ST. HELENA (hel-en'4), an island and British possession in the S. Atlantic, 15° 55' 26" S., 5° 42' 3o" W. (Ladder Hill Ob servatory). Area 47 sq.m., extreme length, south-west to north east 1o4 m., extreme breadth 8-4-. The island is wholly of volcanic origin, the activity being long extinct, whilst subaerial denudation has greatly modified it and marine erosion has formed perpendicu lar cliffs ft. high on the east, north and west sides. Its principal feature, a semi-circular ridge of mountains, with the culminating summit of Diana's peak (2,704 ft.), is the northern rim of a great crater; the southern rim having been breached hypothetically forms the centre of the ring. From the crater wall outwards water-cut gorges stretch in all directions, widening as they approach the sea into valleys, some of which are 1,000 ft. deep. These valleys contain small streams. Springs of pure water are abundant. Along the enclosing hillsides caves have been formed by the washing out of the softer rocks. The lavas are basalts, andesites, trachytes and phonolites ; there is much vol canic ash, tuff, scoriae, etc., and conspicuous features are formed by rocks, representing a late period of activity. Such features are Ass's Ears, Lot's Wife and the Chimney. There are several subsidiary craters. The only practicable landing-place is on the leeward side at St. James's bay. From the head of the bay a nar row valley extends for 1 miles. The greatest extent of level ground is in the north-east of the island, where are the Deadwood and Longwood plains, over 1,700 ft. above the sea.
Although the island is within the tropics its climate is healthy and temperate. This is due to the south-east trade-wind, and to the effect of the cold waters of the South Atlantic current. The temperature varies on the sea level from to in summer and to in winter. The higher regions are about cooler. The rainfall varies considerably.
2 m. wide, the home, for the most part, of the indigenous flora. Of 38 flowering plants all save Scirpus nodosus are peculiar to the island ; several indigenous plants are dying out. The indigenous flora shows affinities with African flora, but in recent years many species have become extinct. The exotic flora gives the island almost the aspect of a botanic garden. The oak, thoroughly naturalized, grows alongside of the bamboo and banana. Among other trees and plants are the common English gorse; Rubus pinnatus, Hypochaeris radicata, the Buddleia Madagascariensis; Physalis peruviana; the common castor-oil plant ; and the pride of India. The flax (Phormium tenax) has been introduced in recent years. The peepul is the principal shade tree in Jamestown, and in Jamestown valley the date-palm grows freely. Orange and lemon trees, once common, are scarce.
St. Helena has no indigenous vertebrate land fauna. The only land groups well represented are the beetles and the land shells. T. V. Wollaston, in Coleoptera Sanctae Helenae (1877), shows that out of a total list of 203 species of beetles are probably aborig inal and 128 peculiar to the individuality perhaps un equalled in the world. More than two-thirds are weevils and a vast majority wood-borers, a fact which bears out the tradition of forests having once covered the island. A South American white ant (Termes tennis, Hagen.), introduced from a slave-ship in 1840, soon became a plague at Jamestown. Practically every thing had to be rebuilt with teak or cypress. Fortunately it can not live in the higher parts of the island. Besides domestic animals the only land mammals are rabbits, rats and mice, the rats being especially abundant. Probably the only endemic land bird is the wire bird, Aegialitis sanctae Helenae; the averdevat, Java sparrow, cardinal, ground-dove, partridge (possibly the In dian chukar), pheasant and guinea-fowl are all common. There are no freshwater fish, beetles or shells. Of 65 species of sea fish caught 17 are peculiar to St. Helena; economically the more important kinds are gurnard, eel, cod, mackerel, tunny, bullseye, cavalley, flounder, hog-fish, mullet and skulpin.