During more than one of the glacial stages, perhaps during the earliest, the Ohio has served as the drainage-way for the waters that escaped from the glacial front. This subject is discussed by Leverett in Monograph XLI of the U. S. Geological Survey. As a result of this conveyance of glacial waters, the great trough of this stream may contain here and there deposits of the Illinoian stage or even of older deposits. Remains of Megalonyx (p. [32]) and of a horse (p. [186]) have been found in the right bank of the Ohio, at Evansville, Indiana. At Bigbone Lick, Kentucky, close to the Ohio, horses have been discovered, Mylodon and Megalonyx. These seem to occur in Sangamon interglacial beds overlying the Illinoian.
The Illinoian drift, probably everywhere in central and northern Indiana, underlies the Wisconsin. For some miles back from its terminal moraine the Wisconsin drift is thin; and possibly the Illinoian may. be found exposed in creek or river banks, or in railroad cuts. Furthermore, Leverett (Monogr. LIII, p. 72) writes:
“Probably a considerable number of the heavy deposits of drift in central and northern Indiana are of pre-Wisconsin age, but as they are largely sand and gravel, or loose-textured material, they can not easily be discriminated from the Wisconsin.”
Such deposits are likely to be covered by only a thin layer of Wisconsin till. In many places in Indiana there have been found, deep down in the drift, old soils, muck beds, and vegetation in various forms. These beds appear to indicate interglacial deposits, most probably the Sangamon. Now, various genera of vertebrates, among them horses, tapirs, and mylodons, are not known to have existed after the Wisconsin glacial stage. If, however, remains of such animals should be collected in central or northern Indiana, or Ohio, or in southern Michigan, they might be reported as having been found in late Wisconsin beds, when really they had been derived from pre-Wisconsin interglacial soils.
It is interesting to observe that when the Wisconsin ice-sheet began to withdraw lakes began to form along its borders. One of these, Lake Chicago, appeared at the south end of the present Lake Michigan and for a long time discharged its waters down Illinois River. Another, Lake Maumee, occupied the basin of Maumee River as far west as Fort Wayne, and emptied down the Wabash. For details connected with the close of the Pleistocene in the region of Lake Michigan the reader should consult Frank C. Baker’s “The Life of the Pleistocene, or Glacial Period” (Univ. Ill. Bull. XVII, 1920).
A brief mention will be made here of the principal Pleistocene vertebrates that have been found in Indiana; also the localities where found, together with citations of the pages where fuller information is furnished.
The ground-sloth Megalonyx has been collected near Evansville (p. [32]). With it were secured remains of an undetermined bison (p. [257]), a Virginia deer (p. [228]), a horse (p. [186]), a tapir (p. [203]), and the dog Ænocyon dirus (p. [32]). Peccaries have been found in Gibson County (p. [216]), in Wabash County (p. [218]), and two species at Williams, Lawrence County (p. [217]). At the same place was discovered the shell of a box-tortoise. Remains of deer have been discovered somewhere in Vanderburg County, including the existing deer and an extinct species, Odocoileus dolichopsis; at Harrisville, Randolph County; and at Roann, Wabash County. Bisons of an extinct species have been secured at Vincennes (p. [258]).
The existing bison appears to have been found in Jasper County (p. [268]). Of musk-oxen, Symbos cavifrons has been collected at Hebron, Porter County (p. [252]); at Wailesboro, Bartholomew County (p. [251]); somewhere in Randolph County (p. [252]); and probably in Beaver Lake, Newton County (p. [252]). The existing musk-ox, Ovibos moschatus, has been discovered near Richmond (p. [252]).
Mastodon remains are not uncommon, especially in the northern half of the State. It is hardly to be supposed that these animals were more abundant there during the late Pleistocene than in many other places in the region east of the Mississippi. The conditions for their preservation were evidently more favorable there than anywhere else, unless in Orange County, New York. Burial in swamp mud kept the bones from decay; and the imperfect drainage protected them from destruction by erosion. The various finds are described on pages [88] to [100].
Elephants are less well represented in Indiana than are the mastodons, but are not rare (pp. 138, 151, 171). Two species were present in the State, Elephas primigenius and E. columbi. Beavers were doubtless abundant, but there appears to be no definite record of any find. However, the giant beaver has been recorded from several localities (pp. 276 to 278).