﻿Yol. 6 I.] THE PHOSPHATIC CHALK OF TAPLOW. 461 



23. On the Age and Relations of the Phosphatic Chalk of Taplow. 

 By Hakold J. Osborne White, F.Gr.S., and Llewellyn 

 Treacher, F.G.S. (Eead April 5th, 1905.) 



Contents. 



Page 



I. Introcl uction 461 



II. Description of the Beds 464 



III. Correlation of the Beds 477 



IV. Some Facts bearing on the Mode of Formation of the 



Phosphatic Chalk 483 



V. Structural Eelations 486 



VI. Summary of Conclusions 492 



I. Introduction. 



In the course of an investigation of the Upper Chalk in the 

 western part of the London Basin, we had occasion, last autumn, 

 to examine the pit at the South Lodge of Taplow Court, to which 

 so much attention was attracted twelve years ago by Mr. A. 

 Strahan's discovery of the richly-phosphatic character of some of 

 the beds therein exposed. 



It was originally intended to devote no more than a few para- 

 graphs to this section, in a short account of the highest beds of the 

 Chalk and their relations with the Lower Eocene sediments in 

 the whole area, which we have in preparation ; but the difficulties 

 in the way of a satisfactory interpretation which presented them- 

 selves at the preliminary inspection referred to, and seemed, for 

 a time, but to increase with succeeding visits, compelled us to 

 undertake a minute examination of the beds, and the results of 

 this work now appear to be of sufficient interest to merit the more 

 detailed discussion obtainable in a separate paper. 



In dealing with the phenomena of a single exposure of a rock 

 having so wide a lateral range as the Chalk, some loss of the sense 

 of continuity and of proportion is usually inevitable ; but a separate 

 treatment of the Taplow-Courb section appears to be justified, no 

 less by the remoteness of the beds from any visible Chalk of a 

 similar age, than by their exceptional lithological character. 



References to the Phosphatic Chalk of Taplow are numerous and 

 widely scattered, but in the present communication it will suffice to 

 give a brief resume of only the more important works on the 

 subject. 



The earliest notice occurs in Mr. Whitaker's memoir on the 

 * Geology of London,' x where it is described as a ' greyish gritty 

 chalk in blocky masses, resembling Totternhoe Stone, without flints,' 

 20 feet in thickness, underlain by 40 feet of white chalk with very 

 few flints, and succeeded by 10 feet of the same. Belemnitella 

 quadratic and Ostrea acutirostrls are stated to be common in the 



1 Mem. Geol. Surv. vol. i (1889) pp. 77 & 78. 



