"About fifteen, which means two hours at least, because the darker it gets the slower we'll be obliged to go till you two get more used to riding the plains," responded Bill. "If we keep on, and I feel stiff in the morning, we'll be there and I shall not be compelled to cover the fifteen miles," mused the younger of the brothers as much to himself as to the others. "I'm for pushing on, too." Laughing at their guest's discomfort, the others readily acquiesced, and they crossed the stream bottom. Save the noise made by themselves, the twitter of birds, and the occasional cry of some prairie dog routed out by their approach, the silence of the plains was intense. At first Tom and Larry did not notice it, but as they rode mile after mile they began to feel its depression. "It often drives men crazy," asserted the ranchman when Larry mentioned his feeling. "That's why we never send a man out alone to herd. Having some one to talk to it a big relief, I can tell you, after you've been a week or so on the prairies with nothing but a bunch of stolid cattle. The very monotony of their grazing and chewing their cuds gets on your nerves." As darkness came on, however, the awful silence was broken. From all sides came the barking of coyotes, as though they were signaling one another their whereabouts. "That howling would scare me a great deal quicker than any ghosts or witches," observed Tom. "My, but it's mournful! Do they keep that up all night?" "Indeed they do," replied Horace, delighted to think one thing had been discovered which the two visitors feared, "only it gets worse the darker it grows. Besides, when they are hungry, they'll follow you and attack you." "That wouldn't be so bad so long as you had a gun with you," interposed Larry. "I'd like to get a shot at one." "Then there's your chance, over on the left," exclaimed Mr. Wilder. Unslinging his rifle, the elder of the Alden boys looked eagerly in the direction indicated. But it was so dark he could see nothing and he said so. "Can't you see those two little balls of fire right opposite you? If you can't, say so. I'll stop him myself," returned the ranchman. Yet even as he spoke the coyote turned and fled. "It's just as well," added Mr. Wilder after he had announced the fact. "You'll have a chance to shoot at something better than a measely prairie wolf to-morrow, I hope." "Or perhaps to-night," chimed in Horace. "Maybe a ghost'll attack our camp." "That will do, youngster. If you talk any more about ghosts, I'll make you ride back to the ranch in the dark. If you keep on, you'll work yourself up so you'll think every sound you hear is a Spaniard from the mine, and there will be no sleep for any of us." This command had the desired effect, and Horace gave up the attempt of trying to frighten his friends.