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57 



VEGETATION OF SOUTH FLORIDA 



northward. These outcrops, although scattered, probably extend north- 

 ward into St. Lucie County, as depicted on the geologic map published in 

 the Second Annual Report of the State Geologist of Florida. These lime- 

 stones are covered by the sand dunes of the east coast, by the sands and peat 

 of the Everglades, and in thickness vary from 1.52 m. (five feet) to 15.24 

 m. (50 feet). For a distance of 48 km. (30 miles) these limestone deposits 

 help to define the eastern rim of the Everglades. 



The geologic map of Florida, published in the second report of the State 

 Geological Survey (199), shows that the area immediately south of the 

 sand hills at Delray, as far south as Cards Sound along the east coast, is 

 characterized by outcrops of oolitic limestone designated as Miami-Key 

 West oolite. The exposures were noted by army officers at the time of the 

 Seminole war,'by Tuomey, L. Agassiz, Shaler, A. Agassiz, and others. Buck- 

 ingham Smith, as early as 1847, found many mollusk shells in the oolite 

 at Miami River and determined the age of this deposit as post-Pliocene. 

 The rock is perhaps younger than the Palm Beach limestone and is younger 

 than the lower part of the Key Largo limestone. The thickness of the 

 Miami-Key West oolite varies, according to the studies made in the drilling 

 of wells. At Ft. Lauderdale it is four meters thick, at Dania 12 meters, 

 at Miami 6 meters. These figures, making due allowance for the scanti- 

 ness of the data and the unreliability of the well records, unless accompanied 

 by samples, show that the maximum thickness may be 16 meters along the 

 coastal outcrops and perhaps more inland. At Miami, the oolite rests on 

 an irregularly cemented aggregate of shell fragments and quartz sand. It 

 rests on "blue sand" at Dania and on sand at Ft. Lauderdale. Litho- 

 logically the rock is a soft, white oolitic limestone, containing thin irregular 

 layers of calcite separating less crystalline streaks, and is discolored by 

 weathering, by the deposit of vegetal mould and the growth of lichens, 

 mosses, and algae. It breaks with an irregular fracture, dresses nicely, 

 hardens on exposure, and makes a good road and building stone. This 

 oolite carries a varying proportion of small, irregular grains of quartz sand, 

 which are more plentiful in the northern part of the area covered by Miami- 

 Key West oolite. The Miami-Key West limestone, which extends to the 

 edge of the Everglades and perhaps beyond, weathers into sharp angular 

 fragments, which lie loosely on the surface, or it is eaten into pockets 

 often filled with sand. The surface, therefore, is very rough and uneven, 



