6 
THE CRETACEOUS ROCKS OF BRITAIN. 
The first endeavour to establish a zonal classification of the beds 
by means of the fossils was made by Caleb Evans, whose paper on 
“ Some Sections of Chalk between Croydon and Oxtead,” was pub¬ 
lished in 1870.* In this district Mr. Evans distinguished six zones 
which he characterised by the following fossils and names : — 
1. Zone with Micraster corangninum =Purley Beds. 
2 . ,, „ „ ,, = Upper Kenley Beds. 
3. ,, ,, Micraster corbovisandHolaster planus = Lower Kenley Beds. 
4 . „ ,, Inoceramus Brongniarti and Galerites subrotundus 
== Whiteleaf Beds. 
5. Zone of A[mmonites peramples and Inoceramus mytiloides= Upper 
Mar den Park Beds. 
6. Zone of Ammonites varians and Belemnitella plena= Lower Marden 
Park Beds (Chalk Marl and Grey Chalk). 
At the end of his paper the following generalised classification is 
given : — 
Feet. 
Upper Chalk (Burley and Kenley Beds) - - 250 
Middle Chalk (Whiteleaf Beds) - - - - - - 75 
Lower Chalk (Marden Park Beds) - - - - - A 190 
In a subsequent paper f Mr. Evans distinguished between some 
of the species of Micraster and referred all the forms found in his 
Parley and Kenley Beds to M. cortestudinarium 
In the same year (1870) Air. G. Dowker subdivided the whole 
of the Kentish Chalk into six groups or stages, based on obvious 
lithological differences, giving them local names. The following is 
his classification J : — 
1. Margate Chalk - - - 
2. Ramsgate Chalk - - 
3. St. Margarets Chalk- 
4. Dover Chalk - - - 
5. Chalk without flints - 
6. Grey Chalk - - - 
r Upper Chalk with flints. 
■I 
j Lower Chalk. 
His “ Grey Chalk ” includes the Chalk Marl, and corresponds 
exactly with what is now known as Lower Chalk. His 4 and 5 
include most of what is now classed as Middle Chalk. The St. Mar¬ 
garets chalk is the nodular chalk which is now recognised as in¬ 
cluding the passage beds from the Aliddle to the Upper Chalk, and 
has the representative of the Chalk Rock at its base. The Rams¬ 
gate Chalk comprises all the chalk which has frequent layers of 
flints, and the Margate Chalk is the comparatively fiintless chalk 
above it. In this classification Air. Dowker really seized upon the 
most prominent divisional planes in the Kentish Chalk, and if he 
had ever completed his collection and examination of the fossils he 
would probably have developed a complete zonal subdivision of 
the Kentish Chalk. 
* Proc. Geol. Assoc. Separate papers, 
f Proc. Geol. Assoc. Vol. v. p. 150. 
J Geol. Mag., V ol. vii. p. 466. 
