1836.] CHANGES IN CORAL-BEEFS. 457 



it must be ever difficult to decide between the effects of a change 

 in the set of the tides and of a slight subsidence : that many of 

 these reefs and atolls are subject to changes of some kind is 

 certain ; on some atolls the 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 date 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 progress 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 remarkable 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 surprise, that the descrip- 

 tions given by MM. Quoy and Gaimard were applicable, not to reefs 

 in general as implied by them, but only to those of the fringing 

 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 geological 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 subsidence 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 sur- 

 prise, that the passages through the reef exactly face valleys in the 

 included land, even in cases where the reef is separated from the 

 land by a lagoon-channel so wide and so much deeper than the actual 

 passage itself, that it seems hardly possible that the very small 



