already
in and did their work with no more trouble.

When gold began to grow less in the California gravel, the miners
looked for it in the rocks on the mountain-side. The placer miners
laughed at them and called their shafts "coyote holes"; but in time
the placers failed, while nearly all of our gold to-day comes from
veins of white quartz in the rocks. A vein of gold is the most
capricious thing in the world. It may be so tiny that it can hardly be
seen, then widen and grow rich in gold, then suddenly come to an end.
This is why a new mine is so uncertain an enterprise. The gold may
hold out and bring fortunes to the investors, or it may fail, and then
all they will have to show for their money is the memory that they
put it into a hole in the ground. The managers of a few of the
well-established mines, however, have explored so far as to make sure
that there is gold enough for many years of digging.

The mining engineer must be a very wide-awake man. It is not enough
for him simply to remember what was taught him in the schools of
mining; he must be bright enough to invent new ways of meeting
difficulties. No two mines are alike, and he must be ready for all
sorts of emergencies. A gold mine now consists of a shaft or pit dug
several hundred feet down into the rock, with levels or galleries
running off from it and with big openings like rooms made where the
rock was dug out. The roofs of the rooms are supported by great
timbers. To break away the rock, the miner makes a hole with a rock
drill worked by electricity or compressed air, puts powder or dynamite
into the hole and explodes it. The broken rock is then raised to the
surface and crushed in a "stamping mill." Here the ore is fed into a
great steel box called a "mortar." Five immense hammers, often
weighing a thousand pounds apiece, drop down upon the ore, one after
another, until it is fine enough to go through a wire screen in the
front of the box. When two hundred or more of these hammers are
pounding away with all their might, a stamping mill is a pretty noisy
place. The ore, crushed to a fine mud, now runs over sloping tables
covered with copper. Sticking to the top of the copper is a film of
quicksilver. This holds fast whatever gold there may be and makes an
amalgam, which is scraped off from time to time, and the quicksilver
is driven from the gold by heat.

Gold that is not united with other metals is called "free milling
gold." Much of it, however,