"What's the trouble out there, I wonder?" said he.
"Go and see," replied the sergeant with a sleepy yawn: "that's the only way to find out."
"Sergeant," said the officer of the guard, "if those horses have had grass enough, have them brought in and tied to the stable-lines. Look well to their fastenings."
"Corporal of the guard, No. 7!" came the call again; and this time it was uttered in a louder and more earnest tone.
Bob, who was walking toward post No. 7 with a very deliberate step, now broke into a run, and George jumped up and followed him. A fortunate thing it was for that camp and its inmates that he did so. His thorough acquaintance with the ways of some of the inhabitants of the Plains enabled him to prevent a catastrophe which would certainly have resulted in a serious loss of life, and brought Captain Clinton's scout to an inglorious end then and there. When he and the corporal reached post No. 7 they found the sentry on duty there lying flat on his stomach and gazing earnestly toward the horizon.
"What's the matter, Sprague?" demanded Bob.
"I don't know, I am sure," replied the sentry. "If the hostiles had made up their minds to pay us a visit, they wouldn't make such a racket as that, would they? There! don't you hear it? Something's coming this way, I tell you, and coming on a keen jump, too."
The three held their breath and listened intently. A second 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."