The Everglades of Florida occupy an irregularly marked shallow slough thirty-five to fifty miles wide and a hundred miles in length. They comprise an area of approximately four thousand square miles, all south of the twenty-seventh parallel of latitude with the exception of a small strip bordering the shores of Lake Okeechobee.¹ The soil of the Everglades is of organic origin.

Bounded on the eastern side by a coastal fringe of sand dunes and on the western side by the Ocaloacoochee Slough and the Big Cypress Swamp, the Everglades extend to the southern and southwestern coast of the state, where the salt-water marshes and the mangrove swamps form the southern border.

The Everglades constitute the third or downstream unit of the watershed of the interior of the Florida peninsula below the twenty-eighth parallel. The first or tributary section of this drainage area, the Kissimmee-Everglades watershed, comprises some five thousand square miles.² The drainage elements of the first area are the Kissimmee River, which drains about two-thirds of the area, and numerous smaller streams such as Fisheating Creek and Taylor's Creek. The second or middle unit of this watershed is Lake Okeechobee, a shallow body of fresh water of seven hundred and twenty square miles whose surface elevation is regulated between fourteen and eighteen feet. The composite area of the three units approaches ten thousand square miles. Under natural conditions, prior to the advent of artificial drainage, the outflow of the waters of the first two units passed onto the third unit.³

Taken as a whole the topography of the Florida mainland has all the aspects of infancy. Drainage is defective, sloughs, shallow ponds and lakes abound. Most of the interior is a swamp, there are no well-defined river systems nor stream valleys. . . . ⁴

. . . but the gradient would have to be greatly increased before running water would begin to cut down the gradually thickening mass of plant remains that makes up the organic soils of the Everglades.⁵

The vegetative accumulation, or soil, varies from an average thickness of eight feet at Okeechobee's shores to the thinnest of deposits at the sides of the Everglades.

The line of demarcation between the glades and adjoining areas is extremely irregular: along this line extends a stretch of grass land that may be under two feet of water at the end of the rainy season, but in most years is dry enough for the cultivation of a winter vegetable crop. The actual boundary between the Everglades and the adjoining prairie is where the sedges of the glades are met by true grasses, cypress, salt marsh, or mangroves.⁶

Scientific interest in the geology of the Everglades began after the middle of the nineteenth century. The first state geologist of Florida, E. H. Sellards, brought together the geological investigations of the peninsula prior to 1908 in a section of his first report. In 1825 James Pierce visited south Florida and observed a great savanna which he estimated to be a hundred miles in circumference, but, "The existence of a large permanent lake located by maps in the southern part of the peninsula is doubted."⁷ The publication of Buckingham Smith's documentary report on the Everglades in 1848 established the existence and general location of the area.

Smith believed the geology of the southern portion of the state to be similar to that of the sea-coasts of Georgia and South Carolina. "Oolitic lime-rock, filled with the shells and corals of species that still exist, forms the great geological feature of the country."⁸ Smith found the rock to be porous and susceptible of easy excavation; exposure to air hardened the rock and made it useful for building purposes.

The same rock forms the bottoms of the openings through the rim of the Ever Glades to an unknown depth. It composes the floor of Biscayne Bay, and of the other bays and sounds, and of the rivers along the coasts on both sides of the peninsula, and also the basin of the Ever Glades.⁹

In 1851 Michael Toumey examined the limestone at the falls of the Miami River leading into the Everglades. These rocks, he found, were of the same age as those he had seen at Key West, and were identical with living shells in the surrounding waters. Toumey regarded the glades as resting on a basin of what he termed Miami limestone, clearly distinguished from the Tertiary limestone at Tampa Bay. The contour of the ridge surrounding the Everglades, together with its structure and the embedded remains, led Toumey to the conclusion that the elevation of the Florida Keys by twenty feet would produce a similar ridge shutting out the sea between the Florida reef and the mainland. Such an elevation, Toumey believed, would produce another basin similar to that of the Everglades, differing only in greater comparative length.¹⁰

Because of their accessibility the fossil-bearing beds of the Gulf Coast and the Caloosahatchee River aroused the interest of geologists before 1900. The geologic formation of the southern part of the peninsula, however, remained obscure for another generation on account of the difficulties of making observations.

. . . The combination of low, flat terrain with few and very shallow river cuts, the difficulty of transportation, the lack of cuttings from deep or shallow wells, and the mantle of muck, marl, sand, water, and vegetation that covers the underlying rocks . . . ¹¹

caused the investigations of early workers to be restricted, to the seacoasts and river banks.

Since the beginning of drainage operations in 1882, the cutting of canals and channels in South Florida has added an abundance of geological information. Other sources of data were found in the excavations made for roads, ditches, and dikes, as well as the samplings of material through which numbers of drills have passed in the sinking of water and oil wells. Had the mass of data now handy for modern geologists been available to Louis Agassiz in 1851, or to Joseph LeConte in 1878, they would never have subscribed, to a coralline theory of growth for the southern part of the state.¹²

The name "Floridian Plateau" has been applied to the great projection southeastward of the continent of North America. This projection separates the deep water of the Gulf of Mexico from the deep water of the Atlantic Ocean.¹³ This Floridian Plateau has been in existence since very ancient times, and appears to have lain east of the epicontinental seas during the Paleozoic era. The plateau probably remained dry land during the Triassic, Jurassic, and Lower Cretaceous epochs, but was covered by the seas during the Upper Cretaceous times. In the Cenozoic era the plateau underwent many shiftings, but the water was never very deep, nor the land high above the sea level.¹⁴ At the western edge of the Everglades, fifty miles from Miami, sedimentary rock exists to a depth of at least ten thousand feet. An examination of the cuttings of an exploratory well for oil showed that the drilling ended in Lower Cretaceous strata, ". . . comparable to the Fredericksburg group of Texas and southern Oklahoma, and suggests that this area is underlain by still older sedimentary rocks."¹⁵

In a resume of the structure and stratigraphy of Florida, Stuart Mossom outlined the sedimentary formations of the state. He found these formations to describe an anticline in a southeasterly direction from the Ocala limestone dome of the Eocene Age. From surface level at Ocala, the Eocene limestone dips to a depth of twelve hundred feet as the Everglades give way to the Gulf. Atop the Ocala formation are the younger groups of Oligocene and Miocene ages which become thicker as they approach the coast lines. The Pliocene and Pleistocene formations do not extend more than one hundred and sixty feet under the surface.¹⁶

The Eocene, Oligocene, and Miocene formations extend to a depth of twelve hundred feet in the Miami area, dipping to the sea in every direction. On account of this anticline and the permeability of the rocks, they are excellent artesian aquifers. "The waters of these formations are not only highly mineralized . . . but are corrosive, rendering them unsatisfactory for most needs."¹⁷ The formations of the Pliocene and Pleistocene, flanking the Miocene, are exposed in many places in and around the Everglades.

Angelo Heilprin, exploring the Caloosahatchee and Lake Okeechobee in 1886 found no evidence to support a coralline theory of growth of Florida; he decided that the growth had been through accessions of organic and inorganic material in the usual methods of sediment and upheaval.¹⁸ Matson and Clapp expressed the joint belief that the deposition of the Pliocene rocks began with an encroachment of the sea which extended beyond the latitude of Lake Okeechobee. Following the deposition of the Pliocene the land emerged to a probable greater height than at present, and "It was during this period that the major features of the present topography were produced."¹⁹

Two Pliocene formations are located in the Everglades, the Caloosahatchee marl and the Tamiami limestone. The Caloosahatchee marl, exposed in the banks of the river of the same name, consists chiefly of fine sand and shells. Its color ranges from white to light gray, blue, or yellow. It appears to underlie a large part of Florida south of the twenty-seventh parallel. Deposited in a warm and shallow sea, this marl contains a large proportion of unbroken shells. Water from the marl has a high chloride content, due in part to Pleistocene sea invasions, and in part to the Miocene rocks underneath it.²⁰

The Tamiami limestone, coming to the surface in the lower reaches of the Big Cypress and appearing as far north as Fort Lauderdale on the east coast, is a wedge-shaped formation, inclining toward the coast, and the source of water for the cities of the east coast. "The calcareous sandstones and sandy limestones of this formation are among the most permeable rocks ever investigated by the Federal Geological Survey."²¹ These rocks were deposited in a warm shallow sea, followed by an elevation above sea level when erosion and solution took place, and a subsequent lowering under the sea brought about a deposition of the Miami oolite on the Tamiami.

The close of the Pliocene epoch witnessed a great change in the climate of the earth. This change brought about the formation of glaciers that covered a third of the northern hemisphere. "The Pleistocene epoch has been divided into four major glacial stages and a minor one . . ."²² during which the sea level fell in producing the massive fields of ice. In the interglacial stages the seas rose again, as the ice melted, and the lower lands of the world were covered by the seas. These successive inundations were accompanied by the deposition of marine materials and were followed by the recessions of the waters which gave the land its approximate present appearance in lower Florida by building up the lands on the north, east, and west of the Okeechobee-Everglades depression. Longshore currents swept sands from the north, along both coasts, which merged with the lime deposits in the south. These mergers built up the edges of the Floridian Plateau and produced the large slough in the area under study.²³

The first of the Pleistocene formations to be laid down was the Miami oolite, present in the southern and eastern parts of the Everglades. The oolite varies in thickness from the merest deposit to thirty feet and is overlain by sand, muck, and marl, and cut through by sandy channels in many places. It is a white or light yellow limestone of very high porosity, easily quarried, and used for rough constructional purposes. Because of its outcroppings along the east coast and in the banks and rapids of the short rivers, it was the first of the south Florida rocks to be noted.²⁴ Modern geologists believe the oolite was formed as a shallowly submerged bar which, as has been suggested, shut off a wide shoal, now the Everglades, from deeper water of the Atlantic. It is possible that Lake Okeechobee marks a deeper part of the sea, as its present bottom is fifteen feet lower than the neighboring Everglades.²⁵

That part of the Everglades soils not underlain by Miami oolite and Tamiami limestone is generally underlain by the Ft. Thompson deposits, also of Pleistocene age. This formation averages ten feet in depth over the northern part of the glades and includes freshwater, marine, and brackish-water limestones and marls. Found at the surface near Ft. Thompson on the Caloosahatchee River, the formation covers the area occupied by Lake Okeechobee when that body of water extended from the present site of the town of La Belle to the present eastern border of the Everglades and south to the Tamiami Trail.²⁶ The alternation of marine and brackish water deposits combined with fresh water shells provides a clear record of the several inundations of the seas. Ground water in the Ft. Thompson formation is found in the shallow wells in the vicinity of Lake Okeechobee, where it is sought for domestic use. "The fact that the Ft. Thompson is relatively low in permeability makes it a valuable asset in areas of ditching and diking for water control."²⁷

The Anastasia and Pamlico formations, found in the coastal ridge on the Atlantic and along the eastern borders of the Everglades, are composed of sand, sandy limestone, and calcareous sandstone. In the strip bordering the Everglades where the sands of these formations are mixed with glades organic soils the lands are valuable for cropping and grazing. Water wells developed in these deposits are of relatively indifferent quality.²⁸

The most recent geological formation in the Everglades is the Lake Flirt marl, composed of soft gray marl or calcareous mud almost universally present under the deeper muck of the upper Everglades. Flirt marl is of value because of its impermeability, which prevents the percolation of ground waters in the organic soils of the region. "Where it is present under sufficient thickness of soil that ditches do not cut through it, the water table can be controlled even in areas of permeable underlying rocks."²⁹ The top fifty feet of rock strata in the northern half of the Everglades is relatively impermeable and subjects this half to water control. In the lower half of the Everglades the strata become looser and highly water-bearing as the rim is approached. Canals cut through permeable strata drain adjacent lands to the limit of the canal; contrariwise, the success of water control by dikes and pumps depends on impermeability.

Lacking modern geological information, yet seeking the truth, John R. Mizell in 1902 compared the Okeechobee-Everglades formations to a large bowl with two rims. The inner basin he likened to the big lake, a small sea within itself. The outer basin he likened to the Everglades, with the rock rim on the east and swamps and sloughs on the west. Mizell believed the normal condition of the glades to be unaffected by the inner basin until the lake was taxed beyond its capacity to relieve itself through the Caloosahatchee Canal. The short streams on the Atlantic side of the Everglades were produced by the head of water from the lake overflow being unable to force its way down the Caloosahatchee, and seeking its way across the low spots in the outer rim.³⁰

Chapter Notes

1 Samuel Sanford, "The Topography and Geology of Southern Florida," Florida State Geological Survey, Second Annual Report (1909), 189; C. Wythe Cook and Stuart Mossom, "The Geology of Florida," Florida State Geological Survey, Twentieth Annual Report (1928), 43; E. H. Sellards, "Geologic Sections Across the Everglades," Florida State Geological Survey, Twelfth Annual Report (1919), 67-68; J. C. Stephens and C. C. Schrontz, "The Principal Characteristics of the Kissimmee-Everglades Watershed," The Soil Science Society of Florida, Proceedings, IV-A (1942), 14, 24.

2 J. C. Stephens and C. C. Schrontz, "The Principal Characteristics of the Kissimmee-Everglades Watershed," loc. cit., 14.

3 C. Wythe Cook and Stuart Mossom, "The Geology of Florida," loc. cit., 43-44.

4 Samuel Sanford, "The Topography and Geology of Southern Florida," loc. cit., 179.

5 Garald G. Parker, "Notes on the Geology and Ground Water of the Everglades in Southern Florida, "The Soil Science Society of Florida, Proceedings, IV-A (1942), 52.

6 Samuel Sanford, "Topography and Geology of Southern Florida," loc. cit., 181.

7 E. H. Sellards, "Geological Investigations in Florida Previous to the Organization of the Present Geological Survey," First Annual Report of the Florida State Geological Survey (1908), 56.

8 Thomas Buckingham Smith, "Report of Buckingham Smith, Esquire, on His Reconnaissance of the Everglades, 1848," Senate Documents, The Reports of the Committees, Number 242, 30 Congress, 1 Session, 15. Hereinafter cited as "Buckingham Smith Report. "

9 Ibid.

10 E. H. Sellards, "Geological Investigations in Florida Previous to the Organization of the Present Geological Survey," loc. cit., 58-59.

11 Garald G. Parker, "Notes on the Geology and Ground Water of the Everglades in Southern Florida," loc. cit. 53.

12 Ibid.

13 C. W. Cook and Stuart Mossom, "The Geology of Florida," loc. cit., 39.

14 C. W. Cook and Stuart Mossom, "The Geology of Florida," loc. cit., 39.

15 Garald G. Parker, "Notes on the Geology and Ground Water of the Everglades in Southern Florida," loc. cit., 54.

16 Stuart Mossom, "A Review of the Structure and Stratigraphy of Florida," Florida State Geological Survey, Seventeenth Annual Report (1926), 171-254.

17 Garald G. Parker, "Notes on the Geology and Ground Water of the Everglades in Southern Florida," loc. cit., 71.

18 Angelo Heilprin, Explorations on the West Coast of Florida and in the Okeechobee Wilderness, 65. Hereinafter cited as Okeechobee Wilderness.

19 George C. Matson and Frederick C. Clapp "A Preliminary Report of the Geology of Florida with Special Reference to Stratigraphy," Florida State Geological Survey, Second Annual Report (1909), 167.

20 C. W. Cooke and Stuart Mossom, "The Geology of Florida," loc. cit., 152-153.

21 Garald G. Parker, "Notes on the Geology and Ground Water of the Everglades in Southern Florida," loc. cit., 71.

22 Garald G. Parker and Nevin D. Hoy, "Additional Notes on the Geology and Ground Waters of Southern Florida," The Soil Science Society of Florida, Proceedings, V-A (1943), 37.

23 Garald G. Parker and Nevin D. Hoy, "Additional Notes on the Geology and Ground Waters of Southern Florida," loc. cit., 41-42, 54-55.

24 C. W. Cook and Stuart Mossom, "The Geology of Florida," loc. cit., 204-205.

25 Garald G. Parker, "Notes on the Geology and Ground Water of the Everglades in Southern Florida," loc. cit., 68.

26 C. W. Cook and Stuart Mossom, "The Geology of Florida," loc. cit., 211-212.

27 Garald G. Parker and Nevin D. Hoy, "Additional Notes on the Geology and Ground Water of Southern Florida," loc. cit., 51.

28 Garald G. Parker and Nevin D. Hoy, "Additional Notes on the Geology and Ground Water of Southern Florida," loc. cit., 50.

29 Ibid., 49-50, 55.

30 Cited in, "Message of Governor W. S. Jennings to the Legislature of Florida Relating to the Reclamation of the Everglades," April 7, 1903, Senate Documents, Number 89, 62 Congress, 1 Session, 88.