They were joined very soon by Shepard, upon whose high boots snow was clinging to the very tops, and he said when Dick looked at him inquiringly: "I see that you're an observer, Mr. Mason. Yes, I've been out on the mountainside. Colonel Winchester suggested it, and I was glad to do as he wished. It was difficult work in the snow, but Mr. Reed, our guide, was with me part of the time, and we climbed pretty high." "Did you see anything?" "No footsteps. That was impossible, because of the falling snow, but I think our friends, the enemy, are abroad in the mountains. The heavy snow may have kept them from coming much nearer to us than they are now." "What makes you think so?" Shepard smiled. "We heard sounds, odd sounds," he replied. "Were they made by a whistle?" Dick asked eagerly. Shepard smiled again. "It was natural for you to ask that question, Mr. Mason," he replied, "but it was not a whistle. It was a deeper note, and it carried much farther, many times farther. Mr. Reed explained it to me. Somebody with powerful lungs was blowing on a cow's horn." "I've heard 'em. They use 'em in the hills back of us at home. The sound will carry a tremendous distance on a still night like this. Do you think it was intended as a signal?" "It's impossible to say, but I think so. I think, too, that the bands--there were two of them, one replying to the other--belong to the Slade and Skelly outfit. Skelly has lived all his life in the mountains and Slade is learning 'em fast." "Then it behooves us to be watchful, and yet more watchful." "It does. Maybe they're attempting an ambush, with which they might succeed against an ordinary troop, but not against such a troop as this, led by such a man as Colonel Winchester. Hark, did you hear that noise?" All of them listened. It sounded at first like the cow's horn, but they concluded that it was the rumble, made by sliding snow, which would be sending avalanches down the slopes all through the night. "Are you going out again, Mr. Shepard?" Dick asked. "I think not, sir. Colonel Winchester wants me to stay here, and, even if the enemy should come, we'll be ready for him." They did not speak again for a while and they heard several times the noise of the sliding snow. Then they heard a note, low and deep, which they were sure was that of the cow's horn, or its echo. It was multiplied and repeated, however, so much by the gorges that it was impossible to tell from what point of the compass it came. But it struck upon Dick's ears like a signal of alarm, and he and all the others of the picket stiffened to attention. CHAPTER XIII DICK'S GREAT EXPLOIT