-eight feet and the thickness of the arch at the keystone is
forty-five feet. The height of the Carolyn Bridge is two hundred and
five feet and the span one hundred and eighty-six feet.

All these bridges span canyons whose depths correspond to the height of
the arched structures. In White Canyon, a few miles below Edwin Bridge,
under its overhanging rock walls, are the ruins of numerous
cliff-dwellings.

The largest natural bridge in the world yet discovered is the
Nonnezoshi. It is in Nonnezoshiboko Canyon, Utah, not far from the place
where the San Juan River enters the Colorado. This mammoth arch is more
of a flying buttress spanning the canyon than a real bridge. Its height
is three hundred and eight feet and its span two hundred and eighty-five
feet.

To visit these bridges from the nearest railway station requires stage
and horseback riding for upward of one hundred and twenty-five miles.
The latter part of the journey is made over a faint trail through a
rugged country; but the scenery amply repays one for the hardships
endured.

The climatic changes during the ages have been such that this region is
now almost inaccessible on account of the lack of water, except in the
early spring when melting snows yield a temporary supply. Even the
cattlemen pasturing their herds in that section keep them there but a
few weeks during the year, so scarce is both water and vegetation.

In the main, natural bridges are the result of one or another of several
causes. A limestone cavern may be partly destroyed by streams of water,
leaving a portion of the cavern with its roof still in place; the part
of the roof thus remaining becomes the arch of the bridge. A branch of
the Southern Railway threads a natural tunnel near Anniston, Ala., and
the tunnel is the remnant of an old limestone cavern.

In other cases a natural bridge is formed when bowlders, or a mass of
rock, tumbling into a deep crevice is wedged and held in place. In still
other instances a layer of hard or slowly weathering rock may rest upon
a layer of rock which weathers rapidly. In such cases, if the rock
layers form the face of a cliff, natural bridges, caverns, and overhangs
are apt to result.

CHAPTER XVIII

STRANGE ROCK FORMATIONS--TABLE MOUNTAIN OF CALIFORNIA

There are many table mountains in different parts of the world, but the
one which I am about to describe is interesting both from geological and
financial stand-points. The so-called T