ANNUAL REPORT-ROAD MATERIALS. 
51 
ably due to a replacement process similar to that de¬ 
scribed for flint and chert. The chemical changes in this 
case involve a rearrangement of the constituent molecules 
as a result of which the non-crystallized material of the 
rock assumes a definite form. When partly crystallized 
the limestone becomes compact and close grained. 
Distribution and 1 Amount of Calcareous Rocks:—The 
calcareous rocks are widely distributed in the State. The 
Vicksburg Limestone, as already stated, lies at or near the 
surface over much of central Florida. Oolitic limestones 
make up an extensive formation running north and south 
from Miami and forming the east border of the Ever¬ 
glades. Coral and oolitic limestones form the founda¬ 
tion of the keys from Miami to Key West. Shell lime¬ 
stone occurs extensively along the Caloosahatchee River. 
Tampa Bay affords a compact limestone which often car¬ 
ries much silica. The Chattahoochee series of compact 
limestones occurs extensively in parts of west Florida. 
The marls are usually of local occurrence and are re¬ 
stricted to no part of the State Shells, thanks to the 
oyster industry of the present, and to the shell mound 
builders of the past, occur in inexhaustible quantities. 
Argillaceous Rocks—Road-Making Clays. 
Fine grained clay mixed in proper proportion with 
coarse, angular quartz, makes a road that has been found 
useful where cheapness of construction is necessary, and 
where the roads have light travel. In mixing sand and 
clay for road purposes the proportion should be so ad¬ 
justed that there is just enough clay in the mixture to 
fill the voids or interstices between the grains of sand. 
If too little clay is added the sand grains will lack bond¬ 
ing power and will not compact into x a solid roadbed. 
If too much clay is added, the sand grains are widely 
separated and the road behaves much as though the sand 
were not present at all. The amount of clay necessary to 
mix with a given volume of any particular sand may be 
