52 GEOLOGY OF THE ISLE OF WIGHT 



Zones. Sub-Zones, 



f Belemnitella mucronata. 

 Actinocamax quadratus. 

 /^ t MI /Off aster pilu la. 

 Offaster pilula J lEchinocorys dep ressus. 



Marsupites / Marsupites. 



testudinarius \Uintacrinus. 

 Micraster cor-anguinum. 

 Micraster cor-testudinarium. 

 iHolaster planus. 

 Middle r Terebratulina lata. 

 Chalk. ^ Inoceramus labiatus. 



c , f Actinocamax 



Lower \ Holaster subglobosus { plenus (at top) 



Chalk - /Schloenbachia varians {Stauronema 



V. V. carten (at base). 



The method of study according to zoological zones is 

 of great interest. The period of the White Chalk was of 

 long duration, and the physical conditions remained very 

 uniform. So that by studying the succession of life during 

 this period we may learn much about the gradual change 

 of life on the earth, and the evolution of living things. 



We have seen that the whole mass of the chalk is made 

 up mainly of the remains of living things, mostly of the 

 microscopic foraminifera. We have seen that sponges 

 were very plentiful in that ancient sea. Of other fossils 

 we find brachiopods different species of Terebratula and 

 Rhynchonella a large bivalve Inoceramus sometimes 

 very common ; the very beautiful bivalve, Spondylus 

 spinosus, belemnites, serpulae ; and different species of 

 sea-urchin are very common. A pretty heart-shaped one, 

 Micraster cor-anguinum, marks a zone of the higher chalk, 

 which runs along the top of our northern downs. Other 

 common sea urchins are various species of Cidaris, of a 

 form like a turban (Gk. cidaris, a Persian head-dress) ; 

 Cyphosoma, another circular form ; the oval Echinocorys 



