304 MINERALOGY OF THE SOUTH OP ENGLAND. 



According to Mr. Webster, it is in this formation, in 

 the Paris basin, that the gypsum beds are situated. 



3. Upper Marine Formation. 



Over the lower fresh water formation in the Isle of 

 Wight, a stratum occurs, consisting of clay and marl, 

 which contains a vast number of fossil shells wholly ma- 

 rine. Ten of the species agree with those found in the 

 London clay, but they differ from them in their state of 

 preservation. Most of them appear to have undergone 

 but little change, and some of the species are even 

 scarcely to be distinguished from recent shells. 



Delicate marine shells, in a state of perfect preserva- 

 tion, occur in some parts ; thus showing that they could 

 not have been brought from great distances, but must 

 have lived near to the spots where they are now found. 

 In other beds we meet with banks of large fossil oyster 

 shells, the greater part of which are locked into each 

 other in the way in which they usually live, and many 

 have their valves united. It is therefore evident, that 

 these oysters had not been removed from a distance to 

 their present situation. 



If we depend upon petrifactions as one of the means of 

 enabling us to discriminate the different floetz strata, we 

 shall see reason to believe, that the last of the marine de- 

 positions in the south of England are nearly allied to the 

 upper marine formation in the basin of Paris. 



In this bed in the Isle of Wight, Mr. Webster found 

 the following petrifactions : 



