The first definite discovery of human relics clearly connected with, glacial deposits in America, and of the same age with them, was made by Dr. C. C. Abbott, at Trenton, N. J., in the year 1875. The city of Trenton is built upon a delta terrace about three miles wide which occurs at the head of tide-water on the Delaware River. This terrace bears every mark of having been deposited by a torrential stream which came down the valley during the closing period of the great Ice age. The material of which the terrace consists is all water-worn. According to the description of Professor N. S. Shaler: [Illustration: Fig. 63.--The glaciated portion is shaded. The shading on the Lehigh and Delaware Rivers indicates glacial terraces, which are absent from the Schuylkill.] "The general structure of the mass is neither that of ordinary boulder-clay nor of stratified gravels, such as are formed by the complete rearrangement by water of the elements of simple drift-deposits. It is made up of boulders, pebbles, and sand, varying in size from masses containing one hundred cubic feet or more to the finest sand of the ordinary sea-beaches. There is little trace of true clay in the deposit; there is rarely enough to give the least trace of cementation to the masses. The various elements are rather confusedly arranged; the large boulders not being grouped on any particular level, and their major axes not always distinctly coinciding with the horizon. All the pebbles and boulders, so far as observed, are smooth and water-worn, a careful search having failed to show evidence of distinct glacial scratching or polishing on their surfaces. The type of pebble is the subovate or discoidal, and though many depart from this form, yet nearly all observed by me had been worn so as to show that their shape had been determined by running water. The materials comprising the deposit are very varied, but all I observed could apparently with reason be supposed to have come from the extensive valley of the river near which they lie, except perhaps the fragments of some rather rare hypogene rocks." [Illustration: Fig. 64.--Palæolith found by Abbott in New Jersey, slightly reduced.] A conclusive proof of the relation of this Trenton delta terrace to the Glacial period is found in the fact that the gravel deposit is continuous with terraces extending up the trough of the valley of the Delaware to the glaciated area and beyond. As, however, the descent of the river-bed is rapid (about four feet to the mile) from the glacial border down to tide-water, the terrace is not remarkably high, being only about fifteen or twenty feet above the present flood-plain. But it is continuous, and similar in composition with the great enlargement in the delta at Trenton. Without doubt, therefore, the deposit represents the overwash gravel of the Glacial period.