[30 CORALS AND CORAL ISLANDS. 



II. STRUCTURE OF CORAL ISLANDS. 

 I. FORMS AND GENERAL FEATURES. 



Coral islands resemble the reefs just described, except that 

 a lake or lagoon is incircled instead of a mountainous islands. 

 A narrow rim of coral reef, generally but a few hundred yards 

 wide, stretches around the inclosed waters. In some parts 

 the reef is so low that the waves are still dashing over it into 

 the lagoon ; in others it is verdant with the rich fohage of the 

 tropics. The coral-made land, when highest, is seldom more 

 than ten or twelve feet above high tide. 



When first seen from the deck of a vessel, only a series of 

 dark points is descried just above the horizon. Shortly after 

 the points enlarge into the plumed tops of cocoa-nut-trees, and 

 a line of green, interrupted at intervals, is traced along the 

 water's surface. Approaching still nearer, the lake and its belt 

 of verdure are spread out before the eye, and a scene of more 

 interest can scarcely be imagined. The surf, beating loud and 

 heavy along the margin of the reef, presents a strange contrast 

 to the prospect beyond, — the white coral beach, the massy 

 foliage of the grove, and the embosomed lake with its tiny 

 islets. The colour of the lagoon water is often as blue as the 

 ocean, although but ten or twenty fathoms deep ; yet shades 

 of green and yellow are intermingled, where patches of sand 

 or coral-knolls are near the surface ; and the green is a delicate 

 apple shade, quite unlike the ordinary muddy tint of shallow 

 waters. 



The belt of verdure, though sometimes continuous around 

 the lagoon, is usually broken into islets separated by varying 

 intervals of bare reef; and through one or more of these 

 intervals a ship-channel often exists opening into the lagoon. 

 The larger coral islands are thus a string of islets along a line 

 of reef 



These lagoon islands are called atolls^ a word of Maldive 

 origin. The king of the Maldives bears the high-sounding 



