COMPARISON WITH SIMILAR ORE DEPOSITS ELSEWHERE. 287 



3. The belt of the earth's most active and extensive recent vulcanism. 



4. A belt showing .similar recently erupted lavas. 



5. A belt showing similar lavas erupted during the Tertiary. 



6. A belt of enormous and roughly uniform later Tertiary mineralization, 

 involving great concentration of silver and gold. 



When it is considered that solutions accompanying (and presumably emanating 

 from) Miocene andesites (to a less extent Miocene-Pliocene rhyolites) in this 

 particular restricted zone have produced a very large proportion of the world's 

 available supply of the precious metals, the rare and special nature of the occur- 

 rences which have called these ore deposits into being becomes evident, and it 

 becomes impossible to entertain any explanation based upon processes uniformly 

 distributed throughout the world. 



