In 7 atollon. [adoption of the native name atollon, atoll, applied to the Maldive Islands, which are typical examples of this structure; prob. = Malayalam aḍal ‘closing, uniting’ (Col. Yule).]
A coral island consisting of a ring-shaped reef enclosing a lagoon. Darwin’s theory, now generally accepted, is that the lagoon occupies the place of a submerged island.
1625. Purchas, Pilgrims, II. 1648. Every Atollon is separated from others, and contaynes in itselfe a great multitude of small Isles … Each of these Atollons are inuironed round with a huge ledge of rocks.
1832. Lyell, Princ. Geol., II. 285. In the centre of each atoll there is a lagoon from fifteen to twenty fathoms deep.
1859. Darwin, Orig. Spec., xii. (1873), 324. Such sunken islands are now marked by rings of coral or atolls standing over them.
b. Comb. and Attrib.
1842. Darwin, Coral Reefs, 107. An atoll-shaped bank of dead rock. Ibid., 169. True atoll-structure. Ibid. (1845), Voy. Nat., xx. 468. The foundations, whence the atoll-building corals sprang.
