﻿Vol. 6 1.] THE GLACIAL CONGLOMERATE IN THE TRANSVAAL. 679 



32. A Contribution to the Study of the Glacial (Dwyka) Con- 

 glomerate in the Transvaal. 1 By Edward T. Mellor, B.Sc., 

 F.G.S. (Read June 21st, 1905.) 



"With 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 Eand derive their importance mainly 

 from their economic value, the interest manifested in the Glacial 

 Conglomerate over a period of fifty years 2 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 3 as far back as 1868, and later supported by 

 G. W. Stow/ Mr. E. J. Dunn, 5 and Dr. A. Schenck, 6 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 investi- 

 gation of the conditions under which the vast glacial deposits of 

 South Africa were laid down. 



Recent Studies of the Glacial Conglomerate. 



A description of the Dwj'ka Conglomerate, as developed in the 

 Vryheid district, now forming the northern portion of Natal, was 

 given by Dr. G. A. E. Molengraaff in 1898. 7 In the following year, 



1 Communicated by permission of the Director of the Geological Surrey of 

 the Transvaal. 



2 For references to the literature of the subject, see G. S. Corstorphine, 

 Ann. Rep. Geol. Comm. Cape of Good Hope for 1899 (1900) pp. 4-17. 



3 < On the Geology of Natal' Pietermaritzburg, 1868. 



4 'On some Points in South-African Geology' Quart. Journ. Geol. Soc. 

 vol. xxvii (1871) pp. 497-548. 



* ' Geological Sketch-Map of South Africa ' London, 1875. 



6 'Die Geologische Entvvickelung Siidafrikas' Peterm. Mitth. vol. xxxiv 

 (1888) p. 225. 



7 ' The Glacial Origin of the Dwyka Conglomerate ' Trans. Geol. Soc. S. A. 

 vol. iv (1898) p. 103. 



