Basutoland is entirely occupied by the upper division (Stormberg series) of the Karroo formation.
A broad ring of crystalline rocks (Swaziland schists) encircles the Transvaal except on the south, where the Karroo formation extends over the Vaal River.
Within this nearly complete circle of crystalline rocks several geological formations have been determined, of which the age cannot be more definitely fixed than that they are vastly older than the Karroo formation and newer than the Swaziland schists.
The following subdivisions have been recognized by Molengraaff Karroo System, Transvaal System, Vaal River System, South African Primary System.
The Karroo System attains its chief development in the southeastern Transvaal in the districts of Ermelo, Standerton and Wakkerstroom.