224 W. M. Davis — Shaler Memorial Study of Coral Reefs. 



ing in Australia during August as a foreign guest, enabled rae 

 to spend the greater part of the year 1914 in visiting a number 

 of islands in the Pacific Ocean with the object of testing the 

 various theories that have been invented to account for coral 

 reefs. Thirty-five islands, namely, Oahu in Hawaii, eighteen 

 of the Fiji group, the entire coast line of New Caledonia, the 

 three Loyalty islands, five of the New Hebrides, Rarotonga in 

 the Cook group, and six of the Society islands, as well as a 

 long stretch of the Queensland coast inside of the Great 

 Barrier reef of northeastern Australia, were examined in 

 greater or less detail. Darwin's theory of subsidence, invented 

 when he was twenty-five years old and before he had ever seen 

 a true coral reef, is in my opinion the only theory competent 

 to account for the coral reefs that I visited, because it is the only 

 theory that will also reasonably account for the features of the 

 encircled volcanic islands ; thus my work leads to the same 

 conclusion as that reached by several other recent students of 

 this old problem. 



The longer voyages between island groups and the shorter 

 excursions among the grouped islands were accomplished 

 much more easily than I supposed would be possible. Many 

 attentions from officials and from merchants, as well as from 

 natives, added an unexpected comfort in far distant places. 

 An abstract of results has appeared in the Proceedings of the 

 National Academy of Sciences for March, 1915, in Science for 

 March 26, and in Nature for April 15, 1915. A full discus- 

 sion of my observations will be published later, probably in the 

 Bulletin of the Museum of Comparative Zoology at Harvard 

 College. A statement of the chief results gained here follows. 



Theories of Coral Reefs. — Before setting out on the voyage, 

 I reviewed various theories of coral reefs in an essay that 

 was published during my absence under the title of " The 

 Home Study of Coral Reefs" in the Bulletin of the American 

 Geographical Society for 1914. The theories there discussed 

 were carefully considered while I was on various Pacific islands 

 with particular reference to the deduced consequences as well 

 as to the initial postulates by which each theory is distinguished 

 from its fellows. In this connection it is important to recog- 

 nize that every one of the several theories proposed to account 

 for coral reefs is successful in explaining the visible features 

 of sea-level reefs themselves, provided the postulated conditions 

 and assumed processes of the invisible past are accepted. 

 Evidently then a study of existing sea-level reefs alone will 

 not suffice to discover which theory really provides a correct 

 mental counterpart of their earlier and unobservable history. 

 I repeatedly took occasion to test the truth of this statement 

 while wading upon a well-formed barrier reef, beaten by the 



