LAKE BAIKAL 215 



possibly have been situated not far off. Thus, during 

 Jurassic and Cretaceous times a gulf of the sea extended 

 over the east of Africa ; its deposits succeed one another 

 as a series extending through the lower Oolites to the 

 upper Cretaceous, and for twenty-five miles inland from the 

 coast we meet with Eocene beds containing nummulites ; 

 but no intercalations of freshwater beds are known among 

 these sediments, so that the gulf seems to have been in 

 free communication with the sea throughout its existence. 

 It is of course conceivable that the most western part of 

 the gulf might have become cut off from the rest by a 

 rising ridge of land, and then converted into an inland 

 sea ; but if this had persisted long enough to give birth to 

 a freshwater fauna, it ought to have left some traces of its 

 existence in the form of sedimentary deposits, but none 

 are to be found. It may be answered that such sediments 

 were formed, but have since been destroyed, or that they 

 are still in existence, but have not yet been discovered ; 

 these apologies may indeed be admitted, but they do not 

 supply the place of evidence. 



At present the problems presented by lake Tan- 

 ganyika are unsolved ; they are of great interest, and their 

 solution will possibly be found to involve important 

 consequences ; all the more necessary, therefore, that it 

 should be based on sufficient evidence : this, we may 

 hope, will be furnished with the progress of exploration. 



A somewhat similar difficulty is presented by lake 

 Baikal ; this, in common with the Caspian, the sea of 

 Aral, and many other sheets of water in Europe, contains 

 relics of the Pontic fauna, but it does not follow that lake 

 Baikal itself is a relic sea ; like Tanganyika, it seems to 

 be of comparatively recent origin. In this case also we 

 must be content to wait for the clue which future 

 discoveries may provide. 



It remains now to refer to the possibility that some 



