346 SUBSIDENCE OF CORAL-REEFS. (CHA* xi. 



for they may be called rude outline charts of the sunken islands over 

 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 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 sub- 

 sidence 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 



A' A'. Outer edges of the barrier-raef t the level of the ea, 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. (7. The lagoon of the 

 Dew atoll. 



N.B. According to the true scale, the depths of the lagoon-channel and lagoon are 

 much exaggerated. 



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 Vanikoro, the lagoon-channel is remark- 

 ably deep, scarcely any alluvial soil has accumulated at the foot of the 

 lofty included mountains, and remarkably few islets have been formed 



* 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. 



