The continent of Africa has an unusual combination of features and environments, including many extreme contrasts. By the late Precambrian, almost the whole Africa had become effectively a large stable craton and most of the central area was never invaded by the sea. However, Palaeozoic marine sediments occur in various parts of North Africa, bounded by a line from Ghana to the Sinai peninsula, and also in the Cape folded belt at the extreme southern end of the continent. At the end of the cycle of deposition of the Cape Supergroup, southern Africa was affected by an intense glaciation that ushered in the long period of sedimentation of the Karroo Supergroup. The Karroo Supergroup spans the period from later Carboniferous to early Jurassic, ignoring the usual break between the Palaeozoic and Mesozoic eras. The Middle Stone Age and Later Stone Age are concepts originally devised in southern Africa to describe the range of archaeological materials clearly younger than the Acheulian.