38 MINERAL RESOURCES OP ALABAMA. 



Pottery or Stoneware Clays. Stoneware clays are interme- 

 diate in their nature between fire clays and pipe clays, that is 

 too impure for the one purpose and too good for the other. In 

 the manufacture of stone ware it is essential that the clay should 

 burn to a dense impervious body at not too high a temperature, 

 and the color after burning should be uniform and good, if the 

 ware is to be unglazed or is to be coated with a transparent 

 glaze. Clays suitable for stone ware occur in the older forma- 

 tions, Cambrian, Silurian, Lower Carboniferous, and in the 

 Lower Cretaceous or Tuscaloosa. This remark applies rather 

 to the clays which have been investigated by the Geological 

 Survey, and it should be understood that stoneware clays occur 

 in other formations and in other parts of the state than those 

 from which the subjoined examples have been taken. 



In the table showing the composition we have given such 

 notes as to color and character assumed in the burning, as will 

 assist one in arriving at a correct estimate of the properties of 

 the clays. 



