The Palæolithic period itself is advantageously subdivided further into two Epochs, an earlier one in which men made “simple” implements only, and a later one in which they manufactured “compound” implements as well. I was the first to point out this distinction, and as I have found it really useful, and as others have also expressed to me the value which it has been to them in this line of research, I will explain it further.[33] A “compound” implement is one composed of several parts adapted to each other, as the bow and the arrow, the spear with its shaft and blade, or the axe with its head and helve and the means of fastening the one to the other. These were not early acquisitions. During long ages man contented himself with such tools or weapons as he could frame of a single piece of wood or stone, simply holding it in his hand. When he found he could increase its effectiveness by fitting it to a handle, the discovery marked an era in his culture. He may indeed in his rudest ages have lashed a stone to the end of his club, or have inserted a spall of flint in the split end of a stick; but these are not compound implements in the proper sense of the term. The expression means an art-product which clearly shows that it was but one part of a mechanical apparatus. The arrow-head with its stem, barbs and body, the stone axe with its grooves or drilled perforation for the handle, are incomplete in themselves, they disclose a preconceived plan for the adjustment of parts which man in his earliest and rudest condition does not seem to have possessed. The most ancient strata in which the remains of human art have been found, either in Europe or America, yield “simple” implements only; “compound” implements are a conquest of his inventive faculty at a later date. So far as America is concerned it is probable that the oldest remains of man yet discovered on the northern continent have been those exhumed in the valley of the Delaware River, in the states of Pennsylvania, New Jersey and Delaware. According to the most careful geological observers that large deposit of gravel covering about five thousand acres on both banks of the river below Trenton is a post-glacial deposit not less than twelve or fifteen thousand years old. Imbedded in this at various depths a large number of true palæoliths have been discovered by Dr. C. C. Abbott, Professor F. A. Putnam, myself and others. Every one of them so far as I am aware belongs to the class of “simple” implements, not an arrowhead nor grooved axe nor stemmed scraper having been reported.