292 E. H. SELLARDS 



Georgia-Florida border. Where exposed on the Choctawhatchee 

 River this formation consists of a glauconitic calcareous sand rock, 

 exposures of which are seen at intervals on the river banks for 

 about one and two-thirds miles downstream from the Georgia- 

 Florida line, beyond which it passes below the bed of the river. 

 The thickness of this formation in Florida has not been determined. 

 The Ocala formation as developed in Florida consists for the 

 most part of very pure limestone. Fossils are abundant, although 

 many of the mollusks are preserved only as casts. The rock as a 

 rule is granular and porous, although in places, by replacement, it 

 has become close-grained and compact. Masses and layers of flint 

 representing limestone replaced by silica are of frequent occurrence 

 in this formation. Aside from the flint masses much of the rock 

 consists of soft white limestone or shell marl. This formation is 

 exposed to a limited extent on the Chipola River near Marianna, 

 and also over a considerable area in central peninsular Florida. 

 According to recent studies by Cushman the thickness of the forma- 

 tion is very moderate, in places not exceeding 40 or 50 feet. 



OLIGOCENE 



The Oligocene as limited by recent investigations includes in 

 Florida only the Vicksburg, Chattahoochee, and Tampa forma- 

 tions. The Ocala formation, which had been placed by Dall and 

 others in the Oligocene, has been placed in the Eocene upon the 

 evidence of the molluscan fauna.' The Alum Bluff formation on 

 the other hand formerly referred to the Upper Oligocene has been 

 placed in recent years in the Miocene on the evidence of the 

 vertebrates and invertebrates.^ 



The Vicksburg formation consists of limestones lithologically not 

 unlike those of the Ocala formation. Exposures of the Vicksburg 

 formation are found in Florida near Marianna and Chipley, in 

 Jackson and Washington counties. 



' G. Wythe Cooke, "The Age of the Ocala Limestone," U.S. Geo!. Siirv., Prof. 

 Paper 95, 1915, pp. 107-17. 



2 E. H. Sellards, "Fossil Vertebrates from Florida; a New Miocene Fauna; New 

 Pliocene Species; the Pleistocene Fauna," Florida State Geo!. Surv., 8th Ann. Rept., 

 1916, pp. 77-119, 5 pis. Carlotta J. Maury, "Santo Domingo Type Sections and 

 Fossils," Bull. Amer. Paleontology, V, No. 30 (191 7), Correlation table. 



