10:1 FLORIDA STATE ^ GEOLOGICAL SURVEY. 
, Oak Grove Sand Member —On paleontologic grounds, Dali 1 has 
correlated the Oak Grove sand member with the typical sands of the 
Alum Bluff formation. The. correlation 2 has been made because of 
the presence in both of Ostrea trigonalis, Pecten say anus, a Pododes- 
mits and Turritella alcida Dali. 
The Oak Grove sand member consists of fine-grained, light gray to 
greenish sands containing many excellently preserved shells. It is a 
sandy shell marl, which often has a considerable admixture of cal¬ 
careous material. The Oak Grove sand member is not fully exposed 
at the type Ideality'and it may attain a thickness of several feet, but 
the observed thickness is only a few feet. 
The fauna of the Oak Grove * sand member is closely related to 
that of the Chipola marl member, but it contains large species of both 
Cardium and Lyropecten, which appear to foreshadow the large 
species of those genera occurring in the Miocene marls. 
Owing to the heavy rains, the. Oak Grove , sand member was sub¬ 
merged at the time that locality was visited. The exposure is said 
to be less than four feet in thickness and to consist of light gray, ex¬ 
tremely fossiliferous. sand. The Oak Grove sand member was subse¬ 
quently examined by . Vaughan 3 who reports the following section: 
Section' of bluffYellow, River, about 100 yards beiozu road bridge. 
Fine yellow sands .. 9 feet. 
Very fossiliferous gray sandy marl extending below level of water in 
the river at least 1 foot... 2 feet. 
Total ......... 11 feet- 
Dr. Vaughan examined an exposure of marl on the south side 
of the river at Crowders Crossing in Section 5 T., 3 N., R. 21 W. At 
this locality, a blue or bluish-green marl rises about two feet above 
the river at a very low stage of water. This exposure is probably the 
stratigraphic equivalent of the Oak Grove sand member. 
Shoal River Marl Member:—The Shoal River marl member, which 
has recently been recognized by Vaughan, 4 lies stratigraphically about 
thirty feet-above the Oak- Grove sand member. It thus, forms the 
upper part of the Alum Bluff formation. In the following section at 
Shell Bluffj the lower sand represents the. Oak Grove sand member 
and the upper fossiliferous marl horizon is the Shoal River marl mem¬ 
ber.. . , 
1 Dali, Wm. H., Cenozoic Geology along the Apalachicola River, Bull Geol. 
Soc. Am., pp. 166-167, and p. 170. 
2 Dali, Wm. H., Tertiary Faunas of Florida, Wagner Free Inst, of Sci. Trans., 
vol. 3,-pt. 6, 1903, p. 1588. . 
3 Vaughan, T. Wayland. Unpublished notes. 
4 Vaughan, T. Wayland... Unpublished notes. . 
