.4 Contribution to the Geologic History of the Floridian Plateau. 139 



In Florida, Upper Oligocene reef corals are known from several 

 localities. The most northern is in Wakulla County, near Wakulla 

 Station, between Tallahassee and St. Marks; fossil corals are also found 

 at White Springs, on the Suwanee River; large heads of Siderastrea are 

 abundant in the vicinity of Alachua, Alachua County, and the chalce- 

 donic replacements of corals from the vicinity of Tampa are widely 

 known. Compared to the total extent of the Upper Oligocene formations 

 in Georgia and Florida, corals play an insignificant role; they possess 

 more importance as furnishing means of correlating geologic formations 

 than as constructional agents. 



Miocene. — No coral reefs of Miocene age are known in the Atlantic 

 and Gulf Coastal Plain. A few fossil species are known and for strati- 

 graphic purposes they are of value. 



Pliocene. — No Pliocene coral reefs are known. Professor Heilprin, 

 in his discussion of the exposures along the Caloosahatchee River, called 

 attention to the comparative scarcity of corals and the great abundance 

 of shells in the Caloosahatchee marl. On Shell Creek corals are rela- 

 tively more abundant, but they are not strictly reef-building species, 

 belonging rather to species that grow on flats, and especially the inner 

 flats behind keys. 



Pleistocene. — The second extensive development of coral reefs in 

 Florida took place in Pleistocene time. 



Attention may be called to Captain Hunt's estimate of the time 

 necessary for the formation of southern Florida. He bases his estimate 

 on two assumptions: first, the rate of growth of corals as observed by 

 him in the neighborhood of Key West ; second, that the whole of south- 

 ern Florida has been built up by the activity of these organisms, whose 

 calcareous remains after having been pounded into sand by the sea go 

 to form great limestone flats. Captain Hunt's estimate of the rate of 

 growth of corals is open to doubt, and his second assumption is funda- 

 mentally wrong. 



