The Foundation Rock Of Florida

The oldest exposed formation along the Coastal Plain of Florida is limestone to which the name Ocala has been given from its typical occurrence in and near the city of that name in the central peninsular. As now placed in the geological time scale the Ocala is of top-most Eocene age. Thus, all the formations of which surface outcrops are known in the State fall within the youngest major geologic era, the Cenozoic, or the age of recent life. All of the epochs into which the Cenozoic is ordinarily subdivided are represented, namely, the Eocene, Oligocene, Miocene, Pliocene, Pleistocene and Recent.

The deposits of marine origin were laid down in a sea of only moderate to shallow depth as is indicated by the fossil content and the character of the materials making up the different formations. Some of the deposits are of brackish and fresh-water origin; some were laid down through the action of rivers and streams, while to a lesser extent the wind has acted as an agent of deposition in some of the more recent formations.

Even though the exposed formations of Florida are all of sedimentary origin and are geologically young it is, however, known from well cuttings that the State has existed, with ups and downs, since ancient time. A well drilled to the depth of 6,180 feet in Marion County, central peninsular Florida, encountered mica shist, slate, and quartzite at a depth of something more than four thousand feet.

This is the first and only well from which such positive data on the thickness of the sedimentary formations in Florida have been obtained. The age of these basement or metamorphic materials has not been determined, but crystalline rocks of Paleozoic age are known in Georgia and Alabama. Apparently therefore what we now know as Florida was aeons ago a part of the land mass of old Appalachia.

Since the formation of these ancient deposits now found at a depth of more than four thousand feet the State has undergone many oscillations of level, remaining dry land for ages, then covered by the sea for other periods, finally through these various vicissitudes becoming the Florida of today. The character of the later deposits, which are now fairly well known, indicates, however, that the sea in which they were laid down was never of great depth.

The Ocala limestone of Eocene age may be considered the foundation rock of Florida. It occurs at the surface over a considerable area in the central part of the peninsula and over a lesser area in western Florida. It has also been recognized in cuttings from well borings at various depths from almost every part of the State.