Geoscience Reference
In-Depth Information
built further seaward as the process of reclamation continues. The Romans were the
first to drain the wetlands for agriculture, although the fields largely returned to marsh-
land when the empire crumbled. Since the early Middle Ages, land has been system-
atically reclaimed from the sea and protected by sea banks. Historically the land was
used for farmland, especially wet pasture. During the last century, the land has been
further used for oil-storage depots, military training ranges and tourism (yachting, mar-
inas, water and jet-skiing) as well as for intensive arable farming on the fertile loamy
soils.
Landscape D: South Essex and the Northern Thames Basin
Most of South Essex is underlain by flat-lying horizontal layers, mainly mudstones of
Tertiary age. Patches of the sandy Bagshot Beds underlie Ice Age deposits in the north-
west corner (
d1
), but most of the region is underlain by London Clay that is covered
by Quaternary river and ice-laid deposits. Around Tilbury (
c3
), near the River Thames,
the older Chalk layer is exposed at the surface, as shown in Figure 214.
Much of the landscape of Essex does not directly reflect contrasts in the erosional
strength of the underlying bedrock. It has a distinctive topography that reflects most
obviously the variety of processes that have shaped it over the last few million years.
The River Thames has been the primary influence on the shape of this Landscape, ac-
counting for much of the erosion of south Essex, although deposition by the Anglian
ice has also played an important role. Consideration of the landforms can help to work
out which processes have been involved.
An undulating plateau (Fig 215
d1
), sometimes reaching 100 m above sea level,
forms the corner of this Landscape, northwest of the Brentwood-Chelmsford A12 trunk
road. Much of this plateau is underlain by Anglian ice-laid material, and the undula-
tions may reflect surface-blanket topography left by the melting ice, although it must
have also been modified later by small stream systems.
To the southeast of the plateau there are more distinctive ridges and slope features,
mostly trending southwest-northeast. The first of these hilly features is a knoll centred
on Danbury (
d2
), which is linked to a ridge continuing northeast towards Tiptree in
Area 14. The slopes and ridges were carved by the Thames or one of its branches be-
fore the arrival of Anglian ice, which seems to have extended southeastwards only as
far as this Danbury-Tiptree Ridge.
Southeast of the Danbury-Tiptree Ridge, the next distinct topographic feature is a
series of lowlands that extend all the way from Thurrock (
d3
), near the Thames in the
southwest, to Maldon (
c1
) in the northeast. This is the Valley of Romford, another old
course of the River Thames, with very distinct margins to the northwest and southeast
(Fig. 221). The northwest margin is a strongly indented southeast-facing scarp which
