152 Papers from the Marine Biological Laboratory at Tortugas. 



SUMMARY OF VICKSBURGIAX EVENTS. 



The following statement of the early history of this Plateau seems 

 substantiated: 



(i) The Plateau was in time of pre-Oligocene origin. 



(2) In Vicksburgian time there was an extensive submarine plateau 



reaching from Central Louisiana to the Atlantic Ocean, with 

 a salient projecting from its southeastern corner as far south 

 as the southern limits of the present land surface of Florida. 



(3) The depth of water on this Plateau probably in no place was so 



great as 100 fathoms, more likely not over 50 fathoms. 



(4) The temperature of the bottom was tropical or subtropical, 



between 70 and 8o° F. 



(5) Over the Plateau currents from the equatorial regions gently 



swept, with the general direction of the ocean drift probably 

 from west to east. As no Vicksburgian strata have been 

 found in Texas and as there is a great thickness of Eocene 

 sediments in that State, it seems probable that there were 

 extensive landmasses west of the Vicksburg Sea as well as 

 north of it, and that these landmasses deflected the currents 

 from the south toward the east. However, the data are 

 not at hand for positively determining whether the main 

 drift toward the east passed over the submarine plateau, 

 or whether there was a countercurrent of warm water mov- 

 ing westward. 



(6) Deposits of both terrigenous and organic origin accumulated 



on this Plateau to a depth ranging from 100 to 200 feet 

 near shore to over 1,000 feet near the southern margin. As 

 the maximum depth at which any of the deposits were 

 formed was probably less than 100 fathoms, the deposition 

 took place on a sinking sea-bottom. The depression, how- 

 ever, kept pace with the deposition of organic and detrital 

 debris, thus permitting a considerable thickness of similar 

 material to accumulate on the sea-floor. 



(7) During the latter part of Vicksburgian time the sea-bottom 



was gradually elevated and a large area was uplifted into 

 dry land. 



THE VICKSBURGIAN-APALACHICOLAN INTERVAL. 



A large area of the Vicksburgian sea-bottom was elevated above the 

 sea-level before the initiation of the Apalachicola deposition; and this 

 elevation extended as far south as Tampa, and perhaps further. The 

 Apalachicola Group is divided into four geological formations, three of 

 which, the Hawthorne, Chattahoochee, and Tampa, were in part at least 

 contemporaneous; the fourth, the Alum Bluff, is geologically younger 

 than the three others. The Chattahoochee formation lies in Florida to the 

 northwest and north of the Vicksburg nucleus, and covers an extensive 

 area in southern Georgia; the Hawthorne formation occurs in Central 

 Florida to the north, northeast, and east of the Vicksburg; and the 



