544 
THE CRETACEOUS ROCKS OF BRITAIN. 
may be argued that by analogy the distribution of land and water 
in the Atlantic area may have been equally different at that period. 
This argument may, indeed, be carried still further, and may 
be used in favour of a presumption that there was both land and 
sea within the area of the North Atlantic. Tor what we 
know of the range and extent of the Chalk formation as a whole 
in Europe suggests that the general trend of the larger land and 
sea areas was from east to west, and it is not improbable that this 
east and west trend was prevalent at that time throughout the 
whole of the northern hemisphere. The Upper Cretaceous Ocean 
may have had a wide extension across both the Atlantic and Euro¬ 
pean regions between the parallels of 30 and 50 degrees N. Lat. 
while the larger continental areas lay to the north and south of 
these parallels, and more especially to the northward. 
I am, therefore, quite ready to admit that there are theoretical 
grounds for assuming the existence of a large sea-space or ocean 
within the area of the North Atlantic during the UpjDer Cretaceous 
period ; but I see no evidence for supposing that it bore any resem¬ 
blance in shape, direction, or depth to the modern Atlantic. 
Our present concern with this possible Atlantic sea is to con¬ 
sider the probable location of the openings which may have 
connected it with the European sea. The first and most obvious 
westward opening is that of the Aquitanian and Pyrenean region. 
The present coast of France cuts apparently through the very 
centre of this basin, out of which the Atlantic lias eaten the great 
bay which we call the Bay of Biscay, and the French term the 
Gulf of Gascony. It is necessary, however, to point out that 
the Turonian deposits in the south of France do not present a 
deep water facies like that of the Paris basin ; they consist chiefly 
of marls or shelly or sub-oolitic limestones, with some sandy beds, 
and the most conspicuous fossils in the calcareous beds are the 
thick-shelled Hippurites and other members of the Kudistean 
family. Thus, unless there was good evidence to the contrary, 
we might imagine that the Turonian sea of the Aquitanian period 
was a dependence of the Mediterranean, and not of the Atlantic, 
being only a gulf or embayment on the border of the western 
Continent. 
French geologists, however, have always believed that this 
Aquitanian sea opened westward into an Atlantic Ocean, and M. 
Ph. Glangeaud, of Clermont-Ferrand, has been kind enough to 
acquaint me with some of the facts on which this belief is based. 
It appears that in the northern part of the basin (the Charentes 
and Dordogne) the lower paid of the Turonian consists every¬ 
where of marly limestones with Ammonites, and it is inferred 
that the water was fairly deep and that there was open communi¬ 
cation with the northern sea through the straits of Poitou. The 
higher part of the Turonian exhibits more differentiation, and in 
Dordogne, south of Perigueux, there are detrital deposits of this 
age, while to the north-west limestones with Rudistce were being 
