186 
Florida geological survey — 15 TH annual report 
fireproofing and drain tile. The clay is slightly sandy and retains a dis¬ 
tinctly porous texture at cone 16, hence a vitrified product could not be 
satisfactorily produced. A sample taken one-half mile south of Burbank 
on the Ocala Northern Railway has the following physical properties: 
Physical Properties of the Burbank Clay (Lab. No. 0 - 20 ). 
Plasticity, judged by feel. Excellent. 
Water of plasticity. 23.20% - 
Linear air shrinkage. 10.60% 
Volume air shrinkage. 24.85% 
Modulus of rupture, average. 279.3 pounds per square inch. 
Slaking test. 20 minutes. 
Fire tests: 
T emperature. 
Linear Shr. 
Per Cent. 
Absorption. 
Per Cent. 
Porosity. 
Per Cent. 
Color. 
950°C. 
0.1 
13.20 
31.95 
Brick red. 
1050 
0.6 
14.10 
29.20 
Brick red. 
1150 
0.6 
12.40 
29.75 
Brick red. 
1190 
0.1 
10.95 
28.95 
Brick red. 
1230 
1.4 
10.42 
28.20 
Brick red. 
1310 
2.1 
10.14 
27.75 
Brick red. 
1370 
10.07 
26.85 
Brick red. 
A lacustrine clay underlies the region adjoining Lake Weir on the 
south. It is grayish to white in color, varies in thickness from three to 
seven feet, and is overlain by sand ranging from three to six feet in thick¬ 
ness. While this clay is only about one-half mile from a Seaboard spur, 
the heavy overburden precludes the deposits having any commercial 
value. 
Coarse, sandy clay, suitable for sand-clay road material, is found 
in the southeastern part of the county. 
MONROE COUNTY 
Monroe County lies at the extreme south end of the peninsula and 
consists chiefly of Pleistocene limestone and sands. No clays are known 
in the county. 
NASSAU COUNTY 
Nassau County is situated in the extreme northeast corner of the 
State and lies between the St. Marys River and the Atlantic Ocean. The 
county is underlain mostly by sands and marls, but the central part of the 
county has some clay deposits. Flood-plain clays are found along the 
St. Marys River. 
