364 \Y. H. HUDLESTON, ESQ., M.A,, P.R.S., ON THE ORIGIN 



by one or other of the sandstone systems (formations post- 

 primaires), yet the latter have been cut clean tliroiigh by 

 streams in many places so that the framework and bones of the 

 skeleton are occasionally displayed throughout the vast region 

 under description. 



The eastern margin of the periphery calls for especial notice, 

 as Professor Cornet considers Tanganyika to be within the 

 limits of the original basin, since the lied Felspathic Grits extend 

 to the east as well as to the west of the lake. Its eastern 

 affluents descend from a granitic or metamorphic district 

 stretching towards the east and also bordering the lake for a 

 considerable distance. When we come to deal more especially 

 with the geology of the shores of Lake Tanganyika it will be 

 seen that these Red Felspathic Grits, almost horizontal in many 

 places, are occasionally tilted in this region, showiiig that 

 Tanganyika is within the influence of the disturbances in 

 connection with the Great Central or East African Eange, 

 whereas the Congo basin, as a whole, is outside these influences. 

 The south end of the lake is bordered with red and variegated 

 grits belonging to the Red Felspathic series which are horizontal 

 and have been transformed by metaniorphism into a kind of 

 quartzite with intercalation of eruptive rocks. At the outflow 

 of the Lukuga are seen grits and red schist? (of the Red 

 Felspathic group) which continue for a distance of 120 kilo- 

 metres westward from Tanganyika. At this point (Wabenza) 

 they are covered by the white friable schists (White Friable 

 Sandstone) of the centre of the basin. This formation also 

 prevails at Nyangwe, but the Red Felspathic Grits reappear at 

 Stanley Falls. 



The limits on the north-east of the periphery are constituted 

 by the western lip of the western arm of the Graben, which 

 contains the lakes belonging to the Upper Nile. The region of 

 the sources of the Aruwimi consists of crystalline rocks. On 

 the north gneiss occurs at several points between the basin of 

 the Uelle and the White Nile. 



On the north-west there is a sandstone plateau of an altitude 

 of 2,000 to 2,800 feet, which occupies the meeting ground of 

 the Shari, Congo and Nile basins, and falls to the north in a 

 plain some 400 feet lower, watered by the Auk, an eastern 

 branch of the Shari, the principal feeder of Lake Tchad.* 



* Chevalier, quoted in the Journal of the Royal Geographical Society, 

 vol. 22, p. 569 (November, 1903). 



