﻿Vol. 6 1.] PHOSPHATIC CHALK OF TAPLOW. 485 



prevailing during its formation. We have not, however, succeeded 

 in recognizing them. 



Some geologists may see satisfactory evidence of shallow water in 



(i) The signs of current-erosion, which, according to Sir John Murray & 

 the late Prof. Renard, 1 is rarely operative at a greater depth than 

 100 fathoms, in open water. 



(ii) The abundance of bottom-living foraminifera — probably upwards of 

 60 per cent., according to Dr. W. F. Hume, 2 including some posi- 

 tively shallow-water forms. 3 

 (iii) The exceptional prominence of Ostrea, which gives the Brown Chalks 



an aspect reminiscent of certain Oolite limestones. 

 (iv) The abundance of Plicatula. i 



(v) The occurrence of the gasteropod Scalaria. 



Others will probably attach more importance to such indications 

 of deeper- water conditions as 



(i) The extreme scarcity of bryozoa. 5 



(ii) The absence of distinctively shallow-water lamellibranchs. 

 (iii) The small size of most of the bottom-living foraminifera. 

 (iv) The insignificant amount of terrigenous material, pointed out by 



Mr. Strahan. 6 

 (v) The small size, and predominant yellow or brown hue, of the phosphatic 

 concretions common to the white and brown beds. 7 



Both lists could be greatly (and, we fear, unprofitably) extended. 



The Senonian Phosphatic Chalks of Northern France, which the 

 Taplow beds so closely resemble, are generally regarded as shallow- 

 water accumulations by the geologists of that country, who refer to 

 the accompanying erosion-features in terms which would, on this 

 side of the Channel, be considered appropriate to the destructional 

 phenomena of the shore. 



But, whatever the bathymetrieal conditions prevailing at Taplow 

 in Marsupites-tim.es — and the question is one into which we are 

 not greatly tempted to enter — , it may be doubted whether those 

 conditions were of cardinal importance among the factors deter- 

 mining the ?lbnorma] character of the deposits at that spot. For the 

 general aspect and disposition of the Upper Chalk in the South of 

 England do not encourage the idea that the depth of water over 

 the southern part of Buckinghamshire at that date was markedly 

 different from that at other localities in Surrejr, Hampshire, and 

 Berkshire, less than 30 miles distant to the south-east, south, and 

 west respectively, where the ordinary type of Chalk was in course 

 of deposition. 



The recognition of the rather wide range in time of the Taplow 

 phosphates will necessitate some modification of those conceptions 



1 Challencjer-TlepoYts, ' Deep-Sea Deposits' 1891, p. 184. 



2 ' The Genesis of the Chalk' Proc. Geol. Assoc, vol. xiii (1894) p. 238. 



3 A. J. Jukes-Browne, ' The Cretaceous Rocks of Britain ; vol. iii, Mem. 

 Geol. Surv. 1904, pp. 372-73 ; and L. Cayeux, Mem. Soc. Geol. du Nord, vol. iv , 

 2 (1897) pp. 503-505. 



4 L. Cayeux, op. cit. p. 504 ; and A. J. Jukes-Browne, op. cit. p. 366. 



5 A. J. Jukes-Browne, op. cit. pp. 370-71. 



6 'Natural Science' vol. i (1892) p. 287. 

 --Reports, ' Deep-Sea Deposits' 1891, p. 392. 



