THE PLIOCENE PERIOD IN WESTERN ESSEX. 261
active denudation. Beyond there is clear evidence of a long
ice lobe (the "Upminster lobe") which moved almost due south
to Upminster between Havering and the Kelvedon-Brentwood
ridge. An interesting feature of this lobe is the occurrence of
isolated ridges of boulder clay, of elongated form, whose longer
axes are parallel with the sides of the depression and with the
inferred direction of ice-motion. Good examples are seen east
of Harold Wood, north of Bedden Court and at Lillyputs, north
of Hornchurch. The writer believes these to be true drumlins.
East of Brentwood it is clear that another ice-lobe (the "Heron-
gate lobe") occupied the low ground between the Warley hills
and Billericay, extending southwards to the neighbourhood of
East Horndon and possibly farther. An excellent example of
the drumlin mounds, more than a mile in length, occurs at Great
Cowbridge and another is to be seen near Little Burstead.
In the country north of Billericay and Brentwood several
tracts of high ground, as at Stock and Galleywood, projected
above the ice. At Galleywood the Boulder Clay, though
plastered against the northern face of the hill, did not override
it. The ice stream split, part of it passing down the Wid valley
to feed the Herongate lobe, while part passed south-eastwards
as a broad lobe (the "Hanningfield lobe") between Stock and
Danbury, reaching as far south as Ramsden Heath and Woodham
Ferrers overlooking the present Crouch valley.
It will be observed that the several ice lobes of Western Essex
are disposed in a radial manner about a centre lying in the region
of the upper Stort and Roding valleys. It would seem that
the check to movement imposed by the barrier of high ground
to the south resulted in a measure of congestion in this northern
depression, which thus became a separate subsidiary centre of
ice dispersal.
The relations of the Boulder Clay edge east of Chelmsford
are strikingly different from those displayed in the west of the
county. There are no outliers in front of the main mass of
Boulder Clay, nor is there any suggestion that the ice-sheet had
a lobate front. It is, in fact, evident that the high ground of
Danbury, continued beyond the Blackwater in the remarkable
ridge which runs from Wickham Bishops through Tiptree
Heath to Messing, formed an effective barrier to the passage of
the ice, which never succeeded in passing over it, though it was