254 W. M. Davis — Shaler Memorial Study of Coral Reefs. 



ity is clearly shown in Mawson's section of a critical locality, 

 which I had opportunity of reviewing, thanks to the most con- 

 siderate attention of various officials. Hence it must be sup- 

 posed that Efate, after standing low enough to receive an 

 extensive cover of marine strata, emerged high enough (about 

 1,000 feet) for the cover to be deeply dissected ; that it was 

 submerged low enough for reefs to be formed on the higher 

 members of the covering marine strata, and then emerged (about 

 800 feet ?) to its present altitude, leaving some of its valleys 

 drowned as bays. As to the reefs at intermediate levels, it is 

 conceivable that they were formed either during pauses in 

 emergence after a rapid submergence, or during pauses in 

 submergence followed by a rapid emergence, or both. Certain 

 details of reef structure in relation to the soapstone foundation 

 lead me to prefer the second explanation ; for of two reefs not 

 differing greatly in altitude, the higher one seemed to lie upon 

 the upper surface of the lower one ; if the lower one were built 

 forward from the frontal slope of the higher one, the first 

 explanation would be preferred. It is quite possible that some 

 reefs were formed during pauses in emergence, while others 

 were earlier formed during pauses in submergence ; but in 

 either case, the unconformable relation here so strongly dis- 

 played demands a double change of level ; unless, indeed, the 

 slope of the soapstone hillside is a fault-scarp that was formed 

 beneath sea level and fringed with reefs during pauses in its first 

 and only emergence : but the general form of the hillside that 

 I ascended and its relations to its neighbors seemed to me to 

 exclude such a possibility. If further observation should dis- 

 cover that the marine soapstone strata lie unconformable 7 on a 

 dissected volcanic foundation, it would then be necessary to 

 conclude that submergence had taken place before the soap- 

 stones were deposited, and thus two double movements would 

 be proved. 



In any event the separation of the Efate reefs in distinct 

 terraces shows that coral growth could not keep pace with the 

 movement — whether emergence or submergence — by which 

 their separation was caused. A similar conclusion is suggested 

 by the narrow-lagoon barrier reef, hardly more than a wide fring- 

 ing reef, on the strongly embayed island of Espiritu Santo, 

 farther northwest in the same group ; for the embayments of 

 that island indicate a liberal measure of submergence, which 

 should have produced a wide-lagoon barrier reef, if the reef had 

 grown upward continuously while submergence was in prog- 

 ress ; bat as the actual reef has only a narrow lagoon, upward 

 growth was probably discontinuous ; the earlier-formed fring- 

 ing reefs having been drowned by successive movements of 

 rapid submergence, and the present sea-level reef having been 



