rce was
played upon the banks of gravel. The banks crumbled, the gravel was
washed into a string of sluices, or long boxes with riffles to catch
the gold. Soon the miners found that if quicksilver was put into these
sluices, it would unite with the gold and make a sort of paste called
"amalgam." Then if this amalgam was heated, the quicksilver would be
driven off in the form of gas, and the gold would remain in a
beautiful yellow mass.

[Illustration: HYDRAULIC GOLD MINING

A placer mine at Gold Point, California, where tremendous streams of
water under high pressure are busy washing away the side of a
gold-bearing hill.]

The ancient rivers had also carried gold to the valleys, and to
collect this a dredge, which the miners called a "gold ship," came
into use. The "ship" part of this machine is an immense flat scow.
Stretching out from one end is something which looks like a moving
ladder. This is the support of an endless chain of buckets, each of
which can bite into the gravel and take a mouthful of five or six
hundred pounds. They drop this gravel into a big drum which is
continually revolving. Water flows through the drum, and washes out
the sand and bits of gold over large tables, where by means of riffles
and quicksilver the gold is captured. This scow was usually on dry
land at first; but its digging soon made a lake, and then it floated.
It must be more fascinating to hold a pan in your own hands and pick
out little grains of gold or perhaps even a big piece of it with your
own fingers, but if the gravel is good the dredge makes more money.

In Alaska the great difficulty in mining is that, except at the
surface, the ground is frozen all the year round. At first, the miners
used to thaw the place where they wished to dig by building wood
fires; but this was a slow method, and now the thawing is done by
steam. They carry the steam in a pipe to the place where the digging
is to be done, and send it through a hose. At the end of the hose is a
pointed steel tube. They hammer this tube into the ground and let some
steam pass through the nozzle. This softens the ground so that picks
and shovels may be used. There is generally cold enough in Alaska, but
once at least the miners had to manufacture it. The gold-bearing
gravel was deep, the ground was flat, and it was often overflowed.
They set up a freezing plant, and shut in their land with a bulkhead
of ice several feet thick. Then they pumped out what water was