has been investigated by the officers of the Geological Survey of
Canada, and by them designated the Laurentian system. It is
now several years since we suggested that these rocks are the
equivalents of the oldest crystalline strata of western Scotland
and Scandinavia.* This identity has since been established by
Sir R I. Murchison in his late remaricable researches in the
northwestern Highlands, and he has adopted the name of the
Laurentian system for these ancient rocks of Eoss, Sutherland,
and the Western Islands, which he at first called fundamental
gneis8.t These are undoubtedly the oldest known strata of the
earth *s crust, and therefore offer peculiar interest to the geologist.
As displayed in the Laurentide and Adirondack mountains, they
exhibit a volume which has been estimated by Sir William Lo-
gan to be equal to the whole palaeozoic series of North America
in its greatest development. The Laurentian series consists of
gneiss, generally granitoid, with great beds of quartzite, some-
times conglomerate, and three or more limestone formations', (one
1000 feet in thickness) associated with dolomites, serpentines,
plumbago, and iron ores. In the upper portion of the series an
extensive formation of rooks, consisting cmiefly of basic feldspars
without quartz and with more or less pyroxene, is met with.
The peculiar characters of these latter strata, not less than the
absence of argillites and talcose and chloritic schists, conjoined
with various other mineraloffical characteristics seem to distin-
guish the Laurentian series tnroughout its whole extent, so far
as yet studied, from any other system of crystalline strata. It

* Esquisse G^olof^qoe da Canada, 1860, p. 17.

f Quur. Journal Oeoi. Society, rot xr, 8&S ; zr, S16.



Digitized by



Google



804 Review of the Progress of -

tppean not improbable that future researohes will enable us to
divide this series of rocks into two or more distinct systems.

Overlyiug the Laurentian series on Lake Iluron ana Superior,
we have the Huronian system, about 10,000 feet in thickness,
and consisting to a great extent of quartzites, often conglomer-
ate, with limestones, peculiar slaty rocks, and great beds of dior-
ite, which we are disposed to regard as altered sediments. These
constitute the lower copper-bearing rocks of the lake region, and
the immense beds of iron ore at Marquette and other places on
the south shore of Lake Superior have latelj^ been found by Mr.
Murray to belong to this series, which is entirely wanting along
the farther eastern outcrop of Uie Laurentian systeuL This Hu-
ronian series appears to be the equivalent of the Cambrian sand-
stones and conglomerates described by Murchison, which form
mountain masses alone the western coast of Scotland, where
they repose in detached portions upon the Laurentian series.

Besides these systems of crystalline rocks, the latter of which
is local and restricted in its distribution, we have along the great
Appalachian chain, from Georgia to the Gulf of St. Lawrence, a
third series of crystalline strata, which form the gneissoid and
mica slate series of most American geologists, the hypozoic
group of Prof. Eogers, consisting of feldspathic gneiss, with
quartzites, argillites, micaceous, epidotic, chloritic, tnlcose and
specular schists, accompanied with steatite, diorites and chromif-
arous oj)hiolites. This group of strata has been recomized by
Saflford in Tennessee, by Bogers in Pennsylvania, ana by most
of the New England geologists as forming the base of Appala-
diian system, while Sir William Logan, Mr. Hall, and the pres-
ent writer have for many years maintained that they are really
altered palaeozoic sediments, and superior to the lowest fossilifer-
oua strata of the Silurian series. Sir William Logan has shown
that the gneissoid ranges in Eastern Canada have the form of

Snclinals, and are underlaid by shales which exhibit fossils in
eir prolongation, while his sections leave no doubt that these
ranges of gneiss, with micaceous, chloritic, talcose and specular
schists, epidosites, quartzites, diorites and ophiolites, are really
the altered sediments of the Quebec group, which is a lower
member of the Silurian series, corresponding to the Calciferous
and Chazy formations of New York, or to the Primal and Au-
roral series of Pennsylvania. Prof Rogers indeed admits that
these are in some parts of Pennsylvania metamorphosed into
feldspathic, micaceous and talcose rocks, which it is extremely
difficult to distinguish from the hypozoic gneiss, which latter,
however, he conceives to present a want of conformity with the
palaeozoic strata.

To this notion of the existence of two groups of crystalline
rocks similar in lithological character but different in age, we



Digitized by



Google



^i^



Americctn Geology, by T. S. Hunt. 395

have to object that the hypoaoic gneiss is identical with the Green
Mountain gneiss, not only in lithological character, but in the
presence of certain rare metals, such as chrome, titanium, and
nickel which characterise its magnesian rocks ; all of these we
have shown to be present in the unaltered sediments of the Que-
bec group, with which Sir William Logan has identified the
gneiss formation in question. Besides which the lithological and
chemical characters of the Appalachian gneiss are so totally dis-
tinct from the crystalline strata of the Laurentian system, with
which Prof. Rogers would seem to identify them, that no one
who has studied the two can for a moment confound them. Prof,
l^ogers is therefore obliged to assume a new series of crystalline
rooks, distinct from both the Laurentian and Hnronian systems,
but indistinguishable from the altered palseozoio series^ or else to
admit that the whole of his gneissic series in Pennsylvania is,
like the corresponding rocks in Canada, of palseozoic age.* We
believe that nature never repeats herself without a difference, and
that certain variations in the chemical and mineralogical consti-
tution of sediments mark anccessive epochs so clearly that it
would be inipossible to suppose the formation in adjacent r^ons
of a series of crystalline schists like those of the AUeghanies con-
temporaneous with the sediments which produced the Laurentian
system. We have elsewhere indicated the general principles
npon which this notion of a progressive change in the composi-
tion of sediments is based, and shown how the gradual removal
of alkalies from aluminous rocks ha^ led to the formation of ar-
gillites, chloritic and epidotic rocks, at the same time removing
carbonic acid from the atmosphere, while the resulting carbon-
ate of soda by decomposing the calcareous and magnesian salts
of the ocean, fumishea the carbonates for the formation of lime-
stones and dolomites, at the same time generating sea salt.f

Closely connected with these chemical questions is that of the
conmiencement of life on the earth. The recognition beneath
the Silurian and Huronian rocks, of 40,000 feet of sediments
analogous to those of more recent times, carries far back into the

• Dr. Bigsbj in 1824 described an extensive tract of gneissoid rocks on Rainy
Lake and £Uce Lacroix, north of Lake Superior. Tbo general coarse of the strata
he states to be ** from N.W. to N. by W., with a corresponding easterly dip ;** but
he elscTrhere speaks of the gneiss as running (dipping ?) E.N.E. Tliis gneiss often
contains beds and disseminated grains of bom blende, and passes in some places into
micaceous, chloritic and greenstone slates, and syenite. Staurotide is abundant in
the mica schists, and octahedral iron ooours in the ddoritic slates. A porphyritic
ffranite containinff bei^l is also met with in this region. This gneisa is reiB^irded by
vr. Bigsby as bdongmg " to transition rocks, from its constant proximity to red
sandstone, the oldest organic limestone, and trap." (Am. Jour. Sci. (1^, viii, 61).
The lithological and minml characters of these cfystalUne strata seem to be distinct
from those of the Laurentian system, and to resemble tboee of the Appalacbiaoi.
Too much praise cannot be ascrilied to Dr. Bigsby for his early and extensire obser-
vations on the geoenosy and mineralogy of British North America.

f This Journal [2], xxr, 102, 445, xxx, 18S ; and Qnar. Jour. Geol Soc, xr, 488.



Digitized by



Google



3M Review of the Progress of

Sast the evidence of the existence of physical and chemical con-
itions, similar to those of more recent periods. But these highly
altered strata exclude, for the most part, organic forms, and it
is only by applying to their study the same chemical principles
which we now find in operation that we are led to suppose the
existence of organic life during the Laurentian period. The
great processes of deoxydation in nature are dependent upon
organization ; plants by solar force convert water and carbonic
acid into hydrocarbonaceons substances, from whence bitumens,
coal, anthracite and plumbago, and it is the action of organic
matter which reduces sulphates, giving rise to metallic sulphu-
rets and sulphur. In like manner it is by the action of dissolved
organic matters that oxyd of iron is partially reduced and dis-
solved firom great masses of sediments, to be subsequently accu-
mulated in beds of iron ore. We see in the Laurentian series
beds and veins of metallic sulphurets, j)recisely as in more recent
formations, and the extensive beds of iron ore hundreds of feet
thick which abound in that ancient system, correspond not only
to great volumes of strata deprived of that metal, but as we may
suppose, to organic matters, which but for the then great diffusion
of iron oxyd in conditions favorable for their oxydation, might
have formed deposits of mineral carbon far more extensive than
those beds of plumbago which we actually meet in the Lauren-
tian strata.

All these conditions lead us then to conclude to the existence
of an abundant v^etation during the Laurentian period, nor are
there wanting evidences of animal life in these oldest strata.
Sir William Logan has described forms occurring in the Lauren-
tian limestone which cannot be distinguished from the silicified
specimens of Stromaiopora rugosa found in the Lower Silurian
rocks. They consist of concentric layers made np of crystalline
grains of white pyroxene in one case and of serpentine in an-
other, the first imbedded in limestone and the second in dolo-
mite ; we may well suppose that the result of metamorphism
would be to convert silicified fossils into silicates of lime and
magnesia. The nodules of phosphate of lime in some beds of
the Laurentian limestones also recall the phosphatic coprolites
which are firequently met with in Lower Silurian strata, and are
in the latter case the exuviae of animals which have been fed
upon Lingula, Orbicula, (hnuUvria and Serpulites^ the shells and
tubes of which we have long since shown to be similar in com-
position to the bones of vertebrates.* So far therefore from
looking upon the base of the Silurian as marking the dawn of
life upon our planet, we see abundant reasons for supposing that
organisms, probably as varied and abundant as tnose of the

* Logan and Honti Amer. Jonr. Sci. [2], xtu, 235.



Digitized by



Google



American Geology, by 7. & Hunt. 397

palsBOzoic age, may have existed during the long Laurentian
period.

Along the northern rim of the great palaeozoic basin of North
America the Potsdam sandstone of the New York geologists is
unquestionably the lowest rock from below Quebec to the Island
of Montreal, and thence passing up the valley of Lake Cham-
plain and sweeping rouna the Adirondack mountains, until it
reenters Canada and soon disappears to the north of Lake Onta-
rio, where the Birdseye and Slack River limestones repose di-
rectly upon the Laurentian rocks, and furthermore overlie the
great Lake Superior group oT slates and sandstones, which re-
posing on the unconformable Haronian system, constitute the
upper copper-bearing rocks of this region. This Lake Superior

froup, as Sir William Logan remarks, may then include the
'otsoam, Calciferous and Chazy, and thus be equivalent in part
to the Quebec group hereafter to be described.

Passing westward into the Mississippi valley we again find a
sandstone formation, which forms the base of the palaeozoic
series, and is considered by Mr. Hall to be the equivalent of the
Potsdam. Here it occasionally exhibits intercalated beds of
silico-argillaceous limestone, in which occur abundant remains of
trilobites of the genera Dikellocepfialus, Menoeephalus, ArionelluSj
and Conocephalus. Passing upwards this sandstone is succeeded
by the Lower Magnesian limestone, which is the equivalent of
the Calciferous sand-rock of New York, and in Missouri, where
it is the great metalliferous formation, alternates several times
with a sandstone, constituting the Magnesian Limestone series,
which in Missouri attains a tnickness of 1800 feet. The same
thing is observed to a less degree in Wisconsin and Iowa;
throughout this region the higher beds of the Potsdam sandstone
are often composed of rounded oolitic granules, and the beds of
passage are frequently of such a character as to lead to the con-
clusion that they have been deposited from silica in solution,
and are not mechanical sediments.* For a discussion of some
facts with regard to the chemical origin of many silicious rocks,
see this Journal, [2], xviii, 381.

Evidences of disturbance during the period of its deposition
are to be found in the breociated beds, sometimes fifty feet in
thickness, which occur in the Calciferous sandrock of the north-
west, and are made of the ruins of an earlier sandstone. In Mis-
souri, the Birdseye and Black River limestones repose directly
upon the Lower Magnesian limestone, while farther north, a
sandstone intervenes, occupying the place of the Chazy lime-
stone.

* See Mr. Hnll's lotroduction, to which we are indebted for many of these facta
regarding the formation of the west, and also the Reports of the Geological Survey
of Missouri.



Digitized by



Google



808 Review of the Progress of

The Potsdam sandstone of the St Lawrence valley, lias fer
the most part the character of a littoral formation, being made
up in great part of pure qnartzose sand, and ofBering upon suc-
cessive beds, ripple and wind marksi, and the tracks of animals.
Occasionally it includes beds of conglomerate, or as at Hemming-
ford, encloaee large rounded fragments of green and black shale;
it also exhibits calcareous beds apparently marking the passage
to the succeeding formation, whicn although called a Calciferous
sandrock, is for the most part here, as in the west, a maenesian
limestone, often geodifeious, and including calcite, pearl spar,
gypsum, barvtes and quartz. Sir William Logan had already
shown that tlie fauna of the Potsdam and Calciferous in Canada
are apparently identical, (Can. Nat, June, 1860 ; This Journal,
[2], xxxi, 18), and Mr. Hall has arrived at the same conclusion
with regard to the more extended fauna of these formations in the
valley of the Mississippi, so that these two may be regarded as
formmg but one group. While in the west VikeUocephalus oc-
curs both in the lower sandstones and the magnesian limestones,
Conocephaiiu mifiiUus^ found in the Potsdam on Lake Cham plain,
and identified by Mr. Billings, has lately been detected by him
in specimens from the sandstones of Wisconsin with Dikelloce-
phaluSj which cenus has there been found to pass upwards into
the magnesian limestones. On the other hand, the sandstones of
Bastard in Canada, having the characters of the Potsdam, con-
tain Lingvia acuminata and Ophileta compacta^ species regarded
as'characteristic of the Calciferous, together with two undescribed
species of OrthoceraSf and in another locality a Pleuroiomaria re-
sembling P. Laurendna. The researches of Mr. Billings have
extended the fauna of the Calciferous in Canada to forty-one
species, and the succeeding Chazy formation to 129 species. The
thickness of this latter division in the St. Lawrence valley is
about 250 feet, and it includes in its lower part about fifty feet
of sandstones with green fucoidal shales and a bed of conglom-
erate. The Calciferous has a thickness of about 800 feet, while
the Potsdam may be estimated at not far from 600 feet.

We have then seen that along the northeastern outcrop of the
great American basin in Canada and New York, the base of the
Pala30zoic series is represented by less than 1000 feet of sand-
stones and dolomites, reposing directly upon the Laurentian
system. A very different condition of tnings is, however, found
in the more central parts of the basin. According to Prof.
Rogers, the older Primal slates, which form the base of the pal-
aeozoic system, attain in Virginia a thickness of 1200 feet, and
are succeeded by 300 feet of Primal sandstone marked by &oli-
thus, which he considers the Potsdam, followed by the upper '
Primal slates, consisting of 700 feet of greenish and brownish
talco-argillaceous shales with fucoids. To these succeed bia^



Digitized by



Google



American C^eology, by T. S. Hunt. 399

Auroral division, consisting of sixty feet or more of calcareous
sandstone, the supposed equivalent of the Calciferous sandrock.
followed by the Auroral limestone, which is magnesian, ana
often argillaceous and cherty in the upper beds. Its thickness
is estimated at from 2600 to 5500 feet, and it is supposed by
Eogers to include the Chazy and Black River limestones, while
the succeeding Matinal division exhibits first, fipom 300 to 500
feet of limestone, (Trenton), secondly, 800 to 400 feet black
shale, (Utica), and thirdly, 1200 feet of shales with red slates and
conglomerates, (Hudson Kiver Group), thus completing the Lower
Silurian series.

In Eastern Tennessee, Mr. Safford describes, (1st.) on the con-
fines of North Carolina, a great volume of gneissoid and mica-
ceous rocks similar to those of Pennsylvania, succeeded to the
west by (2nd.) the Ococee conglomerates and sandstones, with
argillites, chloritic, talcose and micaceous slates, and occasional
bands of limestone, all dipping, like the rocks of the 1st division,
to the S.E, In the 3d place we have the Chilhowee sandstones
and shales, several thousand feet in thickness, including near
the summit beds of sandstone with Scolithus^ and considered by
Mr. SaflFord the equivalent of the Potsdam. (4th.) The Mag-
nesian limestone and shale group, also several thousand feet thick,
and divided into three parts ; first a series of fucoidal sandstones
approaching to slates and including bands of magnesian lime-
stone ; second, a group of many hundred feet of soft brownish,
greenish, and bun shales, with beds of blue oolitic limestone,
which as well as the shales, contain trilobites. Passing upward



Online LibraryW. Steadman (William Steadman) AldisThe American journal of science and arts → online text (page 49 of 59)