188 
FLORIDA GEOLOGICAL SURVEY—15TH ANNUAL REPORT 
The Callahan Brick and Tile Company works a deposit, probably 
marine, ranging from eight to twenty feet in thickness and having an 
overburden of six or eight inches. This deposit is underlain in places by 
a marl. About twenty acres have been worked and about twenty acres 
more have been proven. The deposit probably underlies a much more 
extensive area. 
The plant is located on the Seaboard Air Line Railway near its in¬ 
tersection with the Atlantic Coast Line Railroad. The product is 
shipped to points in south and west Florida. Both a common and a face 
brick are produced. 
This clay may be used for common structural materials where a 
vitrified product is not essential. The fired product retains a porous tex¬ 
ture at cone 15. Its physical properties are: 
Physical Properties of Callahan Clay (Lab. No. 0-29). 
Plasticity, judged by feel... 
Water of plasticity. 
Pore water. 
Shrinkage water .. 
Linear air ’shrinkage. 
Volume air shrinkage. 
Modulus of rupture, average 
Slaking test. 
25.60% 
0.42% 
25.18% 
11.70% 
29.85% ' 
805.2 pounds per square inch. 
3 days. 
Excellent. 
Fire tests: 
T emperature. 
Linear Shr. 
Per Cent. 
A bsorption. 
Per Cent. 
Porosity. 
Per Cent. 
Color. 
950°C. 
0.7 
15.85 
39.75 
Brick red. 
1050 
1.3 
15.70 
39.00 
Brick red. 
1150 
1.8 
14.15 
31.48 
Brick red. 
1190 
2.2 
12.60 
30.25 
Brick red. 
1230 
2.2 
11.95 
28.00 
Brick red. 
1310 
2.2 
11.58 
26.75 
Brick red. 
A brick plant was formerly operated by the Callahan Brick and Tile 
Company about three-quarters of a mile south of Callahan. The clay 
worked is the same as is now being worked at Callahan. 
The region northward between Callahan and the St. Marys River 
is practically all underlain by a slightly sandy clay. 
A brick plant was formerly operated at the “Old Brick Yard Land¬ 
ing” on the St. Marys River, which is about forty miles west of Fernan- 
dina. Here there is an overburden of six to eight inches of soil, two feet 
of weathered, reddish clay, then a considerable depth of a grayish, plastic 
clay. Wells nearby indicate that this clay has a thickness of approxi- 
