ANNUAL REPORT—MINERAL INDUSTRIES. 29 
of the remaining three grades produced, may be inferred 
from the statistics of 1906. Of hard rock there was pro¬ 
duced in Florida in that year 587,598 tons; of land peb- 
bdle phosphate 675,444 tons; of river pebble phosphate 
41,463 tons. 
Location:—The phosphates of Florida lie principally 
in a comparatively narrow curved belt reaching from west 
of the Apalachicola River, southeast and south to the 
Gulf in Manatee and Lee Counties, a distance of 350 
miles.* 
The pebble phosphate occurs in the southern part of 
ihe area. The principal deposits of rock phosphate occur 
in the central part of the area in Columbia, Alachua, Ma¬ 
rion and Citrus Counties. 
Origin and.Occurrence:—The origin and occurrence of 
the Florida phosphates have given rise to extended dis¬ 
cussion, and much additional investigation will be 
required in order to determine doubtful points. First of 
all, it is not to be assumed that all phosphates originate 
in the same way. Moreover, phosphates occur in several 
geological periods and the deposits have been subjected, 
since their formation, to varying conditions. Phosphoric 
acid in solution in the water may replace the carbonate 
of a limestone, forming calcium phosphate. This replace¬ 
ment process is clearly an agent in the formation of rock 
phosphate. Shells are found occasionally in which the 
original calcium carbonate has been changed to phos¬ 
phate, proving the possibility of the formation of the min¬ 
eral in this way. Phosphoric acid in quantities sufficient 
to form large deposits of phosphate may have been sup¬ 
plied from any one of several sources. 
It is well known that phosphatic material in small 
quantities occurs widely scattered through various forma¬ 
tions. As a result of the progressive decay and wearing 
away of the surface rock, phosphatic material is concen¬ 
trated at a lower level, either mechanically, due to the 
*Eldridge, G. H.; A Preliminary Sketch of the Phosphates of 
Florida. Trans. Am. Inst. Min. Eng., Yol XXI, 196-231. 1893. 
