later the
breeze brought to their ears the sound that had attracted the attention
of the sentry--a deep, rumbling sound, faint and far off, but increasing
perceptibly in volume. It resembled the constant muttering of distant
thunder, but they all knew it was not that. Bob's face brightened at
once, but George's grew pale. The corporal did not know the danger that
threatened them, but his companion did; he had heard something like it
before. He had heard it on the night that Fletcher and his band of
raiders stampeded his stock, and he had thrown himself into an old
buffalo-wallow and allowed three hundred frantic cattle to gallop over
his head.

"Why, it must be cavalry from Fort Tyler," said Bob at length.--"But
I'll tell you what's a fact, boys," he added, as a fresh gust of wind
brought the sound more plainly to his ears: "there must be lots of them,
for I never heard such a roar of hoofs before. They are coming this way,
too. I hope they'll not run over us."

"Well, they _will_ run over us," said George, speaking quickly but
calmly, "unless you take immediate steps to prevent it. They are not
cavalry; they are buffaloes."

"Oh! ah!" exclaimed Bob.

"Humph!" ejaculated the sentry, jumping to his feet.--"Don't tell the
boys what I called you out for, will you, corporal? To tell the truth, I
was just a little bit--"

He finished the sentence by shrugging his shoulders, and Bob, who knew
what he meant by that, was about to assure him that he would say nothing
in the hearing of the "boys" that would enable them to "get the laugh"
on him, when George Ackerman broke in with--

"You had good reason to be alarmed, and this is not a matter to be
dropped with an 'ah!' and an 'oh!' and a 'humph!' You are in great
danger, if you only knew it. Those buffaloes are stampeded, and will not
stop until they are all out of breath."

"Well, if they don't want to stop, let them run," said Bob. "Who cares?
They don't owe us anything. They will of course turn aside when they see
us."

"But they will not see you unless you do something to attract their
attention," exclaimed George impatiently. "They will be in among us in
five minutes more, and men and horses will be trampled into the ground
like blades of grass. Wake up and do something, can't you? The safety of
the camp depends upon you, and if you don't move, I will."

"Great Moses!" ejaculated Bob. He was thoroughly aroused by the earnest
words of his companion, but having n