104 FLORIDA GEOLOGICAL SURVEY-NINTH ANNUAL REPORT. 
MIOCENE. 
THE ALUM BLUFF FORMATION. 
The Alum Bluff formation which lies next above the Chattahoo¬ 
chee, includes clays, fuller’s earth, calcareous and phosphatic sands, 
and sandy clays. Formerly the red sandy clays at the surface of 
this area were, supposed to be separable from the Alum Bluff and 
to belong to the Lafayette formation. It does not seem, however, 
that there is any definite or well defined break within this deposit. 
The difficulty in determining the age of the surface materials is due 
to the fact that they contain no fossils, or if fossils were present 
they have disappeared, probably by solution. The red sands lying 
near the surface in this area represent in fact a zone of partial 
decay. If there is a persistent dividing line, such as could be used 
in defining a formation, between the superficial materials and the 
known fossiliferous Alum Bluff deposits beneath, it has not been 
detected, and the whole deposits may for the present be referred to 
the Alum Bluff formation. 
As thus defined the Alum Bluff formation in this area attains a 
thickness of from ioo to 150 feet. These deposits underlie and 
chiefly make up the red hills of Leon County. Near the southern 
margin of Leon County and over most of the eastern half of 
Wakulla County this formation has largely disappeared through 
disintegration, the limestone of the next older formation, as already 
noted, lying near the surface. In the southwestern part of Leon 
and the western part of Wakulla counties, this formation, although 
present, dips below the surface and is concealed by the later forma¬ 
tions. 
TYPICAL EXPOSURES OF THE ALUM BLUFF FORMATION. 
Perhaps the best single exposure in Leon County at the present 
time of beds referred to the Alum Bluff formation is found on the 
Bainbridge road four miles northwest of Tallahassee. The section 
which is seen in the cut of the public road affords an exposure of 
about 38 feet and is as follows: 
Finely laminated clayey sands, passing at the top into the soil-8 feet 
Cross-bedded clayey sands often with white partings-25 feet 
Greenish clay which upon weathering breaks into small pieces- 3 feet 
Yellow sands at the base of the exposure- 2 feet 
