GEOLOGY CHOCTAWHATCHEE AND APALACHICOLA RIVERS. 99 
STRUCTURAL CONDITIONS BETWEEN THE CHOCTAWHATCHEE 
AND AUCILLA RIVERS IN FLORIDA. 
The present paper on the geology between the Apalachicola and 
Choctawhatchee Rivers is the third of a series of brief papers on 
limited areas in Florida in which structural conditions have received 
special consideration. The whole contiguous area now covered by 
these reports includes the territory from the Choctawhatchee to the 
Aucilla Rivers in west or central west Florida. This area is of 
■especial interest because, within it is found the transition from the 
geologic areas of southern Alabama and Georgia to the somewhat 
distinct structural area of peninsular Florida. 
CONTOURS ON THE CHATTAHOOCHEE FORMATION. 
The sketch map, page 80, has been prepared to accompany a 
summary of the results obtained in the study of these three areas. 
The contours shown on the map, marked o, 50 and 100, are placed 
as nearly as practicable on the top surface of the Chattahoochee 
formation. The small key map of figure 3 indicates the data with 
regard to elevations from which these contours were constructed. 
While all the levels are in a sense approximate, owing to the diffi- 
culty in many cases of exactly placing the top surface of this forma- 
tion, some are purely inferred elevations, and these are indicated 
by the use of the “plus-minus” sign. The inferred levels are those 
in the areas where the formation is completely concealed by later 
deposits. 
The. interval between the fullers earth horizon and the apparent 
top of the Chattahoochee formation near River Junction is 66 
feet. The fullers earth exposure, however, is about one mile 
southeast of the limestone exposure, hence, allowing for the dip, 
the actual interval is probably close to 70 feet. The. inferred levels 
on the Chattahoochee Limestone are obtained, where that formation 
is entirely concealed, by deducting this interval, 70 feet, from the 
known level of the fullers earth horizon at that place. 
When placed in accordance with these levels, the ioo-foot con- 
tour is observed to pass from the Apalachicola River somewhat 
south of River Junction in a northeast direction, crossing Little 
River near Attapulgus. From here the contour presumably bends 
to the south, since it comes into Florida again in the northeast cor- 
