46 FLORIDA GEOLOGICAL SURVEY TENTH ANNUAL REPORT. 
Choctawhatchee formation rises to a level of about 73 feet above 
water level in the river at this stage. The. two formations may be 
unconformable at this exposure, since the top of the Choctaw- 
hatchee formation near the south end of the bluff is apparently as 
much as 10 feet higher than at the north end of the bluff. 
To the north of Alum Bluff this formation extends beyond 
the known limits of the Choctawhatchee marl, overlapping upon 
the Alum Bluff formation. To the south 2nd east, the deposits 
may be recognized in numerous exposures. At all places where 
examined the deposit has been found to be non-fossiliferous, and 
when this formation rests directly upon the cross-bedded sands of 
the. upper part of the Alum Bluff formation, it becomes difficult 
in. the absence of fossils to locate the dividing line between the two 
formations. 
This formation is exposed in a steephead on the property of 
J. H. Hunt, 1 mile south of Bristol. Near the. surface at this place 
is found 10 feet of clayey, mottled sand, sufficiently indurated to 
stand vertical. Beneath this sand is 4 feet of drab-colored, heavy 
clay. Below the clay, the sides of the. steephead are sloping and 
covered, but probably include slightly indurated sands. Springs 
emerge at the bottom of the steephead, which has a depth of about 
50 feet. The. surface level at this locality, as indicated by approxi- 
mate levels, is probably about 150 feet above sea. The actual 
elevation of this formation as seen at this exposure is therefore 
from about 100 to 150 feet above sea. At Alum Bluff, 3 miles 
farther north, the formation, as already noted, occupies the inter- 
val from 101 to 154 feet above sea. 
This formation is also exposed in the bluffs bordering Mystic 
lake, about 3 miles south of Bristol. This lake, which has no sur- 
face outlet, evidently owes its existence to the presence of the un- 
derlying calcareous marls of the Choctawhatchee and probably 
of the Alum Bluff formations which have dissolved, permitting 
the subsidence which thus formed the lake basin. 
At the S. D. Johnson place (S26, TiS, R8W), about 75 feet, 
chiefly sands, overlie the Choctawhatchee shell marl. At Hosford 
Mill creek, 12 miles east of Alum Bluff, 40 or 50 feet of sands 
and sandy clays lie above the Choctawhatchee formation. 
To the north from Alum Bluff, this formation is frequently ex- 
posed in streams and in steepheacls. Near the head- waters of Big 
