Page:South African Geology - Schwarz - 1912.djvu/170

 is still living. The white sandstones are used in the Free State largely for building purposes, and are called Steenpan.

The Stormberg Formation

In this system, which is confined to the eastern portion of South Africa, there are three divisions, the lower containing the Molteno, Cyphergat, and Indwe coal seams, and called the Molteno Series, then the Red Beds, and finally the Cave Sandstone.

The Molteno Series consists of alternating shales and massive beds of gritty sandstone. The latter is called glittering sandstone, because the sand grains have been enlarged by quartz being deposited on them, and as the sandstone is coarse-grained, with plenty of pore space, the crystals have grown up with well-marked facets. These reflect the light, and cause the sandstone to glitter in the sun. Often there is a considerable amount of undecomposed felspar and mica in the sandstone, indicating the near proximity of granite, from which the sediment was derived. As the nearest granite on the north is more than 200 ml. away, it is obvious that we cannot look to that as a source of supply; therefore we can establish that the southern granite border of the original Karroo lake was not far distant. The sandstone also becomes very coarsely conglomeratic, with boulders as large as a child's head. Ironstone concretions are frequent. The coal seams mostly lie under the sandstone krantzes, and are thin and laminated with shale, showing that the vegetable matter has been transported from the place where the plants grew, that is, on the southern border of the Karroo lake, the old Madagascar ridge, now sunk beneath the waves.