OF THE HALOLIMNIC FAUNA OF LAKE TANGANYIKA. 353 



Coastal 



Age. 



Superficial Deposits .... Recent, etc. 

 ( Pondoland Series .... Cretaceous. 



\ Uitenhage Series .... Wealden. 



rStormberg Series .... Rhsetic. 



I Beaufort Series .... Triassic. 



Karoo < t;. ^ a ■ 

 I jbjcca Series 



LDwyka Series 



Permo-Carboniferous. 



Cape System .... ? Old Palseozoic. 



Pre-Cape Rocks .... Arcliisan. 



The beds above referred to the Cretaceous and Wealden are 

 simply strips along the coast, and it may be said generally of the 

 principal system, viz., the Karoo, that its fauna and flora are 

 entirely fresh-water or terrestrial. The older beds on which 

 the great Karoo system unconformably rests contain no marine 

 fossils. It is probable that the beds marked as Ehsetic were 

 formerly regarded as Triassic. 



Section h. — We now come to consider the geological structure of 

 Equatorial Africa adjoining the Cape Beds, which lie to the 

 south. With certain exceptions presently to be described, the 

 beds of this region coincide geographically with the Congo 

 basin. Cornet says -of this region that it is constituted by 

 depressed massifs, formed of Archaean and Palseozoic beds much 

 folded ; these are covered by beds almost horizontal extending 

 over immense distances, consisting of conglomerates, sandstones 

 and clay schists, all utterly unfossiliferous. This is the 

 unpromising region which we have to study with sotne degree of 

 detail, but before doing so it will be necessary to glance at the 

 history and structure of the peculiar mountain chain, which 

 though it hangs to the eastern side of the continent, is called 

 by Mr. Moore the great Central Eange. 



The mountain-cha.iii or plctteait-rangc of East Africa. — In 

 the above geological disquisition we must not lose sight of our 

 main object, which is to account, if we can, for the presence of 

 the peculiar halolimnic fauna of Lake Tanganyika. Now this 

 lake, which has a length fiom north to south of 400 miles, lies 

 at the junction of the Great Central Eange with the enormous 

 Congo basin. We shall consider the structure of the Congo 

 basin in some detail presently, but a few words as to the 

 peculiar mountain system with which the lake is connected 

 ought to be useful. If we want to account for anything, we 

 must understand the position on all sides. 



This mountain chain is largely volcanic in its composition, 

 and it will be sufficient for our purpose if we take our start from 

 the great volcanic mountain mass of Abyssinia, whose geological 



B 



