510 R. M. Brydone — Zone of faster pilula 



boundary between the zones of 0. pilula and A. quadratus in the 

 Whiting Pit, and at the same time, owing to developments in the 

 other two pits, to identify the cinctus belt in the old face and the lower 

 belt of 0. pilula in the new workings (and probably also at the lowest 

 point of the old face) of Pit jS^o. 1066, and the lower belt of 0. pilula 

 at the base of Pit jS'o. 1065. The bed, which at the Whiting Pit 

 ends the zone of 0. pilula and contains the typical Offasters of 

 exceptional size and shape, is enclosed by marl seams, but differs from 

 the corresponding bed in all my other exposures in being 4 feet 

 thick, hard, full of sponge remains, and devoid of flints, and the 

 whole upper part of the subzone is notably poor in fossils and flints 

 ,as compared with other Hampshire sections. I suspect that these 

 variations indicate that Mottisfont was within the radius of the 

 exceptional influence which must have been at work in the neigh- 

 bourhood of Salisbury, which is already known through Dr. Black- 

 more for such striking abnormalities as the absence of A. gramilatus 

 at all horizons, and a concentration of Belemnitella lanceolata a few 

 feet above the zone of 0. pilula. It is therefore to be anticipated 

 that in the Salisbury area the zone of 0. pilula will be recognizable 

 by its broad features ; but correspondence in minute details is not to 

 be expected. 



Unfortunately it is an open question whether the zone I have 

 defined can continue to bear the name of " zone of 0. pilula^\ That 

 name was preoccupied by the late Mr. Jukes-Browne in a paper 

 published in the Geological Magazine for July and August, 1912, 

 entitled "The Recognition of two Stages in the Upper Chalk", for 

 a conception which was only defined piecemeal in this papsr and a sub- 

 sequent one in the Geological Magazine for April, 1913, entitled ' ' The 

 Division of the Upper Chalk". It was to correspond in Hants with 

 the subzones of E. scutatus var. depressus and 0. pilula as proposed 

 by Mr. Griffith and myself in The Zones of the Chalk t?i Habits. In 

 Sussex it was to embrace at least all the chalk above the zone of 

 Marsupites exposed in the cliffs. In Yorkshire it was to embrace at 

 least all the chalk above the zone of Marsupites exposed in the cliffs. 

 But for each county he used a different test. The one he applied in 

 Hants was quite vague, as the subzones on which he relied had at 

 that time no defined boundaries except the lower boundary of the 

 subzone of E. scutatus var. depress2is ; but it has since become most 

 definite through the determination of these boundaries by me in The 

 Stratigraphy of the Chalk of Sants. 



The test which he applied in Sussex is clearly the periodical 

 recurrence of bands of 0. pilula, coupled with the occurrence of 

 A. gramilatus. Whether the Chalk of Sussex which he assigns to 

 his zone responds to his test depends on the accuracy of the state- 

 ment that "0. pilula is common at intervals throughout the 170 feet 

 exposed in the cliff between Seaford and Brighton, while A. grami- 

 latus occurs through at least the lower 150 feet" (the italics are 

 mine). This statement, so far as it relates to 0. pilula, is accurately 

 paraphrased from Dr. Rowe,^ but as to half the Chalk in question its 

 truth is, at any rate, highly debatable. So far as the statement 

 •^ Coast Sections, i, p. 342. 



