90 FOYE. 



thickness of coral reefs, such as is required by the Darwinian theory 

 of the formation of atolls and of barrier reefs, is based upon the great 

 thickness of the so-called elevated reefs observed in the Pacific by 



Dana, Darwin, and others That the latter are true coral reefs 



is more than doubtful. Those rocks are probably great masses of 

 limestone similar to the so-called elevated reefs of the West Indies 

 and the Pacific." 



The mere fact of the deposition of limestone on a subsiding base- 

 ment does not, in accordance wdth this statement, establish the truth 

 of Darwin's theory. The elevated masses must be proven to be of 

 coral origin, to have the reef form, and to rest unconformably on a 

 volcanic substructure. 



Several observers have considered the raised rims of such islands as 

 proof of their atoll origin. The writer agrees with Agassiz that such 

 evidence is not always conclusive, since atmospheric solution may 

 lower the surface at the center of an elevated limestone bank faster 

 than the surface at its edge, as instanced by the Florida plateau. 

 Yet, even if this fact is established, one may well question that 

 differential solution is competent to explain the great relative heights 

 of the rims in Kambara and Wangava, which respectively average 

 260 and 300 feet higher than the central depression. If these depres- 

 sions are due entirely to solution, it would appear that the under- 

 ground channels, which conduct the drainage of the islands to the 

 sea, ought long ago to have breached the surrounding rims. 



Again, if these islands are truly raised atolls it may be held that 

 reef limestones should characterize their rims while coral debris and 

 other fine-grained material should dominate in the lagoon deposits. 

 ^Yith this point in mind a study was made of the outer edges of the 

 islands. Coral heads were often found in place, but in no greater 

 abundance than within the lagoon deposits.^ IMoreover, they were of 

 the rounded type and not the fungus-shaped forms that occur at the 

 edges of the present, growing reefs. The writer could not find a 

 locality which might definitely be called the edge of an old atoll. 



However, the atoll hypothesis need not be abandoned. The 

 study of a growing reef shows that the characteristic forms of a 

 reef-edge arc lost a few feet behind that edge. The ocean waters, 

 pressing through the over-lianging, porous edge, are continually 

 destroying the coral heads and throwing their fragments on to the 

 reef-flat. Often blocks of limestone, weighing several tons, are torn 

 from the edge and cast on to the flat. It appears that the growing reef 

 is only a thin veneer covering a mass of debris. If this conception is 



