118 
FLORIDA STATE GEOLOGICAL SURVEY. 
nized at Tampa and thence south along the Gulf coast as far as 
Sarasota Bay. 
MIOCENE. 
The Miocene deposits are well developed in Eastern Florida. 
At the city water works at Jacksonville this formation was en¬ 
countered in excavating for the basin for the city water supply,* 
and was also reached in the city wells at a depth of from 35 to 
36 feet. At Jacksonville this formation has a considerable, al¬ 
though undetermined thickness. It consists of a buff limestone 
grading to a lighter color, more or less phosphatic, grading below 
to phosphatic sands and sandy marls. The formation is in places 
fossiliferous, although the shells are usually preserved as casts. 
In Clay County the Jacksonville formation is extensively ex¬ 
posed along Black Creek. The exposure of this formation appears 
along both the South and North. Fork of Black Creek, some miles 
above Middleburg, and may be observed for five or six miles 
below Middleburg. The following section was observed at High 
Bluff, on the South Fork of Black Creek,, about five miles above 
Middleburg: 
Covered and sloping . 5 feet 
Sloping, some sticky clay exposed... 5 feet 
Yellow sand . 8 feet 
Buff colored sandy limestone, containing a small propor¬ 
tion of black phosphatic pebbles. 12 feet 
Same, with greater amount of phosphate. 5 feet 
Same, with some phosphate. 12 feet 
This is the thickest exposure of the Jacksonville .formation 
observed at any one place along Black Creek. 
The following section was observed in the pit of the Jackson¬ 
ville Brick Company, two miles southwest of Jacksonville: 
Incoherent sand and soil. 2.4 feet 
Sandy clays, the top 5 or 6 feet oxidizes yellow. 16 feet 
Bluish fossiliferous marl .•. 4 feet 
The marl obtained from test holes in the bottom of the pit is 
*Dall, W. H., U. S. Geol. Surv. Bull. 84, 124-125, 1892. 
