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III.—The Geological History of South Africa1
Published online by Cambridge University Press: 01 May 2009
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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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Footnotes
Presidential Address delivered by Dr. F. H. Hatch to the Geological Society of South Africa, 29th January, 1906.
References
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page 163 note 1 Holmes, G. G., “Some Notes on the Geology of the Northern Transvaal”: Trans. Geol. Soc. S. Afr., vol. vii (1904), pp. 55–56.Google Scholar “The Geology of a part of the Rustenburg District”: Trans. Geol. Soc. S. Afr., vol. viii (1905), p. 6.Google Scholar
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page 164 note 1 Mellor, E. T., “The Waterberg Sandstone Formation”: Trans. Geol. Soc. S. Afr., vol. vii (1904), p. 40.Google Scholar Mr. Mellor instances the occurrence of boulders ranging up to 8 feet in diameter. These must have been transported by streams of a torrential character.
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page 168 note 1 “Das Antlitz der Erde,” vol. i, p. 768; Vienna, 1885.Google Scholar
page 168 note 2 Blanford, W. T.: Presidential Address, Proc. Geol. Soc., vol. xlvi (1890), p. 106.Google Scholar
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