But it would narrow further up, he reassured himself. If he could find the mouth of Monument Canyon and hang around there they would surely pick him up. For miles he rode up a flat level floor, green and watered with a brook, while on both sides frowned parapets like the Palisades of the Hudson, about the same height, yet narrowed in closer, so that their grandeur and majesty hemmed him in. Up under the sheer cliffs he could see great hollowed-out caves, with stone ruins peeping out under them, walls shattered and torn, square stone watch towers with their upper stories thrown down, and a detritus of destroyed masonry scattered down the steep, tree-grown slopes. Then a narrow side canyon attracted him. It would be fun to ride up to it and camp there for the night, thought Sid, besides being out of the main canyon and away from possible visits of passing Navahos who might take into their heads to rob a lonely boy camping out. He turned up it, winding his pony through great spruces and firs that rose out of its moist bottom, watered by a little runnel. The stratified stone ledges of the cliffs were moss-covered at their bases. High up through the cleft he could see the blue sky, with yellow sunlight striking the spires of western yellow pines that seemed like pygmy Japanese trees up there from where he was. It was already dim down in here. Swiftly the twilight grew, while the pony slowed to a walk, his feet not making a sound in the soft duff. It was growing eerie and mysterious in here, thought Sid, as a slight shiver ran through him, and he now wished he had stayed out in the open valley. But he fought back that wish as cowardly and foolish. Men did not turn back from what they had once set their hand to! Then a stick cracked, somewhere behind him. Sid reined up and listened. All was still as death; even the birds had gone to roost in the dim twilight of the chasm. But Pinto’s actions told him that that noise was not imagination. His pony’s ears lay flat back and he was shivering all over with fear! Sid watched, intently, down the chasm. He thought he saw a bush move. A second’s concentration on it told him it _had_ moved, for the tips of its lower branches still vibrated. He reached down and drew his army carbine out of its scabbard. For some minutes Sid watched the bush, his heart beating with excitement. A more experienced man than he would have hummed a shot into it to smoke out whatever might be lurking there. But after a time he turned away and urged the pony slowly ahead. The horse jumped as the spurs touched him, and Sid had a wrangle to quiet him at all. They paced on, slowly, both listening behind them, for Pinto’s ears had not pricked forward at all. An uncanny sense that they were being followed,--by something--in the chasm, persisted. Several times Sid looked back, rifle at ready, urged by some half-heard noise.