ld in the quartz, and
the amount of gold is guessed at from the appearance of the rock) is
scattered over the arastra. The grinding continues for about two hours
more, during which time it is supposed the quicksilver is divided up
into very fine globules and mixed all through the paste (which is so
stiff that the metal does not sink in it to the bottom), and that all
the particles of gold are caught and amalgamated. The amalgamation
having been completed, some water is let in three or four inches deep
over the paste, and the mule is made to move slowly. The paste is thus
dissolved in the water, and the gold, quicksilver and amalgam have an
opportunity to fall to the bottom. At the end of half an hour, or
sooner, the thin mud of the arastra is allowed to run off, leaving the
precious material at the bottom. Another charge of broken quartz is now
put in and the process is repeated, and so on. The length of a "run,"
or the period from one cleaning up to another, varies much in different
places. In the rude arastra a run is seldom less than a week, and
sometimes three or four. The amalgam having settled down between the
paving stones, the bed must be dug up and all the dirt between them
carefully washed. In the improved arastra the paving fits so closely
together, that the quicksilver and amalgam do not get down between
them, but remain on the surface, and can readily be brushed up into a
little pan, and therefore cleaning up is much less troublesome and is
more frequently repeated than in the rude arastras; besides there is a
greater need of frequent cleaning up in the improved arastras, because
the amount of work done within a given time is usually greater.

The arastra is a slow instrument, but in some important respects it is
superior to any other method of working auriferous quartz. It grinds
the quartz well, is unsurpassable as an amalgamator, is very cheap and
simple, requires no chemical knowledge or peculiar mechanical skill in
the work, requires but little power, and very little water--all of them
important considerations. In many places, the scarcity of water alone
is enough to enable the arastra to pay a larger profit than any other
method. Again, if a miner finds a rich spot in a lode, he may be
doubtful as to the amount of paying rock which he can obtain. Such
cases very frequently happen in California, and the arastra is just the
thing for the case; for then if the amount of paying rock is small,
nothing is l