WORLD'S WONDERS. 39 



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 bo- 

 fore the island itself comes into view. On the outer side this 

 ring, or atoll, slopes gradually for a hundred yards or more, to 

 a depth 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 one hundred 

 feet is alive ; all above and below this section dead, for the coral 

 insect can live only within this range. 



These 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 1,000 square miles. Some- 

 times a group of atolls becomes partially joined into one, 

 the irregular ring encircling an island-studded lagoon, with open- 

 ings through which a ship may enter. Sometimes these coral 

 formations take the form of long reefs bordering an extensive 

 coast. Such a reef runs parallel to the coast of Malabar for 

 nearly 500 miles. It consists of a series of atolls arranged in a 

 double row, separated by a sea whose depth 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 inland. 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 encompasses it like a great moat 

 is thirty fathoms deep, and is shut out from the ocean by a coral 

 band at a distance of from half a mile to three miles. 



