ORIGIN OF THE BARRIER REEF. 221 



tions of the author afforded him striking illustrations of its 

 truth ; and elucidate some points which were still deemed 

 obscure, establishing the theory, as he believes, on a firm basis 

 of evidence, and exhibiting its complete correspondence with 

 observation. 



The reader may turn again to the chart of the Feejee Group, 

 and glance successively at the islands Goro, Angau, Nairai, 

 Lakemba, Argo Reef, Exploring Isles, and Nanuku. It will 

 be observed that in Goro, the reef closely encircles the land 

 upon whose submarine shores it was built up. In the island 

 next mentioned, the reef has the same character, but is more 

 distant from the shores, forming what has been termed a barrier 

 reef; the name implying a difference in position, but none in 

 mode of formation. In the last of the islands enumerated, the 

 barrier reef includes a large sea, and the island it incloses is 

 but a rocky peak within this sea. 



Can we account for this diversity in the position of barrier 

 reefs, and in their extent as compared with the inclosed land ? 

 There is evidently one way, in accordance with Mr. Darwin's 

 theory, in which these features might have been* produced. If, 

 for example, such an island as Angau were very gradually to 

 subside, from some subterranean cause, two results would take 

 place : — the land would slowly disappear, while the coral reef, 

 ever in constant upward increase, as has been explained, might 

 retain itself at the surface, if the rapidity of subsidence were 

 not beyond a certain rate. This subsidence might go on till 

 the last mountain peak remained alone above the waters. 

 Should we not then have a Nanuku ? Suppose the subsidence 

 not to have proceeded to this extent, but to leave still a single 

 ridge and a few isolated summits above the waves ; would not 

 its condition in this case be that of the Exploring Isles ? On 

 such a supposition, reefs of large size encircling a mere point 

 of rock might be explained even to every feature. The sub- 

 sidence of Goro, on the same principle, would produce an 

 Angau, or, carried further, a Nanuku. 



It may here be remarked, that the fact that changes of level 

 over vast areas of the earth's surface have taken place is fully 



