﻿486 MESSRS. WHITE AND TKEACHER ON THE [Aug. 1905, 



of their origin, which were influenced by the belief that their forma- 

 tion was a mere episode in the parochial history of a single zone. 

 The persistence of the special conditions responsible for the deposition 

 of an unusually-large proportion of calcium-phosphate around the 

 site of the village of Taplow, from near the close of the cor-anguinum- 

 age, throughout Marsupites-times, and possibly down to a later date, 

 is a consideration which must be taken into account in attempting to 

 frame a satisfactory theory. A ' temporary "change in the strength 

 or direction of the local currents " 51 may account for some of the 

 phenomena, but is now clearly inadequate as an explanation of the 

 Phosphatic Series as a whole. 



V. Structukal Relations. 



At the date of publication of Mr. Strahan's account of this section 

 (1891), the Phosphatic Chalk had not been proved to extend many yards 

 beyond the limits of the Lodge pit. It is now known to occur over 

 a wider area, for we have traced phosphatized foraminifera and other 

 characteristic material in the pieces of chalk in the soil of the river- 

 scarp, northwards, for a distance of 200 paces ; and Mr. E. Lodge, 

 the Agent of the Taplow-Court Estate, informs us that a brown chalk, 

 similar to the rich phosphatic bands of the pit, was encountered in an 

 excavation made for drainage-purposes in 1895, at Hill Earm, half 

 a mile to the north-east. 2 These observations bear out Mr. Strahan's 

 inference that the Phosphatic Chalk ' underlies a considerable part, 

 if not all, of the outlier of Tertiary strata on which Taplow 

 stands.' 3 



In the Hill-Earm digging, the Brown Chalk was proved at a depth 

 of about 10 feet below the greensand-base of the Reading Beds ; and 

 Mr. Strahan records that, in the trial-shaft sank in the rising grouud 

 above the Lodge Pit in 1891, the upper brown band (D) of that 

 exposure occurred at a somewhat greater depth (20 feet) below that 

 horizon. 



The phosphatic deposits clearly lie near the upper limit of the 

 Chalk, but we have been no more successful than Mr. Strahan in 

 our search for them in the numerous exposures of beds occurring in 

 a similar or lower position with regard to the Tertiaries in the sur- 

 rounding country. All these exposures, however, so far as we have 

 been able to ascertain, are in the zone of Micraster cor-anguinum, 

 and now that we know the richer phosphatic beds of Taplow Court 



1 A. J. Jukes-Browne, ' The Cretaceous Hocks of Britain ' vol. iii, Mem. Geol. 

 Surv. ]904, p. 373 [quoting A. Strahan, in part]. 



2 [Our apologies are due to Mr. Strahan for having overlooked the existence 

 of a letter by him in the ' Geological Magazine' for 1895, p. 336, announcing 

 this discovery, and giving more detailed information as to the succession of the 

 beds in the excavation than we were furnished with. The letter is not mentioned 

 in the general bibliography of the English Chalk in the Geological-Survey 

 Memoir on the ' Cretaceous Eocks of Britain ' vol. iii (1904). See Mr. Strahan's 

 remarks in the discussion on the present paper, p. 493.— H. J. O. W. Sf L. T., 

 July 15th, 1905.] 



8 Quart. Journ. Geol. Soc. vol. xhii (1891) p. 365. 



