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



phases have not yet been fully worked out. For the northern 

 conglomerates the original term u G-lacial Conglomerate " is as 

 appropriate as ever, and I have preferred it in various descrip- 

 tions of these conglomerates in the Transvaal. 



Distribution of the Conglomerates. — The main area occupied 

 by the Karroo System covers a large part of South Africa, 

 including the major portions of Cape Colony and Natal, nearly 

 the whole of the Orange River Colony and most of the south- 

 eastern Transvaal. This area would be included roughly 

 between lines drawn from a point on the south-east coast of 

 Cape Colony, near to the mouth of the Gualana River, W. to 

 near the head of the Doom River beyond Matjesfontein, NNE. 

 to the Lange Berg on the southern border of Namaqualand, 

 NW. by Prieska and Kimberley to Middelburg and Belfast in 

 the Transvaal, SSE. by Amsterdam to Vryheid, and SSW. to 

 the coast of Cape Colony at the mouth of St. Johns River. 

 This area includes most of the higher portions of South Africa, 

 and almost the whole of it lies above a level of 3000 feet. In 

 the Drakensberg the uppermost portions of the Karroo System 

 attain an elevation of over 8000 feet. 



The series of glacial deposits at the base of the system crop 

 out almost continuously around the margin of the vast area 

 occupied by it, following approximately the lines given above. 

 Along their southern margin the Karroo rocks, particularly the 

 Dwyka Conglomerate, have been affected by the intense folding 

 characteristic of the southern portions of Cape Colony. There 

 the lowest Karroo Beds are frequently highly inclined, and 

 their outcrop is correspondingly reduced in width, but over 

 the whole of the remainder of the area occupied by them the 

 Karroo rocks are practically horizontal, and the outcrops of 

 the various divisions occupy broad tracts of country. This is 

 especially the case with the Glacial Conglomerate and lower 

 portions of the system, which in many places form extensive 

 outliers around the margin of the main area as above defined. 



Relationships and Age. — In its southern portions in Cape 

 Colony the Dwyka Conglomerate grades downwards into a 

 series of greenish shales (Lower Dwyka Shales) some 700 feet 

 in thickness, which in turn lie comformably upon the quartzites 

 of the Witteberg Series. These, together with the Bokkeveld 

 Beds and the Table Mountain Series, constitute the " Cape 

 System" of Cape Colony. 



Passing northwards, the Dwyka Series overlaps the lower 

 divisions of the Cape System, which thin out in that direction, 

 and comes to lie unconformably upon various much older 

 systems of rocks. In all the more northerly localities where 

 the conglomerate has been studied, it lies uncomformably on 

 the older South African rocks, the surfaces of which are fre- 



