546 
CRETACEOUS ROCKS OF BRITAIN. 
may have greatly lessened its height without much diminishing 
its area; consequently, in constructing the hypothetical map 
(Fig. 87), I have assumed that the western land was not very 
different from what it had been in Cenomanian time. 
Farther northward, however, in the north-east of Ireland, we 
have positive evidence of the shallowing of the British Turonian sea 
toward the west. It is uncertain how much of the Irish Cretaceous 
series corresponds with the Middle Chalk of England, and it may 
indeed be doubted whether any of it does. Between the beds 
which are undoubtedly of upper Chalk age (containing Echiuo- 
corys gibbus) and those which are certainly Cenomanian there 
is a great break and plane of erosion throughout Antrim. There 
is nothing which can be compared with the English zone of Rhyn- 
chonella Cuvieri, but Professor Barrois* thought that a certain 
group of glauconitic sands and sandstone containing Exogyra 
columba was the equivalent of the zones of Terebratulina gracilis 
and Holaster planus. Dr. W. F. Hume,f however, is doubtful about 
this correlation, and appears to think that in most of the sections 
there is a great break between the Cenomanian and the Senonian 
(Upper Chalk), and that there is very little which can possibly 
represent the zones of Rh. Cuvieri, Ter. gracilis, or Hoi. planus. 
He admits, however, that the highest part of the Exogyra columba 
sands may belong to the Middle Chalk, and that the Inoceramus 
beds may be partly equivalent to the Chalk Bock. 
It is clear, therefore, that if any Turonian exists in Antrim, it 
has the character of a glauconite sand, and that the base of the 
Upper Chalk is also a sandstone or sandy limestone ; hence there 
can be no doubt that the Turonian sea was there decidedly shallow, 
that land was not far off, and that strong currents prevented the 
deposition of much sediment in that area throughout the whole 
epoch of the Middle Chalk. 
Both Professor Barrois and M. Cayeux have regarded the Cre¬ 
taceous deposits of Ireland and Western Scotland as having been 
formed in a gulf which opened out of the British sea, but had no 
connection with the Atlantic Ocean. M. Cayeux, however, sug¬ 
gests that the main communication between the Cretaceous North 
Sea and the Atlantic was round the northern extremity of the 
British Isles. It is true that the large quantity of flints occurring 
in the surface deposits of eastern Scotland proves that the Creta¬ 
ceous sea extended for a considerable distance to the northward, 
but this is hardly sufficient evidence on which to base such a theory. 
It is a possible view, and that is all that can be said for it. 
In conclusion, I would point out that the evidence in favour 
of free and open communication between the Anglo-Parisian Sea 
and the more eastern seas existing in Turonian time is very strong, 
while the only direction in which there is any good reason for 
* Recherches sur le Terrain cretace de l’Angleterre et de l’lsland^ p. 214. 
t Quart. Journ. Geol. Soc., Vol. liii. pp. 591 and 598. 
