310 EOCENE PERIOD. [Ch, XXII. 
No. 81. 
c j 
I — — , 
4. 
water E, the sediment being drifted through transverse fissures, 
as before explained. In this case, the rise of the formations 
Nos. 1, 2, 3, 4, 5, may have been going on contemporaneously 
with the excavation of the valleys C and D, and with the accu- 
mulation of the strata a. There must be innumerable points 
on our own coast where the sea is of great depth near to islands 
and cliffs now exposed to rapid waste, and in all these the 
denuding and reproductive processes must be going on in the 
immediate proximity of each other. Such ma)' have been the 
case during the rise of the Valley of the Weald, and the 
deposition of the beds of the London and Hampshire basins. 
The theory above proposed requires that the deposits a 
should be composed, for the most part, of a mixture of sue 1 
mineral ingredients as would result from the degradation o 
the secondary groups, Nos. 1, 2, 3, 4, 5. Now the tertiary 
strata answer extremely well to these conditions. They con- 
sist, as we have before seen, of alternations of variously-coloured 
sands and clays, as do the secondary strata from the group 
No. 5 to No. 2 inclusive, the principal difference being, that 
the latter are more consolidated. 
If it be asked, where do we find the ruins of the white chalk 
among our Eocene strata ? We reply, that the flint pebbles 
which are associated in such immense abundance with the sands 
of the plastic clay, are derived evidently from the destruction 
of chalk ; and as to the soft white calcareous matrix, we may 
suppose it to have been reduced easily to fine sediment, and to 
have contributed, when in a state of perfect solution, to form 
the shells of Eocene testacea; or when mixed with the waste of 
the argillaceous groups, Nos. 2 and 4, which have been pecu- 
liarly exposed to denudation, it may have entered into the 
composition of the London clay, which contains no slight 
