A PRELIMINARY report on clays oe elorida 
115 
ton and Walton counties. It consists of a marl member which is over- 
lain by a grayish clay. The clay ranges in thickness from about ten to 
approximately thirty feet. This clay is the southeastward extension of 
the Pascagoula clay which is exposed through portions of the Gulf 
states to Eastern Texas. 
The Charlton formation is a marine Pliocene marl extending along 
the northwest side of Nassau County next to the St. Marys River. It 
is not known to be associated with clays. 
The Nashua formation, also Pliocene, consists of interbedded marls 
and clays and occupies a small area in Volusia, Flagler and Putnam 
counties. The clays are usually of limited extent and frequently thin 
Some of these are calcareous and all are to some extent sandy. Many, 
however, may be used for structural materials. Several of these clays 
have formerly been used in the manufacture of common brick. 
The Caloosahatehee formation, likewise a marine Pliocene marl, 
underlies a small area on the Pinellas peninsula on the west side of 
Tampa Bay, and a much larger area in the region of the Caloosahatehee 
River. A few calcareous clays accompany the marl. 
The Bone Valley formation, Pliocene, occupies a limited area east 
of Tampa in Polk, Hillsborough, Manatee and Hardee counties. It is a 
fluviatile deposit chiefly noted for its pebble phosphate content and is 
extensively worked for phosphate in this region. It also contains a sandy 
clay known throughout this region as the Bartow clay. This term was 
formerly applied to the matrix carrying the pebble phosphate, but now 
the application of the term is limited to the sandy clay overlying the phos¬ 
phate horizon. The Bartow clay is widely distributed in this region and 
is used to some extent as a road-surfacing metal. Its high sand content 
greatly reduces its plasticity, making molding and handling difficult. 
When burned, however, it is suitable for common brick. 
The Alachua clay is a terrestrial Pliocene formation composing 
small disconnected areas in central Florida. This term was formerly 
used to designate deposits of a blue to gray sandy clay which had ac¬ 
cumulated in sinks and ponds during Pliocene times and encased numer¬ 
ous vertebrate remains. It is now understood to include also the hard 
rock phosphates formerly known as Ihe Dunnellon formation. The 
Alachua clay formation contains many local clay deposits in Alachua, 
Levy and Marion counties. 
The Citronelle formation, a Pliocene deposit extending through 
the Gulf states has only a limited extent in Florida. It extends through 
