﻿Vol. 6 1.] THE GLACIAL CONGLOMERATE IN THE TRANSVAAL. 681 



Messrs. A. W. Rogers & E. H. L. Schwarz studied the Conglomerate 

 in the Prieska district of Cape Colony, 1 while in his report for the 

 same year 2 Dr. Corstorphine compared the results there obtained 

 with those of observers in other parts of South Africa, and 

 emphasized the differences existing between the conglomerates, as 

 developed in the southern parts of Cape Colony representing sub- 

 aqueous deposits, and the more northerly phases representing true 

 ground-moraines ; a difference in mode of origin which accounts in 

 part for the difference in the lithological characters between the 

 northern and southern phases of the Conglomerate. This distinction 

 has probably been further emphasized by the effect of the much 

 greater thickness of strata, to the pressure of which the southern 

 deposits were subjected, and also by the earth-movements in which 

 the latter have been involved. The term ' Glacial Conglomerate ' was 

 applied by Mr. E. J. Dunn in 1873 3 to the outcrops in the northern 

 portion of Cape Colony, Wylie's old name ' Trap-Conglomerate ' 

 being retained for those in the south. Two years later, Mr. Dunn 4 

 termed the southern outcrops, as typically developed near the 

 Dwyka Eiver, 'Dwyka Conglomerate,' still keeping the name 

 ' Glacial Conglomerate ' for the northern occurrences, a name which 

 I have preferred to use in this and other descriptions of the Conglo- 

 merate in the Transvaal. 



Although the Glacial Conglomerate occurs extensively in the 

 Transvaal, being generally present at the base of the Karroo System, 

 which occupies the greater part of the south-eastern portion of the 

 Colony, it rarely affords good exposures or sections ; and> perhaps, 

 on this account it has not hitherto received much attention from 

 geologists. The survey of a district lying eastwards from Pre- 

 toria, and extending from the neighbourhood of the diamond-fields 

 to near Middelburg, has recently afforded much additional informa- 

 tion with regard to the local character and disposition of the Glacial 

 Conglomerate in this part of South Africa. The object of the 

 present paper is to give some account of the results thus obtained. 



The Glacial Conglomerate in the Transvaal. 



The situation and extent of the district which is dealt with more 

 particularly here will be best seen by reference to the sketch-map 

 on p. 680 (fig. 1). It lies on the northern edge of the principal 

 area occupied by the Karroo System in South Africa, and includes 

 a number of outliers separated by the progress of denudation 

 from the main body of the formation. These outlying portions 

 frequently include both the Glacial Conglomerate and the over- 

 lying shales, sandstones, and grits associated with coal-seams, which 

 form the upper portion of the Karroo System in the Transvaal. 



1 Ann. Eep. Geol. Comm. Cape of Good Hope for 1899 (1900) pp. G5, 86 

 et segq. 



2 Ibid. pp. 17 et seqq. & pp. 25 et seqq. 



3 ? Geological Sketch-Map of Cape Colony ' London, 1873. 



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



