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 Paléontologie Stratigraphique.” 
