CRAG (a Celtic word, cf. Gael. 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.
Note - this article incorporates content from Encyclopaedia Britannica, Eleventh Edition, (1910-1911)