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Geology of Florida

The Florida Review

1911

The investigations of the State Geological Survey carried on during the past three years have added much information regarding the geology of the state. The results are included in detail in the reports of the survey which have been published and are available for free distribution to those interested. The following is brief sketch of the principal geologic facts of interest regarding the state:

Florida lies within and is a part of the general coastal plains of the United States, which extend along Atlantic and Gulf Coasts from Long Island to Mexico, varying in width and covering the eastern part of New Jersey, Delaware. Maryland, Virginia, North Carolina, South Carolina, Georgia and all of Florida, is well as much the southern part of Alabama, Mississippi, Louisiana and Texas. The formations of the coastal plain are sedimentary, containing much clay, limestone and sandstone, and lie nearly horizontal or with slight dip. The sediment making up these deposits came from higher land to the north and west. The sea occupying the present position of Florida, was in early times remote from the sources of sediment, so that the proportion of wash was much less here than nearer the original shore line. This clear sea was favorable to the existence of shell life, the remains accumulating to form shell rock. Hence in the early history of Florida in particular a large amount of lime and shell rock accumulated.

In its general geology Florida is of comparitively simple structure. The rocks are all of sedimentary origin, no igneous or greatly metamorphosed rocks occurring in the state. The starata lie for the most part either horizontally as formed or with a slightly accentuated dip, and have suffered no great distortion such as often characterises the rock of a mountainous country. These sedimentary formations consist of limestone, sandstone, shales, and clays, the underlying foundation rock throughout the state being a massive and very thick limestone.

Formerly it was believed that the greater part if not all of the state of Florida was of coral formation. This view was founded upon the observations of Louis Agassiz and Joseph LeConte. The first publication upon the subject was by Agassiz and appeared in 1852 as an appendix to the report of the Superintendent of the United States Coast Survey for the year ending November, 1851. Agassiz believed that not only the Florida keys were of coral formation, but that the peninsula as far at least as the 28th degree of north latitude was of similar origin. LeConte's paper appeared in 1857 and to the conclusion of Agassiz added the theory that the keys rested upon a substructure of inorganic sediment carried by the Gulf Stream. Previous to these publications the true character of the limestone of the mainland had been recognized and described by several observers. Nevertheless the views of Agassiz and Leconte gained wide circulation and were for a generation the accepted views as to the origin of the peninsula.

The credit of again establishing the true character of the limestone of the interior Florida is due to Professor Eugene Smith, State Geologist of Alabama. Professor Smith's observations were made during 1880 while acting as special agent for the cotton culture report of the Tenth Census. In this capacity he traveled over much of Florida and correctly described the principal underlying limestone.

The Florida deposits are all comparatively recent date geologically, and belong to the Cenozoic, or latest of the major time divisions. The subdivisions of the Cenozoic are in the order of age: Eocene, Oligocene, Miocene, Pliocene and Pleistocene. All of these except the first mentioned, the Eocene, are represented in Florida.

The oldest formation known in Florida is the Vicksburg limestone, which belongs to the Oligocene division of the Cenozoic. The conditions under which this limestone was formed, as shown by the rock itself, were as follows: A clear sea of medium depth free from land sediment in which marine life, especialy the minute organisms known as foraminifera, abounded, the shells of these small animals along with larger shells making up the limestone. The formation, as seen at the present time, contains in many places large masses of flint formed by replacement of calcium carbonate by silica in solution in the underground waters.

The Vicksburg limestone doubtless underlies the entire state. It is a part of an extensive formation which encircles the Gulf of Mexico from Florida to Louisiana. In Alabama it makes up apparently the middle part of the St. Stephens or white limestone, and has there, according to Professor Smith, a thickness two or three hundred feet.

In Florida this limestone lies at the surface in limited areas, but is for the most part buried beneath later deposits. Good exposures of the formation are seen in the central part of Alachua and in southern Columbia counties. The largest exposed areas lie in Citrus, Hernando, Marion and Levy counties.

The Upper Oligocene deposits its consist of limestone and clays. Over much of the north central and western portions of the state these deposits lie near the surface, forming a thin coating which rests unconformable upon an eroded surface of the older formations. The Suwannee river cuts across these formations along the boundary between Hamilton and Columbia counties They are also cut by the Apalachicola river from Chattahoochee to Bristol. They also crop out along the Hillsboro river and along Tampa Bay in southern Florida, and doubtless extend to the east, in that direction underlying later formations.

The preceding sketch is purposely made very brief and is intended to give some of the principal features of the geology of Florida. Those who are interested may find a more detailed account of the geology of the state in the survey reports and in other publications. The Miocene deposits next above lie along the east side of the peninsula, being well exposed along Black creek in Clay county, and at Rock Spring in Orange county. Deposits representing the same interval are exposed in west Florida along the Ocklocknee and Apalachicola rivers. Marine Pliocene deposits, consisting of marl and shell beds, occur over over much of the southern end of the peninsula, being best exposed along the Caloosahatchee river. Residual and river formed Pleistocene deposits are to be expected locally throughout the state, and marine Pleistocene shell deposits have been reported from a number of localities. The Miami oolitic limestone, forming the eastern border of the Everglades, is the most extensive Pleistocene deposit in the state. The present elevation of this limestone above the sea is due to a mild uplift that occurred during or at the end of Pleistocene time.

The preceding sketch is purposely made very brief and is intended to give some of the principal features of the geology of Florida. Those who are interested may find a more detailed account of the geology of the state in the survey reports and in other publications.

Source:
Excerpt from "Sketch of the Geology of Florida" The Florida Review, June, 1911, pgs 488-490.

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