XX CHANGES IN CORAL-REEFS 505 



the lagoon-channel is remarkably deep, scarcely any alluvial 

 soil has accumulated at the foot of the lofty included moun- 

 tains, and remarkably few islets have been formed by the 

 heaping of fragments and sand on the wall-like barrier-reef; 

 these facts, and some analogous ones, led me to believe that 

 this island must lately have subsided and the reef grown 

 upwards : here again earthquakes are frequent and very severe. 

 In the Society Archipelago, on the other hand, where the 

 lagoon-channels are almost choked up, where much low alluvial 

 land has accumulated, and where in some cases long islets 

 have been formed on the barrier-reefs — facts all showing that 

 the islands have not very lately subsided — only feeble shocks 

 are most rarely felt. In these coral formations, where the land 

 and water seem struggling for mastery, 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 descriptions 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. 



