260 THE AURIFEROUS GRAVELS OF THE SIERRA NEVADA. 
years. The hydraulic method of attacking the gravel deposits has become 
more and more universal of late years, and is now almost the only one em- 
ployed, ordinary placer mining with portable implements for washing having 
been almost exclusively relegated to the Chinese, while tunnel mining is also 
practised on a much less extensive scale than formerly. But in hydraulic 
mining, with sluices many hundred feet in length, nothing can be seen of 
what the gravel may contain of human or other remains, unless under very 
exceptional circumstances. The coarser, larger implements, if sufficiently 
strong to endure the wear and tear of the sluice, would be carried down and 
deposited far away in the tailings and then speedily covered by other ma- 
terials. The finer and more delicate portions, such as bones, are ground to 
powder between the cobble-stones and are lost forever. By the tunnel 
method some portion of the material excavated stands a chance of being 
examined ; or, at least, of being for a while in such a position that it could 
be inspected if there were any one present who had the curiosity to do it. 
Hence most of our evidence of the former existence of man during the 
gravel period comes from a region of former tunnel mining on a large scale, 
and is, much of it, of ancient date, because this region is pretty nearly 
worked out and abandoned. That evidence greatly exceeding in fulness 
and value any that has heretofore been obtained may yet be secured is 
certainly possible, if not probable. It is not necessary, however, to specu- 
late on what may happen in the future, but rather to set forth what is 
already known. 
It will be observed by the reader of the following pages that the bulk of 
the evidence presented is that furnished by the miners themselves, some- 
times supported by the actual presence of the objects found, at other times 
without such support, there being only the bare statement of a former find. 
That the miners themselves should be, in most cases, the persons furnishing 
the evidence is too natural a circumstance to need comment. ‘Their state- 
ments have to be taken —as already suggested when speaking of the occur- 
rence of animal remains in the gravel—for what they are worth, balanced 
against each other, and the most probable result accepted. A long chain of 
circumstantial evidence is frequently more convincing than a single state- 
ment of an eye-witness. It might be asked, Why should not the writer, or 
one of his assistants, have been on the spot when some of these discoveries 
were made, or have taken with his own hands some one of the objects men- 
tioned from its original resting-place? The answer to this is, that such finds 
