STRUCTURE OF MOUND D
The structure of Mound D was clearly indicated by the vertical cross sections ([Fig. 7]). An old humus-stained surface underlying the marginal portions of the mound was sharply defined at an average elevation of 98.0 feet. No artifacts or cultural refuse were found in the floodplain below this surface. Prior to construction of the mound a shallow, circular pit had been excavated in the surface of the floodplain to an average depth of 1.5 feet. The sides of the pit sloped sharply downward, and the floor was approximately level. An embankment of yellow-brown sand, possibly composed of back-dirt from the pit, was mounded up about 1.5 feet high and four to six feet wide around the perimeter of the pit. This light sand zone contained a few artifacts but little or no charcoal.
A hard-packed house floor about 0.2 feet thick lay on the bottom of the pit. This floor zone was composed of compact sandy clay which contrasted sharply with the overlying mound fill. Charcoal, ash, and burned clay daub were found in quantity in the floor zone, but only a few artifacts were recovered. Just above the house floor was a 1-foot thick layer of dark gray-brown sand containing several charred poles and a large amount of charcoal, ash, and burned clay daub. Above that was the sandy fill making up the bulk of the mound. A mantle of surface humus from 0.2 to 0.8 feet thick covered the mound.
A ring of post molds was discovered around the edge of the floor, and other molds on the west side of the house marked the position of an extended entranceway ([Fig. 10]). No interior post molds were discovered.
The pothole, which extended downward through the center of the floor, had apparently removed a centrally located hearth, only slight evidence of burning at the edge of the pothole remaining to show that the hearth had been there.
The entire mound fill, including the embankment around the house, was composed of various shades and textures of sand. All of this material was probably derived from the sandy floodplain surrounding the mound. Small quantities of clay around the hearth and on the house floor could have been acquired at nearby outcrops in the stream channel.
As at Mounds B and C, the circular shape of the house at Mound D was outlined by an area of organically stained soil which extended upward from the house floor almost to the surface of the mound. The flanks of all three mounds were of light colored sand which contrasted sharply with the dark, circular house outlines. The only reasonable conjecture thus far advanced to explain this circumstance is that a low embankment of relatively clean sand had been piled against the exterior wall of each house. Thus when a house burned the embankment would remain standing, well above the house floor, as a sort of mold of the lower portion of the house. Then when a mound was erected over the burned house remains and the standing embankment, the outline of the house might appear in the mound fill as a cast of the house, delineated by the circular embankment.