26 FLORIDA GEOLOGICAL SURVEY-THIRD ANNUAL REPORT.
This Section differs f rom 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. 10, grades belowv into yellow phosphatic clay. The overburden at this pit is not removed as it is f ound practicable to allow the entire 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 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 or clayey matrix. This matrix fills uip the irregularities in the underlying limestone. In several instances the phosphate matrix was seen to fill tip 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............................ to 15 feet
Phosphate matrix.......... ........................... I to 20 f eet
Limestone top surface exceedingly irregular
The, phosphate producing area of southern Columbia and Snwannee Counties lies adjacent to and in the angle between the Snwannee and Santa Fe Rivers including the low ly ing 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 mmn 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.