"Lightning," he muttered, glancing off to the south. "I guess Mr. Stallings was right about the storm." Yet, directly overhead the stars still sparkled. In the distance Tad saw the comforting flicker of the camp-fire, about which the cowmen were sleeping undisturbed by the oppressiveness of the night. "I guess the foreman knew what he was talking about when he said we were going to have a storm," repeated Tad. "I wonder how the cattle will behave if things get lively." As if in answer to his question there came a stir among the animals on the side nearest him. Tad began whistling at once and the cows quieted down. "They must like my whistling. It's the first time anything ever did," thought the lad. Far over on the other side of the herd Big-foot crooned to his charges the song of the "Two little niggers upstairs in bed." "Sanders' stock must be walking in their sleep, too. I wonder----" A brilliant flash lighted the entire heaven, causing Tad Butler to cut short the remark he was about to make. A deep rumble of thunder, that seemed to roll across the plain like some great wave, followed a few seconds later. The lad shivered slightly. He was not afraid. Yet he realized that he was lonely, and wished that some of the other guards might come along to keep him company. Glancing up, Tad made the discovery that the small spot of clear sky had disappeared. By now he was unable to see anything. He made no effort to direct the pony, leaving it to the animal's instinct to keep a proper distance from the herd and follow its formation. The thunder gradually became louder and the flashes of lightning more frequent. The herd was disturbed. He could hear the cattle scrambling to their feet. Now and then the sound of locking horns reached him as the beasts crowded their neighbors too closely in their efforts to move about. Tad tried to sing, but gave it up and resumed his whistling. "I'm glad Chunky is not out on this trick," thought the boy aloud. "I am afraid he would be riding back to camp as fast as his pony could carry him." No sooner had the words left his mouth than a flash, so brilliant that it blinded Tad for the moment, lighted up the prairie. A crash which, as it seemed to him, must have split the earth wide open, followed almost instantly. Another roar, different from that caused by the thunder, rose on the night air, accompanied by the suggestive rattle of meeting horns and the bellowing of frightened cattle. By this time Tad had circled around to the west side of the herd. The instant this strange, startling noise reached him he halted his pony and listened. Off to the north of him he saw the flash of a six-shooter. Another answered it from his rear. Then a succession of shots followed quickly one after the other. The lad began slowly to understand. He could hear the rush and thunder of thousands of hoofs. "The cattle are stampeding!" cried Tad. CHAPTER IX CHASED BY A STAMPEDING HERD "Whoa-oo-ope! Whoa-oo-ope!"