102 FLORIDA GEOLOGICAL SURVEY—NINTH ANNUAL REPORT. 
port, the most serviceable in the study of structure, perhaps, is 
the Chattahoochee limestone. North of Lake Iamonia this rock 
has been found to lie in the'Thompson well, Sec. 23, R. 1 E., T. 3 N. 
as high as 138 feet above sea level. In a well on the Hutchinson 
place, about two miles further east, the top of the rock was reached 
at an elevation of 112 feet, while a few miles further east, in a well 
at Stringer’s store, north of Lake Miccosukee, the rock was found 
at an elevation of 119 feet above sea. Passing to the south the rock 
is found at lower elevations. On the south shore of Lake. Iamonia 
it has been reached at elevations of 98 and 90 feet, respectively, and 
on the north bank of Lake Jackson at 92 feet above sea. At the 
crossing of the Seaboard Air Line Railway, on the Ocklocknee 
River, the rock lies at an elevation of 66 feet above sea. South of 
Lake Lafayette the rock is found at about 54 feet above sea level. 
At Lloyds it is reached in wells at about 57 feet above sea, while on 
Burnt Mill creek, somewhat south of Lloyds, it is exposed in a sink 
at an elevation of 41 feet above sea. Passing farther south it drops 
as already noted gradually to sea level. In determining direction 
and rate of dip, however, it is necessary to use the data with care. 
Owing to disintegration beneath the surface, wells may pass much 
below the level of this rock without encountering it. On the small 
map, figure 4, the top surface of the rock is indicated at a number 
of localities, the elevations having been determined by lines of levels 
from known bases. While the top surface of the limestone is ex¬ 
tremely irregular, owing to disintegration, there is evidence of a 
slow dip to the south. The greatest elevation above sea observed 
for this rock is 138 feet in the well north of Lake Iamonia, and at 
this place is about 40 miles north of the Gulf, where the rock lies as 
sea level, there is indicated an average dip to the south of about 
three and one-half feet per mile. In the Aldrich well near Talla¬ 
hassee the rock lies as high at least as 89 feet above sea, and possibly 
somewhat higher. On the Ocklocknee River, due west, the rock 
lies at about 66 feet above sea, while to the east at Lloyds, as already 
noted, it lies at about 57 feet above sea. These elevations must be 
used with care, although the exposure on the Ocklocknee River 
apparently is near the top surface of the formation, since the rock 
disappears below water level a few miles farther down stream, and 
is succeeded by the Alum Bluff formation. These records , may 
indicate a slight dip to the southwest, as well as a general dip to the 
south. 
