THE DESICCATION OF AFRICA. 175 



and the weir would become more of the nature of an unsub- 

 merged wall. 



To recreate the greater Ngami in its entirety would mean 

 the building of a barrage across the Zambesi, which is too big 

 a scheme to advocate just at present; there are, also, too many 

 interests involved, not the least of which are those of the 

 natives who live in the Ngami depression; if the whole depres- 

 sion were to be flooded, these natives would be drowned out. 

 As the Makarikari depression is 150 feet below the level of 

 Lake Ngami, the proposed Chabe weir would cause a consider- 

 able expansion of the area of Lake Ngami, would turn the 

 Mababe, Mashabe and Chobe Swamps into large lakes, and the 

 overflow would go down the Botletle River and All up the 

 Makarikari basin. A sheet of water of this size, some 15,000 

 square miles in area, in the middle of the Kalahari, would turn 

 this great thirst land from being the source whence all the 

 drought-producing hot winds originate, into an evaporating 

 dish, supplying rain clouds for the whole of South Africa; for 

 moisture in the centre of a continent is not dissipated as on the 

 sea-board, by winds that may blow the rain-laden clouds out 

 to sea, but, as it transpired by the leaves of the forest trees 

 and the grass of the meadows, or evaporated from the surfaces 

 of lakes, it ascends into the air and is precipitated as rain over 

 the adjoining country, and the process is repeated in ever- 

 widening circles. The converse is also true; a desert keeps the 

 air hot and dry, devastating hot winds blow from these 

 regions and scorch up the adjoining lands. In South Africa, 

 whether in the Karroo or the coastal plains on the west, one 

 sees after rain the original vegetation spring up, green and 

 tender, among the hardy, permanent bushes; this " opslag," as 

 the Boers call it, is very short-lived, for in a few days the hot 

 winds come and wither it up. It is a fact, too, that many of 

 the severest droughts in South Africa are not due to deficiency 

 of rainfall, but occur because between the falls of rain the 

 desert winds come and wring out of the soil every drop of 

 moisture. As a case in point, I may mention the drought in 

 the Eastern Province in 191 3- 191 7. With quite a fair average 

 rainfall, the hot winds had so dried the soil that the run-off, 

 after rain, was reduced to 4 per cent, 96 per cent, being 

 absorbed in the ground which had become as dry as ashes; in 

 the latter half of 191 7 the drought broke and a succession of 

 rains fell without the intervening periods of hot winds and, the 

 run-off rose to 80 per cent., only 20 per cent, being required by 

 the soil. 



To revive the whole of the Proto-Orange system is no 

 longer possible ; it is more impossible than to revive the Proto- 

 Congo system. South Africa stands at such an elevation above 

 the sea, that the rivers quickly cut for themselves deep canyons. 



