The pre-Cape rocks are but little understood. They no doubt represent formations of widely different ages, but all that can be said is that they are greatly older than the Cape System. The hope that they will yield fossils has been held out but not yet fulfilled. Their total thickness amounts to several thousand feet. The rocks have been greatly changed by pressure in most cases and by the intrusion of great masses of igneous material, the Namaqualand schists and Malmesbury beds being most altered.
The most prominent member of the Cango series is a coarse conglomerate; the other rocks include slates, limestone and porphyroids. The Ibiquas beds consist of conglomerates and grits. Both the Cango and Ibiquas series have been invaded by granite of older date than the Table Mountain series. The Nieuwerust beds contain quartzite, arkose and shales. They rest indifferently on the Ibiquas series or Malmesbury beds.
The pre-Cape rocks of the northern region occur in the Campbell Rand, Asbestos mountains, Matsap and Langebergen, and in the Schuftebergen. They contain a great variety of sediments and igneous rocks. The oldest, or Keis, series consists of quartzites, quartz-schists, phyllites and conglomerates. These are overlain, perhaps unconformably, by a great thickness of lavas and volcanic breccias (Pniel volcanic series, Beer Vley and Zeekoe Baard amygdaloids), and these in turn by the quartzites, grits and shales of the Black Reef series. The chief rocks of the Campbell Rand series are limestones and dolomites, with some interbedded quartzites. Among the Griquatown series of quartzites, limestones and shales are numerous bands of jasper and large quantities of crocidolite (a fibrous amphibole); while at Blink Klip a curious breccia, over 200 ft. thick, is locally developed. Evidences of one of the oldest known glaciations have been found near the summit in the district of Hay. The Ongeluk volcanic series, consisting of lavas and breccias, conformably overlies the Griquatown series; while the grits, quartzites and conglomerates of the Matsap series rest on them with a great discordance.
Rocks of the Cape System have only been met with in the southern and eastern parts of South Africa. The lowest member (Table Mountain Sandstone) consists of sandstones with subordinate bands of shale. It forms the upper part of Table Mountain and enters largely into the formation of the southern mountainous folded belt. It is unfossiliferous except for a few obscure sheils obtained near the base. A bed of conglomerate is regarded as of glacial origin.
The Table Mountain Sandstone passes up conformably into a sequence of sandstones and shales (Bokkeveld Beds), well exposed in the Cold and Warm Bokkevelds. The lowest beds contain many fossils, including Phacops, Homalonotus, Leptocoelia, Spirifer, Chonetes, Orthothetes, Orthoceras, Bellerophon. Many of the species are common to the Devonian rocks of the Falkland Islands, North and South America and Europe, with perhaps a closer resemblance to the Devonian fauna of South America than to that of any other country.
The Bokkeveld beds are conformably succeeded by the sandstones, quartzites and shales of the Witteberg series. So far imperfect remains of plants (Spirophyton) are the only fossils, and these are not sufficient to determine if the beds belong to the Devonian or Carboniferous System.
The thickness of the rocks of the Cape System exceeds 5000 ft.
The Karroo System is par excellence the geological formation of South Africa. The greater part of the colony belongs to it, as do large tracts in the Orange Free State and Transvaal. It includes the following well-defined subdivisions:—
| Feet. | |||
| Stormberg Serie | Volcanic Beds | 4000 | Jurassic |
| Cave Sandstone | 800 | ||
| Red Beds | 1400 | ||
| Molteno Beds | 2000 | Trias | |
| Beaufort Series | Burghersdorp Beds | 5000 | |
| Dicynodon Beds | |||
| Pareiasaurus Beds | Permian | ||
| Ecca Series | Shales and Sandstones | 2600 | |
| Laingsburg Beds | Carboniferus | ||
| Shales | |||
| Dwyka Series | Upper Shales | 600 | |
| Conglomerates | 1000 | ||
| Lower Shales | 700 |
In the southern areas the Karroo formation follows the Cape System conformably; in the north it rests unconformably on very much older rocks. The most remarkable deposits are the conglomerates of the Dwyka series. These afford the clearest evidences of glaciation on a great scale in early Carboniferous times. The deposit strictly resembles a consolidated modern boulder clay. It is full of huge glaciated blocks, and in different regions (Prieska chiefly) the underlying pavement is remarkably striated and shows that the ice was moving southward. The upper shales contain the small reptile Mesosaurus tenuidens.