Eocene sediments and is overlain by the Hawthorn formation, of Miocene age, which in turn is overlain by a mantle of undifferentiated Pleistocene and Recent materials. The total thickness of the Ocala formation is not known, but it is estimated to be about 500 feet. It is the oldest formation penetrated by wells drilled for water in the county. In parts of Florida the Tampa limestone, of Miocene age, lies between the Ocala limestone and the Hawthorn formation, but in Seminole County the Tampa is believed to be absent, and the upper surface of the Ocala is apparently an irregular eroded surface on which the Hawthorn rests. The Ocala underlies all of the Florida peninsula and is at or near the surface in Sumter County, about 35 miles west of Seminole County, and in other counties in the west-central part of the peninsula.
The Ocala formation consists of almost pure limestone with some chert. Parts of the limestone are porous and contain solution channels that permit free circulation of ground water. According to the reports of drillers, many of the wells penetrating the Ocala limestone in Seminole and Orange counties encounter cavities with vertical dimensions of as much as 20 feet, whereas in other parts of the peninsula where the formation is deeply buried no cavities have been reported. It thus appears that solution channels occur in the limestone where it is or has been at the surface or at moderate depths below the surface. Old solution channels now filled with sand or clay are exposed in some of the quarries in the
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