Daly — The C oral-Reef Zone. 159 



4. Careful study of the geological dates so far deter- 

 mined for crustal movements in and around the western 

 tropical Pacific permits explanation of the Macclesfield 

 and other banks in that region by the new theory ; their 

 explanation does not appear to call for crustal subsidence 

 since the late Tertiary. In general, the Glacial-control 

 theory demands crustal stillstand no more prolonged or 

 but little more prolonged than that demanded by any 

 other theory of reefs yet published. The latest theory 

 demands general stability of the earth's crust in the 

 tropical belt only for the last few hundreds of thousands 

 of years, during which, however, local instability has been 

 pronounced, with effects whose study actually strength- 

 ens the new theory. General subsidence of the tropical- 

 sea floor may have occurred in pre-Glacial time, but, if 

 so, we have no proof of it — especially no proof in the 

 forms of the existing coral reefs. On the other hand, the 

 hypsometry of the wider lagoons and banks, reef-rimmed 

 or not, suggests stability for most of the tropical-sea 

 floor since at least the late Miocene. 



Harvard University, 

 Cambridge, Mass. 



