Geoscience Reference
In-Depth Information
the Blackdown Hills to the south in Landscape C. The hills here owe their height to
the resistance to weathering and river erosion offered by their Devonian bedrock, in
clear contrast to the surrounding lowlands that are underlain by the easily eroded Mer-
cia Mudstone (part of the New Red Sandstone). Further west, however, the New Red
Sandstone bedrock also contains sandstones, pebble beds and breccias that have resis-
ted erosion more successfully and formed hills. The presence of these coarser-grained
sediments represents the more vigorous erosion and transport that occurred in early
New Red Sandstone times along the fringes of the Variscan mountains.
FIG
99.
Area 4, showing river pathways, coastal flooding zone, Landscapes
A
to
I
and
localities (
a1, a2
etc.) mentioned in the text.
North of the Tone valley, the Brendon Hills are separated from the Quantock Hills
by a distinct valley, occupied by the Taunton to Minehead road and the West Somerset
railway line. The bedrock in this valley is again New Red Sandstone, and its detailed
mapping shows that the layers have been much cut by faulting since they were first
deposited. The southwestern edge of the Quantock Hills is straight, steep and often
reaches 200 m in height above the valley floor (Fig. 99). This edge may be an eroded
fault scarp, but it could also be an ancient topographic feature, perhaps a slope dating
from New Red Sandstone times that was excavated again during the Tertiary.
