REEFS AROUND DEEPLY ERODED ISLANDS 



535 



half a mile across, is so fore- 

 shortened as not to be vis- 

 ible between the barrier reef 

 and the shore, both of which 

 are shown by the same sea- 

 level line. In Ear o tonga, a 

 lofty member of the Cook 

 group, drawn in the lower 

 part of figure 12, the shore 

 lowland consists of a slightly 

 elevated reef, which would 

 have been completely smoth- 

 ered by detritus if the deep 

 valleys had not been eroded 

 and the island partly sub- 

 merged before the reef be- 

 gan to grow. The transfor- 

 mation of Fauro, figure 11, 

 in the Solomon group, from 

 the initial form of a vol- 

 canic cone or group of cones 

 into the present "wreck^^ of 

 branching ridges surmount- 

 ing a submerged platform, 

 40 fathoms or more in 

 depth, is utterly impossible 

 by any combination of ero- 

 sion and abrasion, without 

 the aid of recent subsidence. 

 Any incipient reefs that 

 may have been formed 

 around the shores of these 

 islands before the erosion 

 of their valleys must have 

 been soon overwhelmed by 

 outwash detritus; cliff-cut- 

 ting must have thereupon 

 set in, and thereafter the 

 excess of detritus delivered 



XL — Bull. Geol. Soc. Am.. 



Vol. 29, 1917 



