Page:South African Geology - Schwarz - 1912.djvu/201

 of plants which went to form the coal, and hence there is an unconformity between the Dwyka and the coal-bearing series. Elsewhere there is evidence that the conglomerate as originally laid down has been disturbed: the boulders have been washed out and carried to a distance, where they have been again consolidated into a stratum. Such a remade bed is said to be rémanié.

The Coal-measure Series. — Above the conglomerate there are coarse sandstones and shales with coal seams at the base. The sandstone is of the Idutywa type, white and fairly loose in texture, and is used for building stone as in the Free State. The coal occurs in seams up to 20 ft. in thickness. It is often covered with boulders from the Dwyka Conglomerate, and the sandstones above occasionally include numbers of such boulders, clearly indicating land conditions, so that we must assume a considerable break between the Coal-measure Series and the Dwyka Conglomerate. There is no correlation between the Transvaal coal beds and the carbonaceous shales above the Dwyka Conglomerate in the Cape Colony. As far as one can judge, while the southern portion of the Cape Colony was occupied by a deep lake, the northern portion in the Transvaal was a swampy back-water surrounded by tropical forests which grew upon the boulder clay, and from these forests were formed the coal deposits. The coal seams are often broken by lens-shaped layers of sand, which are the deposits of streams which flowed through the marshes, and further prove that the coal was the result of growth in place of the vegetable matter of which it is composed, unlike the Stormberg coals, which are the result of the accumulation of drifted wood which