314 MINERALOGY OP THE SOUTH OF ENGLAND. / 



the wealds belong to it. This formation may be also seen 

 at Sandown Bay, Blackgang, and Compton Chines, Swan- 

 wich Bay, Hastings, Tunb ridge Wells, &c. Fossil shells 

 are rarely found in it ; but brown coal is met with fre- 

 quently. 



14. Purbeck Shell Limestone. 



This formation consists of numerous beds of shells and 

 fragments of shells, cemented together by calcarious 

 spar, and alternating with shell and marl. The Purbeck, 

 and perhaps the Petworth marbles, form part of the se- 

 ries ; and it is further remarkable for containing nume- 

 rous fresh water shells and bones of the turtle ; hence it 

 is conjectured to have been formed from fresh water. 



15. Clay with Gypsum. 



At Swanwich, in Dorsetshire, this is dug under the shell 

 limestone. The gypsum does not occur in great quanti- 

 ty, but is employed for plaister. 



16. Portland Oolite. 



This includes the stone of Tillywhim and Windspit 

 quarries in the Isle of Wight, called Purbeck Portland, 

 and that from Portland Island. It is entirely calcarious, 

 and is formed of small grains or concretions adhering 

 together. It is the only stone used for the fronts of pub^ 

 lie buildings in London. Some of its beds contain many 

 marine shells ; also fossil wood and hornstone. 



1 7. Bituminous Shale, containing the Kimmeridge Coal. 

 This formation may be seen at Kimmeridge, Encombe, 

 and the Isle of Portland. 



The discoveries of Cuvier, Brongniart, and Webster, 

 of which we kave now given a pretty full account, have 



