these _socavones_, or great adits, are of such a size
that a mounted horseman can enter with ease, or a locomotive might
easily traverse them. Indeed, the engineer of to-day hesitates to
attack the mountain sides with such bold adits as the Spaniard, with
inferior materials, drove into them. Similar tunnels were driven by the
Spaniards in some of the famous mines of Peru.[33]

[Footnote 33: See my book, "The Andes and the Amazon."]

Ancient ore-reduction works, _arrastres_, canals, ditches, excavations,
tunnels, pits, ruined buildings, and in some cases falling church
walls, all of this bygone age, are encountered throughout the country,
scattered far and wide. Those who lived and moved and had their being
therein lie mingled with the dust these centuries past, and kind nature
has often covered up the evidences of their handiwork with flower and
foliage.

There was a steady flow of the two precious metals to the City of
Mexico from the innumerable mines of the regions which produced them.
To attempt to describe these mines, even those renowned for their
richness, would fill a chapter alone. Fantastic displays of wealth are
recorded by the owners of some of the great silver-producing mines--the
bridal chambers of a palace, lined by the father of a bride with silver
bars; the footpath from the _plaza_ to the church paved with great
silver ingots, for the bridal party.

A famous hill of iron--standing on the plains of Durango, stands out
also from the historical vista of metallurgical discovery of those
early days. In 1552 Vasquez de Mercado, a Spaniard of wealth and family
in Mexico, living in Guadalajara, heard from the Indians that a great
mountain of pure silver existed on the boundless plateau far to the
north. Arming an expedition he set forth with this vain illusion
actuating him, and travelled on day after day expecting that every
sunrise would gleam upon the burnished slopes of this silver mountain.
Battles were fought with the savage Indians who inhabited the plains,
but vanquishing these the deluded party pushed on. At last, on the
horizon, the hill rose; they approached it: it was iron! Sleeping
sore-hearted at its base that night, Mercado and his companions were
attacked by Indians, various soldiers killed, and he himself wounded.
Returning homeward towards Guadalajara, the unfortunate leader
succumbed to his wounds, fatigue, and the ridicule of his companions,
and he perished. But the great Cerro de Merc