68 FLORIDA STATR GEOLOGICAL SURVEY. 
as integral parts of a single group. While limestones and marls pre¬ 
dominate, the group also includes beds of nearly pure sand and clay. 
The entire period of deposition appears to have been characterized by 
the accumulation of more or less terrigenous materials, and hence the 
limestones are usually rendered somewhat impure by an admixture of 
clay and sand. At certain times the conditions appear to have been 
especially favorable for the development of organic life and some 
horizons, such as the Chipola marl member of the Alum Bluff forma¬ 
tion, and the “silex bed” of the Tampa formation contain very large 
faunas. 
Owing to the lithologic variations and widely separated exposures, 
the exact correlation of the formations of this group is dependent 
upon their organic remains. While the paleontological studies, espe¬ 
cially those made by Dali, have shed much light upon the stratigra¬ 
phic relations of the different beds, there are still many points which 
cannot as yet be fully decided. For this reason it seems best to re¬ 
tain the names of various beds and to indicate as far as possible their 
known relationships. The Apalachicola group is separated into four 
formations—the Chattahoochee, the Hawthorne, the Tampa and the 
Alum Bluff. There is, however, some reason for believing that the 
first three are, in part at least, synchronous, though exact equivalence 
is difficult to determine where outcrops are widely scattered and faunal 
variations are slight. The Alum Bluff formation is clearly younger 
than the Chattahoochee formation, upon which it rests. 
The name Chattahoochee group was first applied by Langdon 1 to 
the beds occurring at a series of exposures along the Chattahoochee 
and Apalachicola Rivers. The localities examined by Langdon extend 
from the final disappearance of the Vicksburg, nine miles by water 
above River Junction (Chattahoochee) to the point where the Oligo- 
cene exposures give place to the overlying sands and marls of younger 
formations. The exposures examined are at Alum Bluff, Rock Bluff, 
Ocheesee and River Junction. 
In 1893 the section along the Apalachicola River was examined by 
Foerste 2 who recognized the presence of three dissimilar groups to 
which he gave the names Chattahoochee, Chipola and Chesapeake. 
His paper gives considerable attention to the character of the materials 
comprising his Chipola and Chesapeake groups, with a view to corre¬ 
lating them with the non-marine deposits grouped under the names of 
1 Langdon, Daniel W., Jr., Some Florida Miocene. Amer. Jour. Sci., 3rd 
ser., vol. xxxviii, 1889, p. 322. 
2 Foerste, A. F. Studies on the Chipola Miocene of Bainbridge, Ga., and 
Alum Bluff, Fla., with an attempt at correlation of certain Grand Gulf Group 
beds with marine Miocene beds eastward. Amer. Jour. Sci., 3rd ser., vol. xlvi, 
1893, pp. 244-254. 
