Introduction >Topo-Eco Divisions Geology References PDF version

General Features

The line of test wells (see figure 1) crosses three relatively distinct topographic subdivisions. The southern part of the line closely approximates the boundary between the Everglades and the Big Cypress Swamp in western Dade and Broward Counties. In eastern Hendry County, from the latitude of the Broward-Palm Beach County boundary, the line of test wells bears northward for about 20 miles along the western edge of the Everglades, then northwestward across the sandy flatlands to the western edge of Lake Hicpochee. Parker and Cooke (1944, p. 38-53) discuss these topographic-ecologic divisions in detail, hence only a brief discussion is included in this report.

The Everglades

The Everglades is a region covered by black organic soils. Although somewhat indefinite, the boundary between the Everglades and the areas to the east and west is generally placed where the saw grass (sedges) of the Everglades is replaced by true grasses or cypress. According to Parker and Cooke (1944, p. 48), the limestone which floors the Everglades is highest in the vicinity of the Miami Canal, 4 miles east of well 24, and slopes gently to the southern margin and northward toward Lake Okeechobee. The rock floor is composed of fresh-water and marine limestones and partially indurated marl of the Fort Thompson formation. Although the Miami oolite was not observed in any of the test wells, it occurs as a thin layer overlying the Fort Thompson formation in the southern part of the Everglades.

Big Cypress Swamp

To the west, the Everglades merges with the Big Cypress Swamp, which is a poorly defined region of alternating swamp and hammock areas. The elevation in general is slightly higher than the Everglades, but lower than the sandy flatlands on the north. The higher portions, where soils are aerated, support the growth of palmettos, pines, and bunch grasses, but the lower areas are marked with typical swamp growth of small cypress and sedges. In contrast with the Everglades, the surface material is mainly limestone and sandstone, but there are numerous small areas where thin marly deposits lie at the surface. The geology, as interpreted from the well cores, pertains only to the eastern edge of the Big Cypress Swamp.

Sandy Flatlands

The northern extremity of the line of test wells crosses the sandy flatlands, which is slightly higher than the Everglades and the Big Cypress Swamp but does not exceed 25 feet. The sands were deposited as part of the marine Pamlico sand of Pleistocene age and are dotted with small shallow ponds and poorly defined marshy areas, one of which is the Devil's Garden. Drainage is chiefly underground through the permeable sand with very little, if any, surface runoff.