Page:Popular Science Monthly Volume 34.djvu/39

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by Metz was laid down by a turbulent ice-bearing river but a few miles from the glacier's margin. The implement, unlike those recorded by Aughey, McGee, and N. H. Winchell, is of the rude type commonly called paleolithic, and thus indicates primitive customs among its makers; but neither alone nor in conjunction with the similar implement found by the same individual under like conditions at Lovelands does it tell whether the inhabitant of the ice-front in the Ohio valley was hunter, fisherman, or husbandman, troglodyte, nomad, or house-builder; and only the geologic evidence suggests conditions of life approaching those of the modern Esquimau.

When the primitive man of Trenton flourished, the later Quaternary mer de glace covered New York and New England, and extended far into northern New Jersey and Pennsylvania. The ice was from five hundred to one thousand feet in thickness near its margin, and overflowed the highest mountains, though they somewhat impeded its progress; the land beneath was somewhat depressed and was tilted northward toward the ice-front; and flooded rivers, born upon and beneath the edge of the icesheet, swept into their lower courses and into the sea, glacial mud, sand, and pebbles, while upon their surfaces floated ice-floes laden sometimes with larger pebbles and anon with great bowlders. Among these rivers was the Delaware, which was transformed in its middle course from a constricted torrent rushing swiftly over a rocky bottom (as it is to-day and as it was anterior to the second ice-epoch) into a broad slack-water estuary, tidal probably to the mouth of the Lehigh. This estuary found its source at the edge of the ice, where now lies the terminal moraine (just below Belvidere); and at what is now the head of tide at Trenton it embouched into a broad, shallow bay. At the ice-front it gathered a harvest of cobble-stones which were washed down-stream and deposited in a series of terraces more than one hundred feet in height and two miles or more in width, extending ten miles down the river; the cobbles growing finer and finer and finally passing into beds of gravel and sand. There, too, the waters became charged with glacial mud—the rock-flour forming the grist of the glacial mill—which was more slowly deposited in the form of fine loam sometimes enveloping the cobbles and abundantly intermixed with the finer gravel and sand as far south as Philadelphia, but most abundantly above Trenton. There, also, the river gathered sand, fine and coarse pebbles, great bowlders, and heterogeneous débris, which were frozen into ice-floes, floated gently down-stream, and dropped as the floes melted, equally far southward, but most abundantly where the river embouched into the bay and where the floes lingered longest in the slackened current, These aqueo-glacial deposits extend continuously from the