INTRODUCTION 
3 
both in the coast-belt and on the plateau is much below the average or may 
fail altogether 1 . If there occurs an uninterrupted succession of such seasons, 
it is reasonable to suppose tliat in many localities certain species — particularly 
annuals — may be completely exterminated, and might indeed disappear 
altogether if the less arid recesses of a suitably situated mountain-range 
did not provide a refuge in which they might persist until the conditions 
became again favourable for their extension beyond its limits. 
The Great Karasberg range lies 350 km. from the coast and 150 km. due 
north from the Orange River at Houms Drift. It rises from the level plain 
of the Kalahari about 200 km. from its western edge, where the rapid fall 
to the coastal desert begins. Its extent is not easy to define, for to the 
Diagrammatic section through Great Karasberg Range from west to east, 
approximately to vertical scale. 
north-east and south it merges into lower foothills which, particularly on 
the east, are of great extent. The higher levels of the range however stietch 
from south to north for a distance of 120 km. through which they maintain 
an approximately uniform breadth of 40 km. The localities 1, 3, 0 (sec 
sketch map) are situated on the western boundary of this main pait of the 
range ; nos. 4 and 5 on the eastern boundary. The conspicuous feature of 
the range as above defined is a broad series of rolling plateaux which < xteud 
1 Pearson, 1906, Phil. Trans. B. vol. 198, pp. 267, 268, 
1—2 
