rocess is too well known to require much description here. Its main
points of advantage are the simplicity--in practice, for its chemistry
is complicated in theory--of its methods and appliances. The principal
agents employed may be said to be mercury and horseflesh, or rather
mule-flesh; the mercury forming an amalgam with the precious metals
under the incorporation brought about by the trampling hoofs of the
mules. The trampling and incorporation of the _torta_, or charge of
pounded ore, mercury, water, salt, copper sulphate, and other
constituents, mixed into a paste, was originally performed by
barefooted natives, but the practice of using mules for the purpose
came from Peru, in 1783, as before mentioned. The _patio_, as its name
implies, consists of a paved yard upon which the crushed mineral is
treated. This is in some cases of very large capacity, one of the most
important in the country, that of the Guadalupe works at Pachuca, which
treats nearly a thousand tons of ore a week, being as large as the
_plaza_ of a city. Upon this the _torta_ is spread, and bands of a
dozen mules, or mules and horses, harnessed together, are driven up and
down from morning till afternoon, through the slushy mass. The animals
are then bathed to remove the chemicals, but notwithstanding this the
work is deleterious, and they last but a few years--the old ones but a
few months--as they become poisoned by the copper sulphate. At some of
the _haciendas_ of Pachuca six hundred horses are employed in this
work, and the total throughout the country is considerable. Constant
efforts have been made for the use of mechanical appliances, to take
the place of the equine mixer, but these have not been found to give
the same efficiency. The process is typical of the country and the
race--time, space, and material are plentiful, and labour is cheap, and
horses--well, they were made for man's use! The innate tendency of the
Spanish-Americans to do without mechanical appliances also is indulged.

The growth of the silver-producing industry of recent years is shown by
the returns, giving approximately a value of seven million Mexican
dollars for 1890 and fifty million for 1902, for export alone. The
total value of the silver production for 1907 was eight million
sterling, which was more than that of the United States, and so Mexico
led the world in that year.

_Gold_.--The gold which was formerly produced in Mexico has come
principally from the silv