.4 Contribution to the Geologic History of the Floridian Plateau. 141 



sedimentation on the Floridian Plateau, although it is indirectly of great 

 importance. The current of greatest direct importance is the counter- 

 current which follows the eastern coast of the United States from Cape 

 Hatteras southward. In the Floridian region it is called the Florida 

 countercurrent and has long been known to be an important factor in 

 building up the Floridian Plateau, as is attested by the writings of 

 Captain Hunt and Mr. Alexander Agassiz ; and Dr. Gulliver has recognized 

 its importance in determining the configuration of the shore-line. This 

 current passes through the Straits of Florida and continues as far west 

 as the Tortugas. The direction of its movement is southward until the 

 southern extremity of the Peninsula is reached, where it turns westward. 

 According to the Pilot Chart of North Atlantic Ocean, March, 1909: 



In the Straits of Florida the countercurrent ^s very uncertain. Under favor- 

 able conditions of weather it extends as much as 11 miles offshore, but it generally 

 makes a westerly course to Sand Key within the line of the reefs, though with 

 certain winds it runs north or south between the keys and northeast around the 

 Tortugas. 



TIDAL CURRENTS. 



The flow of the tides is transverse to the keys, and rather strong 

 tidal currents pass in and out between the keys. These are strong enough 

 to sweep the bottoms of the passages clean. 



WINDS. 



The following data on the winds of southern Florida are taken from 

 the Pilot Charts of the North Atlantic Ocean for the year 1907, published 

 by the Hydrographic Office of the Navy Department. No attempt will 

 be made to present the data in detail, and only the prevailing directions 

 of the winds for each month will be given: 



Jan.: Northeast, east, northwest, north, June: Southeast, east, south. 



southeast. (The component di- July: Southeast, east, south. 



rection is from the northeast.) Aug.: Southeast, east, south. 



Feb, : Southeast, northwest, east, and Sept.: Northeast, southeast, east. 



northeast. Oct. : Northeast, east, north. 



Mar.: Southeast, northwest, northeast. Nov.: Northeast, north, northwest. 



Apr. : Southeast, east, northeast. Dec. : Southeast, northeast, east, north- 

 May : Southeast, east, northeast. west. 



The preceding data show the prevailing direction of the winds to 

 be from the southeast from February to August inclusive, varying from 

 northeast to southeast from February to May, and from southeast to 

 south from June to August; from the northeast from September to 

 January, but with considerable variation. The general direction of the 

 winds is either along or transverse to the line of the keys. 



The tides and winds, as Captain Hunt suggested, tend to carry 

 material from the reefs and flats to the area behind the keys; while the 

 countercurrent moves material southward and westward. The winds 

 and tides by agitating the sea-bottom bring material within the influence 

 of the countercurrent and thus aid in its work of southward transporta- 

 tion. Without this assistance probably the countercurrent would not 

 produce great effects. 



