AILSA

CRAIG  , an island rock at the mouth of the Firth of Clyde, ro m . W. of Girvan, Ayrshire, Scotland . It is of conoidai form, with an irregular elliptic base, and rises abruptly to a height of 1114 ft . The only side from which. the rock can be ascended is the east; the other sides being for the most part perpendicular, and generally presenting lofty columnar forms, though not so regular as those of Staffa . This island is composed of micro-granite with riebeckite, of great interest on account of the rare occurrence of this type in Britain . It is comparatively fine-grained' and of a greyish colour . Its essential constituents are felspar, quartz and riebeckite—a soda amphibole . The last of these minerals occurs in small irregular patches between the idiomorphic felspars which Dr J . J . H . Teall has found to be a soda orthoclase . The rock is allied to paisanite described by C .

A . Osann and has been termed ailsite by

Professor M . F . Heddle . It forms part of an intrusive mass which, on the south and west cliffs of the island, has a columnar arrangement and is traversed by dykes of dolerite, most of which run in a north-west direction . The age of this mass is uncertain, as its relations to other rocks are not visible in the island . As riebeckitegranophyre has been found in Skye it may be of Tertiary age . The rock is a favourite material for curling-stones, about three-fourths (according to estimate) of those in use in the countries where the game obtains being made of it . On this account curling-stones are popularly known as " Ailsas " or " Ailsa Craigs." A columnar cave exists towards the northern side of the island, and on the eastern are the remains of a tower, with several vaulted rooms . Two springs occur and some scanty grass affords subsistence to rabbits, and, on the higher levels, to goats . The precipitous parts are frequented by large flocks of solan geese and other sea birds . The lighthouse on the southern side shows a flashing light visible for 13 m .

In 1831 the twelfth

earl of Cassillis became first marquis of Ailsa, takingthe title from the Craig, which was his property . When John Keats was in Girvan during his Scottish tour in 1818 he apostrophized the rock in a fine sonnet .