"I don't know. Let's drive down and see." As he drew nearer he knew that, though doubtless this wagon had once had a driver, it contained no people at all now. Tad, racing toward it, stopped uncertainly and waited while Mike bristled beside him. The youngster had been halted by sight of the oxen that had once drawn this wagon, but that now lay dead in their yokes. Joe stopped the mules, handed the reins to Emma, and walked slowly toward the wagon. His courage restored by his father's presence, Tad kept pace with him. Joe looked at the oxen, dead too long to have any hope of discovering what had killed them. He swung up to look into the wagon and, as he had expected, found it empty. "What do you think happened?" Tad asked in awed tones. "I don't know." "Indians?" "Could be." "Shucks!" "What's the matter?" "Why couldn't they have waited until we came along?" "Don't talk foolish!" Joe ordered sternly. "Besides, if it was Indians, they'd have taken the wagon too." "Unless," Tad pointed out, "they were driven away by people shooting from other wagons." "That could be too, and maybe some fool driver just drove his oxen to death. Anyhow, we'd better be moving." "My guess is sick or poisoned oxen," he explained to Emma when he got back on the seat and took the reins. "There aren't any bullet holes in the wagon cover." "Oh, I do hope that whoever was in there is all right!" "They probably are," Joe reassured her. "Probably picked up by another wagon." They drove on, sobered by this evidence of certain accident, and possible tragedy, along the Oregon Trail. The hard trail continued; rain country was definitely behind. But a cold north wind still blew and Joe urged on the mules. There was no summer weather behind that wind and he had no desire to be caught out here when snow fell. For a moment they rode in silence, and it seemed that there was something alien among them. Even the children were still, and Emma turned to Joe, vaguely puzzled. "Do you hear anything?" "By gosh, I thought I did." "I too." There was a distant, muted throbbing that came to them in discordant tempo, like a wind that blows in blasts instead of with steady force. But the wind around the wagon was still steady and still from the north. Joe twisted uneasily on the wagon seat, for it seemed to him that there was much he should know about this that he did not know. He had a sense of danger, which was silly, for no danger threatened. The mules bobbed uneasy heads. "Hey, Pa!" Tad's voice was desperate and wild. Running hard, the youngster appeared on a near-by knoll. Joe stopped the team and waited, while fear's cold fingers caressed his spine. Tad's jacket was open, his face sweat-streaked, and he had run so far and so fast that he gasped for breath. "My gosh!" he yelled. "Must be a million of 'em!" "A million what?" "Buffalo!" Tad gasped. "And they're headin' this way!" "Get in quick!" "How about Mike?"