CHAPTER VI. 



THE CHALK FORMATION — SUBDIVISIONS OF THE CRETACEOUS SYSTEM — 

 RANGE OF THE CHALK IN THE ISLE OF WIGHT — THE UPPER AND 



LOWER CHALK CHALK AND FLINT — SILICIFIED FOSSILS OF THE 



I'll VI.K — THE FIRESTONE THE GALT THE GREENSAND — SUMMARY. 



The Chalk formation. — The different mem- 

 bers of the Cretaceous system, though presenting 

 considerable variety of lithological character, are 

 yet essentially of the same type, and are linked 

 together by a peculiar fauna, indicating the pre- 

 valence of a similar oceanic condition, throughout 

 the vast period of time comprised in this geolo- 

 gical epoch. 



The features of a chalk district are so well 

 known, that a brief notice of the physical geo- 

 graphy of that part of the Island which is com- 

 posed of the cretaceous strata, will suffice for our 

 present purpose ; and a reference to the map, 

 PL XX., will render local details unnecessary. 

 The rounded summits of the hills covered with 

 short verdant turf — the smooth undulated out- 

 line of the downs, unbroken save by the sepulchral 

 v o 



