Mv» Webster on the Strata lying over the Chalk. 173 



1 . Chalk formation . * 



2. 'The lowest marine formation over the chalky including the plastic 

 day and sand, together with the London clay. 



3. The lowest freshwater formation, 



4. The upper marine formation. 



5. The upper freshwater formation. 



6. Alluvium. 



Fortunately the complete series of these alternations may be seen at 

 one place in the Isle of Wight, which leaves us no room to doubt 

 their superposition ; and when their characters have been studied in 

 this spot> it is more easy to become acquainted with them in other 

 places. 



§ 1. Chalk Formation. 



The south-east coast of England and that of the Isle of Wight 

 afford us many excellent opportunities of examining the chalk. In 

 numerous natural sections formed by cliffs, as well as in chalk pits, 

 I have observed it as distinguished into at least three strata, each of 

 which has peculiar and distinctive characters. 



The lower stratum is more or less argillaceous, and constitutes 

 what is called the chalk marl. Together with the other strata it 

 frequently forms cliffs of considerable height, and though differing 

 little from them in colour is easily distinguished by its constantly 

 shivering with the frost, which always pulverizes a mass of it when 

 exposed to the air for a few months ; whereas the others resist the 

 weather in a much greater degree, and are often even employed as a 

 material for building. 



* In using the word formation I have followed the example of M. M. Cuvier and 

 Brongnlart, who have employed it to express an assemblage of beds of the same naturCj 

 or of a different nature but formed during the same epoch. 



