34 FLORIDA GEOLOGICAL SURVEY—THIRD ANNUAL REPORT.. 
absent, the phosphate lying at the surface. Usually the sand con¬ 
tains sufficient admixture of clay to give it coherence. Under 
these conditions it oxidizes red near the surface. While this is 
the .prevailing phase of the sand it is nevertheless subject to con¬ 
siderable variation from place to place. Not infrequently the sand 
is firmly cemented forming the so called “hardpan” which gives 
much trouble in prospecting and frequently necessitates blasting 
in mining. (Plate 3, Fig. 2.) In places the sand has a calca¬ 
reous or phosphatic cement. Locally it varies also to an indurated 
rock with innumerable small cavities which gives a vesicular ap¬ 
pearance to the mass. A sample of this rock was found to contain 
I 5 - 5 ( 5 % phosphoric acid (equivalent to 33.97% tri-calcium phos¬ 
phate). 
The phosphate bearing member contains vertebrate remains 
including both marine and land animals. Most of the bones are 
more or less rolled and water worn although occasional whole 
skeletons are found. In the sands above the phosphate, fossils are 
rare. The writer has obtained, however, through the kindness 
of Mr. M. A. Waldo, Manager of the Dominion Phosphate Com- ($ 
pany a single tooth of the mastodon preserved as a cast in the 
phosphatic sands of the overburden. Aside from a few casts 
near the bottom of the phosphate bed invertebrates have not been 
found in this formation. 
MATERIALS LYING ABOVE THE PHOSPHATE FORMATION. 
As in the case of the hard rock section the surface material con¬ 
sists of incoherent pale yellow sand. The depth of this sand is vari¬ 
able, ranging from four to ten or more feet. A very definite and 
often irregular line separates these loose sands from the formation 
beneath. (PI. 3, Figs. 1 and 2, and PI. 4, Fig. 3.) This line Matson 
interprets as an evident unconformity.* This may be true al¬ 
though the fact must not be overlooked that seeming unconfor¬ 
mities in materials lying near the surface may in reality repre¬ 
sent only lines of decay. The writer is inclined to regard the 
loose surface sands in this section as residual, the irregular 
line representing the line' of complete disintegration of the 
original sandy formation. A similar explanation has been 
offered previously by the writer for the surface sands of Gadsden 
Countyt as well as for the sands overlying the hard rock phos¬ 
phate formation, (ante P. 24.) 
^Florida Geol. Survey. Second Annual Report, p. 139, 1909. 
fFlorida Geol. Survey. Second Annual Report, p. 263, 1909. 
