On the Formation and Growth of Coral Reefs and Islands. 47 



break, in the ring of coral occurs, forming an entrance into the lagoon, and 

 thus enabling ships to enter, in which cases they form commodious and 

 safe harbours. 



The reefs and banks of coral not yet above the level of the water, are 

 exceedingly numerous ; we have seen lists of more than a hundred, not to 

 be found in any published chart j these lists are handed on from one cap- 

 tain to another, whose business carries them to the seas of the Pacific. 



The height above the level of the ocean seldom exceeding four or five 

 feet, it often happens that the sea breaks over with great violence at the 

 windward side of the island. 



It is not unusual to see, during a strong easterly wind, the waves of the 

 ocean forced against the abrupt barrier of coral ; where the surf, towering 

 in one vast sheet of water to an immense height, would fall within the 

 lagoon in form of a shower, exhibiting all the iris colours of the rainbow ; 

 and thus, by the continued overflow at the windward side, and by the rush 

 of water upon the ebb tide, through the leeward opening, in this way pre- 

 venting the growth of the corals, is the entrance kept open. But there can 

 be little doubt, that in a series of years tlie increase on the weather side, 

 will form a perfect breakwater ; and then, from the quiescent state of the 

 water within the lagoon, the leeward opening will be choked by the growth 

 of coral, and the fresh supply of water by the flood tides cut off. Evapo- 

 ration going on, salt would be deposited, the zoophytes of the lagoon would 

 lose their vitality ; and at this period a perfectly new order of things 

 would commence, the subsequent formations being deposited horizontally 

 and filling up the vast basin which would then bear some slight analogy to 

 the coal basins of this district, or the more recent basins of London and 

 Paris. 



That many of these islands have actually arrived at this state, is known 

 to navigators ; in these the lagoon is perfect, the ring of reef having no 

 visible opening ; the water, which is accumulated within the lagoon by 

 'the spray dashing over the windward edge, finds the level of the surround- 

 ing ocean, by percolation through the sides of the basin. 



Confining the assertion to the corals before mentioned, because we 

 are aware, that a few genera of Lamarck's second and fourth orders 

 have been found to inhabit great depths, we believe it will not be 

 found that corals commence their growth or origin, at a greater depth 

 than fifteen or twenty fathoms. Quoy and Gaimard, who accompanied 

 Capt. Freycinet, say indeed twenty or thirty feet. 



This assertion is in opposition to a statement of Lamoroux's, a na- 

 turalist, whose name stands most deservedly pre-eminent, from the value 

 of his investigations with regard to the ])articular subject before us. 



He Bays, in a prefatory address appended to his Corallina, speaking of the 

 madreporous islands of the southern pacific : " Their base is fixed on the 



