A Contribution to the Study of the Glacial (Dwyka) Conglomerate in the Transvaal

Abstract

W ith the exception of the gold-bearing conglomerates of the Witwatersrand, the Glacial or Dwyka Conglomerate at the base of the Karroo System has probably attracted more attention from geologists than any other rock occurring in South Africa. While, however, the rocks of the Rand derive their importance mainly from their economic value, the interest manifested in the Glacial Conglomerate over a period of fifty years has depended entirely upon purely-geological considerations. The diversity of views which so long prevailed, as to the origin of the Dwyka Conglomerate, was no doubt largely due to the fact that these views were in many cases necessarily based upon the examination of hand-specimens. The study of the rock in the field, however, can hardly be said to have resulted in any marked unanimity of opinion among local geologists, the majority of whom favoured an igneous origin for the rock in question; and, although the glacial view was stated by P. C. Sutherland as far back as 1868, and later supported by G. W. Stow, Mr. E. J. Dunn, and Dr. A. Schenck, it is only quite recently that the accumulation of evidence in favour of the glacial origin of the rock can be said to have led to a general acceptance of this view. To South African geologists the Glacial Conglomerate affords the only common geological horizon as yet available for the various colonies, while its similarity to corresponding formations in India, Australia, and South America gives a wider interest to the investigation of