A PRELIMINARY REPORT ON CLAYS OF FLORIDA 171

 The upper Tampa clay is exposed in several places along the HillsboroughRiver and has formerly been worked atTampa. Both theTampa Northern Railroad and the Atlantic Coast Line Railroad cross exposures of this clay.
 The Tampa Brick Company's plant, now abandoned, was located about five miles northeast of the city on the Hillsborough River. The deposit consists of about ten feet of a light-green plastic clay containing numerous cherty concretions. A two-foot overburden of loose surface sand and soil overlies the clay.
 This is a grayish, buff-burning clay which is still distinctly porous at cone 15, hence is not suited for any product where vitrification is essential. It may, however, be used for common building-brick and hollow-block ware. Its physical properties are:
 Physical Properties of Tampa Brick Company Clay (Lab. No. 0-34).
 Plasticity, judged by feel............ Excellent.
 W ater of plasticity................. 32.45%
 Pore water ........................ 1.05%
 Shrinkage water ................... 31.40%
 Linear air shrinkage ................ 12.80%
 Volume air shrinkage............... 35.85%
 Modulus of rupture, average........ 598.2 pounds per square inch.
 Slaking test ....................... 5 minutes.
 Fire tests:
Temperature. Linear Shr. Absorption. Porosity. Color.
 Per Cent. Per Cent. Per Cent.
 950*C. 0.3 16.75 31.50 Buff.
 1050 0.3 16.20 31.10 Buff.
 1150 0.2 14.18 29.75 Buff.
 1190 2.2 14.20 27.80 Buff.
 1230 2.2 13.25 27.70 Buff.
 1310 13.20 26.60 Buff.

 The Temple Terrace Tract, located about six miles northeast of Tampa on the Hillsborough River, is underlain by a yellowish and reddish, sandy clay which is -suited only for sand-clay road material. The southern edge of the tract is underlain by the Tampa formation clay which has the same properties as the Tampa Brick Company clay described in the foregoing paragraph.
 The property of Dr. W. P. Chamberlain, two miles north of Sulphur Springs, is underlain by several thin variable clay strata interbedded with sand. The clay is of insufficient quantity and at too great depth to