Introduction 



Both these routes converged to what is, perhaps, the most 

 interesting region of all Africa at the present day : the country 

 known as the Albertine Rift Valley, through which in the 

 north flows the Semliki River to join Lake Albert, while 

 beyond Lake Edward the now elevated Lake Kivu sends 

 its waters southward into Tanganyika to join the Congo 

 system. Clearly, at no very distant interval of time, volcanic 

 disturbances (now made evident in the active and passive 

 volcanoes of Virunga) had not raised Kivu two thousand 

 feet above the level of Tanganyika ; and Livingstone's 

 theory might then have been true, that Tanganyika was the 

 farthest source of the Nile, with its waters flowing northwards to 

 the Albert Nyanza over the bed of the Semliki. But with the 

 bending upwards of this Rift valley, Tanganyika became long 

 isolated (its tribute to the Congo is even now intermittent 

 and liable to interruption). When first discovered by Burton 

 and Livingstone, Tanganyika may have been in one of its 

 phases of isolation with its stagnant, rising water turning to 

 salinity. Its aquatic fauna is very peculiar, suggesting long 

 separation from the Nile basin, yet no great degree of con- 

 nection with Congo waters. Tanganyika is a Rift Valley 

 lake, probably of considerable age and quite different to the 

 broad and — ^in comparison — very shallow Victoria Nyanza. 

 Tanganyika has depths of four thousand seven hundred feet ; 

 the Victoria has no greater depth than about two hundred 

 and forty feet. Tanganyika lies on the eastern frontier of 

 forested Africa, of the region which extends with some inter- 

 ruptions and lessening of its rich and peculiar fauna west- 

 wards across equatorial Africa to the mouth of the Gambia 

 in West Africa. Faunistically speaking, the west and north 

 coasts of Tanganyika are in West Africa, the south and east 



xxxiii 



