"You get to Halifax with that spook talk," said Coyote Pete scornfully. "I'll bet my Sunday sombrero that whatever them things is, there's some sore of human mischief back uv it. But what is it? Who put it up?" "Yes, and what for, and why?" laughed Jack. "I tell you, fellows," he went on, "it's no use of our racking our brains to-night over this. The best thing we can do is to set a watch. Then, if they come again, we can try a shot at them. If not, why then in the morning we'll make an investigation; eh?" "Durn good advice," grunted Coyote Pete. "Now, I'd suggest that ther perfusser takes ther fust watch, and----" "No, no, my dear sir; really, I--I have a cold already. A-hem--ach-oo!" The man of science, it seemed, had really developed serious bronchial trouble in record time. "Why, professor," said Jack mischievously, "haven't I heard you say that you'd like a chance to investigate such a phenomenon as this?" "Hum, yes--yes, my young friend. I may have said so, yes. And any other time I should be only too pleased to--Good Land! what's that?" With the agility of a grasshopper, the professor had jumped fully three feet, as one of the pack-burros, nosing about behind him, accidentally butted him in the small of his back. The others burst into a roar of laughter, which they could not check. The professor, however, adjusted his spectacles solemnly and looked about him with much dignity. "I thought I saw a book I had dropped, almost in the fire," he explained glibly, "so I jumped to get it before a hot ember fell on it." "I had no idea you could jump like that, professor," laughed Jack. "You should have gone in for athletics at Stonefell." It was finally decided that Walt and Ralph should stand the first watch, and Coyote Pete and Jack the last part of the night. The professor, after carefully drawing tight the curtain of his tent, "to keep the cold out," as he explained, retired. Soon after, Jack and the cow-puncher also went to bed till the watch should summon them to go on duty in their turn. But the night passed without any reappearance of the strange shapes which had so upset the tranquility of the little camp, and, viewed in the fresh light of a new and glorious day, somehow the affair did not seem nearly so ominous and awe-inspiring as it had the night before. Breakfast, as you may imagine, was speedily disposed of, and, having seen to the stock, the party started out to explore the mesa itself. As has been said, the side upon which they had camped the night before was nothing but a sheer cliff. Under the guidance of Coyote Pete, they now set out to encircle the strange precipitous formation. Their hearts beat high, and their eyes shone with an aroused sense of adventure as they strode along.