OF THE HALOLIMNIC FAUNA OF LAKE TANGANYIKA. 313 



Jurassic fossils of the Mediterranean hasin. — Hence, if we still 

 cling to the notion of a Jurassic origin, we must go further 

 afield and direct our attention to other Jurassic deposits and 

 especially to those of the Mediterranean basin, as being more 

 likely to give us some inkling of a possible derivation in this 

 direction. T have already referred to the very rich deposits of 

 the Lias-Oolite in Sicily, but we may come to Africa itself, 

 where, in the extreme north, marine Jurassic and Cretaceous 

 beds have been fairly well exploited, both in Algeria and 

 Tunisia. Now, as a proof of the apparent poverty of 

 the Jurassic beds in Gasteropoda, I would observe that 

 Coquand* was only able to enumerate one species, although 

 the Cretaceous and Tertiary beds of this region account 

 for over fifty species ol" Gasteropoda. It may be noted 

 that Voluta, Stromhus, Fusiis and Buccinitm, are quoted 

 from beds of Cretaceous age in Algeria, but this Gasteropod 

 fauna in its entirety has nothing in common with the 

 Tanganyika halolimnics beyond a doubtful shell referred to 

 Trochus. In Tunisiaf the most ancient formations are those of 

 Jurassic age, forming some of the mountain cores such as 

 Zaghouan. In that country the Ammonite fauna is charac- 

 teristic of certain stages of the Jurassic system, but no 

 gasteropods are mentioned. Still following the Mediterranean 

 coast, when we come to Egypt the Jurassics fail us entirely, 

 and beds of Cretaceous age rest directly on the Archii^an.J 



It is not necessary to pursue this line of investigation further, 

 beyond observing that if there are any stepping stones between 

 the Anglo-Norman basin and Central Africa, quel Gasteropods, 

 they remain to be discovered. I wdll now direct attention to 

 another aspect of the Tanganyika problem, viz., the Geology of 

 Equatorial Africa, more especially in connection with the 

 physical history of the Congo basin. 



* Geologic et PaUontologie de la region sud de la Province de Con- 

 stantine^ Marseilles, 1862. 



t Expl. de Carte GeoL Provisoire, par Aubert, circa 1890. 



X By this name I propose, without prejudice, to indicate the 

 Crystalhne complex which is the foundation-stone of the African 

 continent. 



X 2 



