368 M. Fergusson — Hotes on Geology of Tanganyika. 



bottom. The natives can pole their canoes nearly everywhere, only 

 occasionally having to resort to paddles. The lake is not in a 

 'rift' like Tanganyika, but has more the appearance of an overflow. 



Immediately north of Albert Edward, at Katwe Fort George, 

 a white volcanic tuff occurs. [" It is on the occurrence of these tuffs 

 round ' crater-lakes ' that the idea of considerable recent volcanic 

 activity at the foot of Euwenzori mainly depends.^ The present 

 tuff shows signs of stratification, with parallel flakes of biotite and 

 muscovite, so that it has been probably rearranged by water. 

 Microscopic examination shows that it consists by no means 

 wholly of volcanic material. It contains small angular fragments 

 of a biotite-granite or gneiss, oligoclase, quartz, biotite, brown 

 hornblende, pink garnet, and colourless augite. Any doubts, how- 

 ever, which might have been entertained as to the volcanic origin 

 of these ' tuffs ' were set at rest by an examination of the tuff 

 collected by Mr. Scott-Elliot, and referred to as No. 96 in the paper 

 already cited. Under the microscope this tuff is seen to be made 

 up mainly of round lapilli, of which the larger ones consist of a mere 

 shell of glassy volcanic material surrounding fragments either of 

 biotite or of a granitic or gneissic rock, which must have been torn 

 from the walls of the vent during the eruption."] Tuffs with crater 

 lakes, hot springs, and cones continue up to Euwenzori and around 

 the eastern foothills to beyond Fort Gerry. There are salt lakes 

 around Katwe. The foothills of Euwenzori are composed of gneiss ; 

 beyond and above this mica-schists occur, dipping steeply ; and 

 still higher, nearer the centre of the mountain, epidiorite^ is the 

 predominating rock. 



The accompanying Figure shows a section of the mountain as 

 approached from the east. 



Volca nic Gn eiss Mica Schists 



Diagram- Section on the East side of Euavenzoei. 



Proceeding eastwards from Toro, the prevailing rock is gneiss as 



far as Uganda, with occasional dolerite dykes. ["A specimen of these 



dolerites consists of large ophitic plates of a nearly colourless augite, 



felspar laths, and large plates of ilmenite ; in parts in the interstices 



1 Scott-Elliot & Gregory: Quart. Journ. Geol. Soc, 1895, li, p. 674. 



2 Scott-Elliot & Gregory, I.e. 



