W. M. Davis — Shaler Memorial Study of Coral Beefs. 229 



ries were in nearly all cases proposed to replace Darwin's 

 theory of subsidence. So again would it be over-bold at once 

 to reject all the stand-still theories if their inventors had duly 

 considered the embayed shorelines of the volcanic islands 

 within barrier reefs, and had thereupon said : — " Truly these 

 embayments look at first sight as if they had been produced by 

 a departure from the postulated still-stand of the central island, 

 whereby the distal parts of previously eroded valleys have been 

 submerged ; yet as a matter of fact the embayments are not the 

 result of submergence, but of" ... . some other process. 

 Unfortunately, however, no sufficient attention has been given 

 to the embayed shorelines of the central islands in any discus- 

 sion of the stand-still theories : their investigators have passed 

 silently over these significant features as if they had no bear- 

 ing on the problem at issue. 



Dana's Principle of Shoreline Development. — Such neglect 

 of a really essential factor is all the more surprising when it is 

 remembered that as long ago as 1849 the embayment of the 

 central islands of barrier reefs was shown by Dana in the clear- 

 est and most emphatic manner to follow as a necessary conse- 

 quence from Darwin's postulate of subsidence ; for it was 

 Dana who first, when he was on the Pacific ten years earlier, 

 recognized that the subsidence of a dissected land surface must 

 produce an embayed shoreline.* He discovered this important 

 principle — " Dana's principle of shoreline development," as it 

 may be called — and recognized its value as an independent 

 confirmation of the theory of eubsidence, when he crossed the 

 Pacific about four years after Darwin, as he was to a day four 

 years Darwin's junior. It is surprising also that the logical 

 value of Dana's principle in giving independent confirmation 

 to Darwin's theory was recognized by so few of the many 

 geologists who accepted Darwin's theory, and never by Dar- 

 win himself ; and it is certainly disappointing, from the view- 

 point of disciplined scientific investigation, to see that many 

 geologists, who had been brought up on Darwin's theory, later 

 abandoned it for one or another of the stand-still theories 

 against which Dana's principle offers immediate and incontro- 

 vertible evidence as far as barrier reefs are concerned, and very 

 strong presumptive evidence in the case of reefs of other kinds 

 as well ; for it is unreasonable to suppose that a change in the 

 relative level of land and sea should occur only in regions 

 where the central islands of- barrier reefs are present to attest 

 it, and not in neighboring regions where reefs of identical 

 form but without a central island are given the name of atolls. 

 Whether any existing atolls have been built up from still-stand- 



* Dana's Confirmation of Darwin's Theory of Coral Eeefs, this Journal, 

 xxxv, 173, 1913. 



