Siiiiimaiy of Geological Observations. 



In some tlistricts, as at Kailjo and in the ncighljoiirhood of Fort Portal, are 

 found isolated masses, or accumulations of masses, on the summits or the flanks 

 of hilly elevations consisting of laterito. In the specified districts these masses 

 consist of diabase, and we ma_y take it that their presence is due to the resistance 

 of certain rocks, perhaps originally in the form of dikes, and to the metamorphisni 

 which reduced to laterite the gneiss or granite in wliicli they were embedded. 

 In some places it is not improbable that it may lie a question of some kind of 

 transport. 



Vulmukm. — Eecent igneous formations are met at the eastern foot of 

 Kuwenzori. Here they serve to indicate the presence of one or more lines of 

 fracture in relation wdth that great Uift Valley with which originated the 

 depression comprising Lakes Tanganika, Kivu, Albert Edward, Alliert, and the 

 Semliki Valley, and which contributed to the isolation of the liuwen/.nri Kaiige. 

 In the Fort Portal district volcanic action is indicated liy thermal springs 

 (Bntaiuika), and by stratified tuff which cover the ground and form a series of 

 little volcanoes, whose craters are now mostly flooded with tarns. Thev form a 

 chain which is disposed very nearly in the direction from south to north. 



The tuffs of this formation are partly compact and partly of loose structure. 

 All, however, are of subaqueous origin, and thus attest the greater extension in 

 former times occupied by Lake Albert Edward, which nnist piciliably have liccn 

 united with Lake Albert towards the north. 



The compact tuffs are of a dark hue, and very hard, and yield a cement 

 consisting of a basic silicate rich in iron and easily decomposed by acids. Such 

 tuffs occur in all the craters of the series, only more or less transformed, the 

 change consisting in a tendency to acquire a red colour due to the decomposi- 

 tion of the silicate of iron. 



The tuffs of looser structure, which are met partly in the craters and in all 

 the surface formations, are of a colour passing from white to grey. They derive 

 principally from fiagments of the compact tuff cemented by calcite after the 

 complete discoloration caused by the metauKirphic process. The enclosed exotic 

 fragments ;ire numerous, especially in the non-compact variety, and the\' 

 consist of fragments of the most diverse sizes, whether water-borne or not. 

 These ingredients may for the most part be considered as coming from rocks of 

 the Kuwenzori Range, such as gneisses, dialiases, diorites, garnet-bearing rocks, 

 amphibolites, etc. In the hill at Fort Portal the tuffs are, moreover, rich in 

 vegetable remains which, unfortunately, cannot now lie determined. In the 

 Butiti — Fort Portal region, mineral springs are also niuuerous, and the country 

 is suliject to frequent earthquakes. 



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