170 Mr. Webster on the Strata lying over the Chalk. 



3. Marl with freshwater shells. 



4. Dark blue clay without shells. 



These must be placed between the alluvium and the London clay, 

 of the former list. 



In the subsequent pages I shall describe more minutely the form of 

 the basin of the Isle of Wight ; and also that of a similar basin ou 

 which London is placed. I shall enumerate the strata and principal 

 organic remains contained in each, and conclude by pointing out 

 such circumstances of agreement or difference as I have been able to 

 observe between them and the Paris basin. 



II. Extent of the Isle of Wight Basin. 



In tracing the margin of the cavity in which these horizontal 

 depositions of the Isle of Wight are found, I shall begin with the 

 south side. 



The middle range of chalk hills in this island, together with the 

 other highly inclined strata of Alum bay, form part of the ancient 

 border. If we sail west from the Needles in the Isle of Wight, to 

 Handfast point in Dorsetshire, we shall find that this vertical chalk 

 range again makes its appearance in that coast, and may be traced 

 thence through Corfe Castle to some distance beyond Lulworth ; and 

 from the correspondence in the line of direction of the Isle of Wight 

 hills with those of Dorsetshire, and the general agreement in the 

 position and nature of the strata, (the section of the Isle of Purbeck 

 corresponding nearly to that of the Isle of Wight,) it appears 

 extremely probable that at some former period these places were 

 united. 



The clay however over the chalk, and part of the chalk itself, 



