Tor

This article is about a geological formation. For other uses, see Tor (disambiguation).

Birch Tor, on Dartmoor

A tor is a large, free-standing residual mass (rock outcrop) that rises abruptly from the surrounding smooth and gentle slopes of a rounded hill summit or ridge crest. In the South West of England, where the term originated, it is also a word used for the hills themselves – particularly the high points of Dartmoor in Devon and Bodmin Moor in Cornwall.

Name

Mushroom-shaped tors on Colonels Mountain (New Brunswick), Canada (IR Walker 1986)

The word tor (Cornish tor, Old Welsh twrr, Modern Welsh tŵr, Scots Gaelic tòrr), meaning hill, is notable for being one of the very few Celtic loanwords to be borrowed into vernacular English before the modern era – such borrowings are mainly words of a geographic or topographical nature. Similar words include crag (from the Welsh word craig, meaning "rock") and avon (from the Welsh word afon, meaning "river").

Formation

Tors are usually composed of granite or metamorphic rocks, but they can also develop in volcanic rocks and occasionally other hard rocks such as quartzite. They are the result of millions of years of weathering.

For example the Dartmoor granite was emplaced around 280 million years ago and as it cooled it contracted leaving a multitude of mainly vertical cracks; these facilitated hydrothermal circulation which both chemically altered the rock surrounding the cracks and deposited minerals in them. The rocks that overlaid the granite pluton were eroded quickly (in geological terms) and the consequent release of pressure caused the formation of sub-horizontal joints which tended to follow the shape of the land and which started the separation of the upper part of the pluton into blocks of varying sizes.

Further chemical attack by circulating water and later by acidic rainwater caused further weathering along the lines of these joints, resulting in the more or less complete decomposition of the granite into its constituent crystals in regions where the joints were closely spaced. Finally during the ice age the majority of the rotted granite was stripped away and the freeze-thaw cycle levered away larger blocks, leaving them scattered around the now-exposed tors as clitter, where they have provided ready building materials for thousands of years. Eventually the granite is weathered down to a level equivalent to sandy gravel, known as growan, which consists of individual crystals.

Weathering has also given rise to circular "rock basins'" formed by the accumulation of water and the repeated freezing and thawing – a fine example is to be found at Kes Tor on Dartmoor.

Tors on Dartmoor

For more details on Dartmoor's tors, see List of Dartmoor tors and hills.

Panorama of some of Dartmoor's tors in the snow

Dartmoor represents one of the largest areas of exposed granite in the United Kingdom, covering an area of 368 square miles (954 square kilometres). It is part of a chain of granite stretching through Cornwall, as far as the Isles of Scilly.

Some of the more durable granite survived to form the rocky crowns of Dartmoor tors. One of the best known is at Haytor, on the eastern part of the moor, whose granite is of unusually fine quality and was quarried from the hillside below the tor during the 19th and early 20th centuries. Its stone was used to construct the pillars outside the British Museum in London, and to build London Bridge (now in Arizona). The last granite to be quarried there was used to build Exeter War Memorial in 1919.

Ten Tors is an annual weekend hike on Dartmoor.

Hawk's Tor, Bodmin Moor, Cornwall

Other tors

United Kingdom

• Back Tor, Derwent Edge (538m)
• Cow and Calf, Ilkley Moor in West Yorkshire. Made from Millstone Grit.
• Dovestone Tor, Derwent Edge (505m)
• Glastonbury Tor
• Great Tor, Bamford, Peak District
• Hawk's Tor, Bodmin Moor, Cornwall

Higger Tor in the Peak District

• Helman Tor, mid–Cornwall
• Higger Tor (384m) and Over Owler Tor (375m) in the Peak District
• Howshaw Tor, overlooking Sheffield
• Ladybower Tor, Upper Derwent Valley
• Low tor
• Mam Tor (517m)
• Shining Tor
• Stiperstones, Shropshire Hills
• Whinstone Lee Tor
• White Tor, Derwent Moors (487m)
• The Barns of Bynack, Granite tors on Bynack More in the Cairngorms
• The Salt Cellar, Gritstone tor on Derwent Edge in the Peak District
• Tor Bay, one of the sandy beaches near Oxwich Bay on the Gower Peninsula in south Wales, so-called because the beach is framed by a huge outcrop of carboniferous limestone.
• Tor Heard, Long Whatton
• Tor Raynor Broomhill, Sheffield

Externsteine, Germany

Germany

• Externsteine in the Teutoburg Forest, North Rhine-Westphalia
• Greifensteine in the Ore Mountains of Saxony
• Großer Waldstein in the Fichtelgebirge mountains of Bavaria
• Heinrichshöhe and Hohneklippen in the Harz mountains of central Germany
• Wolfenstein in Bavaria

North America

Part of the Angel Rocks formation in Alaska

• Angel Rocks and Granite Tors, Chena River State Recreation Area, Alaska
• Elephant Rocks in Missouri
• Apache Leap Formation in Superior, Arizona

Africa

Kit-Mikayi, a celebrated tor near Kisumu, Kenya

• Kit-Mikayi, Kenya

See also

• List of peaks of the Peak District
• The book Red Shift (novel) the Mow Cop Tor at the centre of its plot.

Further reading

• Mercer, Ian (2009). "The Physical Anatomy of Dartmoor". Dartmoor - A Statement of its Time. London: Collins. pp. 30–78. ISBN 978-0-00-718499-6.