long 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.

The explanation of "agricultural use" is probably correct in some
instances, for frequently the mounds are made of earth gathered up
around their base, and so not only would be of value in a wet season,
but would afford a much greater depth of fertile soil for sustenance
of plants. In some localities modern farmers find that on such mounds
crops are much better than on the low spaces between them. On the
other hand, a majority of the small mounds in the lower counties of
southeastern Missouri are composed either of the hard, reddish, sandy
clay which forms the subsoil of the land above overflow; or of the
tough, waxy, black "gumbo" of the swampy or flat lowlands. In either
case they are almost invariably sterile, so that in a cultivated field
the position of a mound is easily determined even from a considerable
distance by the feebler growth on its surface. Moreover, in many
places, hundreds of them occurring within an area of a few square
miles are built on clay lowlands where crawfis