of argillite, but intermingled with bone implements, and fragments of rude pottery, and alongside of these, implements fashioned of quartzite and jasper. The antiquity assigned to the Delaware implements, as determined by the age of the tool-bearing gravel, is much greater than that of the Trenton gravels previously referred to; but though remains of fifteen different species of animals, including fragments of a human skull, were recovered from the cave or rock-shelter, they include none but existing fauna. But the evidence of antiquity is based most confidently on the discovery of palæoliths _in situ_ in the true Philadelphia red gravel. Professor G. F. Wright remarks, in discussing the relative ages of the Trenton and Philadelphia red gravel, that both he and Professor Lewis came to the same conclusion: assigning the deposition of the red gravel to a period when the ice had its greatest extension, and when there was considerable local depression of the land. “During this period of greatest ice-extension and depression, the Philadelphia Red Gravel and Brick Clay were deposited by the ice-laden floods which annually poured down the valley in the summer season. As the ice retreated towards the headwaters of the valley, the period was marked also by a re-elevation of the land to about its present height, when the later deposits of gravel at Trenton took place. Dr. Abbott’s discoveries at Trenton prove the presence of man on the continent at that stage of the Glacial epoch. Mr. Cresson’s discoveries prove the presence of man at a far earlier stage. How much earlier will depend upon our interpretation of the general facts bearing on the question of the duality of the Glacial epoch,”[25]—a branch of the inquiry which it is not necessary to discuss here. It is sufficient to note that this argillite—an altogether inferior material to the flint, or hornstone of later tool-makers,—appears, thus far, to be a characteristic feature of American palæolithic art. The locality of the native rock is still undetermined; but implements fashioned of it have been found in great numbers along the escarpments facing the river Delaware. Professor Shaler describes the material as a curious granular argillite, the like of which, he says, “I do not know in place.” Should the native rock be hereafter identified, with traces of the manufactured celts in its vicinity, it may help to throw light on the age and history of the primitive American implement-makers.