56 
rorULAR SCIENCE REVIEW. 
purely oceanic, deposited over a wide area, and containing no 
indication whatever of the proximity of land. Confining our 
remarks for the present to England, we see that the Eocenes, 
some 2,000 feet in thickness, are the results of a chain of per- 
fectly natural and connected events which can be traced. They 
are essentially detrital deposits, while the Chalk is oceanic. 
But although we can trace the deposition of the Eocene through 
every stage, as if it were a written book, when we attempt to 
connect its history with the deposition of the Chalk, we find the 
records are missing. How the Chalk area became converted 
from ocean to land, and for how long a time it had been land 
before the deposition of the Eocenes commenced, are questions 
which can only be solved, if solved at all, by a study of the 
rocks of other countries. In France, an older group of Eocenes 
exists than we have here ; but even this is, apparently, quite as 
remotely separated from the Chalk as our Eocenes. The break 
is so absolute and complete, indeed, that the Cretaceous period 
again seems to us as distinctly separate from the Eocene as it 
was thought to be by the earlier geologists. 
We have every reason to believe that the Chalk, being an 
ocean deposit, must have formerly covered wide areas, and that 
the existing masses, although still extensive, are but mere frag- 
ments which have escaped denudation. It is not surprising to 
find, therefore, that besides those portions of Great Britain and 
Ireland which, from its actual presence, were obviously covered 
by a continuous Chalk formation, its former extension over the 
whole of Wales, Scotland, great part of Ireland, and the Scilly 
Isles, has been traced. We may thus safely infer that it stretched, 
at least, continuously over Great Britain and far over Europe 
and the adjacent seas. But we scarcely know at all what were 
the limits on the present land surface even of the ocean which 
deposited it ; for although there are Cretaceous deposits in 
Europe thought to indicate proximity to a shore-line, it is not 
ascertained whether these are truly contemporaneous with the 
Chalk of England, or whether they are the deposits of that later 
period when the ocean began to recede, prior to the elevation of 
part of its bed into prse-Eocene land. 
The denudation of the Chalk, which must have been on a 
most colossal scale, had doubtless proceeded for ages before the 
deposition of the Eocenes commenced, since even their lowest 
beds consist of extensive tracts of flint ground into sand and 
pebbles. It has continued ever since, to how great an extent 
we learn but imperfectly, by the enormous beds of gravel and 
sand which form, to a large extent, the Eocenes, Pliocenes, and 
Pleistocenes, and by the shingle and sand banks of our present 
littoral. 
But, in addition to this evidence, we have other and stronger 
