108 FLORIDA GEOLOGICAL SURVEY-NINTH ANNUAL REPORT. 
road crossing at an elevation of about 70 or 80 feet above sea level. 
On the Sopchoppy River, about 30 miles south, essentially the same 
phase of the formation is exposed practically at tide water level. 
The dip of the Alum Bluff formation to the south is thus seen to be 
2 y 2 or 3 feet per mile. 
APPARENT STRUCTURE WITHIN THE ALUM BLUFF FORMATION. 
Within the Alum Bluff formation in railroad and public road 
cuts is frequently observed what at first appears to be minor struc¬ 
tural features, including very small, although pronounced, anticlines 
and synclines, as well as faults and other distortions of the strata. 
These structural features are perhaps best seen at the present time 
In Leon County on the St. Augustine road, five and one-half miles 
east of Tallahassee, although similar structures may be seen at many 
■other localities. (See Fig. 5, p. 106.) 
Striking as these structures are, it is probable that they are 
merely incidental to the disintegration of the formation. Solution 
In the underlying limestone in this area has resulted in the subsi¬ 
dence of overlying materials. On a small scale this is seen associ¬ 
ated with the formation of sinks, and on a larger scale in the forma¬ 
tion of solution basins, such as those of the many large and small 
lakes of this area. This disintegration by solution will be more 
fully described in connection with the topographic history of the 
region. 
It is to be observed that these apparent structural features are 
found only in localities where the general land surface has been 
lowered through erosion, including underground solution accom¬ 
panied by the formation of sinks and basins. In all.cuts made into 
this formation, where it has not obviously been disturbed by sink 
formations or by slumping and settling, the bedding planes are hori¬ 
zontal or nearly so. 
THE CHOCTAWHATCHEE FORMATION 
The Choctawhatchee formation, which is of upper Miocene age, 
Includes marine shell marls and marine sands. The type locality 
of this formation is at Alum Bluff on the Apalachicola River. In 
the section at this bluff 31 feet are referred to this formation, while 
overlying deposits more than 100 feet thick, consisting of coarse 
