copper, common salt, and quicksilver.
Driving the animals through this mass, ten hours a day for three or four
days, causes the various ingredients to become thoroughly mingled. The
quicksilver finally gets hold of and concentrates the coveted metal. The
quicksilver is afterwards extracted and reserved for continued use,
performing the same function over and over again. There is, of course, a
large percentage of quicksilver lost in the operation, and its
employment in such quantities forms one of the heavy expenses of
milling.

The mills are semi-fortresses, having often been compelled to resist the
attacks of banditti, who have ever been ready to organize a descent upon
any place where portable treasure is accumulated. We were told, on good
authority, that every ton of raw material handled here yields on an
average thirty-three dollars. This figure our informant qualified by the
remark that it was the average under ordinary circumstances. Sometimes
the miners strike what is called a bonanza, and for a while ore is
raised from the bowels of the earth which will produce five times this
amount to the ton; but after a short time the yield will return to its
normal condition. Occasionally, but this is rare, nuggets of pure or
nearly pure silver are found weighing from fifteen to twenty pounds
each. The process of milling here is slow, tedious, and wasteful. The
scientific knowledge brought to bear upon the business in the United
States is not heeded in Mexico, and yet these people obtain remarkably
favorable results. The fact is, the precious metal is so very abundant,
and the profits so satisfactory, that the managers and owners grow
careless, having little incentive to spur them on to adopt more
economical and productive methods. An intelligent overseer of a mine at
Guanajuato said to us in reply to a question relating to the usual
process of milling in Mexico: "We get probably sixty per cent. of the
silver contained in the raw ore which we handle, and that is about all
we can expect." On being asked if the men whom we saw working in the
open bed of the river, far below the mills, did not obtain good results,
the superintendent replied, "They succeed best in getting part of the
quicksilver which has been carried away in the process, which they sell
to us again." These men, we observed, worked mostly with shovels and
earthen pans, or with their hands and a flat, shingle-like piece of
wood.

Guanajuato is built on the sid