THE TANGANYIKA PROBLEM. 81 



the lake. On the lake shore, at certain places, Viuwko and 

 Lumungi, the sandstones were found to rest on granite, 

 which can be seen just above the present water-line ; but 

 north of Lumungi the sandstone deposits disappear, and 

 are succeeded by granites, gneiss and schists, which form 

 the chief constituents of the great mountain range flanking 

 the extreme north of Tanganyika on the east, and which 

 can be seen running away north, parallel with the similar, 

 but even higher, range encircling the lake to the west as 

 far as the eye can see. 



At several points on the shore of Tanganyika, between 

 Ujiji and Usambora, at the extreme north end of the lake, 

 I found, under these great sandstone scarps, layers of 

 modern, broken lake deposit lying with the same dip, about 

 20° to the east, as the sheets of old sandstone on which 

 they rested. These modern lake-beds are now ioo 

 feet above the water-line, and contain the same peculiar 

 halolimnic shells which are now found inhabiting the lake ; 

 but they are broken and upraised abruptly from the 

 present floor of the lake along a line of faulting parallel to 

 the shore, this fact in itself showing that the general 

 upheaval, which has thrust the old sandstones 10,000 feet 

 into the air along the east coast, is still going vigorously on. 



We found, on nearing the north end of Lake Tan- 

 ganyika, that the great valley in which the lake lies 

 (deeply enclosed by lofty, green hills) could be seen ex- 

 tending as a flat-bottomed trough, far beyond the northern 

 shore ; and we found also that the flat floor of this valley, 

 after leaving Kajagga, near the inflowing Rusisi River 

 (which comes from Kivu and opens by five mouths into the 

 lake), was composed chiefly of modern sandstones and 

 alluvium. At first the flat floor of the valley was covered 

 with coarse grass and reeds ; but, as we rose slowly from 



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