348 Transactions of the Boyal Society of South Africa. 
that for three-fourths of its length it is bounded on its right-hand side by 
the escarpment of the Kaap Plateau. 
Considering now the geological character of the area, we find rocks 
belonging to the extremely ancient pre-Cape formations which are, through 
denudation, appearing from beneath the mantle of Karroo deposits by 
which they had been covered in Permian and Triassic times. This 
erosion has revealed a land surface with a drainage system belonging to 
late Palaeozoic times, of which the Kaap Valley formed an important 
branch. The evolution of the modern drainage system has to a very 
considerable degree been influenced and modified by its superposition 
upon that of the palaeozoic continental mass. 
The matter acquires a still higher interest in view of the fact that this 
land surface was intensely glaciated and its minor features considerably 
modified by a vast ice-sheet towards the close of the Carboniferous epoch. 
The area under consideration is well situated for the elucidation of the 
various problems involved, for further to the east and south the old land 
surface becomes buried beneath younger sediments, while to the north and 
west the denudation has been somewhat prolonged and superficial deposits 
frequently conceal the formations, principally in the valleys. 
Physical and Geological Features. 
A notion of the physiography of the area under consideration will be 
gathered from the following account and from the map attached. The 
most striking feature is the vast Kaap Plateau, built up of the nearly flat- 
lying limestones, dolomites, and cherts of the Campbell Eand series. The 
edge of the plateau maintains an altitude of about 4,000 feet above sea-level 
from Yryburg down to near Bead's Drift — a distance of 160 miles — the 
vertical fall into the valley below increasing within that distance from 150 
to 800 feet. From its edge the plateau rises gradually and uniformly 
towards a chain of hills with curiously rounded outlines, known as the 
Asbestos Mountain or Griqua Town Hills, which extend from Prieska to 
beyond Kuruman in a curve convex to the east. The highest point is 
attained on the boundary between Kuruman and Barkly West, namely, 
6,070 feet, and the contours of the Kaap Plateau form even curves round 
this central point. North of this the surface falls towards the Kuruman 
Eiver. 
West of the Asbestos Mountains there is rather rugged country with 
numerous valleys, frequently sandy bottomed, culminating in the quartzite 
ridges of the Langsbergen with a nearly northerly trend. The drainage 
from this quarter is conducted into the Orange Eiver. South of the 
Orange Eiver the same bended jaspers that compose the Asbestos 
Mountains form the Doornberg, a chain of steep-sided hills with similar 
