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 over many years, often centuries. It acquires distinguishing features, such a ...
or
ice sheet 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 un ...
, 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 ma ...
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 plat ...
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), de ...
(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 and
Arthur's Seat, 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, Sc ...
, in
North Berwick, Scotland
* Three in or near
Stirling, 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,
Northern Ireland
Northern Ireland ( ga, Tuaisceart Éireann ; sco, label=Ulster Scots dialect, Ulster-Scots, Norlin Airlann) is a part of the United Kingdom, situated in the north-east of the island of Ireland, that is #Descriptions, variously described as ...
, site of the
Scrabo Tower
*
Ailsa Craig, 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 th ...
continental shelf off
West Antarctica.
See also
*
Drumlin
A drumlin, from the Irish word ''droimnín'' ("littlest ridge"), first recorded in 1833, in the classical sense is an elongated hill in the shape of an inverted spoon or half-buried egg formed by glacial ice acting on underlying unconsolidated ...
*
Roche moutonnée
In glaciology, a roche moutonnée (or sheepback) is a rock formation created by the passing of a glacier. The passage of glacial ice over underlying bedrock often results in asymmetric erosional forms as a result of abrasion on the "stoss" (upstr ...
References
*
Holmes, Arthur, ''Principles of Physical Geology,'' Halsted, 1978, 3rd ed., pp 421 – 422
Glaciology
Glacial landforms
Erosion landforms
Mountains
*
*
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