A HISTORY OF NORFOLK 



acterized by Bekmnitella [Actinocamax) plena. This division has been 

 quarried at Stoke Ferry and Marham, at Hilhngton, Dersingham, 

 Heacham and Hunstanton. At Marham the hard chalk has been used 

 for building-purposes, and elsewhere for lime and whiting. Among other 

 fossils in the Lower Chalk are remains of fishes also Ammonites mantelli, 

 A. rotomagensis, Inoceramus latus, Ostrea vesicularis, Rhynchonella mantelliana, 

 Terebratula biplicata, T'. globosa and Discoidea cylindrica. 



In the beds at Gayton Mr. Whitaker noticed small boulders of 

 granitic and other igneous rocks, a fact of considerable interest as such 

 erratic materials in the Chalk are by no means of frequent occurrence, 

 and they suggest transport by icebergs. 



The boundary between the Lower and Middle Chalk extends from 

 Hockwold-cum-Wilton to Narford and Gaytonthorpe. 



The Middle Chalk comprises hard bedded white chalk with a few 

 seams of marl and many layers of flint, including tabular flints and 

 occasional Paramoudras (see p. 9). Traces of a hard band representing 

 the Melbourn Rock of Cambridgeshire have been noticed at its base 

 at Shernborne and to the south-east of Heacham. The Middle Chalk 

 has been well exposed at Methwold, and again at Sedgeford, Hillington, 

 Great Massingham, Harpley and Docking. 



Among the fossils of this division are Ammonites peramplus (which 

 occasionally measures 2 feet in diameter) , Inoceramus cuvieri, I. mytiloides, 

 Rhynchonella cuvieri, R. pUcatilis and Echinoconus subrotundus. 



It has been found difficult in Norfolk to draw a definite line of 

 boundary between the outcrop of Middle and Upper Chalk owing to the 

 want of evidence of the Chalk Rock, which in many localities further 

 south and south-west forms a marked horizon. This rock has been 

 observed in Norfolk only in one locality west of Swaffham, where it is 

 but a foot thick. 



The Upper Chalk is for the most part a soft chalk, characterized by 

 numerous nodular flints and by huge forms known as Paramoudras. 



These flints were in all cases formed subsequently to the deposition 

 of the chalky mud ; some originated during its consolidation, others 

 like the occasional tabular flints fill horizontal, oblique and vertical 

 planes of shrinkage and faulting. 



The siliceous matter of the nodules is of organic origin due to the 

 presence and decay of siliceous organisms, and especially sponges. Not 

 only sponges, but also mollusca, echinoderms, and occasionally reptilian 

 teeth, acted as nuclei around which the flinty matter was concentrated. 



The nodules, like septaria in clay formations, usually coincide with 

 the planes of stratification, because the superficial layers of chalky mud 

 became saturated with silica due to the subsidence and decay of siliceous 

 organisms. Hence the nodular layers were probably formed stage by 

 stage during the gradual accumulation and consolidation of the Chalk. 

 Dr. G. C. Wallich suggested that the Paramoudras, which sometimes 

 occur in vertical rows, were due to sluggish flows of highly siliceous 

 layers into hollows of the sea-bed. Other observers have suggested that 



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