Vlll 
PREFACE TO 
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 hy this eminent naturalist, who has 
examined more coral formations than almost any other 
man, yet I do not the less admire his work. 1 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-Reefs 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, 
Professor Semper, differs much from me, although he 
seems willing to admit that some atolls and harrier- 
reefs have been formed in the manner in which I 
suppose. I will give in the Appendix, under the head 
1 A friendly reply from Professor Dana, contesting some of the 
points mentioned above, will be found in Nature, Sept. 1874, p. 408. 
