466 



SINKING OF CORAL REEFS, [chap: x* 



and in their arrangement in single or double lines ; fo 

 they may be called rude outline charts of the sunkei 

 islands over which they stand. We can further see hov 

 it arises that the atolls in the Pacific and Indian ocean; 

 extend in lines parallel to the generally prevailing strik( 

 of the high islands and great coast-lines of those oceans 

 I venture, therefore, to affirm, that on the theory of th( 

 upward growth of the corals during the sinking of th( 

 land,* all the leading features in those wonderful structures, 

 the lagoon-islands or atolls, which have so .long exc 



.i«t.c:. 



A" 



\ 







A' A'. Outer edges of the barrier-reef at the level of the sea, with islets on it. 

 B'B'. The shores of the included island. CC. The lagoon-channel. 



A" A". Outer edges of the reef, now converted into an atoll. C. The lagoon 

 of the new atoll. 



N.B.— According to the true scale, the depths o.f the lagoon-channel and 

 lagoon are much exaggerated. 



the attention of voyagers, as well as in the no less 

 wonderful barrier-reefs, whether encircling small islands 

 or stretching for hundreds of miles along the shores of a 

 continent, are simply explained. 



It may be asked whether I can offer any direct evidence 

 of the subsidence of barrier-reefs or atolls ; but it must 

 be borne in mind how difficult it must ever be to detect 

 a movement, the tendency of which is to hide under water 

 the part affected. Nevertheless, at Keeling atoll I observed 



* It has been highly satisfactory to me to find the following passage in a 

 pamphlet by Mr. Couthouy, one of the naturalists in the great Antarctic 

 Expedition of the United States : " Having personally examined a large 

 number of coral islands, and resided eight months among the volcanic class 

 having shore and partly encircling reefs, I may be permitted to state that my 

 own observations have impressed a conviction of the correctness of the theory 

 of Mr. Darwin." The naturalists, however, of this expedition differ with me 

 on some points respecting coral formationa, 



