Staffa, a small uninhabited island of Scotland, one of the inner Hebrides, Argyleshire, about 8 m. W. of Mull. It is irregularly elliptical, about 1½ m. in circumfcreiice. Its surface is an uneven plateau, elevated from 50 to 144 ft. above the sea. It is covered with a rich soil and luxuriant grass, and is pastured by black cattle. The upper rock is composed of a shapeless basaltic mass, with occasional small columns, resting upon a columnar basalt, hard, grayish black, compact, and of perfectly regular forms, which has for its foundation a conglomerate trap or tufa. This columnar basalt, strongly resembling architectural designs, is indented with numerous caves, of which the most remarkable is that known as Fingal's cave. (See Fingal's Cave.) The other principal caves are the Boat cave, the Cormorant cave, so called from the number of these birds which visit it, and the Clam Shell cave, which derives its name from the peculiar form in which the basaltic columns are inclined, giving it the appearance of a shell of the genus pecten; it is 30 ft. high, 16 to 18 ft. broad, and 130 ft. long. Buachaille or the Herdsman is a conical pile of columns rising 30 ft. above the water, and resting on a bed of horizontal columns over which the high tide rises.

Between the Herdsman and Fingal's cave stretches the Great Causeway, formed by the ends of hexagonal upright columns.