A crag (sometimes spelled cragg, or in Scotland craig) is a rocky hill or mountain, generally isolated from other high ground.
Crags are formed when a glacier or ice sheet passes over an area that contains a particularly resistant rock formation (often granite, a volcanic plug or some other volcanic structure).
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.
[1] In older examples, or those latterly surrounded by the sea, the tail is often missing, having been removed by post-glacial erosion.
Examples of crag and tail formations include: This article related to topography is a stub.