THE FLORIDA PHOSPHATE DEPOSITS, 
35 
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. (PI. 4, Fig. 1.) 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 Ibe 
phosphate is probably of Pliocene age. 
In 1892 Dali applied the term Arcadia marl to a marl exposed 
on Mares Creek, six miles above Arcadia.* This marl Dali re¬ 
garded 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 un¬ 
derlying 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 ob¬ 
served in pits Nos. 1 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.......1 to iy 2 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- 
*Dall, Wm. H-, U. S. Geol. Survey, Bull. No. 84, 1892, pp. 131-132. 
