100 Couthouy on Coral Formations 



whether they are on the windward or leeward side, the water 

 falhng into them from the lagoon and fringing plateau, so as 

 to resemble a mill race.* At Raraka, six stout oarsmen, in a 

 swift whale-boat, were a full quarter of an hour, vainly at- 

 tempting to enter the lagoon, though the passage was not 

 above seventy or eighty yards in length ; and finally succeed- 

 ed only by taking an eddy pointed out by the natives. The 

 velocity of the current here could not have been less than six 

 or seven miles an hour, and it was not greater at Rose Island, 

 where the entrance is on the opposite side. The lagoon of 

 this latter is however of comparatively small extent. 



But rapid as it is, this current alone does not account for 

 the existence of such channels. It is difficult to believe that 

 the attrition of the passing water would suffice to prevent 

 their being closed or filled up by the labors of the polypes, 

 when we see these flourishing in the greatest perfection on 

 the margin of the reef, exposed to the unceasing and far more 

 violent action of the surf, which is continually tearing off 

 large masses of rock, and driving them toward the beach. 

 And were we at first sight disposed to consider their formation 

 the result of the powerful tides, a closer examination would 

 convince us of error, by showing that in no portion of the 

 reef is the growth of the encrusting and lamellar corals more 

 profuse than upon the sides (and in some instances the bot- 

 tom also,) of these very channels. Even the more fragile 

 Madrepores are to be seen there, though less in size and num- 

 ber than inside. 



The tides on the weather side of Christmas Island, whirl 

 round it with frightful rapidity, so that it is highly dangerous 

 to venture into them with a boat. The surf also, on this 

 side, runs to an amazing height, especially during the spring 

 tides, rising sometimes, like that of Guam, to the altitude of 

 twenty feet, before it bursts upon the reef Yet though the 

 extreme edge of the plateau has been greatly shattered by 

 these tremendous rollers, the polypes are no where more in- 

 dustrious or numerous than just inside the breakers. 



* Christmas Island is an exception to this rule, the ebb current setting out 

 moderately, owing probably to the shallowness of the lagoon, and unusual width 

 of the passages. 



