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<br />38 <br /> <br />sandstone basins. An analysis of variance for each set (Table 5.4) <br /> <br />shows that the soil depths are the same within each set at a = .05. <br /> <br />...... <br />c.u Finally, the mean soil depths of the two sets of basins were <br />00 . <br />CJj compared for the purpose of checking the soil depth difference <br /> <br />between the two sets of basins according to lithology. The two- <br /> <br />tailed T-test in Table 5.5 indicates that the mean soil depth for <br /> <br />basins underlain by interbedded shale and sandstone is significantly <br /> <br />greater than the mean soil depth for basins underlain by shale at <br /> <br />a = .05. The explanation for this probably is due to the lower <br /> <br />erodibility of sandy soils because of greater infiltration rates and <br /> <br />vegetative cover than the shaley soils (Lusby, et aI" 1963). <br /> <br />Hadley and Lusby (1967) emphasize the importance of hillslope <br /> <br />aspect on soil depth and hillslope erosion. That is, since the north- <br /> <br />facing slopes are colder and retain more moisture, they are expected <br /> <br />to have deeper soil development and shorter, steeper slopes than the <br /> <br />south-facing slopes, Effects of aspect on soil depth, however, were <br /> <br />not studied due to the wide variation of hillslope-facing directions <br /> <br />within each basin. Field observations of hillslope-facing directions <br /> <br />and aerial photo interpretation suggest that aspect plays a relatively <br /> <br />minor role in the geomorphic processes of the area. <br /> <br />5.2.6 Geomorphic Stability of the Badlands <br /> <br />Generally, the badlands of the piedmont are areas of <br /> <br />rapid erosion. The rills and channels are steep, and they are effi- <br /> <br />cient conduits for runoff and sediment transport, The hillslopes are <br /> <br />most fragile during the spring and early summer before the first <br /> <br />summer thunderstorm. All portions of basins are undergoing active <br /> <br />erosion due to the combined effects of rill development, soil creep, <br />