Evidence from geomorphology and mineralogy is presented which indicates that many tropical soils in Uganda are formed on pre-weathered rock. The first cycle of weathering took place before the formation of the African surface, probably in Mid-Tertiary times or earlier. Further weathering and pedological change is taking place in the present cycle.
A variety of profiles are explained on this basis and some catenary relationships are also described. A number of previous ideas are discussed to indicate how the present theory differs from earlier ones.