THE DESICCATION OF AFRICA. 141 



of the water coming down from the Angola highlands in a 

 southern direction into Lake Ngami, instead of rushing 

 uselessly to the sea. A second barrage at the outlet of the 

 Ngami depression, where the Chobe River filters into the 

 Zambesi River, would prevent the waters escaping and would 

 fiood thousands of square miles in the Ngami and Makarikari 

 depressions. From the evaporation from these vast expanses 

 of water the air throughout South Africa would receive a 

 most notable increase in moisture and the humidity of the 

 continent would be permanently increased. The surface of 

 water exposed when these depressions were filled was greater 

 than that of Lakes Victoria and Tanganyika; one can judge, 

 therefore, what an immense loss to the humidity of the 

 continent has ensued since these have been drained. According 

 to Chapman, the Makarikari dried up about 1820, leaving vast 

 quantities of hippopotami, crocodiles and fish which lived in 

 the lake, to perish, when they were devoured by vultures. 

 Even in Chapman's time (1852-4) the Chobe occasionally 

 flowed towards Ngami. The proposed weir at Ngoma on the 

 Chobe would have to be, according to data hitherto published, 

 which, however, are very uncertain, not more than 10-12 feet 

 high. That is, taking Ngami to be 3,117 feet above sea-level 

 and Kasungula at the Chobe-Zambesi confluence 3,084 feet ; 

 between Ngoma and Kasungula there are the Sebuba Rapids 

 formed by a bar of hard rock which crosses both the Chobe 

 and the Zambesi. 



THE AFRICAN RIVER SYSTEM. 



If one glances at the map of Africa, one is at once struck 

 by the extraordinary courses of the rivers. The Niger rises m 

 the coastal mountains of the south-western corner of North 

 Africa, goes north-east to Timbuktoo as if about to run 

 through the desert, then turns right round and enters the sea 

 on the very coast on which it commenced its course. The 

 Congo, likewise, begins by running northwards, then turns a 

 complete semi-circle and pierces the rampart of mountains on 

 the west coast, instead of following the low ground up towards 

 Lake Chad. The Nile is again peculiar in its course, and the 

 Zambesi and Orange alone seem to run straight from source 

 to mouth like normal rivers of the Amazon or Mississippi type^ 

 but these appearances are, as we shall see, deceptive. 



The second noticeable feature in the African map is the 

 prevalance of deserts like the Sahara and the Kalahari. There 

 is a very widespread misconception of the nature of deserts; 

 the Sahara, for instance, is not a waste of drifting sand as is 

 often imagined, but has an Alpine range of mountains, the 

 Tibesti Highlands, in the centre, and on either side are tracts 



