| Abstract/Notes | After the granites, gneisses, schists, and sediments which make up the Swaziland System had been elevated to form a continental area extending over the northern and western portions of South Africa, denudation began, and the material thus produced was carried to the sea to form the Witwatersrand Beds. The nature of these sediments—they consist of conglomerates, grits, and shales—indicates a marine period with shallow-water conditions, which continued almost uninterruptedly during their deposition. They were accumulated first on a sinking, and then on a rising sea bottom, for the lower beds are composed largely of mud and fine sand, conglomerates only becoming abundant in the upper beds, which were formed in the later portion of the period when the sea had become sufficiently shallow to allow of the accumulation of shingle and gravel. There is evidence in the Southern Transvaal that the land from which the sediments were mainly derived lay to the west, the sea to the east, for the lower Witwatersrand Beds, which consist solely of mudstones and fine sandstones in the east, gradually develop conglomerates with a decreasing amount of shale towards the west. |
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