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 Amici , 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 
