THE TANGANYIKA PROBLEM. 
39 
though the upthrust has been far greater along the Great 
Central Range in the interior of the continent, it is obvious 
that these same earth movements have affected in a less 
degree an area which is at any rate as wide as the 
continent itself. We are, in fact, here in Africa encounter- 
ing again phenomena similar to those noticed by Darwin 
as having gone forward in the gradual elevation of that 
part of the earth’s surface which finds its maximum of 
expression along the crests of the Southern Andes. The 
effect of crinkling such as this, greatest along an axial line 
running approximately north and south in Africa, and 
becoming less and less as we pass from this longitudinal 
axis, east and west, would if it had gone on evenly and 
uninterruptedly have tended to raise the continent into a 
great hog’s back ; and south of the equator, this is as a 
matter of fact the form which it actually possesses, 
the earth’s surface has been bent up into a great 
arch ; but as we become better acquainted with the 
phenomena, it is also apparent that the changes which have 
produced this effect have not operated altogether evenly ; 
and owing to this, during their progress thev have given 
rise to subsidiary effects : to all sorts of parallel foldings 
and crinklings of the surface, which in some of their ex- 
pressions are extremely interesting. By far the most striking 
of these subordinate geological changes which the gradual 
upraising of the African interior has produced, are a series of 
great chasms, the “ Graben” of Suess, the long, deep valleys 
to which I have just alluded and which are found to run 
among, and parallel with, the ridges of the Great Central 
Range. These vast fold-like depressions in the surface 
of the earth have been noticed now by a large number 
of explorers. By Stanley, Stuhlmann, Cassati, Gbtzen, 
Teleki, and many others, and the accumulated information 
