3o6 Sir H. C. Englefield's Additional Obfervations on 



ttie upper parts of the flratum between fiffure and fiffure drop out, 

 much in the fame way as bricks are apt to do out of the flat arch 

 over a window; the harder contiguous ftrata ferve as walls to the 

 gallery, but are by degrees perforated in different parts, and become 

 irregular pillars, fupporting the vaft weight of the hill above, until 

 the adion of the fea weakens them fo far, that they fail, and a part 

 of the face of the hill goes with them: fo that the cave is con- 

 ftantly, although flowly, changing its form. 



Large maffes of the harder ftrata, defended by their flint coating, 

 alfo (land up in the bay as infulated rocks of different fhapes, and 

 much refembling the Needle rocks, which are exa6lly of the fame 

 materials, and formed by the fame procefs. In this part of the 

 chalk ftratum I faw feveral folTil remains,- which I had fought in 

 vain in the pits I had vifited. One was fmgular. It had the ap- 

 pearance of pait of a very large fhell, regularly flriated, and almoft 

 flat. I have often {qqxi fmall fragments apparently of a fimilar 

 fhell, in chalk, but never a large piece. It was fo firmly fixed as 

 not to be removed without a chifel; which I had not. 



Tothefe obfervations on the chalk of the ifland I muft add, that 

 this whole range, although really chalk, is much harder than the 

 chalk of the South downs ; infomuch that the carpenters cannot 

 ufe it for drawing lines, but import chalk for that purpofe from 

 Portfdown hill, above Portfmouth. They alfo call the ifland chalk 

 by the name of marie, which is, however, only the Breton name for 

 chalk, and appears in many compound names, fuch as Marl-borough 

 on the Wiltfhire chalk hills, and the very fignificant one of Albe- 

 marie ^ or white chalk. 



As I made feme further obfervations on the fouthern ransfe of 

 hills which form the back of the ifland, I will trefpafs on your pa- 

 tience a little longer, particularly as they in fome degree contradi6l» 



or 



