As stated on another page, James Hall concluded that the pot-holes belonged to some preglacial time. Professor H. L. Fairchild has expressed in a letter to the present writer the following opinion:
“When the ice-sheet melted from Cohoes the locality was 355 feet lower than it is to-day. Deep estuary deposits partially filled the Hudson Valley and buried the Cohoes district. The Mohawk channel at Cohoes is excavated through marine sediments. There is no suggestion of any river channel there previous to the present river work. The pot-holes are post-glacial, but they probably represent a more copious and vigorous flow than that of the present river. That was supplied by the diminishing Iromohawk, the latest outflow through the Mohawk Valley of the Iroquois water. In this view the pot-holes were drilled by the latest glacial waters.”
It appears that, when the mastodon skeleton fell into the pot-holes, these had been drilled long before; for the principal one had become filled with gravel to a depth of at least 10 feet. They were, therefore, probably well above the stream-level, except in times of high-water. However the carcass reached the locality, it must have arrived in a complete state. Had it already attained an advanced stage of decay, some limbs or the feet or the lower jaw, probably the whole head, weighted down as it was by the heavy tusks, would have dropped off. It may be assumed that the skeleton was lying on land or in some pond not far above the pot-holes. The flesh was not wholly decayed, and the bones were held together by the ligaments. While the skeleton was in this condition the river rose and swept it over the first pot-hole, where the right leg dropped off; and then onward over the second, where more of it was deposited. Some unimportant parts may have been carried farther, and some of the missing bones may have decayed in the pot-holes. After the bones were deposited there the pot-holes became slowly filled up, probably mostly during times of high-water, with muck and branches and trunks of trees of several species (Hay, Science, n. s., vol. XLIX, 1919, p. 378).
The retreat of the Wisconsin ice-sheet far beyond the St. Lawrence and the rise of the land to its present elevation, 350 feet above the sea at Cohoes, belong to the closing chapter of Pleistocene history. When the Cohoes mastodon was buried the ice-sheet was probably already north of the St. Lawrence and, as Professor Fairchild writes, 150 feet of the rise of the land had already occurred. The time could, therefore, not have been long before the beginning of the Recent epoch. If these animals lived at such a late time at Cohoes they doubtless existed at the same time in all parts of the eastern region where their remains have been discovered. They may have been able to occupy Long Island a little earlier than places further north, but the interval would be geologically inconsiderable.
The writer has learned of no discoveries of mastodon bones in materials laid down by the marine waters that occupied Lake Champlain, the St. Lawrence Valley, and that of Ottawa River, or in deposits overlying these marine beds.
On the basis of one of Professor H. L. Fairchild’s plates (Bull. 127, N. Y. State Mus., plate XXXV) the writer has prepared map [34], which is intended to show the position of the Wisconsin ice-sheet in New York after it had retired somewhat north of the divide. This divide is marked by a line of dots. The area then occupied by the ice is stippled. Lake Erie was already nearly free from ice and was discharging its water by way of the Mississippi. Impounded waters from the melting glacial ice were collecting in the region of the Finger Lakes, forming Newberry Lake, and escaping down the Susquehanna. The Mohawk afforded outlet for the water from the southeastern lobe of ice. Fairchild’s plates 36 to 42 show the successive positions occupied by the ice-front as it retired northward and the various lakes that were formed.
Although not many species of vertebrate animals have been found in the Pleistocene deposits of New York, a large number of localities have furnished remains of the mastodon, Mammut americanum. These localities are recorded and brief descriptions of the remains and their geological environment have been presented on pages [48]–63. The localities are indicated on map [34]. It will be seen that several specimens have been found on Long Island and many in Orange County, in the southeastern corner of the State. In the western half of the State most of the finds occur within the area once occupied by the successive lakes. The animals could have lived there only after the ice-sheet and the lake waters had disappeared. It will be seen that a few finds have been made close to the shores of the present lakes. The animals must have lived there at the very end of the Pleistocene, if not within the Recent epoch.
The finds of other vertebrates are recorded on the following pages: Equus sp. indet. on page [183]; Platygonus compressus on page [212]; Bison bison on page [266]; Odocoileus virginianus on page [226]; Cervus canadensis on page [235]; Rangifer caribou on page [245]; Elephas columbi on page [149]; Elephas primigenius on page [131]; Castor canadensis on page [272]; Castoroides ohioensis on page [272].
In 1850 (Proc. Amer. Assoc. Adv. Sci., vol. II, pp. 255–256), W. C. Redfield reported that he had received remains of a fox of the genus Vulpes from Gulf Summit, Broome County. The lower jaw and other bones had been discovered in a cutting of the New York and Erie Railroad, 40 feet below the natural surface. The deposit above these bones was evidently the Wisconsin drift. The fine clay inclosing the bones may have belonged to the Sangamon, or even some older interglacial deposit. It is impossible to say whether this fox was Vulpes fulvus or Urocyon cinereoargenteus.