LIFE ON THE EARTH. 147 



The Crinoidea mentioned in connexion with the 

 Coral-reefs may perhaps be quoted independently 

 as favouring the opinion of a prevalent high tem- 

 perature in these northern regions in the Palaeozoic 

 periods, for the living Pentacrinite, very similar to 

 the fossil groups in the London Clay and Mesozoic 

 Strata, has been found only in the West Indian 

 Seas. If we look at a map of isothermal lines, it 

 will appear that a mean temperature like that to be 

 inferred for the land of the Coal-measures from 

 the evidence of Plants, ought to be assigned to the 

 sea of the same period from the evidence of the 

 Marine Radiata. 



This inference, according to discoveries in the 

 northern parts of America, would seem to carry the 

 warmth of ancient times very much beyond the ex- 

 perience of geologists in Europe even to the shores 

 of the Arctic Sea where mean temperatures below 

 that of congelation now prevail. 



The Mollusca of Tertiary Strata in Europe may 

 sometimes be appealed to for evidence of the former 

 connexion of the basins in which they were collected 

 with the ocean, in such a manner as to allow of at 

 least occasional communication ; so that Voluta, 

 Conus, Cyprsea, Nautilus, &c. might be introduced 

 among the fossils of the basins of London and Paris. 

 But in earlier geological periods, evidence of this 



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