456 R. M. Brydone — Zone of 0. piliila, S. English Chalk. 



attempt at measuring the thickness down to the zone of Marstipites 

 at the west end of Cockpit Head. 



Returning to my starting-point, the cascade, it is pretty clear that 

 up to the angle just west of it the cliff is wholly composed of chalk 

 171 situ. But at this angle the upper part of the cliff at once begins 

 to bear a rubbly appearance, which at the cascade has extended some 

 way down the cliff, and within 20 feet west of the cascade the cliff, 

 now more a bank than a cliff in the ordinary sense, becomes definitely 

 alluvial almost to the bottom. There is chalk washed clean at its foot 

 all the way to the stream, but even close to the cascade this chalk 

 had a very boulder-like appearance, and for the greater part of the 

 way it seems clearly to be composed of loose blocks in an alluvial 

 setting. Certainly there is no chalk between the cascade and the 

 stream which, looks likely to be in situ. Much of the chalk above 

 the cascade and between it and the stream is noticeably softer than 

 any chalk in Arish Mell which is undoubtedly in situ. 



I find it difiicult to reconcile this state of things with Dr. Eowe'a 

 description. In the first place we seem to be largely at variance as 

 to the thickness of his quadratus zone. His description does not 

 afford any means of accurately identifying the point at which he 

 placed its upper boundary, but from a careful study of his plate VI on 

 the ground it appears to be just about the cascade. This is confirmed 

 by the cascade being as nearly as possible 182 feet from the stream 

 where it cuts the line of the bay. (Dr. Rowe speaks of his starting- 

 point as being about 182 feet from the 'sluice', but he must have 

 intended to write ' stream ', for the sluice is much more than 182 feet 

 from any point that can be reconciled with the indications given.) It 

 is therefore probable that we adopted practically tlie same starting- 

 point, but Dr. Howe gives a thickness of 354 feet for his quadratus 

 zone, while I find that 260 feet takes me well into the subzone of 

 E. scutatus, var. depressus. Even allowing for the rest of this 

 subzone a further 45 feet, which is almost the full thickness of the 

 subzone on the opposite side of Arish Mell, I only get 305 feet for 

 the combined zones of A. quadratus and 0. pilula, the equivalent of 

 Dr. Howe's quadratus zone. This shows a discrepancy of about 50 feet, 

 which is very considerable for a piece of measuring of which the 

 greater part is quite straightforward. 



Another point of difficulty lies in Dr. Eowe's account of mucronata 

 chalk at the head of the bay. When I first read this account the 

 impression I derived from it was that it recorded a section reaching 

 182 feet up into the zone of B. mucronata ; and I relied upon this 

 impression in discussing ' the probability of Magaspumilus ranging down 

 to the base of that zone. Since familiarizing myself with the locality 

 I have read Dr. Howe's account again very carefully to see whether 

 I had overlooked some other construction which would harmonize 

 better with my own experience, but I am satisfied that I put the 

 natural interpretation on Dr. Howe's account. He states (p. 29) that 

 there are " about 182 feet of the B. mucronata chalk exposed ". Similar 

 expressions occurring in abundance throughout his works refer 



^ The Stratigraphy of the Chalk of Hants, p. 9. 



