A Contrihuiion to the Geologic History of the Floridian Plateau. 131 



nent of this formation is coral, usually in the form of large heads of 

 McBandra and Orbicella (plate 15, figs, b and c). The interspaces are 

 filled with various kinds of calcareous debris derived from marine organ- 

 isms. Over the surface there is frequently a hard crust composed of 

 colored, laminated, amorphous calcareous material. The lime of the 

 coral heads is frequently crystalline. 



These three limestones are the principal geologic formations sur- 

 rounding the bays and sounds of southeastern Florida. Toward the 

 interior of the State, however, both the Miami oolite and the Lostman 

 River limestone are overlain by the great interior swamp deposits, the 

 most extensive and famous of which are the Everglades. 



There is in this region another important limestone formation, the 

 Key West oolite, which closely resembles the Miami oolite in appearance 

 (plate 14, figs, b and c; plate 15, fig. a). It is a soft, white or cream- 

 colored limestone, mostly composed of oolitic granules embedded in a 

 loose matrix of amorphous, or occasionally crystalline, calcium carbonate. 

 The structure of the granules of the two is the same, except silica is rarer 

 in the Key West oolite. The thickness of this formation is unknown, 

 but is tentativeh' placed by Sanford at 50 feet. It is the rock composing 

 all the keys from No Name and Little Pine to Boca Grande, except the 

 purely mangrove keys. 



Although the Key West and Miami oolites are so similar and may 

 be geologically contemporaneous, they are not known to be in contact 

 anywhere, as both the Key Largo and Lostman River limestones inter- 

 vene between their respective outcrops. 



TOPOGRAPHY OF SOUTHERN FLORIDA. 



The whole of the area under consideration is one of low relief, the 

 greatest elevation known being perhaps 30 feet. The Miami oolite forms 

 a limestone ridge extending southward from the vicinity of Del Ray to 

 beyond Homestead. The elevations along this ridge are about 8 feet at 

 New River, Fort Lauderdale; perhaps 30 feet south of Miami, and about 

 8 feet on Long Key in the Everglades. In the vicinity of Miami there 

 is a steeper sea-face with a westward slope, the rock passing beneath and 

 forming the floor of the Everglades. The width of this ridge west of 

 Miami is about 3 miles. 



The Everglades are a vast interior swamp, the surface of which is 

 mostly an enormous saw-grass marsh with mottes of timber here and 

 there breaking the monotonous expanse. The altitude is almost the 

 same as that generally prevalent over this section of the State. Some 

 determinations along the eastern margin are: "west of Lantana, 18 

 feet; west of Hillsboro Inlet, 14 feet; west of Fort Lauderdale, 17 feet; 

 at the pool at the head of Miami River, 6.2 feet. South of the Biscayne 

 pineland and Long Key the height of the Everglades is less than 6 feet " 

 (Sanford) . The maximum elevation of the keys east of Key West perhaps 

 does not exceed s or 6 feet. 



VEGETATION OF SOUTHERN FLORIDA. 



The vegetation of the area presents three different types. The 

 oolite ridge is mostly covered by pines, the soil is thin and the surface 

 of the ground rocky (plate 8, fig. a); in the Everglades (plate 7, figs. 



