make themselves
heard above the now thunderous roaring of the strange noise.

A shout of surprise that rose even above the mysterious roaring,
followed the striking of the match. Beyond the turn the path took a
steep drop downward, and beyond that--the boys could hardly believe
their eyes as they gazed--was the glint of rushing water.

"The subterranean river!" was the amazed cry that broke from the lips
of all three.

CHAPTER X.

A NEW MEXICAN STYX.

"The subterranean river!"

The words echoed back weirdly from the vault-like chamber into which
they had now penetrated, and at the bottom of which the stream, upon
which the light of the match had glistened, flowed rapidly. Within
this spacious place the noise was not nearly so loud as it had been
when confined in the narrow tunnel, which, in fact, acted much as a
speaking-tube would have done.

"It can't be!" gasped Ralph, unwilling to believe his own eyes.

"But it is," cried Jack, as, all thoughts of their predicament
forgotten in this strange discovery, they made lavish use of their
matches on gaining the edge of the stream. The river was about twenty
feet in width, and they speedily saw that the roaring sound they had
heard during their progress through the tunnel was produced by a
waterfall some distance above, over which the river plunged into a sort
of basin at their feet.

But this was not the most astonishing thing they found in that first
brief but comprehensive inspection. Affixed to the rocky wall at one
side of the chamber was a large, bronze lamp. An eager overhauling of
the utensil showed it to be filled with oil, and apparently it was not
so very long since it had been lighted.

Hastily applying a match, Jack soon had the rocky chamber lighted, and
they could now survey the place into which they had blundered, at their
ease. In size it was about the same dimensions as the Council Hall of
the mesa, which lay, they knew not how many feet, above them. The
river roared down along one side of it, forming a deep, turbid pool
just beneath the waterfall, by which it entered the place.

To their astonishment, the boys now spied in one corner of the chamber
several empty boxes piled up. Remains of excelsior and sacking were
within them, and they bore the stencilled marks, "Agricultural
Machinery, With Care."

Instantly what Pete had related to him concerning the conversation of
the men accompanying Black Ramon flashed into Jack's mind.