Daly— The Coral-Reef Zone. 1 53 



The argument just presented implies explanation for 

 the cliffless Murea, a close neighbor of Tahiti ; for of the 

 two Murea is both smaller and lower. Perhaps its petrog- 

 raphy is significantly different. However, even if Tutu- 

 ila, Murea, or Tahiti were proved to have sunk recently, 

 there would still be little warrant to extend the explana- 

 tion by subsidence to barrier reefs and atolls generally. 

 The fundamental objections to Darwin's theory, founded 

 on the forms of reefs, lagoons, and submarine banks, 

 would have lost practically nothing of their force ; and 

 these objections have not yet been overcome. 18 



4. Depths of Lagoons. — Variation in the depths of 

 lagoons has been charged against the Glacial-control 

 theory. Yet variations within limits are positively 

 demanded by that theory. 



The pre-Glacial shelves, benches, and banks had sur- 

 face levels varying because of : differing absolute age ; 

 differing duration of their exposure to marine abrasion 

 as well as marine aggradation; differing constitution, so 

 that a muddy shelf would be covered with water deeper 

 than that expected on a sandy shelf, to say nothing of a 

 rock bench — all formed under similar conditions of wave 

 and current strength; crustal warping, etc. 



The submarine flats "sand-papered" by Pleistocene 

 abrasion and the new Pleistocene detrital shelves would 

 also have initially varying depths below present sea-level, 

 for the same reasons, to which must be added the compli- 

 cations induced by repeated changes of wave-base and 

 current-base during the Glacial period. 



On those initial plateaus are veneers of post-Glacial 

 detritus and organic growths ; the veneers can not be uni- 

 form in thickness. 



Hence, for at least three sets of reasons, lagoon depths 

 should not now be uniform, if developed according to the 

 terms of the Glacial-control theory. The theory does 



18 For example, no effective reply has been made to one deep-seated trouble 

 with the subsidence theory. The ocean charts fail to show even one well- 

 defined ' ' moat ; ' inside barrier or atoll reef, as foretold by the theory. 

 Lagoon waves are weak and said to be "nearly negligible ' ; (Davis) as cliff - 

 ing agents ; hence they are unlikely to aggrade wide, deep lagoons so rapidly 

 as in all cases to obliterate the ' ' moat. ; ' Lagoon waters do, of course, 

 become turbid with suspended sediment during storms, but this sediment 

 is normally obtained in the shallows and the turbidity does not at all prove 

 the ability of the waves to stir sediment already deposited in the larger, 

 deeper part of the lagoon. Appeal to lagoon currents as agents competent 

 to obliterate moats with sufficient rapidity is no more successful. 



