THE TANGANYIKA PROBLEM. 
35 
than the mountains and the great elevated plateaux of the 
hio-h 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 
3 * 
