A Contribution to the Geologic History of the Floridian Plateau. 153 



Tampa lies to the south. The stratigraphic relations of each of these three 

 formations to the Vicksburg have been studied by a number of geologists, 

 and they have been found to rest in the eroded surface of the Vicksburg. 

 Matson and Clapp have described these relations in detail in their Pre- 

 liminary Report on the Geology of Florida.^ 



The uplift of the Plateau produced differential movement, and it is 

 desirable to ascertain the relative amounts of movement in different 

 directions, but at present sufficient data bearing on the problem are not 

 available. 



EVENTS OF APALACHICOLAX TIME. 



The events of Apalachicolan time need separation into an earlier 

 stage, represented by the deposition of the Chattahoochee, Hawthorne, 

 and Tampa formations; and a later, represented by the Alum Bluff 

 formation. 



Earlier Stage. 



SHORE-LINE. 



The elevation which is described in the preceding section was 

 followed by subsidence, and large areas that had been dry land were 

 lowered beneath sea-level. The interior margin of the Apalachicolan 

 Sea lay considerably to the north of the Florida-Georgia line in Georgia, 

 and extended from the southwest corner of Decatur County northeast- 

 ward to the boundaries of Burke and Screven counties on Savannah 

 River. This sea was a shoreward portion of the Atlantic Ocean, but it 

 seems probable that a small area in Florida, in northeastern Marion 

 County, may not have been entirely submerged, and that in other areas 

 over the Vicksburg nucleus these sediments were ver\' thin. In Apalach- 

 icolan time a dome of Vicksburg rocks already existed. This land area 

 in the Apalachicolan Sea, however, could not have been extensive, as 

 rocks of Apalachicolan age occur as patches overlying the Vicksburg in 

 Hernando County, the town of Brooksville being on one of them, and 

 on the highland 6 miles west of Dade City, Pasco County, the Apalachi- 

 cola forms the ridge from the altitude of 150 feet to the hill summit, 

 200 feet or somewhat higher. The Apalachicola therefore, it appears, 

 entirely covered the summits of Hernando County and has been removed 

 b}^ erosion. Another outlying area of this group is at Levyville, Levy 

 County. If the outlying patches are connected according to altitude with 

 themselves and the main Apalachicola area, the only area remaining 

 which was probably an island is the one near Orange Lake, on its south- 

 west side, in Marion County. 



MATERIAL OP THE SEDIMENTS. 



The nature of the deposition in the Apalachicolan Sea varied greatly. 

 Although calcareous constituents were common, argillaceous and are- 

 naceous material frequently predominated. Matson and Clapp state, 

 Florida Geological Survey, Second Annual Report: 



^ Florida Geol. Surv., 2d Ann. Report, pp. 69, 75, 86. 



