Summary of Geological Observations. 
All the gneiss and granitic rocks are strikingly conformable in their 
structure and composition, and their characters agree, broadly speaking, with 
the descriptions already given by those writers who have occupied themselves 
with the crystalline formations of South and Central Africa, thus further 
showing the prevailing uniformity in the constitution of the extensive archaean 
plateau. 
In the first arc-haean zone, that is, between the shores of the lake and the 
overlying primitive formations near Mitiana, the mica-schists seem to prevail, 
these being associated with gneiss and thick quartzite beds. The mica of the 
micaceous schists is the muscovite variety, which occurs in large laminae, thus 
forming rocks of a very marked schistose type, but always highly reddened, and 
often somewhat disintegrated by aerial denudation. 
When we pass beyond the palaeozoic and thus re-enter the archaean zone, 
we find the region between Kasiba and Muyongo constituted entirely of a large- 
grained granite, which appears to form a range running about south to north. 
In this granite are noticed hydiomorphie forms of felspar, which in their greatest 
development reach two inches and more. In the granular mass of the rock 
quartz abounds, while the biotite mica is, as a rule, relatively scarce. Throughout 
the whole region the granite is always profoundly metamorphized, a fact which 
contrasts with the relatively fresh aspect of the rock in the granitic outcrops of 
the palaeozoic zone. 
At Muyongo the mica-schists again become associated with gneiss, the 
latter predominating. Such association, always accompanied by quartzite beds, 
and in places by minute biotite mica-schists, and by talc-schists, is continued right 
up into the Ruwenzori Range, into the constituents of which it largely enters. 
The gneiss is of a schistose character which is never very distinct, hence is 
to be considered as a granitic gneiss, the micaceous element of which is biotite, 
and presents an always more or less pronounced kataclastic structure. Charac¬ 
teristic of this rock are everywhere the really considerable abundance of the 
ferruginous minerals, such as magnetite, ilmenite, and hematite (the changes of 
which explain the frequent reddish surface of gneiss), and the constant presence 
of microcline, which becomes the prevailing, one may even say often the 
exclusive, felspar variety in this rock. This indeed is a fact which has already 
been recorded in other parts of Central and South Africa. 
In the neighbourhood of Ruwenzori biotite gneiss, either normal or with 
a predominance of microcline, is partly replaced by amphibolic gneisses. In 
several districts, but especially in the granitic range between Kasiba and 
Muyongo, are noticed outcrops of pegmatite and micro-granite ; here the 
pegmatite has never the coarse-grained structure comparable to that of granite, 
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