Geoscience Reference
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stone is the most distinctive feature of the folds, and one of its most famous features
is the Avon Gorge ( d1 ; Figs 162 and 163) at Bristol. The cliffs of the gorge are up to
100 m high, and have been formed partly by rainwater dissolving the rock and partly
by gravitational collapse of the highly fractured limestone.
Away from the hills, the surrounding landscape is often underlain by a sequence
of Late Carboniferous sediments broadly grouped as the Coal Measures. The Coal
Measures are predominantly mudstone, but also contain coals and sandstones. Being
mostly mudstone, the coalfields have tended to be preferentially eroded by younger
rivers and streams, resulting in rather lower landscapes. This was also the case during
Triassic times, because the distribution of Triassic sediment in many of the coalfield
areas provides evidence that these areas were low-lying when sediment was accumu-
lating. The large volume of Triassic sediment present indicates that much of it was not
simply being derived from local sources, but was being transported over longer dis-
tances, probably from the central peaks of the Variscan mountain range to the south.
FIG 162. The Avon Gorge, looking downstream from the Clifton Suspension Bridge (Fig.
156, d1 ). (Copyright Landform Slides - Ken Gardner)
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