26 
FLORIDA GEOLOGICAL SURVEY—THIRD ANNUAL REPORT. 
This section differs from the preceding chiefly in the presence 
of the red clayey sands which are sufficiently coherent to form a 
vertical wall in the pit. This clayey sand stratum when present 
is referred to by the miners as “hardpan.” , 
The phosphate matrix in this exposure as in Dutton No. io, 
grades below into yellow phosphatic clay. The overburden at 
this pit is not removed as it is found practicable to allow the en¬ 
tire overburden to be taken up with the phosphate and to pass 
through the washer. 
In the pit of the Fort White Hard Rock Company one-half 
mile southeast of Ft. White, the foundation rock, as is usual in 
this section, is the Ocala Limestone. The top of this limestone 
is exceedingly irregular, projecting as rounded peaks. Shells, sea ur¬ 
chins, and other fossils are partly eroded away, the limestone 
having a comparatively smooth surface. The phosphate rock 
consists chiefly^ of angular fragmental pieces, plates, pebbles and 
boulders imbedded in a sandy or clayey matrix. This matrix 
fills up the irregularities in the underlying limestone. In sev¬ 
eral instances the phosphate matrix was seen to fill up cavities and 
solution channels in the limestone. Slickensides occur due to the 
settling of the phosphate matrix as the underlying limestone dis¬ 
solved away. Limestone inclusions and siliceous boulders occur 
in the phosphate stratum. The following section is seen in an 
abandoned'pit of this plant. 
Pale yellow incoherent sand.i to 15 feet 
Phosphate matrix... ....... 1 to 20 feet 
Limestone top surface exceedingly irregular 
The phosphate producing area of southern Columbia and Su¬ 
wannee Counties lies adjacent to and in the angle between the Su¬ 
wannee and Santa Fe Rivers including the low lying and intensively 
eroded parts of each County. The limestone lies near the surface 
in this section and as. a rule the phosphate is mined out by dry min¬ 
ing, the limestone being exposed in the abandoned pits. Dredging 
which is applicable in the southern part of the phosphate area is 
not used in this section. 
ALACHUA COUNTY. 
The west central part of Alachua County is actively produc¬ 
ing phosphate, twenty-two plants having operated in this county 
during 1909. 
Pit No. 25 of the Central Phosphate Company west of 
Clark, gave the following section: 
