54 



ECONOMIC GEOLOGY 



and their metamorphic derivatives proves that gold is more likely 

 to be found in the acidic than in the basic rocks. It has, however, 

 been found in basic rocks, and this occurrence is not rare. 



o s 

 o;^ 



11 



' 



u 



02 G 



" 



w 



2 -a 



The auriferous quartz veins are doubtless free from silver in 

 most cases. In some cases, it has been suggested by J. E. Spurr 

 of the United States Geological Survey, that they represent 



