170 
FLORIDA GEOLOGICAL SURVEY-I5TH ANNUAL REPORT 
Physical Properties of Brooksville Hammock Clay (Lab. No. 0-59). 
Plasticity, judged by feel... 
Water of plasticity.. 
Pore water .. 
Shrinkage water. 
Linear air shrinkage. 
Volume air shrinkage. 
Modulus of rupture, average 
Slaking test. 
Excellent. 
27.40% 
1.49% 
25.93% 
12.1 % 
28.8 % 
215.3 pounds per square inch. 
3 minutes. 
Fire tests: 
T emperature. 
Linear Shr. 
Per Cent. 
Absorption. 
Per Cent. 
Porosity. 
Per Cent. 
Color. 
950°C. 
0.47 
16.16 
34.80 
Brick red. 
1050 
0.4 
16.64 
34.40 
Brick red. 
1150 
1.6 
15.80 
33.50 
Brick red. 
1190 
2.4 
16.00 
27.75 
Brick red. 
1230 
2.9 
15.49 
23.75 
Brick red. 
HIGHLANDS COUNTY 
Highlands County lies in the south-central part of the peninsula 
just northwest of Lake Okeechobee. The Alum Bluff formation under¬ 
lies the central part of the county from Lake Childs northwestward and 
contains abundant coarse, red, sandy clay very suitable for sand-clay 
road material. The remainder of the county is underlain by sand and 
marls. No clays suitable for burned products are known. 
HILLSBOROUGH COUNTY 
Hillsborough County lies on the western side of the peninsula at 
the head of Tampa Bay. It is underlain by the Tampa, Alum Bluff and 
Bone Valley formations. The Bone Valley Gravel carries the Bartow 
clay which is found in numerous localities from Plant City southward 
to the Manatee River. (For a description of the Bartow Clay see Polk 
County, page 195.) 
The Alum Bluff formation contains some phosphatic and sandy 
clays, but none having any usefulness for burned products. 
The Tampa formation consists of two distinct strata of light-green 
plastic clays separated by a limestone. The upper clay is exposed in 
numerous localities, while the lower one has very few, if any, natural 
exposures and is found chiefly in excavations and wells. Residual clays 
from the Tampa limestone are of common occurrence. 
