CORAL-REEFS. 31 



growth of coral-reefs, and that the almost universal law of 

 ''consumed and be consumed," holds good even with the 

 polypifers forming those massive bulwarks, which are able 

 to withstand the force of the open ocean. 



Considering that Keeling atoll, like other coral forma- 

 tions, has been entirely formed by the growth of organic 

 beings, and the accumulation of their detritus, one is 

 naturally led to inquire how long it has continued, and 

 how long it is likely to continue, in its present state. Mr. 

 Liesk informed me that he had seen an old chart in which 

 the present long island on the S.E. side was divided by 

 several channels into as many islets ; and he assures me 

 that the channels can still be distinguished by the smaller 

 size of the trees on them. On several islets, also, I 

 observed that only young cocoa-nut trees were growing on 

 the extremities; and that older and taller trees rose in 

 regular succession behind them; which shows that these 

 islets have very lately increased in length. In the upper 

 and south-eastern part of the lagoon, I was much surprised 

 by finding an irregular field of at least a mile square of 

 branching corals, still upright, but entirely dead. They 

 consisted of the species already mentioned ; they were of a 

 brown colour, and so rotten, that in trying to stand on 

 them I sank halfway up the leg, as if through decayed 

 brushwood. The tops of the branches were barely covered 

 by water at the time of lowest tide. Several facts having 

 led me to disbelieve in any elevation of the whole atoll, I 

 was at first unable to imagine what cause could have killed 

 so large a field of coral. Upon reflection, however, it 

 appeared to me that the closing up of the above-mentioned 

 channels would be a sufficient cause; for before this, a 

 strong breeze by forcing water through them into the head 

 of the lagoon, would tend to raise its level. But now this 



