Geology of Cornwall
From Wikipedia, the free encyclopedia
The Geology of Cornwall (The Cornish peninsula) is mainly comprised of granite. There is also some slate, and unusual glacial-alluvial deposits exist near the cape.
Cornwall forms the tip of the south-west peninsula of the islandGreat Britain, and is therefore exposed to the full force of the prevailing winds that blow in from the Atlantic Ocean. The coastline is composed mainly of resistant rocks that give rise in many places to impressive cliffs.
The north and south coasts have different characteristics. The north coast is more exposed and therefore has a wilder nature. The prosaically-named High Cliff, between Boscastle and Tintagel, is the highest sheer-drop cliff in Cornwall at 735 ft (224 m). However, there are also many extensive stretches of fine golden sand which form the beaches that are so important to the tourist industry, such as those at St Ives, Perranporth and Newquay. The only river estuary of any size on the north coast is that of the Camel, which provides Padstow with a safe harbour.
The south coast, dubbed the "riviera", is somewhat more sheltered and there are several broad estuaries formed by drowned valleys or rias that offer safe anchorages to seafarers, such as at Falmouth and Fowey. Beaches on the south coast usually consist of coarser sand and shingle, interspersed with rocky sections of wave-cut platform.
The interior of the county consists of a roughly east-west spine of infertile and exposed upland, with a series of granite intrusions, such as Bodmin Moor, which contains the highest land within Cornwall. From east to west, and with approximately descending altitude, these are Bodmin Moor, the area north of St Austell, the area around Camborne, and the Penwith or Land's End peninsula. These intrusions are the central part of the granite outcrops of south-west England, which include Dartmoor to the east in Devon and the Isles of Scilly to the west, the latter now being partially submerged.
The uplands are surrounded by more fertile, mainly pastoral farmland. Near the south coast, deep wooded valleys provide sheltered conditions for a flora that likes shade and a moist, mild climate. These areas lie mainly of Devonian sandstone and slate. The north east of Cornwall lies on Carboniferous rocks known as the Culm Measures. In places these have been subjected to severe folding, as can been seen on the north coast near Crackington Haven and several other locations.
The geology of the Lizard peninsula is exceptionally interesting, as it is Britain's only example of an ophiolite. Much of the peninsula consists of the dark green and red rock, Precambrian serpentine, which forms spectacularly beautiful cliffs as at Kynance Cove, and when carved and polished forms attractive ornaments. This ultramafic rock also forms a very infertile soil which covers the flat and marshy heaths of the interior of the peninsula. This is home to rare plants, such as the Cornish Heath, which has been adopted as the county flower.[1]
The intrusion of the granite into the surrounding sedimentary rocks gave rise to extensive metamorphism and mineralisation, and this led to Cornwall being one of the most important mining areas in Europe until the early 20th century. It is thought that Cassiterite (Tin oxide) was exploited in Cornwall as early as the Bronze Age. Over the years, many other metals such as copper, lead, zinc and silver have all been mined in Cornwall. Alteration of the granite also gave rise to extensive deposits of China Clay (Kaolinite), especially in the area to the north of St Austell, and this remains one of Cornwall's most important industries.
Historically extensive tin mining has occurred in the region, as well as arsenic and china-clay extraction. As of 2006 there are no active metalliferous mines remaining. However, tin deposits still exist in Cornwall, though the price of tin means extraction is not currently economical.
