296 E. H. SELLARDS 



rests. The Alachua formation contains the workable deposits 

 of hard rock phosphate. Both the Bone Valley and Alachua forma- 

 tions contain a vertebrate fauna on the basis of which the formations 

 are referred to the Pliocene. The Bone Valley formation rarely 

 exceeds 100 feet in thickness and as a rule is less. The Dunnellon 

 formation likewise is usually less than 100 feet in thickness. Both 

 the Nashua and Caloosahatchee formations so far as known are 

 thin and may not exceed 50 or 100 feet. 



PLEISTOCENE 



The Pleistocene formations of Florida include river alluvial and 

 marine deposits. The marine or chiefly marine Pleistocene deposits 

 of the state have been described under the heading of Palm Beach 

 limestone, Miami oolitic limestone, Key Largo limestone, Key West 

 limestone, Lostmans River limestone, and Fort Thompson beds. 

 The five first named are all of marine origin. The Fort Thompson 

 beds include an alternation of fresh-water and marine deposits. All 

 of these deposits are found in southern Florida and the interrelation 

 of the several named units remains to be determined on more 

 detailed stratigraphic work than has yet been done. Alluvial 

 Pleistocene deposits are widely distributed over the state, especially 

 in the stream valleys. In places these stream deposits contain 

 vertebrate and invertebrate fossils. 



GEOLOGIC SKETCH MAP 



The sketch map (Plate II) shows in a general way the surface 

 distribution of the Florida formations. Owing to the small scale 

 of the map it has been necessary to combine the formations. It is 

 also impracticable to show limited exposures, such for instance as 

 the exposures of the Ocala Eocene on the Chipola River near 

 Marianna, or of the Claiborne Eocene on the Choctawhatchee River 

 near the Georgia-Florida state line. Outliers and remnants of some 

 of the formations are omitted for the same reason. Thus over both 

 the Eocene and the Oligocene of peninsular Florida are found 

 remnants of the Lower Miocene, indicating probably the former 

 extension of the Alum Bluff formation over the entire state. No 

 attempt has been made to show the Alachua formation, which rests 

 chiefly upon the Eocene of Alachua, Levy, Marion, and Citrus 



