1 64 CORAL-REEFS. 



would not have remained all this time stationary, but would 

 frequently have undergone movements of elevation. This 

 supposition, we shall immediately see, holds good to a 

 remarkable extent; and although a stationary condition 

 of the land can hardly ever be open to proof, from the 



quite at rest, and therefore the corals in the lagoon, from being con- 

 stantly laved by the rippling water, might extend their branches to 

 a little greater height than they could, when the lagoon became enclosed 

 and protected. Christmas atoll (2 N. lat.), which has a very shallow 

 lagoon, and differs in several respects from most atolls, possibly may 

 have been elevated recently ; but its highest part appears (Couthouy, 

 p. 46) to be only ten feet above the sea-level. The facts of a second 

 class, adduced by Mr. Couthouy, in support of the alleged recent 

 elevation of the Low Archipelago, are not all (especially those refer- 

 ring to a shelf of rock) quite intelligible to me; he believes that certain 

 enormous fragments of rock on the reef, must have been moved into 

 their present position, when the reef was at a lower level; but here 

 again the force of the breakers on any inner point of the reef being 

 diminished by its outward growth without any change in its level, has 

 not, I think, been borne in mind: We should, also, not overlook the 

 occasional agency of waves caused by earthquakes and hurricanes. Mr. 

 Couthouy further argues, that since these great fragments were deposited 

 and fixed on the reef, they have been elevated; he infers this from the 

 greatest amount of erosion not being near their bases, where they are 

 unceasingly washed by the reflux of the tides, but at some height on 

 their sides, near the line of high-water mark, as shown in an accompany- 

 ing diagram. My former remark again applies here, with this further 

 observation, that as the waves have to roll over a wide space of reef 

 before they reach the fragments, their force must be greatly increased 

 with the increasing depth of water as the tide rises, and therefore I 

 should have expected that the chief line of present erosion would have 

 coincided with the line of high-water mark; and if the reef had grown 

 outwards, that there would have been lines of erosion at greater 

 heights. The conclusion, to which I am finally led by the interesting 

 observations of Mr. Couthouy is, that the atolls in the Low Archipelago 

 have, like the Society Islands, remained at a stationary level for a long 

 period : and this probably is the ordinary course of events, subsidence 

 supervening after long intervals of rest. 



