CRAG, a steep rock. The word (of Celtic origin, cf. Gael. creag, Manx Greg, and Welsh and Modern Scots craig) appears in many place-names in north Britain, and is probably connected with "carrick," of similar meaning, which also occurs in place-names. In geology, the term is applied to strata in which a shelly sand deposit is found, and, in the expression "crag and tail," to a gla ciated land form in which one side of a hill is precipitous and lofty and the other slopes or "tails" gradually away, as in the Castle Rock on which Old Town Edinburgh was built.