A PRELIMINARY REPORT ON CLAYS OF FLORIDA 109

 ward, in a somewhat broken succession in Florida, to almost the extreme west end of the State. It is probably the most widespread formation exposed in the State.
 The Jacksonville formation is a term applied to deposits known in the vicinity of Jacksonville and having a limited extent. Its fauna indicates a later age, but otherwise it closely resembles the Alum Bluff formation.
 The Choctawhatchee formation consists of marls, sands, and clays exposed in portions of west Florida.
 PLIOCENE
 To the Pliocene are assigned several formations consisting essentially of marls, sand and clays representing marine and fresh-water conditions of sedimentation. Several of these formations are probably contemporaneous.
 PLEISTOCENE
 The Pleistocene deposits, which here includes those of Recent age, as well, are of widespread distribution and variable lithologic character, representing both terrestrial and marine conditions. They are found principally in the southern extremity of the State and along both the Atlantic and Gulf coasts. Numerous deposits of this age, while relatively thin, are widely distributed over the interior portions of the State.
 GEOLOGIC AGE, OCCURRENCE AND DISTRIBUTION OF THE CLAYS
 There is not space within the limitations of this r.eport to treat exhaustively the geologic age of the clays of Florida. In reconnaissance work it is often difficult and at times impossible to ascertain the horizon to which a clay deposit should be assigned, owing to its frequently limited areal extent, lack of fossils and imperfect exposures. The geologic map issued with the Fourteenth Annual Report of this Survey (1922) has been largely conformed to in assigning clays to formations already established and somewhat widely distributed within the State. It is to be noted, however, that within an extended area of exposure of one formation there may be numerous deposits of a more recent age. This is particularly true in Florida where the great number of sink-holes, swamps, and small streams of low gradient have afforded conditions favorable for the formation of clay deposits. Sellards' has pointed out that the sinks pos1S'ellards, E. H., The Relation of the Dunnellon Formation to the Alachua Clay, Sixth Annual Report, Florida Geol. Survey, p. 162, 1914.