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 they 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, Gotzen, 

 Teleki, and many others, and the accumulated information 



