GLACIAL STRATIGRAPHY OF WEST ESSEX 321
face, being largely overlain by 5 to 20 feet of what is here termed
"head." This surface layer, the main part of which lies between
345 and 370 feet O.D-, is notable for its lack of stratigraphic co-
herence, being described variously as firm to stiff (mottled)
orange, orange-brown or grey sandy clay with scattered gravel
giving way in parts to silty or sandy clays of equally varied
colours without contained stones; chalk fragments are conspi-
cuously absent. To the north, as already stated, similar material
is overlain at one point by Chalky Boulder clay; to the south it
overlaps both Pebble Gravel and Claygate Beds, and a detached
mass of the same clay occurs downslope at Coopersale Street and
Gaynes Park (61-62).
This stony clay lying above the Pebble Gravel occurs else-
where on the Epping Forest ridge. Whitaker (1889 p. 272) de-
scribed a "clay or loam with pebbles" overlying Pebble Gravel
at High Beech as possible weathered till, while Monckton (1890
p. 200) suggested that the "clayey deposit which overlies pebble
gravel at Coopersale Common and at High Beech is decomposed
boulder clay". Both authors regarded the deposit as contem-
porary with the Chalky Boulder clay. Similar beds at Jack's
Hill (Fig. 1), were described in detail by Weils and Wooldridge
(1923 p. 248), but they ascribed them, on the basis of their suite
of western erratics, to an ice advance from the west which "pro-
bably antedated by a considerable period the main glaciation of
S. E. England" (ibid. p. 250). Further west towards Welwyn, the
existence of a glacial Western Drift of pre-Great Interglacial age
has been recently substantiated by Wooldridge and Cornwall
(1965) and its probable equivalent in S.E. Hertfordshire has been
described by Thomasson (1961) as "Pebbly Clay Drift."
In terms of its morphological relations with the Chalky
Boulder clay and its non-calcareous character, the Coopersale
Common "head" is clearly analogous to the Western Drift, but
this suggestion obviously requires petrographic confirmation.
A preliminary analysis of the surface drift in the vicinity
of Gernon Bushes (TL 480030) indicated an abundance of sub-
angular and rounded Tertiary flint pebbles (with some large
unworn flints), small white quartz pebbles and traces of red
(Bunter) quartzite and chert embedded in a groundmass of firm,
structureless mottled grey and brown sandy clay and fine quartz
particles. No Jurassic, Cretaceous or other northern material
was detected. There are, therefore, no petrographic objections
to the Coopersale Common "head" being regarded as the local
equivalent of the Western Drift. If the correlation proves to be
correct, the site of bore GB 27 may assume critical importance,
since it might then constitute the only known occurrence of
Western Drift clearly overlain by Chalky Boulder clay. In any
event though, the Coopersale Common deposit cannot be iden-
tified with Clayton's Hanningfield Till (1957) since, unlike the
latter, the "head" does not pass downwards into unweathered
calcareous boulder clay even to a maximum depth of 20 feet.