Formation and General Features of Runenzori. 



and south-eastward on the eastern part of the chain, southward 

 on the southern part, and south-westward on the western part 

 so as to form a tectonic semi-elhpse. 



Resuming in its main oTithnes the origin t)f tlie group of 

 mountains and of the high peaks of its central portion, we 

 may ascribe it to three causes, geotectonic, stratigraphic and 

 lithologic, namely : — ■ 



1. The upheaval en hloc of a whole portion of the 

 archaean rocks of Central Africa with a main slope for the 

 rise from west to east. This rise is mainly In relation to 

 the gigantic western fracture, with its relative vertical 

 displacements, which originated the Semliki Valley, and also 

 with otlier fractures which have taken place to the east of 

 the group, and which are marked by a series of recent 

 volcanoes like those of the Province of the Toro District. 



2. To a marked elevation — ellipsoid or anticlinal, with 

 general direction from north to south, and strata more or less 

 considerably uplifted in the Ruwenzori group. 



3. To the existence in tlie central region of a group of rocks 

 which have resisted tlie physico-chemical action of external 

 agents (amphibolite, diorite, diabasis, amphibolic gneiss), 

 whereas the gneiss-rocks and mica-schists of the lower zone 

 oppose far less resistance to such agents. 



To these main causes we may add the probable existence of 

 internal fractures in the group, with a main direction from 

 north to south, which would have contributed to the isolation 

 of the several groups. An important geological feature of 

 Ruwenzori is the vast development of the glaciers diu-ing the 

 glacial period. The proofs of this are manifest, especially at 

 Nakitawa. At one time the valleys of the Mahoma, of the 

 Mobuku and of tlie Bujuku were tilled with large glaciers 



