OF THE HALOLIMNIC FAUNA OF LAKE TANGANYIKA. 329 



" Drmniuoncrs beds " towards the nortliern end of Lake Nyassa 

 present similar traces of this fauna in association with a series 

 of conglomerates, red grits and shales, and as they are not far 

 from tlie south-east rim of the Congo basin, their evidence is all 

 the more valuable.* 



There is good reason, on the whole, for supposing that the 

 lied Felspathic Grits of the Congo basin are the equivalents in 

 time, and to a certain extent in composition, of part of the 

 Karoo system of the Cape. If this view be accepted, we might 

 roughly correlate the White Friable Sandstone series with the 

 Upper Karoo, which may possibly extend upwards as high as 

 the Ehsetic period. It should be distinctly borne in mind that 

 no marine organisms occur in any of these beds referred to the 

 Karoo. Mons. Barrat, in his map of the Congo basin, boldly 

 correlates the whole of the post-primary sandstone systems of 

 that basin with the Karoo, and in a general sense he is probably 

 not far w^rong. Cornet himself considers that the Bassin 

 primitif du Congo," at the period of the horizontal deposits, 

 was separated by a chain of mountains from a region lying 

 towards the south, south-east and east, where the beds of the 

 real Karoo were being deposited.! 



It is difficult to conceive the precise physical conditions 

 under which these lifeless masses were accumulated during a 

 period which may be regarded as very early mesozic (including 

 the Permo- Carboniferous). That the mountainous periphery 

 already described was being ground down by atmospheric 

 causes and its products distributed by some sort of water action 

 throughout the central depressed area seems certain, and it is 

 also highly probable that during the greater part of the 

 time there was no drainage outlet, so that this part of 

 Equatorial Africa became the dumping ground of a mass of 

 mechanical sediments, which had no means of escape by the 

 usual method of rivers flowing towards the ocean. But a time 

 came, perhaps towards the middle of the mesozoic epoch, when 

 deposit ceased to be the order of the day and these intermin- 

 able sandstones themselves became subject to the laws of 



* The Drummond's beds of Nyassa are described as a small system of 

 grits, schists and limestones with fish (Acrolepis), molluscs {Mutela 

 oblonga) and plant remains. Other localities are quoted where the Red 

 Felspathic Grits contain remains of vegetation, according to the 

 traveller, Thompson. 



t It is admitted that the Karoo beds of the Cape constitute a 

 somewhat indefinite system, yet within certain limits their horizon may 

 be accepted as fairly well understood. 



Y 2 



