112 FLORIDA GEOLOGICAL SURVEY—I5TH ANNUAL REPORT 
Aucilla in Jefferson County and at River Junction in Gadsden County. 
Some of the Chattahoochee residual clays may be looked on with favor 
for the manufacture of common brick. 
The Tampa formation is likewise of Oligocene age and is consid¬ 
ered. to be contemperaneous with the Chattahoochee formation. It con¬ 
sists of a hard silicious limestone exposed at the head of Tampa Bay, 
westward to the Gulf, and northeastward through Pinellas, Hills¬ 
borough, Pasco and Hernando counties, with some outliers extending 
farther northward. The limestone is locally weathered to residual clay. 
Sedimentary clay is also widely distributed in this formation. Some of 
these clays, both sedimentary and residual, are suitable for common 
brick. 
A brick plant now being operated at Brooksville is using a residual 
Tampa formation clay. The upper two feet of the deposit is dark brown 
and somewhat sandy. The lower member averages about eight feet in 
thickness and is of a very light color. The clay grades into a limestone at 
the bottom of the workings and contains numerous flint concretions and 
fragments in the lower portion. The contact between the upper dark 
clay and the lower white clay is well defined and probably represents a 
former water table. 
Several abandoned brick plants have in the past used the Tampa 
clay. One of these, the Old Tampa Brick Co., worked an exposure on the 
Hillsborough River about five miles northeast of Tampa. This deposit 
had the following section : 
White sand and soil (Pleistocene) . 2 feet 
Unconformity . 
Light green plastic clay (Tampa). 10 feet 
The clay contained numerous cherty concretions. This same clay 
is exposed in several places along the Hillsborough River, near Oldsmar 
on Tampa Bay, and at several points on the Gulf coast in the vicinity 
of Tarpon Springs. 
The Tampa formation has a sedimentary light green plastic clav 
above the chief limestone horizon and another clay strata of similar char¬ 
acter below the limestone. This lower clay was found to range from 
forty-one to sixty-four feet in thickness in wells drilled at the Tampa 
Water Works. The upper clay horizon is the one most frequently ex¬ 
posed and is the one formerly used in the manufacture of brick. 
