Geoscience Reference
In-Depth Information
Landscape D: New Red Sandstone and younger bedrock
Along the eastern edge of Area 2, relatively unfolded New Red Sandstone of Permian
and Triassic age rests on the folded Devonian and Carboniferous sediments of Land-
scapes
B
and
C
. The junction of the younger material with the older was formed when
the younger sediment was deposited on the eroded margins of the Variscan hills. The
New Red Sandstone occurs in a wide, north-south trending belt, extending southwards
as far as Torquay (
d1
) and Paignton, and with fingers extending westwards to the north
of Dartmoor (Fig. 37). Along the coast, from Exmouth (
d4
) southwards via Dawlish
(
d3
) and Teignmouth (
d2
), the New Red Sandstone has been quarried and penetrated
by the tunnels of the main coastal railway to the Southwest. The sandstone forms dra-
matic red cliffs, and marks the western edge of the World Heritage Site that extends to
the east along the coast of Dorset.
The New Red Sandstone consists of sandstones, gravels and mudstones that
formed as alluvial fans, desert dunes and in short-lived lakes along the edge of an irreg-
ular hilly landscape of older bedrock. The characteristic red colour so typical of many
Devon soils has largely been derived from these New Red Sandstone rocks. In the
Exeter area (
d5
), roads have been spectacularly cut through the New Red sediments,
and also through some scattered deposits of volcanic rock, mainly lava. These lavas
have been highly altered and have not resisted weathering at the surface any more than
the sediments of the succession, so they have not had much influence upon the scenery.
An intriguing feature of the New Red Sandstone is the way the original landscape
on which it formed is reappearing as the present landscape erodes. For example, the
Crediton Basin (
d6
), north of Dartmoor, is now obvious as a remarkably finger-like
strip of sediment, only 2-3 km across north to south, but extending almost 40 km west
to east (Fig. 37). Detailed examination of the New Red sediment in this basin shows
that it was deposited as the fill of a long, narrow valley, with material being derived
from north and south as well as along its length from the west. The valley formed par-
allel to the folds and faults of the earlier Carboniferous bedrock on each side of it, and
must have been cut first by river erosion in Permian times, controlled by the earlier
folds and faults that were formed during the Variscan mountain convergence. A few
kilometres further north, the Tiverton Basin in Area 3 has a similar west-to-east trend,
though it is more open and less elongate.
From Exeter (
d5
) to Torquay (
d1
), the base of the New Red Sandstone reveals
topography of hollows eroded westwards into a higher ground of Devonian and Car-
boniferous bedrock. The New Red Sandstone pattern is of alluvial fans radiating down-
stream, but generally draining towards the east, and it bears a striking general similarity
to the present drainage and scenery of the area (Fig. 77). During Variscan convergence,
