The Evolution of the Biver System of Griqiialand West. 353 
intimately connected with the gentle warping of the strata in that region. 
It is most suggestive to find that the two principal directions of the rivers 
are north-west and south-west, and that to the latter belong the head of the 
Orange Eiver, the Kraai Eiver, and Caledon Eiver, all flowing in gentle 
synclines, though the explanation of the course of the Vaal is not quite 
clear. 
Whatever may have been the character of the Karroo drainage when 
initiated, it is not unlikely that it had been considerably modified even at 
the early period at which it can be recognised in the area under discussion. 
It has been pointed out that as a result of denudation an extensive pene- 
plain was produced at the 6,000-foot level in the Stormberg area at a 
period when the continent stood at a much lower level than now ; from 
this peneplain there rose to a height of from 2,000 to 5,000 feet — possibly 
higher — such portions of the volcanic masses of the Drakensberg and 
Basutoland as had escaped erosion by the head-waters of the Orange 
Eiver. A peculiarity of the present main watershed right through the 
Karroo is that the northerly flowing streams take their rise at the edge 
of an escarpment which faces the south ; owing to the cutting back of the 
latter there can be no doubt that the crest has gradually been shifted 
northwards and that the divide formerly lay very much further to the 
south of its present position. 
Following this period of planation which was caused either by the 
cessation of the upward movement of the Continent, or possibly by a 
slight subsidence, there came a renewal of the uplift of such an amount 
that the river meanders were incised to a depth of over 1,000 feet between 
the Drakensberg and Aliwal North, and ultimately the present surface 
was formed at an altitude of between 4,000 and 4,500 feet over the area 
north and north-west of the Stormberg. 
It is of great significance to find that in the area under consideration 
the oldest recognisable peneplain is that whose lowest altitude stands now 
somewhere about 4,000 feet above sea-level and into which the Orange 
Eiver near Prieska has cut its channel to a depth of about 1,000 feet. 
This remarkable physiographic parallelism in two areas, 250 miles 
apart, namely, a period of extensive planation followed by incision of the 
valleys to a similar amount in each case, subsequent to which there has 
been comparatively little variation in the character of the erosion, is very 
suggestive. The probability is therefore considerable that the same forces 
operated over the whole of the area in question and that the planation in 
Griqualand West was synchronous with that in the Stormberg. 
A large portion of the Griqualand West peneplain remains hardly 
modified in the Kaap Plateau, with its gradual and uniform rise of from 
15 to about 25 feet per mile from its edge (4,000 feet) towards the north- 
west. It is cut in crystalline limestones and dolomites, and the few 
