Page images
PDF
EPUB

stripped of its bark, to thus survive for three seasons?

Jas. Lewis HOWE. WASHINGTON AND LEE UNIVERSITY,

LEXINGTON, VA.

SPECIAL ARTICLES. PHYSICAL CHARACTERS AND HISTORY OF SOME

NEW YORK FORMATIONS." We are accustomed to define historical geology as the history of the earth and its inhabitants, and this definition no doubt fully covers the subject. But it may be questioned if, in the ordinary treatment of the subject, such as it receives in our current text-books and lecture halls, we do it justice to the full extent suggested by our definition. Is it not too often merely the history of the inhabitants of the earth that we are treating, giving the history of the earth itself, i. e., its physical development, only scant recognition? I believe I am not going too far when I say that we give proportionately too much attention to the biologic or paleontologic side, and too little to the physical or stratigraphic. I do not wish to be understood to say that paleontology receives too much attention in our institutions of learning. Far from it. Paleontology is not receiving a fraction of the attention it requires, and which it will receive in the future when our curricula are more normally balanced. But paleontology is not the whole of historical geology. Stratigraphy, or the physical characters and physical history of the rocks of the earth's crust-paleophysiography (if I may use a pet term, in spite of objections raised against it)-is fully one half of his torical geology.

It is true, of course, that historical geology reposes on a foundation of paleontology—the divisions of the earth's history are based on the progress of life, and not, as has been too often assumed, on breaks in the sedimentary series, extensive and important as these may be. The standard of comparison must be a series of sediments which contain a continuous record of development, and since it is only in

1 An address delivered before Section E, American Association for the Advancement of Science, Syracuse meeting, July 21, 1905.

marine sediments that we get a continuous series, only marine formations, and such as do not represent merely local conditions, must be selected as our standard of reference.

Much as we prize, and justly prize, the classical standard of our North American Paleozoic series—the incomparable column furnished by the strata of the state of New York—and loath as we may be to attack any part of it, yet we must confess that it is not a perfect column throughout, and that the imperfection which it embodies can not be overlooked. Indeed, the sworn guardians of this monument have themselves recognized that it is an incomplete structure, and have introduced such foreign elements as the Cincinnatian group and the Richmond formation, besides accepting emendations proposed by others, such as Acadian and Georgian. They have, however, sought consolation for this forced recognition of the imperfections of the New York series, by proposing that the world at large accept the broader terms of the New York classification-Taconic, Champlainic, Ontaric—in place of the better known, though not always prior, terms Cambric, Ordovicic and Siluric.

But it is one thing to recognize the absence of an element in the standard series and to fill the gap by a foreign representative, and another to regard an old and well-known formational unit as imperfect, and as inexpressive of the time element which it represents, and to acquiesce in its replacement by another. Yet I believe this is what we shall come to in the case of such old standards as the Medina sandstone and the Salina group, not to speak of the Oneida conglomerate, formations which are still tolerated in the standard scale of North American Paleozoic formations, but which in a very imperfect manner represent the chronologic epochs for which they are commonly used. This is due to the fact that they were not deposited in the open sea, but rather under peculiar conditions, i. e., estuarine, if not continental, in the case of the Oneida and Medina, and salt sea, if not desert, conditions in the Salina. Moreoyer, it is now pretty well ascertained that the typical Oneida conglomerate of Oneida County is the time equivalent of the Upper Medina of the Niagara section, and that both probably should be united to the Clinton, while the lower 1,100 feet of the Medina of western New York may possibly represent the continental or estuarine phase of deposits, representing elsewhere the later Richmond period.

A satisfactory standard for the Lower Siluric is found in the island of Anticosti; and although this belongs to another geographic province of the Siluric seas, it represents far more completely the progress of biologic development than do the lower beds of the New

Siluric beds deposited in the Siluric Mediterranean; unless the Mayville beds of Wisconsin should prove to represent the lowest Siluric.

To go, for a moment, outside of New York state, the same argument applies to the sediments of the mid-Carbonics, or Pennsylvanian, of eastern United States. Though now taken as a standard for comparison, to which all other Carbonic formations of North America are referred, they are manifestly unfit for this important position, not only because they represent continental conditions, and do not furnish us with a standard of marine sedimentation, but because it is obviously impossible to determine, at least with our present means, how complete the series is. There may be, and probably are, vast breaks in this series of non-marine sediments, breaks which may or may not be revealed in the floral succession. A far more satisfactory standard, and one more nearly comparable with the European standard, is that furnished by the mid-Carbonic sediments of Arkansas, Missouri and Kansas, or by those of Texas. When these sediments and their marine faunas have been fully studied we shall have a mid-Carbonic standard worthy of the name; and when that is accomplished—as we have good hopes that it will be before long, judging from the results already achieved by the labors of the earnest workers in those fields—then let us hope that the inappropriate term Pennsylvanian will be replaced by one more expressive of the marine sedimentation of that age.

but I am not here to speak of the imperfection of the geologic record, an imperfection which I think is more apparent than real, nor of the imperfection of our classification, which is more real than apparent. What I have said, however, will serve to define my position with reference to the importance of paleontology to the geologist. Let me return, then, to the consideration of the importance of the physical characters of our formation. I believe that the general neglect which this phase of the subject has suffered is in part due to the clumsy and unrefined nomenclature which we have inherited from the fathers of our science, and which, with the tacit, if not expressed, understanding that what was good enough for them is good enough for us, we have retained to the present time. So long as we express in our nomenclature that all stones composed of lime are limestones, and nothing more, so long, I believe, progress in the study of physical stratigraphy will be hampered. So long as we are content to use indiscriminately the structural terms slate and shale for rocks which have no other claim to these names than that clay generally enters into their composition-if that may be considered a claim—so long progress in this direction will be retarded. Naumann and Hauy long ago proposed textural terms for the three great types of clastic rocks, but these have been mostly overlooked by modern writers except the Germans, who are far ahead of us in the study of physical stratigraphy. It is true the terms of Naumann and IIauy, derived from the Greek, are not very euphoneous, nor do they lend themselves readily to composition, yet they are much better than indefinite descriptive phrases. Calcopsephyte and calcopsammyte do not fall pleasantly on the ear, yet they are far better than the indefinite terms, brecciated limestone—which might mean limestone brecciated by subsequent causes—or granular limestones—which might mean a number of different things. Certainly calcopelite is far better than the vague and roundabout phrase: “compact, fine-grained limestone with conchoidal fracture,' which leaves you still in doubt whether the rock in question is a clastic, composed of lime flour, or a massive organic rock in which all organic structure has been obliterated. Personally, I prefer terms derived from the Latin as being more adaptable in composition in this instance than the Greek terms of Naumann and Hlauy; but whether we say calcopsephyte, calcopsammyte and calcopelyte or calcirudyte, calcarenyte and calcilutyte, is of minor significance, so long as we employ a term which will express exactly the physical characters of the rock. If the name at the same time expresses, in part, the history of the rock, by indicating it to be a clastic and not an organic rock, this can only be regarded as a further advantage. Certainly, if you understood that a lutyte was a clastic rock composed of fine rock flour, you would, I think, be in favor of describing many of the beds of the Manlius and water-lime of this region as argillaceous calcilutytes or pure calcilutytes, as the case may be, rather than to speak of them as: 'compact, finely-bedded argillaceous limestones with conchoidal fracture and of an impalpable grain. I should, at any rate; for, if nothing more than brevity is gained, the short term is a distinct advantage.

But the application of a more precise nomenclature to the clastic rocks is only a first step in the right direction. The lithic character of the rocks must be studied with reference to their origin, i. e., the lithogenesis of the formations must be considered, and the bearing which this has on the distribution of land and sea in past geologic epochs. The careful study of local sections, the measurements of thicknesses and the determination of the distribution of fossils, are of course, an important preliminary. But while this is done, a careful diagnosis of the lithic character of the rock and a determination of its source should be made, and special care should be given a precise description of its relationship to adjacent formations. The latter feature is too often neglected, when it is of the greatest importance, as an example will show. Most of the descriptions of the Chattanooga black shale which I have been able to find speak of it as a black bituminous shale, with some few additional remarks on its petrographic character. They mention the

fossils which are found in it and refer the formation to the Devonic, with sometimes a more precise reference to the Marcellus or the Genesee of New York. But its relation to the succeeding formation is almost never discussed. Here and there in the literature we find a hint, and only a hint, that it grades up into the overlying rock. Rarely is there a more precise description of this gradation, like William's description of its relation to the overlying Grainger shale. And yet this is of very great importance, for if the Chattanooga shale of eastern Tennessee is Devonic, then there is not only a pronounced hiatus at its base, but another at its top, for the immediately overlying Fort Payne beds represent in some localities the St. Louis, in other the Keokuk. In still other localities we find beds of Chester age following immediately upon the black shale, which often is only a few feet thick, while in other localities again these black shales are succeeded by beds of Burlington or Kinderhook age. If, as I strongly suspect, and as seems to be occasionally hinted at in the literature, there is no hiatus at the top of the black shale, but a transition to the overlying formation, then the black shale surely represents the basal formation formed by a sea transgressing southward and eastward over a peneplained land surface, and its age varies in different localities. At the type locality, Chattanooga, Tennessee, the age of the black shale is in that case Burlington or perhaps early Koekuk, while at others its age is St. Louis, or even later. Only in the northern region, where it is succeeded by Kinderhook beds, as at New Albany, Indiana, and at Big Stone Gap, Virginia, is the black shale of Devonic age.

And this brings me to the consideration of another factor which is all too often overlooked in stratigraphic work. This is the phenomenon of progressive overlap, and the complementary one, which, for lack of a better term, we may call regressive overlap. We all agree that in normal sedimentation coarse clastic rocks are formed near shore, finer farther out and the finest impalpable flour is only deposited at a great distance from the normal shore, while clastic limestone may be

formed anywhere under favorable conditions. to the crystalline rock, find a quartz sandBut we do not generally apply this principle rock (silicarenyte) resting immediately on the in the elucidation of our rock sections. When, crystalline, followed by a calciferous sand for example, a prolonged subsidence of the rock (calcareous silicarenyte), which grades up land occurs, resulting in the overflow of the into siliceous calcarenyte, and finally into pure land by the sea, the waves of the advancing calcarenytes or clastic limestones. Lithically sea will work over the residual soil of the considered, this section might be regarded as land which it overflows and will spread a representing the whole series from Potsdam basal layer of conglomerate or sand or, in rare up, whereas in reality the basal bed is Beekcases, of mud over the old land thus sub- mantown, if not Upper Chazy. : merged, the nature of the basal bed depending Regressive movements of the sea, by which on the character of the rock débris which large tracts of previously submerged land becovered the old land, the slope of this old come exposed, also leave a record in the sediland and the consequent depth of the en- mentary series which, by careful consideration, croaching sea, and the rapidity of the sub- can be detected. Thus a comparison of secmergence. This latter may be so great that tions shows that we have in the Mohawk Valareas of land are suddenly submerged, while ley some three or four hundred feet of Beekthe shore is transferred far up on to the old mantown, which in places, as at Little Falls, land, so that offshore deposits, like organic rests directly upon the gneiss with a basal limestones, may form directly on the old land rudyte. These Beekmantown beds probably surface.

represent the lower, though probably not the The basal layer thus formed will not be of lowest, members of that formation, judging the same age throughout, but will rise in the from the presence of Opheleta complanata. scale with the advance of the sea. Seaward, Not more than a hundred and fifty miles finer deposits will be laid down upon the basal south, in central Pennsylvania, the Beekmanformations, these finer deposits corresponding town is represented by over two thousand feet in age to the basal sandstone at that time of similar strata, followed by some two to forming near the shore. To illustrate: the three thousand feet of the Stone's River group, basal sands of the Cambric Ocean were spread which in the Mohawk is represented by less by an advancing sea over the crystalline rock than a hundred feet of its upper portion, and floor. East of Lake Champlain this basal there known as Lowville. Similarly, in the sandstone belongs to the Lower Cambric, but upper Mississippi region the Lower Magnesian westward it rises in the scale until at the foot limestones, which indicate a continuous deof the Adirondacks it is the Potsdam sand- position from the Upper Cambric, are less stone of Upper Cambric age, while the corre- than three hundred feet in thickness and repsponding deposits further east are clay and resent the lowest Beekmantown. The Stone's lime-rocks. Again, while on the east of the River, or Chazy, is represented by less than Adirondacks, at the point of present outcrops, a hundred feet of strata, which grade upward the basal sandstone is Potsdam, followed by cal into the Black River, as do the corresponding ciferous sand-rock and by purer calcarenytes strata-Lowville—in the Mohawk and Black of Beekmantown age, the outcrop on the west River Valleys. These Stone's River beds of of the Adirondacks shows similar basal quartz Minnesota, from their relation to the overlying sandstones, followed by calciferous sand-rock beds, and from their fossils, are seen to be the and later by pure calcilutytes, but all, from uppermost portion of that series. Between the base up, of Lowville or Upper Chazy age. the lowest Beekmantown and the highest The Beekmantown and Potsdam are here over- Chazy (or Stone's River) lie about 200 feet lapped by the later deposits, which, however, of pure quartz sandstone-a typical silirepeat the lithic seguence seen in the section carenyte-known as the St. Peter sandstone. of earlier age on the east of the Adirondacks. This sandstone has been traced very widely Wells sunk in the neighborhood of Syracuse over the Mississippi Valley region; but as we follow it southward the thickness of Peter, thus representing a retreatal sandstone, Beekmantown below and Chazy above in- worked over by the winds, also represents a creases more or less regularly, until in In- basal bed of an advancing sea; and while the dian Territory, where the St. Peter thins last remnants of it in southern United States away, we have nearly two thousand feet mark practically no break in the sedimentary of the Beekmantown and more than that of series, this same rock in southern Minnesota the Chazy or Stone's River. These facts occupies the interval between all but the lowest point to a very remarkable episode in North Beekmantown and all but the highest Chazy.' American Ordovicic history, namely, the slow Now, in New York state we have no St. retreat of the sea from the upper Mississippi Peter, but we have the other conditions preValley, which as it retreated gradually washed cisely like those of the upper Mississippi Valthe sands of the northern shore seaward, ley. The lowest Beekmantown is followed spreading them over the previously deposited by the highest Chazy, the interval unrepreoffshore beds. As the sea retreated, deposition sented between the two being marked in cencame, of course, to an end. Thus when the tral Pennsylvania by over 4,000 feet of sediretreat had reached southern Minnesota, only ment. This break, or stratigraphic unconthe lower 250 feet of Beekmantown had been formity, long suspected, has recently been acdeposited, and there deposition stopped. When tually located in the Mohawk Valley by Prothe retreating seashore had reached central fessor Cushing. It should be remarked that United States, only the lower thousand feet during all the time that central and western of Beekmantown had been deposited, and only New York was dry land, i. e., during the time in southern United States, which was not laid occupied by the formation of 4,000 feet of bare, was there a complete deposition of the limestone strata elsewhere, continuous or calcarenytes and organic limestones of the nearly continuous deposition went on in what Beekmantown. The area uncovered—the is now the Champlain Valley. whole of central United States-was spread We must now consider a somewhat more over by the sand left by the retreating sea, complicated series. In western New York the and this was no doubt blown about by the Lorraine beds—considered the highest of the wind, the grains rounded and the remarkable Ordovicic—are followed by red lutytes and structure and purity of the St. Peter-probably arenytes (mud-rocks and sand-rocks), over a the best example of an ancient desert rock thousand feet thick, and unfossiliferous. At extant-was thus produced. When the sea the base is a quartz sandstone, about 75 feet again advanced over this desert area, the thick, and over it are about a hundred feet of upper portion of these sands was worked over quartz sandstones, mostly red, and some shales and became true water-laid deposits, and at which contain marine fossils closely allying the same time graded up into the overlying them to the overlying Clinton. I speak, of calcareous beds. By the time the sea had course, of the Medina formation. A little advanced half way to the old northern shore, south of Utica, the Lorraine shales, reprea thousand feet, more or less, of the lower sented only by their lower hundred feet, are Chazy had been deposited in the southern succeeded by the Oneida conglomerate, a pure states. At the point then reached Chazy quartz-pebble conglomerate with well-rounded deposition began with the middle members of pebbles. This conglomerate, less than 50 feet the formation. By the time the sea had thick, is followed by the shales, sand, mud reached its northern shore, from which it orig- and lime rocks of the Clinton. The base of inally retreated, and which was somewhere the conglomerate is fossiliferous, the fossilnorth of Lake Superior—the whole of the Arthophycus harlani—being the same which Chazy--nearly 2,000 feet had been deposited is restricted to the top beds of the Medina in in the southern states, the upper thousand in western New York. In the cement region of the central states, but only the uppermost 50 Dr. C. P. Berkey will shortly publish a deor 75 feet in southern Minnesota. The St. tailed discussion of the St. Peter problem.

« PreviousContinue »