272 Transactions of the Boyal Society of South Africa. 
running water only takes place in the belts, for it stops when the water 
disappears in the sand of the succeeding terraces. The positions of the 
open springs and the short streams issuing from them change owing to 
the choking up of the springs by vegetation and, at the present time, 
owing to the opening of new w^ater-holes, which develop into springs, for 
animals to drink at. Probably heavy rains in Bushmanland cause water 
to break out at fresh spots on the belts and to overflow at waters already 
open. 
