Aprils 1836. theory of lagoon island. 



561 



land at the foot of the mountain was very small in quantity^ 

 the channel extremely deep^ and the islets on the reef itself^, 

 which result from the gradual accumulation of fragments^ 

 singularly few in number; all of which^ together with the 

 wall-like structure of the reef both inside as well as outside, 

 indicated to my mind, that, without doubt, the movements 

 of subsidence had lately been rapid. At the end of the 

 chapter, it is stated that this island is shaken by earthquakes 

 of extreme violence. 



I may here mention a circumstance, which to my mind 

 had the same weight as positive evidence, though bearing on 

 another part of the question. M. Quoy, when discussing in 

 general terms the nature of coral reefs, gives a description 

 which is applicable only to those which, skirting the shore, 

 do not require a foundation at any greater depth than that 

 from which the coral-building polypi can spring. I was at 

 first astonished at this, as I knew he had crossed both the 

 Pacific and Indian oceans, and must, as I thought, have seen 

 the class of widely-encircling reefs, which indicate a sub- 

 siding land. He subsequently mentions several islands as 

 instances of his description of the general structure; by a 

 singular chance, the whole can be shown, by his own words, 

 in different parts of his account, to have been recently ele- 

 vated. Therefore, that which appeared so adverse to the 

 theory, became as strong in its confirmation. 



Continental elevations, as observed in South America and 

 other parts, seem to act over wide areas with a very 

 uniform force ; we may therefore suppose that continental 

 subsidences act in a nearly similar manner. On this 

 assumption, and taking on the one hand, lagoon islands, 

 encircling and barrier reefs, as indications of subsidence; 

 and on the other, raised shells and corals, together with 

 mere skirting reefs, as our proof of elevation, we may test 

 the truth of the theory, — that their configuration has been 

 determined by the kind of subterranean movement,^ — by 

 observing whether any uniform results can be obtained. I 

 think it can be shown that such is the case in a very 



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