distance inside the seaward edge of the platform and 

 does not grow on the edge of deep water in the way 

 that true atolls and barriers do. 



Such conditions were present in the marginal seas 

 of the Atlantic. These stretch from the Parcel das 

 Paredes reefs of middle Brazil, by way of Cape San 

 Roque to the north, along the lesser Antilles and, 

 finally, to the Florida Keys and Bermuda. In most 

 cases earlier reefs were present up to 50 million years 

 ago, long before the glacial period, in the warmer seas 

 of what geologists call Tertiary times. A great part of 

 the platforms upon which the present day reefs grow 

 was formed by wearing down of this old coral forma- 

 tion. 



Bermuda has a most interesting history. Briefly, dur- 

 ing the geologic age known as the Eocene, between 40 

 and 50 million years ago, it was a volcano which later 

 subsided below the surface of the ocean and was worn 

 down by wave action. It sank further and at the same 

 time became covered with marine sediments of a lime- 

 stone character in the later Tertiary period. There is 

 some evidence that an atoll grew on the bank during 

 this period. Subsequently, however, the mass was ex- 

 posed once more, well above the water level, and formed 

 an island of about 230 square miles, according to Davis. 

 This may have been due to a drop in ocean level of 

 between 100 and 150 feet which resulted from the 

 withdrawal of water to the ice caps during glaciation. 



While exposed above the ocean surface during glacial 

 time the land was worn by wind action and much of 

 the present rock surface is formed from windblown 

 limestone. Further wear due to wave action and a sub- 

 marine accumulation of debris formed a platform. 



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