186 



GEOLOGY OF THE ISLE OF WIGHT. 



variety passes into a hard calcareous sandstone, 

 termed in Surrey Firestone. Deposits of green 

 sand, with layers and concretions of chert, and 

 seams and nodules of coarse chalcedony, charac- 

 terise this group in some districts, and are largely 

 developed in the Undercliff. The bands of sili- 

 ceous limestones and calcareous sandstones, with 

 veins and nodules of chert which appear in the 

 inland cliff of that district, belong to this division 

 of the cretaceous system. 



NAUTILUS ELEGAXS. 



From the Chalk-marl, near Ventnor. 



The chalk-marl in most localities abounds in fossils ; 

 it contains numerous species of Ammonites, Nauti- 

 lus, Turrilites, and other cephalopoda, which are 

 cither of excessive rarity, or altogether absent in t lie 

 upper chalk strata. The Nautilus and Ammonites 



