M. Fergnsson — Notes on Geology of Tanganyika. 367 



Around the large cone, Kirunga-cba-gongo, there are many 

 smaller cones which appear to radiate off along definite lines of 

 weakness. Thus : — 



N.W. 

 O 



o 



"^^w^ 



o 



o 



o o o o 

 S.W. S.E. 



The great Western or Congo Eange here consists of granite, gneiss 

 and schists, the schists increasing in proportion as it gets further 

 north, till at the Albert Edward the whole range appears to be 

 composed of mica-schist. 



Lake Kivu, whose only outlet is the Rusisi, does not seem to 

 have fallen in level at any time, as tbei"e are no signs of old terraces 

 round the shores, and there are many old trees growing close down 

 to the shore, cemented in by a sort of concrete wall formed by spray 

 dashing up on the boulders and pebbles, evaporating and leavino* 

 a deposit of carbonate of magnesium. The floor of the lake is in 

 places paved with this deposit. 



Generally the lake is deep right up to the shore. It has every 

 appearance of having been formerly simply a river running down 

 the valley northwards into the Albert Edward, The volcanic 

 eruptions then took place in the valley, filling it up with lava and 

 damming up the water, which gradually rose and flooded the banks 

 till it found an outlet south by way of the Rusisi into Tanganyika. 

 The natives call it 'The River.' 



A curious point about the water of Kivu is that, unlike ordinaiy 

 water, which contains a solution of calcium carbonate, it contains 

 a solution of magnesium carbonate. The floor of the lake is paved 

 with what appears to be a pi'ecipitate of this substance, and the 

 pebbles and boulders around the shore are cemented with it. There 

 are no dolomites or other magnesium rocks, as far as I could see in 

 the district ; therefore the inference is that springs containino" 

 magnesium carbonate in solution must be feeding the lake and 

 keeping up a constant supply. 



[" The quantity of water received and the state of preservation 

 were not such that reliance could be placed on quantitative I'esults, 

 but from analyses made by Mr. J. Hart Smith, A.R.C.S., it is 

 evident that magnesium replaces calcium in the water, the analytical 

 and spectroscopic evidence showing that ti-aces only of calcium salts 

 are present. Fragments obtained from the lake floor, consisting of 

 a calcareous tufa evidently deposited round vegetable debris, were 

 analyzed by Mr. W. Robertson, A.R.C.S., and were found to contain 

 CaO 28-65, MgO 12'66 per cent, as the mean of two closely 

 agreeing analyses." — W. E. W.] 



Lake Albert Edward is a shallow lake throughout, with a sandy 



