"Yes," rejoined Walt with a shudder, "and but for Providence, we should
have plunged downward into it ourselves."

"Ugh!" exclaimed Jack, in a voice filled with repulsion. "Don't let's
think of it. See, the path takes a turn here. Come on, let's go
ahead, but follow me closely and keep in to the wall."

"Not likely to take any chances of missing the road, after seeing
that," spoke up Walt, as once more the three youths, who had been so
strangely plunged into this predicament, began to tread the
subterranean regions once more.

As you may imagine, they went with due caution. But no more dangers
menaced them, and as they progressed the path began to widen. All the
time, however, the strange roaring sound had been growing louder, until
now it had attained almost deafening proportions. Still they had come
upon no explanation of what it could be. Jack had privately concluded
it to be the sound of the wind, forcing its way into some crevice.
This theory seemed to be the more tenable as the last match which he
had struck had only been kept alight with difficulty, so strong had
been the draught that now puffed up toward them.

Far from alarming them, however, this gave them renewed hope. It meant
that, in all probability, they were nearing an outlet of the strange
underground place. Had it not been for the predicament in which they
had left the professor and Coyote Pete, the three lads would have felt
a real interest in exploring the cavern, now that they had grown
accustomed to their surroundings. So far as they had been able to make
out, the tunnel they had been treading was partially the work of human
hands and partially the work of Nature. The great rift in which lay
the accumulation of human remains was evidently the result of some
volcanic upheaval. The path, however, was so graded and formed that
there seemed no reason to doubt that it had, at one time, been made by
the ancient mesa dwellers.

"Seems to me we ought to find out what that roaring sound means before
we go any farther," suggested Ralph suddenly.

"That's a fine Irish bull," laughed Jack. "How are we going to find
what it is unless we do go farther?"

"That's so," agreed Ralph, somewhat abashed. "Come on, then."

A few paces more brought them to an abrupt turn in the path, as they
could feel by their constant touching of the inner wall.

"Better strike another match," said Walt.

"Yes; here goes," agreed Jack. Both boys shouted, to