THE TANGANYIKA PROBLEM. 35 



than the mountains and the great elevated plateaux of the 

 hioh central ridges are to be viewed as such. Both mountains 

 and depressions are the products of igneous forces similar 

 to those which have raised the Alps and the Caucasus in 

 Europe ; and as is the case with the Alps, so also in Africa 

 we find old aqueous deposits of all sorts, piled up at high 

 angles on the flanks of the great central core. This is 

 particularly well seen in the region of Nyassa about 

 Mount Waller, and at the north end of the lake ; all over 

 the Tanganyika districts and beyond them to the north in 

 the region of the Mountains of the Moon. 



It will be convenient in the first place to consider the 

 surroundings of Lake Nyassa. We find that the lake lies in 

 a deep depression, which has the form of a vast fold in the 

 earth's surface, and such in reality it appears to be. The 

 depression in which the lake lies runs also along the 

 very top of this portion of the continent, its opposite 

 edges here representing the highest crests of the Great 

 Central Range. In certain places there are old sandstone 

 deposits stretching across the present site of the depression, 

 and these deposits have been broken along its course, in 

 such a manner that, beyond its eastern edges, they slope 

 away towards the Indian Ocean, while on the west they 

 trend in a similar manner towards the opposite sea coast. 

 The existence of these deposits shows in the first place 

 that the trough now occupied by the lake was formed 

 subsequently to their deposition. It is evident indeed that 

 throughout the whole length of the Great Central Range 

 there has been much of this local elevation and depression ; 

 for in almost every district there may be seen faulting, tilt- 

 ing and smashing of the old lake deposits, and other strata, 

 which overlay these regions before such movements took 

 place. The Central African Range appears in this region 



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