Data are presented on three profiles formed under prairie from Late Wisconsin to Recent age local alluvium of moderately fine texture. In the upper 20 inches nitrogen and base saturation values are quite similar to those found for normative upland Brunizems. Below 20 to about 50 inches, nitrogen and base saturation values decrease and increase, respectively, more slowly in the local alluvium-formed soils. It is suggested that the classic ABC soil genesis concept does not apply to the local alluvium-formed soils of this study. Rather, through cumulative effects of new parent material at the surface, this new C was transformed to an Ac horizon (c for cumulative effect), the former A1 was transformed to a Bc horizon, and the former B became a substratum Cc horizon. Soil genesis effects in such cumulative soil genesis systems need further attention, as these soils comprise about one-fourth of the land area of Iowa, are important agriculturally, and an understanding will further knowledge of other soils of Iowa
