“Twenty-two feet eight inches from the outcrop, measured from its inner face, there is still another outcrop.... This marks the opposite side of the hollow.... It is evident how admirably the place was adapted to the wants of the early hunters of the Delaware valley, whether it be as a shelter, or as a place of defence against their enemies.... Let us look at the layers of earth that filled it, these being intermingled with rude implements, broken bones, and charcoal, indicating that man at times had resorted to the spot.
“Layer C [the lowest]. This was composed of schist, resting on the bedrock of the shelter. A layer of aqueous gravel, of the same type as that underlying Philadelphia, rested on the decomposed schist. The greatest depth of the red gravel layer was four feet two and one fourth inches, measured from the layer of decomposed schist. Least depth of gravel observed, one foot three inches....
“Layer A [next above]. This was a layer of grayish-white brick clay mixed with yellow clay, similar to that underlying Philadelphia, on top of which was a layer mixed with sand.... Stone implements were discovered in this layer. They were but few in number and very rude, exclusively of argillite, and palæolithic in type. Greatest depth of layer, two feet one and one half inches. No implements of bone were found....
“Layer T [next above]. This was of reddish gravel, intermingled with decomposed schist, cinders, and broken bones of animals. Fragments of a human skull were found ... in this layer. A fragment of a human rib was also preserved. The fragments of the skull are covered here and there by dendritic incrustations. Rude spears and implements of argillite were found in this layer. Depth of layer, thirteen to eighteen inches.
“Layer D [next above]. Composed of reddish-yellow clay. Depth, two feet three inches. No implements.
“Layer M [next above]. In this layer were numerous implements of argillite and some of bone, intermingled with rude implements of quartzite and jasper and fragments of rude pottery, with charcoal. Greatest depth, one foot one and one half inches. Least depth, three inches.
“Layer R [next above]. Yellow clay. Greatest depth, two feet one and one half inches; least depth, eight inches. No implements.
“Layer W [next above]. This contained chipped implements; those made of jasper and quartzite predominating over those of argillite. In the lowest part of this layer were fragments of rude pottery. In the upper portion of the layer were potsherds decidedly superior in decoration and technique to those from the lower portion. Geological composition of this layer, yellow clay loam. Greatest depth, three feet four inches. Least depth, two and one half inches.
“Layer L [top]. This consists of leaf mould seven inches thick, converted into swamp muck by decomposing action of water from springs. No implements.... No remains of extinct animals were found.”[1564]
Professor Putnam thus proceeded to comment upon these discoveries: “We have a series of objects, taken from the several layers of the shelter, giving us a chronology of the utmost importance, as each period of occupation of the shelter was followed by a natural deposition, separating the different periods of occupation. The stone implements ... are taken from the lowest layer, indicating the earliest period of occupation of the rock-shelter; and ... they correspond in shape and rudeness of execution with those taken from the gravel-bed at Trenton; and like most of the latter they are all of argillite. The specimens from the second period are of argillite, and while many are chipped into slender points, they are still of very rude forms; and these in turn correspond with the argillite points found by Dr. Abbott deep down in the black soil, or resting upon the gravel, at Trenton. In the upper layers of the cave we observe ... the gradual introduction of implements chipped from jasper and quartz, and corresponding in form with those found upon the surface throughout the valley. And as a further indication of this later development, it was only in the upper layers that pottery, bone implements, and ornaments were found; the three distinct periods of occupation of the Delaware valley are thus distinctly shown; and this cave-shelter is a perfect exemplification of the results which Dr. Abbott had obtained from a study of the specimens which he has collected upon the surface, deep in the black soil, and in the gravel, at Trenton.”