Vol. 51.] ON THE GEOLOGY OF MOUNT KUWENZORI. 677 



and Busoga, but the western limit of the volcanic rocks was 

 uncertain. 



The Archaean rocks are first seen at the western foot of the Nandi 

 Hills, and extend thence across a wide extent of country in Northern 

 Kavirondo. Around Mumia's the series is represented by a fine- 

 grained syenitic gneiss, almost identical in character with some in 

 the Taita Mountains. The gneissic series extends thence along the 

 northern shore of the Victoria Nyanza, through Busoga, Buganda. 

 and Buddu; it disappears at length beneath tne sediments of 

 Karagwe and Ankole at Butunguru, a little to the west of Kitangule, 

 on the last great bend of the Kagera Biver. Then the Archaean 

 rocks appear again farther west, at Kiarutanga and Kasagama's,. 

 and form the whole platform on which Buwenzori rests. 



(2) The Sedimentary Rocks. 



Speke 1 has recorded the existence of a series of sedimentary 

 rocks on the western slopes of the Nyanza basin, in the districts of 

 Karagwe and Ankole. More recently, the late Mr. Joseph Thomson ~ 

 recorded the occurrence of a wide expanse of old sediments in the 

 upper part of the Congo Basin, where they have been described in 

 some detail by M. Cornet. 3 In the absence of fossils it is impos- 

 sible to correlate the various members of this series or determine 

 their ages. Shales of Permo-Carboniferous age occur on the Sabaki. 

 and there are general reasons for considering that the sedimentary 

 formations of the interior are older than these. It is therefore 

 probable that they are Palaeozoic, and possibly pre-CarboniferoUs ; 

 but beyond this very indefinite conclusion it is unsafe to go. 



The Nandi Hills afford the first opportunity for a study of these 

 sedimentary rocks, and here their superposition on the gneiss can 

 be clearly seen. 



The lower part of the eastern slope is formed of a fine quartzite 

 containing a little mica [35]. Followed up the hill, this is suc- 

 ceeded by a black, massive, cherty-looking quartzite [36], which is 

 apparently continuous with a coarser pink quartzite [39]. The 

 main part of the western slope is occupied by a series of amphi- 

 bolite-schists [40] which rest on a fine-grained syenitic gneiss [41 ] T 

 both of which must belong to the Archaean series. The summit 

 of the hills is occupied by a mylonitic gneiss [38] which is ap- 

 parently interbedded in the quartzites, and thus belongs to the 

 sedimentary and not the Archaean series. The foliation of this 

 gneiss is vertical, and its characters are very different from any in, 

 the Lower Archaean series. 



After leaving the Nandi Hills the gneisses are crossed as far as- 



1 J. H. Speke, ' Journal of the Discovery of the Source of the Nile,' I860, 

 p. 196. 



2 Jos. Thomson, ' To Lake Bangweolo and the Unexplored Region of British 

 Central Africa,' Geogr. Journ. vol. i. (1893) pp. 116-117. 



3 J. Cornet, ' Les Formations Post-Primaires du Bassin du Congo,' Ann. Soc. 

 geol. Belg. vol. xxi. (1895) Mem. pp. 193-279. 



Q. J. U. S. No. 204. 3 b 



