The islands of volcanic origin are more or less circular in outline; are
usually considerably elevated, with rapid slopes; and are of moderate
size. Sometimes two or more volcanoes, clustered together, form a single
island of larger size and more irregular outline.
Occasional islands rise but little above the surface of the sea, their
craters being filled by sea water. Many, however, rise to Alpine
heights--like the peaks of Hawaii, in the Hawaiian Islands, nearly
fourteen thousand feet in elevation; Pico de Teyde, in the Canaries,
fourteen thousand feet; and Tahiti, in the Society Islands, over seven
thousand feet above the level of the sea.