1,"(5 SUBSIDENCE OF OORAL.REEFS. [..-HAP. xx. 



which they stand. We can further see how it arises that the 

 atolls in the Pacific and Indian Oceans extend in lines parallel to 

 the generally prevailing strike of the high islands and great coast- 

 lines of those oceans. I venture, therefore, to affirm, that on the 

 theory of the upward growth of the corals during the sinking of 

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

 the lagoon-islands or atolls, which have so long excited the atten- 

 tion 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 on all sides of the lagoon old cocoa-nut 

 trees undermined and falling; and in one place the foundation- 

 posts of a shed, which the inhabitants asserted had stood seven 

 years before just above high- water mark, but now was daily washed 

 by every tide : on inquiry I found that three earthquakes, one of 

 them severe, had been felt here during the last ten years. At 

 Yanikoro, the lagoon-channel is remarkably deep, scarcely any 

 alluvial soil has accumulated at the foot of the lofty included 

 mountains, 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 archi- 

 pelago, 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 sub- 

 sided only feeble shocks are most rarely felt. In these coral 

 formations, where the land and water seem struggling for mastery, 



* 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 partially 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 formations 



