The Nature of Clay, and its Significance in the Weathering Cycle

Abstract

THE characteristic constituent of the natural substance, clay, has been the subject of numerous investigations both by chemists and by pedologists. It is generally believed to be colloidal, and the residual product of the hydrolytic decomposition of mineral silicates. Whilst attempts have been made to study this complex by methods of acid extraction, the most promising line of advance has been the study of the finest fraction obtained in mechanical analysis—the so-called colloidal clay. Although this fraction, as isolated by some workers, may contain small proportions of unweathered material, we shall probably not err greatly in equating it with the weathering complex, particularly if a critical settling velocity of less than 10^-4 cm./sec. has been used in its separation by means of sedimentation.