had a vague sort of desire
to prove that he was right. Having nothing else to do he watched
them.

The nearer sentinel grew lazier in his walk, and his beat became
shorter. At last he dropped his rifle to the ground, leaned his
folded arms on its muzzle, and gazed toward the camp, where, so
far as he could see, there was nothing but darkness and sleep.
The other presently did the same. Then they began short walks
back and forth, but soon both sat down on the ground, with their
rifles between their knees, and after that they did not stir.
Watching as closely as he could Dick could not observe the
slightest movement on the part of either, and he knew that they
were asleep. He laughed to himself, pleased, in a way, to know
that he had been right, although it was only another evidence of
the carelessness and indifference general throughout the train.

He fell asleep himself in another half hour, but he awoke about
midnight, and he was conscious at once that he had been awakened
not by a troubled mind, but by something external and unusual.
He was lying with his right ear to the ground, and it seemed to
him that a slight trembling motion ran through the solid earth.
He did not so much hear it as feel it, and tried to persuade
himself that it was mere fancy, but failed. He sat up, and he no
longer observed the trembling, but when he put his ear to the
ground again it was stronger.

It could not be fancy. It was something real and extraordinary.
He glanced at the sentinels, but they were sound asleep. He felt
a desire to rouse somebody, but if it proved to be nothing they
would laugh at him, or more likely call him hard names. He tried
ear to earth once more. The trembling was still growing in
strength, and mixed with it was a low, groaning sound, like the
swell of the sea on the shore. The sound came with the wind from
the north.

Dick sprang to his feet. There, in the north was a faint light
which grew with amazing rapidity. In a minutes almost it seemed
to redden the whole northern heavens, and the groaning sound
became a roll, like that of approaching thunder.

A shadow flitted by Dick.

"What is it, Bright Sun?? What is it?" exclaimed the boy.

"The dry grass burns, and a mighty buffalo herd flees before it."

Then Bright Sun was gone, and the full sense of their danger
burst upon Dick in overwhelming tide. The flames came on, as
fast as a horse's gallop, and the buffaloes, in thousands and
tens o