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

Extract

I Claim to have now shown that the zone of O. pilula as established in 1912 for Hants and the Salisbury area holds good in its broad features also for Sussex, the Isle of Wight, and Dorset, and that it is almost equally constant in some of its minor features, especially the way in which it ends in a bed 2 ft. 6 in. to 3 feet thick with a flint seam in the middle of it and enclosed by two marl seams. I am only prevented by a single section in Hants from setting this up as the universal rule in all sections I have seen. In The Stratigraphy I assigned pits Nos. 1065, 1066, and 1067, the last of which will be more readily recognized as Mottisfont Whiting Pit, to the zone of A. quadratus, because on examining them for the purposes of that work for the first time since 1892 I had failed to find evidence of more than a seam of O. pilula without any others of the associated fossils of the zone. At the time of that examination all the pits were in a most unfavourable condition. Since then I have been keeping regular watch on the Whiting Pit (No. 1067), and I soon found that the subzone of abundantO. pilula must be represented at its base, and then that the upper belt of O. pilula in that subzone must be exposed: but it was only this spring that I was able to fix the absolute position of the boundary between the zones of O. 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 O. pilula in the new workings (and probably also at the lowest point of the old face) of Pit No. 1066, and the lower belt of O. pilula at the base of Pit No. 1065.