108 FLORIDA GEOLOGICAL SURVEY ELEVENTH ANNUAL REPORT. 
and for railroad ballast. A limited amount is also used for roof- 
ing purposes. The total production of sand and gravel for 1917 
was 262,971 tons, valued at $145,579. 
The companies reporting the production of sand and gravel in 
Florida during 1917 are the following: 
1 
Atlantic Coast Line Railroad Company. 
Akerman and Ellis, Lake Weir. 
Interlachen Gravel Company, Interlachen. 
Stone Products Company, Bartow. 
Tampa Sand and Shell Company, Tampa. 
A. T. Thomas Company, Ocala. 
SAND-LIME BRICK. 
The materials used in the manufacture of sand-lime brick are 
sand and lime. The bonding power of the brick is due to the 
chemical reaction between these ingredients. The chemical changes 
occur in the presence of heat, pressure and moisture and result in 
the formation of hydro-silicates of calcium and magnesium. 
The sand used in the manufacture of sand-lime brick should 
be comparatively pure and preferably with some variation in the 
size of the grains. The mixture of lime, sand and water, is cut in 
the form of bricks and conveyed to a hardening cylinder. Neces- 
sary heat and pressure are obtained in the hardening cylinder 
adapted for the purpose. The sand-lim'e bricks are placed i.n this 
cylinder and subjected to a pressure and temperature which vary 
according to the method of treatment. 
Two companies were actively engaged in the manufacture of 
sand-lime brick in Florida during 1917 as follows: 
The Bond Sandstone Brick Company, Lake Helen. 
The Plant City Composite Brick Company, Plant City. 
The production of sand-lime brick in Florida during 1917, 
although not separately listed, is included in making up the total 
mineral production of the State. 
