Page:South African Geology - Schwarz - 1912.djvu/159

 shore line retreated again northwards the sands became again covered with deeper-water sediments. That the shore was to the north we know from the fact that in the western province the sandstone bands are practically absent in the southern portion about Swellendam and Caledon, whereas as we go northwards into Ladysmith and Willowmore they are very conspicuous, indicating a nearer approach to the shore.

The Karroo Formation

At the base of this formation there is a thick deposit of Dwyka Conglomerate interlain between two bands of shale. Above this comes the Ecca Series, and then the Beaufort and Idutywa series. Many authors include the Stormberg Formation in the Karroo System, but there are many reasons why it is better to separate the two, the most conspicuous being that the fossils of the Karroo System form a compact group entirely different from the fossils of the Stormberg, while the rocks themselves are of quite different texture and nature. The beds of the Karroo System are characterized by a peculiar fern called Glossopteris, which is not found in the beds above or below.

The Dwyka Series is best described by explaining how it was formed. The Southern Hemisphere became glaciated, owing, as has been mentioned above, to the abstraction of the carbon dioxide from the atmosphere by the intense limestone formation of the lower Carboniferous rocks of Europe and America, and again by the immense coal formation of the Upper Carboniferous. The rivers ceased to flow, and instead glaciers poured blocks of ice broken off from the seaward ends by the waves into the Karroo lake. The icebergs floated over