A PRELIMINARY REPORT ON CLAYS OF FLORIDA 157

 A common-brick plant was formerly operated at Bluff Springs in the northern end of the county. This plant used a surface, sandy clay.


 FLAGLER COUNTY
 Flagler County lies on the east coast between the St. Johns River valley and the ocean. Its surface exposures show chiefly sands and marls with a few thin local clays, with the exception of the western part of the county where some fairly extensive clays of good quality bordering Crescent Lake are found.
 The western portion of the county is not served by a railroad, but Crescent Lake offers facilities for water transportation by its connection with the St. Johns River. Periodical freight service is maintained by at least one of the lines operating on that river.
 A gray clay exposed in numerous places in the vicinity of Shell Bluff has a thickness of more than eight feet and underlies a considerable area in this section of the county. Its overburden consists of less than three feet of sand and soil. Its plasticity is excellent; it dries without difficulty and its workability is, in general, satisfactory. In most places it is underlain by marl or shell beds. The clay, however, contains numerous calcareous concretions which render fine grinding and thorough mixing necessary in order to avoid subsequent swelling of the ware due to slaking of the lime. These concretions are too small to be successfully screened out without first drying the clay.
 When properly ground and mixed this clay may be used for common brick, drain tile and hollow-block ware. It is not suited, however, for the manufacture of any product where vitrification is desired as the ware has a distinctly porous, open texture at cone 15.
 A sample of the clay taken from a boring near the office of the Southern Farm Land Company at Shell Bluff has the following physical properties: :hl
 Physical Properties of Shell Bluff Clay (Lab. No. 0-76).
 Plasticity, judged by feel ............ Excellent.
 W ater of plasticity................. 22.30%
 Pore water ........................ 1.19%
 Shrinkage water ................... 21.11%
 Linear air shrinkage................ 10.5 %
 Volume air shrinkage............... 28.3 %
 Modulus of rupture, average........ 789.9 pounds per square inch.
 Slaking test ....................... 3 minutes.