A PRELIMINARY REPORT ON CLAYS Or FLORIDA 129






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 FiG. 7.-Black Creek Barge Landing, ne~ar Middleburg, Clay County. Formerly used for shipping brick. Dismantled kiln may be seen on extreme right.

clays. Some calcareous and phosphatic clays occur in the southwestern portion of the county.

 A clay exposed in the vicinity of Doctors Inlet in the northern pa *rt of the county and underlying several square miles between the Atlantic Coast Line and the St. Johns River has good dry strength and color, but has a high air-shrinkage. It may, however, be used for a good grade of common brick, drain tile, hollow blocks, etc. The exact thickness of this deposit was not determined, but is known to be over six feet in places. It is overlain 1)y sand and loami ranging from one to two feet. A sample of this clay taken beside the Green Cove Springs-Jacksonville highway, about one-half mile east of Doctors Inlet station, has the following physical properties:

 Physical Properties of Doctors Inlet Clay (Lab. No. o-,5o).
 Plasticity, judged by feel. ............ Excellent.
 W ater of plasticity ................ 32.25%
 Pore water ........................ 2.31%
 Shrinkage water ......... .......... 29.94%
 Linear air shrinkage ............... 14.8 %
 Volume air shrinkage .............. 36.6 %
 Modulus of rupture, average .. .. .. 504.2 pounds per square inch.
 Slaking test ....................... 10 m inutes.
 Steel hard at cone 1.
 Overfires at cone 9.