CHAPTER I. 



ORE DEPOSITS. 



The preceding chapters have been devoted almost exclusively to the 

 consideration of the geological structure of the district. This subject has 

 been treated at considerable length, not only because it presents many facts 

 which seemed of sufficient interest to geologists in general to justify such 

 treatment, but also because a thorough knowledge of the geological struct- 

 ure of a region is an essential and indispensable basis for the study of its 

 ore deposits ; a fact which is too often lost sight of by those practically 

 engaged in mining. For a time the miner may develop his mine success- 

 fully by simply following the ore lead, guided by the empirical rules which 

 experience has taught him, and without regard to the geological phenomena 

 presented by the country rocks, their structural conditions, or the probable 

 origin and manner of formation of the deposits ; but the time is sure to 

 come when without this knowledge he will be liable to make mistakes 

 which may cost him more than he has gained by all his previous labors. 



Before proceeding to a detailed description of the various ore deposits 

 of the region studied in the course of this investigation, it may aid the 

 reader to have a brief resume of their principal characteristics and a con- 

 cise statement of the conclusions which have been arrived at with regard 

 to their origin and manner of formation. 



CLASSIFICATION. 



To a scientific description of natural objects the most valuable aid 

 is a rational and universally accepted system of classification. The first 

 obstacle one encounters in attempting the description of ore deposits is 



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