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, b.u.mping and sc.r.a.ping painfully in the darkness. Terror had deprived them of speech or the power of uttering a sound, or they would have shouted. As it was, however, when they finally landed in a heap on some hard surface at the foot of the steep declivity down which they had fallen, it was some seconds before any of them breathed a word. Then it was Jack who spoke.

"Fellows!"

"Yes, Jack." The rejoinder came out of the darkness in Walt Phelps'

voice.

"Ralph, are you there?"

"No; I'm dead. That is, I feel as if every bone in my body had been broken. What in the name of Old Nick has happened?"

"Thank goodness there are no bones broken," breathed Jack thankfully, as Ralph spoke, "as to what happened, you can take your own guess on it. My idea is that there was some sort of hinged trap-door at the bottom of that altar, and that when our combined weight came upon it at the time I pulled Ralph down, the blamed old thing tipped and dumped us down in here."

"That's my idea, too," chimed in Walt. "Can't account for it in any other way. But what is 'here'? Where are we?"

"You can answer that as well as I can," was the rejoinder. "Anybody got a match? Oh, here; all right, I've got some, plenty in fact--a whole pocketful."

Jack struck a lucifer, and as its yellow glare lit up their surroundings, they could not repress a cry of astonishment. They had landed at the foot of a steep flight of stairs, at the summit of which they correctly surmised was the trap-door through which they had been so startlingly dumped.

"Good gracious, did we fall down all those?" murmured Ralph, rubbing his elbow painfully.

"Guess so. I know I feel as if I'd been monkeying with a buzz-saw,"

same [Transcriber's note: came?] from Walt Phelps.

"Well, fellows," said Jack, as the light died out, "the question now before us is, what are we going to do?"

"Try to get out again," said the practical Walt Phelps.

"All right, Walt. Then we'd better remount those steps--slower than we came down them--and try to reopen that trap-door. We can't leave Pete and the injured professor like this."

The boys clambered up the steps without difficulty. They were deep and shallow, and were cut out of the living rock. At the head of the stairs, however, a disappointment awaited them. Try as they would, they could not discover any means of reopening the stone trap-door in the floor of the hollow altar. Apparently, after dumping them through, it had closed as hermetically as before.

The flickering light of the matches from Jack's store illuminated looks of despair on their faces as they realized that they were trapped.

"Try pounding on it and shouting," suggested Ralph.

Although Jack deemed it of little use, he and Walt followed this suggestion, and together the three boys beat and hammered on the ma.s.sive stone above them till their hands were raw. There was no response, however. Apparently the stone was too thick for a sound to penetrate to the outer air. Terror, that was almost panic, seized Walt and Ralph, as they realized that they were prisoners in this hermetically sealed dungeon. Worse than prisoners, in fact. Prisoners had food and at least hope. They, unless they could find a way out, were buried alive. Even Jack's stout heart experienced a deadly feeling of depression, as he realized this. He concealed his despair from his companions, however, and, with all the cheerfulness he could muster, addressed them in the darkness. Matches had now grown too precious to squander.

"Well, fellows, we've got to find another way out."

"Oh, it's no good," moaned Ralph despairingly, "we're doomed to die here. We might as well sit down and wait for death to come."

"Say," cut in Jack briskly, "if it was light enough to see, I'd give you a good licking. Doomed to die, indeed! Not much. It's a cinch, isn't it, that if there is an entrance to this place there must be an outlet, too? Very well, then," he hurried on, without waiting for an answer, "let's find that outlet."

The logic of this speech might be questioned, but of its good sense, under the circ.u.mstances, there was no doubt.

"You're right, Jack," said Ralph. "I'm ashamed of myself for doing the baby act. Come on, let's set out at once."

"That's the talk," said Walt heartily; "if there's a way out, we'll find it."

"And if not?" asked Ralph, his spirits flagging again.

"We'll discuss that later," declared Jack briskly.

Returning again to the landing--if such it might be called--upon which they had terminated their abrupt descent into the interior of the mesa, some more of the precious matches were lit. As the last flickered out, the boys fancied that some feet from them they could see a black mouth, like the entrance of a tunnel, or rather a continuation of the one into which they had been thrown.

"Come on, boys," exclaimed Jack. "It's the only thing to do. We can't turn back, and, as Pete says, 'there ain't nothing to do but go ahead.'"

Not without some misgivings did the three lads plunge forward in the darkness, feeling their way with outstretched hands as they entered the tunnel. A close, musty smell, as of things long mildewed and moulded, filled the air, and an oppressive silence lay on everything.

Unconsciously, since entering this place, their conversation had been all in whispers.

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 creva.s.se were illuminated by a feeble flame, he shrank back with a sharp intake of his breath.