112 FLORIDA GEOLOGICAL SURVEY-TWELFTH ANNUAL REPORT 
recent years in the study of the geology of Florida has made neces¬ 
sary a number of 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 fol¬ 
lowing table. A recently discovered fact in regard to the geology 
of Florida is the presence of Comanchean formations forming the 
sub-structure of the peninsula and extending as far west at least as 
Tallahassee.* Scarcely less remarkable is the complete absence 
so far as any records yet obtained indicate of the Cretaceous for¬ 
mations (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 peninsular land mass was produced 
thus dates back at least into the Mesozoic era. 
TABLE OF GEOLOGIC FORMATIONS IN FLORIDA 
Pleistocene 
Palm Beach Limestone 
Miami Oolitic Limestone 
Key Largo Limestone 
Key West Limestone 
Lostmans River Limestone 
Ft. Thompson Beds 
Pliocene 
Bone Valley Formation 
Alachua Formation 
Caloosahatchee Formation 
Nashua Formation 
Miocene 
Choctawhatchee Formation 
Jacksonville Formation 
Alum Bluff Formation 
*Cushman, Joseph, A., This volume. 
