igo THE POPULAR SCIENCE MONTHLY 



other conditions are constantly enabling the gold miner to treat ores of 

 lower and lower grade. Ores that were once considered of too low grade 

 to be of value are now treated at a large profit, and many a mine aban- 

 doned years ago as worked ont has been reopened and has become very 

 profitable; while the old waste dumps have been sorted over for ore 

 that was thrown away as worthless in the early days. 



In placer mining the same progress has taken place. The early 

 work by hand with pans and cradles was replaced by sluices, then these 

 by hydraulic machinery and sluices, while later the system of dredging 

 the gravel was introduced. Each method marked a step in the eco- 

 nomical evolution of gravel mining, and to-day in many parts of the 

 west gravels are being worked which have already been handled several 

 times over by older methods. 



An important amount of gold comes as a by-product from the treat- 

 ment of copper and lead ores, and to some extent zinc, iron and other 

 ores, and as the amount of base metals mined is constantly increasing, 

 the gold from this source will also probably increase. 



When w6 consider the probability of new gold discoveries in the 

 United States, the longer life of known mines under improved con- 

 ditions, the increased production as a by-product from the base metals, 

 the future of gold in the United States seems bright. For a long time 

 to come the present production of approximately $100,000,000 yearly 

 should easily be maintained and there is a strong probability that it 

 may in time be greatly exceeded. 



