10 BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



by Professor Bonney,^ that Darwin has noticed most of the causes on 

 "which stress is laid by his critics, it should also be remembered that 

 Darwin did not observe the phenomena subsequently examined, but 

 merely suggested them as possibilities, and his critics may be excused 

 for giving their observations a relatively greater value than to his 

 theoretical views. 



The whole argument of the great thickness of coral reefs based upon 

 the analogy of the so called raised reefs of Cuba, described by Prof. 

 Crosby and myself, or of the fossil reefs, is of little value, as it has been 

 pretty conclusively shown that these elevated reefs, not only in Cuba 

 but in the Pacific, are beds of tertiai-y limestone intercalated with beds 

 of moderate thickness in which corals are found, and the same is true of 

 older fossil reefs. Furthermore, these huge masses of tertiary limestone 

 which form the substratum upon which both in Cuba and in the Pacific 

 recent corals have found a footing, have played no part in the shaping 

 of the bari'ier or encircling reefs, or atolls, which, as we have attempted 

 to show, owe their origin in the main to mechanical causes. 



Professor Bonney states that " Much stress is laid upon the fact that 

 many coral islands afford evidences of a certain amount of upheaval ; this 

 amount, in most cases, is but slight, and its significance appears to me to 

 have been exaggerated" ; and he considers these indications to prove only 

 oscillation. As far as the Fijis are concerned, the elevation extended 

 over the whole group, and has been shown to amount to more than 

 a thousand feet. In Australia it extended along the whole east coast of 

 Queensland for more than a thousand miles, and was more than twenty- 

 five hundred feet in height ! He further says, " If the coral reef be only 

 a sort of cap concealing a hill of pre-existent rock, we may reasonably 

 be surprised that the ' ashlar rock ' of coral limestone has in no case 

 so far yielded to the action of the atmospheric agencies as to lay bare its 

 inner support." VTe can answer this point most decidedly. In Florida 

 the substratum underlying the recent coral reefs crops out at many 

 places, and the highest points of some of the Keys consist of it. So do 

 some of the hummocks in the southern part of the Everglades near Key 

 Biscayne. In the Bermudas the greater part of the land of that group 

 consists of the seolian rocks which underlie the recent coral reef. In 

 the Bahamas the same is the case, and along the northern coast of Cuba 

 the tertiary limestone formmg the substratum of the recent reefs crops 

 out in all directions, while in Australia rocks underlying the Great Barrier 



1 Loc. cit., p. 324. 



