172 NEOZOIC TIME. [CHAP. X. 



quartz grains were well rounded and worn, while in those 

 of the Isle of Wight the proportion is probably greater. 



The G-ault of Norfolk is a deposit formed in deeper 

 water than that of Folkestone, and has a greater resem- 

 blance to the Chalk Marl than to the G-ault clays of the 

 southern counties ; that it was formed at a distance from 

 any land whence detritus was carried seaward is proved 

 by the microscopical investigations of Mr. W. Hill. He 

 has shown that the amount of inorganic matter, such 

 as recognizable particles of quartz felspar and mica, de- 

 creases as the gault is traced northward, while in the 

 Norfolk marls the proportion of organic material (Forami- 

 nifera and shell fragments) becomes very large ; and it is 

 doubtless to this gradual elimination of the transported 

 sediment, and the consequent concentration of the calca- 

 reous matter, that the thinning out of the Gault is due. 1 



Just as the upward succession at Folkestone, from the 

 blue pyritous clay of the Lower Gault to the grey marly 

 clays of the Upper Gault, indicates the deepening of the 

 sea in which they were deposited, so the lateral passage 

 from the argillaceous Gault of Bedford and Cambridge to 

 the marls and limestones of West Norfolk points to an 

 increasing depth of water and distance from land. 



Borings in the east of England prove that the Gault 

 underlies the whole of it, and rests on the surface of 

 Palaeozoic rock which was left uncovered by the Veetian 

 Sands. It thins, however, to the north and north-east, and 

 at Holkham in Norfolk there is only 10 feet of clay over- 

 lain by 8 feet of red marly chalk, a section which may be 

 compared with that of Eoydon. 



Nothing comparable to the Gault occurs either in Ireland 

 or Scotland, the basement bed being a glauconitic sand 

 containing Pecten asper and Ammonites varians, fossils 



1 Quart Journ. Geol. Soc.," vol. xliii. p. 580. 



