GEOLOGY 



they were formed around large sponges whose subsequent decay gave rise 

 to the central cavity. 



Paramoudras or Pot-stones were first noticed by Dr. Buckland in the 

 Chalk of Antrim, and the name is probably derived from an Erse word 

 signifying ' sea pear.' In form many are smooth pear-shaped bodies from 

 8 inches to 2 feet and more in length, and from 8 inches to i foot or more 

 in diameter. Others are of very irregular shape, with numerous flinty 

 protuberances. All have a central cavity, and occasionally two cavities 

 have been observed. They were noticed by Lyell in 1825 at Horstead, 

 and they occur in many of the pits near Norwich. Noteworthy 

 examples are also to be seen on the foreshore at Sheringham and Runton, 

 where sometimes they are surrounded by rings of nodular flints.^ 



Tabular flints occur in the Chalk near SwafFham and Wells. At 

 Swaffham some layers are eight or more feet in length, and from 9 to 

 12 inches thick. At Thetford the Chalk contains cylindrical flints 

 which are very sonorous when struck. 



The lowest portion of the Upper Chalk at Swaffham, North and 

 South Creake, and Burnham Overy, is characterized by Micraster 

 coranguinum ; Echinoconus conicus is also found in it. 



The middle portion of the Upper Chalk, as at Wells, Walsingham, 

 and perhaps at Diss, is characterized by Marsupites; while the upper 

 portion, so well exposed near Norwich, is known as the Belemnitella 

 Chalk, containing Belemnitella mucronata and B. lanceolata, also Pecten 

 nitUus, P. concentricus, Terebratula carnea, Echinocorys vulgaris^ Cardiaster 

 granulosus, and remains of a large reptile allied to Mosasaurus. 



On the Norfolk coast the Chalk which appears at Hunstanton does 

 not again form cliffs until we reach Weybourne, where it rises to about 

 20 feet and is covered by the Crag and Glacial Drifts. It disappears 

 below the sea-level east of Cromer, to reappear only for a short distance 

 in the cliffs of Trimingham. 



The very highest Chalk observable in Norfolk is that at Trimingham, 

 which has been disturbed by Glacial agency (see p. 19). It contains 

 many porous spongiform flints, and one sandy seam a foot thick. Among 

 the fossils are Belemnitella mucronata, which serves to link it with the 

 Norwich Chalk ; also a large Gryphcea, Magas pumilus, and the true form 

 of Terebratulina gracilis. 



The Chalk has been largely worked for lime-burning, for whiting, 

 and for its flints near Norwich ; and often the pits have been extended 

 underground in galleries of great length in order to avoid moving the 

 superficial strata or ' uncallow.' Some of these workings, as on Heigham 

 Hill, date back more than three hundred years. Chalk from Whitling- 

 ham has been sent to Burgh Castle, near Yarmouth, where mixed with 

 river-mud it has been manufactured into Portland cement. 



The black flints have been extensively used for building purposes, 

 and notably for the inlaid flint-work so characteristic of church towers 



* See C. B. Rose, Proc. Geol. Assoc, vol. v. p. 514, and C. Reid, ' Geology of Cromer ' 

 {Geol. Survey), 1882, p. 4. 



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