100 HANDY BOOK OF 



islands, where Captain Fitzroy found no bottom with a line 

 of 7,200 feet, scarce a mile from land — it was formerly 

 believed that the Lithophytes built up their precipitous 

 walls from the depths of ocean; an opinion which is no 

 longer tenable, since Q,uoy and Gaymard, Ehrenberg, 

 Darwin, and other distinguished naturalists, have proved 

 that the depth at which the reef-forming Corallines can 

 exist (Astreae, Porites, Millepores, etc.), is, at the most, 

 twenty to thirty fathoms. 



Quoy and Gaymard, who accompanied the circumnavi- 

 gator Freycinet on board the Uranie frigate, have expressed 

 an opinion that the Corallines merely formed a proportion- 

 ally thin crust on the crest of submarine chasms of moun- 

 tains, or the circular edges of volcanoes ; and in this manner 

 explained, not only the remarkable appearance of the 

 Atolls, but also the precipitous descent beyond their rings. 

 But this theory has not stood the test of a more careful 

 investigation ; for no known crater has ever attained such 

 an expanse as, for instance, several Atolls in the Radack 

 Archipelago, one of which is thirty -two miles long and 

 twenty broad. 



Besides, the numerous volcanoes, on whose edges the 

 Atolls were afterwards formed, must have all approached 

 the surface to the slight depth in which the reef-forming 

 Coral varieties can alone exist : a supposition which is most 

 improbable ; for where on land can we find large and 

 broad mountain-chains whose elevations attain such an 

 altitude ? 



Further, the Corals do not grow higher than to the verge 

 of the lowest water-mark at ebb tide, or, at the most, four 

 to six inches above it ; and though the waves may pile up 

 loosened fragments to a height of thirty feet, still they 

 could not form Coral islands sixty feet in height, like 

 Tongataboo, or, as at Eua, elevate the reef three hundred 

 feet above the water-mark. 



But this fact the Quoy and Gaymardian theory took as 



