PEESIWICH CSAQ-BEDS OF STTPFOLK AND NOKPOLK. 



473 



The relation which these species (155, including the varieties) 

 show to the Eed and Coralline Crags of Suffolk is as follows : — 



Bi- Uni- ^ J 

 yalves. valves. 



Common to the Eed Crag 69 ... 68 = 137 or 88 per cent. 



Common to the Coralline Crag 54 ... 33 = 87 or 56 „ 



"We have before (ante, p. 352) seen that the number of species of 

 the Eed Crag found in the Coralline Crag was 62 per cent. 



With regard to the proportion, in the Norfolk-Crag period, of 

 existing species to those not known as living, the following is the 

 result, after excluding the 16 varieties and doubtful species : — 



TofL living. Bxtinol. S^^fpTcil 



139 130 9 6-5 per cent. 



Comparing the three Crags, the respective proportions of extinct 

 and living species of Mollusca in each is as under : — 



Extinct. Living. 



In the Norfolk Crag 6-5 93'5 per cent. 



In the Eed Crag of Suffolk 7-7 92-3 „ 



In the Coralline Crag 16-0 84-0 „ 



showing so close a relation between the Norwich and Eed Crags 

 as to afford good reason for considering them to be both of the same 

 age*. 



"With respect to the geographical range of the 216 living species 

 (exclusive of varieties and extraneous species) of the Red Crag, and 

 of the 130 species of the Norwich Crag, some marked differences 

 are noticeable, as shown in the following Table. 



Table of Geographical Distribution of the Mollusca of the Med 

 and Norwich Crags. 



Eed Crag. 



Bi- 

 valves 



Arctic 21 



North American 7 



Scandinavian 63 



British 77 



West European 80 



Mediterranean 79 



Atlantic 35 



Uni- 

 valves. 



19 



10 



72 

 80 

 76 



Total. 



Norwich Crag. 



Bi- 

 valves, 

 18 

 7 

 42 

 42 

 37 

 33 

 18 



1; 



Uni- 

 valves. 



18 

 7 



44 



45 



36 



34 



20 



Total. 



36 

 14 

 86 

 87 

 73 

 67 

 38 



40 



17 



135 



157 



166 



88 = 167 



49 = 84 



Special localities. — Africa, 1 ; South Africa, 1 ; West Indies, 1 ; 

 Gulf of Mexico, 1 ; Japan, 3. 



* Taking Aldeby to represent the upper division (or the Chillesford Sands) 

 and the lower beds at Bramerton the lower division (or the equivalent of the 

 Eed Crag of Sutton, Waldringfield, &c.) of the Norwich Crag, we have the fol- 

 lowing results : — 



Proportion of 



extinct to 



living species. 



per cent. 



Aldeby 71 56 53 38 



Bramerton 64 6 58 24 



Total 

 species. 



Numbers common to the 

 I * — -..^ 



Eed Crag. Coralline Crag. 



