PEBBLE PHOSPHATE DEPOSITS. 
35 
that it contains throughout more or less phosphatic material. The 
formation is of special interest in connection with the pebble phos¬ 
phate from the fact that it forms the bed rock of the phosphate 
mines and, as will be subsequently shown, is the parent formation 
from which the pebble phosphate deposits were derived. 
The type locality of the Alum Bluff formation is at Alum Bluff 
on the Apalachicola River. At this place the Alum Bluff consists 
chiefly of gray phosphatic and calcareous sands. Among the de¬ 
tailed sections on the Apalachicola River described by the writer and 
Herman Gunter in the Second Annual Report of this Survey were 
the following: 
Section at Rock Bluff. , 
Rock Bluff lies five and one-half miles in a direct line south of southwest 
of Aspalaga Bluff, or twelve and one-half miles from the State line. It is the 
second point at which the river in Florida strikes the east border of the river 
valley. That part of Rock Bluff which faces the river lies near the southwest 
corner of Section 17, R. 7 west, T. 2 north. The basal part of the following 
section is made near the north end where the river channel first strikes the bluff. 
From this point the level was transferred north across a small stream to that 
part of the bluff which does not now directly face the river. 
Thickness Height above river 
of stratum, (stage of Mar. 5, 1909). 
11. Covered in the line of the section to the 
top of the bluff from the river, about 
mile - - - 
100 
feet 
100 
to 
200 
feet. 
10. 
Fuller’s earth (exposed) 
3 
feet 
97 
to 
100 
feet. 
9 - 
Ledge with shells--- 
1 
foot 
96 
to 
97 
feet. 
8. 
Gray sand - 
5 
feet 
9 i 
to 
96 
feet. 
7 - 
Ledge with shells 
2 
feet 
89 
to 
91 
feet. 
6. 
Gray sand with lime inclusions - 
5 
feet 
84 
to 
89 
feet 
5 - 
Covered — — - 
2 
feet 
82 
to 
84 
feet 
4 - 
Light gray calcareous sand containing 
a trace of phosphate (by transfer¬ 
ring the level across a small branch 
to the north the section is continued) 
30 
feet 
52 
to 
82 
feet 
3 - 
Bluish green to gray sands, variable in 
i 
character. Lime inclusions begin to 
appear in these sands at 20 feet from 
the base. These become more num¬ 
erous until the material passes 
gradually into the sandy-marl above- 
34 
feet 
18 
to 
52 
feet. 
2. 
Compact sandy marl with concretions 
near the base and with an ostrea 
layer 6 feet above the base 
8 
feet 
10 
to 
18 
feet. 
1. 
Chattahoochee limestone above water 
level 
10 
feet 
0 
to 
10 
feet. 
