THE SECOND EDITION. VII 



remained at a stationary level often present the false 

 appearance of having been slightly elevated. 



Although I thus demur to some of the remarks and 

 criticisms made "by this eminent naturalist, who has 

 examined more coral formations than almost any other 

 man, yet I do not the less admire his work. It has 

 also afforded me the highest satisfaction to find that 

 he accepts the fundamental proposition that lagoon- 

 islands or atolls, -and barrier-reefs, have been formed 

 during periods of subsidence. 



The late Professor Jukes, in his account of the 

 voyage of H.M.S. Fly, published in 1847, devoted a 

 chapter to the Barrier-Keefs of Australia, and thus 

 concludes : .' After seeing much of the Great Barrier- 

 reefs, and reflecting much upon them, and trying if it 

 were possible by any means to evade the conclusions to 

 which Mr. Darwin has come, I cannot help adding that 

 his hypothesis is perfectly satisfactory to my mind, and 

 rises beyond a mere hypothesis into the true theory of 

 coral-reefs.' 



On the other hand, a distinguished naturalist, Pro- 

 fessor Semper, differs much from me, although he 

 seems willing to admit that some atolls and barrier- 

 reefs have been formed in the manner in which I 

 suppose. I will give in the Appendix, under the head 

 of the Pelew Islands, which were carefully examined 

 by him, some account of his objections, and I will here 



