MHE FLORIDA PHOSPHATE DEPOSITS.

RELATION TO THE UNDERLYING FORMATION ARCADIA MARL?
The land pebble formation rests upon a pale yellow phosphatic marl, referred to by the miners as "bed rock". The relation is apparently as stated by Matson, that of unconformity. This is observed in the pit of the Pierce Phosphate Company, six miles south of Mulberry. The marl as exposed in this pit has a very roughly eroded surface. (P1. 4, Fig. I.) The phosphate
matrix fills these irregularities. The "bed rock" although varying in character is found to underlie the phosphate wherever observed in Hillsboro, Polk and DeSoto Counties. The marl beneath ihe phosphate is probably of Pliocene age.
In 1892 Dall applied the term Arcadia marl to a marl exposed on Mares Creek, six miles above Arcadia.* This marl Dall regarded as slightly older than the Caloosahatchee marl. Matson is of the opinion that the Arcadia marl may be only a phase of the Caloosahatchee marl. The exposure on Mares Creek examined by the writer occurs at and near the mouth of the creek. The marl as seen here has in lithologic character no very striking resemblance to the Caloosahatchee marl but is lithologically very similar to the marls seen at numerous places elsewhere on Peace Creek and underlying the Bone Valley formation. From the continuity of
exposures and similarity in character it seems probable that the "bed rock" of the land pebble phosphate is the Arcadia marl.
LOCAL DETAILS.
HILLSBORO COUNTY.
The northernmost plant in the land pebble section is that of the Coronet Phosphate Company located in Hillsboro County three miles southeast of Plant City. The following sections were observed in pits Nos. I and 2 of this plant.
SECTION IN PIT NO. I, CORONET PHOSPHATE COMPANY.
Pale yellow incoherent sand ............................... 4 feet
Gray indurated sand .................................... 4 feet
Conglomerate of phosphate pebble, bone fragments, water
worn flints and pebbles ............................... I to I2 feet
Buff yellow and olive green clay .......................... 2 to 5 feet
Yellow clay and marl, "bed rock" at bottom of pit.
SECTION IN PIT NO. 2, CORONET PHOSPHATE COMPANY.
Incoherent sand .......................................6 feet
Indurated sands grading at base into a conglomerate of phos*DaIl, Win. H., U. S. Geol. Survey. Bull. No, S4, 1892, pp. 131-132..

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