Geoscience Reference
In-Depth Information
Landscape C: The Wealden Greensand
Much of the sediment that accumulated in Area 6 during the later part of the Early
Cretaceous has been assigned to the Lower Greensand. This unit consists of alterna-
tions of mudstones and sandstones, ranging up to a maximum total thickness of about
400 m. The sediments seem to have formed in a shallow sea, and shelly fossils found
in them have allowed a fairly precise age for the rocks to be worked out. The deposits
vary from place to place, depending on their position in the succession, and this re-
flects the changing patterns of the Early Cretaceous shallow marine environment and
the variable way that sandy material was being supplied to the sea floor by rivers.
In the western third of this Landscape, the lowest thick sandstone layer of the
Lower Greensand (the Hythe Beds) has resisted stream and river erosion to produce
an escarpment that is particularly clear between Midhurst and Haslemere. Here the
Vale of Fernhurst (
b1
) has been eroded down into the Low Weald by what is now a
small stream flowing along the line of a gentle west-to-east trending upfold. The small
stream runs parallel to the much larger River Rother, which flows about 10 km further
to the south, under the shadow of the South Downs Chalk escarpment (Figs 129 and
136). Valley-slope processes in the Vale of Fernhurst have resulted in escarpments to
the north and south that are steep enough to have collapsed by land-slipping.
Further east in this Landscape, the bedrock has not produced any clear slope fea-
tures in the Wealden Greensand belt.
Landscape D: The South Downs
The South Downs provide a classic example of a linear range of hills that have been
formed by the erosion of a bedrock succession containing a sloping, more resistant,
layer, in this case the Chalk. In Area 6, the slope is typically southwards at only a few
degrees, although gentle and open folds with higher slopes are present locally.
The most famous scenery of this Landscape occurs where the sea has cut the spec-
tacular coastal cliffs between Eastbourne, Beachy Head (
d1
), the Seven Sisters (
d2
)
and Seaford Head (
d3
). The Beachy Head photograph (Fig. 131) shows how a recent
rock fall produced a lobe of debris extending outwards towards the lighthouse. Fur-
ther to the west, the Seven Sisters provide a beautiful example of the way that reced-
ing coastal cliffs can reveal a perfect cross-section through a pre-existing landscape of
parallel ridges and valleys (Fig. 132). Beyond is the valley of the Cuckmere, where an
artificial channel has been used to bypass the highly meandering lower stretch of the
river (Fig. 133). The object of this was to improve drainage to make the floodplain less
liable to flooding.
