File:The Quarterly journal of the Geological Society of London (12684399623).jpg

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PROCEEDINGS OF THE GEOLOGICAL SOCIETY. .Apr. 21.
Fig. 7. — Diagram showing the conditions that would have resulted
from the deposition of the Cretaceous Beds on the edge of a shoal
formed by the previous elevation of the Weald.
N. S.
Elevated mass of the Weald.
Cretaceous beds.
1 & 2. Lower Cretaceous strata, thinning out to the south,
whilst the Upper strata overlap successively
upon the Wealden rocks.
Fig. 8. — Diagram showing the relative thickness of the Lower Creta-
ceous beds, and the denudation of the Chalk, over the Weald.
N. Shoal or Island S.
in the Tertiary Sea.
c. Chalk.
d, e. Upper Greensand and Gault.
/. liower Greensand.
g, Wealden.
.The lower beds of Chalk below x should have been represented as rather thicker and the
Lower Greensand rather thinner..
of the Upper Greensand period and at the dawn of that of the Chalk ;
still it was not of that extent to prevent the extension over the southern
area of an important mass of lower chalk and of the middle chalk with
flints. Neither the upper nor the lower chalk, however, possess that
great development which they do in Herts and Cambridgeshire' — the
one apparently having been removed by denudation, and the other
originally deposited in a thicker mass.
On either alternative, of a depression in Cambridgeshire or an ele-
vation in Kent, the result would still be the same, in that we should
have the chalk surface relatively higher and nearer to the sea-level in
the latter than in the former county. This would favour the wear-
ing down of the chalk by the action of the sea over the present area
of the Weald, and as we see reason to believe that the chalk within
that area was removed or reduced to a thin shell, it is probable that
some of the underlying beds of the green-sand or even of the Wealden
might have become exposed to the denuding action. See fig. 8.
There is no appearance, however, in the Lower Tertiaries of debris
derived from any large mass of clay such as the Wealden, whereas
the light-coloured sands, with traces of greensand and occasionally
of carbonate of lime, forming the Thanet Sands, have a mineral cha-
racter perfectly harmonising with a reconstruction out of the Upper
Greensand chiefly, with the Gault and upper part of the Lower Green-
sand partially. It would thus seem that only these portions of the
lower cretaceous series had, together with the Chalk, at that time been