176 FLORIDA GEOLOGICAL SURVEY-I5TH ANNUAL REPORT

tling, having excellent plasticity but a high air shrinkage. It occurs in a bed two and one-half feet thick overlain by six feet of sand. The overburden is too heavy for a clay of that thickness to be of commercial importance.
 The Keystone Brick Company at Whitney works a lacustrine deposit ranging from seven to twelve feet in thickness and overlain by about eighteen inches of sand. The clay is also underlain by sand. Two pits about sixty yards apart have been opened. The clay in one of these is a little more sandy than in the other.
 A good grade of common brick is made which is shipped to markets throughout peninsular Florida. Tampa and St. Petersburg use the greater part of the output. This plant is located on a branch of the Seaboard Air Line Railway. The Keystone brick, while nbot particularly a semi-refractory product, is widely used in South Florida for fire-box lining under boilers.
 This clay retains a soft, porous texture at cone 15 and may be used only for common building-brick. Its physical properties are:
 Physical Properties of Keystone Brick Company Clay (Lab. No. o-54).
 Plasticity, judged by feel........... Excellent.
 W ater of plasticity................. 23.90%
 Pore water ........................ 1.58%
 Shrinkage water ................... 22.40%
 Linear air shrinkage................ 10.9 %
 Volume air shrinkage................ 32.3 %
 Modulus of rupture, average........ 491.3 pounds per square inch.
 Slaking test ....................... 5 minutes.
 Fire tests:
Temperature. Linear Shr. Absorption. Porosity. Color.
 Per Cent. Per Cent. Per Cent.
 950*C. 0.6 19.84 33.40 Brick. red.
 1050 1.1 11.49 30.20 Brick red.
 1150 1.1 9.43 26.90 Brick red.
 1190 1.6 9.78 26.50 Brick red.
 1230 2.1 9.69 24.20 Brick red.
 1310 2.6 8.40 23.50 Brick red.
 Another brick plant was formerly operated near Whitney by the Whitney Brick Company. The deposit was a sandy lacustrine clay, from which a red common brick was made.

 LEE COUNTY
 Lee County lies between Lake Okeechobee and the Gulf of Mexico and is underlain by sands, marls and limestones of Pleistocene age. No clays of importance are known.