All at once, from their rear, they heard shouts and bugle calls. Jack turned a shade paler. The demonstration was much too close to be pleasant. He had hardly believed that it was possible for the Mexicans to have gained upon them so rapidly. "Guess we're up against it," muttered Walt Phelps, in his usual laconic manner. "Not yet, by a good sight," pluckily retorted Jack. "Come on--into this gulch. It takes a turn above here, and we may find some means of getting out of their sight altogether." Almost on their haunches, the horses were urged down the steep bank of the gully to which Jack had referred. It was about twenty feet in depth, with steep sides at the point at which they entered it, and bare. Farther on, though, it took a turn, and was covered almost to the bottom with chaparral and brush. As Jack had said, if they could gain this portion of it, it ought to afford them an ideal hiding-place. Rapidly they pressed forward along the rough bottom of the gulch, which was evidently a roaring water-course in times of heavy rain, but which was now as dry as a bone. It was stiflingly hot, too, but none of them noticed that. Other things far more overwhelming in importance, were upon their minds just then. Evidently, such skilled trackers as the Mexicans, had not been at fault in locating the woods into which the boys had vanished. The yells and cries, which Jack had heard, were rapidly drawing nearer in the woods above them. But, if they could only gain the shelter of the overgrown part of the gulch, they might still be safe. It was in this extremity that Jack bethought himself of an old trick he had heard the cow-punchers talk of at his father's ranch. They had used it in old frontier days, when the Indians were thick and hostile. The deception was a simple one. It consisted in the hunted person slipping from his horse at a suitable hiding-place and then letting the animal wander on. The pursuers would naturally be guided by the sound of the horses' hoofs, and would follow them up, leaving the concealed victim of the chase at liberty, either to double back upon his trail, or remain where he was. His intention of putting this trick into execution Jack rapidly confided to his two companions. They rode forward through the thick brush, which they had now gained, gazing eagerly at the walls of the gulch for some cave, or other suitable place of concealment. Suddenly Walt spied the very place which they were in search of, apparently. It was a small opening in the rocky wall of the gully, which appeared from below to penetrate quite some distance back into the earth. Its mouth was sheltered with brush and creepers, and but for the fact that a bird flew out from it as they passed, and thus attracted their attention, they might have passed it unnoticed. A brief inspection showed that it was a small cave, about twenty feet in depth, and, as has been said, well screened from below.