THE TANGANYIKA PROBLEM. 355 



long ago, in fact, that the animals composing this fauna are 

 now for all practical purposes so many lingering shadows of 

 the past, and consequently the discovery of the identity 

 which exists between the halolimnic and marine Jurassic 

 shells is after all nothing but what we might have been led 



o o 



to expect from a consideration of other lines of evidence ; 

 the comparison merely puts the finishing touch to a series 

 of investigations, all of which persistently converge towards 

 the same point and gives us a direct indication of the 

 geological age during which Tanganyika ceased to be 

 directly stocked with organisms from the ancient seas. 



Up to the present time this brings us to the conclusion of 

 the whole matter, but it may be useful to briefly recapitulate 

 the broader results of the foregoing enquiries. 



It has been seen that a vast succession of related 

 geological changes have gone on throughout the equatorial 

 regions of Africa, and that up to the present time these 

 changes have resulted in the incipient formation of a great 

 mountain chain. These same changes have gone on at 

 different times, and where there were once obviously vast 

 and deep depressions, the old aqueous deposits of the 

 interior have been broken and thrust up into the crests of 

 the Great Central African Range, now thousands of feet 

 above the' sea. There is no evidence of the extension of 

 Tanganyika to the north or east, but there is, as we have 

 seen, an obvious probability that it did extend to the west 

 along the Congo depression. The geology ol the districts 

 west of Tanganyika and of the upper and lower portion of 

 the Congo basin thus afford a most promising field for 

 future exploration, and the same may be said of the whole 

 Congo system, for so far as it is at present known, it has 

 yielded the most intensely interesting results. 



During the course of the geological changes which have 



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