Abstract: A comparative study of two soil profiles derived from a biotite-granite and from a metagabbro in the Piedmont Province of North Carolina was made. Intensive weathering of the granite has yielded a soil (Durham) with a clay fraction composed of a kaolinite-halloysite intermediate, mica, and quartz. Restricted weathering of the metagabbro has resulted in a soil (Iredell) with a clay fraction composed of a complex assemblage of chlorite, beidellite, vermiculite, interlayered talc-like minerals, and quartz.
The data indicate that the Durham soil is derived from the severe alteration of a granite and that it represents an advanced stage in soil formation. The Iredell soil has been derived from the less active weathering of a metagabbro and represents a retarded, youthful stage in soil formation. The clay mineral assemblage of the Durham is that of a comparatively stable end product of weathering; that of the Iredell is indicative of a complex, unstable early stage in weathering.