Park Service, showing mangrove and tidal marsh 

 areas in Everglades National Park. Most man- 

 grove areas are shown on navigation charts and 

 topographic maps. Tidal marsh is not desig- 

 nated as such on charts and maps; only "marsh" 

 or "swamp" is designated. Tidal marsh was 

 separated from freshwater marsh by assuming 

 that it penetrated inland to less than the 5-ft 

 (1.5-m) contour and that wooded marsh shown 

 on most topographic maps is essentially fresh- 

 water habitat. Local field checks verify our 

 assumption. We did not verify the boundaries 

 by field observations along the entire coast. 



Submerged vegetation was mapped freehand 

 on 1,200-Series navigation charts by consulting 

 aerial photographs of coastal areas. The photog- 

 raphy was made available for study by virtually 

 every county engineering or tax assessor's office 

 on the west coast. The photography was gen- 

 erally 1: 400 scale, less than five years old, and of 

 excellent quality for our purpose. Field checks 

 usually verified our interpretation of the photo- 

 graphs. 



We calculated the relative areas characterized 

 by mangroves, tidal marsh, submerged vegeta- 

 tion, and unvegetated bottom (Fig. 27). If the 

 total area of estuaries (3,003,213 acres = 

 1,215,400 ha) is considered to be the area of 

 open water plus the area of mangrove swamps 



Figure 27. — The percentage of mangrove swamp, tidal 

 marsh, submerged vegetation, and unvegetated bottom. 



and tidal marshes, approximately one-half of the 

 area is unvegetated; the remaining half is about 

 equally divided among mangrove swamps, tidal 

 marshes, and submerged vegetation. The area 

 of submerged vegetation (520,431 = 210,618 ha) 

 is about one-quarter of the open-water surface 

 area. 



GEOLOGY 



The Floridian Plateau originated as a massive 

 appendage of the North American continent in 

 mid-Triassic time (200 million years ago) when 

 an enormous land mass, Pangaea, began to break 

 up into the continents of today. The southern 

 tip of the Floridian Plateau then occupied a po- 

 sition near the present location of Ascension 

 Island (midway between South America and 

 Africa and just south of the equator) from which 

 it migrated northwesterly some 4,300 nautical 

 miles (8,000 km) to its present position. The 

 entire continent including Florida plus the Gulf 

 of Mexico continues its westerly migration to 

 this day (Dietz and Holden, 1970). 



The Florida peninsula represents the above- 

 water portion of the Floridian Plateau, which 

 separates the deep water of the Atlantic Ocean 

 from the deep water of the Gulf of Mexico. The 

 Plateau consists of thick layers of limestone and 

 unconsolidated sediments that rest on a founda- 

 tion of ancient sandstone and volcanic rock (Fig. 

 28) . The limestones and the sediments accumu- 

 lated intermittently as the land was alternately 

 covered and uncovered by shallow seas over the 

 past 150 million years. The thickness of the de- 

 posits is 3,300 to 16,500 ft (about 1,000 to 5,000 

 m) , the difference correlating with a tilt south- 

 ward and westward of the underlying ancient 

 rock caused by uplift in northeastern Florida 

 (Cooke, 1945; Lynch, 1954; Puri and Vernon, 

 1959; Schnable and Goodell, 1968). 



Uplift was exerted mainly along two parallel 

 ridges in the northeast — the Peninsular Arch 

 and the Ocala Uplift — and secondarily by the 

 Chattahoochee Arch to the west (Figs. 28 and 

 29). The Peninsular Arch has acted since 

 Mezozoic time (200 to 75 million years ago) and 

 the Ocala Uplift since Eocene time (50 million 

 years ago). Uplift has accelerated erosion in 

 the northeastern peninsula and the north central 

 panhandle resulting in exposure of much older 

 rock there than elsewhere (Fig. 30). 



52 



