mals which are always present in the ocean in countle 

 millions and which are continually falling to the bottoi 

 This is not so improbable as at first sight might appe; 

 since it is well known that large areas of chalky ro 

 now part of land were originally formed by simil 

 deposits on the ocean floor. Murray's theory was tt 

 the silt would accumulate upon the submarine rid^ 

 or mounds until they reached within 100 feet or so 

 the surface, where active coral growth could take plac 

 Since coral grows more rapidly on the outside of a re 

 and tends to die as a result of sediment in the mc 

 sheltered inner portions, this would account for t 

 innumerable ring-shaped atolls, without the need f 

 assuming widespread sinking of the earth's crust. 



Further suggestions advanced include the theory th 

 non-reef building corals, which are able to live in de 

 water, were responsible for building up the platforn 

 Others are based upon a belief that islands might 

 cut down by wave action and water currents to foi 

 the base upon which the reefs have grown. The mc 

 important contribution to the subject, however, is t 

 Glacial Control Theory advanced by R. A. Daly. 



According to Professor Daly, all existent coral re( 

 have been formed since the last glacial epoch. Durii 

 the period of glaciation the poles were covered by i 

 caps several thousand feet thick and extending co 

 siderably below the polar circles into what are now t 

 temperate latitudes. The result of trapping such gre 

 quantities of water at the poles was that the genei 

 level of the ocean was lowered by about 175 feet ai 

 all previously formed coral reefs were killed by col 

 The former ocean bottom, exposed by the withdraw 

 of water, and no longer protected by reefs was cut ba 



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