Daly — The Coral-Reef Zone. 157 



the present reef. Davis, another upholder of the subsi- 

 dence theory, prefers the view that the lower part of the 

 boring penetrated lagoon deposits ; while Skeats, a third 

 advocate, seems to think the boring remained throughout 

 in "true reef." 21 Such failure of agreement illustrates 

 the vital need of properly correlating upgrowth, lagoon 

 filling, and the formation of external talus. The chance 

 that the boring should remain throughout in "true reef" 

 is exceedingly slight, if one may judge from the correla- 

 tions so far made by special students of the problem. 

 Moreover, the difficulty of stating what "true reef" is, 

 and the still greater one of distinguishing it from reef- 

 talus rock, are only now beginning to be thoroughly 

 realized. 



Skeats has tried to strengthen the case for the older 

 theory by citing the discovery of dolomite in the deeper 

 part of the Funafuti bore. He suggests that dolomite is 

 formed only in "shallow" water and therefore concludes 

 that there is new evidence for subsidence. However, his 

 premise is subject to grave doubt, which is not lessened 

 by an examination of his argument, based on the varying 

 solubilities of carbonates in carbonated water under pres- 

 sure. Mere pressure of overlying sea-water has almost 

 no effect on the concentration of carbon dioxide ; labora- 

 tory experiments made with water under pressure and 

 saturated with the gas evidently do not reproduce the 

 conditions in the ocean. 



Omitting further discussion, the writer will simply 

 express his adhesion to the opinion of some members of 

 the Funafuti Committee, appointed by the Royal Society 

 of London — that they found no confirmation of the sub- 

 sidence theory in this rock-boring. 



Summary. 



Conceivably the living coral reefs have been formed in 

 several distinct ways, but, as observed in the writer's 

 1915 paper, plenty of facts tend to corroborate Darwin's 

 conclusion that some one general explanation is 

 demanded. Principles not organically connected with 

 the general explanation may apply to the understanding 

 of a reef here or there. These relatively few exceptions 



21 W. M. Davis, Jour. Geol., vol. 26, Fig. 1 and p. 208, 1918 ; E. W. Skeats, 

 this Journal, vol. 45, p. 84, 1918. 



