Again that same shrill whistling scream of dreadful agony and fear, that had caused them to rein up their horses so suddenly a moment before, came from the valley beyond the brow of the little hill up which they had been slowly riding, and chilled the very marrow in their bones with the terrible intensity of its fear and anguish. Then all was still. "What--what was it?" and Thure turned a startled face to Bud. "It didn't sound human and I never heard an animal scream like that before. What can it be?" "I don't know," Bud answered, his face whitening a little; "but I am going to find out. Come on," and, swinging his rifle into position where it would be ready for instant use, he started up the hill, his eyes fixed in the direction whence had come those fearful screams. "We'd better go a little slow, until we find out what it is," cautioned Thure, as he quickly fell in by the side of Bud, his own rifle held ready for instant use. "It might be Indian devilment of some kind. You know dad's last letter from the mines said that the Indians were getting ugly; and if it is hostile Indians, we want to see them first." "You bet we do," was Bud's emphatic rejoinder, as he again pulled up his horse. "Now, just hold Gray Cloud and I'll scout on ahead and see what's going on down there in the valley before we show ourselves," and, sliding swiftly from Gray Cloud's back, he tossed his bridle rein to Thure, and, rifle in hand, started swiftly and as silently as an Indian toward a thick clump of bushes that grew directly on the top of the little hill. Thure deftly caught the bridle rein; and then sat silent and motionless on the back of his horse, his eyes on his comrade, waiting in tense expectancy for the moment when he would reach the clump of bushes and look down into the valley beyond and see the cause of those strange and terrible cries that had so suddenly and so fearfully startled them. Bud, carrying his cocked rifle at trail, his form bent so that the least possible part of his body showed above the grass of the hillside, ran swiftly until he had almost reached the brow of the hill and the clump of bushes. Then, crouching closer to the ground, he crept cautiously and slowly to the bushes and, gently working himself into their midst, carefully parted the branches in front of his face until he had a clear view of the little valley below. At the first sight he uttered an exclamation of surprise and wrath and threw his rifle to his shoulder; but, with a regretful shake of his head, he almost instantly lowered the gun, and, turning quickly about, motioned excitedly for Thure to advance with the horses and started on the run to meet him. "Indians! Is it Indians?" Thure cried anxiously, the moment Bud was at his side.