A PRELIMINARY REPORT ON CLAYS OF FLORIDA 135

and makes it worthless for burned products. For its physical properties see Lab. samples Nos. 0-19 and 0-72 under Manatee County, page 184.
 The Bartow clay is exposed in the northern portions of the county. See page 195 for a detailed description of the Bartow clay, Lab. Sam-. ple No. 0-53.
 DIXIE COUNTY
 Dixie County lies in northern Florida and adjoins the Gulf of Mexico. No clays other than very loose sandy ones are known in this County.
 DUVAL COUNTY

 Duval County is situated in the lower St. Johns River valley. Some sandy clays suitable only for sand-clay road material occur in the extreme southwest corner of the county along the Trail Ridge. Floodplain clays are common along the St. Johns River and several of -these have been worked in the past for common brick, while one plant at South Jacksonville is now engaged in the production of structural materials from two beds of these clays.
 Two clays are exposed in the Gamble and Stockton Brick and Tile Company's plant at the end of Hendricks Street in South Jacksonville. A section of the deposit is as follows:

 Sand, loose, brow n ........................................... 2 feet
 Clay, red m ottled ............................................ 8 feet
 Sand, w hite ................................................. 2 feet
 Clay, blue, very plastic ....................................... 10 feet plus


 The exact depth of this lower clay is not known as the workings have not reached the bottom. The loose brown surface sand at the top of the section is removed by a scraper. The white sand is mixed with the red and blue clays to reduce shrinkage and the two clays are used in equal proportions.
 This deposit is now being used for the production of common and face brick, interlocking hollow block tile, and drain tile. The ware is molded in a stiff mud end cut machine and burned at cone 3 in circular down-draft kilns. Seger cones are used to indicate the progress of burning.