After the offerings had been flung into the fire, while it was yet glowing on the altar, earth or sand was heaped over them for a few inches, then successive layers of earth and sand, or ashes, clay, or gravel. Sometimes the altars were used several different times, in which case a layer of clay several inches thick was laid over the old altar. In one case three layers had been burned in before the final addition of earth and sand were heaped over it. These strange monuments of a by-gone people hint to us of mysterious rites. We wish we had more positive knowledge of the ceremonies they commemorated; but at present we must rest satisfied with conjecture. The next class of mounds are known as burial mounds, some of which are stratified, and resemble the so-called altar mounds. A mound explored in Butler County, Ohio, had in the center a layer of clay an inch thick, which had been burned until it was red. Underneath this was another layer of clay, beneath which was found charcoal, burnt cloth, and charred bones. Mr. Foster thinks that in this mound the body was placed on a rude altar, fires were lit, and that while yet burning, clay was thrown over it all, and that then fires were built all over the mound, sufficient to burn the clay for an inch in thickness.21 We have also a description of a group of mounds explored near the Mississippi River, in which there were evident signs of cremation. At least in several mounds fires had been built close above the bodies. But in cremation other victims may have been burned to accompany the departed chiefs or warriors. In one mound evidence of such a custom was observed. In another mound the center was found to be a mass of burned clay interspersed with calcined human bones. No less than ten or fifteen bodies had been burned here. “They must have worshiped some fierce ideal deity, and the ceremony must have been considered of great importance to have required so many victims.” This may have been, however, nothing more than simple cremation.22