THE SOILS OF FLORIDA. 
51 
these is found in varying quantities quartz, mica, and other miner¬ 
als. Sandstones consist largely of quartz sands, while the conglom¬ 
erates may be of any material, although flint pebbles usually pre¬ 
dominate. 
The limestones in the secondary formations are either of chemical 
or organic-chemical origin. The bases, calcium and magnesium, are 
taken into solution and carried by running water to the lakes and 
the ocean. Subsequently under certain conditions they may be pre¬ 
cipitated from the water to form limestone, thus ‘ constituting the 
chemically formed limestones. More frequently, however, organic 
processes are involved, the constituents being taken from the water 
through the agency of organisms, chiefly shells and corals, which 
have the power of extracting from solution the materials from which 
the calcareous skeleton is built. After the death of the animal the 
skeleton remains to form the limestone. Shells accumulate in this 
way to form the shell limestones, and corals in some instances accu¬ 
mulate to form a coral limestone. The foraminifera, animals having 
a minute calcareous shell, accumulate in such abundance as to make 
up extensive limestones, the formation known as the Vicksburg 
Limestone underlying Florida, being composed in places chiefly 
of these small shells. The oolitic limestones such as the Miami 
Oolite in southern Florida is probably chiefly chemically formed, 
although many shells and some corals are included. 
The term marl is somewhat loosely applied to calcareous forma¬ 
tions, several varieties of which are found in Florida. When con¬ 
sisting largely of shells these marls are known as shell marl. Some 
of the marls which accumulated in bogs contain few or no shells, 
having been apparently chemically formed. 
Some of the other secondary rocks are purely of chemical origin. 
Among these may be mentioned the bog iron ore frequently found in 
old swamps. The iron in these deposits has been brought into the 
swamps in solution and subsequently precipitated owing to the 
organic acids present in swamp water. The flint masses found fre¬ 
quently in limestone formations are due to segregation of silica 
through chemical action. 
Owing to the assorting processes which accompany the forma¬ 
tion of the secondary or sedimentary rocks, they are, as previously 
stated, much less complex chemically than are the igneous rocks. 
This absence of chemical complexity has an important bearing on 
the formation of soil, and there are well-marked differences to be 
noted between soils derived from igneous and those derived from 
sedimentary rocks. 
