ost, whereas the erection of a stamping-mill would cost
much time and money, and before it could get into smooth operation the
rich rock would be exhausted, and the mill perhaps become worthless. No
other simple process of amalgamation is equal to that of the arastra;
and it has on various occasions happened in California, that Mexicans
making from fifty to sixty dollars per ton from quartz, have sold out
to Americans who have erected large mills at great expense, with patent
amalgamators, and have not been able to get more than ten or fifteen
dollars from a ton. The arastra is sometimes used for amalgamating
tailings which have passed through stamping-mills.

_Chilean Mill._--The Chilean mill has a circular bed like the arastra,
but much smaller, and the quartz is crushed by two large stone wheels
which roll round on their edges. In the centre of the bed is an upright
post, the top of which serves as a pivot for the axle on which both of
the stones revolve. A mule is usually hitched to the end of one of the
axles. The methods of managing the rock and amalgamating with the
Chilean mill, are very similar to those of the arastra. The Chilean
mill, however, is rarely used in California; the arastra being
considered far preferable.

_Stamps._--Nine-tenths of the quartz crushed in California is
pulverized by stamps, of which there are two kinds, the square and
rotary. The square stamp has a perpendicular wooden shaft, six or eight
feet long, and six or eight inches square, with an iron shoe, weighing
from a hundred to a thousand pounds. The wooden shaft has a mortice in
front near the top, and a cam on a revolving horizontal shaft enters
this mortice at every revolution. When the cam slips out of the
mortice, the stamp falls with all its weight upon the quartz in the
"battery" or "stamping-box." The rotary stamp has a shaft of wrought
iron about two inches in diameter, and just before falling this shaft
receives a whirling motion, which is continued by the shoe as it
strikes the quartz. The rotary stamp is considered superior to the
square, its advantage being that it crushes more rock with the same
power, that it crushes more within the same space, and that it wears
away less of the shoe in proportion to the amount of rock crushed.
There are usually half a dozen square stamps or more, standing side by
side in a square-stamp mill, and these do not all fall at the same
moment, but successively, running from the head to the f