56 CORAL-REEFS. 



hand, several islets, and even some of those which are 

 believed to be very old, are now fast wearing away. The 

 work of destruction has, in some instances, been completed 

 in ten years. Capt. Moresby found on one water-washed 

 reef the marks of wells and graves, which were excavated 

 when it supported an islet. In South Nillandoo atoll, the 

 natives say that three of the islets were formerly larger : in 

 North Nillandoo there is one now being washed away ; and 

 in this latter atoll Lieut. Prentice found a reef, about six 

 hundred yards in diameter, which the natives positively 

 affirmed was lately an island covered with cocoa-nut trees. 

 It is now only partially dry at low water spring-tides, and is 

 (in Lieut. Prentice's words) " entirely covered with live 

 coral and madrepore." In the northern part, also, of the 

 Maldiva Archipelago and in the Chagos group, it is known 

 that some of the islets are disappearing. The natives 

 attribute these effects to variations in the currents of the 

 sea. For my own part I cannot avoid suspecting that there 

 must be some further cause, which gives rise to such a cycle 

 of change in the action of the currents of the great and 

 open ocean. 



Several of the atolls in this Archipelago are so related to 

 each other in form and position, that at the first glance one 

 is led to suspect that they have originated in the dissever- 

 ment of a single one. Male consists of three perfectly 

 characterised atolls, of which the shape and relative position 

 are such, that a line drawn closely round all three, gives a 

 symmetrical figure; to see this clearly, a larger chart is 

 required than that of the Archipelago in Plate III.; the 

 channel separating the two northern Male atolls is only 

 little more than a mile wide, and no bottom was found in it 

 with ioo fathoms. Powell's Island is situated at the 

 distance of two miles and a half off the northern end of 



