petroleum possibilities oe elorida 
115 
Bluff formation (Miocene) is evidently present under the surface forma¬ 
tions, as indicated by well logs in which the phosphatic clays and marls 
are recorded. The Eocene limestones are probably reached at from 400 
to 500 feet from the surface. The following log of a well at Callahan 
indicates the drilling conditions to a depth of 489 feet.* 
Depth in feet. 
Sand ...-.-.-. 0- 2 
Red clay ....-...-. 2- 10 
Blue clay and sand...... 10- 45 
Shell deposit, including a thin layer of hard rock at 52 feet. Water 
above and below this rock comes to within 10 feet of surface. 45- 60 
Blue marl, with occasional beds of shells 3 or 4 feet thick, and contain¬ 
ing black to dark gray, water-worn pebbles.............. 60-200 
Medium coarse sand, with numerous very small, black grains or peb¬ 
bles. A flow was obtained at this depth...... 200-212 
Limestone (sample) .,........ 212-255 
Blue marl and fine sands, with inclusions of several thin strata of shell. 
(Sample) .....|. 255-355 
Very hard rock ... 355-364 
Indurated gray sand and blue marl... 364-418 
Rock, hard and soft strata, with increase of flow upon penetrating each 
hard stratum. No increase reported below 460 feet. Driller reports 
the rock to be closer grained from 460 to 489.7 feet, and not contain¬ 
ing much water ....... 418-489.7 
OKALOOSA COUNTY 
Okaloosa County, in western Florida, extends from the Alabama line 
to the Gulf of Mexico. In the north northeastern part of this county are 
found numerous exposures of shell marls of the Alum Bluff formation 
(Miocene). These marls may be seen on Yellow River, near Oak 
Grove, this being the type locality of the Oak Grove member of the Alum 
Bluff formation. On Shoal River, near the east county line, are shell 
marls referred to the Shoal River member of the Alum Bluff formation. 
The dip of the formations in this county is south or southwest. Ap¬ 
proaching the Gulf coast, formations later than the Alum Bluff probably 
come into the section. However, from lack of exposures the age and 
character of these later formations are unknown. 
No deep wells have been drilled in this county. 
OKEECHOBEE COUNTY 
Okeechobee County lies north of Lake Okeechobee. The land is level, 
affording few exposures. From well records it is known that Pleisto- 
*FIa. Geol. Surv., 5th Arm. Rept, p. 166, 1913. 
