Mounds of this class are very numerous. They are generally of considerable size, varying from 6 to 80 feet in height, but having an average altitude of from 15 to 20 or 25 feet. They stand without the walls of enclosures at a distance more or less remote from them. Many are isolated, with no other monuments near them; but they frequently occur in groups, sometimes in close connection with each other, and exhibiting a dependence which was not without its meaning. They are destitute of altars, nor do they possess the regularity which characterizes the "temple mounds." The usual form is that of a simple cone; sometimes they are elliptical or pear-shaped. These mounds invariably cover a skeleton (in very rare instances more than one, as in the case of the Grave Creek mound), which at the time of interment was enveloped in bark or coarse matting, or inclosed in a rude sarcophagus of timber, the traces and in some instances the very casts of which remain. Occasionally the chamber of the dead is built of stone, rudely laid up, without cement of any kind. Burial by fire seems to have been frequently practiced by the mound-builders. Urn burial also appears to have prevailed to a considerable extent in the Southern States. With the skeletons in these mounds are found various remains of art, comprising ornaments, utensils, and weapons.[26] For the purpose of conveying to the mind a clear idea of the character of these mounds, I give here a copy of their figure of one of them (Fig. 19), and also of the wooden vault found in it (Fig. 20). This mound, as was the case with most of the burial mounds opened by them, although comparatively large, is without any distinct stratification. In some cases (see Ancient Monuments, Figs. 52 and 53, p. 164) a layer of bark was first spread on the natural surface of the ground after it had been cleared, leveled, and packed; on this the body was laid at full length. It was then covered with another layer of bark and the mound was heaped over this. Although no mounds containing stone sepulchers fell under their notice during their explorations, they obtained satisfactory evidence that one within the limits of Chillicothe had been removed, in which a stone coffin, "corresponding very nearly with the _kistvaen_ of English antiquarians" was discovered. [Illustration: FIG. 19.--Ohio burial mound (after Squier and Davis).] [Illustration: FIG. 20.--Wooden vault (after Squier and Davis).]