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A tor, which is also known by
geomorphologist Geomorphology (from Ancient Greek: , ', "earth"; , ', "form"; and , ', "study") is the scientific study of the origin and evolution of topographic and bathymetric features created by physical, chemical or biological processes operating at or ...
s as either a castle koppie or kopje, is a large, free-standing rock
outcrop An outcrop or rocky outcrop is a visible exposure of bedrock or ancient superficial deposits on the surface of the Earth. Features Outcrops do not cover the majority of the Earth's land surface because in most places the bedrock or superficia ...
that rises abruptly from the surrounding smooth and gentle slopes of a rounded hill
summit A summit is a point on a surface that is higher in elevation than all points immediately adjacent to it. The topographic terms acme, apex, peak (mountain peak), and zenith are synonymous. The term (mountain top) is generally used only for a m ...
or
ridge A ridge or a mountain ridge is a geographical feature consisting of a chain of mountains or hills that form a continuous elevated crest for an extended distance. The sides of the ridge slope away from the narrow top on either side. The line ...
crest. In the South West of England, the term is commonly also used for the hills themselves – particularly the high points of Dartmoor in
Devon Devon ( , historically known as Devonshire , ) is a ceremonial and non-metropolitan county in South West England. The most populous settlement in Devon is the city of Plymouth, followed by Devon's county town, the city of Exeter. Devo ...
and
Bodmin Moor Bodmin Moor ( kw, Goon Brenn) is a granite moorland in north-eastern Cornwall, England. It is in size, and dates from the Carboniferous period of geological history. It includes Brown Willy, the highest point in Cornwall, and Rough Tor, a sl ...
in
Cornwall Cornwall (; kw, Kernow ) is a Historic counties of England, historic county and Ceremonial counties of England, ceremonial county in South West England. It is recognised as one of the Celtic nations, and is the homeland of the Cornish people ...
.Ehlen, J. (2004) ''Tor'' in Goudie, A., ed., pp. 1054-1056. ''Encyclopedia of Geomorphology.'' Routledge. London, England.


Etymology

Although English topographical names often have a
Celtic Celtic, Celtics or Keltic may refer to: Language and ethnicity *pertaining to Celts, a collection of Indo-European peoples in Europe and Anatolia **Celts (modern) *Celtic languages **Proto-Celtic language *Celtic music *Celtic nations Sports Foo ...
etymology, the
Oxford English Dictionary The ''Oxford English Dictionary'' (''OED'') is the first and foundational historical dictionary of the English language, published by Oxford University Press (OUP). It traces the historical development of the English language, providing a c ...
lists no
cognate In historical linguistics, cognates or lexical cognates are sets of words in different languages that have been inherited in direct descent from an etymological ancestor in a common parent language. Because language change can have radical ef ...
s to the Old English word in either the Breton or
Cornish language Cornish (Standard Written Form: or ) , is a Southwestern Brittonic language of the Celtic language family. It is a revived language, having become extinct as a living community language in Cornwall at the end of the 18th century. However, ...
s (the
Scottish Gaelic Scottish Gaelic ( gd, Gàidhlig ), also known as Scots Gaelic and Gaelic, is a Goidelic language (in the Celtic branch of the Indo-European language family) native to the Gaels of Scotland. As a Goidelic language, Scottish Gaelic, as well as ...
''tòrr'' is thought to derive from the Old English word). It is therefore accepted that the English word ''Tor'' derives from the
Old Welsh Old Welsh ( cy, Hen Gymraeg) is the stage of the Welsh language from about 800 AD until the early 12th century when it developed into Middle Welsh.Koch, p. 1757. The preceding period, from the time Welsh became distinct from Common Brittonic ...
word ''tẁrr'' or ''twr'', meaning a cluster or heap.


Formation

Tors are landforms created by the
erosion Erosion is the action of surface processes (such as water flow or wind) that removes soil, rock, or dissolved material from one location on the Earth's crust, and then transports it to another location where it is deposited. Erosion is d ...
and
weathering Weathering is the deterioration of rocks, soils and minerals as well as wood and artificial materials through contact with water, atmospheric gases, and biological organisms. Weathering occurs '' in situ'' (on site, with little or no movement ...
of rock; most commonly
granite Granite () is a coarse-grained ( phaneritic) intrusive igneous rock composed mostly of quartz, alkali feldspar, and plagioclase. It forms from magma with a high content of silica and alkali metal oxides that slowly cools and solidifies un ...
s, but also
schist Schist ( ) is a medium-grained metamorphic rock showing pronounced schistosity. This means that the rock is composed of mineral grains easily seen with a low-power hand lens, oriented in such a way that the rock is easily split into thin flakes ...
s,
dacite Dacite () is a volcanic rock formed by rapid solidification of lava that is high in silica and low in alkali metal oxides. It has a fine-grained ( aphanitic) to porphyritic texture and is intermediate in composition between andesite and rhyo ...
s,
dolerite Diabase (), also called dolerite () or microgabbro, is a mafic, holocrystalline, subvolcanic rock equivalent to volcanic basalt or plutonic gabbro. Diabase dikes and sills are typically shallow intrusive bodies and often exhibit fine-grain ...
s,
ignimbrite Ignimbrite is a type of volcanic rock, consisting of hardened tuff. Ignimbrites form from the deposits of pyroclastic flows, which are a hot suspension of particles and gases flowing rapidly from a volcano, driven by being denser than the surro ...
s, coarse
sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicat ...
s and others. Tors are mostly less than high. Many
hypotheses A hypothesis (plural hypotheses) is a proposed explanation for a phenomenon. For a hypothesis to be a scientific hypothesis, the scientific method requires that one can test it. Scientists generally base scientific hypotheses on previous obse ...
have been proposed to explain their origin and this remains a topic of discussion among
geologist A geologist is a scientist who studies the solid, liquid, and gaseous matter that constitutes Earth and other terrestrial planets, as well as the processes that shape them. Geologists usually study geology, earth science, or geophysics, althou ...
s and
geomorphologist Geomorphology (from Ancient Greek: , ', "earth"; , ', "form"; and , ', "study") is the scientific study of the origin and evolution of topographic and bathymetric features created by physical, chemical or biological processes operating at or ...
s, and
physical geographers Physical may refer to: * Physical examination, a regular overall check-up with a doctor * ''Physical'' (Olivia Newton-John album), 1981 ** "Physical" (Olivia Newton-John song) * ''Physical'' (Gabe Gurnsey album) * "Physical" (Alcazar song) (2004) * ...
. It is considered likely that tors were created by
geomorphic processes Geomorphology (from Ancient Greek: , ', "earth"; , ', "form"; and , ', "study") is the scientific study of the origin and evolution of topographic and bathymetric features created by physical, chemical or biological processes operating at or ...
that differed widely in type and duration according to regional and local differences in climate and rock types. Twidale, C. R., and Romani, J. R. V. (2005) ''Landforms and Geology of Granite Terrains.'' A. A. Balkema Publishers Leiden, The Netherlands. 359 pp. For example, the
Dartmoor granite Dartmoor is an upland area in southern Devon, England. The moorland and surrounding land has been protected by National Park status since 1951. Dartmoor National Park covers . The granite which forms the uplands dates from the Carboniferous P ...
was emplaced around 280 million years ago. When the cover rocks eroded away it was exposed to chemical and physical
weathering Weathering is the deterioration of rocks, soils and minerals as well as wood and artificial materials through contact with water, atmospheric gases, and biological organisms. Weathering occurs '' in situ'' (on site, with little or no movement ...
processes. Where
joint A joint or articulation (or articular surface) is the connection made between bones, ossicles, or other hard structures in the body which link an animal's skeletal system into a functional whole.Saladin, Ken. Anatomy & Physiology. 7th ed. McGraw- ...
s are closely spaced, the large crystals in the granite readily disintegrate to form a sandy
regolith Regolith () is a blanket of unconsolidated, loose, heterogeneous superficial deposits covering solid rock. It includes dust, broken rocks, and other related materials and is present on Earth, the Moon, Mars, some asteroids, and other terrestr ...
known locally as ''growan''. This is readily stripped off by solifluction or surface wash when not protected by vegetation, notably during prolonged cold phases during the
Quaternary ice age The Quaternary ( ) is the current and most recent of the three periods of the Cenozoic Era in the geologic time scale of the International Commission on Stratigraphy (ICS). It follows the Neogene Period and spans from 2.58 million ye ...
s – periglaciation. Where joints happen to be unusually widely spaced, core blocks can survive and remain above the weathering surface, developing into tors. These can be monolithic, as at Haytor and Blackingstone Rock, but are more usually subdivided into stacks, often arranged in avenues. Each stack may include several tiers or ''pillows'', which may become separated: rocking pillows are called logan stones. These stacks are vulnerable to frost action and often collapse leaving trails of blocks down the slopes called ''clitter'' or ''clatter''. Weathering has also given rise to circular "rock basins" formed by the accumulation of water and repeated freezing and thawing. An example is found at Kes Tor on Dartmoor. Dating of 28 tors on Dartmoor showed that most are surprisingly young, less than 100,000 years of surface exposure, with none over 200,000 years old. They probably emerged at the start of the last major ice age ( Devensian). By contrast the Scottish Cairngorms, which is the other classic granite tor concentration in Britain, the oldest tors dated are between 200 and 675 thousand years of exposure, with even glacially-modified ones having dates of 100–150,000 years.Adrian Hall
"New perspectives on a classic landscape of selective linear glacial erosion"
''The history of the Cairngorms: granite, landscape and processes''.
British Geological Survey The British Geological Survey (BGS) is a partly publicly funded body which aims to advance geoscientific knowledge of the United Kingdom landmass and its continental shelf by means of systematic surveying, monitoring and research. The BGS hea ...


See also

* * * * *


References


Further reading

* {{Commons category, Tors Rock formations Weathering landforms