But while the two, or rather the four slept, something was moving far out on the plain.
It was an immense black mass with a front of more than a mile, and it was coming toward Ned and Obed. This mass had been disturbed by a great danger and it advanced with mighty heavings and tramplings. Ned and Obed slept calmly for a long time, but as the black front of the moving mass drew closer to the creek and its thin lines of trees, the boy stirred in his blankets. A vague dream came and then a state that was half an awakening. He was conscious in a dim way of a low, thundering sound that approached and he sprang to his feet. The next instant a neigh of terror came from one of the horses and Obed, too, awoke.
"Listen!" exclaimed Ned. "Hear that roar! And it's drawing near, too!"
"Yes, it's a buffalo herd!" said Obed. "We're far enough north now to be within the buffalo ranges, and they're coming down on us fast. But they must be scared or be drawn on by something, because it's not yet dawn."
"All of which means that it's time for us to go."
"Or be trodden to death."
Naturally, they had slept in their clothes and they quickly gathered up their arms and baggage. Then they released their frightened horses, sprang upon their backs and galloped toward the north. They felt secure now, so far as the herd was concerned. Their horses could easily take them out of its reach.
"Maybe they'll stop at the creek," said Ned. "I should think that the water would hold anything in this thirsty land."
Obed shook his head, but offered no further answer. The thunder of the hoofs now filled their ears, and, as the sound advanced steadily, it was evident that the creek had not stopped the buffalo herd.
The dawn suddenly came up sharp and clear after the manner of southern lands. The heavens turned blue, and a rosy light suffused the prairie. Then Ned saw the front of the buffalo herd extending two or three miles to right and to left. And he saw more. He saw the cause of the terror that had smitten the herd.