476 CHANGES IN CORAL-REEFS. [CHAP. xx. 



are subject to changes of some kind is certain ; on some atolls 

 che islets appear to have increased greatly within a late period ; 

 on others they have been partially or wholly washed away. The 

 inhabitants of parts of the Maldiva archipelago know the dale 

 of the first formation of some islets ; in other parts, the corals 

 are now flourishing on water-washed reefs, where holes made 

 for graves attest the former existence of inhabited land. It is 

 difficult to believe in frequent changes in the tidal currents of an 

 open ocean ; whereas, we have in the earthquakes recorded by 

 the natives on some atolls, and in the great fissures observed on 

 other atolls, plain evidence of changes and disturbances in pro- 

 gress in the subterranean regions. 



It is evident, on our theory, that coasts merely fringed by 

 reefs cannot have subsided to any perceptible amount ; and 

 therefore they must, since the growth of their corals, either have 

 remained stationary or have been upheaved. Now it is remark- 

 able how generally it can be shown, by the presence of upraised 

 organic remains, that the fringed islands have been elevated : 

 and so far, this is indirect evidence in favour of our theory. I 

 was particularly struck with this fact, when I found to my sur- 

 prise, that the descriptions given by MM. Quoy and Gaimard 

 were applicable, not to reefs in general as implied by them, but 

 only to those of the f ringing-class ; my surprise, however, ceased 

 when I afterwards found that, by a strange chance, all the several 

 islands visited by these eminent naturalists, could be shown by 

 their own statements to have been elevated within a recent geo- 

 logical era. 



Not only the grand features in the structure of barrier-reefs 

 and of atolls, and of their likeness to each other in form, 

 size, and other characters, are explained on the theory of sub- 

 sidence which theory we are independently forced to admit in 

 the very areas in question, from the necessity of finding bases 

 for the corals within the requisite depth but many details in 

 structure and exceptional cases can thus also be simply explained, 

 I will give only a few instances. In barrier-reefs it has long 

 been remarked with surprise, that the passages through the reef 

 exactly face valleys in the included land, even incases where the 

 reef is separated from the land by a lagoon-channel so wide ano 

 o much deeper than the actual passage itself, that it seems hardly 



