VINE : POLYZOA OF THE LOWER AND UPPER GREENSAND. 253 
ing to the old nomenclature this sub-division of the Chalk was called 
Upper Greensand in order to distinguish it from members of the 
Neocomien, or Lower Greensand Series below the Gault, to which the 
name of Greensand had been applied. Besides the reasons before 
given (265) for abandoning this nomenclature, it is objectionable in 
this instance as leading the uninitiated to suppose that the divisions 
thus named, Upper and Lower Greensand, are of co-ordinate value, 
instead of which the chloritic sand is quite a subordinate member of 
the Upper Cretaceous group ; and the term greensand has very com- 
monly been used for the whole of the Lower Cretaceous Rocks, which 
are almost comparable in importance to the entire L^pper Cretaceous 
Series. .... The pliosphatic bed in the suburbs of Cambridge must 
have been formed partly by the denudation of pre-existing rocks of 
cretaceous age."'" 
Mr. A. J. Brownet also regards the Cambridge Greensand as the 
base of the Chalk i\Iarl, it having been formed from the erosion of 
the Gault by marine currents. Where the Greensand Bed exists the 
true Upper Greensand is absent, and the Gault is incomplete, Mr. 
Browne also traces the beds through Cambridge, Bedfordshire, and 
Buckinghamshire, and shows that in passing from Cambridge S."VV. 
the Upper Gault first appears near Barton, the true L'pper Greensand 
near Tring. The most important factor in this paper, in a palseonto- 
logical sense, is the list of fossils. These the author divides into 
two groups : Lst, Those proper to the deposit ; 2nd, Those derived 
from other horizons. The number of invertebrate species is 254, and 
208 or 210 of these are said to be derived, consequently about 46J 
species belong to the Cambridge chloritic deposit, whilst with the 
remainder their chief affinity is with those of the Upper Gault. 
These conclusions of the author are, so far, valuable, but the entire 
absence in the list of any reference to the probable existence of a 
Polyzoan fauna was perhaps unavoidable at the time, and as far as I 
* Ibid, pp. 282, 283. 
t Jour. Geol. Soc. vol. xxxi., p.p. 256, 316. 
% The lists of Mr. Browne, 1875 and 1881, differ in some few particulars, but 
as I am not making any special point of this difference, it will be far more 
satisfactory if the student will look at Mr. Browne's lists before endorsing the 
above. 
