490 KEELING ISLAND 



stayed a long time in the lagoon, examining the fields of coral 

 and the gigantic shells of the chama, into which if a man were 

 to put his hand, he would not, as long as the animal lived,, be 

 able to withdraw it. Near the head of the lagoon, I was much 

 surprised to find a wide area, considerably more than a mile 

 square, covered with a forest of delicately branching corals, 

 which, though standing upright, were all dead and rotten. At 

 first I was quite at a loss to understand the cause ; afterwards 

 it occurred to me that it was owing to the following rather 

 curious combination of circumstances. It should, however, first 

 be stated, that corals are not able to survive even a short 

 exposure in the air to the sun's rays, so that their upward limit 

 of growth is determined by that of lowest water at spring tides. 

 It appears, from some old charts, that the long island to 

 windward was formerly separated by wide channels into several 

 islets ; this fact is likewise indicated by the trees, being j'ounger 

 on these portions. Under the forrrier condition of the reef, a 

 strong breeze, by throwing more water over the barrier, would 

 tend to raise the level of the lagoon. Now it acts in a directly 

 contrary manner ; for the water within the, lagoon not only is 

 not increased by currents from the outside, but is itself blown 

 outwards by the force of the wind. Hence it is observed that 

 the tide near the head of the lagoon does not rise so high 

 during a strong breeze as it does when it is calm. Thi's 

 difference of level, although no doubt very small, has, I believe, 

 caused the death of those coral -groves, which under the former 

 and more open condition of the outer reef had attained the 

 utmost possible limit of upward growth. 



A few miles north of Keeling there is another small atoll, 

 the lagoon of which is nearly filled up with coral- mud. 

 Captain Ross found embedded in the conglomerate on the 

 outer coast a well-rounded fragment of greenstone, rather 

 larger than a man's head ; he and the men with him were so 

 much surprised at this, that they brought it away and preserved it 

 as a curiosity. The occurrence of this one stone, where every 

 other particle of matter is calcareous, certainly is very puzzling. 

 The island has scarcely ever been visited, nor is it probable 

 that a ship had been wrecked there. From the absence of any 

 better explanation, I came to the conclusion that it must have 

 come entangled in the roots of some large tree ; when, how- 



