326
THE ESSEX NATURALIST
continuous till sheet, rendering the local Hanningfield Till synony-
mous with Springfield Till.
In southern Essex the Hanningfield Till was differentiated
from Springfield Till on (a) its morphology and (b) its depth of
surface weathering (Clayton, 1957). Now it has already been
implied that, in the west Essex context at least, the method of
dating tills by depth of weathering is open to question since it
wrongly assumes a uniform rate of decalcification. Indeed in the
Harlow-Epping area the higher Hanningfield tills were not found
to be decalcified to any great depth (ibid. p. 15), and although this
was explained by a local loss of the leached zone by erosion, it is
clear that in any event the Hanningfield-Springfield distinction in
west Essex is solely a morphological one.
Thomasson (1961 p. 296) and Wooldridge (1.965 p. 229) have
already criticised the assumptions implicit in this particular
morphological method, and the present data support their criti-
cism. The physiographic distinction of the Hanningfield and
Springfield Tills rests on the assumption that the Chalky Boulder
clay ice advanced, on two separate occasions, over different land
surfaces, depositing till at discrete levels within the landscape
(1957 p. 21). The cross-section through Harlow New Town (p. 16)
certainly conveys this impression i.e. that the Hanningfield Till
rests on a higher (and earlier) land surface than that on which
Springfield Till lies. But to the east of Harlow (at Potter Street)
the two tills merge imperceptibly, indicating that thetwo surfaces
are really contemporaneous. The morphological break separating
them at Harlow is a recent (i.e. post-Springfield Till) erosional
feature undoubtedly related to the intense erosion known to be
currently taking place along the steep east bank of the Lower Lea.
Nowhere else in west Essex are the Hanningfield and Springfield
Tills separated morphologically. In fact, the ambiguous morpho-
logical relations already noted in the section (Fig. 1 68-100) are
widespread in the Epping and Ongar area (see map p. 125, 1964),
the two tills being divided by an arbitrary line corresponding, in
most instances, to the 275-foot and 300-foot contours. Yet, despite
immediate juxtaposition of the two deposits in these localities,
Springfield Till has never been observed to overlie Hanningfield
Till.
On the basis of the borehole descriptions and soil mechanics
analyses therefore, it is argued that the Chalky Boulder clay in
west Essex is an essentially single formation and that no litho-
logical, stratigraphic or indeed morphological evidence warrants
its subdivision into Hanningfield and Springfield Till types. The
intermediate Maldon Till is discussed below.
Sub-Boulder clay sands and gravels
The persistent occurrence of glacial sands and gravels under-
lying Chalky Boulder clay in Essex and Suffolk has long been