5o6 Sir H. C. Englefield's /Additional Obfervations on 



the upper parts of the ftratum between fiffure and fifiure drop out, 

 much in the lame 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 diiferent parts, and become 

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

 the aiftion 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- 

 flantly, although flowly, changing its form. 



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

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

 much refembUng the Needle rocks, which are exadlly of the fame 

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

 chalk ftratum I faw feveral foflil remains, which I had fought in 

 vain in the pits 1 had vifited. One was fingular. It had the ap- 

 pearance of part of a very large fhell, regularly ftriated, and almoft 

 flat. I have often feen fmall fragments apparently of a fimilar 

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

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



To thefe obfervations on the chalk of the ifland I mufl 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 oi Albe- 

 marle, or white chalk. 



As I made feme further obfervations on the fouthern range of 

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

 tience a little longer, particularly as they in fpme degree contradiift, 



or 



