184 Papers front the Marine Biological Laboratory at Tortugas. 



barely below sea-level to 25 or 30 feet. The temperature north of the 

 latitude of the southern end of Lake Okeechobee was slightly cooler than 

 in Pliocene time, but it was still warm. In this shallow, warm sea 

 sediments of diverse kinds were deposited. Sands and shell marls are 

 probably the most extensive, forming widespread deposits over almost 

 the entire submarine bank. The sands extend beneath the limestone 

 formations as far south as Miami, and perhaps to the southern keys. 

 Along the more northerly portions of the bank coquina accumulated. 

 Along a curve, first southward and then bending westward, from Biscayne 

 Bay, a coral reef flourished, separated by a channel of deeper water from 

 the main bank, on which the Miami oolite was forming or had formed in 

 shoal water strongly agitated by currents. Along the southwestern por- 

 tion of this bank, also in shoal water, the Lostmans River limestone 

 accumulated. West of the coral reef, on an extensive flat in the shoal 

 water over them, the Key West oohte was formed. Toward the close 

 of the Pleistocene the previously formed sands, marls, and limestones 

 southward beyond Miami received a thin coating of siliceous sand. 

 Contemporaneous with this purely marine work, the terracing of rivers to 

 the north was taking place. 



Pleistocene time was closed by an uplift, which may have been 

 intermittent or may have been accompanied by oscillations. There is 

 some evidence of slight depression since the principal uplift. After this 

 uplift the hving coral reefs developed, the Everglades were formed, and 

 the Florida of to-day was the result. 



This summary will be closed by an account of the roles played by 

 deformation and ocean currents in the history of the Plateau. 



DEFORMATION. 



The Floridian Plateau owes its origin to a fold of the sea-floor in 

 pre-OHgocene, probably Eocene time, producing a platform on which 

 sediments during the later geologic periods were laid down. The whole 

 earthmass, since the origin of the platform, has been subjected to a 

 succession of deformations due to compression between forces acting 

 from the east and west, resulting in the axes of the gentle folds being 

 coincident in direction with the longitudinal axis of the Plateau, and to 

 downward and upward tilting around a landward fulcrum. The initial 

 uplift with deformation took place, as nearly as can be determined, 

 toward the close of the Vicksburgian deposition period. The Vicks- 

 burg nucleus lay nearer the eastern than the western margin of the 

 Plateau surface, and was roughly dome-like in form, but with a longer 

 north-and-south than east-and-west axis. The subsequent growth of 

 the Peninsula was by filling the channel between the island of older 

 Oligocene (Vicksburg) rocks and the mainland, and by growth east- 

 ward and southward from it. There was little or no westward growth. 

 There was additional deformation in later Oligocene (Apalachicolan) 

 time, between the Apalachicolan and Miocene deposition periods, between 

 the Miocene and Pliocene, between Pliocene and Pleistocene, and suc- 

 ceeding the Pleistocene deposition. The result of each of the series of 

 deformations was to add, beginning with the Miocene-Pliocene member 



