102 Couthouy on Coral Formations 



The lagoon is everywhere full of sand-banks and patches 

 of coral, having only a few inches of water upon them, and 

 as will be seen by reference to the figures, is not so deep 

 by from ten to eighteen feet as the channels in the reef. 

 Whatever may be thought of the other passages, it is clear 

 that the one leading to the island is not owing to the action 

 of currents, as from its sheltered situation, and the shallowness 

 of the water between the beach and margin of the reef, they 

 are scarcely felt, 



I cannot, therefore, in view of these facts, coincide with 

 those who entertain the opinion that the lagoon entrances 

 were primarily hollowed in the reef by the rush of surplus 

 waters from the enclosed basin, and have been kept open ever 

 since by the tides. If we adopt the- doctrine of a general 

 subsidence of the land, with its attached shore reef, during 

 which the latter has been maintained at its original level by 

 the polypes ; it appears to me that the facts admit of an ex- 

 planation more probable, though not covering perhaps every 

 difficulty. 



I believe that these reef channels, in almost every instance, 

 originated during the primal condition of the islands, in the 

 influence of fresh water streams preventing the growth of the 

 coral where they emptied themselves. Instances of the same 

 thing now happening, are frequent in all the volcanic islands 

 of Polynesia. I observed especially at the Samoan and 

 Hawaiian islands, that there were openings in the shore reefs 

 opposite the mouths of streams, and sometimes very insignifi- 

 cant ones, which I am convinced were caused by the fresh 

 water acting detrimentally upon the polypes. While the 

 island remained above the sea, or rather while the stream 

 continued to flow, the same causes in which it originated 

 would keep the channel open. When the subsidence had 

 reached that point at which these causes ceased to operate, 



chart engraved for the third number of the Hawaiian Spectator, by a native 

 scholar of the Mission Seminary at Lahainaluna, Maui, from surveys by Capt. 

 Brown, who remained upwards of five months on the island, with his crew. 

 " The only fresh water is what drains through the sand, after the heavy rains.'' 

 —[Haw. Spec. July, 1838.] 



