XXXIV.] THE WATEK-SHEDS OF AFRICA. 445 



mountains, which do not fall into any one of the main basins, 

 and as a rule only receive the rain-fall of a small portion of the 

 country, need not, in a sketch like the present, be classed inde- 

 pendently. 



Besides these basins, there are also the great deserts of the 

 Sahara and the Kalahari, which separate fertile tropical Africa 

 from fertile temperate Africa. 



Of these, the Sahara is by far the largest and most sterile ; the 

 Kalahari during the rainy season being covered with vegetation 

 which affords sustenance to innumerable wild animals, while the 

 Sahara, except in an oasis around an occasional spring, always 

 presents the same sandy and parched appearance. 



Having as yet such scanty data for our geographical knowl- 

 edge of Africa, it is difficult to trace the precise water-shed be- 

 tween any two systems, and therefore my observations on the 

 subject must necessarily be liable to great modifications as ex- 

 ploration gradually opens out regions now unknown. 



The basin of the Nile is probably bounded on the south-west 

 by the water-shed i-eached by Dr. Schweinf urth ; on the south 

 of the Albert Nyanza, by the highlands between that lake and 

 Tanganyika, whence the water-shed pursues a tortuous course 

 to Unyanyembe (where, I believe, the basins of the Nile, 

 Kongo, and Lufiji approach each other), and then follows a 

 wave of high land running east till it turns up northward along 

 the landward slopes of the mountains dividing the littoral from 

 the interior. Passing by Kilima ISTjaro and Keuia, it extends 

 to the mountains of Abyssinia, where the sources of the Blue 

 Mle were discovered by Bruce, and so on to the parched 

 plains bordering the Red Sea, where no rains ever fall. The 

 western boundary of the Nile basin is, of course, the eastern 

 portion of the desert. 



The basins of the Niger and the Ogowai can not yet be de- 

 fined with any degree of exactitude, and the northern boundary 

 of the basin of the Kongo has still to be traced. 



The Zambesi drains that portion of the continent south of 

 the Kongo system, and north of the Kalahari desert and the 

 Limpopo, the northern boundary of the Transvaal Republic ; 

 some of its affluents reaching to within two hundred and fifty 

 miles of the West Coast. 



