Relationships between Regolith, Lithology and Slope in a Humid Tropical Region: Johor, Malaya

Statistical analyses of soil samples from the eluviated A horizon of the upper layer of the regolith in terrain with a local relief of 65 m in Johor, Malaya, show that textural variations are related primarily to rock type. Catenary variations are related more to position on the profile than to form of slope element or slope steepness, a decrease in the clay-silt content being noted down the slope profile. SEVERAL factors affect the texture of the upper layer of the regolith. Some of the more significant would appear to be lithology, slope, intensity of chemical weathering, eluviation of fine fractions into lower layers of the soil, lateral sub-surface movement of fine fractions, the nature and rate of mass movement, pH of the leaching solution and amount and type of clay. The paper examines the role of the first two of these factors in determining the textu- ral characteristics of the finer fractions (<io mm) in the upper layer of regolith for a humid tropical region. Emphasis is laid upon areas of low relief which are more variable in gradient and slope form than the more uniform, steeper slopes of areas of higher relief (Swan, I970). PHYSICAL BACKGROUND