Geology of Cornwall

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A map showing the simplified geology of Cornwall Cornwallgeologymap2.jpg
A map showing the simplified geology of Cornwall
A simplified map showing the granite intrusions and mafic igneous rocks of Cornwall CornwallBasaltGraniteMap.jpg
A simplified map showing the granite intrusions and mafic igneous rocks of Cornwall

The geology of Cornwall , England, is dominated by its granite backbone, part of the Cornubian batholith, formed during the Variscan orogeny. Around this is an extensive metamorphic aureole (known locally as killas) formed in the mainly Devonian slates that make up most of the rest of the county. There is an area of sandstone and shale of Carboniferous age in the north east, and the Lizard peninsula is formed of a rare section of uplifted oceanic crust.

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Coasts

Chevron folding in the cliffs at Millook Haven, North Cornwall. Millook cliffs enh.jpg
Chevron folding in the cliffs at Millook Haven, North Cornwall.
Quaternary deposits at Porth Nanven including raised beach and head Climate history revealed^ - geograph.org.uk - 71736.jpg
Quaternary deposits at Porth Nanven including raised beach and head

Cornwall forms the tip of the south-west peninsula of the island Great 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 St Gennys, 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, Hayle, 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. Raised beaches can be identified in various places these being geological evidence of past changes in sea levels.

Interior

Rough Tor on the northwest flank of Bodmin Moor RoughTor.jpg
Rough Tor on the northwest flank of Bodmin Moor

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 (including St Austell Downs), the area south of Camborne and Redruth, and the Penwith or Land's End peninsula. These intrusions are the central part of the granite outcrops of south-west Britain, 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 are mainly of Devonian sandstone and slate. [1] 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 be seen on the north coast [2] near Crackington Haven, spectacularly at the Whaleback Pericline on the beach just south of Bude and at several other locations.

Granite

Land's End Land's End, Cornwall, England.jpg
Land's End
Land's End granite at Porthcurno beach Land's End Granite Cornwall.jpg
Land's End granite at Porthcurno beach

The intrusion of the granite into the surrounding sedimentary rocks [3] gave rise to extensive metamorphism and mineralisation, [4] and this led to Cornwall being one of the most important mining areas in Europe until the early 20th century. It is thought that tin ore (cassiterite) 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. [5] 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.

Granite was used as a building stone as early as the Bronze Age. Before the 17th century the granite was not quarried as it was far too difficult to cut the stone at that time. Builders used blocks lying about on the moors, known as moorstone, instead. By the later Middle Ages the masons were adept enough at dressing moorstone to use it in church building. Moorstone blocks were also used for bridging streams and for walls, stiles, posts and troughs. [6]

The Lizard peninsula

A simplified map showing the geology of the Lizard peninsula, Cornwall LizardGeologyMapCornwall.jpg
A simplified map showing the geology of the Lizard peninsula, Cornwall

The Lizard complex is Britain's most complete [7] example of an ophiolite. Much of the peninsula consists of the dark green and red rock, serpentinite, which forms cliffs as at Kynance Cove, and can be carved and polished to create ornaments. This ultramafic rock forms a very infertile soil which covers the flat and marshy heaths of the Goonhilly Downs.

Mining and quarrying

Extraction of tin began in Cornwall in prehistoric times and continued until the late 20th century. Historically extensive tin and copper mining has occurred in Cornwall and Devon, as well as arsenic, silver, zinc and a few other metals. Granite, slate and aggregate are still quarried and china-clay extraction continues on a large scale. There are ample supplies of granite worth the cost of shipping out of the county and much Cornish granite has been used in distant places. It is one of the most appropriate materials for memorials and examples are found in most parts of Cornwall. As of 2007 there are no active metalliferous mines remaining. However, tin deposits still exist in Cornwall, and there is talk of reopening South Crofty tin mine.[ citation needed ]

Geological studies were made worthwhile due to the economic importance of mines and quarries: about forty distinct minerals have been identified from type localities in Cornwall, e. g. endellionite from St Endellion.

See also

Related Research Articles

<span class="mw-page-title-main">Cornwall</span> County of England

Cornwall is a historic county and ceremonial county in South West England. It is recognised as one of the Celtic nations, and is the homeland of the Cornish people. Cornwall is bordered to the north and west by the Atlantic Ocean, to the south by the English Channel, and to the east by the county of Devon, with the River Tamar forming the border between them. Cornwall forms the westernmost part of the South West Peninsula of the island of Great Britain. The southwesternmost point is Land's End and the southernmost Lizard Point. Cornwall has a population of 568,210 and an area of 3,563 km2 (1,376 sq mi). The county has been administered since 2009 by the unitary authority, Cornwall Council. The ceremonial county of Cornwall also includes the Isles of Scilly, which are administered separately. The administrative centre of Cornwall is Truro, its only city.

<span class="mw-page-title-main">Perranporth</span> Village in Cornwall, England

Perranporth is a seaside resort town on the north coast of Cornwall, England, United Kingdom. It is 1 mile east of the St Agnes Heritage Coastline, and around 8 miles south-west of Newquay. Perranporth and its 2 miles (3 km) long beach face the Atlantic Ocean. It has a population of 3,066, and is the largest settlement in the civil parish of Perranzabuloe. It has an electoral ward in its own name, whose population was 4,270 in the 2011 census.

<span class="mw-page-title-main">North Cornwall</span> Area of Cornwall, England

North Cornwall is an area of Cornwall, England, United Kingdom. It is also the name of a former local government district, which was administered from Bodmin and Wadebridge 50.516°N 4.835°W. Other towns in the area are Launceston, Bude, Padstow, and Camelford.

<span class="mw-page-title-main">Mount's Bay</span> Bay on the south coast of Cornwall, England

Mount's Bay is a large, sweeping bay on the English Channel coast of Cornwall, United Kingdom, stretching from the Lizard Point to Gwennap Head. In the north of the bay, near Marazion, is St Michael's Mount; the origin of name of the bay. In summer, it is a large, benign, scenic, natural harbour. However, in winter, onshore gales present maritime risks, particularly for sailing ships. There are more than 150 known wrecks from the nineteenth century in the area. The eastern side of the bay centred around Marazion and St Michael's Mount was designated as a Marine Conservation Zone in January 2016.

<span class="mw-page-title-main">Porthtowan</span> Human settlement in England

Porthtowan is a small village in Cornwall, England which is a popular summer tourist destination. Porthtowan is on Cornwall's north Atlantic coast about 2 km (1.2 mi) west of St Agnes, 4 km (2.5 mi) north of Redruth, 10 km (6.2 mi) west of Truro and 15 km (9.3 mi) southwest of Newquay in the Cornwall and West Devon Mining Landscape, a World Heritage Site.

<span class="mw-page-title-main">Crackington Haven</span> Village in Cornwall, England

Crackington Haven is a coastal village in Cornwall, England, United Kingdom. It is in the civil parish of St Gennys at grid reference SX140972 at the head of a cove on the Atlantic coast. The village is seven miles (11 km) south-southwest of Bude and four miles (7 km) north-northeast of Boscastle.

<span class="mw-page-title-main">Aire Point to Carrick Du SSSI</span> Site of Special Scientific Interest in Cornwall, England

Aire Point to Carrick Du SSSI is a Site of Special Scientific Interest on the Penwith Peninsula, Cornwall, England. It is 5.98 square kilometres in extent, stretching from grid reference SW360279 to grid reference SW513410. The site is designated both for its biological and its geological interest.

<span class="mw-page-title-main">Geevor Tin Mine</span>

Geevor Tin Mine, formerly North Levant Mine is a tin mine in the far west of Cornwall, United Kingdom, between the villages of Pendeen and Trewellard. It was operational between 1911 and 1990 during which time it produced about 50,000 tons of black tin. It is now a museum and heritage centre left as a living history of a working tin mine. The museum is an Anchor Point of ERIH, The European Route of Industrial Heritage. Since 2006, the mine has been part of the UNESCO World Heritage Site Cornwall and West Devon Mining Landscape.

<span class="mw-page-title-main">Carnewas and Bedruthan Steps</span> Coastline and cliffs in Cornwall, United Kingdom

Carnewas and Bedruthan Steps is a stretch of coastline located on the north Cornish coast between Padstow and Newquay, in Cornwall, United Kingdom. It is within the parish of St Eval and is part-owned by the National Trust. The trust maintains a shop and café, and the cliff–top views of rocks stretching into the distance along Bedruthan beach make the area a popular attraction for tourists and painters. The property affords walks along the coast path and the steep steps at Bedruthan allow access to a series of rocky beaches at low tide. Signs at the top of the steps down to the beaches warn visitors not to risk swimming in these waters due to heavy rips, fast tides, and submerged rocks.

<span class="mw-page-title-main">Mining in Cornwall and Devon</span> Mining in the English counties of Cornwall and Devon

Mining in Cornwall and Devon, in the southwest of England, began in the early Bronze Age, around 2150 BC. Tin, and later copper, were the most commonly extracted metals. Some tin mining continued long after the mining of other metals had become unprofitable, but ended in the late 20th century. In 2021, it was announced that a new mine was extracting battery-grade lithium carbonate, more than 20 years after the closure of the last South Crofty tin mine in Cornwall in 1998.

<span class="mw-page-title-main">St Agnes, Cornwall</span> Human settlement in England

St Agnes is a civil parish and a large village on the north coast of Cornwall, UK. The village is about five miles (8 km) north of Redruth and ten miles (16 km) southwest of Newquay. An electoral ward exists stretching as far south as Blackwater. The population at the 2011 census was 7,565.

Joseph Carne was a British geologist and industrialist.

<span class="mw-page-title-main">Geography of Cornwall</span> Overview of the geography of Cornwall

The geography of Cornwall describes the extreme southwestern peninsula of England west of the River Tamar. The population of Cornwall is greater in the less extensive west of the county than the east due to Bodmin Moor's location; however the larger part of the population live in rural areas. It is the only county in England bordered by only one other county, Devon, and is the 9th largest county by area, encompassing 3,563 km² (1,376 mi²). The length of the coast is large in proportion to the area of the county. Cornwall is exposed to the full force of the prevailing south-westerly winds that blow in from the Atlantic Ocean. To the north is the Celtic Sea, and to the south the English Channel.

<span class="mw-page-title-main">Cornubian batholith</span> Granite rock in southwest England

The Cornubian batholith is a large mass of granite rock, formed about 280 million years ago, which lies beneath much of Devon and Cornwall, the south-western peninsula of Great Britain. The main exposed masses of granite are seen at Dartmoor, Bodmin Moor, St Austell, Carnmenellis, Land's End and the Isles of Scilly. The intrusion is associated with significant quantities of minerals particularly cassiterite, an ore of tin which has been mined since about 2000 BC. Other minerals include china clay and ores of copper, lead, zinc and tungsten.

<span class="mw-page-title-main">Zennor Head</span> Headland on the north coast of Cornwall, England

Zennor Head is a 750-metre (2,460 ft) long promontory on the Cornish coast of England, between Pendour Cove and Porthzennor Cove. Facing the Atlantic Ocean, it lies 1 kilometre north-west of the village of Zennor and 1.6 kilometres east of the next promontory, Gurnard's Head. The granite (Killas) cliffs rise over 200 feet (60 m) from the sea and the highest point of the headland is 314 feet (96 m) above sea level, with an Ordnance Survey triangulation station. Zennor Head is on the South West Coast Path, which follows the cliff edge closely, skirting the entire perimeter of the headland. The promontory is part of the Penwith Heritage Coast, and is the largest coastal feature in the United Kingdom that begins with the letter "Z". It gets its name from a local saint, Senara. Zennor Head was mined for copper and tin in the Victorian Era. There is no longer any residential or commercial occupancy on the headland, but it is occupied by a variety of coastal animals and plants, such as kestrels and gorse.

<span class="mw-page-title-main">Outline of Cornwall</span> Overview of and topical guide to Cornwall

The following outline is provided as an overview of and topical guide to Cornwall: Cornwall – ceremonial county and unitary authority area of England within the United Kingdom. Cornwall is a peninsula bordered to the north and west by the Celtic Sea, to the south by the English Channel, and to the east by the county of Devon, over the River Tamar. Cornwall is also a royal duchy of the United Kingdom. It has an estimated population of half a million and it has its own distinctive history and culture.

Presented below is an alphabetical index of articles related to Cornwall:

The geology of Maine is part of the broader geology of New England and eastern North America.

This article describes the geology of Dartmoor National Park in Devon, in south-west England. Dartmoor gained national park status in 1951 but the designated area of 954 km2 (368 sq mi) extends beyond the upland of Dartmoor itself to include much of the surrounding land, particularly in the northeast. The geology of the national park consists of a 625 km2 (241 sq mi) core of granite intruded during the early Permian period into a sequence of sedimentary rocks originating in the Devonian and Carboniferous periods. These rocks were faulted and folded, sometimes, intensely, during the Variscan orogeny. Thermal metamorphism has also taken place around the margins of the granite pluton altering the character of the sedimentary rocks whilst mineral veins were emplaced within the granite. A small outlier of Palaeogene sediments occurs on the eastern boundary of the national park.

References

  1. In the Tintagel and Camelford district the succession of strata is Tredorn phyllites, Trambley Cove beds, Volcanic series, Barras Nose beds, Woolgarden phyllites, Delabole slates, and Slaughterbridge beds (lowest); R. M. Barton (1964) An Introduction to the Geology of Cornwall. Truro: D. Bradford Barton; p. 89
  2. Enfield, M. A. [et al.] (1985) Structural and sedimentary evidence for the early tectonic history of the Bude and Crackington Formations, north Cornwall and Devon, Proceedings of the Ussher Society 6(2), 165-172.
  3. Henley, S. (1976) Rediscovery of a Granite Dyke at Perranporth, Cornwall, Transactions of the Royal Geological Society of Cornwall, XX(4), pp. 286-299
  4. Durrance, E. M. [et al.] (1982) Hydrothermal Circulation and Post-magmatic Changes in Granites of South-west England, Proceedings of the Ussher Society, 5(3), pp. 304-320
  5. Barton, D. B. (1963) A Guide to the Mines of West Cornwall. Truro: D. Bradford Barton, 52 pp.
  6. Clifton-Taylor, Alec (1970) "Building materials", in: Pevsner, N. Cornwall; 2nd ed. Harmondsworth: Penguin; pp. 29-34; p. 30
  7. Chandler, P. [et al.] (1984) A Gravity Survey of the Polyphant Ultrabasic Complex, East Cornwall, Proceedings of the Ussher Society 6(1), pp. 116-120

Bibliography

Further reading