THE TANGANYIKA PROBLEM. 73 



these animals had entirely disappeared. The valley of 

 Nyassa is, however, as we have seen, continued into that 

 of Lake Rukwa, and this in turn has been shown by Dr. 

 Kohlschiitter to run into the great trough of Tanganyika it- 

 self. The Rukwa valley appears bodily to cross Tanganyika 

 in the vicinity of Karema and the Luakuga gap, and to 

 continue westward into the great Congo depression. Un- 

 fortunately little or nothing is known of the deposits in the 

 northern extension of the Nyassa valley in which Rukwa lies, 

 but it appears from the observations of Dr. Fulleborn 

 that the fauna of Rukwa differs from that of Nyassa, 

 or of any of the lakes to the south with which he was 

 acquainted.* 



Thus it would appear that there was once a marine, 

 possibly a triassic or Jurassic, fauna in the region of the 

 north end of Nyassa, the existence of which entirely 

 anteceded the northward extension of the present lake ; 

 that there is now no trace of this fauna in Nyassa or to 

 the south of it ; that the structural fold in which Nyassa 

 lies can be traced to a junction with that of Rukwa; that 

 the fauna of Rukwa differs from that of Nyassa or any 

 of the other African lakes with which Fulleborn was 

 acquainted ; that the valley of Rukwa intersects that of 

 Tanganyika and passes to the west, and lastly, that at 

 the present time there is what appears to be the remains 

 of a marine fauna containing jelly-fishes, the old ganoids, 

 and what are apparently Jurassic gastropods, still living in 

 Tanganyika. 



From these considerations it would appear that the 

 old sea which was once in the vicinity of Nyassa retreated 

 west (it may be shown eventually that it retreated east 



* I do not know whether any definite result of Fulleborn's investigations of Lake 

 Rukwa have yet been published, and Dr. Kohlschiitter says he does not either. 



