70 
FLORIDA GEOLOGICAL SURVEY-I 4 TH ANNUAL REPORT 
the Oligocene. At or near the Suwannee River in going east we enter 
the extensive area of central peninsular Florida where the Eocene, 
except for occasional remnants of other formations, is at the surface. 
This belt of Eocene extends south to Sumter and Citrus Counties, west 
to the Gulf of Mexico and east to eastern Alachua and central Marion 
Counties. Beneath a thin covering of Eocene limestones in most, if not 
all, of this region, are found Cretaceous sediments. 
To the south of this area on the Gulf side of the peninsula, including 
southern Hernando, Pinellas and Hillsborough Counties, the Oligocene 
lies at the surface, while farther to the south, as well as to 1 the east, the 
surface formations are those of the Miocene and later periods. 
On the accompanying sketch map are indicated the subdivisions into 
which the state may conveniently be divided for descriptive purposes, 
and in the following pages will be found an account of the formations to 
be penetrated and the drilling conditions to be expected for each sub¬ 
division. 
In order to facilitate comparison with adjoining states there is in¬ 
cluded here a table in which is given the principal formations as recog¬ 
nized in the coastal plains of the Gulf States. The formations known 
to be oil-bearing in places and under favorable structural conditions are 
indicated in the table by a star. (See following page.) 
GEOLOGIC SUBDIVISIONS IN FLORIDA WEST OF THE 
SUWANNEE RIVER 
THE marianna-chipley area 
The Marianna-Chipley Area lies west of the Apalachicola River and 
includes all or part of the following counties: Jackson, Holmes, Wash¬ 
ington and Walton. Bay and Calhoun Counties lie between this area and 
the Gulf coast. The surface formations in this area, as already noted, are 
those of the Oligocene and Eocene with Miocene coming into the sec¬ 
tion to the east, south and west. Underneath the surface formations in 
this area are to be found other Tertiary and the Cretaceous series of 
formations. 
The Tertiary formations include the following, named in the order in 
which they are encountered in drilling: Ocala, Claiborne, Wilcox and 
Midway. Of these the Ocala is regarded by Cooke as the equivalent of 
