112 FLORIDA GEOLOGICAL SURVEY-15TH 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 considered to be contemperaneous with the Chattahoochee formation. It consists of a hard silicious limestone'exposed at the head of Tampa Bay, westward to the Gulf, and northeastward through Pinellas, Hillsborough, 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 colot. 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:
 W hite sand and soil (Pleistocene) ............................. 2 feet
 U nconform ity ................................................
 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 clay above the chief limestone horizon and another clay strata of similar character 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 exposed and is the one formerly used in the manufacture of brick.