FLORIDA GEOLOGICAL SURVEY


clayey sands or the underlying porous limestone. The solution-
riddled limestone formations, which underlie the clay deposits,
comprise the Floridan aquifer, the principal source of artesian
ground water in the State. Where present, the clay forms an
aquiclude which retards the rate of water movement between the
aquifers.
 The principal artesian aquifer was first described by Stringfield
 (1936) and later named the Floridan aquifer by Parker (1955).
 According to Parker, the Floridan aquifer includes those limestone
 formations ranging in age from the middle Eocene (Lake City
 Limestone) to perhaps early and middle Miocene (Hawthorn
 Formation). In the Green Swamp area the following formations
 comprise the Floridan aquifer (from youngest to oldest); the
 Suwanee Limestone; the Ocala Group which includes the Crystal
 River, Williston, and Inglis Formations; and the Avon Park
 Limestone. The base of the aquifer is considered to be near the
 base of the Avon Park limestone at the first occurrence of gypsum
 because the presence of gypsum probably indicates poor circulation
 of ground water.

 FORMATIONS

 The formations that underlie the Green Swamp area are
presented in table 4. Generalized geologic cross sections, shown in
figure 8 were prepared based on data from wells located along lines
A-A', B-B' and C-C'.

 UNDIFFERENTIATED CLASTIC DEPOSITS

 Undifferentiated plastic deposits, ranging from late Miocene to
 Recent in age, underlie the Green Swamp area except in the western
 part where Tertiary limestones are exposed at the surface. The
 deposits consist primarily of clayey sand or sandy clay. The
 following lithologic sequence (from youngest to oldest) is indicated:
 (1) fine quartz sand surficiall sand) with varying amounts of clay
 and organic material; (2) variegated (red-orange-tan) fine to
 coarse quartz sand with little clay; (3) white fine to very coarse
 quartz sand with varying amounts of white-green kaolinitic or
 montmorillonitic clay; and (4) white silty quartz sand with varying
 amounts of mica flakes.
 Generally, the deposits range from 100 to 200 feet in thickness
 beneath the ridges that rim the Green Swamp area; however, they
 are thin or absent in the western part and tend to become more