478 THE TKOPICAL WORLD. 



a great portion of which has sunk beneath the waters, and these islands are but the 

 peaks and tuble-hinds of that lost continent. The other theory is that these islands 

 have been for unknown ages, and now are, slowly being lifted up from the depths 

 below. Both theories rest upon so wide an induction of facts that both must be 

 accepted as true ; or rather as parts of the one great truth, that the crust of the earth 

 which we are wont to consider so firm and stable is now, as it always has been, rising 

 and falling, as truly as the surface of the water rises and falls by the attraction of the 

 sun and moon ; only that these periodic changes are measured by ages instead of by 

 hours. Who shall say that in the higher knowledge which we shall gain during the 

 ao'cs of the future wc may not attain to the understanding that the rise and sinking of con- 

 tinents is like tliat of the tides governed by law, and that we may not be able to express 

 in fio-ures, which will then be quite finite to us. though now seeming infinite, the 

 years that have elapsed since when " in the beginning heaven and earth rose out of 

 chaos ?" 



Volcanic islands are found in all oceans. Iceland has its Heckla, Sicily its Etna, 

 Hawaii its Mauna Kea and Mauna Loa, Niphon its Fusiyama. From Sumatra, Java, 

 and Sumbawa, Ternate and Tidore, Borneo, Celebes, and Gilolo, close by the equator,' 

 thence northward and north-westward to the Kurile Islands, hard by the frozen coast 

 of Kamchatka, is one great belt of volcanic islands, spreading out like a fan through 

 Polynesia. But in the tropical seas, and there alone, are coralline islands, built up, 

 grain by grain, by minute living beings. 



The simplest form of these coral islands is a ring enclosing a portion of the ocean. 

 Sometimes this ring is barely two miles in diameter ; sometimes it reaches a hundred 

 miles, rising only a half-score of feet above the level of the water, and owing to the 

 convexity of the surface of the ocean invisible from the deck of a ship at a distance of 

 a mile or two. unless they happen to be covered with tall palms or pandanus. The 

 roar of the surf dashing upon their windward side is often heard long before the island 

 itself comes into view. Un the outer side this ring, or atoll, slopes gradually for a 

 hundred yards or more, to a deptli of twenty-five fathoms, and then plunges sheer 

 down into the waters with a descent more rapid than the cone of any volcano. At a 

 distance of five hundred yards no bottom has been reached with a sounding line of a 

 mile and a half in length. All below the surface of the water to the depth of 100 

 feet is alive, all above and below this section dead, for the coral insect can live only 

 within this range. 



Those atolls assume every form and condition. Sometimes they are solitary specks 

 in the waste of waters. Oftener they occur in groups. The Caroline Archipelago 

 has sixty groups extending over a space of a thousand square miles. Sometimes a 

 group of atolls becomes partially joined into one, the irregular ring encircling an 

 island-studded lagoon, with openings through which a ship may enter. Sometimes 

 these coral formations take the foim of lonjj reefs borderinnr an extensive coast. Such 

 a reef runs parallel to the coast of Malabar for nearly five hundred miles. It consists 

 of a series of atolls arranged in a double row, separated by a sea whose depths no line 

 has sounded ; yet from outer to inner edge of the double row is a space of but fifty 

 miles. Such a broken coral reef often girdles a volcanic island. Tahiti, the largest 

 of the Society group, is a fine example of this kind. The island rises in mountains 

 7,000 feet high, with only a narrow plain along the shore. The lagoon which encora- 



