Geoscience Reference
In-Depth Information
Bodmin and 621 m for Dartmoor). This gradient is overall only about 3 m per km. The
geophysical data on the large, deep granite body (Fig. 44) recognised below the surface
granite bodies do not provide independent evidence for a slope of this sort deep down.
Some tilting of the landscape downwards towards the west may have occurred, or the
slope may simply reflect the greater proximity of the western granite bodies to the sea
and repeated episodes of marine erosion.
Ice Age episodes
Ice sheets do not appear to have covered the present land of the Southwest Region to
any important extent during any of the major cold episodes of the Ice Age. In the Isles
of Scilly, material deposited directly from a grounded ice sheet has been recognised
and is thought to be Devensian (last cold phase) in age (Fig. 49). Various giant boulders
derived from metamorphic sources are a notable feature of some localities on the North
Devon coast, some of which appear to have come from Scotland. However, it is not
clear whether they were transported to their present locations by a large ice sheet or by
floating ice.
In spite of the lack of an actual ice sheet, the repeated cold episodes of the Ice Age
must have had a considerable effect upon the weathering style of the bedrock, for ex-
ample influencing the granite tors, mobilising material to move down slopes and chan-
ging drainage patterns and the surface blanket of soft materials.
FIG
49.
Map showing the greatest extent of the last main (Devensian) ice sheet across
England and Wales.
