GEOLOGY 



cent, of carbonate of lime, from 8 to lo per cent, of peroxide of iron, and 

 a little sand and clay. Whether the iron ore was original or derived 

 from the underlying ferruginous carstone is a question difficult to answer. 

 Tiny pebbles or grains of quartz are met with in the bed, which is but 

 4 feet thick. In its upper part it contains a branching structure, formerly 

 supposed to be a fossil, and named Spongia paradoxica. This occurs also 

 in the lowest part (' Sponge bed ') of the White Chalk. It has been 

 shown by Prof. T. McK. Hughes to be simply a concretionary structure.* 



Fossils occur abundantly in the Red Chalk, as is the case elsewhere 

 with formations that are represented in an attenuated condition. It was 

 evidently formed slowly, and the zonal distinctions elsewhere met with 

 in equivalent strata cannot be defined. Belemnites minimus and Terebratula 

 biplicata are abundant. 



In a well-boring at Holkham a bed resembling Red Chalk was found 

 beneath the White Chalk, and above a bed of Gault clay, and it is 

 probable that in one form or another the Gault extends from its outcrop 

 in West Norfolk eastwards beneath the greater portion of the county. 



CHALK 



The White Chalk undoubtedly forms the foundation of the main 

 part of Norfolk. Its base, exposed in the cliff at Hunstanton, extends 

 southwards along the borders of the Gault in the west of Norfolk, while 

 the whole formation is inclined very gently (at an angle of less than i°) 

 towards Norwich and Yarmouth, where on the coast its upper limit 

 occurs about 500 feet below sea-level. Probably the Chalk attains its 

 full local thickness where it is covered by Eocene strata at Yarmouth, 

 and it has been estimated to be about 1,400 feet. At Norwich the 

 Chalk was proved to a depth of 1,152 feet, and some further thickness is 

 exposed in the adjacent hills. 



The Chalk is divided into Lower, Middle, and Upper Chalk, but the 

 scenery produced by the formation in Norfolk differs markedly from that 

 in the southern and southern-midland counties. We find no conspicuous 

 escarpments nor downs, because the Chalk has been abraded and covered 

 by Glacial Drifts, which greatly modify its features. 



The Lower Chalk in Norfolk is for the most part a hard white lime- 

 stone with the ' Sponge-bed ' before noticed at its base, and it exhibits in 

 places the curved jointing so conspicuous in the Cambridge clunch. It 

 is a comparatively pure chalk with 95 per cent, of carbonate of lime, but 

 it contains occasional seams of marl. It is characterized by Ammonites 

 varians. 



Overlying the Lower Chalk is a representative of the Totternhoe 

 Stone — a sandy and glauconitic chalk with green-coated phosphatic 

 nodules, from 2 to 4 feet thick, and yielding Holaster subglobosus. This 

 bed was first observed near Stoke Ferry and Roydon by Mr. William 

 Whitaker. Above it is a hard grey chalk 35 to 40 feet thick, char- 



* Quart. Journ. Geol. Soc, vol. xl. p. 273. 



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