MIDDLE CHALK—CONDITIONS OF DEPOSIT. 
545 
formed. Again in the southern part of the basin there are lime¬ 
stones with Ammonites at Roquefort in the west, while in the 
Cor bier es, on the east, there are sandstones both at the base and 
the top of the formation, with Rudistean limestones in the middle. 
M. Glangeaud is therefore of opinion that there was a deep and 
open sea to the westward, and that at the close of the Turonian 
age the openings both into the northern and the Mediterranean 
seas were narrow and shallow. 
Passing now to the northward, there is in the first place every 
reason to believe that Brittany was united to Cornwall in Turonian 
time, as it was in the Cenomanian, and that no westward opening 
existed along the line of the English Channel at any epoch of Cre¬ 
taceous time. I argued for this view in 1892,* and am pleased 
to find that M. Cayeux is of the same opinion. He remarks 
(Op. cit., p. 560): — “ I do not know of any fact which would favour 
the existence of a strait connecting the Anglo-Parisian sea with 
the ocean on the site of the English Channel; on the contrary , 
I see several objections to such a view.” He mentions the rapid 
thinning of the Turonian series westward from Eecamp, but does 
not refer to a fact which seems still more conclusive, namely, the 
small Cretaceous outlier in the Cotent in, where chalky limestone, 
with Senonian fossils, rests upon sands which are generally sup¬ 
posed to be of Cenomanian age, but might possibly be Lower 
Turonian ; in either case there is a complete absence of any 
Turonian chalk. 
Coming now to England, we find in Devonshire evidence that 
at the beginning of Turonian time the coast-line was still not 
far distant and that the water was not very deep. The Beer 
stone is not a chalk but a shell-sand, and its residue contains a 
variety of minerals which have clearly been derived from land 
consisting of Granite and Palaeozoic rocks such as occur in 
South Devon and Cornwall. It is equally clear, however, that 
a considerable subsidence ensued, for not only does the chalk 
of the Terebratulina zone in Devon resemble that of more eastern 
counties, but it is actually thicker than in Dorset or Wiltshire. 
Such a thickness of pure chalk (90 to 100 ft.) seems to indicate 
that the depth of water had increased and that the shore-line had 
receded to some extent. 
We are therefore at liberty to speculate upon the possibility 
of the western land being so lowered and broken up that, if 
there was an Atlantic sea beyond, a communication with it 
may have been opened up across the north of Devon and across 
the Irish Sea, At the same time, it must be admitted that such 
an idea must remain a pure speculation; there is no positive 
evidence for it—merely the fact that in East Devonshire we find 
no trace of a shore line for the Turonian Sea, Moreover, the 
land may have risen steeply from the sea, and the subsidence 
* The Geographical Evolution of the English Channel, Contemporary 
Review, Vol. lxi. p. 855 (1891). 
