THE FLORIDA PHOSPHATE DEPOSITS. 
23 
worn, dark colored flint pebbles. This phase of the formation 
may be seen through a distance of ten or fifteen feet along the 
side of the pit. Water worn pebbles weighing one or more pounds 
occur occasionally in the northern part of the field. 
The invertebrate fossils found are mostly contained in the lime¬ 
stone inclusions which come largely from the underlying Vicks¬ 
burg limestones. The vertebrate remains occurring in the phos¬ 
phate include among others, shark teeth, manatee, turtle and mas¬ 
todon remains. 
Phosphate rock, although the constituent of special economic 
interest, nevertheless makes up a relatively small part of the forma¬ 
tion. The phosphate in this section occurs as fragmentary rock, 
boulder rock, plate rock or pebble. A certain portion of soft phos¬ 
phate, unavoidably lost in mining, is also present. The relative 
amount of material that it is necessary to handle to obtain a definite 
amount of phosphate is always variable with each pit and with the 
different parts of any one pit. In general the phosphate rock ob¬ 
tained from the matrix of the grade demanded by the market will 
not exceed ten to twenty percent of the whole. The workable 
deposits of phosphate lying within this formation or representing 
locally a phase of 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 
of some acres in extent, elsewhere a deposit appearing equally prom¬ 
ising on the surface, may be found to be in reality of very limit¬ 
ed extent. As to location, depth from the surface, extent into 
the ground, lateral extent, quantity and quality, the hard rock 
phosphate deposits conform to no rule. The desired information 
regarding location, character and extent of deposits is to be obtain¬ 
ed only by extensive 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 in¬ 
stances the phosphate is interbedded with the sands. Such inter¬ 
bedding of sand and phosphate was observed by the writer in the 
Central Phosphate Company pit No. 25 about three miles west 
of Clark. This phase of the relation of sand and phosphate occurs 
not infrequently and is confined to no particular part of the phos¬ 
phate field. Gray sands surrounding the phosphate rock may be 
observed as previously stated in practically every pit throughout 
the phosphate section.' As a rule the phosphate rock extends to 
and rests upon the underlying limestone. This relation, how¬ 
ever, is by no means invariable as gray sands were observed under¬ 
lying the phosphate rock at several localities. Gray sands above 
