"Pile into the next car, then. We'll send it through without any ore this time. There would not be room if we were to load the car. I think it will be a novel experience for you."

And Tom Phipps smiled significantly.

Directing the switch man to shift the car back to the return track, the mining engineer told the lads to climb in and sit down on the floor, which they did promptly.

Only the tops of their heads projected above the sides of the ore car.

"Under no circ.u.mstances must any of you straighten up unless you wish to get your heads smashed."

"Why, there is plenty of room for our heads here," replied Ned. "We could stand up and yet have some to spare."

"Right here, yes. We shall go through some places that you would not want to stand through, I imagine."

"Are you ready?"

"Yes."

Tom Phipps climbed over into the car.

"All right, Jim," he called.

Immediately the car began to move and in a few moments had attained a high rate of speed.

"Now, boys, remember your heads," cautioned their guide.

Instinctively each crouched lower as their vehicle was all at once plunged into sudden darkness. Drops of water now and then spattered down on their bare heads. The noise of the car in the dark was deafening. The sound was as if many ore cars instead of one were crashing through the dark tunnel. The lads experienced a strange thrill when the realization came to them with its full force, that they were shooting through the earth, far beneath the surface at the speed of an express train.

"Why don't you have lights in here?" asked one of the pa.s.sengers.

"Not necessary," said Mr. Phipps. "It is seldom that anyone has occasion to go through this tunnel--practically never unless something happens to a car in here. There are lights along that may be turned on if necessary, but it would be a needless expense to keep them going all the time--"

"What's that loud noise?" asked Tad.

His ears had caught a booming roar that was a new note in the terrifying sounds of the underworld through which they were traveling.

The boys started uneasily.

"It's water," shouted the guide. "A cataract in an underground water course. These courses have cut channels all through the limestone rocks in the Ozark Uplift."

This somewhat calmed the nerves of the lads, though not wholly so.

Faster and faster rolled the car and louder and louder grew the roar of the cataract.

"Are we almost out of here?" demanded Walter uneasily.

"Yes. We shall be clear of it in five or six minutes now. You notice that we strike little grades occasionally, which cause the car to slow down considerably and for that reason the journey seems longer than it really is."

"If we have slowed down at any time I have failed to observe it,"

laughed Tad.

"What if we should jump the track in here?" suddenly suggested Ned.

"But we won't," answered the guide. "We--"

A grinding, crunching sound cut short his words. The car appeared to pause and tremble throughout the length of its frame; then followed a deafening crash, accompanied by the sound of breaking timbers and splintering wood.

A deep silence, broken only by the roar of the cataract, settled over the scene. The ore car lay a broken, twisted, hopeless wreck.

CHAPTER XX

A MESSAGE THAT THRILLED

Out of the silence came the voice of Ned Rector.

"Help, I'm pinned down," he groaned. "Get me out of this awful hole."

"I'm coming as soon as I can get free of what's on top of me,"

answered Tad. "Is everybody else all right? W-a-l-t! Mr.

Phi-ipp-s!"

Tad struggled desperately and in a brief time succeeded in freeing himself. What had happened to the guide and to Walter he did not dare to think.

First upon getting clear of the obstruction that pinned him down, he rushed to Ned Rector and succeeded in releasing him without great difficulty. Neither boy was hurt much.

"Where's the other two?" cried Tad in a voice of anxiety.

"I don't know. Don't know where I am myself," groaned Ned.

"Hurry, help me find them."

Together the boys groped about in the black tunnel.

"I've got one," called Ned.

"Which one?"

"I don't know. Yes, yes, it's Walt. He's breathing. What shall I do?"

"Drag him over to one side. I've got Mr. Phipps here. I'll have him over there in a minute."

Tad began tugging, with hands under the shoulders of the guide, understanding instinctively that he must get him where they could work over him and try to bring him back to consciousness.

Something whizzed by in the darkness, the rush of air nearly knocking both boys over, and leaving them trying to catch their breaths.

"Wh--what's that?" gasped Ned.