Stealthily withdrawing again, until well beyond sight of the group, he began carefully descending the side of the ridge toward the open prairie. In doing so, he avoided doubling on his own trail, for at any moment some of the Sioux were liable to start out on a tour of investigation, which would bring them face to face with him. With all his senses on the alert, he threaded his way among the trees and around the rocks and bowlders, until he stood on the base of the elevation, with the broad plain, across which he and his friend had fled in such desperate haste, stretching out before him for many miles. But another sight interested him. Along the foot of the ridge were scattered nearly a dozen Indian ponies, cropping as best they could the grass, whose tops faintly showed above the thin coating of snow. Their owners had abandoned them in their haste, without thought of securing them to any of the limbs, confident that they would be found within reach when wanted. They were tough little animals, without saddle or bridle. The majority had a blanket roughly secured over the back, with a thong about the upper part of the neck, which was all that was needed to guide them wherever their masters willed. But there was one animal worth all the rest for whom the eyes of the youth eagerly searched among the group, scattered at varying distances. He would have given anything for a sight of his own Jack at that moment. To his astonishment, he saw nothing of him. Through some unaccountable cause, he had vanished as utterly as if he had never existed. In the vain hope of discovering him, Warren glanced from one to the other, until he had surveyed each one several times over. But there was no mistake; Jack was invisible. The fact caused him keen regret, but it would not do to tarry, with the certainty that the Sioux would soon learn the truth and be after him like a whirlwind. One or two of their ponies were almost as fleet as Jack, and Warren was a good enough horseman to ride them as well as their masters could without saddle. Fixing his attention on the best looking animal, which happened also to be the nearest, he moved briskly toward him, with the purpose of bounding upon his back and dashing away; but his abruptness defeated his intention. It frightened the pony, who with a snort threw up his head, trotted several rods out on the prairie, and then turned and looked at him. The alarm of this animal communicated itself to the others, who also hurriedly trotted beyond his reach. The situation was critical. The action of the ponies was almost certain to be heard by their owners a short distance off, and they would be quickly on the spot. If they caught sight of the youth on foot trying to steal one, his position would be far more hopeless than when among the rocks and trees.