ROAD MAKING MATERIALS. 
The rocks of the earth's crust may be classed for con¬ 
venience of a brief treatment as either igneous or sedi¬ 
mentary. The igneous rocks are those which appear with 
more or less certainty to have cooled from a molten con¬ 
dition, such as trap, basalt, obsidian, and the granites. 
The sedimentary rocks are those which are formed by the 
accumulation of sediments. The sediments may be of 
purely mechanical origin as in the case of sandstones, 
shales and clays; or of organic origin as in the case of 
the limestones. In a broad sense, the sedimentary rocks 
are made to include even those which are of chemical 
origin, such as bog| iron ore formations. Should one 
attempt a minute and exhaustive classification of rocks 
these two main divisions would be found insufficient. 
Chemical changes are going on incessantly in the earth's 
crust and affect all rock formations. Chemical and physi¬ 
cal forces have in many instances so profoundly altered 
formations that it is no longer possible to determine 
whether they were originally igneous or sedimentary. It 
has been found necessary to establish for these a third 
division known as metamorphic rocks. With regard to 
the Florida deposits, however, the classification is not 
greatly complicated. 
The following summary relates to the rock materials 
occurring within the State, and available for country 
roads at a slight expense. The more expensive products 
used in paving city streets are not included. 
No igneous formations occur in Florida. All of the 
rocks of this State are sedimentary. Two classifications 
are given below. In the first the rocks are classified 
according to origin; in the second according to chemical 
composition. 
