﻿Vol. 6 1.] PHOSPHATIC CHALK OF TAPLOW. 479 



Prof. Gosselet believes that the Actinocamacc verus in the lowest 

 rich phosphate-beds (Craie grise inferieure) of the .French sections 

 has, in every instance, been derived from the local equivalent of the 

 (A) beds of the Taplow-Court pit. This, however, is questioned by 

 M. Lasne ; and the fact that M. Eabelle l has found this fossil 

 associated with A. quadratics in the higher bands of phosphate at 

 Ribemont, on the Oise, shows that its range in the French deposits 

 of this class is not quite so limited as Prof. Gosselet seems to imply. 

 The examples of A. verus found at Taplow are, as already noted, of 

 Marsupites-Zone form, and there is nothing in their appearance 

 which particularly suggests a remanie origin. The species is very 

 rare in the Micraster cor-anguinum- and Marsujntes-Zones in the 

 western part of the London Basin, only one doubtful specimen 

 (from the former) having been as yet recorded. 2 



It is of interest to note that Ostrea semiplana, which also appears 

 to be confined to the lower part of the Lower Brown Chalk here, is 

 found in a like position at Hardivillers (Oise). 3 



The 16 feet of less-phosphatic White Chalk which succeeds the 

 Uintacrinus-be&ring brown band is singularly devoid of fossils 

 possessing a primary, or even a secondary, zonal value, — at least in a 

 recognizable form. The occurrence of Marsipites-remdAns above 

 and below it may, perhaps, be considered to favour its inclusion in 

 the Marsupites-^a,nd. On the other hand, the solitary plate of that 

 crinoid found below this division may well be one of those sporadic 

 and ' premature ' occurrences which are not unknown in the midst 

 of the Uintacrinus-JSeaid of other localities ; and, as this white 

 chalk passes insensibly into the brown beds below, and is sharply 

 separated from those above, it is safer to refer it to the latter 

 subdivision of the Marsupites-Zone. So far as we have seen, and 

 have learned from other observers, this relatively-barren group of 

 beds has no analogue in the coast-sections of the zone. In the 

 western part of the London-Basin area, however, belts of practically- 

 unfossiliferous chalk are a not uncommon feature of the Uintacrinus- 

 Band, and it is possible that the (C) division of this exposure may 

 be a local development of one of these. 



The abrupt change from the zoologically-poor and uninteresting 

 Middle White Chalk to the very fossiliferous Upper Brown Chalk, with 

 its remains of Marsupites, Micraster, and Echinocorys, its unfailing 

 supply of Actinocamacc -granulatus guards, and its multitude 

 of oysters, appears to mark the incoming of the Marsupites- 

 Band proper. In the latter division (D), plates of Marsupites are 

 nowhere abundant, and can rarely be found at a greater distance 

 than 1 foot above the nodular rock-bed at the bottom. At that 

 horizon, Echinocorys scutatus has been seen by us only in the form 

 of small fragments, and the well-preserved examples collected 

 from 2 to 7 feet above — which may be regarded as succeeding 



1 Ann. Soc. Geol. du Nord, vol. xxi (1893-94) p. 344. 



2 A. J. Jukes-Browne, ' Cretaceous Eocks of Britain : vol. iii — The Upper 

 Chalk of England' Mem. Geol. Surv. 1904, p. 221. 



3 A. de Grossouvre, Bull. Soc. Geol. France, ser. 3, vol. xxii (1894) p. lviii. 



