"Just my way of looking at it," agreed Phil. "It's a regular hide-and-seek game, this locating a mine among these rocks." For a long time the three boys sat by themselves, talking about days at Oak Hall, and about the folks left at home and about those now traveling through Yellowstone Park. It seemed a long time since they had received letters. "I suppose there are letters at the hotel in Butte," said Dave, with a little sigh. "I'd give something to have them here," added Phil. "If only I knew how dad was making out," murmured the senator's son. "I suppose he is waiting every day to hear from me!" "I hope the folks in the Park are having a good time," said Dave, after a pause. "I suppose the main body of tourists have started for home by now." "Yes, they went yesterday, according to the advertised plan," answered Phil. "I've got an idea," said our hero, after another pause. "Do you see that hollow just below here? Well, we haven't looked around that much. Why not try it to-morrow?" "Abe Blower and Mr. Dillon both seem to think the opening to the mine was above that, Dave," said Roger. "True, but the landslide changed things, remember. We may now find an opening down there,--not the opening your uncle made, but another, made by the slide." "It won't do any harm to look down there. While we are here I am going to look in every spot I can reach." "Sure thing!" cried Phil. "But say, if we are going to climb around these rocks all day to-morrow I am going to bed and get a good night's rest." "I guess we all need a rest, so we'll turn in at once," answered Roger. Their camp was located between the rocks and not far from the trail by which they had come to the vicinity. The horses were tethered at a point where a patch of coarse undergrowth gave them something to nibble at. The animals were of no use to them, now they were in the district where the lost mine was supposed to be located. It was a little after nine o'clock when the boys turned in, and a few minutes later the two old miners followed them. So far they had not deemed it necessary to have a guard, for none of their enemies nor wild beasts had come to annoy them. Roger and Phil were soon sound asleep, and it was not long before their snoring told that Abe Blower and Tom Dillon were likewise in the land of dreams. But Dave, for some reason he could not explain, was restless, and he turned over several times, sighing heavily. "If I were at home I should say I had eaten too much supper," he told himself. "But here rations are too scarce. I don't know what keeps me awake, unless it is that I'm too tired to go to sleep." The campfire had burned so low that the spot was almost in total darkness. There was no moon and only a few stars shone in the sky, which was partly obscured by clouds. A gentle breeze was stirring, but otherwise all was quiet.