( 347 ) 
THE EVOLUTION OF THE EIVEE SYSTEM OF GEIQUA- 
LAND WEST.- 
By Alex L. du Toit, B.A., F.G.S. 
(Eead March 17, 1909.) 
(With Map. Plate XXV.) 
The present river system of Griqualand West and the adjoining 
Transvaal and Orange Eiver Colony has proved to possess a history 
probably more complex than any other yet described from South Africa, 
and one that can be traced back clearly to a geological period considerably 
more remote. The factors concerned in the development of the drainage 
lines have been so varied and uncommon that, although much still remains 
to be learnt concerning this and the adjoining area, the author has thought 
that it might be well to put on record a general account of the evolution of 
the drainage system of this portion of Cape Colony. 
The Dry Harts Eiver, flowing nearly due south from Vryburg in a 
narrow but widening valley, joins at Taungs the Harts Eiver, which 
drains the south-western corner of the Transvaal, there acquiring a more 
south-westerly trend. The Vaal Eiver possesses a course nearly parallel 
to it from Warrenton to Eiverton, but makes a bend at Barkly West, and 
at Delports Hope enters the Harts Eiver at right angles. 
The Vaal Eiver Valley from this point onwards is a continuation of 
that of the Harts, and receives the Eiet and Orange Elvers from the east, 
also at right angles. The latter changes its course to south-west — a direc- 
tion which it maintains as far as Prieska, and is joined by the Brak Eiver 
from the south a little above the point where it resumes its north-westerly 
direction of flow. 
There is thus one continuous valley extending with a gradual curve 
from Vryburg to Prieska, a distance of 235 miles, and receiving from the 
left the Harts, Vaal, Eiet, Orange, and Brak Elvers. 
This valley, which, strangely enough, possesses no single name 
applicable throughout its entire length, although geographically so 
entitled, will in what follows be styled the Kaap Valley, from the fact 
* Published with the permission of the Geological Commission. 
