130 FLORIDA GEOLOGICAL 'SURVEY-I5TH ANNUAL REPORT

 Fire tests:
Temperature. Linear Shr. Absorption. Porosity. Color.
 Per Cent. Per Cent. Per Cent.
 950*C. 1.2 6.60 18.40 Brick red.
 1150 2.7 5.69 17.10 Brick red.
 1050 2.7 7.22 17.90 Brick red.
 1190 4.2 3.69 17.20 Brick red.
 1230 5.7 3.04 16.10 Brick red.
 A clay similar to the Doctors Inlet clay is exposed on Black Creek about two miles east of Middleburg on the property of Frank Mooney. A brick plant formerly operated at this place was only abandoned about ten years ago and one kiln and parts of the dismantled machinery are still standing at the yard. This plant was located at a barge landing on Black Creek where tidewater shipping facilities are available. shipment was formerly made by barge to Jacksonville and other points on the St. Johns River.
 The clay pit is situated about'one-half mile northward from the site of the plant. From six to ten feet of clay are exposed. This is overlain by from one to three feet of soil and sand. The clay underlies a part of the adjoining property owned by the Bryan Jennings Artesian Farm Land Company.
 This Middleburg clay also has a high air shrinkage, but is suitable for face brick, common brick, drain tile and hollow ware. A sample taken from the unweathered portion of the old pit has the following physical properties:

 Physical Properties of the Middleburg Clay (Lab. No. o-73).
 Plasticity, judged by feel............ Excellent.
 W ater of plasticity ................ 27.90%
 Pore water ........................ 2.07%
 Shrinkage water ................... 25.83%
 Linear air shrinkage................ 12.5%
 Volume air shrinkage............... 41.5%
 Modulus of rupture, average........ 585.3 pounds per square inch.
 Slaking test ....................... 10 minutes.
 Steel hard at cone 010.
 Overfires at cone 9.
 Fire tests:
Temperature. Linear Shr. Absorption. Porosity. Color.
 Per Cent. Per Cent. Per Cent.
 950*C. 2.5 8.49 18.90 Brick red.
 1050 3.5 2.82 9.65 Brick red.
 1150 3.5 2.33 7.68 Gray.
 1190 5.5 1.63 6.00 Gray.
 1230 5.5 1.38 4.50 Chocolate brown.