On some physical properties of Transvaal soils

Extract

Much work has been done in the past on the chemical composition of South African soils. The study of the physical properties of soils has, however, been somewhat neglected.

Transvaal soils differ from those of European countries in several important respects. In the first place, a large proportion of the soil is derived in situ from igneous rocks, and secondly, the country has never been glaciated in recent geological times. These two factors bear directly on the physical properties of the soils. Soil formation takes place chiefly by the chemical decomposition of rocks and only to a limited extent by mechanical disintegration. As a consequence we find in our soils very fine material, resulting from the chemical decomposition of easily weathered minerals, and rather coarse material which represents those rock constituents which are only subject in a limited degree to decomposition. In comparison with European soils particles of intermediate size do not play any dominant part in the mechanical make-up of Transvaal soils. Soils of alluvial origin are, of course, excepted. These latter occupy only a small area, but they are of considerable importance in the present stage of development of the country. Another factor which differentiates Transvaal soils from European ones is the presence in many of the former of finely divided hydrated ferric oxide. This feature will be discussed later.