86 FLORIDA GEOLOGICAL SURVEY ELEVENTH ANNUAL REPORT, 
TOPOGRAPHY AND GEOLOGY. 
E. H. SELLARDS. 
In its topographic forms this area presents some apparent 
anomalies. In passing inland from the coast, the land surface 
rises gradually to a maximum height, 40 miles inland, of about 322 
feet. From this elevation the land surface drops abruptly to 135 
feet above sea within a distance of 4 miles. From here the eleva- 
tion again rises very gradually to 156 feet near the State line. 
The escarpment marked by this slope which amounts to between 
150 and 200 feet, extends across the area from the Choctawhatchee 
to the Chipola-Apalachicola river valleys. At the east side of the 
Apalachicola, a similar escarpment extends beyond the boundary of 
Florida. A less well marked escarpment is found on the west side 
of the Choctawhatchee river. To the north of this escarpment in 
this area the country is underlaid by limestones, and has a varied 
topography including sinks and solution valleys. Under the 
plateau, south of the escarpment, the limestones lie at a much 
greater depth, and their influence on topography is not so obvious. 
The development of the topography in this area may conveniently 
be described after an account has been given of the geology of the 
region. 
RIVERS. 
The Apalachicola river at the east margin of this area is the 
largest river in Florida. Originating in the highlands of Georgia, 
this river carries a heavy load of sediment and is one of the few 
muddy-water streams of the State. The Chipola river, its chief 
tributary in Florida, on the contrary, is a dear-water stream. The 
Choctawhatchee river borders the western margin of this area. 
THE DEAD LAKES OF THE CHIPOLA RIVER. 
The valley of the Apalachicola river is being rapidly aggraded 
by reason of the load of sediment carried by that stream ; the val- 
ley of the Chipola, on the other hand, is being built up, much more 
slowly. The result has been a blocking of the Chipola at its en- 
trance into the Apalachicola by sediment carried by the main 
stream, thus forming the body of water known as the “Dead 
Lakes” in Calhoun County. Pine Log creek, a tributary entering 
