A PRELIMINARY REPORT ON CLAYS OP 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. 
plagle;r 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 numer¬ 
ous 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 com¬ 
mon 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: 
Physical Properties of Shell Bluff Clay (Lab. No. o-j6). 
Plasticity, judged by feel. Excellent. 
Water 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. 
