The marked feature of the group was found in No. 16, a remarkably symmetrical mound 65 feet in diameter and 10 feet high. After passing downward 6 feet, mostly through a hard gray layer, a vault partly of timber and partly of stone was reached. A vertical section of the mound and vault is shown in Fig. 11, and the ground plan of the vault in Fig. 12. This vault or crypt was found to be rectangular in form, inside measurements showing it to be 13 feet long and 7 feet wide, surrounded by a sandstone wall 3 feet high. Three feet from each end was a crosswall or partition of like character, thus forming a main central chamber 7 feet square, and a narrow chamber or cell at each end something over 2 feet wide and 7 feet long. The whole had been completely covered with a layer of logs from 6 to 12 inches in diameter, their ends reaching slightly beyond the side walls in the manner shown in Fig. 12. [Illustration: PL. III. GROUP OF MOUNDS AND VERTICAL SECTION OF BLUFF, EAST DUBUQUE, ILL.] In the center chamber were found eleven skeletons: six adults and five children of different ages, including one infant, the latter evidently buried in the arms of one of the adults, possibly its mother. Apparently they had all been buried at one time, arranged in a circle, in a squatting or sitting posture, against the walls. In the center of the space around which they were grouped was a fine specimen of _Busycon perversum_, which had been converted into a drinking-cup by removing the columella. Here were also numerous fragments of pottery. [Illustration: FIG. 11.--Section of mound 16 (Pl. III) showing vault.] [Illustration: FIG. 12.--Plan of vault, mound 16 (Pl. III).] The end cells, walled off from the main portion, as heretofore stated, were found nearly filled with a very fine chocolate-colored dust, which gave out such a sickening odor that the workmen were compelled to stop operations for the day in order to allow it to escape. The covering of the vault was of oak logs, most of which had been peeled and some of the larger ones somewhat squared by slabbing off the sides; and the slabs and bark thus removed, together with reeds or large grass stems, had been laid over them. Over the whole was spread layer after layer of mortar containing lime, each succeeding layer harder and thicker than that which preceded it, a foot or so of ordinary soil completing the mound.