Geological History of the Gouritz River System. 371 



between the dolerite and the folded sedimentary rocks, that is, the 

 separation of the two in space, seems to me a very remarkable and 

 important point. In the extreme north-west of the area occupied by 

 the rocks which form the Zwartebergen and Langebergen, a part of 

 the country which was affected only by the Cederberg movements, 

 and to a very slight extent by them, the dolerite dykes extend out- 

 ward from the great area occupied by the intrusive masses in the 

 Karroo, into the older rocks " ; and again in Pondoland, where the 

 lowest member of the Cape System lies nearly horizontally, the 

 dolerite has invaded it. These facts appear to me to confirm the 

 supposition that the dolerite intrusions could not approach the rocks 

 that were being folded, or which had just been folded. It is not 

 improbable that the dolerite, which is so extensively spread through 

 the rocks between Bushmanland and Natal, and which everywhere 

 presents a striking uniformity in petrographical character, was 

 intruded during one period, the limits of which are of course difficult to 

 determine, but which lay between the time of the deposition of the 

 Stormberg Series and that of the Cretaceous rocks of Pondoland, 

 probably much nearer the former than the latter ; f for the former 

 were invaded by the dolerites and the latter contain boulders derived 

 from the intrusive rock. If, therefore, the relationship between the 

 Zwartberg folds and the dolerite intrusions is of the nature I have 

 supposed, the date of the dolerite intrusions, approximately deter- 

 mined in Pondoland, gives us an idea as to the date of the formation 

 of the great anticlines of the southern part of the Colony, viz., during 

 the deposition of the Stormberg Series, or between the deposition of 

 the upper part of the Beaufort Series and that of the upper part of the 

 Stormberg. It is impossible at present to fix the date of the Zwartberg 

 movements more closely, or rather the date of their maximum, for 

 they must have lasted a long time geologically speaking. 



The question of the former western limits of the Stormberg Beds is 

 of great interest, but there is no direct evidence to decide it. At the 

 present day the Stormberg Beds do not occur to the west or south- 

 west of Steynsburg, but they must formerly have extended beyond 



* A dyke of dolerite some fifteen miles long traverses the Dwyka Series on 

 Beukes Fontein in the western or Ceres Karroo, where the Series has been tilted 

 to the east by the same earth-movements that completed the Cederberg anticline. 

 This dyke is some forty miles distant from the dolerite area of the Roggeveld and 

 Nieuweveld. 



t It seems likely that the intrusion of the dolerite was connected with the 

 volcanic phenomena of the Drakensberg, which belong to the latest stage of the 

 Stormberg Series. For a discussion of the volcanic and intrusive rocks of the 

 Drakensberg, see E . H. L. Schwarz on "The Geology of Matatiele," Ann. Hep. 

 Geol. Comm. for 1902. 



