366 CLAYS AND CLAY INDUSTRY. 



weathered. There is an inexhaustible quantity of the material, 

 but the great objection to it is its lack of plasticity, for the 

 shale is very lean. Weathering improves it, and as much of the 

 weathered material as can be obtained is mixed with the less 

 weathered portion. It burns to< a good red color and becomes 

 steel-hard at a moderately low temperature, but is not at all re- 

 fractory. 



The shale is used for making nreproofing, and its physical 

 characters are given under Warren county. 



