GENERAL ACCOUNT OF THE CHALK. 
7 
In 1876 Professor Ch. Barrois published a detailed account of 
the whole Upper Cretaceous series in England and Ireland, and 
showed that the same zones which he and others had established 
in France could be followed throughEngiand, * and could be grouped 
under the main divisions proposed by D’Orbigny. His classifica¬ 
tion mav be summarised as follows : — 
* ; *- s*-«: r ' 
Divisions. 
Senonian 
TURONIAN 
Zones. 
{ Zone of Belemnites. 
Zone of Marsupites. 
Zone of Micrasters. 
I" Zone of Holaster planus. 
Zone of Terebratulina gracilis. 
I Zone of Inoceramus labiatus. 
Cenomanian - 
'Zone of Belemnites plenus. 
Zone of Holaster subglobosus. 
Chloritic Marl. 
Zone of Pecten asper. 
.Zone of Ammonites inflatus. 
In the zone of Holaster planus he placed tl Le Chalk Rock, 
so that the line between the Senonian and Turonian was 
drawn at nearly the same horizon as that which Mr. Whitaker 
had recognised as dividing the Upper and Lower Chalk. The most 
important result of his work, to English geologists, was the defini¬ 
tion of the lower limit of the Turonian, and the consequent estab¬ 
lishment of a Middle Chalk. This, as we have seen, had been 
tentatively suggested by Mr. Caleb Evans, but Professor Barrois 
established it on a surer basis by showing that the real line of separa¬ 
tion between the Turonian and Cenomanian fauna lay between 
his zones of Inoceramus labiatus and Belemnites plenus, that is 
lower than the line taken by Caleb Evans. 
It was, therefore, Professor Barrois who first demonstrated to 
English geologists that it was not only possible to divide the English 
Chalk into three parts or stages, but that the distribution of the 
fossils made this a natural and necessarv mode of classification, 
It will be noticed, however, that his Cenomanian includes beds 
which lie below our Lower Chalk and form part of our Selbornian 
stage. 
During the years 1875 to 1879 Mr. W. H. Penning and the writer 
were engaged on the survey of the neighbourhood of Cambridge, 
and the publication of Professor Barrois’ Researches gave an impetus 
to our desire to establish some definite divisions in the Chalk of 
Cambridgeshire. We had found what appeared to be the repre¬ 
sentatives of the Chalk Rock and of the Totternhoe Stone, identifi¬ 
cations which were confirmed by Air. Whitaker himself ; and I 
had noticed that the marly layer which Professor. Barrois identified 
with his zone of Belemnites plenus was often associated with beds 
of very hard rocky chalk. A special examination of the line of 
•- . ~ ~ : -- /' — t ~ —' • • . -;- : - 
* Recherches sur le. terrain Cretace Superieur de~ rAngleterre' et do 
l’lrlande. Mem. Soc. Geol. du. Nord, 1876. 
considerably 
