Sect. I. KEELING ATOLL. 21 



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 half way 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 eleva- 

 tion 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 

 cannot happen, and the inhabitants observe that the 

 tide rises to a less height, during a high S.E. wind, at 

 the head than at the mouth of the lagoon. The corals, 

 which, under the former condition of things, had at- 

 tained the utmost possible limit of upward growth, 

 would thus occasionally be exposed for a short time to 

 the sun, and be killed. 



Besides the increase of dry land, indicated by the 

 foregoing facts, the exterior solid reef appears to have 



