FORMATIONS BELOW CHALK. 313 



it is always found below the two last strata. 

 Jt may be readily distinguished from chalk by its falling 

 in pieces on being wetted and dried again. Some va- 

 rieties of it, when burnt, form an excellent cement for 

 building ; it is also a valuable manure, 



1 1 . Green Sandstone, 



This formation consists of siliceous earth united by 

 salcarious matter; and contains also mica and green 

 earth. From the variety in the proportion of the latter 

 ingredient, it is by some divided into the green sand and 

 gray sand, a distinction which cannot always be made, 

 since these alternate and pass into each other. It is 

 found in the wealds of Kent and Sussex, at the foot of the 

 chalk downs ; and is dug at Rygate and Measham for 

 freestone. It is seen also at Folkstone, Beachy-head, 

 the Culver and Compton Bay, in the Isle of Wight, Pew- 

 sey, in Wiltshire, &c. Alternating with it are often 

 beds of limestone, as a JMaidstone, in Kent, where they 

 are called Kentish Rag; also in the Undercliff, Isle of 

 Wight, beds of hornstone occur in it. It abounds in or- 

 ganic remains. 



12. Blue Marl. 



This bed may be seen under the former very distinctly 

 in the Isle of Wight; as at Sandown Bay, many parts of 

 the Undercliff, Niton, and Compton, Jt contains very 

 few petrifactions. 



13. Ferruginous Sand. 



This formation consists of an alternation of quartzy 

 sandstone, clay, and limestone. The sandstone contains 

 always more or less oxide of iron, sometimes in such 

 quantity, as in the wealds of Kent and Sussex, that it was 

 formerly employed as an ore of iron. The clay tracts of 



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