10 



Geology and Physiography- 



nodules but little or no pyrites; limestone bands occur, some made up 

 almost entirely of Serptila wtestinalis. The fauna is muddy-water moUuscan 

 in character, with very rare echinoids in the limestone bands. To the east, 

 in borings near Southery in West Norfolk, the AmpthiU Clay is about 

 70-80 ft. thick. 



Coral Rag and Coralline Oolite are known only at Upware, where CoraUian 

 limestone protrudes through the Cretaceous and extends over an area of about 

 3 miles by i mile. The Coralline Oolite is a cream-coloured limestone, 

 fuU of small cavities, with large, irregularly shaped ooliths. Lamellibranchs 

 and gastropods are common, usually as casts ; the echinoids are all irregular. 

 The Coral Rag is in places a hard compact limestone, with many lenticular 

 colonies of reef-building corals. The characteristic fossils include thick- 

 shelled forms, both of regular echinoids and lamellibranchs. The coral 

 colonies are usually a few inches thick, and from 2 to 3 ft. in diameter; 

 they are often separated and surroimded by oolitic limestones in which 

 thin-shelled lamellibranchs, gastropods, and brachiopods occur. Attempts 

 have been made to explain the position of the various exposures of the 

 Rag and Oolite by hypotheses involving folding and faulting, but it is at 

 least equally likely that these facies interdigitate. 



KIMERIDGE CLAY 



The Kimeridge Clay was described in detail by Roberts in 1892; Kitchen 

 and Pringle have since classified some of the horizons in terms of a more 

 modern zoning, and their results, summarised by Dr Arkell, are given in 

 the right-hand column of the following correlation table : 



This succession is seen in the Roslyn (Roswell) Pit at Ely, where a band 

 of large septarian nodules separates the two upper zones. Roberts con- 

 sidered beds exposed at Littleport to be older, and proposed a zone of 

 Ostrea deltoidea [delta] to include the base of the Kimeridge as exposed 



