118 DETAILED REPORT ON ALABAMA CLAYS. 



Ball clays are used to mix with kaolin in the manu- 

 facture of porcelain and white- ware in order, to give plas- 

 ticity to the mass. They should be as free from fluxing 

 impurities and mineral fragments as possible, and some- 

 times have to be washed. They generally burn nearly as 

 white as kaolin. Ball clays should have a good tensile 

 strength, not less than 60 lbs. to the square inch. They 

 are often dark brown or even black from the. presence of 

 abundant organic matter, but this color disappears on 

 heating. This organic matter exerts no other effect on 

 the clay than to increase the plasticity and air-shrinkage. 



The Alabama clays included under this heading are 

 those which burn white or very nearly so at a moderate- 

 ly high temperature. Many of the specimens examined 

 are quite siliceous, and consequently exhibit a low 

 shrinkage in burning, while nearly all of them are of 

 sedimentary origin, a few, such as those associated with 

 the bauxite deposits, having an origin in common with 

 them. 



In respect to their geological relations the china clays 

 here reported on come from three horizons, (1) the Cam- 

 brian and Silurian limestone, e. g. No. A. S. from Rock 

 Run; No. 190 from near Gadsden; and No. 205 from 

 near Kymulga, in Talladega Co. (2) the lower Sub-car- 

 boniferous cherty limestone; e. g. Nos. B. S; 128, and 214, 

 from Willis' Valley, between Fort Payne and the Georgia 

 state line. (3) the lower Cretaceous or Tuscaloosa forma- 

 tion, e. g. No. 38. S; No. 85; No. 37. S from Chalk Bluff 

 and vicinity, Marion county: No. 37. S from Pearce's 

 Mill, Marion county, and No. 56. S from Pegram in Col- 

 bert county. 



Of the above, only the clays from Will's Valley have 

 been regularly mined. 



