t as trackless as the sand which hides so many of
their relics in a tawny sepulchre. We may be certain, however, that
the remnants who survive are the representatives of myriads who once
made most of the American valleys palpitant with life, but over whom
oblivion has swept like a huge tidal wave, leaving the scattered
fragments of their history like peaks rising from a submerged world.

[Illustration: A TWO-STORY CLIFF PALACE.]

The best conclusions of scientists in regard to the geological
periods of our planet consider that the Glacial Epoch began about two
hundred and forty thousand, and ended about eighty thousand, years
ago. Traces of the existence of men in North America during that
glacial period have been found in abundance, and make it probable
that a human population existed, toward the close of that era, all
the way from the Atlantic Coast to the Upper Mississippi Valley.
Where these men of the Ice Age originally came from is a matter of
conjecture; but it seems probable that they migrated hither from the
Old World, since it is certain that during the various elevations and
depressions of the two continents, it was possible, several times,
for men to go from Europe or from Asia into America without crossing
any ocean, either by the northwestern corner of Alaska, which has
been repeatedly joined to Siberia through the elevation of the
shallow Bering Sea, or by the great Atlantic ridge which more than
once has risen above the ocean between Great Britain and Greenland.
Yet, though the first inhabitants of America, in all probability,
came thus from the Old World at a very distant period of antiquity,
it is believed by the best students of the subject that, until within
the last few centuries, there had been no intercourse between America
and either Europe or Asia, for at least twenty thousand years. Hence
the Aborigines of this continent developed in the course of ages
peculiarities which distinguish them from other races, and justify
their being regarded as, practically, native to the soil.

[Illustration: AN EARLY PLACE OF SHELTER.]

The Indians of New Mexico and Arizona were, probably, fugitives from
more fertile lands, whence they had been expelled by the ancestors of
the bloodthirsty and cruel Apaches. The country to which they came,
and where they made a final stand against their predatory foes, was
well adapted to defense. For hundreds of square miles the land is
cleft with chasms, and dotted with pe