586 



FORMATION OF CORAL REEFS. 



[Ch. XLIX. 



centres. 



The largest was 30 



miles in diameter, and the 

 smallest less than a mile. All were increasing their dimen- 

 sions by the active operations of the lithophytes, which ap- 

 peared to be gradually extending and bringing the immersed 



Fig. 154. 



a, &. 

 .6, 6'. 



d, d. 



Section of part of a Coral Island, 



Habitable part of the island. 



Slope of the side of the island, plnnging at an angle of forty -five to the depth of 

 fifteen hundred feet. 



Part of the lagoon. 



Knolls of coral in the lagoon, with overhanging masses of coral resembling the 

 capitals of columns. 



parts of their structure to the surface. The scene presented 

 by these annular reefs is equally striking for its singularity 

 and beauty. A strip of land a few hundred yards wide is 

 covered by lofty cocoa-nut trees, above which is the blue 

 vault of heaven. This band of verdure is bounded by a beach 



mar 



cled with a ring of snow-white breakers, beyond which are 

 the dark heaving waters of the ocean. The inner beach en- 

 closes the stiU clear water of the lagoon, resting in its greater 

 part on white sand, and when illuminated by a vertical sun, 



Certain species of zoophytes abound 



most ,.,.^ t- 



most in the lagoon^ others on the exterior margin, where 

 there is a great surf. ' The ocean/ says Mr. Darwin, ' throw- 

 ing its breakers on these outer shores, appears an invincible 



means 



^hich 



N'o 



of repose are granted, and the long swell caused by the steady 

 action of the trade wind never ceases. The breakers exceed 

 in violence those of our tem]3erate regions, and it is impos- 



s 



sible to behold them without feeling a conviction that rock 



Itimately yield and be demolished 

 Yet these low insignificant coral 



by such irresistible forces. 



islets stand and are victorious, for here another power, as 



antagonist to the former 



the contest. The 



organic forces separate the atoms of carbonate of lime one by 



* Darwin's Journal, &c.; p. 540, and new edit., of 1845, p. 453. 



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