Chapter XII: A Century of Zoology in America. Wesley R. Coe 391 (7)

The accumulation and study of facts constituted the best cure for an erroneous theory. The publications of the Journal contributed toward this end by articles along several lines. The most original contributions were those which dealt with the areal and structural geology of eastern North America, but equally valuable at that time for the broadening of scientific interest were the studies on the volcanic activities of the Hawaiian Islands, published through many years. Perhaps most valuable from the educative standpoint were the extensive republications in the Journal of the more important European researches, making them accessible to American readers. In volume =13= (1828), for example, a digest of Scrope’s work on volcanoes is given, covering forty pages; and of Daubeny on active and extinct volcanoes, running over seventy-five pages and extending into vol. =14=. Through these comprehensive studies the nature of volcanic action became generally understood during the first half of the nineteenth century and the original publications in the Journal were valuable in giving a knowledge of the activities of the Hawaiian volcanoes.

Early in the nineteenth century the whole of America still remained to be explored by the geologist. The regions adjacent to the centers of learning were among the first to receive attention and the Triassic basin of Connecticut and Massachusetts yielded information in regard to the nature of igneous intrusion. This basin, of unmetamorphic shales and sandstones, is occupied by the Connecticut River except at its southern end. The Formation contains within it sills, dikes, and outflows of basaltic rocks which because of their superior resistance to erosion constitute prominent hills, in places bounded by cliffs.

Silliman in 1806[80] described East Rock, New Haven, Connecticut, as a whinstone, trap, or basalt, and accounted for its presence on the supposition that it had

“actually been melted in the bowels of the earth and ejected among the
superior strata by the force of subterraneous fire, but never erupted
like lava, cooling under the pressure of the superincumbent strata and
therefore compact or nonvesicular, its present form being due to
erosion.”

In these conclusions Silliman was correct. With but a limited amount of experience he was able to discriminate between the intrusive and effusive rocks and saw that the prominence of this hill was due to the erosion of the sediments which once surrounded it.

An extensive paper on the geology of this region was published by Edward Hitchcock in 1823,[81] then just thirty years of age. This paper shows the evidence of extensive field observations, and his comments in regard to the trap and granite are of interest. Hitchcock gives five pages to the subject of “Greenstone Dykes in Old Red Sandstone” (=6=, 56–60, 1823) and makes the following statements:

“Professor Silliman conducted me to an interesting locality of these
in East-Haven. They occur on the main road from New-Haven to
East-Haven, less than half a mile from Tomlinson’s bridge ... (p. 56).

They are an interesting feature in our geology, and deserve more
attention; and it is peculiarly fortunate that they should be situated
so near a geological school and the first mineral cabinet in our
country ... (p. 58).

Origin of Greenstone.

Does the greenstone of the Connecticut afford evidence in favour of
the Wernerian or of the Huttonian theory of its origin? Averse as I
feel to taking a side in this controversy, I cannot but say, that the
man who maintains, in its length and breadth, the original hypothesis
of Werner in regard to the aqueous deposition of trap, will find it
for his interest, if he wishes to keep clear of doubts, not to follow
the example of D’Aubuisson, by going forth to examine the greenstone
of this region, lest, like that geologist, he should be compelled, not
only to abandon his theory, but to write a book against it. Indeed,
when surveying particular portions of this rock, I have sometimes
thought Bakewell did not much exaggerate when he said in regard to
Werner’s hypothesis, that, ‘it is hardly possible for the human mind
to invent a system more repugnant to existing facts.’

On the other hand, the Huttonian would doubtless have his heart
gladdened, and his faith strengthened by a survey of the greater part
of this rock. As he looked at the dikes of the old red sandstone, he
would almost see the melted rock forcing its way through the fissures;
and when he came to the amygdaloidal, especially to that variety which
resembles lava, he might even be tempted to apply his thermometer to
it, in the suspicion that it was not yet quite cool ... (p. 59).

By treating the subject in this manner I mean no disrespect to any of
the distinguished men who have adopted either side of this question.
To President Cooper especially, who regards the greenstone of the
Connecticut as volcanic, I feel much indebted for the great mass of
facts he has collected on the subject. And were I to adopt any
hypothesis in regard to the origin of our greenstone, it would be one
not much different from his” (p. 60).

By 1833 and more clearly in 1841 Hitchcock had come to recognize the distinction between intrusive and extrusive basaltic sheets in the Connecticut valley. Dawson also came to regard the Acadian sheets as extrusive, and Emerson in 1882 recalled again the evidence for Massachusetts (=24=, 195, 1882). Davis, however, went a step further and by applying distinctive criteria not only separated intrusive and extrusive sheets throughout the whole Triassic area, but by using basalt flows as stratigraphic horizons unraveled for the first time the system of faults which cut the Triassic system. His preliminary paper (=24=, 345, 1882) was followed by many others.

From 1880 onward begins the period of precise structural field work. The older geologists mostly conceived their work after reconnaissance methods. From 1870 to 1880 a group of younger men entered geology who paid close attention to the solid geometry and mechanics of earth structures. In their hands physical and dynamical geology began to assume the standing of a precise and quantitative science. In the field of intrusive rocks the opening classic was by Gilbert, who in his volume on the geology of the Henry Mountains, published in 1880, made laccoliths known to the world. With the beginning of this new period we may well leave the subject of intrusive rocks and turn to the progress of knowledge in regard to those deeper and vaster bodies now known as batholiths. These, since erosion does not expose their bottoms, Daly separates from intrusives and classifies as subjacent. The batholiths consist typically of granite and granodiorite, and introduce us to the problem of granite.

_Views on the Structural Relations of Granite._

Conscientious field observations were sufficient to establish the true nature of the intrusive and extrusive rocks. The case was very different, however, with the nature and relations of the great bodies of granite, which may be taken in the structural sense as including all the visibly crystalline acidic and intermediate rocks, known more specifically as granite, syenite, and diorite.

The large bodies of granite, structurally classified as stocks, or batholiths, commonly show wedges, tongues, or dike networks cutting into the surrounding rocks. The relations, however, are not all so simple as this. Granites may cover vast areas, they are usually the older rocks, they are generally associated with regional metamorphism of the intruded formations, which metamorphism is now understood to be due chiefly to the heat and mineralizers given off from the granite magma, associated with mashing and shearing of the surrounding rocks. The granite was often injected in successive stages which alternated with the stages of regional mashing. A parallel or gneissic structure is thus developed which is in part due to mashing, in part to igneous injection. Where the ascent of heat into the cover is excessive, or where blocks are detached and involved in the magma, the latter may dissolve some of the older cover rocks, even where these were of sedimentary origin.

Thus between mashing, injection, and assimilation the genetic relationships of a batholith to its surroundings are in many instances obscure. Nevertheless, attention to the larger relations shows that the molten magma originated at great depths in the earth’s crust, far below the bottoms of geosynclines, and consists of primary igneous material, not of fused sediments. From those depths it has ascended by various processes into the outer crust, where it crystallized into granite masses, to be later exposed by erosion. The amount of material which can be dissolved and assimilated must be small in comparison with the whole body of the magma. The original composition of the magma was probably basic, nearer that of a basalt than that of a granite. Differentiation of the molten mass is thought to cause the upper and lower parts of the chamber to become unlike, the lighter and more acidic portion giving rise to the great bodies of granite. With the exception of certain border zones the whole, however, is regarded as igneous rock risen from the depths.

The complex border relations, but more particularly certain academic hypotheses, led to a period of misunderstanding and retrogression in regard to the nature of granites. It constitutes an interesting illustration of the possibility of a wrong theory leading interpretation astray, chiefly through the magnification of minor into major factors. This history illustrates the dangers of qualitative science as compared to quantitative, of a single hypothesis as matched against the method of multiple working hypothesis. This flux of opinion in regard to the nature of granites may be traced through the volumes of the Journal.

E. Hitchcock in 1824 (=6=, 12) noted that in places granite appeared bedded, but in other places existed in veins which cut obliquely across the strata. Silliman, although careful not to deny the aqueous origin of some basalts, yet held that the field evidence of New England indicates for that region the igneous or Huttonian origin of trap and granite (=7=, 238, 1824).

In 1832 the following article by Hitchcock appeared in the Journal (=22=, 1, 70):

Report on the Geology of Massachusetts; examined under the direction
of the Government of that State, during the years 1830 and 1831; by
Edward Hitchcock, Prof. of Chemistry and Natural History in Amherst
College.

A footnote adds that this is “published in this Journal by consent of
the Government of Massachusetts, and intended to appear also in a
separate form, and to be distributed among the members of the
Legislature of the same State, about the time of its appearance in
this work. It is, we believe, the first example in this country, of
the geological survey of an entire State.”

This article includes a geological map of the state and covers the subject of economic geology. The report brought forth the following remarks from a French reviewer in the _Revue Encyclopédique_, Aug. 1832, quoted in the Journal (=23=, 389, 1833):

“A single glance at this report, is sufficient to convince any one of
the utility of such a work, to the state which has undertaken it; and
to regret that there is so very small a part of the French territory,
whose geological constitution is as well known to the public, as is
now the state of Massachusetts. France has the greater cause to regret
her being distanced in this race by America, from her having a corps
of mining engineers, who if they had the means, would, in a very short
time furnish a work of the same kind, still more complete, of each of
the departments.”

The complete report published in 1833 is a work of 700 pages. Pages 465 to 517 are devoted to the subject of granite. Numerous detailed sketches are given showing contact relations. Nine pages are given to theoretical considerations and many lines of proof are given that granite is an igneous rock, molten from the internal heat of the earth, and intruded into the sedimentary strata. His statement is the clearest published in the world, so far as the writer is aware, up to that date, and marks Edward Hitchcock as one of the leading geologists of his generation in Europe as well as America. Unfortunately his views were largely lost to sight during the following generation.

In 1840 the first American edition of Mantell’s Wonders of Geology gave currency to the idea that granite is proved to be of all geological ages up to the Tertiary (=39=, 6, 1840). In 1843 J. D. Dana pointed out (=45=, 104) that schistosity was no evidence of sedimentary origin. He regarded most granites as igneous as shown by their structural relations, but considers that some may have had a sedimentary origin.

_Rise and Decline of the Metamorphic Theory of Granite._

Up to 1860 granite was regarded on the basis of the facts of the field as essentially an intrusive rock, but gneiss as a metamorphic product mostly of sedimentary origin. It seemed as though sound methods of research and interpretation were securely established. Nevertheless, a new era of speculation and a modified Wernerism arose at that time with a paper by T. Sterry Hunt, marking a retrogression in the theory of granite which lasted until his death in 1892.

In November, 1859, Hunt read before the Geological Society of London a paper on “Some Points in Chemical Geology” in which he announced that igneous rocks are in all cases simply fused and displaced sediments, the fusion taking place by the rise of the earth’s internal heat into deeply buried and water-soaked masses of sediments (see =30=, 133, 1860). The germ of this idea of aqueo-igneous fusion was far older, due to Babbage and John Herschel, neither of them geologists, but such sweeping extensions of it had never before been published. Hunt had the advantage of a wide acquaintanceship with geological literature and chemistry. He wrote plausibly on chemical and theoretical geology, but his views were not controlled by careful field observations. In fact he wrote confidently on regions which apparently he had never seen and where a limited amount of field work would have shown him to have been fundamentally in error. A man of egotistical temperament, he sought to establish priority for himself in many subjects and in order to cover the field made many poorly founded assertions. Building on to another Wernerian idea, he held that many metamorphic minerals had a chronologic value comparable to fossils—staurolite for example indicating a pre-Silurian age—and on this basis divided the crystalline rocks into five series. Although there is much of value buried in Hunt’s work it is difficult to disentangle it, with the result that his writings were a disservice to the science of geology. Although carrying much weight in his lifetime, they have passed with his death nearly into oblivion.

Marcou, with a limited knowledge of American geology, and but little respect for the opinions of others, had published a geologic map of the United States containing gross errors. In support of his views he read in November, 1861, a paper on the Taconic and Lower Silurian Rocks of Vermont and Canada. In the following year he was severely reviewed by “T,” who states positively in controverting Marcou (=33=, 282, 283, 1862) that “the granites (of the Green Mountains) are evidently strata altered in place.”

“Mr. Marcou should further be informed that the granites of the Alpine
summits, instead of being, as was once supposed, eruptive rocks, are
now known to be altered strata of newer Secondary and Tertiary age. A
simple structure holds good in the British Islands, where as Sir
Roderick Murchison has shown in his recent Geological map of Scotland,
Ben Nevis and Ben Lawers are found to be composed of higher strata,
lying in synclinals. This great law of mountain structure would alone
lead us to suppose that the gneiss of the Green mountains, instead of
being at the base, is really at the summit of the series....

We cannot here stop to discuss Mr. Marcou’s remark about ‘the
unstratified and oldest crystalline rocks of the White mountains’
which he places beneath the lower Taconic series. Mr. Lesley has shown
that these granites are stratified, and with Mr. Hunt, regards them as
of Devonian Age. (This Journal, vol. =31=, p. 403.) Mr. Marcou has
come among us with notions of mountains upheaved by intrusive
granites, and similar antiquated traditions, now, happily for science,
well nigh forgotten.”

It is seen that Marcou, notwithstanding the general character of his work, happened to be nearer right in some matters than were his critics, and that “T” had adopted to the limit the views of Hunt.

The recovery of geology from this period of confusion was partly owing to the slow accumulation of opposed facts; especially to a recognition of the fact that the overplaced relation of the granite gneisses in western Scotland was due to great overthrusts; also to the evidence of the clearly intrusive nature of many of the Cordilleran granites. The recovery of a sounder theory was hastened, however, by the application of criticisms by J. D. Dana in the Journal. In 1866 (=42=, 252) Dana pointed out that sedimentary rocks in Pennsylvania, in Nova Scotia, and other regions which had been buried to a depth of at least 16,000 feet are not metamorphic. Mere depth of burial of sediments was not sufficient therefore to produce metamorphism and aqueo-igneous fusion. The baseless and speculative character of the use of minerals as an index of age and of Hunt’s interpretation of New England geology in general was shown by Dana in 1872 (=3=, 91). The following year Dana pointed out clearly that igneous eruptions in general have been derived from a deep-seated source and did not come from the aqueo-igneous fusion of sediments. As to gradations between true igneous rocks and fused and displaced sediments he makes the following statements (=6=, 114, 1873):

“Again, the plastic rock-material that may be derived from the fusion
or semifusion of the supercrust, (that is, of rocks originally of
sedimentary origin,) gives rise to “igneous” rocks often not
distinguishable from other igneous rocks, when it is ejected through
fissures far from its place of origin; while crystalline rocks are
simply _metamorphic_ if they remain in their original relations to the
associated rocks, or nearly so.

Between these latter igneous rocks and the metamorphic there may be
indefinite gradations, as claimed by Hunt. But if our reasonings are
right, the great part of igneous rocks can be proved to have had no
such supercrust origin. The argument from the presence of moisture or
of hydrous minerals in such rocks in favor of their origin from the
fusion of sediments has been shown to be invalid.”

The injected marginal rocks and the post-intrusive metamorphism of most of the New England granites has, however, obscured more or less their real igneous nature so that the gradation from metamorphic sediments through igneous gneisses to granites could be read in either direction. These features misled Dana who accepted the prevailing idea of the general metamorphic origin of granite. Dana makes the following statement (=6=, 164, 1873):

“But Hunt is right in holding that in general granite and syenite (the
quartz-bearing syenite) are undoubtedly metamorphic rocks where not
vein-formations, as I know from the study of many examples of them in
New England; and the veins are results of infiltration through heated
moisture from the rocks adjoining some part of the opened fissures
they fill.”

Granite, although regarded at this time as the extreme of the metamorphic series and originating from sediments, was looked upon as typically Archean in age, though in some cases younger. Such a doctrine permitted such extreme misinterpretations as that of Clarence King and S. F. Emmons on the nature of the intrusive granite of the Little Cottonwood canyon in the Wahsatch Range. This body cuts across 30,000 feet of Paleozoic rocks and to the careful observer, as later admitted by Emmons, shows clear evidence of its transgressive nature. But at that time it was generally considered that granite mountains were capable of resisting the erosion of all geological time. Consequently it did not seem incredible to King and his associates that here a great granite range of Archean origin had stood up through Paleozoic time until gradual subsidence had permitted it to be buried beneath 30,000 feet of sediments.[82]

It may seem to the present day reader that such a misinterpretation, doing violence to fundamental geologic knowledge as now recognized, was inexcusable; but in the light of the history of geology as here detailed it is seen to have been the interpretation natural to that time. It is true that a careful examination of the facts of that very field would have proved the post-Paleozoic and intrusive nature of that great granite body now known as the Little Cottonwood batholith, but Emmons has explained the rapid and partial nature of the observations which they were compelled to make in order to keep up to their schedule of progress (=16=, 139, 1903).

Whitney had found some years earlier that the granites of the Sierra Nevada were igneous rocks intrusive into the Triassic and Jurassic strata. The Lake Superior geologists began to show in the eighties that granite was there an intrusive igneous rock. R. D. Irving and Wadsworth noted these relations. Lawson in 1887 pointed out emphatically (=33=, 473) that the granites of the Rainy Lake region, although basal, were younger than the schists which lay above them. The granite gneisses he held were of clearly the same igneous origin as the granites and neither gave any field evidence of being fused and displaced sediments. From this time forward the truly igneous nature of granite became increasingly accepted until now the notion of its being made of sedimentary rocks softened and recrystallized by the rise of the isogeotherms through deep burial is as obsolete as the still older doctrine of the Neptunists that granite was laid down as a crystalline precipitate on the floor of the primitive ocean.

The recognition of the truly igneous nature of granites has been followed in the present generation by a series of studies on their structural relations and mode of genesis. A number of important initial articles on various aspects of structure and contact relations have appeared in the Journal, but this sketch of the history of the subject may well stop with the introduction to this modern period.

_Orogenic Structures._

_Views of Plutonists and Neptunists._

Orogenic structures are, as the name implies, those connected with the birth of mountains. Nearly synonymous terms are deformative or secondary structures. On a small scale this division embraces the phenomena exposed in the rock ledge or quarry face, or in the dips and dislocations varying from one exposure to another. These structures include faults, folds, and foliation. On a larger scale are included the relations of the different ranges of a mountain system to each other, relations to previous geologic history, relations to the earth as a whole, and to the forces which have generated the structures.

In order to see the stage of development of this subject in 1818 and its progress as reflected through the publications of a century, more particularly in the Journal, it is desirable to turn again to those two treatises emanating from Edinburgh at the beginning of the nineteenth century and representing two opposite schools of thought, the Plutonists and Neptunists.

Playfair, in 1802, devotes nineteen pages to the subject of the inflection and elevation of strata.[83] He places emphasis on the characteristic parallelism of the strike of the folds throughout a region, as shown through the intersection of the folds by a horizontal plane of erosion. He contrasts this with the arches shown in a transverse section and enlarges on our ability to study the deeply buried strata through the denudation of the folded structure. He argues from these relations that the structures can not be explained by the vague appeal of the Neptunists to forces of crystallization, to slopes of original deposition, or to sinking in of the roofs of caverns. The causes he argues were heat combined with pressure. As to the directions in which the pressure acted he is not altogether clear, but apparently regards the pressure as acting in upward thrusts against the sedimentary planes, the latter yielding as warped surfaces. His method of presentation is that of inductive reasoning from facts, but he stopped short of the conception of horizontal compression through terrestrial contraction.

Jameson, professor of natural history in the same university, in 1808 contemptuously ignores the work of Hutton and Playfair in what he calls the “_monstrosities_ known under the name of Theories of the Earth.” In a couple of pages he confuses and dismisses the whole subject of deformation. He states:[84]

“It is therefore a fact, that all inclined strata, with a very few
exceptions, have been formed so originally, and do not owe their
inclination to a subsequent change.

When we examine the structure of a mountain, we must be careful that
our observations be not too micrological, otherwise we shall
undoubtedly fail in acquiring a distinct conception of it. This will
appear evident when we reflect that the geognostic features of Nature
are almost all on the great scale. In no case is this rule to be more
strictly followed than in the examination of the stratified structure.

By not attending to this mode of examination, geognosts have fallen
into numberless errors, and have frequently given to extensive tracts
of country a most irregular and confused structure. Speculators
building on these errors have represented the whole crust of the globe
as an irregular and unseemly mass. It is indeed surprising, that men
possessed of any knowledge of the beautiful harmony that prevails in
the structure of organic beings could for a moment believe it
possible, that the great fabric of the globe itself,—that magnificent
display of Omnipotence,—should be destitute of all regularity in its
structure, and be nothing more than a heap of ruins.”

This was the attitude of a leader of British opinion toward the subject of deformational geology from which the infant science had to recover before progress could be made. The early maps were essentially mineralogical and lithological. The order of superposition and the consequent sequence of age was regarded as settled by Werner in Germany and not requiring investigation in America. The early examples of structure were sections drawn with exaggerated vertical scales and those of Maclure do not show detail.

_Recognition of Appalachian Structures._

Following the founding of the Journal in 1818 there is observable a growth in the quality and detail of geological mapping. Dr. Aiken, professor of natural philosophy and chemistry in Mt. St. Mary’s College, published in the Journal in 1834 (=26=, 219) a vertical section extending between Baltimore and Wheeling, a distance of nearly 250 miles, on a scale of about 7 miles per inch. The succession of rocks is carefully shown and the direction of dip, but no attempt is made to show the underground relations, the stratigraphic sequence, and the folded structures which are so clear in that Appalachian section. The text also shows that the author had not recognized the folded structure. Furthermore, where the folds cease at the Alleghany mountain front, the flat strata are shown as resting unconformably on the folded rocks to the east.

R. C. Taylor, geologist, civil and mining engineer, was from 1830 to 1835 the leading student of Pennsylvanian geology as shown by the publication in 1835 of four papers aggregating over 80 pages in the Transactions of the Geological Society of Pennsylvania. His work is noticeable for accuracy in detail and no doubt was influential in setting a high standard for the state geological survey which immediately followed.

H. D. and W. B. Rogers have been given credit in this country, and in Europe also, as being the leading expounders of Appalachian structure. Merrill speaks of H. D. Rogers as unquestionably the leading structural geologist of his time.[85] To the writer, this attributed position appears to be due to his opportunities rather than to scientific acumen. The magnificent but readily decipherable folded structure of Pennsylvania, the relationships of coal and iron to this structure, the considerable sums of money appropriated, and the work of a corps of able assistants were factors which made it comparatively easy to reach important results. In ability to weigh facts and interpret them Edward Hitchcock showed much more insight than H. D. Rogers, while in the philosophic and comprehensive aspects of the subject J. D. Dana far outranks him.

H. D. Rogers in his first report on the geological survey of New Jersey, 1836, recognizes that the Cambro-Silurian limestones (lower Secondary limestones) were deposited as nearly horizontal beds and the ridges of pre-Cambrian gneiss (Primary) had been pushed up as anticlinal axes (p. 128). He also clearly recognized the distinction between slaty cleavage and true dip as shown in the Ordovician slates (p. 97). Between 1836 and 1840 he had learned a great deal on the nature of folds as is shown in his Pennsylvania report for 1839 and the structure sections in his New Jersey report for 1840.

R. C. Taylor, who had now become president of the board of directors of the Dauphin and Susquehanna Coal Company, published in the Journal in 1841 (=41=, 80) an important paper entitled “Notice of a Model of the Western portion of the Schuylkill or Southern Coal Field of Pennsylvania, in illustration of an Address to the Association of American Geologists, on the most appropriate modes for representing Geological Phenomena.” In this paper he calls attention to the value of modeling as a means of showing true relations in three dimensions. He condemns the custom prevalent among geologists of showing structure sections with an exaggerated vertical scale with its resultant topographic and structural distortions. Taylor was widely acquainted with the structure of Pennsylvania, Maryland, and Virginia.

_Nature of Forces Producing Folding._

In 1825 Dr. J. H. Steele sent to Professor Silliman two detailed drawings and description of an overturned fold at Saratoga Lake, New York. As to the significance of this feature Steele makes the following statement (=9=, 3, 1825):

“It is impossible to examine this locality without being strongly
impressed with the belief that the position which the strata here
assume could not have been effected in any other way than by a power
operating from beneath upwards and at the same time possessing a
progressive force; something analogous to what takes place in the
breaking up of the ice of large rivers. The continued swelling of the
stream first overcomes the resistance of its frozen surface and having
elevated it to a certain extent, it is forced into a vertical
position, or thrown over upon the unbroken stratum behind, by the
progressive power of the current.”

So far as the present writer is aware this is the first recognition in geological literature of the evidence of a horizontally compressive and overturning force as a cause of folding.

To E. Hitchcock belongs the credit of being the first to describe overturning and inversion of strata on a large scale, but without clearly recognizing it as such. In western Massachusetts metamorphism is extreme in the lower Paleozoic rocks in the vicinity of the overthrust mass of Archean granite-gneiss which constitutes the Hoosic range. The Paleozoic rocks of the valley to the west are overturned and appear to dip beneath the older rocks. Farther west the metamorphism fades out and the series assumes a normal position. Such an inverted relation, up to that time unknown, is described in 1833 as follows by Hitchcock in his Geology of Massachusetts (pp. 297, 298):

“But a singular anomaly in the superposition of the series of rocks
above described, presents a great difficulty in this case. The strata
of these rocks almost uniformly dip to the east: that is, the newer
rocks seem to crop out beneath the older ones; so that the saccharine
limestone, associated with gneiss in the eastern part of the range,
seems to occupy the uppermost place in the series. Now as
superposition is of more value in determining the relative ages of
rocks than their mineral characters, must we not conclude that the
rocks, as we go westerly from Hoosac mountain, do in fact belong to
older groups? The petrifactions which some of them contain, and their
decidedly fragmentary character, will not allow such a supposition to
be indulged for a moment. It is impossible for a geologist to mistake
the evidence, which he sees at almost every step, that he is passing
from older to newer formations, just as soon as he begins to cross the
valley of Berkshire towards the west. We are driven then to the
alternative of supposing, either that there must be a deception in the
apparent outcrop of the newer rocks from beneath the older, or that
the whole series of strata has been actually thrown over, so as to
bring the newest rocks at the bottom. The latter supposition is so
improbable that I cannot at present admit it.”

Hitchcock tried to reconcile the evidence by a series of unconformities and inclined deposition, but finds the solution unsatisfactory.

In this same year, 1833, Elie de Beaumont, a distinguished French geologist, published his theory of the origin of mountains. He advanced the idea that since the globe was cooling it was condensing, and the crust, already cool, must suffer compression in adjusting itself to the shrinking molten interior. He concluded from the evidence shown in Europe that the collapse of the crust occurred violently and rapidly at widely spaced intervals of time. This hypothesis introduced the idea of mountain folding by horizontal compressive forces. The theoretical paper of de Beaumont, together with further observations by Hitchcock and others, led the latter in 1841 to a final belief in the inversion of strata on a large scale by horizontal compression. His conclusions are expressed in an important paper published in the Journal (=41=, 268, 1841) and given on April 8, 1841, as the First Anniversary Presidential Address before the Association of American Geologists. This comprehensive summary of American geology occupies 43 pages. Three pages are given to the inverted structure of the Appalachians from which the following paragraphs may be quoted:

“We have all read of the enormous dislocations and inversions of the
strata of the Alps; and similar phenomena are said to exist in the
Andes. Will it be believed, that we have an example in the United
States on a still more magnificent scale than any yet described?...

Let us suppose the strata between Hudson and Connecticut rivers, while
yet in the plastic state, (and the supposition may be extended to any
other section across this belt of country from Canada to Alabama,) and
while only slightly elevated, were acted upon by a force at the two
rivers, exerted in opposite directions. If powerful enough, it might
cause them to fold up into several ridges; and if more powerful along
the western than the eastern side, they might fall over so as to take
an inverted dip, without producing any remarkable dislocations, while
subsequent denudation would give to the surface its present
outline....

Fourthly, we should readily admit that such a plication and inversion
of the strata might take place on a small scale. If for instance, we
were to press against the extremities of a series of plastic layers
two feet long, they could easily be made to assume the position into
which the rocks under consideration are thrown. Why then should we not
be equally ready to admit that this might as easily be done, over a
breadth of fifty miles, and a length of twelve hundred, provided we
can find in nature, forces sufficiently powerful? Finally, such forces
do exist in nature, and have often been in operation.”

The advanced nature of these conceptions may be appreciated by contrasting them with those put forth by H. D. and W. B. Rogers on April 29, 1842, before the third annual meeting of the same body (=43=, 177, 1842) and repeated by them before the British Association at Manchester two months later. In their own words, the Rogers brothers from their studies on the folds shown in Pennsylvania and Virginia, conceived mountain folds in general to be produced by much elastic vapor escaping through many parallel fissures formed in succession, producing violent propulsive wave oscillations on the surface of the fluid earth beneath a thin crust. Thus actual billows are assumed to have rolled along through the crust. They did not think tangential pressure alone could produce folds. Such pressures were regarded as secondary, produced by the propagation of the waves and the only expression of tangential forces which they admitted was to fix the folds and hold them in position after the violent oscillation had subsided (=44=, 360, 1843). The leading British geologists De la Beche and Sedgwick criticized adversely this remarkable theory, stating that they could see no such analogy in mountain folds to violent earthquake waves and that in their opinion the slow application of tangential force was sufficient to account for the phenomena (=44=, 362–365, 1843).

H. D. Rogers in the prosecution of the geological survey of Pennsylvania displayed notable organizing ability and persistence in accomplishment, even to advancing personally considerable sums of money, trusting to the state legislature to later reimburse him. Finally, after many delays by the state, the publication was placed directly in his charge and he produced in 1858 a magnificent quarto work of over 1,600 pages, handsomely illustrated, and accompanied by an atlas. It is excellent from the descriptive standpoint, standing in the first class. Measured as a contribution to the theory of dynamical geology, the explanatory portions were, however, thirty years behind the times. The same hypotheses are put forth in 1858 as in 1842. There is no acceptance of the views of Lyell concerning the uniformitarian principles expounded by this British leader in 1830, or of the nature of orogenic forces as published by Elie de Beaumont in 1833. Rogers rejects the view that cleavage is due to compression and suggests “that both cleavage and foliation are due to the parallel transmission of planes or waves of heat, awakening the molecular forces, and determining their direction.”[86] Thus a mere maze of words takes the place of inductive demonstrations already published.

In following the play of these opposing currents of geologic thought we reach now the point where a period of brilliant progress in the knowledge of mountains and of continental structures begins in the work of J. D. Dana. In 1842 Dana returned from the Wilkes Exploring Expedition and the following year began the publication of the series of papers which for the next half century marked him as the leader in geologic theory in America. His work is of course to be judged against the background of his times. His papers mark distinct advances in many lines and are characterized throughout by breadth of conception and especially by clear and logical thinking. His work was published very largely in the Journal, of which after a few years he became chief editor. His first contribution on the subject of mountain structures, entitled “Geological results of the earth’s contraction in consequence of cooling,” was published in 1847 (=3=, 176). The evidence of horizontal pressure was first perceived in France as shown by the features of the Alps. Elie de Beaumont connected it, by means of the theory of a cooling and contracting globe, with the other large fact of the increase of temperature with descent in the crust. Dana credits the Rogers brothers with first making known the folded structures of the Appalachians, but objects to their interpretation of origin. He showed by means of diagrams that the folds are to be explained by lateral pressure, the direction of overturning indicating the direction from which the driving force proceeded.

The Rogers brothers and especially James Hall, in working out the Appalachian stratigraphy, had noted that the formations, although accumulating to a maximum thickness of between 30,000 and 40,000 feet, showed evidences that the successive formations were deposited in shallow water. It suggested to them that the weight of the accumulating sediments was the cause of subsidence, each foot of sediment causing a foot of down sinking. This idea has continued to run through various text books in geology for half a century, yet Dana early saw the fallacy and in 1863 in the first edition of his Manual of Geology (p. 717) states “whether this is an actual cause or not in geological dynamics is questionable.” In 1866 in an important article on “Observations on the origins of some of the earth’s features,” Dana deals more fully and finally with this subject (=42=, 205, 252, 1866). He shows that such an effect of accumulating sediment postulates a delicate balance, a very thin crust and no resistance below. If such a weakness were granted it would be impossible for the earth to hold up mountains. Furthermore such subsidence was not regular during its progress and finally in the long course of geologic time gave place to a reverse movement of elevation.

Hall had pointed out the fact that the sediments were thickest on the east in the region of mountain folding and thinned out to a fraction of this thickness in the broad Mississippi basin. Hall argued that the mere subsidence of the trough would produce the observed folding and that the folding was unrelated to mountain making or crustal shortening. In supposed proof he cited the fact that the Catskills consist of unfolded rock, are higher than the folded region to the south, and nearly as high as the highest metamorphic mountains to the east.[87] Hall and all his contemporaries were handicapped in their geological theories by a complete inappreciation of the importance of subaërial denudation. For subscribing to these errors of their time even the ablest men should not be held responsible. Hall was the most forcible personality in geology in his generation. His contributions to paleontology were superb. His perception of the relation existing between troughs of thick sediments and folded structures was a contribution of the first importance; yet in the structural field his argument as to the production of the Appalachian folds by mere subsidence during deposition indicates a remarkable inability to apply the logical consequences of his hypothesis to the nature of the folds as already made known by the Rogers. Dana pointed out in reply to Hall that the folding did not correspond to the requirements of Hall’s hypothesis, especially as the folding took place not during, but after the close of the vast Paleozoic deposition. Dana states in conclusion on Hall’s hypothesis (=42=, 209, 1866) that “It is a theory of the origin of mountains with the origin of mountains left out.”

_The Theory of Geosynclines and Geanticlines._

The fact that systems of folded strata lie along axes of especially thick sediments and that this implied subsidence during deposition was Hall’s contribution to geologic theory, but curiously enough he failed, as shown, to connect it with the subsequent nature of mountain folding. He did not see why such troughs should be weak to resist horizontal compression. The clear recognition of this relationship was the contribution of Le Conte, who in a paper on “A theory of the formation of the great features of the earth’s surface” (=4=, 345, 460, 1872), reached the conclusion that “mountain chains are formed by the mashing together and the up-swelling of sea bottoms where immense thicknesses of sediment have accumulated.”

As to the cause why mashing should take place along troughs of thick sediments Le Conte adopts the hypothesis of aqueo-igneous fusion proposed independently long before by Babbage and Herschel and elaborated into a theory of igneous rocks by Hunt. Under this view, as the older sediments became deeply buried, the heat of the earth’s interior ascended into them, and since they included the water of sedimentation a softening and metamorphism resulted. Dana had shown, however, six years previously (=42=, 252, 1866), as the following quotation will indicate, that metamorphism of sediments required more than deep burial and that no such weakening as was postulated by Herschel had occurred:

“The correctness of Herschel’s principle cannot be doubted. But the
question of its actual agency in ordinary metamorphism must be decided
by an appeal to facts; and on this point I would here present a few
facts for consideration.

The numbers and boldness of the flexures in the rocks of most
metamorphic regions have always seemed to me to bear against the view
that the heat causing the change had ascended by the very quiet method
recognized in this theory....

But there are other facts indicating a limited sufficiency to this
means of metamorphism. These are afforded by the great faults and
sections of strata open to examination. In the Appalachian region,
both of Virginia and Pennsylvania, faults occur, as described by the
Professors Rogers, and by Mr. J. P. Lesley, which afford us important
data for conclusions. Mr. Lesley, an excellent geologist and
geological observer, who has explored personally the regions referred
to, states that at the great fault of Juniata and Blair Cos.,
Pennsylvania, the rocks of the Trenton period are brought up to a
level with those of the Chemung, making a dislocation of at least
16,000, and probably of 20,000, feet. And yet the Trenton limestone
and Hudson River shales are not metamorphic. Some local cases of
alteration occur there, including patches of roofing slate; but the
greater part of the shales are no harder than the ordinary shales of
the Pennsylvania Coal formation.

At a depth of 16,000 feet the temperature of the earth’s crust,
allowing an increase of 1° F. for 60 feet of descent, would be about
330° F.; or with 1° F. for 50 feet, about 380° F.—either of which
temperatures is far above the boiling point of water; and with the
thinner crust of Paleozoic time the temperature at this depth should
have been still higher. But, notwithstanding this heat, and also the
compression from so great an overlying mass, the limestones and shales
are not crystalline. The change of parts of the shale to roofing slate
is no evidence in favor of the efficiency of the alleged cause; for
such a cause should act uniformly over great areas.”

The next contribution to the theory of orogeny was a series of papers published in 1873 by Dana, entitled “On some results of the earth’s contraction from cooling, including a discussion on the origin of mountains and the nature of the earth’s interior.”[88] This contribution, viewed as a whole, ranks among the first half dozen papers on the science of mountains. The following quoted paragraphs give a view of the scope of this article:

“_Kinds and Structure of Mountains._”

“While mountains and mountain chains all over the world, and low
lands, also, have undergone uplifts, in the course of their long
history, that are not explained on the idea that all mountain
elevating is simply what may come from plication or crushing, the
_component parts_ of mountain chains, or those simple mountains or
mountain ranges that are the product of one _process of making_—may
have received, _at the time of their original making_, no elevation
beyond that resulting from plication.

This leads us to a grand distinction in orography, hitherto neglected,
which is fundamental and of the highest interest in dynamical geology;
a distinction between—

1. A simple or _individual_ mountain mass or range, which is the
result of _one process of making_, like an individual in any process
of evolution, and which may be distinguished as a _monogenetic_ range,
being _one in genesis_; and

2. A composite or _polygenetic_ range or chain, made up of two or more
monogenetic ranges combined.

The Appalachian chain—the mountain region along the Atlantic border of
North America—is a _polygenetic_ chain; it consists, like the Rocky
and other mountain chains, of several _monogenetic_ ranges, the more
important of which are: 1. The Highland range (including the Blue
Ridge or parts of it, and the Adirondacks also, if these belong to the
same process of making) pre-Silurian in formation; 2. The Green
Mountain range, in western New England and eastern New York, completed
essentially after the Lower Silurian era or during its closing period;
3. The Alleghany range, extending from southern New York southwestward
to Alabama, and completed immediately after the Carboniferous age.

The making of the Alleghany range was carried forward at first through
a long-continued subsidence—a _geosynclinal_ (not a _true_ synclinal,
since the rocks of the bending crust may have had in them many true or
simple synclinals as well as anticlinals), and a consequent
accumulation of sediments, which occupied the whole of Paleozoic time;
and it was completed, finally, in great breakings, faultings and
foldings or plications of the strata, along with other results of
disturbance.

These examples exhibit the characteristics of a large class of
mountain masses or ranges. A geosynclinal accompanied by sedimentary
depositions, and ending in a catastrophe of plications and
solidification, are the essential steps, while metamorphism and
igneous ejections are incidental results. The process is one that
produces final stability in the mass and its annexation generally to
the more stable part of the continent, though not stable against
future oscillations of level of _wider range_, nor against denudation.

It is apparent that in such a process of formation elevation by direct
uplift of the underlying crust has no necessary place. The attending
plications may make elevations on a vast scale and so also may the
shoves upward along the lines of fracture, and crushing may sometimes
add to the effect; but elevation from an upward movement of the
downward bent crust is only an incidental concomitant, if it occur at
all.

We perceive thus where the truth lies in Professor Le Conte’s
important principle. It should have in view alone _monogenetic_
mountains and these only _at the time of their making_. It will then
read, plication and shovings along fractures being made more prominent
than crushing:

Plication, shoving along fractures and crushing are the true sources
of the elevation that takes place _during the making_ of geosynclinal
monogenetic mountains.

And the statement of Professor Hall may be made right if we recognize
the same distinction, and, also, reverse the order and causal relation
of the two events, accumulation and subsidence; and so make it read:

Regions of monogenetic mountains were, previous, and preparatory, to
the making of the mountains, areas each of a slowly progressing
geosynclinal, and, _consequently_, of thick accumulations of
sediments.

The prominence and importance in orography of the mountain
individualities described above as originating through a geosynclinal
make it desirable that they should have a distinctive name; and I
therefore propose to call a mountain range of this kind a
_synclinorium_, from _synclinal_ and the Greek ὄρος, mountain.

This brings us to another important distinction in orographic
geology—that of a second kind of monogenetic mountain. The
_synclinoria_ were _made through a progressing geosynclinal_. Those of
the second kind, here referred to, were _produced by a progressing
geanticlinal_. They are simply the upward bendings in the oscillations
of the earth’s crust—the geanticlinal waves, and hardly require a
special name. Yet, if one is desired, the term _anticlinorium_, the
correlate of _synclinorium_, would be appropriate. Many of them have
disappeared in the course of the oscillations; and yet, some may have
been for a time—perhaps millions of years—respectable mountains.

The geosynclinal ranges or synclinoria have experienced in almost all
cases, since their completion, true elevation through great
geanticlinal movements, but movements that embraced a wider range of
crust than that concerned in the preceding geosynclinal movements,
indeed a range of crust that comes strictly under the designation of a
polygenetic mass.”

“_The Condition of the Earth’s Interior._”

“The condition of the earth’s interior is not among the geological
results of contraction from cooling. But these results offer an
argument of great weight respecting the earth’s interior condition,
and make it desirable that the subject should be discussed in this
connection. Moreover, the facts throw additional light on the
preceding topic—the origin of mountains.

It seems now to be demonstrated by astronomical and physical
arguments—arguments that are independent, it should be noted, of
direct geological observation—that the interior of our globe is
essentially solid. But the great oscillations of the earth’s surface,
which have seemed to demand for explanation a liquid interior, still
remain facts, and present apparently a greater difficulty than ever to
the geologist. Professor Le Conte’s views, in volume iv, were offered
by him as a method of meeting this difficulty; yet, as he admits in
his concluding remarks, the oscillations over the interior of a
continent, and the fact of the greater movements on the borders of the
larger ocean, were left by him unexplained. Yet these oscillations are
not more real than the changes of level or greater oscillations which
occurred along the sea border, where mountains were the final result;
and this being a demonstrated truth, no less than the general solidity
of the earth’s interior, the question comes up, how are the two truths
compatible?

The geological argument on the subject (the only one within our
present purpose) has often been presented. But it derives new force
and gives clearer revelations when the facts are viewed in the light
of the principles that have been explained in the preceding part of
this memoir.