Jack and Ralph nodded agreement.

"On the other hand, if this river really leads out into Mexico, we can take the subway to freedom and then, when we emerge, find out the best thing to do. Maybe we can fall in with some government troops or authorities of some kind."

"But suppose the insurrectos are in power wherever this river comes out?"

The question came from Ralph.

"We'll have to take chances on that, I suppose."

"Hark!" came suddenly from Jack.

Far back somewhere in the tunnels they had threaded they could hear loud shouts and cries. The sound of the pursuit boomed out even above the noise of the waterfall.

"They're after us!" exclaimed Jack.

"Shall we take the boat?" Walt's usually calm voice shook a little as he asked the question.

"It's our only chance. Come on, in with you, Ralph."

Ralph hesitated no longer, but jumped into the little contrivance. A sort of oar lay in the bottom. He thrust it over the side.

"The water's only about three feet deep," he announced.

"So much the less chance of our being drowned," rejoined Jack.

The lad had his knife out--a heavy-bladed hunting weapon. As soon as all was ready he would cut the ropes and set the boat free on the turbulent current.

"All right!" cried Walt, as he clambered in and took his place by Ralph.

Jack gave a hasty look around, and the next instant made a flying leap into the little craft. So fast had Black Ramon and his followers taken up the trail after they had discovered that the boys had found the secret of the hollow altar, that they were already entering the chamber.

Ramon was in the lead. The glare of the lamp fell full on his parchment-like features, as with a roar of recognition, he sighted the boys.

Ping!

Something whizzed past Jack's ear, and, chipping the rock above, showered the occupants of the boat with fragments. The sharp report of the Mexican's revolver filled the place. With a quick movement, Jack slashed the rope nearest him. If he had not been in such a hurry, he would have seen that the other should have been severed first. As it was, he had cut the one that held the boat's bow to the stream.

Instantly the flat-bottomed craft swung dizzily around, and still held by her stern mooring, dashed against the bank.

For a minute the boys feared she was stove in, but there was no time to waste on an examination.

Slash!

One stroke of the knife severed the remaining rope, already drawn as taut as a piano wire. But, as Jack's knife fell, the place became filled with shouts and confusion.

Ramon had been a little in advance of his men, and now they were all in the place. A second's glance showed them what had happened. Not only were the boys about to escape, but if they did not stop them the secret of their underground route across the border would be discovered, and its usefulness at an end.

No wonder they strained every nerve to reach the boys. Ramon himself had bounded to the side of the subterranean river as the boat swung round. As her gunwale had struck the bank, he had leaped aboard. But before he could use his revolver, Walt's powerful arm knocked the weapon out of his hand, and it fell on the bottom of the boat. With a snarl of rage, Ramon flashed round on the boy. But whatever the Mexican might have been able to do with knife or pistol, he was no match for the muscles of the American lad.

Walt fairly picked the lithe form of the gun-runner from the floor of the boat as Jack's knife fell across the remaining rope. With a splash and a loud cry, Ramon pitched overside into the stream. As he fell, though, he managed to clutch the side of the craft and he hung on, desperately endeavoring to draw himself up into the boat.

His followers, seeing what had happened, rushed down on them. A tempest of bullets rattled about the boys' heads as they felt the rope part. It was no moment for sentimental hesitation. Walt raised his foot, and the next instant brought his heavy boot down with crushing force on Ramon's clinging fingers.

With a yelp of pain, the fellow let go and was rolled over and over in the river, while half a dozen of his men waded in to rescue him.

"Yip-ee-ee-ee! We're off!" yelled Jack, with a true cowboy yell. The lad was carried away by the excitement and thrill of the adventure.

With a lurch and a b.u.mp, the frail craft carrying our three young friends shot forward. The lamp-lit panorama as Ramon, dripping and cursing, was hauled out of the water by his band, flashed before their eyes for a brief moment. The next instant dense darkness fell about them.

At what seemed to be a mile-a-minute pace they were hurried forward into the unknown.

CHAPTER XI.

THE CAMP OF THE GUN-RUNNER

Jounced against the rough, rock walls, b.u.mped over shoal places, and at times whirled almost broadside on by the swift current, the queer, flat-bottomed boat containing our three young friends was hurried through the darkness. It was the maddest ride any of them had ever taken, and, as we know, they had been through some thrilling experiences since they had first stood on the railroad station platform at Maguez. Had they known it, they could have controlled the boat more or less with the rough oar--the one with which Ralph had sounded the depth of the river--but, of course, they were inexpert in the management of such a craft. They could do nothing but keep still and trust to luck to bring them safely out of their extraordinary predicament.

After some ten minutes of this, the current seemed to slacken a little and the walls narrowed. Jack stretched out a hand and, to his astonishment, his fingers were swept along a rope stretched down the side of the tunnel. This solved a problem he had been revolving in his mind--namely, how did the Mexicans get their boat back after it had delivered its cargo of arms? The explanation was now a simple one.

Evidently they hauled it back by the use of this rope. "It must have been hard work, though," thought Jack.

Conversation was impossible in the confines of the tunnel which, in places, was a mere tube in the rocks; the roar of the water was almost deafening. It was so black, too, that they could not see one another's faces. Of real alarm Jack did not feel much, and for an excellent reason. It was apparent that the Mexicans had used this underground route across the border many times, and, if they could make the pa.s.sage--terrifying as it seemed--in safety, there was every reason to suppose that the boys could make it with the same security.

What worried Jack most about their situation proceeded from a far different cause. There was little reason to doubt that at the other end of the tunnel, wherever that might be, Black Ramon or his superiors, arming the insurrectionists, had guards posted to receive the smuggled guns. If no opportunity of escaping from the boat presented itself before they were hastened out of the exit of the tunnel, their situation would be just as bad as ever. Ramon would, of course, lose no time in following them up, either by a spare boat, which he might have had concealed in the vaulted chamber, or else on his fast, coal-black horse which he might ride across the rocky range, far above the subterranean stream.

In the event of their falling once more into the hands of Ramon, Jack could not repress a shudder as he thought of what the probable fate would be. Ugly stories had from time to time floated across the border concerning the manner in which Ramon, in his cattle-rustling days, dealt with his prisoners,--stories of torture and suffering that made one shudder even to listen to. If the apparent leader of the insurrectionist gun-runners had cause for animosity against the boys before, it was surely redoubled now. Not only had they accidentally penetrated the secret of the Haunted Mesa, but they had toppled the former leader of the cattle-rustlers ignominiously into the water, an insult which Jack knew the man's nature too well to suppose he would easily either forgive or forget.

In such gloomy reflections was he occupied when a sudden shout from the others roused him from his reverie, and, looking up, he saw that the tunnel through which the river flowed was growing higher, broader, and lighter. The darkness had now been exchanged for a sort of semi-gloom, in which the almost black rock gleamed wetly where the hurrying current of the stream had washed its base.

"We're near the end!" shouted Walt to the others.

Jack nodded. Suddenly his eye fell on Ramon's revolver, which lay at the bottom of the boat as it had fallen when he toppled overboard. One cartridge had been discharged, leaving but four good sh.e.l.ls in the chamber, but in an emergency those four, the lad knew, would be better than no weapons at all. He regarded this as distinctly a piece of good luck--this finding of the pistol. He examined it and found that it was a heavy weapon of forty-four caliber.

Hardly had he had time to observe all this before the boat, without the slightest warning, shot out into daylight, very much as a railroad train emerges from a tunnel. A swift glance at their surroundings showed Jack that they had floated into a sort of natural basin amid some wild, bare-looking hills. The banks of this basin were clothed with a sort of wild oat and interspersed with a small blue wild flower.

Here and there were clumps of chapparal. But what pleased the lad most was the fact that, although not far from them a rude hut stood upon the bank, there was so far no sign of human occupancy of the place.

Seizing the steering oar, Jack ran the boat up alongside a spot where the bank shelved gently down to the water's edge, and ran her, nose up, on the sand.

"Hoo----" began Ralph jubilantly, his spirits carrying him away, but Jack's hand was over his mouth in a second.

"The less noise we make the better," he breathed, stepping out of the boat on tiptoe and signing to the others to do the same. With scarcely a sound, they landed and stood at length on the gra.s.sy carpet sloping down to the sandy beach.

So far not a sound had proceeded from the hut Jack turned to his companions with a cautious gesture.

"Wait here while I investigate," he whispered, "and be ready to jump back into the boat and shove off at a minute's notice."

They nodded and turned to obey, as Jack, as silently as he could, crept on toward the hut, his revolver clasped ready for use at the slightest alarm. The Border Boy did not mean to be caught napping. In this manner he reached the wall of the hut nearest to the river, in which there was a small, unglazed window. Cautiously raising himself on tiptoe, Jack peered within.