28 FLORIDA GEOLOGICAL SURVEY TENTH ANNUAL REPORT. 
GEOLOGY. 
The geologic formations found at the surface within this area 
are chiefly of Oligocene and Miocene age, although more recent 
deposits may overlie these near the coast. The materials of these 
formations include limestones, sands, clays, sandy clays, and shell 
marls. The shell marls are those of the Alum Bluff and Choc- 
tawhatchee formations (Miocene). The limestones are chiefly 
those, of the Chattahoochee formation (Oligocene), although more 
recent limestones are found in places near the coast. 
The following table presents a summary of the formations of 
this area, as understood at the present time, all of which are. of 
Cenozoic age : 
Pleistocene — No marine fossiliferous Pleistocene known within the area. 
Pliocene-Miocene — Chiefly coarse sands and unfossiliferous sandy clays. 
Pliocene — Marine Pliocene may be present near the coast. 
Miocene — Choctawhatchee formation ; shell marls and sands. 
Miocene — Alum Bluff formation; calcareous sands and clays. 
Oligocene — Chattahoochee formation ; limestones and calcareous clays. 
Eocene — Not exposed at the surface, although probably reached* by the deep- 
est wells. 
OLIGOCENE. 
CHATTAHOOCHEE FORMATION. 
The type locality of the Chattahoochee formation is within this 
area at the Chattahoochee Landing on the Apalachicola river in 
Gadsden county. The thickness of the rock exposed in the cut for 
the public road at this landing is as much as 65 feet, and the full 
thickness of the formation is evidently considerably greater. The 
rock of this formation as exposed at this place consists of rather 
impure limestone, the. impurity being chiefly clay. The deposits 
are stratified, ledges of rock of medium hardness alternating with 
softer, more clayey or marly layers. The inclusion of clay in the 
rock is about in the proper proportion to form a natural cement, 
the rock nearby at River Junction having formerly been used in a 
limited way for that purpose. 
The Chattahoochee limestone underlies the whole of this area 
