30 
FLORIDA STATE) GEOLOGICAL SURVEY. 
removed from the pit. It is also necessary to operate a rock 
crusher in connection with all hard rock phosphate mines to 
reduce the larger pieces of rock to a size suitable for shipping. 
A certain portion of soft phosphate unavoidably lost in mining 
is also present. The relative amount of material that it is neces¬ 
sary to handle to obtain a definite amount of phosphate is always 
variable with each pit and with the different parts of any one pit. 
The workable deposits of phosphate lying within this formation 
occur very irregularly. While at one locality the phosphate may 
lie at the surface, elsewhere it may be so deep as not to be 
economically worked; while a deposit once located may cover 
more or less continuously a tract of land some acres in extent, 
elsewhere a deposit appearing equally promising on the surface, 
may in reality be found to be of very limited extent. As to loca¬ 
tion, depth from surface, extent into the ground, lateral extent, 
quantity and quality, the hard rock phosphate deposits conform 
to no rule. The desired information is to be obtained only by 
extensive and expensive prospecting and sampling. 
The phosphate rock may lie beneath the gray sands, or above 
the gray sands or may be entirely surrounded by them. In some 
instances the phosphate is interbedded with the sands. Such 
interbedding of sand and phosphate was observed by the writer 
in the Central Phosphate Company pit number 25, about three 
miles west of Clark. This phase of the relation of sand and phos¬ 
phate occurs not infrequently and is confined to no particular part 
of the phosphate field. It is frequently stated by the phosphate 
miners that there is a relation between the local clay lenses and 
the occurrence of phosphate. It is evident, however,, that there 
are many exceptions to this general statement. 
THICKNESS. 
The thickness of the phosphate bearing formation is as vari¬ 
able as its other characteristics. It rests upon the Vicksburg 
Limestone, the top surface of which owing to solution by under¬ 
ground water, has become extremely irregular. The limestone 
projects as peaks into the phosphate formation. In Citrus County 
the phosphate bearing formation is known to reach a thickness of 
