The various Precambrian areas of the Sahara region are very similar geologically. Within the basement complex, the Pharusian unconformity separates two great groups of crystalline rocks. The older group, generally katamorphic, corresponds to the Suggarian cycle; the younger, generally epimorphic, corresponds to the Pharusian cycle. In the latter, several distinct phases can be distinguished which have not as yet been correlated between the different areas. Throughout the region the Precambrian is separated from younger beds by the Tassilian unconformity.