Page:South African Geology - Schwarz - 1912.djvu/140

 deposits are laid down, and therefore the animals that swarmed in the seas at that time elsewhere, and became embedded in the sediments when they died, had no chance of being represented in the area in question. Thus, in South Africa all the forms that occur in the Cambrian, Ordovician, and Silurian rocks of Europe, Asia, and America are not found. While the sediments of these periods were being deposited, South Africa stood out as dry land above the sea, and the whole era is represented by the unconformity at the base of the Table Mountain Sandstone. Another possibility may happen, namely, that the area in question may be covered with a freshwater lake. The Karroo sediments were laid down in a lake, and therefore the animals whose remains are found in the Karroo sediments are totally different from the animals found as fossils in the marine Trias and Permian of other countries. Conversely, the Devonian rocks of South Africa are marine, whereas the Devonian rocks of Scotland are freshwater-deposits, and the fossils of the Scottish freshwater beds, or, as they are called, the Old Red Sandstone, are freshwater fish and giant water-scorpions forms unknown in our beds.

The Transvaal, Cape, and Karroo Systems consist of conformable series of beds one above the other; but it is evident from the table that there is a gap in the time succession represented by Bokkeveld and Witteberg Series, although the two rock series follow each other without a break. This may be due to the fact that the scale as worked out in England or America is not a correct one as regards the time succession; indeed there are so many gaps in the rocks, caused by land periods when no sediments were laid down, that it is hardly likely that