182 Davis — Dana's Confirynation of 



Now, in view of the remarkable accordance that is thus 

 fonnd between several peculiar consequences of the theory of 

 subsidence and several features of the central islands in barrier 

 reefs, and in memory of the failure of certain consequences of 

 the theories of outward growth and of sea-cut platforms to 

 match observed facts, an open-minded inquirer cannot hesitate 

 in making choice among the several explanations that have 

 been suggested for barrier reefs, and with them of atolls. We 

 cannot now, as Guppy did,* "pass over the theory of sub- 

 sidence because the more recent facts concerning the ocean 

 depths and the regions of living and upraised reefs compel us 

 to regard it as no longer necessary." In view of the peculiar 

 features of the central islands of barrier reefs, the theory of 

 subsidence is to-day as valid as it ever was. Indeed, after one 

 has' fully appreciated the value that attaches to a successful 

 confrontation of unexpectedly deduced consequences with pre- 

 viously unobserved facts in the verification of a theory from 

 which such consequences have been derived, it is difficult to 

 refrain from giving full acceptance to Darwin's theory, not- 

 withstanding the doubts that have been raised against its 

 sufficiency by more recent investigators. But nothing is 

 gained by over-hasty confidence in a good case. Before one 

 adopts a final conclusion as to the origin of certain reefs, the 

 evidently desirable thing would be to have the whole problem 

 examined again in the Pacific by an investigator who should 

 impartially bear in mind all the theories and all their conse- 

 quences. 



In the meantime, however, I desire to emphasize the point 

 that it is to Dana that we owe the discriminating test above 

 mentioned, which may be applied to the several theories that 

 have been proposed to account for coral reefs, particularly for 

 barrier reefs ; for it was Dana who first directed careful atten- 

 tion to the features that ought to be expected on a subsiding 

 central island as a means of testing the theory of subsidence, 

 and hence o other theories also. 



Dana first learned of Darwin's theory, when the Wilkes Ex- 

 pedition reached Sydney near the end of 1839. It was several 

 months earlier, during " the ascent of Mt. Aorai on Tahiti, in 

 September of 1839," that he first conceived the production of 

 an embayed shore line as a necessary result of the subsidence 

 of a dissected land-mass. " Sunk to any level above that of 

 five hundred feet, the erosion-made valleys of Tahiti would 

 become deep bays, and above that of one thousand feet, fiord- 

 like bays, with the ridges spreading in the water like spider's 

 legs." It is important to notice that this principle, simple as 

 * Victoria Inst., 1888, 1-16 ; see p. 6. 



