THE TANGANYIKA PROBLEM. 83 



on the Rusisi River, matters change ; the floor of the 

 valley rises rapidly, for some 2,300 feet, and the rising 

 ground is composed of old folds of gneiss and schist, 

 covered with deep red soil, and against which the modern 

 lake deposits to the south, finally terminate. Upon these 

 gneissic ridges there is no trace of any lake-deposit or 

 stratified material of any kind, and the great valley of 

 Tanganyika is here, in fact, to a large extent filled up, but 

 it is not actually obliterated. The flanking ranges could, 

 as a matter of fact, be seen to continue east and west 

 of us as we approached the southern extremity of Lake 

 Kivu, at which point the floor of the great central 

 eurycolpic fold begins to sink again. At present, the water 

 of Lake Kivu stands at an altitude of 4,801 feet, and the 

 outflow of the lake rushes away to the south in a white 

 lace-work of foam, through a gorge in the hills as the 

 Rusisi River, which in turn falls in a succession of swift 

 cataracts down the great valley, until it eventually opens 

 out by five mouths into Lake Tanganyika. 



The upper part of the Rusisi gorge is not much worn, 

 and does not appear to be very old ; and from being a 

 narrow depression in the south, the valley of Lake Kivu 

 enlarges beyond Ishangi until it once more assumes the 

 character of the great Tanganyika and Nyassa valleys ; a 

 broad expanse of water running north for 60 miles and 

 about 30 to 40 miles broad, between high, flanking ranges, 

 which, in places, reach an altitude of 10,000 feet. 



Although, from a scenic point of view, the shores of Lake 

 Kivu are exceedingly beautiful, their geological characters, 

 with the exception of one peculiar feature, are excessively 

 monotonous. The flanking ranges round the lake were 

 found to be composed entirely of schist and gneiss, which, 

 inland, enclose deep valleys like those of Uganda, and 



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