Geoscience Reference
In-Depth Information
AREA 8: BRISTOL
The boundary of this area runs along the coast of the Bristol Channel, up the Severn
Estuary and along the banks of the River Severn (Figs 154 and 155). Bristol and Bath
are the most important cities. We shall consider the origins of the complex pattern of
hill areas and the landscapes of gorges (Avon) and caves (Cheddar, Wookey Hole etc.).
In contrast, we shall also examine the origins of the low and very flat Somerset Levels.
The following detailed discussion of the scenery of Area 8 is organised into six
Landscapes, labelled
A
to
F
in Figure 156. The main river pathways and coastal flood-
ing zone are shown in Figure 157.
Landscape A: The Quantock Hills and Fringes
The patch of higher land in the southwest corner of Area 8 is the northern tip of the
Quantock Hills, which rise to an elevation of 310 m at Beacon Hill (
a1
), some 3 km
from the coast of the Bristol Channel. The bedrock underlying the Quantocks is hard-
wearing Devonian sandstone and slate, similar to the bedrock of Exmoor in the west.
The resistance of this bedrock to landscape weathering and erosion is the reason for the
high ground in both cases.
FIG
154.
Location map for Area 8.
As in the rest of Area 8, the Variscan Unconformity marks the important end-
of-Variscan episode when the Triassic and Jurassic layers surrounding the Quantocks
were deposited on folded Devonian bedrock (Fig. 152). Much of the younger, overly-
ing material is mudstone, which has been eroded preferentially over the last few milli-
on years to form small hills and valleys at a lower level than the Quantocks themselves
