124' PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



graphs, accompaDied by such comments as seem necessary to show 

 their application to what I will venture to distinguish as the " Cas- 

 pian theory " of the Wealden series above the Portland stone. 



The Caspian Sea, instead of being " extremely salt*," is de- 

 scribed (except in the vicinity of brine springs) as "so slightly 

 saline, that even in a part of it far removed from rivers and streams, 

 its waters are said to be potable" (p. 308). A communication from 

 M. Eichwald is afterwards quoted, wherein he says, " I can assure 

 you the Caspian is much less salt than the Black Sea, and possesses 

 one-sixth part only of the saltness of the ocean" (p. 323). The 

 Wealden fossils undoubtedly indicate that the rocks containing them 

 were formed in a similar medium, and reasons have been already 

 given for rejecting the estuary theory. 



The " zoological character" of the Aralo-Caspian limestones is 

 stated (p. 309) to be " persistent and almost monotonous." This is 

 also the case with the inhabitants of the present sea, and the ex- 

 pression is equally applicable to the aquatic animals whose remains 

 occur in the Wealden beds. 



Rejecting, on the authority of M. Deshayes (note, p. 307)> the 

 subdivisions of Cardium proposed by M. Eichwald, the shells of the 

 Aralo-Caspian limestones and those of the modern inland sea belong 

 to the following twelve genera (pp. 301 and 306): — Paludina, 

 Lymneus, dielanopsis, Rissoa, Neritina, Sulla, Mactra, Cyclas, 

 Dreissena, Mytilus, Donax and Cardium. Those printed in italics 

 also occur in the Wealden series of the south-east of England ; and, 

 except Cyclas, which is only represented by the single C, ustuer- 

 tensisy Eichw., of the Aralo-Caspian limestones, the species referable 

 to each genus bear nearly the same numerical proportion in both 

 the ancient and existing basins. 



No remains of fishes appear to have been yet discovered in the 

 Aralo-Caspian limestones; but as regards the modern Caspian, it is 

 said (p. 308), on M. Eichwald's authority, that " the greater num- 

 ber of its fishes belong to freshwater genera and species." As 

 M. Agassiz has not hitherto succeeded in discovering any characters 

 by which the marine and freshwater genera of this class of animals 

 are distinguishable from each other, it would be premature to say 

 whether the observation of M. Eichwald applies to the Wealden 

 ichthyolites or not. Certain genera, whose remains are found both 

 in the Wealden deposits and in the marine members of the Jurassic 

 system, had probably, as previously suggested, the same habits as 

 most of the recent Salmonidae. It may also be remarked, that 

 although the existing Squalidse (using the word in its most compre- 

 hensive sense) appear to be strictly oceanic, this cannot have been 

 the case with the extinct representatives of the family, since their 

 spines and teeth are of frequent occurrence both in the Wealden 

 beds and in certain so-called freshwater strata of the Carboniferous 

 epoch. 



The Aralo-Caspian limestones appear to rest exclusively on 

 Miocene strata. In the same waj^, the Wealden deposits of the 

 * Dr. Traill's Phys. Geog. in 7th ed. of Encyc. Brit. 



