176 GEOLOGY OF THE ISLE OF WIGHT. 



Chalk formation, and Cretaceous system, are syno- 

 nymous terms, and designate the entire series of 

 deposits between the Wealden and the lowermost 

 eocene stratum. 



The Chalk— signifies the white chalk, including 1. the 

 upper or flinty chalk ; and 2. the lower or hard 

 chalk, in •which hut few, if any, flints occur. 



TnE Firestone or Glauconite — comprises the chalk- 

 marl, without any intermixture of green particles, as 

 well as the limestone called in Sussex malm-rock ; 

 and the sands and arenaceous marls and limestones 

 full of green particles of silicate of iron, and termed 

 by geologists the upper-green-sand and firestone. 

 This group is the Glauconie crayeuse, of the French 

 geologists. 



The Galt — a deposit of stiff blue clay underlying the 

 firestone, and characterised by particular species of 

 organic remains : called also Folkstone marl, and 

 Blue chalk-marl. 



The Greensanh — designates the scries of clays, sands, 

 sand-tones, and arenaceous limestones; comprising 

 the Iron-sand of Mr. Webster, the Lowcr-greensand 

 of Dr. Fitton (and of tbc map PI. XX.) ; the Shank- 

 Hit sands of the author; and tbc lower argillaceous 

 group, termed the Neocomian or Aiherfield deposits. 



Range of the Chalk formation m the 

 Island. — The various members of the cretaceous 

 system, as previously stated, constitute the 

 southern half of the Island ; a range of chalk 

 hills, broken through by the transverse valley of 

 the Medina, extending from east to west, and 



