eft, except Casa Grande ruin, by which the early accounts of
Spanish explorers in North America can be checked and
interpreted--none other of its class exists in the United States.
Casa Grande ruin is, therefore, a relic of exceptional importance
and of essentially unique character.

Unfortunately this structure, like others erected by the most
advanced among the native races in the southwest, is of perishable
material; it is built of adobe, or rather of cajon, i.e., of a
puddled clay, molded into walls, dried in the sun. Such walls would
stand a short time only in humid regions; but in the arid region the
material is desiccated and baked under cloudless sky and sun for
many months at a time, and becomes so hard as to resist, fairly, the
rare storms of the region. It is by reason of climatal conditions
that cajon and adobe have come into general use for building in
southwestern United States, as in contiguous parts of Mexico; and it
is by reason of the same conditions that a few of the ancient
structures remain, and the best preserved of all is found in the
Gila valley, one of the most desert regions on the western
hemisphere. Yet the best of the cajon structures is perishable; so
long as the roof remains and the summits of the walls are protected,
disintegration proceeds slowly; but when the projecting roof is
removed, the rare but violent storms attack the walls, and they are
gradually channeled and gullied by the storm waters, while the
exterior surface gradually disintegrates and falls away under the
alternate wetting and drying. Even in the most arid regions, the
earth-built structures typical of the southwest are surely, albeit
slowly, ravaged and destroyed.

Several years ago Casa Grande ruin was brought into general notice
throughout the United States in consequence of southwestern
explorations; and in 1889, in response to a petition from several
illustrious Americans, the Congress of the United States, at the
instance of Senator Hoar, of Massachusetts, made an appropriation of
$2,000 for the purpose of undertaking the preservation of this ruin.
This appropriation was expended in works urgently required to
prevent the falling of the walls and final destruction of the ruin;
they included metal stays for the walls, with brickwork for the
support and protection of the walls at their bases. Subsequently an
area of about 480 acres, including