ABSTRACT
The larger part of the continent of Africa consists of a great continenta shield, stretching between the Atlas in the north and the Cape Ranges in the south, and comparable in form and origin with the Brazilian or Laurentian shields. Over vast areas the basement rocks of Pre-Cambrian age may be seen, and it is these ancient basement rocks, sometimes referred to as Archaean, which underlie virtually the whole continent. Following the Pre-Cambrian period there is usually a great gap in geological record, representing the first of many long intervals of erosion to which Africa has been subjected. Over the whole of southern Africa, for instance, outcrops of Lower Palaeozoic sediments are very restricted in extent, and the next major rock series belongs mainly to the Devonian. The Tertiary period saw the gradual withdrawal of the sea from northern Africa. The effects of faulting on the African block are demonstrated on an immense scale in rift valleys of East Africa.
