“I suppose the tigers don’t bother them; they are too small to make even a mouthful.” A herd of very large, black animals, with low-swinging heads and short, curved horns suddenly hove into sight. They emerged from a clump of forest in a long, straggling formation, and moved to the centre of the largest clearing. “Buffaloes,” Stanley gasped. “A herd of buffaloes. But what are they doing out in the open?” “I should think they would hide at night, like the other animals we saw. But they do not seem to be worrying about anything.” A shrill wail rose clear and piercing from somewhere in the darkness and echoed back and forth among the rocky walls. It was not repeated. “That sounds like a puma,” Ted hazarded after listening in vain for a repetition of the cry. “I wonder what next!” Just then one of the buffaloes gave a sharp bellow of alarm. The herd became charged with life instantly, and rushed into a compact mass so quickly it was impossible to follow their movements. But when they again became quiet it was seen that they were standing in a solidly packed circle. The cows and calves were in the centre, and the males, facing outward with lowered heads and bristling horns, formed an unbroken stockade around them. “Now I see their scheme,” Stanley exclaimed. “They have taken their stand for the night out in the open, where they have a chance for their lives. I doubt if even the sabre-tooths would dare charge that front of horns and hoofs. In the forest they could pick them off singly without much trouble, but----” A small stone struck Ted’s shoulder, dropped to the ledge, bounded off, and rattled down to the ground. “Where did that come from?” he asked with a start. They looked up along the face of the stone wall, but saw nothing. “Just a loose fragment,” Stanley explained with a nervous laugh. “Probably small pieces are dropping all of the time, or an owl may have started it in alighting.” Again they strained their eyes toward the moonlit floor of the crater. “I don’t remember seeing that stone before--the one right below and a little to the left.” “Nor I. But it must have been there, just the same, for stones can’t walk.” “How smooth and round it looks. The moonlight and shadows make it appear more conspicuous than before; that is why we notice it now.” “Yes; I guess you are right.” Another pebble came rattling down from above, struck the ledge, and bounded down into the crater. “There is something up there. Stones like that would not drop one at a time unless something started them,” Ted whispered. “I am going to watch the top while you keep your eyes on the bottom.” But a short time elapsed. Stanley nudged his companion. “Look!” he whispered. “The smooth, round stone is moving. It is creeping along as stealthily as the shadows themselves, and it is coming in our direction. It must be an animal of some kind.” “There is one above, too,” Ted returned with bated breath. “They are stalking us from the top and the bottom.”