At Dover, in Racine County, in 1878, a proboscidean tusk and some bones were found in a peat-bog. They have been identified as those of a mastodon, but of this one can not be certain. The age of the deposits is that of the Late Wisconsin stage, after the withdrawal from that vicinity of the ice, but how long after one can not say. The Milwaukee Public Museum has a tooth of a mastodon (p. [111]), labeled as found at Waukesha. Its geological age is that of the other remains here referred to. In the collection of the University of Wisconsin is a large vertebra of a proboscidean which was found in Lake Monona. Its time of burial must have been late Wisconsin. Inasmuch as no remains of vertebrate animals have yet been found in Wisconsin, in the area covered by the Illinoian drift, it is not necessary to dwell on this region. It is not certain that there is beneath it a still older drift; but there are, according to Alden, some indications of such deposits.

For a knowledge of the driftless area, first of all, may be consulted the report made by Chamberlin and Salisbury in 1885 (6th Ann. Rep. U. S. Geol. Surv., pp. 199–322, with plates). Alden’s work above referred to maps a part of the region. Grant and Burchard have studied the geology of the Lancaster and Mineral Point Quadrangles (Folio U. S. Geol. Surv. 145). Their text-figure 1 is here reproduced, inasmuch as it shows the relation of the region to the surrounding glaciated areas (fig. 14). The topographical map of Folio 145 and that of Chamberlin and Salisbury will show the uneven character of the surface. This has resulted from the erosion undergone during the whole of the Pleistocene. Much of the area is covered with a coating of loess. Along Mississippi River this may be as much as 10 feet thick, but at a distance of from 30 to 40 miles it becomes reduced to a few inches. Considering this erosion, one might conclude that few vertebrate remains would be preserved; nevertheless they are not wholly missing.

In 1862 (Geol. Surv. Wisconsin, vol. I, p. 136), J. D. Whitney stated that he had found in a crevice at Blue Mounds, Wisconsin, remains of the mastodon (p. [111]), a peccary (p. [219]), bones and teeth of a buffalo (p. [270]), and a wolf which he referred with doubt to Canis latrans. The depth was uncertain, but it may have been as much as 40 feet. The fossils were embedded in reddish clayey loam, the usual crevice earth. On page 422 of the same volume, Jeffries Wyman referred the wolf remains to two distinct species, Canis occidentalis and C. latrans. In 1876, Dr. J. A. Allen (Amer. Jour. Sci., ser. 3, vol. XI, pp. 47–49) described from the same lot of bones the species C. mississippiensis. This apparently did not include jaws and teeth that Wyman had referred to C. occidentalis. In Wyman’s paper, on page 422, he assigned three teeth to Dicotyles torquatus, an existing peccary, without stating that it had been found at Blue Mounds. In 1869 (Jour. Acad. Nat. Sci. Phila., ser. 2, vol. VII, p. 384), Leidy referred this peccary to his Dicotyles lenis, an extinct species. Inasmuch as the peccaries found at Galena were identified by Leidy (Whitney, vol. cit., p. 424) as Platygonus compressus (p. [218]), it appears pretty certain the Dicotyles lenis (Tagassu lenis) was among the fossils collected at Blue Mounds (p. [219]). It must, however, be kept in mind that Whitney, on page 35, stated that he had collected bones and teeth of the same animal near Dubuque, Iowa. Allen regarded the buffalo as belonging to an extinct species; but it is really undeterminable. Accordingly there may be credited to this locality the following species: Tagassu lenis, Bison sp. indet., Mammut americanum, Canis nubilus (C. occidentalis), C. mississippiensis, C. latrans.

Fig. 14.—Relation of driftless region of Wisconsin, Iowa, and Illinois to glaciated areas. From Grant and Burchard. Unshaded area represents driftless region.

In Whitney’s report, on page 133, he announced the finding of a large quantity of bones of mastodons at Sinsinawa Mound (p. [111]), but he did not know at what depth they occurred. It seems probable that they had been met with in one or more crevices.

It seems probable that the animals found in crevices in the lead region of Wisconsin, Illinois, and Iowa belong approximately to one geological stage of the Pleistocene. The following appears to include all known to have occurred in such situations:

The writer was at one time inclined to believe that these animals belonged to the time succeeding the withdrawal of the Wisconsin ice-sheet. Baker (“Life of the Pleistocene,” p. 353) thinks that they belong probably to the Peorian, inasmuch as the region is covered by Iowan loess, beneath which many of the bones have been found. It is quite probable that those crevices were open during at least some part of the Pleistocene and that animal remains collected in them. The fossils are reported as being sometimes inclosed in a matrix of cave or fissure materials which are cemented together by iron. The considerable number of extinct species, certainly 7 out of about 18, makes it probable that the fauna is not so recent as the Late Wisconsin.

It appears to be determined that the Iowan loess was formed immediately after the retirement of the Iowan ice-sheet. It might, therefore, be a question whether all of these animals might have got into those crevices in time to be covered in by the loess. On the other hand, the Illinoian drift was, for a long time, exposed to weathering and erosion before the Iowan drift and loess were laid down. Also, the Sangamon interval was probably much longer than the Peorian, so that the chances for the accumulation of the fossils were greater. It seems, however, that we can only say that the fossils are post-Illinoian and probably pre-Wisconsin.