METHODS OF WORKING CLAY DEPOSITS. 31 



1. In the case of high-grade clays. 



2. Where there is much overburden as compared with the 

 thickness of the clay deposit. 



Tunnel 



z — ■ :__ Fire clay 



■Sun J 



Fig. 22. 



Underground method of working a deposit by a tunnel into the hillside. 



Fig. 23. 



Mining clay by a shaft and tunnels. 



3. There should, if possible, be a solid dense layer overlying 

 the clay stratum, otherwise the expense of timbering for support- 



