312 MINERALOGY OF THE SOUTH OF ENGLAND. 



most northerly of the vertical strata. Bognor rocks are 

 subordinate to this bed. It agrees in its petrifactions, 

 and geognostic situation, with the lower beds of the 

 coarse marine limestone of the Paris basin. 



T. Plastic Clay and Sand. 



The clay in this formation is often extremely pure, 

 and fit for the potter. It is much employed in the pot- 

 teries in Staffordshire. It is seen in Alum Bay, the 

 trough of Poole, and at the bottom of the blue clay in 

 many parts of the London basin. A kind of bituminous 

 wood is sometimes found in it. This formation is con- 

 jectured to correspond to the French plastic clay, which 

 lies over the chalk. 



8. Chalk with Flints; 



This formation is not known in Scotland, but in Eng- 

 land extends from Flamborough Head, in Yorkshire, to 

 a little beyond Lyme Regis to Devonshire ; and where 

 it is not covered with the newer floetz rocks, forms the 

 chalk-hills or downs. It is distinguished by the regular 

 layers of flint nodules. 



9. Chalk without Flints. 



The inferior stratum of chalk in the southeast part of 

 England is always without flints ; when the chalk with 

 flints is wanting, it forms the surface. The relations of 

 both may be seen at the Culver, and Compton Bay, in 

 the Isle of Wight, Handfast Point, Beachy-head, Guil- 

 ford, Dorking, &c. It differs from the former princi- 

 pally in the absence of flints, in the beds being thicker, 

 and the chalk being sometimes a little harder. 



10. Chalk Marl. 

 This stratum consists of chalk and an intimate mixture 



