THE TANGANYIKA PROBLEM. 327 



which is presented by the mixed fauna of Lake Tanganyika, 

 of the present day. 



Whatever opinion may be held respecting the view that 

 the salinity of the ocean has been a prime factor in pro- 

 ducing some of the characteristics which the fresh-water and 

 marine faunas of the present day actually possess, is a 

 matter which is wholly independent of the particular 

 Tanganyika problem with which this work is primarily 

 concerned. 



These more general subjects were merely introduced in 

 order that some foreseen confusions might possibly be 

 avoided, and the ground made clearer, for the consideration 

 of the Tanganyika problem itself. But before finally 

 approaching this particular problem by a systematic ex- 

 amination of the different components of the fauna of 

 Tanganyika, and the other African lakes, I dealt generally 

 with what is known of the geology of the districts of 

 Central Africa. This course was necessary, in the first 

 place, because our conceptions of the country have been 

 somewhat altered by the observations acquired during the 

 Tanganyika expeditions. No support has been lent by 

 these to the view that the marine origin of the halolimnic 

 fauna of Lake Tanganyika is opposed to our knowledge of 

 the geological nature of the African land-mass. On the 

 contrary, it was shown that there was no evidence what- 

 ever against such a view, and that there is a good deal 

 which, more or less, distinctly favours it. 



These preliminary matters have been considered, the 

 fauna of the great African lakes was described, and 

 subsequently the halolimnic fauna was defined as something 

 distinct from the general fresh-water fauna of the African 

 continent. In the first place, it was shown to be a group 

 of organisms of diverse nature, but a group all the 



