July 1, 1910] 



SCIENCE 



25 



laeMcolan-Miocene Interval. After this fol- 

 lowed the Miocene subsidence. The Miocene 

 subsidence was not so extensive as that of the 

 preceding deposition period, and although it 

 seems probable, it is not positively proved, that 

 the Suwanee Strait was again open water. 

 The Miocene deposits did not extend so far 

 inland as the margin of the Apalachicolan sea, 

 and there were extensive land areas west of 

 the present longitudinal axis of the peninsula. 

 The plateau had approximately its present 

 outline, and thick deposits of arenaceous sands 

 were formed practically to its southern limits, 

 positively as far south as the locality of Key 

 Vaca. The sea was shallow (perhaps 25 fath- 

 oms is a safe maximum), there was depression 

 coincident with deposition on the east coast; 

 the waters were cool, a cold inshore counter- 

 current lowering the temperature to that at 

 present prevalent in the region between Cape 

 Hatteras and Long Island. This southward 

 moving counter-current, aided by the winds 

 and the tides, is largely responsible for the 

 greater thickness of sediments on the east 

 than on the west coast, and it is the fore- 

 runner of the series of counter-currents so 

 important in the later history of the region. 

 Toward the close of the Miocene period uplift 

 was again initiated, and the Suwanee Strait, 

 should it not have been previously closed, was 

 then assuredly above sea-level, and the north 

 and south Trail Ridge was formed. The up- 

 lift seems to have been greater on the east 

 than on the west, for no Miocene is above sea- 

 level from Levy to Pasco counties on the west 

 coast, while submerged Miocene is apparently 

 present ofE the mouth of Tampa Bay. 



The Pliocene submergence was extensive, 

 over half of the present land surface of the 

 peninsula lying below sea-level. The sub- 

 mergence of the present land surface extended 

 down the west side of St. Johns River valley 

 along the east coast, and entirely across the 

 median portion of the peninsula northwest of 

 Lake Istokpoga. No known marine Pliocene 

 occurs on the west coast north of the Charlotte 

 Harbor localities. The general outline of the 

 plateau remained as it was in Miocene time; 

 the water was shallow, usually between 20 

 and 30 feet in depth; the temperature was 



tropical in the southern, Caloosahatchee area; 

 and warm, but slightly cooler, in the north- 

 eastern area in the vicinity of Nashua. The 

 oceanic currents over the Pliocene bank must 

 have been a warm counter-current — a counter- 

 current because sands were brought from the 

 north and deposited on the Pliocene submarine 

 bank. 



While Pliocene marine deposition was 

 taking place, important lacustrine and fluvial 

 deposits were accumulating on the land sur- 

 face above the sea. 



Pliocene deposition was closed by another 

 uplift of the plateau. Data for a precise esti- 

 mate of the height of the land during this 

 emergence are not available, but the evidence 

 obtainable indicates that it was not over 200 

 or 250 feet as a maximum, and as the previous 

 movements of the plateau were differential it 

 is most probable that only portions were sub- 

 jected to oscillations so great. Accompanying 

 this oscillation a shallow syncline was devel- 

 oped along the axis now occupied by the Kis- 

 simmee River, with low anticlines on each 

 side. Probably a third anticline was devel- 

 oped west of Peace Creek. The axes of these 

 folds are parallel to the longitudinal axis of 

 the peninsula, and have been important in 

 influencing the drainage courses of middle 

 Florida. 



The Pleistocene submergence was as exten- 

 sive as that of the Pliocene — all Pliocene 

 areas, perhaps, but not probably, excepting one 

 between St. Johns River and the east coast, 

 being resubmerged, and there is a border of 

 Pleistocene on the west coast and the western 

 extension where Pliocene is not now known. 

 The plateau during Pleistocene time preserved 

 its general outline. Shallow water conditions 

 prevailed over its entire submerged portion, in 

 no place were the known deposits laid down 

 in water much deeper than 50 feet, and usu- 

 ally from 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 wide-spread deposits over 



