Rock Weathering and Soil Formation in the North Carolina Piedmont Region

THE character and distribution of large areas of important soil series in the Piedmont region of the eastern United States are determined by the rocks from which they are derived. The landscape is physiographically and chronologically old, but lithology is still clearly reflected in the properties of the soils. In many instances, apparently minor rock differences appear to be the cause of rather striking differences in soils. Among the features related to the parent material factor are depth of weathering, mineralogical composition of the clay, soil texture, .and certain aspects of soil structure. Investigations concerning the effect of parent material upon the composition and morphology of soils have been in progress in the Bureau of Plant Industry laboratories for a number of years. Of particular interest has been weathering of certain rocks to soils such as the Iredell series in which the clay is predominantly montmorillonite, while nearby in the identical environment rocks of similar composition produce kaolinitic soils such as the Davidson (6). Profiles representing different kinds of weathering products are being completely studied by petrographic, chemical, and physical methods in order to follow changes in the original rock minerals and the weathering products through the parent material and the soil profile. These detailed studies are intended to locate the point in time or space where the course of weathering and the kinds of minerals formed are determined and to identify the peculiarities of rock or weathering regime that are responsible for formation of different soils. This paper presents a report on some general mineralogical aspects of two profiles. Future work will set forth more of the detailed quantitative chemical and mineralogical data, and profiles representing other parent materials will be included. SOILS AND PROCEDURES