CHARACTERISTICS AND DISTRIBUTION OF LAKES 567 
water, from which a stream flowed towards the south ; on his second 
visit he could only find water by digging. 
The Kalahari region includes several secondary basins — wide 
depressions partly crossed by river-courses, partly occupied by lakes 
Fig. 68. — Inland drainage area of Southern Africa (Kalahari). 
[The inland drainage area is stippled.] 
and marshes. These basins are separated by even stretches of rising 
ground, which here and there form connected ridges. While the 
bottom of the basins is covered with recent sand, the ground rock 
crops out in places on the ridges, and these places are of great import- 
ance, for there good water is found either as springs or in chalk-pans — 
I 
