﻿480 MESSES. WHITE AND TKEACHEE ON THE [Aug. I905, 



rather than as associating with Marsupites — have already the 

 blunted pyramidal and sub-gibbous forms typical of that higher 

 portion of the zone, as denned by Dr. Rowe, 1 in which the name- 

 fossil is normally scarce, or w T anting. The occurrence of these 

 depressed types of Echinocorys, the short vertical range of Marsu- 

 pites, and the presence of Ostrea lateralis var. striata in the 

 overlying White Chalk (E), show that the base of the Actinocamax- 

 quadratus Zone is not far distant, and even suggest that a small 

 thickness of that zone is represented in the highest beds of the 

 section. 2 Unfortunately, these beds are not onlj- much obscured, 

 but are also of such a hardness as to be almost unworkable for 

 fossils, and their examination has thus far produced negative 

 results. 



The Upper White Chalk, although possessing some distinctive 

 features, is yet so closely connected with the underlying division 

 that it must, in the absence of definite evidence to the contrary, be 

 assigned to the Marsupites-l^&nd. 



In view of the occurrence of indurated layers at the top of each 

 of the preceding white chalks, the upward increase in its hardness 

 suggests the proximity of a third rich phosphatic belt ; but the 

 coincident decrease in the proportion of brown granules in the 

 borings does not encourage that idea. 



The broad stratigraphical and zonal features of the section may, 

 then, be tabulated as follows : — 



E. Upper White Chalk. \ Marsupites-Band. ~] 

 D. Upper Brown Chalk. | 24 feet exposed. 



[Erosion.] ! Zone of Marsupites. 



C. Middle White Chalk. \ Uintacrinics-Band., J 44 feet exposed. 

 B. Lower Brown Chalk. / 20 feet. 



[Erosion.] J 



A. Lower White Chalk. Higher part of the zone of Micraster cor-anguinurn. 



17 feet exposed. 



On comparing the distribution of the fossils in the Phosphatic 

 Marsupites-Chalk of Taplow with that in the normal Chalk of the 

 same zone in other, inland or coastal, exposures in the South of 

 England, one is impressed by the exceedingly-small thickness of the 

 beds yielding the characteristic crinoids. In view of the evidences 

 of intra-formational erosion which are to be seen in the derived 

 material within, and the uneven floors below, them, it seems not 

 unlikely that each of these beds may represent only the highest 

 part of a mass of sediment of similar paheontological characters, 

 the rest of which was swept away soon after its deposition. There is, 

 however, nothing to prove that the above-mentioned erosion accom- 

 plished anything more than the disintegration and removal of an 

 irregular layer of the underlying White Chalk a foot or so in depth ; 



1 ' The Zones of the White Chalk of the English Coast : Pt. I ' Proc. Geol. 

 Assoc, vol. xvi (1900) p. 338. 



2 Dr. Rowe has hitherto regarded Ostrea lateralis var. striata as charac- 

 teristic of the zone of Actinocamax quadratics, op. cit. pp. 345, 365. 



