[Illustration: FIG. 104.--MINING THE GRAVEL OF AN OLD RIVER-BED]

Not all quartz veins carry gold. There are many in which not a single
speck of the precious metal can be found. Gold usually prefers the
society of quartz to that of other substances, for minerals, like
people, seem to have their likes and dislikes. Along the Mother Lode,
however, gold is sometimes found in little bunches and "stringers"
scattered through slate. In such cases the slate is mined and sent
to the mill.

Some miners devote themselves to pocket mining. They trace the
little seams in the rock, and where two seams cross they sometimes
find what they call a "pocket." This is a mass of nearly pure gold
of irregular shape, varying from a few dollars to thousands of
dollars in value. This kind of mining is very uncertain in its
results, for a man may make hundreds of dollars in one day, and
then not find anything more for months.

The western slope of the Sierra Nevada mountains was once covered
with the camps of thousands of placer miners. Piles of boulders and
gravel are scattered along the creeks where the eager workers took
out millions of dollars' worth of gold-dust and nuggets. Now many of
the streams and gulches are entirely deserted. But in other places,
where the quartz veins outcrop, there are scores of stamp-mills at
work, night and day, pounding out the gold. Some of the mines have
been sunk more than a half mile into the earth, and the gold is
still as abundant as ever.

In some portions of the mountains hydraulic mining is more common
than quartz-mining. Years ago many of the rivers occupied different
channels from their present ones. The gravels of these old channels
in the Sierra Nevada mountains, and in other parts of the West
where gold-bearing veins occur, are rich in gold. In these channels
the gold is so deeply buried that it cannot usually be obtained by
means of pick and shovel. In order that the overlying gravel may
be removed as cheaply as possible, water is supplied by means of
ditches, often many miles long. From some near-by hill the stream
is conducted down to the mine in strong iron pipes. It thus acquires
a great force, and when directed against a gravel bank rapidly
washes it away. Torrents of water bearing boulders, gravel, and
sand, together with the particles of gold, are turned into sluice
boxes lined at the bottom with quick-silver. This metal catches
the gold and forms an amalgam as it does in the quartz-m