FURTHER OBSERVATIONS ON THE ORIGIN OF THE 

 RAND BANKETS. 



By Professoi Ernest H. L. Schwarz, A.R.C.S., F.G.S. 



(Plate 3.) 



Continuing the comparison of the W'itwatersrand area with 

 that of Cape Colony,* we find a remarkable similarity in the 

 igneous intrusions in the two areas; just as there can be traced 

 in the sediments several recurring periods in which the same 

 conditions on land produced the same nature of the deposits under 

 water, so in the up- welling of liquid rocks there is a close paral- 

 lelism in the Transvaal and Cape Colony in successive periods. 

 In the Transvaal there is a great laccolite, two hundred and fifty 

 miles in longest diameter, which occupies the Bushveld to the 

 north of Pretoria ; it is surrounded by an areole of dykes and 

 sills which considerably increase its area. In the Cape Colony 

 there is no central body of a laccolite apparent, but the whole of 

 the Karroo, from Natal to the western coast nearly, is per- 

 meated by a vast number of dolerite dykes and sills which make 



Fig. 1. 



a. — The Bushveld (Transvaal) type of laccolite. 

 h. — The Karroo type of laccolite (cedar-tree type). 



up what is known as a cedar-tree type of laccolite. It will be 

 the purpose of this paper to describe these two laccolites. The 

 bearing of them on the question of the title-subject of the paper 

 is that in both cases to the south there is a vast thrust-area, which 

 has been planed down and obscured in the Transvaal, but which 

 in Cape Colony can still be clearly recognised in the .folded 



* See pages 52 to 59 of this volume. 



A 



