The tunnel they were now traversing was bored on a pretty steep down grade. So steep, in fact, that Jack concluded, after about a quarter of an hour of slow and cautious traveling, that they must be below the level of the desert. For the last few minutes they had been conscious of a peculiar thing. This was that the silence of the tunnel had given place to a deep-throated roaring, not unlike the voice of a blast furnace. Where it came from, or what it was, they had no idea. It was a most peculiar sound, though, steady as a trade-wind, and seeming to fill the whole place with its deep vibrations.
"What can it be?" gasped Walt, as they paused by common consent to listen.
"Maybe the wind roaring by the entrance to this place," suggested Jack hopefully.
This thought gave them new courage, and, on Ralph's suggestion, Jack struck another match from his store. As it flared up, they all three recoiled with expressions of dismay.
At their very feet—so close that the tips of their boots almost projected over it—was a deep chasm. The black profundity of it loomed in front of them gapingly. A few paces more, and they would have been precipitated into the abyss. Jack, suppressing a shudder, leaned forward and held the match as far over the edge as he dared. As the depths of the great crevasse were illuminated by a feeble flame, he shrank back with a sharp intake of his breath.
[Illustration: As it flared up, they all three recoiled with
expressions of dismay. At their very feet was a deep chasm.]
The place was a charnel house!
No mystery now as to what had become of the human remains of the grisly sacrifices of the ancient mesa dwellers. There, piled in that dark chasm beneath them, were great piles of decaying bones and gleaming skulls. Hundreds of them extended toward the surface in a ghastly pyramid. No wonder the underground place into which they had penetrated smelled musty and unpleasant.