182 FLORIDA GEOLOGICAL SURVY-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 Apalachicola 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.
 Feel. 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 micaceous. 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 earthenware. Its physical properties are as follows:

 Physical Properties of Estiffanulga Bluff Top Clay (Lab. No. o-39).
 Plasticity, judged by feel........... Excellent.
 W ater of plasticity................. 30.65%
 Pore water ....................... 0.45% 
 Shrinkage water .................. 30.20%
 Linear air shrinkage............... 9.10%
 Volume air shrinkage.............. 29.20%
 Modulus of rupture, average........ 281.8 pounds per square inch.
 Slaking test ....................... 20 minutes.
 Steel hard at cone 05.
 Fire tests:
Temperature. Linear Shr. Absorption. Porosity. Color.
 Per Cent. Per Cent. Per Cent.
 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 properties: