GEOLOGY BETWEEN APALACHICOLA AND OCKLOCKNEE RIVERS. 3 7 
placed as very close to 70 feet above sea. From this record it ap- 
pears that the Chattahoochee formation lies as low, if not lower, on 
Little river than on the Ocklocknee river. The dip of the Chat- 
tahoochee formation south of east, therefore, amounts to as much, 
at least, as between 75 or 80 feet in 21 miles, or about 4 feet per 
mile. The dip may be greater since the top of the Chattahoochee 
formation is not actually exposed in Little river. These measure- 
ments which are consistent with others previously obtained indicate 
that the Chattahoochee formation dips to the east from River Junc- 
tion and rises somewhat again at the Ocklocknee river. 
A slight interruption in the dip of this formation was first sug- 
gested by the writer to account for the anomalous course of the 
Ocklocknee river*. At that time it was pointed out also that the 
topography supported this suggestion, since east of the Ocklocknee 
there has been developed lakes occupying solution basins in the 
limestone, and with these a characteristic limestone topography, 
while in the belt of country immediately west of the river, on the 
other hand, there are almost no indications of limestones lying near 
the surface except in the extreme northeast part of Gadsden county, 
and of course at the extreme west along the Apalachicola river. 
Measurements subsequently made indicate that near the Georgia 
line the base of the Alum Bluff formation is close to 105 feet above 
sea (sink of Ponto Branch), while a few miles farther east in Leon 
County the Chattahoochee limestone rises to an elevation of 127 and 
135 feet at the recorded exposures. It would seem therefore, that 
as indicated both by topography and stratigraphy, there is a slight 
interruption of dip near the Ocklocknee river. 
MIOCENE. 
THE ALUM BLUFF FORMATION. 
The Alum Bluff formation which lies next above the Chatta- 
hoochee, includes clays, fullers earth, calcareous and phosphatic 
sands, and sandy clays. The type, locality of this formation is at 
Alum Bluff, in Liberty county. The formation is well shown also 
at many other localities throughout the area. The maximum ex- 
* Florida Geol. Surv., 9th Ann. Rpt., pp. 130-132, 1917. 
