STRUCTURK OF CORAL ISLANDS. 



155 



that the ring-forined reefs are based on a shallow foundation 

 instead of on the floor of the open sea, and that instead of being 

 scattered irregularly, they are grouped closely together." — " It 



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appears from the charts on a large scale, that the ring-like 

 structure is contingent on the marginal channels or breaches 

 being wide, and, consequently, on the whole interior of the- 



