370 RESUME AND THEORETICAL DISCUSSION. 
point. During that Survey, great efforts were made to obtain the necessary 
information, and since that time, at a considerable number of points, more or 
less systematic accounts have been kept, the chief results of which, so far as 
the same have been accessible, are laid before the reader in the present 
volume. From these data certain conclusions of value can be drawn; while 
in regard to other important points, we are left quite in the dark. 
It will be evident to all that there is little account to be made of any state- 
ment of average value for the whole body of the high gravels. Neither is 
the highest value an element of much importance: it may be taken for 
granted that there are places, usually on or near the bed-rock surface, where 
the gravel is immensely rich.* Tunnel claims of course give higher results 
than the hydraulic mines do, because the former cannot be profitably worked, 
except when the ground is rich. It is not at all uncommon for the bed-rock 
surface to have been worked over by drifting, and the overlying gravel after- 
wards washed off by the hydraulic process.t 
The most desirable practical result to be obtained in regard to the hy- 
draulic mining operations is an answer to the question, How low a tenor of 
gravel can be profitably handled by this process? Here a difficulty arises, for 
the fact that a large amount of gravel has been worked, the average yield 
of which has been low, is not a proof that the operation has been conducted 
with profit or even without loss.t 
The following instances, however, of low rates of yield may be cited. At 
Blue Tent, where the Company owns its own ditch, and consequently gets 
its water at the lowest possible cost, a large quantity of top gravel was 
hydraulicked, yielding 2.6 cents per cubic yard. The gravel was loose and 
sandy, and easily moved. In this case the receipts “ were barely sufficient 
to cover expenses.” This, perhaps, may be set down as being the poorest 
* The writer has seen $36 worth of gold panned out from as much dirt as could be conveniently carried away 
in a lady’s handkerchief ; the auriferous material was scraped from the bed-rock surface under a heavy deposit of 
gravel. But Mr. Goodyear speaks of $1,100 in value having been obtained from a single pan of dirt. (See ante, 
ps Lidia) 
+ While the gold, for reasons already given, is usually most concentrated on and near the surface of the bed- 
rock, there are some exceptions to this rule ; and there are also occasionally very curious irregularities in the dis- 
tribution of the precious metal: sometimes it is all in the upper layers of the gravel ; sometimes concentrated in 
one or two pay-streaks, which may be very thin, while the intervening strata are entirely barren. But such 
exceptional cases are, on the whole, quite rare. 
~ Mining operations have been prosecuted, in repeated instances, for many years in succession, and on the 
largest scale, involving an expenditure of millions, without any return whatever having been received. This state- 
ment refers particularly to some of the mines on the Comstock Lode ; but what has been done there on a grand 
scale may easily have been repeated elsewhere, although perhaps on a considerably smaller one. 
