Geoscience Reference
In-Depth Information
FIG
41.
Zigzag folding due to horizontal convergence during the Variscan mountain build-
ing is spectacularly exposed at Hartland Quay (Area 3). (Copyright Will Brett/
www.lastrefuge.co.uk)
FIG
42.
Zigzag folding due to horizontal convergence during the Variscan mountain build-
ing, this time at Bude (Area 2). (Copyright Dae Sasitorn & Adrian Warren/
www.lastrefuge.co.uk)
Some of the bedrock of this Lizard Complex is called
serpentinite
, after the com-
mon occurrence of the green mineral serpentine in sinuous cracks and veins. This gives
the rocks an attractive colour patterning, and the absence of quartz makes them surpris-
ingly easy to work with steel tools, giving rise to a local industry of carving serpentin-
ite ornaments.
Granites and valuable minerals
The granites of Southwest England are an important later feature of the Variscan moun-
tain belt. Granites are igneous rocks with coarse (millimetre across) crystals that have
grown, interlocking with each other, as the molten material cooled slowly and solidi-
fied at some depth in the Earth's crust. The minerals of the granite are most commonly
quartz (typically about 30 per cent) and feldspar, generally with some other minerals
such as mica (Fig. 43). The granite liquid (often called magma) formed as a result of
melting deep within the outer layers of the Earth and was then forced upwards, some-
times pushing aside the overlying bedrock and sometimes replacing it by melting. The
granites solidified at depths of several hundred metres or more below the surface and
are now at, or near, the surface because of landscape erosion. The main granite areas
include the Isles of Scilly in the west, followed by Land's End, Carnmenellis, St Aus-
