Besides the vertebrate fossils referred to above, a few others, especially mastodons (pp. 110, 111), have been found at other places, but so little is known of the conditions of their interment that they furnish little geological information.
A very interesting region is found in the western part of the State, in Dunn and Pepin Counties. This has been examined with great care by Dr. Samuel Weidman, State geologist of Wisconsin. About Menomonie there are several brickyards, whose excavations furnish opportunities for studying the formations at that point. Sections of one of these brickyards are described and illustrated by Dr. E. R. Buckley, in Bulletin VII, part 1 (1901), page 194, plate XXXVII. A section and brief description is found also in a paper by Dr. Hussakof (Jour. Geol., vol. XXIV, p. 688). In that region are found outwash gravels which have been definitely correlated by Weidman with Iowan drift. In some places this is overlain by loess. These gravels vary from 10 to 20 feet in thickness at Menomonie. Beneath the gravels are found lacustrine clays varying in thickness from 20 to 40 and even 60 feet. These are stratified and consist of layers from 1 to 12 inches in thickness, with intervening thin layers of sand. Toward the bottom the sand increases in amount. Beneath the clay-bearing formation is a bed of sand attaining a maximum thickness of about 150 feet. This is underlain by coarse sand and gravel. The lacustrine clays and the underlying sands and gravels are included by Weidman in his Menomonie formation, and this is believed by him to be of Sangamon interglacial age. In northwestern Wisconsin are found other glacial deposits believed to belong to the Illinoian drift epoch.
In the lacustrine clay at Menomonie have been found remains of the great lake trout, Cristivomer namaycush (Hussakof, as cited above), of a deer (p. [230]), a caribou (p. [247]), and probably a mastodon. The deer is represented by a single vertebra, identified by Dr. W. D. Matthew. The supposed mastodon is indicated by the distal end of the right femur, the caribou by an antler of a young and probably female individual and by the shaft of a large individual.
At Woodville, in St. Croix County, about 20 miles west of Menomonie, has been found a forest bed regarded as belonging to the Aftonian. This was described by Arthur Koehler (Amer. Forestry, vol. XXVI, Feb. 1916, p. 92, 3 figs.). Wood was found that was identified as that of spruce.
In 1913 (Science, n. s., vol. XXXVII, p. 457), in a brief abstract, Weidman reported that in Wisconsin he recognized drift deposits of Wisconsin, Iowan, and Kansan ages and another still older. No localities were mentioned, but his statements were doubtless based mostly on his work in the western part of the State. The loess was found to be laid down after the Iowan and before the Wisconsin. Interglacial deposits were found between the Kansan and the Iowan.
In 1905 (Jour. Geol., vol. VIII, pp. 238–256) and in 1910 (Jour. Geol. vol. XVIII, pp. 542–548), Dr. R. L. Chamberlain presented the results of his investigations on the “Pleistocene Geology of the St. Croix Region in Western Wisconsin.” His conclusion (p. 548) was that in that part of the State there were present (1) a surface mantle of gray Wisconsin drift deposited by a glacier from the Keewatin center; (2) red Wisconsin drift deposited by a glacier coming from the Labrador center; (3) a red drift left by an ice invasion from the Labrador center, its age consistent with Illinoian; (4) a grayish-black till that had come from the Keewatin center and whose age was probably Kansan.
MARYLAND AND DISTRICT OF COLUMBIA.
For obvious reasons the Pleistocene geology of the District of Columbia is considered in connection with that of Maryland. This region is of especial interest, because of the long time and the care which has been bestowed on it by geologists and because the conclusions reached have been applied to the geological study of States both toward the north and toward the south.
The most complete exposition of the Pleistocene geology of the region is to be found in the volume of the Maryland Geological Survey entitled “Pliocene and Pleistocene,” published in 1906. The geological treatise itself was written by George Burbank Shattuck and is illustrated by many maps and text-figures. Included in this is a bibliography of the subject which occupies 17 pages. There is a chapter by W. B. Clark, Arthur Hollick, and F. A. Lucas, on the interpretation of the palæontological criteria; another by F. A. Lucas on the mastodons and the elephants. The Pleistocene mollusks found in the State, 40 species, were described and figured by W. B. Clark; while the plants, also nearly 40 in number, were described and figured by Arthur Hollick.
The history of the development of our present knowledge of the geology of Maryland and the classification of its formations up to 1906 is given by Shattuck in the volume just cited (pp. 25–40). This geologist recognized in the superficial deposits of the State five formations (fig. 15). These are, beginning with the oldest, Lafayette, Sunderland, Wicomico, Talbot, and Recent.