6 THE TANGANYIKA PROBLEM. 



gastropods and those of the Jurassic seas presents us at once 

 with a possible solution of the whole Tanganyika mystery. 

 The strange animals, the jelly-fishes, the molluscs, the 

 sponges, etc., which appear in Tanganyika, and apparently 

 nowhere else in Africa now, may be regarded as the relic 

 of a time when the lake basin was in connection with an 

 ancient sea, and consequently filled with the representatives 

 of its ancient fauna. Moreover, the date of the lake's 

 connection with the sea, which this view of the nature and 

 origin of the halolimnic fauna necessitates, is so remote, that 

 it can easily be made to fit in with our revised notions of the 

 past history of the continent ; and I may point out that 

 there is nothing unnatural or strange in the isolated per- 

 sistence of even specific forms which have elsewhere be- 

 come extinct or greatly changed, for such ancient forms 

 have persisted repeatedly all over the world, like the ganoids 

 Polypterus and Amia, the scorpions and the brachiopods. 



But although in this manner, and as a result of the first 

 Tanganyika expedition, we reached a tenable hypothesis 

 respecting the nature and origin of the jelly-fishes and other 

 marine organisms in Lake Tanganyika, it was very obvious 

 that much remained to be done. We did not know, for 

 example, whether there were marine organisms in any of the 

 other great lakes, Kivu, the Albert Edward, the Albert 

 Nyanza, the Victoria Nyanza or Lake Rudolf ; neither did 

 we know anything of the geology of Lake Tanganyika nor 

 of the districts north of it, as far as the Albert Nyanza. But 

 about the same time, Suess had put forward some most 

 interesting views concerning the nature of these very 

 regions. He had shown that Tanganyika lies near the 

 south end of the more westerly, and greater, of two vast 

 series of valleys which run from the south, through Central 

 Africa, like a couple of converging horse troughs, until they 



