534i THE CRETACEOUS ROCKS OE BRITAIN. 
On the other hand, with whiter chalks of the Cretaceous System 
the relative proportion of recognisable Foraminifera is generally 
small. It is a curious fact that this was pointed out by Dr. Mantell 
so long ago as 1845*; it was re-stated by Mr. Hill in 1889+ and 
independently by M. L. CaveuxJ in 1891, and was discussed at 
length by the same author in 1897.1|i M. Cayeux points out that the 
abundance of Foraminifera varies greatly in different localities, that 
in some cases they do not form more than 5 per cent, of the mass, 
though in others they may amount to as much as 75 or 80 per cent., 
but it must be remembered that in this amount he includes what 
we call Spheres. Mr. Hill informs me that in English chalks 
of the Middle and Upper divisions, the proportion of Foraminifera 
is always small, and that though there are some horizons and 
localities where they are more abundant than usual, the average 
proportion is not more than 10 per cent, of the mass, and is often 
only about 5 per cent, (excluding Spheres). 
With respect to the Globigerince in particular, they cannot be 
regarded as the dominant form in Cretaceous chalk. M. Cayeux 
says (op. cit., p. 457) that “ the role of Globigerince is on the whole 
quite secondary, and is often almost negligeable.” This statement is 
confirmed by Mr. Hill, who writes as follows :—“ As to Globigerince , 
though fairly common in Melbourn Bock and in Chalk Bock, and 
though some specimens of chalk contain a few more than others, 
I entirely agree with M. Cayeux that they are frequently a negli- 
geable quantity in the constitution of the chalk.” He further 
remarks that the genus Textularia is in reality the dominant form 
of foraminiferal life in the English Chalk. This is in accordance 
with observations made long ago bv Ehrenberg and Mantell. 
There are two other particulars in which some of the Turonian 
and Senonian chalks, both in England and France, differ from 
modern deep-sea deposits. These are the presence often in great 
abundance of the spherical calcareous bodies described on p. 500, 
and the frequent occurrence of small angular shell-fragments. 
Both Spheres and shell-fragments are often so numerous that they 
must be regarded as important constituents of the Chalk as a 
whole, though the quantity of each of these constituents varies 
greatly in different zones, and to a less extent in different localities. 
Spheres are very abundant in the Middle Chalk, especially in the 
lower 50 to 80 feet, and again in the upper 40 to 50 feet. Mr. 
Hill’s experience is that “ in the lower 50 feet of the Middle Chalk 
Spheres are vastly more abundant than Globigerince or any other 
constituent except the prismatic fragments of Inoceramus- shell; ” 
*Ann. Mag. Nat. Hist., Vol. xvi., p. 75. 
fin the “Geology of London,” by W. Whitaker, Mem. Geol. Survey. 
Vol. i., p. 519. 
I Ann. Soc. Geol. du Nord, T. xix., p. 100. 
1 !Contribution a letude Micrographique des Terrains Sedimentaires, 
Lille, 1897, pp. 452-478. 
