600 



DR. W. A. CUNNI.NGTON ON THE 



comprises two or more formations. In any case all the evidence 

 goes to prove that these sandstones and conglomeiates, whatever 

 their age, were laid down under continental, i.e. fresh- water and 

 terrestrial conditions, and thus afford no support foi- the view 

 that the ocean formerly extended over these large tracts in the 

 heart of Africa. 



There is yet another geological objection to the view that 

 Tanganyika contains relict forms from an ancient sea, and that 

 is, that the depression itself would not appear to date back to 

 the remote times required by Moore s hypotliesis. There is every 

 reason to believe that the extensive faulting which produced the 

 Great "Rift Valley took place in Middle-Tertiary times, and if 

 this be accepted, the basin of Tanganyika was actually not 

 in existence at the time when the Jurassic theoiy supposes it to 

 have received its marine fauna*. 



Clearl}^ the geological evidence does not favour a marine 

 "relict" origin for the peculiar fauna of Tanganyika, and it has 

 been shown that the testimony of zoology is against it. In order 

 to be convincing, a theory must not run counter to the findings 

 of either branch of science. 



Since it does not seem possible to accept the hypothesis put 

 forward by Moore, alternative suggestions have now to be con- 

 sidered. In the first place, it is important to point out that 

 shells of the tlialassoid Tanganyika genus Pao^amelania ha,d been 

 compared by White (202 : 203) and Tausch (186j with those of 

 the fresh-water Cretaceous genus Fyrgulifera some time before 

 Moore drew his comparisons with marine Jurassic shells. It has 

 been held by conchologists that the resemblance in this case is 

 every whit as close as between any of the forms compared by 

 Moore. This may constitute slender evidence on which to 

 theorise, but it is significant that the beds from which the fossil 

 type comes are not only moi-e recent, but are fresh -water in 

 character and not marine. Thus, if any value attaches to the 

 evidence, it wouhl suggest that the unusual molluscan genera 

 should be regarded as the little modified representatives of a late 

 secondary fresh- water assemblage rather than those of a much 

 earlier marine one. This view, which implies that the thaJassoid 

 Gasteropods are relics of an ancient lake fauna preserved in this 

 basin, obviously did not find acceptance by Moore. He urged 

 against it the pertinent fact that in such a case, similar types, 

 living or fossil, ought to be found in other areas, and yet they are 

 conspicuously absent (137, p. 335). While agreeing that this 

 constitutes a serious objection, the same objection, to my mind, 

 may be raised with equal force against the marine Jurassic 

 hypothesis. 



Reference has already been made to the fact that certain fossil 

 Gasteropods from the Balkan Peninsula exhibit a considerable 

 resemblance to some of the thalassoid types from Tanganyika 



* Certain geological experts, indeed, regard the Tanganyika basin as more recently 

 produced than other parts of the Rift Valley system. 



