136 FLORIDA GEOLOGICAL SURVEY-I5TII ANNUAL REPORT








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 FiG. 8.-Clay pit. Gamble and Stockton Brick and Tile Company, South Jacksonville, Duval County. Two different beds of clay separated by a
 layer of sand are exposed in this pit.

 The upper red mottled clay has the following physical properties

 Physical Properties of Gamble and Stockton Upper Red Clay (Lab. No. 0-58).
 Plasticity, judged by feel............ Excellent.
 W ater of plasticity ................ 23.20%
 Pore water ........................ 1.25%
 Shrinkage water ................... 21.95%
 Linear air shrinkage................ 8.7 %
 Volume air shrinkage............... 24.2 %
 Modulus of rupture, average........ 608.7 pounds per square inch.
 Slaking test ....................... 1 hour.
 Steel hard at cone 9.
 Overfires at cone 12.
 Fire tests:
Temperature. Linear Shr. Absorption. Porosity. Color.
 Per Cent. Per Cent. Per Cent.
 950*C. 1.2 14.58 32.40 Brown.
 1050 1.2 15.43 33.00 Brown.
 1150 1.3 14.73 32.60 Brick red.
 1190 1.3 13.32 32.00 Brick red.
 1230 1.3 12.61 27.40 Brick red.
 1310 1.5 12.63 26.60 Brick red.