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Cretaceous Corals. 

 The Cretaceous period was one of long duration, and almost 

 as important, in a palseontological point of view, as the Jurassic. 

 Its various stages cover a great part of the earth's surface, and 

 contain the remains of a fauna which impart well marked 

 characters to them. The Cretaceous group in England comprises 

 the following formations, ascending from the base to summit: — 



1. Tlie Lower Greensand. — The lowest stage, which rests 

 conformably on the Wealden formation, and is extremely well 

 exposed in the fine coast sections on the western shores of the 

 Isle of Wight and Coast of Kent, is a great arenaceous 

 formation, composed of ferruginous Sands with green grains, 

 dark-coloured Clays, and clayey Sands. In some localities, as 

 at Hythe and Maidstone, there are bands of Limestone known 

 as Kentish Eag. The equivalent of this formation is the 

 Terrain Neocomien of Swiss and French authors, and it is the 

 Etage Ai^tien of D'Orbigny. The Lower Greensand attains a 

 thickness of 800 feet in the Isle of Wight. 



2. The 8peeton Clay. — A local formation found at Filey Bay, 

 on the Yorkshire coast, near Flamborough Head. It is a 

 grayish-coloured Clay, its upper portion containing !N"eocomian, 

 and the lower portion Portlandian species of fossil shells. 



3. The Red Chalh, another local member of the Cretaceous 

 group, consists of a thin bed of hard, red Chalk, deeply coloured 

 by the peroxide of Iron, and having numerous small siliceous 

 grains and pebbles of Quartz, &c., strewed throughout the mass. 

 It forms a conspicuous member of the fine picturesque section 

 of Hunstanton ClifF, Norfolk, and is seen m situ in Filey Bay, 

 Torkshii-e. It is supposed to be the equivalent in these regions 

 of the next stage. 



4. TJie Gault, a dark-blue tenacious Clay, sometimes marly, 

 and containing concretions. It is well exposed in the Isle of 

 Wight, and at Folkestone, Charmouth, and Cambridge, and has 

 yielded a fauna of beautiful fossils which are special to it. The 

 Grault forms the Etage Alhien of D'Orbignt, and is about 100 

 feet in thickness. 



