The Shell Beds Of Florida

While the Miocene fauna is but incompletely known additional fossils are from time to time being uncovered thus helping to piece together the story of the past mammalian life of Florida. The Pliocene epoch was also one of continued shallow water or estuary type of deposition. It was during this time that the beds of phosphate, which have contributed so generously to the mineral wealth of the State, were being accumulated. The discovery of phosphate in Florida dates back to 1888. Nearly 60,000,000 tons, with a value of more than $200,000,000, have so far been produced in Florida. Also, in other areas, one of the most profusely fossiliferous shell marls in the world was being laid down, namely the Caloosahatchee, which is typically exposed along the upper part of the Caloosahatchee River in southern Florida. Shell beds of Pliocene age occur not only on the Caloosahatchee River but also over a rather extended area in southern Florida as well as in the valley of the St. Johns River in the east-central portion of the State.

In western Florida and through the central portion of the Peninsula materials of a different character were laid down. These were composed mostly of sand, gravel and clay; the latter including the high-grade, white-burning, sedimentary kaolin deposits, these being of particular economic value. These were evidently accumulated as river, beach or perhaps delta deposits. During this period, too, the mammalian life was more abundant and widespread, many remains having been recovered in the process of mining both the hard rock phosphates of west-central Florida and the land pebble phosphates of southern Florida. These include various species of horse, the heavy-bodied rhinoceros as well as a type of rhinoceros more like the recent form, a beardog animal, peccary, camel, and mastodon. Of the latter special mention should be made of the early serrate-toothed, four-tusked type, having tusks in the lower as well as the upper jaws.

The mastodons are old world migrants doubtless reaching America from Asia. During the Pliocene they were evidently well established in Florida as shown by the remains so far recovered. With the ushering in of the Pleistocene, or the last geological period, when different ice sheets covered approximately the northern one-half of North America, Florida was in large part covered by a shallow sea in which, during minor oscillations, were laid down sand, shell marls, limestones and swamp deposits, which are encountered today along the East Coast, throughout the Everglades and southern Florida, with lesser areas in other sections. It was in this period, too, that the Keys, or coral reefs, off the southern tip of Florida, were being built up and the white oolitic limestone, used so extensively in construction work of all kinds along the lower East Coast in the vicinity of Miami, was also being deposited.