﻿462 MESSRS. WHITE AND TREACHER ON THE [Aug. I905, 



middle greyish bed, the occurrence of the former and the scarcity 

 of flints suggesting ' a correlation of this Chalk with the well-known 

 Margate Chalk or the zone of MarsupitesJ A diagrammatic section 

 is given (op. cit. p. 78), showing the Micraster cor-anguinum Chalk 

 of the country between Marlow and Maidenhead passing, south- 

 eastwards, beneath the Taplow Beds. 



In his paper ' On a Phosphatic Chalk with BelemnitelJa qiiadrata 

 at Taplow,' x which forms the most important investigation of the 

 subject hitherto published, Mr. Strahan briefly describes the Taplow- 

 Court Lodge Pit, draws attention to the phosphatic nature of the 

 ' greyish ' chalk above mentioned, and details the results of a 

 chemical, mineralogical, and microscopical examination of the richer 

 layers of phosphate. The latter are compared with similar beds 

 found at several horizons in the Chalk of Northern Prance and 

 Belgium ; and their relation to the ordinary Chalk of the district 

 and some evidence of their strictly-local occurrence are also 

 considered. 



Mr. Strahan points out that there are two well-marked phos- 

 phatic bands, separated by a considerable thickness of white chalk, 

 the higher and thicker band including Ecliinocorys vulgaris, Breyn., 

 and Gidaris sceptrifera, Defrance (sic), in addition to the two forms 

 already named. A short list of foraminifera (prepared by Prof. T. 

 Eupert Jones) is included in the paper ; but, with the exception of 

 Inoceramus, no other macroscopic fossil is recorded from any part 

 of the section. 



The Taplow Chalk is indirectly referred to the zone of Marsupites, 

 that is, ' to the same horizon approximately ' as the phosphatic 

 deposits of Doullens, Hardivillers, etc., in the North of Prance, 

 which ' may .... be attributed to ' that zone. 



A short article on ' Phosphatic Chalk,' by the same author, 

 published in 'Natural Science' for June 1892, 2 relates chiefly to 

 the same deposit, with regard to which it is observed : — 



' It is, doubtless, of a lenticular form, and probably of no great extent. The 

 other pits and. sections in the neighbourhood .... seem, in the few cases where 

 they expose the right zone in the Chalk, to lie beyond the limits of the lenticle. 

 What these limits are, and in what directions the lenticle extends, can only be 

 determined by borings or by tunnelling from the known outcrop. . . .' 



It is pointed out that, although the deposit is at a horizon which 

 here lies 



' close beneath the Tertiary beds, .... in other districts, and even in the 

 immediate neighbourhood of Taplow, these strata rest upon other parts of the 

 Upper Chalk, either higher or lower than that in which the phosphatic beds 

 are situated,' and that ' therefore we require [in searching for the phosphate- 

 bearing zone in this country] a surer guide than that afforded by the Tertiary 

 boundary.' 



Such a guide Mr. Strahan appears to find in the Chalk-Bock, but 

 he does not show how it is to be employed, and he suggests that 

 ' some further assistance may be rendered by the existence of zones in the 

 Upper Chalk, characterized by certain fossils.' 



1 Quart. Journ. Geol. Soc. vol. xlvii (1891) pp. 356-66. 



2 Vol. i, pp. 284-87. 



