Dr. F. H. Hatch — Geological History of South Africa. 167 



petrographical habit of these amygdaloids to the lavas of the "Volcanic 

 Group of the Drakensberg and Malutiberg. In this connection, the 

 discovery by the Survey of a ' pipe amygdaloid ' in the Bushveld 

 lavas, similar to the characteristic rock of the Stormberg Volcanic 

 Group, is noteworthy. 



The dolerite intrusions, which are so widely distributed in the 

 Karroo rocks, and form such a striking feature in their scenery, 

 belong to a period somewhat posterior to the volcanic eruptions 

 of the Stormberg epoch ; their late limit is fixed by the fact that 

 boulders of the typical dolerite have been found in the Umtamvuna 

 (Upper Cretaceous) rocks of the Pondoland coast. ^ Intermediate in 

 age between the Stormberg volcanoes and the period of intrusion of 

 the Karroo dolerites, are the volcanic pipes so well known on 

 account of the diamond being a constituent of their breccia filling at 

 Kimberley and in the Transvaal. The facts on which this argument 

 is based are as follows : — The Stormberg lavas are occasionally 

 penetrated by dykes,^ which probably belong to the Karroo dolerites, 

 while Messrs. Eogers and Du Toit ^ have shown that the Sutherland 

 pipes, which are analogous to the diamond-bearing deposits, except 

 that they do not yield diamonds, are of later age than the latter. 



The exact period at which the Cape Formation and the overlying 

 KaiTOO Beds were folded to form the great mountain ranges of the 

 Southern Cape (the Zwarteberg, Langeberg, etc.) cannot be fixed, 

 but it was after the deposition of the Lower Karroo Beds, as these 

 are involved in the folding, and before the deposition of the 

 Uitenhage Beds, since the latter lie undisturbed on the folded Cape 

 Formation. 



To summarise : we have in South Africa evidence of the former 

 existence of at least three periods during which the greater portion 

 of South Africa was elevated above sea-level, besides the one we 

 live in, which has endured since Karroo times. The first of these is 

 indicated by the break in the succession below the Witwatersrand 

 System ; the second by the volcanic and fluviatile deposits of the 

 Ventersdorp System, and the unconformity between the latter and 

 the succeeding Potchefstroom System ; and the third by the break 

 between the Potchefstroom and the Waterberg Sandstone. Between 

 these must have intervened three periods, during which a large 

 portion of South Africa was submerged, and the marine and littoral 

 sediments of the Witwatersrand, the Potchefstroom, and the Cape 

 Systems were deposited ; and a long period of fresh- water sedi- 

 mentation during which the Karroo rocks were accumulated by the 

 agency of vast river systems discharging into great lakes. The 

 coastal deposits (the Uitenhage and Umtamvuna Series), which are 

 marine deposits of a later (Cretaceous) period, are not considered 

 here, as they play only an insignificant part in the geology of South 

 Africa ; and I have limited myself to the close of the Karroo period. 



1 Rogers & Schwarz : Ann. Eep. Geol. Comm., 1901, pp. 25-46 ; Capetown, 1902. 



2 A. C. du Toit, " The Forming of the Drakensberg " : Trans. S. Afr. Phil. Soc, 

 vol. xvi (1905), p. 67. 



3 Eogers & Du Toit, "The Sutherland Volcanic Pipes and their Relationship 

 to other Vents in South Africa" : Trans. S. Afr. Phil. Soc, vol. xv (1901), p. 61. 



