284 



OUR COMMON BRITISH FOSSILS. 



two main parts, with a third subordinate bed. The 

 lowest of these consists of a series of calcareous sands, 

 rich in fossil shells. The second bed is more solid, 

 and is formed of the remains of shells, etc., cemented, 

 together with fossil Polyzoa, into a rock so hard that 

 it can sometimes be quarried for a building stone. 

 The third and uppermost layer consists of a few feet 



Fig. 275. — Natka 



monilifera 

 (Crag and recent). 



Fig. 277. — Nassa 

 {Crag and recent). 



Fig. 279. — Cyprcpa Eti7'oI>cea 

 (Crag and recent). 



Fig, 280.— Pho/as in us 

 burrow. 



of the abraded material of the last bed, reconstructed 

 in shallow water, and bearing strong marks of current 

 bedding. The thickness of the rockier stratum has 

 been calculated at about eighty feet, but there is reason 

 to believe this is too great an estimate. In the neigh- 

 bourhood of Sudbourne, and especially in one or two 

 pits in the park, near to the hall, the Coralline Crag is 



