THE FLORIDA PHOSPHATE DEPOSITS.

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 limestone inclusions which come largely from the underlying Vicksburg limestones. The vertebrate remains occurring in the phosphate include among others, shark teeth, manatee, turtle and mastodon remains.
Phosphate rock, although the constituent of special economic interest, nevertheless makes up a relatively small part of the formation. The phosphate in this section occurs as fragmentary rock, boulder rock, plate rock or pebble. A certain portion of soft phosphate, 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 obtained 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 promising on the surface, may be found to be in reality of very limited extent. As to location, depth from the surface, extent into the ground, lateral extent, quantity and quality, the hard rock 1-hosphate deposits conform to no rule. The desired information regarding location, character and extent of deposits is to be obtaincd 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 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 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 phosphate 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, however, is by no means invariable as gray sands were observed underlying the phosphate rock at several localities. Gray sands above.

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