THE TANGANYIKA PROBLEM. 85 



The water of Lake Kivu is very deep, often more than 

 100 fathoms, within a few hundred yards of the shore. But, 

 owing to the fact that we had no other boats besides native 

 canoes, and to the persistent stormy, squally character of 

 the weather which we encountered, we were unable to carry 

 out any sounding operations far from the land. 



The east, west and south shores of Kivu are, as I have 

 said, composed entirely of schist and gneiss ; but the northern 

 shore of the lake is quite different. It is formed wholly of 

 the modern volcanic materials, the layers of lava and ash, 

 which have been ejected by the still active Mfumbiro 

 Mountains. As we approached the northern limit of the 

 lake, the trough-like sides of the great valley were seen to 

 continue northwards, after the lake had come to an end, 

 just as the sides of the same great valley were seen to 

 run on beyond the north shore of Lake Tanganyika. But 

 here, instead of the floor of the trough rising gently, in 

 a series of raised alluvial flats, the whole space, between 

 the lateral ramparts of the depression, is filled up and 

 blocked to the north by a group of great and modern 

 volcanic cones. These cones extend in a string or chain, 

 not parallel with the valley, but from east to west ; form- 

 ing, in fact, a vast transverse dam, which stretches in this 

 place completely across the floor of the depression. The 

 numerous peaks of which the chain is composed are very 

 lofty ; one of them, Karisimbi, being often snow-capped, and 

 reaching an altitude of about 14,000 feet. 



An examination of the individual volcanic cones shows 

 that those to the east are, unquestionably, the oldest. They 

 are, in the first place, quite extinct, while their old crater- 

 walls are much denuded, and partially enclose secondary 

 cones, and the irregular products of the last efforts of their 

 activity. The slopes of the two great cones to the west of 



