1836.] BARRIER-REEFS. 469 



a broad and rather deep channel of water, analogous to the 

 lagoon within an atoll. It is remarkable how little attention 

 has been paid to encircling ba rrier- reefs ; yet they are truly 

 wonderful structures. The following sketch represents part of 



the barrier encircling the island of Bolabola in the Pacific, as 

 3een from one of the central peaks. In this instance the whole line 



of reef has been converted into land ; but usually a snow-white line 

 of great breakers, with onlj here and there a single low islet 

 crowned with cocoa-nut trees, divides the dark heaving waters 

 of the ocean from the light-green expanse of the lagoon-channel. 

 And the quiet waters of this channel generally bathe a fringe of 

 low alluvial soil, loaded with the most beautiful productions of 

 the tropics, and lying at the foot of the wild, abrupt, central 

 mountains. 



Encircling barrier-reefs are of all sizes, from three miles to 

 no less than forty-four miles in diameter ; and that which fronts 

 one side, and encircles both ends, of New Caledonia, is 400 miles 

 long. Each reef includes one, two, or several rocky islands of 

 various heights ; and in one instance, even as many as twelve 

 separate islands. The reef runs at a greater or less distance 

 from the included land ; in the Society archipelago generally 

 from one to three or four miles ; but at Hogoleu the reef is 

 20 miles on the southern side, and 14 miles on the opposite 

 or northern side, from the included islands. The depth within 

 the lagoon-channel also varies much ; from 10 to 30 fathoms 

 may be taken as an average ; but at Vanikoro there are spaces no 

 less than 56 fathoms or 336 feet deep. Internally the reef either 

 slopes gently into the lagoon-channel, or ends in a pprpendicular 



