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 
