24 
FLORIDA GEOLOGICAL SURVEY—THIRD ANNUAL REPORT. 
the phosphate are ordinarily of frequent occurrence both in pits 
and in prospect holes. 
MATERIALS LYING ABOVE THE PHOSPHATE. 
A superficial deposit of pale yellow incoherent sand occurs 
generally throughout the phosphate section. The thickness of 
this sand varies exceedingly. Five to fifteen feet may be given 
as an average as seen in the pits, although a thickness of as much 
as thirty feet has been observed. The character and manner of 
occurrence of these sands leads the writer to the belief that they 
may be residual in origin. 
These incoherent sands rest in some localities upon a red clay¬ 
ey sand stratum known to the miners as “hardpan.” This 
sand stratum contains sufficient clay to give it coherence and 
stands usually as a vertical wall in mining. This stratum is fre¬ 
quently absent, and when present varies greatly in thickness. 
The top surface of this red sand stratum presents irregularities 
which might be taken to mark an unconformity between this for¬ 
mation and the incoherent sands above. Such irregularities as 
occur in the top surface, however, present rounded depressions 
rather than sharp irregularities. Moreover the top surface of 
the red sands frequently conforms to the surface contour. Both 
the superficial sands and the red sands are, as far as the writer 
has observed, non-fossiliferous. 
RELATION OF THE PHOSPHATE-BEARING FORMATION TO THE 
UNDERLYING FORMATIONS. 
The phosphate-bearing formation rests in this section, wher¬ 
ever observed, upon the Vicksburg limestones. In the northern part 
of the section the pits are ordinarily worked out to the limestone, 
affording favorable opportunity for observing the contact. The 
top surface of the limestone is strikingly irregular, the rock pro¬ 
jecting as rounded peaks. The numerous shells and other inver¬ 
tebrate fossils of which the limestone is largely made up are eroded 
off plane with the surface of the limestone. Passing to the south 
the limestone lies as a rule at a greater distance beneath the sur¬ 
face, and frequently is not reached by the ordinary processes of 
mining. It is occasionally reached, however, and wherever seen, 
throughout this entire section the relation between the phosphate 
formation and the limestone is the same, that is. the phosphate¬ 
bearing formation lies upon and fills up irregularities in the top sur¬ 
face of the limestone. (PI. 2, Fig. i and PI. 5) 
