Crag (a Celtic word, cf. Gaelic creag, Manx creg, and Welsh and modern Scots craig), a steep rock. The word appears in many place-names in the north of England and in Scotland, and is also connected with 'carrick', a word of similar meaning, also found in place-names. In geology the term is applied to the strata in which a shelly sand deposit is found, and, in the expression 'crag and tail', to a formation of hills, in which one side is precipitous and lofty and the other slopes or 'tails' gradually away, as in the Castle Rock in Edinburgh.
Being the entry for CRAG in the 1911 Encyclopedia Britannica, the text of which lies within the public domain.