t stood within a few hundred yards
of the eastern brink of the hill which, in its turn, was another
mystery. The eastern extremity was not a mere precipice, it was a vast
overhang which left Yellow Creek, upon whose banks the mining camps
were pitched, flowing beneath the roof of a giant tunnel supported by
a single side.

The rock on the plateau reared its misshapen head to the heavens at a
height of something over two hundred feet, and its great base formed a
vast cavern out of which, fanwise, spread a lake of steaming water,
which flowed on to the very brink of the hill where it overshadowed
the creek below. Thus it was, more than half the lake was held
suspended in mid-air, with no other support than the parent hill from
which its bed projected. It was an awesome freak of nature, calculated
to astonish even eyes that were accustomed to the sight of it.

But Buck was not thinking of these things now. He was looking at the
view. He was looking at the sky. He was looking from this great height
for an explanation of the curious, ruddy light in the sunless sky, the
teeming haze which weighted down the brain, and, with the slightest
movement, opened the pores of the skin and set the perspiration
streaming.

In all his years of the Montana hills he had never experienced such a
curious atmospheric condition. Less than an hour ago he had left the
Padre at the fur fort under a blazing summer sky, with the crisp
mountain air whipping in his nostrils. Then, quite of a sudden, had
come this change. There were no storm-clouds, and yet storm was in
every breath of the superheated air he took. There was no wind, nor
anything definite to alarm except this sudden blind heat and the
purple hue which seemed to have spread itself over the whole world.
Thus it was, as he neared the mysterious mountain, he had made up his
mind to its ascent in the hope of finding, there upon the unwholesome
plateau, the key to the atmospheric mystery.

But none seemed to be forthcoming, so, turning at last to the patient
Caesar, he once more returned to the saddle and rode on to the barren
shores of Devil's Lake.

The lake was a desolate spot. The waters stretched out before him,
still, and silent, and black. There was not even a ripple upon its
steaming surface. Here the haze hung as it always hung, and the cavern
was belching forth deep mists, like the breathing of some prehistoric
monster. He glanced up at the birdless rock above, and into the br