GEOLOGY OF FLORIDA 291 



changes in the classification of the formations of the state. Of the 

 formation names formerly in use, one or two have been discarded, 

 and on the other hand several new names have been added. The 

 classification which at present best represents our knowledge of the 

 geology of the state is expressed in the table (p. 290). A recently 

 discovered fact in regard to the geology of Florida is the presence of 

 Comanchean formations forming the substructure of the peninsula 

 and extending at least as far west as Tallahassee.^ Scarcely less 

 remarkable is the complete absence, so far as any records yet 

 obtained indicate, of the Cretaceous formations (Upper Cretaceous). 

 If any of these formations were present they were removed by 

 erosion previous to the deposition of the late Eocene formations. 

 Their absence in any case can be accounted for only by a long period, 

 previous to the late Eocene, during which the Florida land mass 

 Stood above water-level. The earth structure by which this pen- 

 insular land mass was produced thus dates back at least into the 

 Mesozoic period. 



STEATIGRAPHIC SUCCESSION 

 COMANCHEAN FORMATIONS 



The oldest formations that have been recognized in Florida are 

 those encountered in well drilling and known at present only from 

 well cuttings. The fossils found in these cuttings indicate the 

 presence of Comanchean formations under all of the peninsula and 

 a part at least of west Florida. The discussion of these formations 

 together with the data from which they have been determined has 

 been given by Dr. J. A. Cushman in the Twelfth Annual Report of 

 the Florida Geological Survey. The thickness of the Comanchean 

 underlying Florida has not been determined. The formations are 

 chiefly limestone. The Cretaceous (Upper Cretaceous) is wanting 

 in' all deep wells of which record has been obtained. 



EOCENE 



The Eocene deposits are represented in Florida by the Claiborne 

 and Ocala formations. The Claiborne formation comes into Florida 

 for only a short distance on the Choctawhatchee River near the 



' Joseph A. Cushman, "The Age of the Underlying Rocks of Florida as Shown by 

 the Foraminifera of Well Borings," Florida State Geol. Surv., 12th Ann. Rept., 1919. 



