Geoscience Reference
In-Depth Information
forms the edge of the Hanningfield Plateau (
d7
), whereas the southeastern margin is
the Rayleigh-Dengie Ridge. The lowlands are also crossed by distinctive smaller ridges
at Purleigh (northwest of
d6
) and the Langdon Hills (
d4
). The northwestern margin
of these lowlands contains a series of arcuate hollows which probably formed when
freeze-thaw processes in the largely clay bedrock triggered land-slipping down slopes.
On a more general scale, the lowlands appear to have encroached on the surrounding
hills by a combination of Ice Age land-slipping processes and removal of the slumped
mud by river action.
FIG
221.
Slope map of Area 12, showing the extent of Anglian ice, along with former and
present drainage pathways.
To the southeast of the Valley of Romford, erosion has picked out slopes that are
often capped by the more sandy Claygate Member, which forms the uppermost part of
the Early Tertiary London Clay Formation. Hadleigh Castle (
d5
), shown in Figure 222,
has been built on a particularly distinctive point of the 70 m high Southend scarp. It is
from here that John Constable captured remarkable light effects in his views towards
the mouth of the Thames Estuary (see Area 14).
An interesting insight into more recent landscape development comes from the
flat Dengie and Rochford peninsulas, north and south of the Crouch Estuary (
d6
). Field
boundary patterns, apparently dating from Iron Age times, about 2,000 years before
the present, show a remarkably parallel alignment on the two sides of the tidal Crouch
Estuary. This observation, along with evidence of early bridging and fording of the
channel, confirms that a very recent rise in sea level must have taken place, drowning
ancient fields and crossing places to form today's 400 m wide estuary.
