animals themselves, but everything they carry is vital to the success
of the expedition, and there is always a danger that, for instance,
your camera and photographic outfit, and the priceless collection of
negatives already taken, may roll down a precipice.

A mule with its bulky pack is, to a certain extent, helpless on these
narrow mountain trails. Old and experienced animals often manoeuvre
their packs with a cleverness that is almost human: yet, whenever a
mule runs accidentally against some projection, or its foot slips,
the poor beast invariably loses its balance, and over it goes,
down the hill with ever-increasing velocity.

On one occasion I heard a noise coming from above without being at
first able to discern what caused it. A few stones came tumbling down,
and were presently followed by a donkey, pack and all, turning over
and over with astounding speed. It cleared a perpendicular rock some
twenty feet high and landed at its base, rolling over twice. Then,
to my amazement, it rose to its feet in the midst of its scattered
cargo. And do you know what that cargo consisted of?--a case of
dynamite and our tool chest! As fast as their legs could carry them,
two Mexicans were by its side, promptly reloading the donkey and
leading it up to the trail as coolly as if nothing had happened. A
very fine mule, raised on the plains of Arizona, was naturally giddy,
and met with such a mishap three times in one day, tumbling down 150
to 200 feet without, however, being seriously hurt. At first I was
greatly shocked to see the animals thus rolling over and over with
their packs, down the mountain sides, never stopping until checked by
some large tree or rock, sometimes 200 feet below. But the Mexicans
were evidently quite accustomed to such happenings, which seemed to
be in the regular line of their travel.