CHAP. XII. NORFOLK AND SUFFOLK TERTIARIES. 209 



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

 rable monograph on the fossil shells of these British pliocene 

 formations. He has vmt himself given us an analysis 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 " 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. 



N^anber of hnown Species of Marine Testacca in the three English Pli- 

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

 Crags. 



Brachiopoda 6 



Conchifera 206 



Gasteropoda 230 



Total 442 



Distribution of the above Marine Testacea. 



Number of Species. 



Norwich Crag 81 



Red Crag 225 



Coralline Crag 327 



Species common to the 

 Norwich and Red Crag (not in Cor.) 33 

 Norwich and Coralline (not in Red) 4 

 Red and Coralline (not in Norwich) 116 

 Norwich, Red, and Coralline 19* 



Proportion of Becent to Extinct Species. 



Percentage of 

 Kecent. Extinct. Kecent. 



Norwich Crag 69 12 ,... 85 



Red Crag 130 95 57 



Coralline Crag 168 159 51 



Recent Species not living now in British Seas. 



Northern Species. Southern. 



Norwich Crag 12 



Red Crag 8 16 



Coralline Crag 2 



27 



* These 19 species must be added to the numbers S.^, 4, and 116 respectively, 

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



