A Contribution to the Geologic History of the Floridian Plateau. 183 



maximum; there was depression coincident with deposition on the east 

 coast; the waters were cold, a cold inshore countercurrent lowered the 

 temperature to that of the region between Cape Hatteras and Long 

 Island. This southward-moving countercurrent, aided by winds and 

 waves, is largely responsible for the greater thickness of sediments on 

 the east than on the west coast, and it is the forerunner of the series of 

 countercurrents so important in the later history of the region. Toward 

 the close of the Miocene period upHft 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 

 UpHft 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 off the mouth of Tampa 

 Bay. 



The Phocene submergence was extensive, over half of the present 

 land surface of the Peninsula lying below sea-level. The submergence 

 of the present land surface along the east coast extended down the west 

 side of St. John's River valley, and entirely across the median portion 

 of the Peninsula northwest of Lake Istokpoga. No known marine Plio- 

 cene occurs on the west coast north of the Charlotte Harbor locahties. 

 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 tem- 

 perature was tropical in the southern, the Caloosahatchee area; and 

 warm, but slightly cooler in the northeastern area, in the vicinity of 

 Nashua. The oceanic current over the Pliocene bank must have been a 

 warm countercurrent- — a countercurrent because it brought sands from 

 the north and deposited them on the Pliocene submarine bank. 



While the Pliocene marine deposition was taking place important 

 lacustrine and fluvial deposits were accumulating on the land surface 

 above the sea. 



Pliocene deposition was closed by another uphft of the Plateau. 

 Data for a precise estimate 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 

 subjected to oscillations so great. Accompanying this oscillation a 

 shallow syncline was developed along the axis now occupied by the 

 Kissimmee River, with low anticlines on each side. Probably a third 

 anticline was developed west of Peace Creek. The axes of these folds are 

 parallel to the longitudinal axis of the Peninsula, and have been impor- 

 tant in influencing the drainage courses of middle Florida. 



The Pleistocene submergence was as extensive as that of the Plio- 

 cene, all Pliocene areas, perhaps, but not probably, excepting one be- 

 tween St. John's 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 throughout Pleistocene 

 time preserved its general outline. Shallow-water conditions pre- 

 vailed over its entire submerged portion. In no place were the known 

 deposits laid down in water much deeper than 50 feet, and usually from 



