352 R. M. Br y done — The Belemnitella mucronata Zone. 



recorded precisely this contrast between the quadratus and mucronata 

 chalk in Portsdown as separated on palseontological evidence.' 



The second point at which palseontological grounds are quoted in 

 support of the view that the mucronata chalk has been wholly- 

 removed is pit No. 3 (A.fton Down). Here the position corresponds 

 almost exactly with that at pit No. 11. There is a pit in which the 

 presence of the quadratus zone is established by palseontological 

 evidence, as Mr. Griffith and I recognized in the nineties; but the 

 principal face and talus, from which this recognition was made, are 

 at the back of the pit, some 80 feet from the Tertiary boundary. 

 The chalk towards the mouth of the pit seems of different character 

 from that at the back, and in it I have found what appears to be 

 a broken specimen of Thecidea Brydonei, which is only known from 

 the basal mucronata chalk of Portsdown. Here, again, there is 

 nothing in the evidence cited by Dr. E-owe to warrant the statement 

 that the quadratus zone extends to the mouth of the pit, much less 

 to the Tertiary boundary ; and there is some suggestion of evidence 

 to the contrary. 



As zonal indications are so scarce, it is perhaps worth mentioning 

 that it was in this pit that I found the type of Memhraniporella 

 Gahina'^ many years ago on the talus, but in what .part of the pit 

 I cannot say for certain. I naturally attributed it to the zone 

 undoubtedly represented in the pit, that of A. quadratus. At the 

 time of desci'ibing the species I had only two other specimens, one 

 a very doubtful one from the floor of this same pit near the mouth 

 and one from the zone of B. mucronata at Portsdown. I have since 

 recognized several other specimens all from indisputable mucronata 

 chalk either in the Isle of Wight or at Portsdown. I think there is 

 some justification for the view that this species, which has never yet 

 been found in undoubted qtiadratus chalk, actively as the top beds of 

 that zone have been exploited in Hants, is restricted to the mucronata 

 zone, and has only been found in this pit because chalk of that zone 

 is or has been exposed in it. 



The third place at which the zone of B. mucronata is represented 

 on palseontological evidence as entirely removed is at Ryde Water- 

 works (pit No. 45). Here we may remark, as in the two previous 

 cases, that the critical section does not extend to the Tertiary 

 boundary by some 90 feet, and cannot therefore afford evidence as 

 to the nature of the chalk in contact with the Tertiaries. Even for 

 the alleged quadratus horizon of the section itself the palseontological 

 evidence given by Dr. E,owe is very scanty and purely negative, and 

 scanty negative evidence can hardly form a satisfactory basis for the 

 assertion of an exceptional state of things. In this case again there 

 are grounds for doubting the reference of, at any rate, the whole of 

 the section to the quadratus zone. The barrenness of the chalk is 

 not in the least exaggerated by Dr. Rowe, but I have found on the 

 talus below the section a small damaged Echinocorys likely to be the 



^ The Stratigraphy of the Chalk of Hants, p. 8 (London, Dulau & Co., 

 1912). 

 ^ Geol. Mag., 1917, p. 494, PI. XXXII, Fig. 8. 



