FAUNA OF THE AFRICAN LAKES. 



599 



aninuils from different groups which constituted Moore's halo- 

 limnic series, none are accepted as peculiarly marine save the 

 Polyzoon Arachnoidea and the medusa. 



But more than this. The endemic animal forms have been 

 described almost without exception as specialised and not primi- 

 tive types. It is true that Moore regarded the remarkable 

 Gasteropods as essentially primitive in nature, but this view is 

 not shared by other writers (p. 550). If the halolimnic animals 

 are inueed relict forms, they must have been cut off* at some 

 remote era — though it need not have been the Jurassic period — 

 and ought in consequence to exhibit primitive rather than 

 specialised characteristics. 



Tliis review of the zoological evidence makes it clear that on 

 such grounds it is impossible to justify the contention that 

 Tanganyika was connected with the sea in Jurassic times, or 

 indeed that a connection with the sea ever existed. It is there- 

 fore necessary to inquire what light may be thrown on the subject 

 by the evidence of geology. 



In his book, Moore maintained that resting on the Archaean 

 granites, gneisses, and schists which appear to constitute the 

 basement rocks of the continent, three types of sedimentary rock 

 are to be recognised. The lowest of these consists of beds of 

 sandstone and shale, which are not only well developed in the 

 neighbourhood of the great lakes, but appear to extend over vast 

 areas of the African interior, including a large part of the Congo 

 basin. Then follow the beds discovered by Drummond north- 

 west nf Nyasa, and covering these in turn, white shelly deposits 

 (Pleistocene) laid down by the lakes themselves. Drummond's 

 beds being regarded as Triassic in age and probably estuarine, 

 Moore considered the great beds of sandstone and conglome]'ate 

 as evidence of an extensive ocean which at some still earlier 

 period covered a great part of the lake regions of Central Africa 

 (137, p. 65 et seq.). 



It is particularly to this last point that exception is taken by 

 other writers on the geology of these regions. Some regard Drum- 

 mond's beds and the great sandstone seiies as of like age, and 

 on the evidence of the fossils occurring in the former, regard the 

 whole as beds of the lower Karoo (Trias) — or at least as a forma- 

 tion of corresponding age, deposited under similar conditions. A 

 very i-ecent writer on the stratigraphy of this part of the continent 

 (Behrend) speaks of the unfossiliferous conglomerates, quartzites, 

 and sandstones which are particularly well displayed in the 

 neighbourhood of tlie great lakes, as the "Tanganyika System" 

 (14, p. 52). These beds he distinguishes as of different age from 

 similar rocks occuriing near Nyasa and in parts of the Congo 

 basin, assigning them to an earlier period — Devonian or even 

 prior to that (14, p. 73 and Taf. iii.). While it may be that the 

 relative age of these different strata is by no means conclusively 

 fixed, these recent investigations show that Moore's lowest 

 series — the " Old African sandstones " as he calls them — really 



