ECONOMICAL CONSIDERATIONS. 369 
will be easily comprehended after a perusal of the facts set forth in the 
preceding pages. 
In the first place, as to the yield of the gravel as worked by the hydraulic 
method. This question presents itself in two aspects: How much gold does 
the gravel contain? And how large a portion of it is obtained by the work- 
ing? or, in other words, how efficacious are the means employed for saving 
the metal? It will not require much consideration to make it apparent that 
no satisfactory answer can be given to these questions; for the amount of 
gold in the gravel cannot be accurately determined by assay or any other 
method.* All that can be positively known is the amount obtained at the 
clean-up: of that which has escaped being caught in the sluices, no account 
can be had. Still some miners have their ideas of the proportion lost, 
although it is not easy to ascertain on what these ideas are based. That 
tail-sluices of great length have been put in below the ordinary ones, where 
the conditions were favorable, and that these have paid a profit on their cost 
-and maintenance, seems to be proof that no inconsiderable portion of the 
gold escapes unless the sluices are very long.t That any other method of 
saving the gold will be invented to take the place of the sluice, and give 
better results, seems in no way probable. It may also be added, as will 
already have been made manifest to the reader, that by no other method 
of attack than the hydraulic could the high gravels of the Sierra be handled 
with profit. 
If, then, the total amount of gold existing in the gravel at any point cannot 
be ascertained, we have to fall back on the quantity actually obtained, with 
special reference to the question how low a grade of material can be handled 
with profit. The total amount produced at any mine is not usually known 
with exactness, either for the whole time during which the workings have 
been carried on, or for any particular part of it for which the number of 
cubic yards washed away can be determined. When the more detailed 
survey of the gravel region was entered on by the writer and his assistants, 
there seemed to be no definite information to be had touching this important 
known with any certainty whatever, different estimates (of those likely to have been best informed) varying by 
numbers as great as 10,000. 
* The miner, by panning a sufficient number of samples, judiciously selected, can form a pretty good idm. 
whether the gravel is likely to pay for working ; but this is not by any means the same as ascertaining the exact 
amount of gold which it contains. 
+ Such tail-sluices are very long, and require but little expenditure, except the first cost of putting in, as they 
are usually cleaned up only after running for several months. 
