E. T. Mellor — Glacial Conglomerate of South Africa. 109 



quently glaciated. In Cape Colony and Natal the Dwyka 

 Conglomerate passes upwards into the Ecca Shales, a series of 

 shales and mudstones identical in character with the shales 

 occurring with the Dwyka Conglomerate, and in composition 

 corresponding with the liner portions of the matrix of that 

 rock. The Ecca shales are succeeded by a very extensive 

 series of sandstones and shales, attaining a maximum thickness 

 of some thousands of feet, and including on at least two dif- 

 ferent horizons seams of coal. These, together with the Ecca 

 Shales and Dwyka Conglomerate, constitute the Karroo System 

 of South Africa. Intrusive sheets of diabase occur throughout 

 the Karroo rocks, and the uppermost portion of the system 

 consists, for the most part, of a succession of lava- flows usually 

 amygdaloidal and of basaltic composition interbedded with 

 sandstones containing much fragmental material of volcanic 

 origin. 



The Bokkeveld Beds of Cape Colony have yielded a numer- 

 ous assemblage of fossils related to the Devonian fauna of 

 Europe ; the Witteberg beds which succeed them and underlie 

 the Dwyka Series have so far afforded only a few imperfect 

 specimens showing general Carboniferous affinities. With the 

 Ecca Shales in Cape Colony and with the beds associated with 

 the Coal Seams of the Transvaal, which sometimes, as at 

 Vereeniging, lie immediately above the Glacial Conglomerate, 

 a fossil flora is associated of Permo-Carboniferous age* having 

 a number of genera in common with the lower part of the 

 Indian Gondwana System, and the Coal Measures of New 

 South Wales. 



Compared with the southern and eastern margins of the 

 Karroo area, the northern outcrops of the Glacial Conglomerate 

 and associated beds show a considerable diminution in thick- 

 ness, a feature shown also by the other divisions of the Karroo 

 System. In the southern outcrops in Cape Colony the Dwyka 

 Conglomerate has a thickness of about 1000 feet ; on the north 

 of the Colony, in the neighbourhood of Prieska, it is stated not 

 to exceed 500 feet.f In Natal and the eastern Transvaal the 

 thickness of the conglomerate is about 300 feet,;}; while on the 

 northern border of the formation, in the central portions of the 

 Transvaal, it rarely reaches 100 feet, and may be locally absent 

 altogether. As will be seen from the descriptions given below, 

 this difference in thickness corresponds with differences in com- 

 position, and in general characters dependent upon variations 

 in the original conditions of deposition in the different localities. 



* A. C. Seward, Notes on the Plant Remains from Vereeniging, Q. J. G. S. 3 

 vol. liv, pp. 92-93. London, 1898. 



f A. W. Eogers, The Geology of Cape Colony, London, 1905. 



\ G. A. F. Molengraaff , Geology of the Transvaal, Edinburgh, 1904, p. 73. 



