GEOLOGY CHOCTAWHATCHEE AND APALACHICOLA RIVERS. 95 
cuts on the Atlanta and St. Andrew’s Bay railway are seen ex- 
posures which appear to represent this formation. Likewise on 
the west banks of the Choctawhatchee River a considerable thick- 
ness of similar material is found overlaying the Choctawhatchee 
formation. These deposits presumably represent the westward 
extension of the materials found overlying the Choctawhatchee 
formation between the Apalachicola and Ocklocknee Rivers. 
SANDS AND GRAVELS. 
At places within this area are found coarse sands, gravel, and 
pebbles. The pebbles are chiefly fragments of quartzite rocks. 
These pebbles vary from a few ounces to from one-half to one or 
two pounds in weight. Most of them are water worn and rounded, 
although occasionally rocks are. found that are distinctly angular. 
Deposits of these gravel found four miles south of Cottondale 
(S13, T3N, R12W), are being utilized in road building in Bay 
County. Other deposits as yet not utilized are found near by. 
The gravel beds that are being worked are found near the base 
of the escarpment which divides the lower lands of the northern 
part of the area from the higher lands farther south. However, at 
a locality about one mile west of Round Lake is found a bed of 
gravel consisting of medium seized pebbles that lies well up on 
the highlands. The position of this bed suggests that the deposits 
found at the lower level may be concentration products from the 
higher lands. Samples of these pebbles were submitted for exami- 
nation to the U. S. Geological Survey. In com'menting upon the 
pebbles, the acting director of the Survey states :* The pebbles 
that you submitted seem to be quartzite but whether they origi- 
nated in the Coastal Plain or in the region of metamorphic rocks 
seems to be indeterminate. 
TOPOGRAPHIC AND PHYSIOGRAPHIC DEVELOPMENT OF LAND 
FORMS. 
The geologic structure in this area has influenced the. topo- 
graphic and physiographic development. The position and direction 
of the principal streams seem to have been determined by the 
structure. As has been shown the Eocene and Oligocene lime- 
* Letter of July 10, 1918. 
