"I thought so," he said softly. "I thought I saw something there the other day, but the sand fell in and hid it. I didn't know the old-timers went in for subways in Little Rhyolite." And Rawson looked as did Smithy, in wondering amazement, at the roughly round opening in the sand, a tunnel mouth, driven through the shifting sands--a tunnel, if Rawson was any judge, lined with brown glistening glass. Understanding came quickly. "The jet of flame!" he exclaimed half under his breath. "They melted their way through; the sand turned to glass; they held it some way for an instant while it hardened." He walked cautiously toward the dark entrance and peered inside. Darkness but for the nearer glinting reflections from walls that had once been molten and dripping. The tunnel dipped down at a slight angle, then straightened off horizontally. Rawson could have stood upright in it with easily another two feet of headroom to spare. "And that," said Smithy, "is how the dirty rats got over to the camp. Like moles in their runway. No wonder they could pop up from nowhere. But, Dean, old man, I'm thinkin' we're up against something we haven't dared speak of to each other. Don't tell me that it's just men we've got to meet--" "Wait," Rawson begged in a hushed whisper. "Wait till we know. That's why I didn't dare go out without something definite to report. We'll go up--but not here. We'll get a line on this up top." * * * * * He led the way from the crumbling walls and skirted the mountain's base to the place where he had climbed before. And, with the help of a supporting arm at times, he found himself again in the great cleft in the rocks. Darkness now made the passageway a place of somber shadows. The broad cupped crater lay beyond in silent waiting; the vast sand-filled pit seemed, under the starlight, to have been only that instant cooled. The twisted rocks that formed the rim had been caught in the very instant of their tortures and frozen to deep silence and eternal death: the black masses of tufa, protruding from the packed ashy sand might have been buried by the smothering mass but a moment before. It was a place of death, a place where nothing moved--until again the breeze that whirled gustily over the saw-tooth crags snatched at the sand in that lowest pit and drew it up in a spiral of dust. The word was on Rawson's lips. "Dust--dust in the crater. Fool! I said I could read sign; I thought I was a desert man." "Dust? And why shouldn't there be dust? How do you usually have your volcanoes arranged, old man?" "Fine dust!" Rawson interrupted in the same whisper. He was glancing sharply about him as if in fear of being overheard. "See, the wind is blowing it. Coarse sand and pumice--that's to be expected; but light dust in a place that the winds have been sweeping for the last million years! I don't have them arranged that way, Smithy--not unless the sand has been recently disturbed!"