R. M. Brydone — The Belevmitella onucronata Zone. 851 



case at the east end of Tapnell Down, as this is probably due to the 

 combined effect of an imperfect junction between the sections and of 

 exigencies of space leading to the exclusion of part of the chalk 

 area.) Of these five cases, two appear to be arrived at by assumption 

 only, but three are connected with palseontological evidence from 

 sections and will be considered first. 



The most interesting of these is undoubtedly the one just west of 

 Freshwater by pit 11 (Rowe), for, as Dr. Rowe points out, it is but 

 2 miles from Alum Bay with its great thickness of niucronata chalk. 

 The palseontological evidence given by Dr. Rowe is that the shells in 

 the pit are white, and that two examples of Echinocorys of quadratus 

 type were found. The former statement does not seem to have any 

 bearing on the question unless it is established that no white shells 

 are to be found in the lower mucronata chalk of the Isle of Wight. 

 I know of no authority for such a proposition, and it is not in accord 

 with any experience of mine, although Mr. Griffith and I long ago 

 noted redness in the shells as a feature of the tipper beds of the 

 mucronata chalk. The phrase '■^ Echinocorys of quadratus type" 

 conveys no meaning to me. No shape of Echinocorys typical of 

 upper quadratus chalk has, so far as I know, been defined in any 

 way by Dr. Rowe, much less one which while typical of quadratus 

 chalk cannot be found in low mucronata chalk, and only such a form 

 would be of any value for assigning a section to the former zone to 

 the exclusion of the latter. Even if such a form had been defined 

 and definitely recognizable specimens found in this pit they would 

 prove very little. All probability is in favour of Echinocorys recorded 

 from thi^s pit having been found on the extensive talus, the surface 

 of which is obviously derived from the chalk high up at the back of 

 the pit. In ordinary horizontal or slightly inclined chalk the 

 identification of the quadratxis zone at the top of a pit close to the 

 Tertiary boundai-y would afford a strong presumption that no 

 mucronata chalk was preserved at that point. But the Isle of Wight 

 chalk is nearly vertical, and therefore the identification of the 

 quadratus zone at the top of this pit — as to the accuracy of which 

 I do not suggest any question, it having also been made by 

 Mr. Griffith and myself many years ago — leaves the whole thickness 

 between the back of the pit and the Tertiary boundary, a distance 

 of some 120 feet, corresponding to a thickness of at least 100 feet 

 of chalk, open to reference to either the quadratus zone or the 

 mucronata zone. To carry the matter a step further, even if an 

 absolutely decisive Echhiocorys were found at the most northerly 

 point where chalk is still exposed in the pit, there would still 

 remain between that point and the Tertiary boundary some 30 feet 

 of chalk, and this could not be ruled out of the mucronata zone on 

 any palseontological ground. 



As a matter of fact, there is some slight positive ground for 

 holding the view that the miicronata zone is exposed within the pit. 

 There is now a sideway extension, which I do not remember in the 

 nineties, cut parallel with and close to the footpath, and some of the 

 chalk exposed here is gritty and hard, contrasting rather sharply 

 with the soft and fine-grained chalk at the back of the pit. I have 



