﻿Vol. 6 1.] PHOSPHATIC CHALK OF TAPLOW. 471 



rock-bed, which was also about the position of the single, slightly- 

 ornamented scute representing Marsupites. 



The examples of Actinocamacc vents and Ostrea semiplana were 

 all obtained within a foot of the bottom, and occurred throughout the 

 length of the exposure of this division. The guards of A. verus are of 

 slender form, with the rather acutely-pyramidal anterior end figured 

 by Schliiter in ' Palaeontographica,' vol. xxiv (1876-77) pi. lii, fig. 9. 



Micraster cor-anguinum, Ventriculites, and Coscinopora occur as 

 phosphatized casts, and are, most probably, derived from the under- 

 lying bed, to the upper surface of which, and to the glazed nodules, 

 the more or less completely-phosphatized examples of Spondylus, 

 Plicatula, Serpula, and Crania were attached. 



The foraminifer Nodosaria Zippei is here of sufficient size and 

 frequency to be included in a list of macroscopic fossils. It has 

 not been recognized in the form of a phosphatic cast. The 

 remaining forms were scattered through the division, but more 

 sparingly in the upper than in the lower half. 



Porosphcera globidaris is rare and very small (diameter = 3 mm.). 



Division (C). 



The lower rich phosphatic band assumes a lighter cast towards 

 its upper limit, owing to the decrease in the proportion of the 

 brown grains (and also, in some measure, to a loss of the yellowish 

 tinge of their fine calcareous paste), and, somewhere between 4 and 

 5 feet above its base, passes into a soft white chalk, with brownish- 

 grey seams and patches. Wherever this middle white division of 

 the section is examined, grains of phosphate are clearly visible. It 

 is a true Phosphatic Chalk, and its separation from the richer, brown 

 band below, although convenient for descriptive purposes, seems a 

 somewhat arbitrary proceeding from the lithological standpoint. 



Besides the disseminated brown grains, large borings, both regular 

 and irregular, filled with the same, occur at all levels ; and 

 though but little of the middle part of the division is accessible, we 

 doubt the possibility of obtaining a cubic foot of the chalk free 

 from such perforations at any horizon. Towards the upper limit 

 they are so closely set, as almost to replace the white chalk between 

 them, and to give the rock the aspect of a breccia, 1 



Pale-brown earthy concretions, with soft chalky inclusions are 

 locally very prominent, and attain a larger size (1-^ inches in 

 diameter) than in other parts of the section. 



The top of these beds is marked by a hard nodular layer, from a 

 few inches to 1 foot thick, possessing the undulate upper surface, 

 and, less prominently, the brown glazing, manganese-dendrites, and 

 many of the other lithological features of the bed that occupies 

 a similar position in the Lower White Chalk; but it is generally 

 distinguishable from the latter in hand-specimens by its paler, 



1 A similar pseudo-breccia in the phosphatic beds near Fresnoy-le-Grand 

 (Aisne), is figured by Prof. J. Gosselet, Ann. Soc. Geol. du Nord, vol. xxi 

 (1893-94) p. 154. 



