Appendix C. 
the mountain is essentially constituted of gneiss, the biotite variety and rnicrocline 
being common on the lower parts of the mountain. This gneiss, associated 
with mica-schists, may be traced from Ibanda by the Mahoma Valley, not only 
up to the crests of the mountain, but probably also extends to the south and 
west of the range. 
It should be mentioned that in Mt. Luigi di Savoia there are large dikes of 
macroscopic 'pegmatite rich in garnet and tourmaline, haplite and micro-granite in 
the neighbourhood of Stairs Peak; diabase, which crops out at Sella Peak, where 
it abounds in fulgurites ; diorite, epidosyte and crystalline chalk, which seems to 
point at contact between the gneisses and the amphibolic schists. 
Mt. Speke. —The prevailing rock appears to be a granitoid gneiss with 
biotite and abundant epidote; with the gneiss would appear to be associated 
diorite, amphibolite and micro-granite. 
Mt. Emin. —Yields quartzite and a diorite analogous to that of Mt. Stanley. 
Mt. Gessi. —The dominant rock again appears to be amphibolic schist in 
association with quartzite and epidosyte. 
In the Bujuku Valley the prevalent form appears to be of a type analogous 
to that occurring on Mt. Speke. This valley, as well as that of the Mubuku, 
would seem in its upper reaches to open out in contact with gneiss and 
amphibolic rocks. 
Tectonic Structure. —The tectonic feature by which the Ruwenzori Massif is 
outlined and clearly characterized is represented by two great zones of fracture. 
One lying to the west is of vast size, having given rise to the Semliki Valley, 
and in this direction completely isolated the enormous mass of the Ruwenzori 
Range. The other (eastern) zone of fracture is less marked, but well outlined 
by the volcanic formations, in which are included those of Fort Portal. 
In relation with the two main zones of fracture, others occur in the interior 
of the range, and these are disposed in two different directions, one west and 
east—that is to say, normal to the chief trends—the other, on the contrary, 
running in parallel lines from south to north. To these lines of inner fracture 
are due several valleys and many of the secondary glens, which tend to give 
their characteristic isolation to all the principal heights. 
The stratigraphic disposition is regular. As we ascend the Mobuku 
Valley, we everywhere notice in the gneiss and mica-schist beds an incline from 
east to south-east. This incline is, on the whole, maintained in Mt. Baker, 
and is clearly seen, for instance, in Cagni Peak. In Mt. Luigi di Savoia the 
east-south-east slope recurs, with a tendency to the south which farther on 
becomes due south. In Mt. Staidey the south-east tends to change to west 
or north-west, although the south-east to east incline reappears in the Bujuku 
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