GEOLOGY
Figures 1 and 2 show the distribution of the main deposits and are based on
Geological Survey Sheets 256 (North London) and 257 (Romford) with minor
amendments (Adams 1974). The memoir to the Romford Sheet (Dines &
Edmunds 1925) describes the deposits.
Solid deposits
The oldest deposit in the district, forming the basement to the succeeding
deposits and constituting the main mass of the Epping Forest Ridge, is the
London Clay. It is a marine clay of Eocene age laid down on the floor of a
middle Tertiary sea. Fossils found in the borings at Waterworks Corner,
Woodford, include gastropods, brachiopods, crabs and other crustacea, and a
variety of seeds indicative of a warm climate on the neighbouring land mass. At
depth the London Clay is blue-grey and calcareous in parts, but the upper few
metres are weathered brown. The London Clay passes upwards to the Claygate
Beds which consist of inter-stratified clays and fine sands, yellow, lilac and
greyish in colour. The beds are 20 m thick on the Epping Forest Ridge, and
more loamy in character than elsewhere, but in general the proportion of sand
increases upwards until the yellowish false-bedded fine sands of the Bagshot
Beds are reached above. This succession suggests that the Claygates are passage
beds (Dines & Edmunds 1925) between the London Clay and the Bagshot Beds,
indicating a shallowing of the Tertiary sea and a transition to deltaic or
estuarine conditions. The Bagshot Beds occur in three separate areas on the
summit of the ridge. In one of these, near the Kings Oak Public House, ex-
cavations showed light-coloured yellowish sands with thin seams of pipe clay.
Elsewhere in Essex an upper pebble bed has been mapped, but this has not been
reported from Epping Forest. The base of the Bagshot Beds lies generally at
about 100m O.D. but is not always easy to define when cappings of later drift
(mainly Pebble Gravel) overlap the junction. Hence springs and flushes from
the base of these relatively permeable beds may be displaced slightly downslope
from the true junction, and lithological variation within the Claygate Beds
below giving rise to similar minor springs, can confuse the picture. Springs can
also occur at the base of the Claygate Beds, but the junction is not clearly
defined topographically, although stream valleys tend to widen out downslope
from it.
Drift deposits
Deposits later than the Eocene and attributed to the Pleistocene or Recent
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