130 
FLORIDA GEOLOGICAL SURVEY—I5TH ANNUAL REPORT 
Fire tests: 
Temperature. Linear Shr. Absorption. 
Per Cent. 
Per Cent. 
950°C. 
1.2 
6.60 
1150 
2.7 
5.69 
1050 
2.7 
7.22 
1190 
4.2 
3.69 
1230 
5.7 
3.04 
A clay similar to the Doctors Ii 
about two miles east of Middleburg 
Porosity. 
Per Cent. 
Color. 
18.40 
Brick red. 
17.10 
Brick red. 
17.90 
Brick red. 
17.20 
Brick red. 
16.10 
Brick red. 
clay is exposed on Black Creek 
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. Ship¬ 
ment 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. 0 - 78 ). 
Plasticity, judged by feel.... 
Water of plasticity. 
Pore water. 
Shrinkage water. 
Linear air shrinkage. 
Volume air shrinkage. 
Modulus of rupture, average 
Slaking test. 
Steel hard at cone 010. 
Overfires at cone 9. 
Fire tests: 
Excellent. 
27.90% 
2.07% 
25.83% 
12.5% 
41.5% 
585.3 pounds per square inch. 
10 minutes. 
Temperature. Linear Shr. Absorption. 
Per Cent. 
Per Cent. 
950°C. 
2.5 
8.49 
1050 
3.5 
2.82 
1150 
3.5 
2.33 
1190 
5.5 
1.63 
1230 
5.5 
1.38 
Porosity. Color. 
Per Cent. 
18.90 
Brick red. 
9.65 
Brick red. 
7.68 
Gray. 
6.00 
Gray. 
4.50 
Chocolate brown. 
