Soil Formation in Southern Nigeria. (The “Ilepa” Profile.)

Abstract

Summary1. The typical profile of south-western Nigeria formed over acid igneous rocks under alternating conditions of percolation and evaporation is described. The profile being (a) brown sandy soil, (b) concretion layer, (c) red clay, (d) mottled red and white clay, (e) whitish clay, (f) rotting rock. Acidity increases with depth.2. Analyses of the concretion layer show that it consists chiefly of silica (quartz), ferric oxide, and occasionally some manganese. Alumina does not occur to a large extent.3. From studies of the mobility of the iron and soluble salts throughout the profile it is suggested that the profile is developed by a rise of an iron sol which is deposited on a layer of quartz to form the concretions.4. The Yoruba name “Il***pa” has been adopted by the authors for describing such a profile.