Beringer, J. J. <br/><br/>
Bulletin of the Institution of Mining and Metallurgy,  ;   No. 134 

 - Londres-XXK :   The Institution of Mining and Metallurgy,   1915. 
 - p. 13-19 :   maps. 
 - Mensual 
 - No. 134(Nov.1915) 
 - Bulletin of the Institution of Mining and Metallurgy,  ;   No. 134 .