"That was all covered up before," Garry stated; "buried for thousands of years, I suppose. But it can't be a cave; not a natural one, at least. There are no caves in this rock." He stopped at times for breath, and his wonder grew as he climbed and the black mark took clearer form. At last he stood panting before it, to stare deep into the utter blackness of a passageway beyond an entrance of carved stone. It was carved; there was no mistaking it! Here was a passage that nature had never formed. He took a quick stride forward to see the tool marks that showed on hard walls where symbols and figures of strange design were carved. An intrusion of harder rock had formed a roof, and they had cut in below-- "They!" He spoke the word aloud. Who were "they?" * * * * * He remembered the scientist who had stopped at the ranch some time before, and he recalled enough of the talk of Aztec and Toltec and Mayas to know that none of these old civilizations could explain the things he saw. "This goes way back beyond them--it must," he reasoned. And there were pictures, long forgotten, that came to his mind to show him a vision from the past--figures whose coppery faces shone dark above their brilliant, colored robes--slaves, toiling and sweating to drive this tunnel into solid rock. He was suddenly a-quiver with a feeling of the presence of living things. His breath seemed stifled within him as he stepped into the dark where a pencil of light from his pocket-flash made the blackness more intense. He tried to shake off the feeling, but an indefinable oppression was heavy upon him; the weight of the uncounted centuries these walls had seen filled him with strange forebodings. His feet stumbled and scuffed over chips of stone; he steadied himself against the wall at times as he followed the corridor that went down and still down before him. It turned and twisted, then leveled off at last, and Garry Connell drew himself up sharply with a quick-drawn breath. His flash was making a circle of light a dozen steps ahead, and showed a litter of sharp stone fragments. And, scattered over them, a tangle of bones shone white; one skull stood upright to stare mockingly from hollow sockets. The sudden white of them was startling in the black pit. "Bones!" he said, and forced himself to disregard the echoes that tried to shout him down; "just bones! And the old-timers that wore them haven't been using them for thousands of years." He moved forward with determined steps to the end of the passage that finished in solid stone. He stopped abruptly. At closer range was something that froze him to a tense, waiting crouch. This wall of solid stone--it was not solid as it had seemed. There was a doorway; the stone was swung inward; and at one side in a straight-marked crack, he saw a thread of light.