An Assessment of Prairie Mound Origin Theories |
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Fieldwork was conducted at the University of Arkansas Experimental Farms on 10 October 1998. Many of the prairie mounds appeared to be truncated from plowing. Two mounds of relatively high relief were chosen for study. Three soil cores were recovered with a Giddings-rig core machine. One core was taken from the estimated center of each mound, and one core was taken from the lowest point of the saddle between the mounds. Mound topography and core locations were mapped with an alidade and plane table as a series of three transects with points at two meter intervals, the first transect crossing both mounds, and the second two at right angles to the first (Fig. 2). Soils were described at the University of Arkansas soils laboratory (Appendix A). Methods employed for the description of these cores follow the procedures of the U.S. Soil Conservation Service (Soil Survey Staff, 1996, 1981). Samples were taken from the cores at 20 cm intervals for grain size analysis (Appendix B). The sand fractions were separated by wet sieving into the following grain sizes: very fine sand (2 microns to 0.0063 mm), fine sand (0.0063 mm to 0.013 mm), medium sand (0.013 mm to 0.25 mm), coarse sand (0.25 mm to 0.5 mm), very coarse sand (0.5 mm to 1.0 mm), and gravel (>2 mm). The silt and clay fractions were analyzed by the pipette method (Day, 1965). Draws were taken at 4, 6, 8, and 9 phi to determine percentages of coarse silt (62.5 to 15.6 microns), medium silt (15.6 to 3.9 microns), fine silt (3.9 to 2.0 microns), and clay (<2 microns). Aerial photographs taken in 1941 and USGS digital orthophoto quads were examined to determine the position and extent of the mound field. Construction has leveled many of the mounds, however, and ground observation reveals that some extant mounds are not well expressed in the aerial views.
Figure 2. Topography and profiles of mounds studied. Click image for larger vivew. |
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