Ailsa Craig, an isolated rocky islet of Ayrshire, Scotland, 10 m. off the coast at Girvan, and 25 m. S. S. W. of Ayr; lat. 55° 15' 12" N., lon. 5° 7' W. It is of conical shape, about two miles in circumference at the base, and rises 1,098 feet above the surface of the ocean. Its summit can only be gained on the E. side; the other sides are nearly perpendicular, two of them resembling in structure the columns of Fingal's cave. The top is covered with verdure, and is the resort of great numbers of sea birds, goats, and rabbits; and there are the ruins of an ancient three-story tower. The island is the property of the marquis of Ailsa, who takes his title from it.