198 THE OCEAN WORLD. 



New Caledonia, only two lengths of his ship from the reef, Captain 

 Kent found no bottom in 150 fathoms. This was verified at Gambier 

 Island in the Pacific Ocean, in Qualem Island, and at many others. 



According to Mr. Darwin, the barrier reef situated on the western 

 coast of New Caledonia is 400 miles long ; that along the eastern 

 coast of Australia extends almost without interruption for 1,000 

 miles, ranging from twenty or thirty to fifty or sixty miles from 

 the coast. As to the elevation of the islands thus surrounded 

 with reefs, it varies considerably. The Isle of Tahiti rises 6,800 

 feet above the level of the sea ; the Isle of Maurua to 600 ; Aituaki 

 to 300 ; and Manonai to about fifty feet only. 



Around the Isle of Gambier the reef has a thickness of 1,060 feet, 

 at Tahiti of 230. Round the Fiji Islands it is from 2,000 to 3,000. 



The fringing reefs immediately surrounding the island, or a 

 portion of it, might be confounded with the barrier reefs we have 

 been describing, if they only differed in their smaller breadth ; but the 

 circumstance that they abut immediately on the coast in place of 

 being separated by a channel or lagoon more or less deep and con- 

 tinuous, proves that they are in direct communication with the slope 

 of the submarine soil, and permits of their being distinguished from the 

 barrier reefs. The dangerous breakers which surround the Mauritius 

 are a striking example of the fringing reef. This island is almost 

 entirely surrounded by a barrier of these rocks, the breadth of which 

 varies from 150 to 330 feet ; their rugged and abrupt surface is worn 

 almost smooth, and is rarely uncovered at low water. Analogous 

 reefs surround the Isle of Bourbon ; all round this island the 

 polyps construct on the volcanic bottom of the sea detached masses, 

 which rise from a fathom to a fathom and a half above the water. 



Coral coasting reefs present themselves also on the eastern coast 

 of Africa and of Brazil. In the Red Sea, reefs of corals exist which may 

 be ranked among the coasting reefs, in consequence of the limited 

 breadth of the gulf. Ehrenberg and Hemprich examined 150 

 stations in the Red Sea, all of which had outlying fringing reefs of 

 this description. 



It may be asked, With what rapidity are these coral banks 

 formed, so as to become atolls and fringing reefs ? To answer this 

 question even approximately is very difficult. On the coast of the 

 Mauritius, according to M. d'Archiac,* one of the learned professors 



* " Cours de Paleontologie Stratigraphique." 



