﻿Vol. 6t.] phosphatic chalk of taplow. 493 



(vi) It occurs as an intercalation between the normal (Micraster 

 cor-anguinum) Chalk and the Lower Eocene (Heading) Beds ; and 

 occupies a structural trough which coincides with, and is probably 

 due to, a synclinal flexure. 



Our thanks are due, in the first instance, to Mr. W. H. Grenfell, 

 M.P,, for kindly permitting us to examine the sections in his 

 grounds, and to Mr. E. Lodge, his agent, for information bearing on 

 the lateral range of the Phosphatic Chalk. 



We are very deeply indebted to Dr. A. W. Rowe, who has not 

 only most kindly placed his vast knowledge of the English Chalk- 

 zones at our service, but has also enabled one of us, by his well- 

 known hospitality, to compare the Taplow fossils with the extensive 

 series from the same and from other horizons of the normal Chalk 

 in his collection. But for his guidance, we should probably have 

 fallen into the old error with regard to the species of Actinocamaoe 

 occurring in the upper part of the Lodge section. 



We also gratefully acknowledge the assistance received from 

 Messrs. A. J. Jukes-Browne, G. C. Crick, and H. A. Allen, with the 

 first of whom we have had the advantage of discussing some of the 

 stratigraphical and tectonic problems presented by the rocks in 

 the Taplow district. 



Discussion. 



Mr. Stkahan expressed his sense of the value of the zonal work 

 done by the Authors. It supplied a distinct deficiency in our 

 knowledge of a district. At the time of his examination of the 

 pit, no distinction had been recognized in this country between 

 Actinocamax (then known as Belemnitella) quadratus and A. granu- 

 latus. The correlation of the Taplow Chalk with the Marsupites- 

 Zone, which he had adopted from the London Memoir, had been 

 proved to be substantially correct, but the identification of a lower 

 zone in the pit was a new and important point. The Authors* 

 identifications seemed to imply a considerable attenuation of some of 

 the zones, as exhibited in the Lodge Pit — a most interesting circum- 

 stance, taken in connection with the occurrence of phosphatized 

 deposits and other evidences of arrested sedimentation. 



The second pit, referred to as proving the existence of phosphatic 

 chalk, had been described by him in the ' Geological Magazine ' for 

 1895. There a band of this material, 2 feet thick, was separated 

 from the Tertiary base by 8 feet of Chalk, as compared with 18 feet 

 at the Lodge Pit. This suggested an unconformity; but the overlap 

 appeared unusually rapid, in view of the approximate parallelism 

 of the Tertiary deposits and the Chalk in the neighbouring parts of 

 England. He had not grasped the evidence on which a synclinal 

 structure was attributed to the Taplow Chalk. He desired to 

 congratulate the Authors on a piece of useful work, carried out 

 under considerable difficulties. 



Dr. A. W. Howe stated that, when the Eellows had been able 

 to read the paper, they would find that an exceptionally-difficult 



