From under the thick blanket of sediments of pre-Karroo age (i.e. Carboniferous or older) which so largely preponderate in the South African stratigraphical column, there protrude immense masses of crystalline rock. In Southern Rhodesia these last consist of granite interrupted at times by still older metamorphic schists, but in places round the borders of the colony, and over the frontier in Portuguese East Africa, they are replaced by gneisses. Recent work has indicated that some of the gneiss is younger than the schists, in spite of the less altered condition of the latter. It is currently accepted, following Maufe, that the gneisses of the northern part of Mashonaland and the southern part of Northern Rhodesia are the metamorphosed representatives of the Lomagundi beds, equivalent to the Transvaal System of the south. The chief difficulty in the way of accepting this view was the presence of less altered limestones and other pre-Karroo sediments resting on the upturned edges of the gneisses and crystalline limestones along some of the Zambezi tributaries. These strata might well be taken to represent the Transvaal System, but the recognition of the widespread distribution of the still younger Waterberg System (= Kundelungu, of the Congo) removes the difficulty introduced by the presence in the area of sediments with a considerable resemblance to the Transvaal beds.