May 6, 1920] 



NATURE 



29/ 



The Kalahari and Oratnboland. 



By Prof. E. H. L. Schwarz. 



''pHE Kalahari and Ovamboland belong- physio- 

 i- graphically to one and the same province ; the 

 former is a region of red sand and the latter of 

 white sand. The whole area, some 350,000 square 

 miles, is blocked by an encircling ring of hard 

 rocks, breached on the east by the Victoria Falls, 

 on the south by the Aughrabies Falls on the 

 Orange River, and on the west by the great 

 cataract {300 ft. high) on the Cunene River. The 

 consequence of this peculiarity is that the whole 



300 miles long by 100 miles broad; part of the 

 breadth in the northern half is occupied by sand 

 dunes, so that the effective area is now less than 

 that of Victoria Nyanza ; but before it was tapped 

 by the Zambezi it must have been a little larger. 

 The Zambezi enters the depression at the Mam- 

 bove Falls, follows the northern boundary, and 

 leaves the old lake at Kasungula. It is not certain 

 when the Zambezi first breached the wall and let 

 out the waters of the lake ; the Portuguese maps 



Scale of Miles 



region is flat and the rivers have scarcely any fall, 

 the floods seeping rather than flowing along the 

 sandy river-beds and blocking up the channels 

 with bars made of branches, reeds, and other 

 rubbish, so that there has been a constant chang- 

 ing in the distribution of the water. 



On the west there are two great depressions, 

 the Makarikari and the greater Ngami. Living- 

 stone obtained the impression that the two formed 

 the bed of one enormous lake, but the map of 

 Passarge shows the two very clearly defined. The 

 greater Ngami is a depression elongated in a 

 south-westerly direction, with parallel sides, and 

 NO. 2636, VOL. 105] 



before Livingstone's time showed the river begin- 

 ning not so very far above Zumbo, and we know 

 that the Portuguese had a very good idea of the 

 country so far back as the sixteenth century. The 

 Falls cannot be of very great age, because the 

 gradient below them is more than 15 ft. to the 

 mile, and a great river like the Zambezi would 

 have flattened out the gradient if it had been 

 of any considerable age. The recent earthquake 

 at New Langenburg, at the head of the Loangwa 

 River, shows that the area is one of great seismic 

 activity, so that the original idea of Livingstone 

 and Murchison, that the crack was formed bv 



