92 
FLORIDA STATE GEOLOGICAL SURVEY. 
them was given by Vaughan 1 in 1901. The Oak Grove sand member 
was described by Dali 2 in 1893. 
Exposures of limestone on the Sopchoppy and Ocklocknee Rivers, 
some five or six miles from the town of Sopchoppy, have been called 
the “Sopchoppy limestone.” This rock was first described by Dali 3 
who assigned it to about the horizon of the Chipola marl member. In 
this report it is tentatively included with the Alum Bluff formation. 
Further investigation is needed to determine its exact stratigraphic 
relations. 
The limestones and marls on the Manatee River near Ellenton 
were thought by Heilprin 4 to belong to the Miocene, but are probably 
somewhat older. They are here referred tentatively to the Oak 
Grove sand member of the Alum Bluff formation, but this correla¬ 
tion is subject to revision, if subsequent investigations should show 
that the fauna is characteristic of some other horizon. 
Stratigraphic Position:—The Alum Bluff formation is conformable 
upon both the Chattahoochee and the Hawthorne formations. This is 
inferred from the facts that no distinct evidence of a stratigraphic 
break between the two groups has been noted, and their faunas are 
closely related. At Alum Bluff, on the Apalachicola River, and Jack- 
son’s Bluff, on the Ocklocknee River, the marls of Miocene age rest 
upon an eroded surface of the Alum Bluff formation, but farther west, 
in Walton County, it is possible that they may be conformable. 
Lithologic Character: — The Alum Bluff formation consists of 
marl, sand and clay, which are sometimes fairly distinct, but more 
often interbedded. Limestones also occur in the formation, but they 
are not extensively developed and usually contain enough earthy ma¬ 
terial mixed with the carbonate of lime to form marls. Shell marls 
with a calcareous or sandy matrix are common and they often occur 
interbedded with nearly pure sand. In general, the beds belonging to 
this formation are light gray, but occasionally shades of green or yel¬ 
low prevail. 
At Alum Bluff, on the Apalachicola River, Dali 5 gives the follow¬ 
ing section: 
1 Vaughan, T. Wayland. Fuller’s earth; U. S. Geol. Survey, Mineral Re¬ 
sources of the United States, 1901, pp. 921-934. 
2 Dali, Wm. H. Cenozoic Geology Along the Apalachicola River, Geol. Soc. 
Am. Bull., vol. v, 1893, pp. 166-167. 
3 Dali, Wm. H., Neocene of North America, U. S. Geol. Survey, Bull. No. 84, 
1892, pp. 119-120. 
4 Heilprin, Angelo. Explorations on the west coast of Florida. Wagner 
Free Inst., Trans., vol. 1, p. 13. 
5 Dali, Wm. H., Geol. Soc. Am., vol. v, 1893, p. 157. 
