146
EPPING FOREST
belong to the Eocene series. In other words, the
Bagshot Beds were deposited above the London
Clay in the sea in which the latter had been laid
down, no interval having existed during which
upheaval of the area, and, consequently, more or
less erosion of the London Clay, occurred. The
change was simply in the nature of the sediment,
which became more sandy. Thus it becomes
evident that the London Clay, was not reduced
in thickness during the deposition of the Lower
Bagshot Beds, while it is certain that a similar
remark cannot be made in the case of any other
of the deposits which overlie the London Clay.
Consequently, only where the London Clay is
capped by Bagshot Beds can its full thickness be
ascertained. And the only spot within the Forest
area where this occurs is High Beach.
There is a very considerable interval, as regards
age, between the London Clay and Bagshot Beds
and the gravel which is found here and there
capping the ground in the higher parts of the
Forest, sometimes resting, as at High Beach, on
Bagshot Beds, sometimes on London Clay. It
may be seen at High Beach and Jack's Hill within
the area of the present Forest, and at Gaynes Park
and Coopersale Common just outside its limits.
The late Sir Joseph Prestwich classed this gravel,
which has a very wide distribution, as " Westleton
Shingle." But those who wish to know what is
meant by that term must be referred to his im-
portant paper on the " Westleton Beds " in Quart.
Journ. Geol. Soc. for 1890, pp. 84-181. He gives
the approximate composition of the gravel at
Tack's Hill as :—