CHAP. XII. 



NORFOLK AND SUFFOLK TERTIARIES. 



209 



We are indebted to Mr. Searles Wood, F.Gr.S., for an 

 admirable monograph on the fossil shells of these British 

 pliocene formations. He has not himself given us an ana 

 lysis of the results of his treatise, but the following tables have 

 been drawn up for me by Mr. S. P. Woodward, the well- 

 known author of the 6 Manual of the Mollusca, Eecent and 

 Fossil' (London, 1853-6), in order to illustrate some of the 

 general conclusions to which Mr. Wood's careful examination 

 of 442 species of mollusca has led. 



Number of known Species of Marine Testacea in the three English 

 Pliocene Deposits, called the Norwich, the Red, and the Coralline 

 Crags. 



Brachiopoda 



Conchifera 



Gasteropoda 



Total 



6 



206 

 230 



442 



Distribution of the above Marine Testacea. 



Number of Species. 



Norwich Crag . . . .81 



Bed Crag .... . . 225 



Coralline Crag . . .327 



Species common to the 

 Norwich and Ked Crag (not in Cor. ) 33 

 Norwich and Coralline ( not in Ked) 4 

 Ked and Coralline (not in Norwich) 116 

 Norwich, Ked, and Coralline . 19* 



Proportion of Eecent to Extinct Species. 



Recent. 

 Norwich Crag . . . .69 



Ked Crag 130 



Coralline Crag . . . .168 



Extinct. 



12 



95 

 159 



Per-centage of 



Recent. 



85 



57 



51 



Recent Species not living now in British Seas. 



Norwich Crag 

 Ked Crag 

 Coralline Crag 



Northern Species. 

 . 12 

 . 8 



2 



Southern. 





 16 



27 



* These 19 species must be added to the numbers 33, 4, and 116 respectively 

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



