well established by evidence was the case. Some of the mounds were of enormous size, the famous one at Cahokia, Illinois, being one of the highest and largest on the continent. Its altitude is about ninety feet, and it contains nearly 500,000 cubic yards of earth. Its purpose is, of course, not known, but it probably supported some religious structure of wood. Many of the mounds, as pointed out in the chapter on dwellings, were merely supports for buildings, religious or otherwise. Others were connected with religious rites in other ways. Doubtless the figures of birds found in Wisconsin represented the “Thunder-bird,” of which there are legends and traditions in many tribes. It was to the Amerind the cause of the thunder and lightning. These great and small earthworks were constructed in the United States by scooping up earth from the vicinity and carrying it in baskets to the designated spot. The United States mounds are, as a rule, made of earth, those of Mexico and Central America of clay or adobe brick, faced with stone or wholly of stone. “It is often the case,” says Thomas, speaking of the burial mounds of the Mississippi valley, “when a mound is carefully excavated and closely scanned as the work proceeds, especially where the material is clay or muck, that the individual loads can be readily discerned. As the earth of which the mounds is composed is usually gathered up from the surrounding surface, the interior will vary in color and character only as the soil so gathered up varies.... The places from whence material was taken to build the small or moderate-sized mounds are seldom discernible at the present day, but depressions plainly mark the points about the larger works, as the Cahokia and Etowah mounds and some of the enclosures of Ohio and elsewhere.[307] In some cases the one act has been made to serve two purposes, that is to say, the earth used to construct the mound or other work has been taken from one or two points so as to leave a basin-shaped excavation for holding water, or to form a trench to serve as a protective moat, or for drainage or other purposes.” For a long time it was believed by a great many persons, scientific and otherwise, that these piles of earth, often called pyramids quite erroneously, could not have been made by ordinary Amerinds, but as the study of the native American proceeded and the data of what he did and does actually do began to be recorded, it was perfectly plain that it was not at all necessary to look beyond the “Indian” for the origin of the mounds—that is, beyond the “Indian” as he was known in the region where the mounds occur. It was found that he had erected mounds after the arrival of the whites, and if he built one or several he might have built all. It was not a very difficult operation to dig up earth and carry it a few hundred feet and drop it on a pile. The transportation of the stones referred to above was far more laborious, and modern Amerinds do a great deal harder work.