

298 



RESUME AND THEORETICAL DISCUSSION. 







it will not be desirable to take the space which would be necessary for stat- 

 ing them, in advance of their presentation in the proper order as developed 

 in the ensuing pages. 



Section III. 







— The General Distribution of the Detriial and Volcanic Materials 



on the West Slope of the Sierra Nevada. 



In proceeding to a general discussion of the phenomena of the gravel 

 deposits, it will be desirable, in the first place, to give an account of their 

 geographical distribution, and of the various materials of which they are 



made 



up 



In considering the position of the hydraulic mines of California, one could 

 hardly foil to be struck at once with the fact that they are concentrated 

 within quite a limited space as compared with the whole area of the State. 

 It will also be apparent that gravels which are auriferous in character occur 

 where no hydraulic mining has been attempted ; and, furthermore, that large 

 deposits of superficial detritus exist where no mining at all is carried on. 

 Each of these conditions has its special and rather complicated set of causes, 

 the nature of which has already been explained, to some extent, in the pre- 

 ceding pages,* but in regard to which a few words must be added in the 

 present connection. 



Supposing that gravel existed in large quantities in any region, the first 

 question in regard to working it would be, Is it auriferous ? If this were 

 found to be the case, the next point would be, the quantity of water which 

 could be obtained and the cost of the same. The existence of hydraulic 

 mines in any region implies the presence of large bodies of auriferous gravel, 

 and also of facilities for obtaining large quantities of water at a cost not too 

 high in proportion to the yield of the gravel. There may bo so much gold 

 present that a high price can be paid for water, or a heavy expenditure in- 

 curred in bringing it to the spot; or, on the other hand, there may be so 

 little gold in the gravel as to make the obtaining of it a remunerative enter- 

 prise only when water is abundant and cheap. Again, the deposits of detrital 

 material may be fairly rich, or even very rich, and yet too thin to make it 

 worth while to establish the necessary plant for hydraulic mining, which 

 necessarily presupposes the occurrence of the material on a large; scale. 

 Another set of conditions connect themselves with the nature of the operations 

 by which the gold-bearing detritus is handled and with the profit resulting 



* See ante, pp. 74 - 78. 







I 



