276 
FLORIDA STATE GEOLOGICAL SUEVEY. 
Rock Bluff (No. 4 of the section). No. 2 is from Alum Bluff (No. 2 
of the section). No. 3 from an exposure on a tributary to Sweet Water 
Creek Sec. 5, T. 1 N., R. 7 W. All samples were collected by the 
writers. . 
Analyses made for the State Survey in the office of the State 
Chemist, B. H. Bridges, Analyst. 
No. 1. No. .2. No. 3. 
Silica (Si0 2 ) . 48.44 53.02 34.03 
Calcium carbonate (CaCCh) 1 .. 38.57 38.5.7 35.35 
Magnesium carbonate (MgCCh) 1 . 1.68 1.84 26.00 
Iron and Alumina (Fe 2 0 3 and A1 2 0 3 ). ........ 2.88 3.96 3.20 
Phosphoric acid (P 2 0 5 ) . Trace 0.22 Trace 
Sulphate (SO.) . Trace Trace Trace 
Moisture (100 degrees F.) .. 1.37 1.60 1.32 
Above this stratum at Rock Bluff is found gray and- blue sands 
leading up to the workable fullers earth stratum. At Alum Bluff the 
fullers earth fails to appear, and the top surface of the calcareous sand 
stratum is irregular as if by erosion. In some parts of the bluff fossilif- 
erous Miocene marl rests directly upon these sands. Usually, how¬ 
ever, the calcareous sands are separated from the Mioceng by laminat¬ 
ed or cross bedded sands and clays often carrying vegetable remains. 
At Rock Bluff the calcareous sands have a total thickness of 30 feet. 
At Alum Bluff, owing to the irregular top surface, the thickness is 
variable. At one point near the middle of the bluff this stratum is 
lacking although elsewhere it has a thickness of 9 to 16 feet. 
The cross bedded sands and laminated sands and clays lying above 
the calcareous sands are extremely variable in thickness, being not 
infrequently absent. They seem in fact merely to occupy irregularities 
in the top surface of the calcareous sands. An exposure about 300 feet 
from the north end of the bluff gives the following section: 
Covered to the top of the hill. 
Dark colored alum tasting clays . 10 feet. 
Fossiliferous Miocene marl ... 10 fefct. 
Unconformity. 
Laminated clays and sands with plant remains, and blue sands. 7 feet. 
Irregularity or unconformity. 
Calcareous sands . 13 feet.. 
Sloping from the water’s edge.. .... 15 feet. 
A small stream enters just below this section. At this point is seen 
sands with buff colored clay partings, and plant remains, grading at 
1 Calculated from the oxides. No. 1, Calcium oxide, 21.60; magnesium oxide, 
0.80. No. 2, Calcium oxide, 21.60; magnesium oxide, 0.88. No. 3, Calcium 
oxide, 19.80; magnesium oxide, 12.39. 
