The surface of this mound was covered with the layer of pebbles and coarse gravel already mentioned as characterizing the mounds of the first class; but the sand strata were absent. Around the base had been laid, with some degree of regularity, a large quantity of flat stones, constituting a sort of wall for the better support of the earth. These stones must have been brought from the hills, which are here nearly half a mile distant. Why the altar as well as the skeleton had been enclosed, and why the floor of the mound had been so carefully levelled, cast over with clay, and then hardened by fire, are questions which will probably remain unanswered and unexplained unless future investigations serve further to elucidate the mystery of the mounds. At any rate, this singular mound can prove no greater puzzle to the reader than it has to the authors of these inquiries.
A detached mound stands on the bank of Walnut creek, about three miles below the one just described, which is entirely anomalous in its character. It is about nine feet in height by forty base. The following section will best explain its construction.
Fig. 69. The principal portion of the mound, which is darkly shaded in the section, resembles long exposed and highly compacted ashes, and is intermingled with specks of charcoal, small bits of burned bones, and fragments of sandstone much burned. Beneath this, and forming the nucleus as it were of the entire mound, is a mass of very pure white clay, of somewhat regular outline; but whether this regularity was accidental or designed, it is not undertaken to say. The clay rested upon the original soil, and did not appear to have been subjected in any degree to the action of fire. The carbonaceous deposit, if we may so regard it, seems from this circumstance to have been brought here and not to have been produced by burning on the spot. The mound could not possibly have been designed for a «look-out», inasmuch as it stands immediately at the base of the table lands, and commands but a very limited view.
Two other mounds, numbered 6 and 7 in the map, Plate II, exhibited some features in common with the one last mentioned, though neither had the clay deposit at the base. After penetrating a foot or twenty inches into these, traces of ashes and other carbonaceous matter, with here and there small quantities of burned bones in fine fragments, became abundant,—indeed the remainder of the mound seemed entirely constituted of such materials. In some instances, if not in all, the fragments of calcined bones were of the human skeleton. It has been suggested that these mounds were composed of the ashes of the dead, burned elsewhere, but finally thus heaped together. It is not impossible that such was the case in a few instances, though mounds possessing these features are too few in number and too small in size to justify the conclusion that such was the general custom.