The animal-shaped mounds and accompanying oblongs and ridges, constituting the first of the above series, are composed of whitish clay or of the subsoil of the country. The mounds of the second series, or burial mounds, are usually composed of black mould or loam, promiscuously intermixed with the lighter-colored subsoil. BURIAL MOUNDS OF THE ILLINOIS OR UPPER MISSISSIPPI DISTRICT. This district, as heretofore stated, includes eastern Iowa, northeastern Missouri, and northern and central Illinois as far south as the mouth of the Illinois River. Although we are justified in concluding that this area was occupied during the mound-building age by tribes different from those residing in the Wisconsin district, yet the distinguishing characteristics are more apparent in the forms of the works than in the modes of burial and internal construction of the burial mounds. We shall see by the illustrations hereafter given that at least one of the types found in one district is common in the other. But this is to be expected and is readily explained by the supposition that the tribes which have occupied these regions moved back and forth, thus one after another coming upon the same area. The absence of evidence of such movements would indicate that the mound-building period was of comparatively short duration, a theory which I believe has not been adopted by any authority, but to which I shall have occasion again to refer. One class of the burial mounds of this district is well represented in a group, explored by the members of the Davenport Academy of Natural Sciences, on the Cook farm, near Davenport, Iowa. The mounds of this group are situated on the immediate bank of the Mississippi at a height not exceeding 8 to 12 feet above high-water mark; they are conical in form and of comparatively small size, varying in height from 3 to 8 feet. Nine of them were opened, of which we notice the following: [Illustration: FIG. 7.--Section of burial mound, Davenport, Iowa. [From the Proceedings of the Davenport Academy of Sciences.]] In No. 1 the layers from above down were, first, a foot of earth; then a layer of stones 1-1/2 feet thick; then a layer of shells 2 inches thick; next a foot of earth, and lastly a second layer of shells 4 inches thick. Immediately under this, at the depth of 5 feet, were found five skeletons stretched horizontally on the original surface of the ground, parallel to each other, three with heads toward the east and two with heads west. With them were found one sea-shell (_Busycon perversum_), two copper axes, to which fragments of cloth were attached, one copper awl, an arrow-head, and two stone pipes, one representing a frog.