FIG. 30.- Implement of argillite found in gravel nine feet from sur. face, Florence Heights, N. J., by Dr. C. C. Abbott in 1878. hundred cubic feet in volume, the whole imbedded in a matrix of sand and loam. The entire mass is unquestionably water-laid; its continuous bedding is indicative of wave-action, and thus of shallow waters; and the bowlders scattered throughout it are evidently ice-borne. Within the Trenton gravels two types of implement are found-viz. turtle-backs' and the rude leaf-shaped' implements regarded by Abbott as of Esquimau pattern. Both types are chipped from a peculiar argillite which is found in the deposit only as (presumptively) finished implements or as large bowlders. The implements, which occur in such numbers that over twenty-five thousand have been collected by Abbott, are seldom water-worn though frequently weathered, while the bowlders are somewhat worn by water and similarly weathered. It is significant that the turtle-back' type is found throughout the deposit from top to bottom, but most abundantly in the lower half and in progressively diminishing abundance from bottom to top of the upper half, while the 'leaf-shaped' type is found only in the upper half and in progressively increasing abundance upward; it is also noteworthy that both types of implement are occasionally found over contiguous surfaces of the Columbia formation (which were above water-level when the Trenton gravels were deposited), commonly associated with chipped implements of higher type, and it is equally noteworthy that the implements of higher type occur over the surface of the Trenton gravels but never within them, while the ruder implements found within the gravels do not occur upon the gravel surface. 66 The geologic evidence of the environment of the celt-users of the Delaware River is complete and intelli gible: the continuity of the deposits proves that the Trenton gravels were laid down while the northern part of the country was occupied by ice, and while the terminal moraine was forming; their structure and composition prove that they were laid down in shallow floe-bearing waters; their distribution indicates unmistakably the geography of the period; and this physical testimony is corroborated by the association of remains of extinct or boreal animals (mastodon, reindeer, bison, etc.) with the human relics. So definite, indeed, are the data, that the geography of the period may be depicted graphically. Fig. 31 is a bird's-eye sketch of the present head of Delaware Bay, based upon the admirable topographic surveys of New Jersey and upon personal studies, and represents with reasonable accuracy the general features of the region; and Fig. 32 is a similar sketch of the region as it existed during the Trenton gravel period, based upon the same surveys and upon the shore-lines brought to light thereby, and probably represents the configuration of the earlier period with equal fidelity." Mr. McGee goes on to compare the earlier condition of the head of Delaware Bay, as shown in Fig. 32, with the present condition of the head of Chesapeake Bay, which the reader may, in part, gather from a glance at any good map of the latter. Chesapeake Bay, with its warm, shallow waters, whose depth does not, in most places, exceed fifteen to thirty feet, supports such a growth of aquatic plants, teems with such myriads of fish and crustaceans of many species, and is so frequented by many |