318 THE ESSEX NATURALIST
From the early monoglacial interpretation of the Essex
drifts (4), so prevalent in the writings of Wood and Whitaker,
there has been a growing tendency in the literature towards in-
creasing subdivision of the Chalky Boulder clay, largely to accomo-
modate an emerging multiglacial theory of the lower Thames
area (Wooldridge and Cornwall, 1964). So much so in fact that
Wooldridge wrote that it is now "indefensible and misleading
to speak of the Chalky Boulder Clay glaciation, ignoring its evi-
dently composite character" (ibid. p. 232). That the Essex
glacial deposits are composite cannot be denied, but, in the ab-
sence of a local interglacial datum, the precise relation between
their composition and the number of glaciations responsible for
their deposition has been more a matter of personal preference
than of strict stratigraphic reasoning.
At the present time, 3 main systems of subdivision are re-
cognised. These are:—
(a) The existence of a high-level (350-400 feet O.D.) weathered
drift assigned, on the basis of morphology and erratic con-
tent, to a western glaciation antedating the Chalky Boulder
clay (Wells and Wooldridge, 1923; Wooldridge and Cornwall,
1964).
(b) The subdivision of the Chalky Boulder clay into "Lowestoft"
and "Gipping" types on the empirical basis of matrix litho-
logy (Baden-Powell, 1948) and stone orientation (West and
Donner, 1956).
(c) The alternative subdivision of the Chalky Boulder clay into
Hanningfield, Maldon and Springfield Tills on the basis of
morphology, depth of decalcification and very localised
stratigraphy (Clayton, 1957, etc).
Acute problems of correlation become apparent in attempt-
ing to reconcile these three schemes (Baden-Powell, 1951; Wool-
dridge, 1957; Wooldridge and Cornwall, 1964; and Turner, 1970),
so that a re-examination of their stratigraphic validity seems
necessary. In the light of newly-available borehole data in west
Essex (the M.11 Soil Survey), two of the above schemes — (a)
and (c) — are thus examined. A consideration of (b) is deferred
until more data are forthcoming.