DWIGHT W. TAYLOR 
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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