30 vaughan: geologic history of coral reefs 



The evidence presented shows that the platform on which the 

 present barrier reef of Florida is growing has, geologically just 

 antecedent to its present relation to sea level, stood 30 feet or 

 more higher, and has been brought to its present position by 

 depression. 



The Pleistocene barrier reef, which is 105 feet thick according 

 to the boring on Key Vaca, was formed during the period of sub- 

 sidence which followed uplift at the close of Pliocene deposition. 



SUMMARY OF THE GEOLOGIC HISTORY OF THE FLORIDA REEF TRACT 



The geologic history of the Florida reef tract may be summa- 

 rized as follows : During Pleistocene time along a curve from the 

 eastern side of Biscayne Bay, first trending southward and then 

 bending westward, a barrier coral reef flourished. This was sep- 

 arated by a channel from the main bank on which the Miami 

 oolite was forming or had formed in strongly agitated waters. 

 West of the coral reef, on an extensive flat in shallow water, the 

 Key West oolite was forming, while still farther westward the 

 Tortugas were outlined under the influence of winds and cur- 

 rents. This period of events was succeeded by elevation of the 

 entire key region to probably 50 feet above its previous level. 

 The last period of uplift was succeeded by one of depression, 

 lowering the surface 30 feet or more and establishing prac- 

 tically the same relation of the sea level to land as now prevails. 

 Subsequent to the beginning of this depression the present 

 barrier reef has developed seaward of the keys on a platform 

 already prepared for it, the Marquesas have been formed by 

 winds and currents, and coral reefs have again established them- 

 selves in the Tortugas. 



COMPARISONS OF THE FLORIDA REEF TRACT WITH THOSE OF 

 ANDROS ISLAND, BAHAMAS, CUBA AND AUSTRALIA 



Hayes, Vaughan, and Spencer showed in 1902, as is evidenced 

 by the pouch-shaped harbors of the Cuban coast and by the 

 submerged filled channels, such as the one in Havana harbor, 

 that the last movement of the Cuban coast was downward. 

 Therefore, the platform on which the Cuban reefs occur has 



