182 
FLORIDA GEOLOGICAL SURVEY—15TH ANNUAL REPORT 
Apalachicola rivers. Its surface exposures are sands, clays and marls 
of the Alum Bluff, Choctawhatchee and Pleistocene formations. 
Flood-plain clays are common along the Ocklocknee and Apalachi¬ 
cola rivers. Two of these clays are found at Estiffanulga Bluff on the 
Apalachicola River. The section here is as follows: 
Section at Estiffanulga Bluff, Apalachicola River. 
Feet. Inches. 
Soil . 8 
Clay (Top, Lab. Sample No. 0-39). 20 
Sand .. 3 
Clay (Bottom, Lab. Sample No. 0-46).. 5 plus 
Only five feet of this lower clay are exposed above the river level. 
Its exact thickness is not known. Both of these clays are highly micace¬ 
ous. Neither of them have been worked. The Apalachicola River offers 
water transportation to points northward and southward. 
The top clay has excellent plasticity, working and drying qualities 
and burns to a light-red color at cone 010. This clay may be used for 
common or face brick, hollow-block ware, drain tile and red earthen¬ 
ware. Its physical properties are as follows: 
Physical Properties of Estiffanulga Bluff Top Clay (Lab. No. o-yg). 
Plasticity, judged by feel... 
Water of plasticity. 
Pore water . 
Shrinkage water . 
Linear air shrinkage. 
Volume air shrinkage. 
Modulus of rupture, average 
Slaking test. 
Steel hard at cone 05. 
Excellent. 
30.65% 
0.45% 
30.20% 
9.10% 
29.20% 
281.8 pounds per square inch. 
20 minutes. 
Fire tests: 
Temperature. 
Linear Shr. 
Per Cent. 
Absorption. 
Per Cent. 
Porosity. 
Per Cent. 
Color. 
950°C. 
1.9 
23.55 
41.30 
Brick red. 
1950 
3.9 
23.45 
40.75 
Brick red. 
1150 
6.9 
14.95 
30.90 
Brick red. 
1190 
5.9 
9.23 
20.75 
Brick red. 
1230 
5.9 
9.39 
21.10 
Brick red. 
1310 
11.9 
5.78 
15.75 
Brick red. 
The lower clay is also highly plastic and has excellent working and 
drying qualities. It is cream-burning up to cone 12 where it changes to 
a gray. This clay may be used for stoneware and terra-cotta as well as a 
good grade of structural materials. It has the following physical prop¬ 
erties : 
