OF THE HALOLIMNIC FAUNA OF LAKE TANGANYIKA. 373 



Jurassic origin for the Tanoanyika shells has been mooted, the 

 PalsBontological evidence brought forward in Part I may now 

 be briefly recapitulated. I must confess that the possibility of 

 tracing a connection between the Inferior Oolite fauna of the 

 Anglo-Norman basin and the fauna of Lake Tanganyika had a 

 considerable fascination for me, and I rather hoped that as we 

 approached the Mediterranean basin there might have been 

 some evidence in favour of these views. On the contrary, 

 except in Sicily, no really important gasteropod fauna has been 

 discovered in the intermediate areas, and even in the case of 

 the Sicilian fossils the prevailing assemblage of gasteropods 

 lends but little countenance to any theory of a Jurassic origin 

 for our halolimuic shells. 



These considerations were originally based upon a hope that 

 there might be some evidence of a Jurassic derivation by way 

 of the Congo basin, but the more I studied this part of the 

 question the less faith I had in ray original expectations. 

 Supposing, as is by no means improbable, that there may have 

 been a communication with Tertiary and even with Mesozoic seas 

 on the northern side of the Congo basin at some period of its 

 history, the misfortune is that we obtain no palseontological 

 evidence in the direction required. If we take North Africa, 

 the Iberian Peninsula, or even the south-west of Prance, where- 

 ever Jurassic deposits are known, they have never yielded a 

 fauna approaching that of the Anglo-Norman basin, and 

 therefore do not help us in the least towards covering the 

 immense distance in space which exists between that classical 

 region and the centre of Equatorial Africa. As regards 

 Jurassic deposits within the limits of the African tropics, such 

 as those of Abyssinia and Madagascar, we have already seen 

 that their fauna, so far as known, has no analogy with the 

 Tanganyika gasteropods. This, however, is a fact of minor 

 importance, since the Madagascar deposits especially occupy a 

 region which there is good reason for believing on geological 

 grounds, has never had any counection with the Congo basin, in 

 which Lake Tanganyika is situated. 



The argument from geology. — Since neither the zoological 

 nor the palseontological evidence favours the notion of an 

 Inferior Oolite origin for the halolimuic gasteropods, we must 

 endeavour to ascertain how far the geological history of this part 

 of Equatorial Africa tends to throw any light upon the subject. 



In Part II, I have endeavoured to sketch a brief outline 

 of this history, dwelling more especially on the geological 

 structure of the Congo basin, and of that portion of the East 



