212 FLORIDA GEOLOGICAL SURVEY-15TH ANNUAL REPORT

the Gulf of Mexico. It is underlain by the Chattahoochee, Alum Bluff, Choctawhatchee and Pleistocene formations. The same sandy-clay mantle, so commonly present in Florida, also covers much of Walton County.
 A reddish and gray mottled clay is used at the Glendale Brick Works, at Glendale, in the production of common brick. This deposit is more than thirty feet in thickness and underlies at least forty acres, and probably more, in the vicinity of Glendale.
 This plant is now operated only at intervals to supply local trade. Formerly a logging railroad connected this place with DeFuniak Springs and thus afforded an outlet for the product, but the railroad is now abandoned.
 The clay is well suited for an excellent grade of common structural materials and red earthenware. Its physical properties are:

 Physical Properties of Glendale Clay (Lab. No. o-rr).
 Plasticity, judged by feel........... Excellent.
 W ater of plasticity................. 27.50%
 Pore water ....................... 0.46%
 Shrinkage water .................. 27.04%
 Linear air shrinkage............... 8.7 %
 Volume air shrinkage.............. 29.9 %
 Modulus of rupture, average........ 139.1 pounds per square inch.
 Slaking test .......................
 Steel hard at cone 1.
 Overfires at cone 16.

 Fire tests:
Temperature. Linear Shr. Absorption. Porosity. Color.
 Per Cent. Per Cent. Per Cent.
 9500C. 0.2 20.20 37.20 Light red.
 1050 1.3 20.50 37.15 Light red.
 1150 5.8 18.80 28.20 Light red.
 1190 5.8 11.58 19.35 Light red.
 1230 5.8 8.35 20.75 Light red.
 1310 6.3 5.30 17.10 Light red.
 1370 6.8 4.68 15.30 Light red.
 1430 8.3 4.65 14.20 Light red.

 Mr. G. H. Murphy, who operates the Glendale Brick Works, and who was employed to manufacture the brick for the Allentown Consolidated School, in Santa Rosa County, (see page 202), is preparing to operate a brick plant on the property of R. J. Edwards in Sec. 14, Twp. 3 N., R. 18 W., three miles north of Argyle. Part of the machinery has already been installed.