670 THE GEOLOGY OF MOUNT RUWENZORI. [Nov. 1895. 



conclusion : — ' Many things go to show that the existence of these 

 peaks is due to volcanic causes. The greatest proof that this is so 

 lies in the numbers of conical peaks clustering round the central 

 mass on the western side. These minor cones have been formed 

 by the central volcano getting blocked in its crater.' 1 



For the first definite geological information about Ruwenzori we 

 are indebted to Dr. Franz Stuhlmann, who visited the district with 

 the late Emin Pasha in 1891. He ascended to the height of 

 15,000 feet (by aneroid), made some valuable botanical collections 

 from it, and clearly showed that the volcanic theory could not be 

 maintained. He says that ' the neighbourhood of the mountain, its 

 aspect, and its massive cloud-formations have been described by 

 Stanley with a master-hand. "With his geological explanation I 

 cannot, however, agree.' 2 



Stuhlmann's own interpretation of the mountain is that it is a 

 ' faltungsgebirge ' situated between two lines of dislocation. To 

 the west is the great dislocation which runs along Tanganyika, up 

 the valley of the Rusisi and Ruchuru, across the Albert Edward 

 ^Tyanza and down the Semliki to the Albert Nyanza ; to the east 

 is a secondary dislocation which runs along Lake Ruisamba. 

 Between these two lines is a mass of old eruptive rocks (granite 

 and diabase), which has been forced up through the ' U rschiefer ' 

 (mica-schists, quartzite, and clay-slates), which have been thrown 

 back. In his map he marks the whole mountain as diorite and 

 diabase. It has therefore been generally regarded as a normal 

 plutonic massif. 



Topographically, Ruwenzori is a long narrow ridge which extends 

 for about 50 miles in a direction from JNf.N.E. to S.S.W. Its 

 summit attains the height of 16,500 feet, and thence there is a long 

 eastward slope to the valley of the Wimi at Kyatwa. The slope to 

 the west is at an angle of 22°, and that to the east at about one 

 of 4°. The most convenient method of studying the geology of the 

 mountain is therefore to make a few sections across it at right 

 angles to its trend. 



II. Sections across and Structure oe Ruwenzori. 

 (1) The Kivata Section. 



The first section will be taken from Kasagama's, westward along 

 the course of the Kivata, past Diwona, to the summit of the 

 northern end of the ridge of Ruwenzori. The country around 

 Kasagama's is at the level of about 5200 feet, and is formed of 

 hornblendic gneisses of a type common in the Archaean series of 

 the Central African Plateau. In some cases [123] 3 the rock has 



1 H. M. Stanley, ' In Darkest Africa,' 1890, vol. ii. p. 257. 



2 b\ Stuhlmann, ' Mit Emin Pasha,' [1893] 1894, p. 298. 



3 The numbers in square brackets in the text are those of the specimens in 

 the collection, which is now in the Mineralogical Department of the British 

 Museum (Natural History). 



