164 A NATURALIST IN MID-AFRICA. 



west shore, and a line drawn from this point to 

 a place called Kiarutanga, near the east shore of 

 the Albert Edward, represents roughly its south- 

 western border. 



I have attempted on the map to show its 

 extent in more detail. It only reaches the east 

 side of Buwenzori about Butanuka, and from there 

 nortrrwards ; but it is even in this part interrupted 

 by a volcanic chain at Vijongo. South of Buta- 

 nuka it is separated by the ancient level of Lake 

 Buisamba from the mountain and, further down, 

 at the Kaihura straits, by a considerable district 

 which is covered by recent volcanic tufa and olivine 

 basalt. 



This enormous area, which I estimate at 360,000 

 square miles, represents the erosion of the Nile, and 

 the sedimentary rocks which may have formerly 

 covered it are probably now portions of Egypt and 

 the Soudan. 



It is a country fundamentally of gneissose rocks, 

 which not infrequently form very curious detached 

 hills, as, e.g., between Mumia's and the Samia hills, 

 where their appearance is fantastic to a degree. 

 Usually speaking it is an endless succession of low 

 rolling hills, separated by inconveniently abundant 

 swamp-rivers. These hills are, as a rule, covered 

 by laterite which, so far as I understand, is a baked 

 crust of rock due to sunlight, the carbonic acid of 

 rainwater, and iron salts combining with the under- 

 lying rock to form a shell which greatly resists 

 denudation. 



