THE TANGANYIKA PROBLEM. 69 



While these changes were in progress there were de- 

 posited under the more permanent of the retreating waters 

 sediments represented by those covering the Old African 

 sandstones at such places as Masswa on Tanganyika, round 

 the source of the Luakuga on the same lake, and at the 

 north end of Nyassa ; and the triassic character of the 

 organic remains which some of these, the Drummond's beds, 

 have been found to contain gives us a clue as to the geolo- 

 gical period during which the folding of the central range 

 and the formation of the eurycolpic folds actually began to 

 take place. 



There does not seem to be any valid reason why the 

 broad conclusions thus reached respecting the geological 

 nature of the African interior, and the past history of this 

 continent should not be accepted as, at any rate, a first 

 approximation to a correct reading of the facts, and, 

 although there can be no doubt that, as we become better 

 acquainted with the country and the details of its composi- 

 tion, our conceptions of the history of particular portions of 

 the area will be enormously elaborated by an infinity of 

 fresh illustration, I have a strong conviction that our con- 

 ception of the formation of the land-mass will remain domi- 

 nated by the conceptions respecting its past history which 

 have just been sketched. 



Up to this point the geological characters of the great 

 African lake region have been dealt with in a very general 

 way, and from the outset this method has been intentionally 

 pursued. There are, as we have seen, certain broad 

 features of the structure of Africa as a land-mass which 

 forcibly proclaim themselves now that we are becoming- 

 better acquainted with the interior, and it is above all 

 things important that these- matters should be fully 

 apprehended during the future attempts which will 



