ORIGIN OR THR HARD ROCK PHOSPHATE'S. 
33 
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.” 
In the pit of the Fort White Hard Rock Company, one-mile south¬ 
east of Ft. White, the foundation rock, as is usual in this section, is the 
Vicksburg Limestone. The top of this limestone is exceedingly irregular, 
projecting as rounded peaks. Shells, sea urchins, 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 clayey matrix. This matrix 
fills up the irregularities in the underlying limestone. In several 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 dissolved 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. 1 to 15 feet 
Phosphate matrix . 1 to 20 feet 
Limestone top surface exceedingly irregular. 
The phosphate producing area of southern Columbia and Suwannee 
Counties lies adjacent to and in the angle between the Suwannee 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 mining, 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 producing phos¬ 
phate; fourteen plants were operated in this county at the close of 1912. 
Pit No. 25 of the Central Phosphate Company, west of Clark, gave 
the following section: 
Pale yellow incoherent sands. 5 to 10 feet 
Red clayey sands. 5* to 10 feet 
Phosphate-bearing formation . 10 to 25 feet 
Limestone at bottom of pit. 
The phosphate matrix consists of gray sands, yellow, buff and blue 
clays, and phosphate rock. At one place in this pit a stratum of gray 
sand Id to 2 feet thick is seen interbedded with the phosphate reck. 
