OF THE HALOLIMNIC FAUNA OP LAKE TANGANYIKA. 



357 



almost on the Equator, will serve not only as a description 

 of the immediate region, but may in many respects be regarded 

 as typical of Peninsular Africa, both east, south and west. 

 In particular the section shows : 



(1) That fossiliferous deposits are a mere coastal fringe, or 



at least get no further inland than the Foot Hills, 

 and, 



(2) The enormous development of old crystalline and more 



recent volcanic rocks. 



FIG. 2. — SECTION ACROSS BRITISH BAST AFRICA (AFTER GREGORY : " RIFT 

 VALLEY," p. 222.) 



Victoria 

 Nyanzft. 



Graben. 



Volcanic 

 chain. 



Primitive 

 crystalline 

 mountains. 



Foot hills. 



^ 



Indian Oc ean 



GEOLOGICAL SIGNS. 



(a) Coastal deposits : raised coral-reefs and old sea beaches with much 

 wind-borne sand. 



(6) The foot plateau. The seaward portion consists of shales, etc., of 

 middle Jurassic age as proved by their ammonites ; the middle 

 portion of bright coloured sandstones, probably of Triassic age, but 

 without marine fossils ; the western portion of shales of probably 

 Permo-Carboniferous age, with land plants and fresh-water mollusca 

 {Palaeanodonta). 



(c) The portion of the Archsean rocks to the eastward of the volcanic 

 region. 



{d) Volcanic region, consisting of plateaux, mountains (Kenya, Kilima 

 Njaro, etc.), and Graben. 



(c') Archaean rocks west of the volcanic region. N.B. — The Archaean 

 system is said to cover something like two-thirds of British East 

 Africa, and there can be little doubt that it underlies the greater 

 part of the rest. 



(e) Lower Palaeozoic rocks without fossils on the horizon of the Karagwe 

 series — here and there on the shores of the Victoria Nyanza. 



An old crystalline axis is well shown in the above generalized 

 section, and, as we perceive, these crystalline rocks are stated 

 to cover two-thirds of this part of the country. Indeed it has 

 always been an idea of mine that the immense extent of old 



