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bone which "resembles that of the Irish elk," all, (as in Ohio, above the Erie clay or lower till (except in one instance), in what he considers to be a lacustral deposit. The stratum containing the remains is reported from the counties of Dubois,27 Dearborn, Ohio, and Switzerland,28 Warren, Lawrence, and Knox,29 -Brown,30 Jennings, Ripley, and Montgomery.31 In Dubois county the shrubs and grapevines were of "enormous growth," indicative of the "luxuriance ofia warmer clime ;" in Warren county the "roots of trees, shrubs and plants," are spoken of as "of pre-glacial age," being covered with drift (though it seems to have been, as is usually the case here, a part of the Erie clay, nothing else being ever spoken of as "glacial drift"); and in Jennings county the wood "had been very much crushed and twisted, showing that it had been subjected to very great force." The wood was so little metamorphosed here, however, as to be used as fuel, half a cord or more being burned. These reports show that in Indiana the forest bed (there can be no doubt that in some of these cases, if not in all, the wood is of the same age as in the Ohio forest bed) is sometimes distinctly above the Erie claj' or lower till, as is usually the case in Ohio, and sometimes intercalated with its strata —when it exhibits stratification. It is subjacent to rearranged drift materials, as in Ohio, when at the top of the Erie clay, and never, so far as recorded, covered by uumodifled drift, as in the localities examined by Whittlesey and in that described in this paper.
In Nebraska, a section on Oak creek, Lancaster county, where the surface is covered by the loess, showed the following sequence : —
The forest bed is common to many parts of Nebraska. It is "found in the glacial drift, and separates it into two portions."33
•» " Geological Survey of Indiana," Ann. Eep. 1872, p. 193.
« Ibid., p. 402, et let/.
«» Ibid., 1873, pp. 194, 270, 318.
•« Ibid., 1874, p. 83.
«Ibid., 1875, pp. 172-173, 190, 393.
»>" Superficial Deposits of Nebraska " (second ed. — from Hay den's Report for 1874), p. 8.
"Ibid., p. 11.
The Assistant State Geologist of New Hampshire, Prof. Warren Upham, mentions the division of the till into two members, by Otto Torell, of Sweden, "the lower characterized by its blue color, its compactness and hardness and its glaciated stones; the upper being marked by a yellow and reddish color, comparative looseness of the mass, and its angular or unworn bowlders ;" and he adds that the same division is found in New Hampshire, where, however, the lower till is dark grey in color, and is distinctly laminated.34 The occurrence of organic remains in any part of the drift is not recorded in this connection.
Mr. James Geikie, the Scottish geologist, gives a more detailed description of the Scandinavian drift in his "Great Ice Age." "It consists of two distinct layers, the lower of which is generally darker in color, and containing fewer big stones than the upper."35 Between the two is found the equivalent of the Ohio forest bed, or at least a stratum corresponding with it, from which five species of shells and two of plants have been recognized, and which is supposed by the Swedish geologists to represent a warmer interglacial era. The same author tells us that in Switzerland the lowest glacial deposit is "a dark tough clay packed with scratched and well-rubbed stones, and containing here and there some admixture of sand, and irregular beds and patches of earthy gravel."36 It is quite unstratitted, if we except these occasional intercalated gravel-beds. Overlying this is found sometimes, as at Diirnten and Wetzikon, in the canton of Zurich, the hoinologue of the forest bed here taking the form of beds of lignite from two to twelve feet in thickness.37 Numerous remains of trees, identical with or related to the species now inhabiting the same region, are found, from an examination of which, Prof. Heer (than whom there is no higher authority) concludes that the climate of Switzerland during the inter-glacial period was not materially different from now. Associated with these have been found the bones of the Asiatic elephant, a species of rhinoceros, the urus, the great stag, and the cave bear, which affords evidence that the deposit of that formation was synchronous with that of our own forest bed. Above this are found "a considerable thickness of gravel and sand, in beds which are surmounted with several large alpine erratics."
"Am. Jour. Set., Ill, Vol. XIV, Dec, 1677, p. 402.
"A similar succession of deposits has been detected by Professor Hanns Hofer, as occurring in Carinthia," where the organic stratum yields remains of the woolly rhinoceros, the steinbock, and Bos tawrws.38 To these instances of inter-glacialbeds Mr. James Croll, the author, of "Climate and Time," adds others at Dranse (Switzerland), Hoxne, Chapelhall, Craiglockhart, Lieth-walk, Redhall Quarry, Beith, Crofthead, and Kilmaurs in Great Britain, with others at many localities.39 In every such case the organic stratum is found between beds of true glacial drift, often unmodified. Indeed, the presence in Great Britain of a lower till usually stained with protoxide of iron, resting on the older rocks with or without the infraposition of a thin gravelly or sandy stratum, and overlaid by first, a deposit containing organic remains in abundance, and second, a true glacial drift, has long been known ; and descriptions of the phenomena by Croll, Geikie, Belt and others, are within the reach of all — though Mr. Belt's ideas, relative to the deposit of the materials, differ from those of the first-named geologists in important particulars.
These references will be sufficient to show that not only the formation here described as member number four, but the general succession of deposits in northeastern Iowa, are not peculiar to a limited area, but are co-extensive with glacial indications.
As has been seen, there is some variation in the position of the forest bed or carbonaceous stratum, with relation to the bowlder clay or laminated till, causing an apparent discrepancy between sections taken at different localities. While it is found in Ohio to overlie the Erie clay and be clearly separable from it, no such distinction is observable in the counties here described. The inter-glacial formations of both insular and continental Europe are also in most cases quite distinct from both tills, though Mr. Geikie speaks of the reported finding of "bones" and " horns" in the lower member.40 The finding by Whittlesey, also, of the bones of Elephas primigenius, with sticks and leaves, clearly above the blue clay at Cleveland,41 and in other instances in the same member (when it was distinctly stratified—see sections pp. 12, 13), would seem to indicate that the proper stratigraphical position of
hoc. eit., p. $77.
Op. cit., p. 239, et ttq.
the forest bed is above the lower drift, but that in some cases the materials have been re-assorted by aqueous action and the organic remains submerged below or elevated above their true place. Hence, in northeastern Iowa where the lower till is thin, it has been generally so thoroughly modified and worked over, that wood may be found in any part of it or even in the gravel below it. The position of the carbonaceous stratum varies so much that I have not assigned any specific division to it in my sections. It is also noteworthy that when the lower till is stony, it is not laminated or clearly stratified, nor does it rest upon a pebbly stratum—the member number five of this paper. Thus it is in such cases identical with the unmodified bowlder clay of other localities. This would indicate that this deposit may or may not be modified — a conclusion already arrived at indeed by Dr. Newberry, induced by the laminated and pebbly character of the upper and lower members respectively of the Erie clay in Ohio. The occurrence of this member in Ohio, Indiana, Missouri, and Kentucky, without the supraposition of member number three, as in Iowa, Wisconsin, and northern Illinois, would also indicate that its range southward is greater.
The origin of the five members described, beginning with the lowest, may be provisionally attributed to the following agencies :—42
An unbroken ice-sheet extended over the greater part of the northern hemisphere north of about latitude 40° N., and in its southerly motion ground the surfaces of the older rocks and reduced their upper strata to bowlders, pebbles, coarse gravel, fine gravel, sand, and impalpable powder. These were deposited below its base in depressions of the surface, and at its margin as it retreated northward. "Where there were aqueous currents these materials were deposited to some extent in the order of their fineness — the coarser and heavier near the bottom with but little arrangement, and the lighter near the top, where, being subjected to the action of the glacial floods, they were still further re
"Thnt any explanation of drift phenomena can only be provisional is obvious, when we remember that there is the widest difference of opinion among compcteut geologists as to the agencies producing kamcs, glacial stria), and even the drift itself; and as that here offered introduces a new element, it must, a fortiori, be looked upon as liable to require modiiication or abandonment, Uiough it seems to accord fully with the facts as observed.
arranged. Thus we have at the base of the glacial deposits a coarse pebbly clay containing bowlders (member number five) overlaid by a fine clay frequently laminated and stratified (member number four). Where the total thickness of this glacial deposit is great, as in Ohio, we find a thick stratum of bowlder clay overlaid by an equally thick stratum of finely comminuted and horizontally laminated materials. Where there were no powerful aqueous currents accompanying the grinding up of the rocks, the materials were laid down indiscriminately mixed, and with little or no stratification, forming the typical bowlder clay. During the final melting and disappearance of the glacier, when the greater part of the surface was acted upon by powerful currents of water, further assortment and stratification of the materials probably took place, together with the formation in some places of kames and eskers. This will explain the irregularities in surface and stratification sometimes exhibited in the blue clay, as attested by the sections of Whittlesey, Newberry, and Geikie."13 Previous to this glacier, outcrops of hornblendic rocks, syenite, diorite, and porphyry, probably existed associated with or overlying the granitic strata of Minnesota, the material from which was all carried away and distributed over the surface far to the southward, where it now occurs as bowlders and pebbles, nearly always much worn and sometimes striated. After the final retreat of the glacier, the rivers and streamlets eroded their valleys afresh, and the topography assumed nearly its previous aspect.
Next ensued a period of mild climatal conditions which must have been of immense duration, during which a luxuriant flora covered the surface, and a characteristic fauna was developed. Where the surface deposits were thin, they were almost wholly metamorphosed by the reconversion of their elements due to the action of vegetation, and a layer of vegetable humus, many times as thick as that now existing was spread over the surface. Indeed it is probable that the whole or nearly the whole of the underlying drift was modified in color at least by the vegetable accumulations above. As before stated, the lower till owes its blue color to the presence of protoxide of iron. Now it was long ago shown by Dr. T. Sterry Hunt that the presence of decomposing vegetable matter is requisite to extract the iron from earth and rocks, after which it
— Whittlesey, loc. cii., p. 12, et seq. Newberry, toe. cit., pp. 24,35-36. Gelkle. loc. cit. pp. 138-140, 164, 169.
A. A. A. 8., VOL. XXVII. 15