The Evolution of the Biver System of Griqtialand West. 361 
country, unfortunately not for the better ; the overstocking of the farms 
and their deforestation are reducing the Karroo to a barren tract. 
SUMMAEY. 
In Palaeozoic times a continent extended over the area in question, and 
the drainage from it was directed southwards, the Kaap Valley forming 
the principal channel. At the close of the Carboniferous epoch this con- 
tinent, which stood at a lower level than it does now, was intensely 
glaciated and finally buried beneath the Permo-Triassic Karroo deposits ; 
upon the surface so formed the modern drainage was initiated. 
The denudation of the newly formed continent has been greatly aided 
by the elevation which has in time brought it to its present altitude ; but 
this uplift has been spasmodic, and appears to have acted during several 
distinct periods in late Jurassic and in Cretaceous and Tertiary times. 
With each cessation of movement the rivers have been enabled to cut 
a peneplain, and one of the most important of these surfaces extended 
from the Stormberg probably into Griqualand West, where it is represented 
by the Kaap Plateau. Since late Cretaceous or early Tertiary times this 
surface has experienced denudation ; the rivers have cut down and laid 
bare in this area the pre-Karroo floor with its drainage lines, and the 
development of the modern river system has been greatly influenced by 
reason of its superposition upon that of Palaeozoic times. The Karroo 
owes its peculiar type of scenery in part to its geological structure, in 
part to the prolonged nature of the erosion to which it has been subjected, 
and in part to the climatic conditions which existed during its develop- 
ment. 
