Practically, however, the northern limit of this type, in great numbers, is in St. François County, near Farmington. From here they extend almost continuously into Louisiana and Texas.
In nearly every part of southern Missouri east of the Iron Mountain Railway they occur in closely connected groups, reaching sometimes for miles except where the continuity is broken by a slough or other unfavorable condition. They are found everywhere—on high, well-drained levels; on sloping ground, sometimes so steep that it may well be called a hillside; in low "crawfish land"; in swamps where, in the driest weather, even after a prolonged drought, they can be reached only by wading through water or muck. The last, however, may have been more easily accessible when built, their present condition being due to the general subsidence of this region during the earthquake period of 1811. The existing sloughs and sluggish bayous are the widenings and extensions of streams which at the time these mounds were constructed were no doubt bordered by banks above ordinary overflow and readily reached by canoes. Manifestly the country was well populated, and therefore presumably practically timberless; consequently the flood water would rapidly pass away and the streams not be choked by drift and other débris as is the case at present.
Various theories, most of them advanced by persons who are but slightly, if at all, familiar with the country, have been propounded to account for mounds of this character. Their vast number has led some writers to believe that they can not be artificial but must be due to natural phenomena; as, for instance, that these, as indeed all mounds, were piled up by floods, Noachic, glacial, or local; or that they result from the industry and energy of burrowing animals, such as foxes, badgers, ground hogs, rabbits, prairie dogs, gophers, chipmunks, or even ants; the character of the assumed flood or the species of the supposed burrower depending to some extent upon locality, but principally upon the theorizer's insufficient knowledge of animal industry or of the action of torrential waters. Others are convinced they are formed by the piling up of earth around a bush, clump of grass, stone, or other object acting as a nucleus about which wind-borne material may accumulate—overlooking the fact that clay, gravel, or gumbo soil can not be carried by wind, and that lighter soil or sand will form elongated instead of circular masses. Another supposition is that they are due to stream erosion; flood waters washing away the soil between them and thus leaving the earth composing the mound in its original position. The same objection applies to this as to the wind-blown theory, namely, that we can not imagine water acting with such mathematical regularity and intelligent discrimination, especially upon slopes which lie at all sorts of angles with the trend of the current.
Persons who recognize their human origin have suggested that they were erected as stands for hunters, from which they could detect game at a greater distance, or could take better aim as the animal passed; or perhaps as camping places while waiting; but in many places more than half the area of the ground over several acres is occupied by such piles of earth, promiscuously distributed. This implies more hunters than animals.
For a long time it was supposed that they were burial mounds, like so many such structures found over the country; but this idea has been dispelled by the failure to discover in them any evidences of such purpose; no human bones nor any of the artificial objects commonly placed with the dead have ever been found in them unless under such conditions as to show their presence was accidental.
Two very plausible theories have found general acceptance: That they were the sites of dwellings, placed on them to be out of the mud in wet weather; and that they were in the nature of garden beds, thus elevated for growing any food products which needed a comparatively dry soil, or might be injured by temporary accumulation of water from excessive rainfall.
But they were not "residence mounds" or "house sites" in the sense that they furnished a base or foundation for structures which were used as dwellings; for there has never been found on their surface or in the earth immediately around them any of the débris invariably accompanying Indian huts or houses, such as fireplaces, ash beds, burned rocks, broken implements, or fragments of bones and pottery. These considerations also interfere with a full acceptance of the hypothesis that they are remains of houses built of wood and covered with earth. It is true that such evidence is very frequently found in other localities; but to establish the fact that they were residence sites, refuse of this kind should be found wherever the mounds occur.
J.B. Thoburn arrived at this conclusion from the resemblance of some of them in their outlines to the grass-covered houses of the Pawnees; and it is believed that this tribe in its migration from the south followed approximately the route along which these small elevations are found. When the Pawnees—assuming they were the builders—passed on westward they could not procure timbers of sufficient strength to hold up the earth, so they used light frames and covered them with grass.
Bushnell arrived earlier at the same conclusion. He says, concerning a few mounds of this character in Forest Park, St. Louis: "In the case of the seven mounds on the elevated grounds, the finding of potsherds, pieces of chipped chert, and the indication of fire, all on what appeared to have been the original surface, would point strongly to their having been the remains or ruins of earth-covered lodges." He gives citations from early explorers in support of this theory, and adds, "But in other mounds these indications did not occur."[4]
Such an explanation finds support in the vast number of these structures. In building, the aborigines naturally chose the sort of timber which was soft and light, consequently easy to cut and to handle, such as willow or cottonwood. This soon decays. But no matter what variety of wood was utilized, not many years would be required, under the conditions supposed, to weaken its fiber until it could no longer uphold the weight of earth on the roof, and a new house must be erected. Several such renewals would be needed in the course of a century; so that the ruins of an ordinary village might create the impression that a large settlement had existed on its site.