262 OUR COMMON BRITISH FOSSILS. 



so-called "Sussex marble," also formed chiefly of a 

 species oi Pahidina, which, can hardly be distinguished 

 from that which still abounds in English rivers. In 

 the Isle of Wight the Wealden is also fossiliferous, 

 especially near Sandown, the commonest fossil being 

 a fresh-water bivalve Uiiio Valdensis. 



At Punfield, in Dorsetshire, fresh-water shells, 

 such as Cyrena, Cyclas, Unio, etc., are mixed with 

 oyster-shells, indicating brackish-water conditions. 



The Cretaceous, or Chalk formation, includes the 

 Neocomian (better known, perhaps, as Lower Green- 

 sand), the Gault and Upper Greensand, and the Upper 

 or Grey and White Chalk beds. At Speeton and 

 Tealby, in Lincolnshire, there is a bed of clay five 

 hundred feet thick belonging to the former sub- 

 division, and this is remarkable for a very large 

 bivalve, Pecten cinctus, which is sometimes as much 

 as a foot in diameter ; Perna Mtdletii is another 

 characteristic fossil. The Lower Cretaceous beds are 

 extensively developed in Surrey, Kent, Sussex, 

 Oxfordshire, Bedfordshire, Hampshire, Wiltshire, 

 Norfolk, etc. At Atherfield, in the Isle of Wight, 

 the common fossils are Perna^ Area, Astarte, Panopcea, 

 Gervillea, Tingonia can data, Exogyra simtata, etc. 

 Near Maidstone there are numerous fossiliferous 

 localities ; the quarries where the well-known "Kentish 

 rag " is worked are good fossiliferous places, where 

 Exogyra and Trigonia more or less abound. Other 

 localities are Godalming, Godstone, Folkestone, 



