MINERAL INDUSTRIES. 
29 
ROAD MATERIALS. 
The materials available in Florida for making improved roads 
include crushed stone, marl, shell, sand, gravel and sand-clay. In 
addition cement, asphalt and vitrified brick are being imported into 
the State for this purpose. The kind of road constructed depends 
largely upon the materials available that are cheap enough to be 
economically used. Sandy clays suitable for country roads are 
widely distributed and at the present time the mileage of roads built 
of sand-clay in the State equals the mileage of roads built of all 
other materials combined. Marl, limestone and shell are the next 
most widely distributed materials, while flint, bog ore, gravel and 
phosphate rock are more restricted. While it is impossible to get 
complete statistics on road materials it is known that more than 
$56,000 worth of rock was produced in Florida during 1915 for the 
purpose of road construction. 
In the following table the rocks that are found in Florida are 
classified according to their origin. A second table is added in 
which the rocks are classified according to their chemical composi¬ 
tion. The rocks of the State as may be seen from the lists given in 
these tables are all of sedimentary or of sedimentary-chemical origin, 
as no' igneous or highly metamorphic rock are known in the State. 
ROCKS OF FLORIDA CLASSIFIED ACCORDING TO ORIGIN. 
Mechanical origin 
Organic origin 
Chemical origin 
Sandstone, 
< Shales, 
Clays. 
{ Shell limestone, 
Infusorial earth, 
Muck, peat, lignite. 
Bog iron ore. 
Oolitic limestone, 
< Flint or chert, 
Crystallized limestone, 
, Phosphate rock. 
Disregarding mode of origin and placing the rocks according to 
chemical composition, the classification may be arranged as follows: 
