GEOLOGY BETWEEN APALACHICOLA AND OCKLOCKNEE RIVERS. 43 
formity between this formation and the overlying sands, or is due 
merely to disintegration is not clear in this section, although an 
unconformity is probably indicated. The Choctawhatchee forma- 
tion rests uncon formably on the underlying Alum Bluff formation. 
The shell marl phase of the Choctawhatchee formation con- 
tains a rich and varied invertebrate fauna. No plant fossils have 
been found in this formation. Bone fragments are not uncommon, 
although no recognizable vertebrate fossils have been secured. 
The level of the base of the Choctawhatchee marl has been 
taken at several localities. On the Apalachicola river the north- 
ernmost exposure of the shell marl phase of the formation that has 
been observed is found in the road-cut leading to Watsons Land- 
ing about 2 miles north of Alum Bluff (Si, TiN, R8W). The 
base of the formation at this place was found to be 56 feet above 
water level in the river. The. water level in the river at this place 
at the time the section was made, was estimated to be 41 feet 
above sea level. Hence the actual level of the base of the forma- 
tion at this exposure is about 27 feet above sea. 
At Alum Bluff the water level in the river was estimated from 
the known levels at River Junction and at Blountstown to be 40 
feet above sea. Near the north end of this bluff the base of the 
Choctawhatchee marl is 36 feet above the water in the river, or 
about 76 feet above sea. Near the middle of the bluff the base 
of this formation is above water 30 feet, or above sea level about 
70 feet. 
The southernmost exposure of this formation observed on the 
Apalachicola river is on the property of S. D. Johnson (S.36, TiS, 
R8W). The base of the shell marl at this exposure is 22 feet 
above water level in the river. The water level in the river at 
this date at Blountstown was 35 feet above sea. As this locality 
is down stream from Blountstown about 6 miles, the river level 
probably is between 3 and 4 feet lower than at Blountstown, or 
about 31 feet above sea. The level of the base of the formation at 
this place is therefore about 53 feet above sea. The distance in a 
direct line between Watsons Landing and Johnson’s farm is about 
10 miles. The dip in the formation in this distance according to 
