A crag (sometimes spelled cragg, or in Scotland craig) is a rocky hill or mountain, generally isolated from other high ground.

Origin

Crags are formed when a

glacier A glacier (; ) is a persistent body of dense ice that is constantly moving under its own weight. A glacier forms where the accumulation of snow exceeds its Ablation#Glaciology, ablation over many years, often Century, centuries. It acquires dis ...

ice sheet In glaciology, an ice sheet, also known as a continental glacier, is a mass of glacial ice that covers surrounding terrain and is greater than . The only current ice sheets are in Antarctica and Greenland; during the Last Glacial Period at Las ...

passes over an area that contains a particularly resistant rock formation (often

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 undergro ...

, a

volcanic plug A volcanic plug, also called a volcanic neck or lava neck, is a volcanic object created when magma hardens within a vent on an active volcano. When present, a plug can cause an extreme build-up of high gas pressure if rising volatile-charged mag ...

or some other

volcanic A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most often found where tectonic plates a ...

structure). The force of the glacier erodes the surrounding softer material, leaving the rocky block protruding from the surrounding terrain. Frequently the crag serves as a partial shelter to softer material in the wake of the glacier, which remains as a gradual fan or ridge forming a tapered ramp (called the tail) up the leeward side of the crag. In older examples, or those latterly surrounded by the sea, the tail is often missing, having been removed by post-glacial erosion.

Examples

Examples of crag and tail formations include: * Castle Rock (the crag, site of

Edinburgh Castle Edinburgh Castle is a historic castle in Edinburgh, Edinburgh, Scotland. It stands on Castle Rock (Edinburgh), Castle Rock, which has been occupied by humans since at least the Iron Age, although the nature of the early settlement is unclear. ...

) and the

Royal Mile The Royal Mile () is a succession of streets forming the main thoroughfare of the Old Town of the city of Edinburgh in Scotland. The term was first used descriptively in W. M. Gilbert's ''Edinburgh in the Nineteenth Century'' (1901), des ...

(the tail), in

Edinburgh Edinburgh ( ; gd, Dùn Èideann ) is the capital city of Scotland and one of its 32 Council areas of Scotland, council areas. Historically part of the county of Midlothian (interchangeably Edinburghshire before 1921), it is located in Lothian ...

, Scotland *

Salisbury Crags Holyrood Park (also called the Queen's Park or King's Park depending on the reigning monarch's gender) is a royal park in central Edinburgh, Scotland about to the east of Edinburgh Castle. It is open to the public. It has an array of hills, loc ...

and

Arthur's Seat Arthur's Seat ( gd, Suidhe Artair, ) is an ancient volcano which is the main peak of the group of hills in Edinburgh, Scotland, which form most of Holyrood Park, described by Robert Louis Stevenson as "a hill for magnitude, a mountain in virtue ...

, in Edinburgh *

North Berwick Law North Berwick Law, sometimes abbreviated to Berwick Law, is a conical hill which rises conspicuously from the surrounding landscape (this is the definition of the Lowland Scots word "law"). It overlooks the East Lothian town of North Berwick, ...

, in

North Berwick North Berwick (; gd, Bearaig a Tuath) is a seaside town A seaside resort is a town, village, or hotel that serves as a vacation resort and is located on a coast. Sometimes the concept includes an aspect of official accreditation based on th ...

, Scotland * Three in or near

Stirling Stirling (; sco, Stirlin; gd, Sruighlea ) is a city in central Scotland, northeast of Glasgow and north-west of Edinburgh. The market town, surrounded by rich farmland, grew up connecting the royal citadel, the medieval old town with its me ...

, Scotland, including the rock on which

Stirling Castle Stirling Castle, located in Stirling, is one of the largest and most important castles in Scotland, both historically and architecturally. The castle sits atop Castle Hill, an intrusive crag, which forms part of the Stirling Sill geological ...

stands * "Scrabo Hill" in

Newtownards Newtownards is a town in County Down, Northern Ireland. It lies at the most northern tip of Strangford Lough, 10 miles (16 km) east of Belfast, on the Ards Peninsula. It is in the Civil parishes in Ireland, civil parish of Newtownard ...

Northern Ireland Northern Ireland ( ga, Tuaisceart Éireann ; sco, label= Ulster-Scots, Norlin Airlann) is a part of the United Kingdom, situated in the north-east of the island of Ireland, that is variously described as a country, province or region. Nort ...

, site of the

Scrabo Tower Scrabo Tower is a high 19th-century lookout tower or folly that stands on Scrabo Hill near Newtownards in County Down, Northern Ireland. It provides wide views and is a landmark that can be seen from afar. It was built as a memorial to Charle ...

Ailsa Craig Ailsa Craig (; sco, Ailsae Craig; gd, Creag Ealasaid) is an island of in the outer Firth of Clyde, west of mainland Scotland, upon which microgranite has long been quarried to make curling stones. The now-uninhabited island comprises the r ...

, famous for curling stone mining * Crag and tail features have been identified on the

Amundsen Sea The Amundsen Sea, an arm of the Southern Ocean off Marie Byrd Land in western Antarctica, lies between Cape Flying Fish (the northwestern tip of Thurston Island) to the east and Cape Dart on Siple Island to the west. Cape Flying Fish marks the ...

continental shelf off

West Antarctica West Antarctica, or Lesser Antarctica, one of the two major regions of Antarctica, is the part of that continent that lies within the Western Hemisphere, and includes the Antarctic Peninsula. It is separated from East Antarctica by the Transant ...

References

Holmes, Arthur Arthur Holmes (14 January 1890 – 20 September 1965) was an English geologist who made two major contributions to the understanding of geology. He pioneered the use of radiometric dating of minerals, and was the first earth scientist to grasp ...

, ''Principles of Physical Geology,'' Halsted, 1978, 3rd ed., pp 421 – 422 Glaciology Glacial landforms Erosion landforms Mountains * * {{glaciology-stub

Origin

Examples

See also

References