118 FLORIDA GEOLOGICAL SURVEY-15TH ANNUAL REPORT

are practically nil. The source of the material forming the clays and other sediments must be sought elsewhere.
 During the Eocene and Oligocene periods the sediments were marine, representing shallow-water deposition and were formed probably while all of Florida and the coastal plain sections of Georgia and Alabama were yet submerged. These formations were deposited under conditions which were uniform over wide areas.
 The Floridian peninsula partially emerged from the sea early in the Miocene period. Erosional forces set at once to rework and alter the configuration of the then existing surface. Solution of the underlying limestones and the resultant formation of sinks also began about this time, affording depressions for the accummulation of lacustrine deposits. Thus conditions very similar to those existing today began and have continued with but little change to the present time.
 As deposits of transported clay may differ in thickness, character, and extent, according as the material has been deposited in flood-plains, lakes, swamps, estuaries or the open sea, corresponding variations are found in the Florida clays. Clays deposited in the shallow sea or tidal marshes are usually widespread and more uniform. Thus the Chattahoochee, Tampa and Choctawhatchee clays are fairly uniform over the areas they occupy. Under fluviatile and lacustrine conditions, on the other hand, variations in current and variations in the amount and character of the sediments carried resulting from erosional and climatic conditions, cause deposits of these types to differ widely in character. Thus the Alum Bluff, Citronelle and many- Pleistocene deposits display marked irregularities.
 The subsequent erosion and reworking of formations already deposited has been an important process in Florida. This accounts for the numerous isolated remnants or outliers of formations to be found in the State. The sedimentary kaolin deposits are an example of this condition. It also accounts for the presence of one distinct kind of material in two or more formations. Thus phosphatic material has been derived from the Alum Bluff formation, sorted and concentrated in later deposits to such an extent as to make mining profitable. This is also the origin of the Bartow clay.
 The clays of Florida were derived either directly or indirectly from the crystalline rocks of the southern Appalachians exposed in Tennessee, North and South Carolina, northern Georgia and Alabama.