Page:Ballantyne--The Coral Island.djvu/313

 "The islands of the Pacific," said our friend, "are of three different kinds or classes. Those of the first class are volcanic, mountainous, and wild; some shooting their jagged peaks into the clouds at an elevation of ten and fifteen thousand feet. Those of the second class are of crystallized limestone, and vary in height from one hundred to five hundred feet. The hills on these are not so wild or broken as those of the first class, but are richly clothed with vegetation, and very beautiful. I have no doubt that the Coral Island on which you were wrecked was one of this class. They are supposed to have been upheaved from the bottom of the sea by volcanic agency, but they are not themselves volcanic in their nature, neither are they of coral formation. Those of the third class are the low coralline islands usually having lagoons of water in their midst; they are very numerous.

"As to the manner in which coral islands and reefs are formed; there are various opinions on this point. I will give you what seems to me the most probable theory,—a theory, I may add, which is held by some of the good and scientific missionaries. It is well known that there is much lime in salt water; it is also known that coral is composed of lime. It is supposed that the polypes, or coral insects, have the power of attracting this lime to their bodies; and with this material they build their little cells or habitations. They choose the summit of a volcano, or the top of a submarine mountain, as a foundation on which to build; for it is found that they never work at any great depth below the surface. On this they work; the polypes on the mountain top, of course, reach the surface first, then those at the outer edges reach the top sooner than the others between them and the centre, thus forming the coral reef surrounding the lagoon of water