M. Fergusson — Notes on Geology of Tanganyika. 365 



they bend east a little and form a large open fertile plain, enclosed 

 by these mountains on the one side and by the Western Congo 

 Range on the other. 



Referring to the question of Tanganyika having been once 

 connected with the sea, it is impossible to state definitely any ideas 

 on the subject from the limited observations I was able to make, 

 but the enormous thickness and extent of the sandstones on the 

 southern shore, extending southwards forty miles and then bending 

 round and continuing west, give one the idea that this might have 

 been an old arm of the sea connecting Tanganyika westward by 

 way of the Congo. If the sandstones could be traced towards the 

 Congo the problem might be solved. Connection northwards at any 

 time seems to me impossible. The mountain range at Kivu forms 

 a dividing barrier, in fact is a north and south watershed, from 

 which the waters flow south to Tanganyika and north to the Nile. 



North of Tanganyika is a broad fertile alluvial plain covered with 

 grass, euphorbias, and scrub, extending north for about 25 miles. 

 Then spurs come down from the main ranges east and west, and 

 from here the country is hilly. 



Just south of Butagata, the German station on the Eusisi, occur 

 some hot springs. From here the country rises again sharply for 

 about 2,300 feet, with rounded hills covered with deep red soil 

 showing no outcrop of rock. This continues round the south-eastern 

 shore of Lake Kivu. Then gneiss and schists come in which continue 

 northwards as far as the volcanic area. In one place, on the north- 

 eastern shore at which we landed, I found a white fissile rock. [" This 

 rock is very similar to rocks from Abyssinia, which have been referred 

 to solvsbergite (see Min. Mag., 1900, xii, p. 265), the fissile character 

 being due to the platy arrangement of the felspars. Under the 

 microscope it shows a trachytic felt of small felspar laths with 

 interstitial, minute, ragged patches of a pale-green augite. From its 

 poorness in coloured minerals the rock is best referred to the 

 bostonites."] 



The main eastern range comes down to the lake and extends 

 along the east and north shores as far as Kumchengi, then 

 continuing north ; the western range also follows the lake shore 

 and strikes north, forming a valley similar to the Eusisi Valley 

 north of Tanganyika; but this valley of Kivu is filled with lava 

 which has been poured out from several volcanoes, of which two 

 are still active, emitting steam and sulphurous fumes. The larger 

 of these, Kirunga-cha-gongo, is 11,350 feet in height, and the crater 

 is about one and a half miles in diameter at the top. It has been 

 recently eruptive, as can be seen by the streams of lava cutting 

 through the forest. 



The lava seems to be extremely scoriaceous everywhere, and has 

 poured down southwards into the lake and northwards almost as far 

 as the Albert Edward, The line of volcanic action seems to be 

 proceeding from east to west, as there are six or seven large extinct 

 cones almost in a line east of this, and the two active ones are at the 

 western extremity. 



