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CHAPTER IV. 
THE SUPERFICIAL GEOLOGY OF TIIE REGIONS OF THE 
GREAT LAKES. 
In the preceding chapter it was seen that the whole of the 
geology of a very large portion of Central Africa is sub- 
ordinated to, and is in fact an expression of, the gradual 
folding and elevation of the earth’s surface in wrinkles 
running parallel with the theoretical axis of the Great 
Central Range. That there was a time in which no central 
range existed goes without saying, and that there were also 
many periods during which the characters of the interior 
were not those of the present day, is made clearly evident, 
as we have seen, by the simple fact that at some time 
horizontal strata stretched across the present site of 
greatest elevation and distortion, both in the region of 
Lake Nyassa and Lake Tanganyika ; while, lastly, it 
is made clear by the observations I have described relating 
to the recent depression of the floor of Nyassa in the 
north, and the elevation elsewhere of the bottom of the 
lake, which has occurred as late and later than post- 
pleistocene times, that the activity of the continent with 
respect to the Great Central Range is not yet dead. There 
has, moreover, evidently occurred a succession of efforts in 
such movements, and these efforts are, in several places, 
