REPORT OF INVESTIGATIONS NO. 42


biologic environment. Generally, the mineral content of water in
streams varies inversely with discharge. Surface waters are
usually highly colored and acidic. Sodium and chloride, although
in very low concentrations, are the principal dissolved mineral
constituents and may be present as a result of wind and rain-borne
salts from the ocean.
 The quality of ground water in the Green Swamp area generally
meets the requirements for most municipal, industrial, domestic,
and agricultural uses. Ground water of lowest mineral content
occurs along the eastern and western boundaries of the area and
is lowest near the lakes. Ground water of highest mineral content
occurs in the central part of the Green Swamp. The principal
dissolved mineral constituents are calcium and bicarbonate which
are products of limestone solution. Relatively high concentrations
of calcium in the water cause hardness which is probably the most
objectionable characteristic of the ground water in the Green
Swamp area.

 GEOLOGY'

 Topographically, the surface of the Green Swamp area
 resembles a basin, or trough, opening to the north. However,
 geologically, the Green Swamp is part of an eroded, faulted
 anticline. The oldest formations are exposed along the axis of the
 anticline and eroded remnants of younger formations rim the flanks
 and present a basin-like feature.
 The Green Swamp area is underlain by several hundred feet of
 limestone and dolomite that have been periodically exposed to
 solution-weathering and erosion. The surface is mantled with a
 varying thickness of plastic material (sand and clay) that was
 deposited in fluctuating shallow seas. No attempt has been made
 to differentiate the formations within the plastic material because
 of its complexity and the lack of data.
 The upper part of the elastic sediments, composed of clayey
 sands, forms a distinct hydrologic unit, commonly referred to as
 the nonartesian aquifer. The basal portion of the plastic sediments,
 composed mostly of clay and some interbedded limestone
 (secondary artesian aquifer), is less permeable than the overlying,

 1The classification and nomenclature of the rock units conform to the usage
 of the Florida Geological Survey and also with those of the U. S. Geological
 Survey, except for the Fort Preston Formation (?), the Tampa Formation,
 and the Ocala Group and its subdivisions.