206 SUCCESSIVE REFRIGERATION OF CLIMATE. [Ch. XIH. 



Distribution of the above Marine Testacea. 



Norwich Crag, - - 110 — of which 34 are peculiar. 



Red Crag, - - 219— " 43 " 



Coralline Crag, - - 317— " 188 



Species common to the 



Norwich and Red Crag, and not in Coralline, 



42 



Norwich and Coralline, and not in Red, 



3 



Red and Coralline, and not in Norwich, 



103 



Norwich, Red, and Coralline, - - 



31* 



Proportion of Recent to Extinct Species. 





Eecent. Extinct. Per-centage of Recent, 



Norwich Crag, - - 98 12 



89 



Red Crag, - - 132 87 



60 . 



Coralline Crag, - - 165 152 



52 



Recent Species not living noio in British Seas. 



Northern. 



Southern 



15 







11 



19 



1 



28 



Red Crag, - 

 Coralline Crag, 



In the above list, the shells of the Glacial beds, those, for example, 

 of the Clyde, Errol, and Elie, and Moel Tryfaen (pp. 154 and 158), 

 and other British deposits newer than the Norwich Crag, have not been 

 included. The land and freshwater shells have also been purposely- 

 omitted, as well as some London Clay shells, and others suspected to 

 be spurious. 



By far the greater number of the recent marine species included 

 in these tables are still inhabitants of the British seas ; but even these 

 differ considerably in their relative abundance, some of the com- 

 monest of the Crag shells being now extremely scarce ; as, for ex- 

 ample, Buccinum Dalei, and others rarely met with in a fossil state, 

 being now very common, as Murex erinaceus and Cardium echina- 

 tum. 



The last table throws light on a marked alteration in the climate of 

 the three successive periods. It will be seen that in the Coralline 

 Crag there are 28 Southern shells, including 26 Mediterranean and 1 

 West Indian species (Erato Maugeriw). Of these only 13 occur in 

 the Red Crag, associated with 3 new Southern species, while the whole 

 of them disappear from the Norwich beds. On the other hand, the 

 Coralline Crag contains only 2 shells closely related to living Northern 

 forms, namely, Admete and Limopsis ; whereas, in the Red Crag, as 



* These 31 species must be added to the numbers 42, 3, and 103, respectively, 

 m order to obtain the full amount of common species in each of those cases. 



