360 R. M. Brydone — Zone of Offaster pilula 



Other noteworthy fossils of the zone are Ostrea canaliculata, var. 

 striata,^ and Bourgueticrinus Forms 1 and 2, very characteristic of 

 the subzone of abundant 0. pilula ; JSchinocorys scutatus, var. cinetus, 

 so characteristic of the middle belt of the same subzone that 

 I propose to call it the Cinetus belt ; E. scutatus, var. truncatus, 

 confined to the lower belt of the same subzone and a few feet 

 below it ; TerehratuUna Rowei, reappearing at the base of the same 

 subzone after disappearing at the top of the zone of Marsupites, and 

 occurring chiefly in the lower belt, but occasionally also in the middle 

 and upper belts ; Rhagasostoma palpigerum, strongly associated with 

 the subzone of abundant 0. pilula ; a free ramose form of Porosph(Bra 

 with thick flattened branches, perhaps confined to the same subzone ; 

 Bourgueticrinus Form 5, reappearing for a short time in the upper 

 part of the subzone of E. scutatus, var. depressus, after disappearing at 

 the top of, if not some way down in, the zone of Marsupites and 

 Bourgueticrinus Form 6, a very reliable guide to the subzone of 

 E. scutatus, var. depressus, and particularly its lower beds. To these 

 may be added a darkish, thick-shelled, and often gracefully curved 

 form of Ostrea incurva, which is very closely associated with the upper 

 belt of the subzone of abundant 0. pilula and almost confined to it. 



I. Sussex. 

 From Black Rock, Brighton, to l^ewhaven, a distance of some 

 1^ miles, there is a continuous cliff. This cliff is composed entirely 

 (except for about a mile at the Brighton end, and about half a mile 

 in Friars Bay) of chalk of the zones of 0. pilula and A. quadratus, 

 lying in gentle folds. 



A. Suhzone of E. scutatus, var. depressus. 

 The base of this subzone no doubt comes in at the top of the cliff 

 at or near Black Rock, and a gentle easterly dip brings it down to the 

 base of the cliff a little to the east of Eoedean School. This easterly 

 dip continues towards Rottingdean, but without ever bringing the 

 succeeding subzone in reach at the base of the cliff. A little west of 

 Rottingdean the beds become practically level and so continue across 

 the gap and part of the way through East Hill. Close to Saltdean 

 Bottom the beds rise in a slight anticline, which culminates at 

 Saltdean Bottom and brings up on the foreshore, but not into the 

 cliff, the highest beds of the zone of Marsupites. The anticline 

 has a very flat top and the beds remain practically horizontal for 

 about half a mile ; they then dip steadily eastwards and the top 

 of the subzone passes below the foot of the cliff just east of the 

 sewer at Portobello. The subzone is brought up again by the Friars 

 Bay anticline, coming into the cliff about a quarter of a mile east 

 of Friars Bay with a gentle dip which does not carry the top of the 

 subzone out of reach until the west horn of Friars Bay is reached. 

 The dip then increases and the whole thickness of the subzone passes 

 up into the cliff, together with some 8 feet of the zone of Marsupites, 

 before a series of minor faults appear and so neatly counteract the 



■^ The mystery surrounding the origin of this most useful varietal name has 

 not been cleared up by Mr. Woods' recent monograph. It probably originated 

 with Dr. Blackmore. 



