42 , FLORIDA GEOLOGICAL SURVEY. 
manufactured to a limited extent from a natural cement 
rock near River Junction. The output from this plant in 
1898 is given as 7,500 barrels.* 
The formation from which the cement was made is the 
Chattahoochee Limestone, which is extensively exposed 
along the Apalachicola and Chattahoochee Rivers above 
and below River Junction. It is reported that the cement 
made from the rock at River Junction was of a good 
quality. It was placed on the market under the trade 
name of “White Roman Hydraulic Cement of Florida.” 
Portland Cement. 
Portland cement is made from raw materials mixed in 
such manner as to supply the proper constituents for 
cement manufacture. Ordinarily clay and some form of 
limestone is used. The clay supplies the silica and 
alumina, while the limestone supplies calcium or calcium 
and magnesium. Marl, chalk, or slag, or in fact, any 
material which supplies the necessary calcium oxide with¬ 
out introducing substances deleterious to the cement may 
be used if desired instead of limestone. Both the clay 
or mixture of clays and the limestone must be selected 
with a view to securing the right proportion of constit¬ 
uents in the resulting mixture. Since both clays and 
limestone vary greatly in composition each must be 
selected with a view to supplementing the other. While 
no Portland cement is being made at present in Florida, 
both clays and limestone available for this purpose doubt¬ 
less occur. 
SAND-LIME BRICKS. 
The materials used in the manufacture of sand-lime 
bricks are sand and lime. The bonding power of the 
brick is due to the chemical reaction between these ingre¬ 
dients. The chemical changes occur in the presence of 
• 20th Ann. Rept. U. S. Geol. Sur., pt. VI (cont.), p. 547. 1899. 
