Page:South African Geology - Schwarz - 1912.djvu/191

average came down to 12 dwt. The average of the Rand varies from month to month, according to the amount of the low-grade ore which is passed through the mills.

The Kheis Formation

The Kheis Formation occupies stratigraphically much the same position as the Witwatersrand System. It forms a great range of hills from west of Prieska to Uppington and northwards into Bechuanaland, where it has not yet been followed. It consists of—

Kheis
System.

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Wilgenhout Drift Series …          …          …          …          …          …          …          …          …          …          …          …          …          …          …          …          …          …          …          …          …          …          …          …          …          …          …          …

Green lavas and sediments of vol­canic origin.

Kaaien Series …          …          …          …          …          …          …          …          …          …          …          …          …          …          …          …          …          …          …          …          …          …          …          …          …          …          …          …

White quartzites and quartz schists.

Marydale Series …          …          …          …          …          …          …          …          …          …          …          …          …          …          …          …          …          …          …          …          …          …          …          …          …          …          …          …

Ferruginous quartzites, slates, and limestones.

The beds are intensely folded and metamorphosed, and to the west the bottom only of steep synclines remain as isolated outliers of the system. The granite that is found traversing the beds may have been squeezed in during the folding, that is, was older than the sedimentary beds, or it may have intruded the Kheis Beds subsequently, though on the latter view it is hard to see what supported the Kheis Beds before the granite came up.

The Koras Series is an uncorrelated series of coarse conglomerate and lavas which occurs along the Orange River from Groot Drink to Koras. The basal conglomerates consist of boulders of mica schist and quartzite in an arkose matrix, the boulders running to 18 in. diameter. Above these come quartz-porphyries and basalts and on top red sandstones and conglomerates, like the Waterberg Sandstone.