CONSTITUTION - OF CHALK AND FLINT. 
145 
Origin and extent of the Chalk as a marine deposit .—The origin of 
the Chalk, with regard to its deposition, was touched upon in Mr. 
Lobley’s lecture, hut I think we may enlarge upon it a little. Here 
is a rough map (after M. Elie de Beaumont) of what was the sea- 
area in which the Chalk was deposited; the blue representing the 
sea where the chalk beds were being formed, the yellow the lands, 
and the light tints where one or the other are not known for certain. 
If you look at the geographical conditions, you will see that cities 
and towns which now exist look very oddly placed with regard to 
land and sea in that map. The sites of London and Southampton 
are in the midst of the old sea, and so also are those of Cambridge, 
Hamburg, and Copenhagen, to the N.E., and of Paris and Tours 
to the S. A great stretch of main-land and islands occupies the 
middle of what is now Europe, but to the S. and the E. the sea is 
open; for it stretched away into the African area by Nubia, and 
over the East-European into the Western and Central Asiatic regions. 
In the far West the Cretaceous Ocean covered various areas 
where the North-American Continent now stands. My map, how¬ 
ever, indicates only one stage in the extent of this great sea; it 
had been less; and as every sea-coast has its true littoral deposits, 
and as with the deepening of the sea (that is, the sinking of the 
sea-bed and neighbouring land) these shallow-water sands and 
shingles (if not washed away by the waves) are covered up by the 
advancing mud, shell-banks, or ooze of deeper water, there must 
be strata of both kinds laid down successively near the coast-lines, 
and yet the members of each set are continuous over more or less 
of the sinking tract. This is shown by my diagram here of inter¬ 
calating beds of rough and fine materials at the foot of the cliffs of 
a sinking shore; each layer of pebbles and sand being continuous, 
and therefore contemporaneous, with sands and shell-beds of the 
deep water of the same period. 
Many of you, doubtless, have found that in studying geology 
you must forget most of the principal features of existing geo¬ 
graphy. The present conditions, shapes, and heights of land have 
little to do with the extent of land in the times of which we have 
been speaking. 
The geography of the present day has come out from an older 
geographical condition. The geographical arrangement of sea and 
land was not persistent,—it had been something else, and it became 
something else in the course of a few ages. The map marks only 
at one stage the arrangement in that Cretaceous period. Never¬ 
theless, as already intimated, the different kinds of strata, such as 
would be formed in deep water and in shallow water, respectively, 
guide the geologist in mapping out where coasts and shoals and 
abyssal seas formerly existed. The White Chalk itself is such 
a friable limestone, consisting of oceanic Eoraminifera and other 
organisms, as would be deposited in a deep (but not abyssal) ocean; 
indeed the Globigerina-ooze of the Atlantic and Pacific is an 
analogue; and, according to our well-established knowledge, there 
must have been shallower and shallower waters with their muds, 
