May be simply described as a tract of land entirely surrounded with water; but the whole continuous land of the Old World forms one island, and the New World another; while canals across the isthmuses of Suez and Panama would make each into two. The term properly only applies to smaller portions of land; and Australia, Madagascar, Borneo, and Britain are among the larger examples. Their materials and form are equally various, and so is their origin; some having evidently been upheaved by volcanic eruption, others are the result of accretion, and still more revealing by their strata that they were formerly attached to a neighbouring land. The sudden emergence of Sabrina, in the Atlantic, has occasioned wonder in our own day. So has that of Graham's Island, near the south coast of Sicily; and the Archipelago is daily at work.