104 Couthouy on Coral Formations 



as to prevent their being, as yet, obliterated as others have 

 been, by the extremely slow growth of the coral ; and that in 

 the lapse of fjiture ages, they too will disappear, when the 

 lagoons will gradually dry and be partially filled up with 

 detritus from the neighboring beaches. Possibly, the level 

 between the sea and the lagoon of Aitoho, to which I have 

 stated no entrance was seen, may be restored by the water 

 accumulated during fioodtide passing out by subterranean 

 canals, such as are described above. 



It is not improbable that some channels were produced by 

 other causes than that here mentioned, such as originsd in- 

 equalities in the submerged land, or fissures made in the reef 

 by earthquakes, which we may presume to have been, at a 

 former period, as frequent in this region as they now are in 

 those where volcanic fires are still raging ; but I am convin- 

 ced that instances where a passage has been cut through a reef 

 by the action of tides are of exceeding rarity, if indeed they 

 occur at all. So long as it is the tendency of water to seek 

 an uniform level, I cannot conceive how that accumulated in 

 the lagoon during the flood tide, or from the rolling in of the 

 surf, should in flowing out over a reef covered even at low 

 water to a depth of from one foot to ten fathoms, excavate a 

 narrow canal, occasionally (as at Christmas and Ocean Islands,) 

 deeper than the lagoon itself. 



It is my impression that Prof. Lyell described these chan- 

 nels as invariably situated on the leeward reef; yet suggested 

 no cause for their assumed absence on the windward side, ex- 

 cept the inference that as the water was forced into the lagoon 

 from that direction, it would naturally seek to escape in an 

 opposite one ; and at a late meeting of this Society it was 

 asked why, if his reasoning was not just, such should be the 

 case. 



But they are, as I have endeavored to show, confined to no 

 particular portion of the reef, though they certainly do occur 

 most frequently to leeward. Nor will this, upon reflection, 

 appear so singular as it may at first be considered. Admitting 

 that there were originally as many in the weather as in the 

 leeward reef, by far the greater number would long since 



