R. M. Brydone — Zo7ie of 0. pilula, S. English Chalk. 405 



VI. — The Zone or Offaster pilula in the South English Chalk. 



By E. M. Brydone, B.A., F.G.S. 



II. Isle of Wionx. 



rpHE zone of Offaster pilula is probably exposed on the coast in 

 X West Sussex on the foreshore near Eognor, but the nearest cliff 

 exposures to those of East Sussex are those of the Isle of Wight, at 

 Culver Cliff and Scratchells Bay. In both of these the Chalk is so 

 highly inclined that only a very small area of each bed can be reached; 

 and the condition of the accessible surface is such as to make it most 

 improbable that anything beyond the broad outlines of the subzone 

 of abundant 0. pilula, which is the key and pith of the zone of 

 0. pilula, will be detected. 



The first of these exposures in the natural order going westwards 

 from Sussex is Culver Cliff, but that is notoriously abnormal, and it 

 is better to take first Scratchells Bay. 



A. Scratchells Bay. 



One of the peculiarities of Scratchells Bay is that it offers only one 

 secure landing-place, in the extreme east corner, under the Grand Arch, 

 so that the middle of the bay, where the zone of 0. pilula was to be 

 expected, can only be reached by plodding past exposures of the zone 

 of M. cor-anguinum, the Uintacrinus band, and the zone of Marsupites. 

 It was necessary to identify the latter, or at any rate its highest 

 beds, in order to get a starting-point for the zone of 0. pilula, and 



1 took the opportunity of attempting to identify the other boundaries 

 which must be passed. The westward face of the Grand Arch I knew 

 from Dr. Rowe's work ^ to be occupied by cor-anguinum chalk ; this 

 'was abundantly flinty and seemed to be quite devoid of marl seams. 

 For some way westwards along the bay the chalk continued to be 

 flinty and marlless ; then came a short outburst, some 10 feet across, 

 of marly veins, at which I made close but fruitless search for 

 Uintacrinus ; then for some distance the chalk was again marlless, 

 until there appeared a solitary definite seam of marl, in the 

 neighbourhood of which I again made fruitless search for Uintacrinus. 

 It was succeeded by more marlless flinty chalk, and then there 

 appeared a strong tabular seam of flint, which was single in the 

 upper part of the cliff, but forked at its base. Two and a half feet 

 above this there was a strong marl seam, the first of many. Search 

 in the neighbourhood of this marl seam yielded nothing significant 

 below it, but one or two Crinoid brachials in the 2^ feet of chalk 

 immediately above it and a definite plate of Uintaci-inus in the next 



2 feet. It seems, therefore, that the base of the Uintacrinus band 

 may be identifiable with this easily recognizable marl seam, which 

 also marks a substantial lithological change, marl seams continuing to 

 be more or less prevalent well up into the quadratus zone. (In this 

 respect the section is markedly parallel with that of Seaford Head. 



^ Coast Sections, V, p. 228. 



