.4 Contribution to the Geologic History oj the Floridian Plateau. 185 



of the series, one or more anticlinal swells with intermediate synclinal 

 depressions to those that preceded, the additions above sea-level always 

 taking place toward the east, and at each elevation the uphfting was 

 propagated southward. The continued effect of all the uplifts was to 

 elevate the eastern portion of the Plateau above the western, or there 

 has been elevation on the eastern side of the Plateau coincident with 

 stability or erven slight depression on the western side. 



CURRENTS. 



The importance of currents in shaping the land area of Florida has 

 been emphasized in several sections of the preceding discussion. Before 

 the history of the currents of the region can be thoroughly understood 

 it is necessary to know the history of the Hatteras axis of North Carolina. 

 The present Florida countercurrent seems due partly to the impingement 

 of the Gulf Stream against the Hatteras projection, resulting in a portion 

 of the waters being deflected southward along the coast instead of con- 

 tinuing their northward journey. The Hatteras axis has existed as a 

 dividing line between depositional areas apparently since middle Cre- 

 taceous time, and it has been either a region of shoal water, or occasion- 

 ally a land area, since later Eocene time. The Vicksburgian and Apa- 

 lachicolan seas were both warm, tropical or subtropical in temperature. 

 It is not definitely determinable at present whether the warmth of these 

 waters was due to currents directly from the Tropics or to warm return 

 currents produced by the northward flowing Gulf Stream having a por- 

 tion of its waters diverted southward by impinging against a salient 

 from the more northerly land area. 



In Miocene time it is definitely known that a cold inshore current 

 found its way southward to Florida and westward to Pensacola. This 

 current may be due to the Miocene submergence of the Hatteras area 

 sufficiently lowering the sea-bottom ofT Hatteras to permit the Gulf 

 Stream to continue its course unobstructedly northward. Should this 

 hypothesis be correct a re-examination of the faunas of the Miocene 

 deposits of northern North Carolina and Virginia, and those of southern 

 North Carolina (the Duplin marl). South Carolina, Georgia, and Florida, 

 with reference to synchrony may be necessitated. The Miocene south- 

 ward current transported quantities of terrigenous material and deposited 

 it on the eastern border of the Floridian Plateau. 



Since Miocene time there have been constantly return currents of 

 warm water (however, not so warm as the Gulf Stream), and they, aided 

 by winds and tides, have deposited terrigenous material on the east- 

 ward side of the existing land areas, sweeping a portion of it to the 

 southern end of the Plateau. These currents were active during Pliocene 

 and Pleistocene times, and are still active to-day. 



The shape of the upper surface of the Floridian Plateau, the land 

 area of its eastern side, the arrangement of the geologic formations of 

 successive ages, the directions of the stream courses, and the contour of 

 the present coast line, owe their peculiarities and characteristics to the 

 concomitant operation of the forces producing deformation and to 

 oceanic currents. 



