E. H. Davis, Ancient Monuments of the Mississippi Valley
“ Whether any significance may attach to the predominance of stone, in some of the mounds, is a question difficult to answer. It occasionally happens that a mound of stone occurs in the midst of a group composed of earth. Such was the case with one which formerly stood within the limits of Chillicothe. As a general rule, however, the mound is composed of material found upon the spot or taken from pits near by; and stone mounds oftenest occur where, from the hardness of the soil or the abundance of stones, it would be easiest to construct the tumulus of the latter material. ”
