they sank into absolute silence. The three boys
crouched at one end of the hollow altar, the professor and Coyote Pete
bundled together into as small a space as possible at the other.

Voices, conversing in Spanish, could now be heard, and, from the
inflection, the boys judged that whoever was talking was very much
astonished over something.

"I recognize that voice," said Jack suddenly, in a low whisper, "it's
Ramon de Barros."

The other two boys nodded. Ralph Stetson's heart beat so hard and fast
that it fairly shook his frame. Truly the predicament of the party was
a terrible one. Discovery by as wolf-hearted a band of ruffians--if
they were all like their leader--as ever infested the border, was
inevitable within the next few minutes. Taking into consideration
their connection with Black Ramon in the past, it was unlikely in the
extreme that any mercy would be shown them. Never had any of them
looked so closely into the dark face of danger.

Suddenly the listeners, crouching in their hiding-place, heard a shout
of astonishment from the Mexicans.

"They've seen our camp over the edge of the mesa!" exclaimed Pete in a
low, tense voice; "in another minute they'll start looking for us."

As he spoke, the voice which Jack had recognized as Black Ramon's,
uttered a crisp, curt command of some sort. The lads could hear
footsteps hurrying hither and thither. Without doubt, the order that
meant their probable doom had just been given.

"I can't stand this a minute longer," cried Ralph suddenly. The boy's
eyes were blazing wildly. Clenching his fist, he sprang to his feet.

"Come back here, you blockhead," snapped Jack, tugging his friend down.
Ralph came backward sprawling, and landed in a heap in Jack's lap,
knocking Walt Phelps with him. Together the three boys were tangled in
a struggling heap.

"Get up," whispered Jack. "They'll hear us. You----"

He stopped short. All at once an astonishing--an incredible thing--had
happened. The floor beneath them,--the solid floor, as it had
seemed,--began to tremble.

Before any of the amazed lads could utter a word, the foundation upon
which they rested tipped, and, with a loud, ringing cry of terror from
Ralph, they were plunged out of the sunlight into blackness as
impenetrable as the pocket of Erebus.

CHAPTER IX.

IN THE MESA DWELLERS' BURIAL GROUND.

Down, down, they plunged, bumping and scraping painfully in the
darkness. Terror had de