44 FLORIDA GEOLOGICAL SURVEY TENTH ANNUAL REPORT. 
the measurements made amounts to 23 feet, or scarcely 21-3 feet 
per mile. 
The Choctawhatchee marl is exposed on Hosford Mill creek 
on the property of R. F. Hosford about ij 4 miles northwest of 
the present Hosford station. The. level of the marl at this ex- 
posure as determined from the profile of the Apalachicola Nor- 
thern railroad is 88 feet above sea. It is not known what part 
of the stratum is represented in the Hosford exposure since neither 
the base nor the top of the formation is exposed. No nearby bench 
marks are available from which to determine the level of the ex- 
posures of this formation on the Ocklocknee. river. However, the 
water level at the S. A. L. crossing at medium low water is about 
60 feet above sea. From this crossing to the gulf, following the 
general course of the river, is about 45 miles, indicating a fall of 
somewhat more than a foot per mile. From this crossing to Jack- 
son Bluff is about 15 miles. Hence water level at this bluff is 
probably close to 40 feet above sea. The. base of the Choctaw- 
hatchee formation at Jackson Bluff is 29 feet above the river at 
medium low stage. Assuming that the water level in the river 
is 40 feet above sea, the actual level of the base of the formation 
at this place is approximately 69 feet above sea, or but slightly 
less than at Alum Bluff. Jackson Bluff is 20 miles east and 5 
miles south of Alum Bluff. From these records it would seem 
that the Choctawhatchee formation lies almost on a level from 
east to west across this area. 
MIOCENE-PLIOCENE 
Later deposits in this part of the State overlie and rest upon 
the Choctawhatchee formation. These deposits are unfossilifer- 
ous, and their age is not determined, except as indicated by their 
stratigraphic position, which shows them to be later than the Choc- 
tawhatchee formation. Lithologically these later deposits are very 
characteristic. They consist chiefly of sands and clays. The sands 
are prevailingly red in color, and vary from nicely laminated, fine 
sands to very coarse, often cross-bedded sands and pebbles. At 
places in these deposits are found layers of clay free from sand. 
These clay streaks are often variegated in color, including shades 
of pink and red, as well as blue and drab. 
