494 W. M. DAVIS SUBSIDEXCE OF REEF-ENCIRCLED ISLAXDS 



to the best of my knowledge, been utilized, although it is convincing when 

 recognized. 



5. The evidence for subsidence found in the peculiar distribution of 

 submarine banks in the coral seas has never been brought forward with 

 the' emphasis that it deserves. 



6. The proof of subsidence that is furnished by the disappearance of 

 great volumes of detritus from reef-encircled islands has never been duly 

 considered. 



T. Verification of subsidence during the formation of most reefs is 

 found in greater measure than has been generally recognized in the ab- 

 sence of reefs from shorelines of emergence. 



8. Verification of subsidence is found in the unequal depths of lagoons 

 and banks. . And finally : 



9. Evidence for intermittent subsidence is found in the form of spur 

 ends on islands within barrier reefs. Most of these lines of verification 

 do not apply to atolls, which are therefore briefly considered in a special 

 section near the end of this article. The article closes with a short state- 

 ment of Molengraafi's views on the isostatic subsidence of volcanic 

 islands — a new contribution to the coral-reef problem which merits serious 

 attention. 



Embayed Shoeelixes 



dana's coxfirmatiox of darwix's theory 



Geology was not far developed when the Beagle made its voyage round 

 the world, and physiography was not developed at all. Darwin wrote: 

 ^^With respect to subsidence, we can not expect to find in semi-civilized 

 r-ountries proofs of a movement which tends to conceal its own evidence. 

 . . . From the nature of things, it is scarcely possible to find direct 

 proofs of subsidence" (1842, 127, 147). It w^as Dana, Darwin's follower 

 in Pacific exploration, who first adduced (1849) the embayed shorelines 

 of reef-fronted coasts in proof of subsidence. It is true that such shore- 

 lines testify strictly only to submergence, which might be caused by a 

 universal rise of ocean level as well as by a local subsidence of the coasts 

 concerned; but the time required in eroding the valleys of barrier-reef 

 coasts to their pre-submergence form is so varied, and the amount of sub- 

 mergence demanded by the form of the embayed valle5's is frequently so 

 great, that local subsidence, varying in date and amount, gives a much 

 better explanation of the facts as far as barrier reefs are concerned than 

 can be given by a rise of ocean level, which must be everywhere of the 

 same date and measure. 



