Formation and General Features of Ruwenzori. 
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-ellipse. 
Resuming in its main outlines the origin of the 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 bloc 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 other 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 the central region of a group of rocks 
which have resisted the 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 during 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 the Bujuku were filled with large glaciers 
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