"I guess we've got it doped out all right," Chester answered. "All we've got to do now is to go on and see whether we have or not."

The boys pressed on to the back of the first cavern and turned to the right into one which ran parallel with it. Their lights showed that a fire had been built in the tunnel connecting the two. There were also empty tin cans and cardboard food packages scattered about.

"This looks like population," grinned Will.

"Isn't this the spot from which the men disappeared?" asked Chester.

"Unless I am much mistaken," Will returned, "the three men were in front of a fire in this tunnel. Say, but they did get out of sight quick, didn't they? It was like the scene from the Black Crook."

"Then the pa.s.sage they crawled into can't be far away," Chester volunteered, "at any rate, right here's where we want to make our search!"

"There's no knowing where this wrinkle leads to," Will said as the lights pierced the narrow channel. "If we get down there, we may never be able to get back."

"Father must have known of this place," Chester said, "and that's why he talked about moving our camp here."

"Well, if he used the pa.s.sage, we certainly can!" replied Will.

"Are we going down now?" asked Chester.

"I'm game for it."

"Well, then, wait a minute!"

Chester ran to the entrance of the cavern and looked up and down the gorge and valley. When he returned there was a worried look on his face.

He pointed to the dry channel and said:

"We may as well be getting down there. There's some one coming."

"Who is it?" asked Will.

"I couldn't distinguish faces," was the reply.

"Wasn't George and Tommy, was it?"

"No, two men. They're coming along fast, so we may as well get under cover. We don't know where we're going, but we're on our way," he smiled as he dropped down on his hands and knees and scrambled backward into what had once been the channel of a mountain stream.

Will followed in a moment and, after trying his best to draw the boulder into place, scrambled on after his chum.

"Did you get the rock fixed?" asked Chester as they came together on a little level place probably thirty feet down.

"Couldn't budge it!" was the reply.

"Well, then, we'll keep on going."

"Je-rusalem!" exclaimed Will. "I believe this thing runs clear through the ridge. And that would make it something like a mile long!"

"Of course it does," Chester answered. "This ditch was cut by water, and the water had to find an outlet somewhere."

"If your father knows all about this underground network of caverns and channels," Will said in a moment, "we'll have a happy old time finding him! He can dodge us here for a month."

"And those officers will have a fine old job getting the train robbers, too," Chester chuckled, "if they're acquainted with this underground system of highways. It strikes me," he went on, "that these train robbers have been here before."

"That may be!" answered Will. "In fact, it, occurs to me that your father searched out all these subterranean roads and rooms and showed them to the train robbers."

The boys proceeded downward for some distance and then stopped in a tolerably large chamber to rest and investigate.

"There's no use of our going on until we know whether the fellows you saw are coming in here," Will reasoned.

"I'm going up to the top again," said Chester, "and see what's going on there! The fellows I saw may be coming in."

Will waited for a long half hour for the boy's return, and when at last Chester slid down to him his face showed that he was frightened.

"They've got the combination to this channel all right!" he said.

CHAPTER XVI

CULLEN LOSES HIS STAR

"So these are the detectives, are they?" asked one of the train robbers, as the two men crouched against the wall of the cavern.

"That's what they say!" answered Tommy.

"What were they doing to you?"

"They had us pinched."

"What for?"

"They said we belonged to your gang."

The bandit laughed hoa.r.s.ely.

"To our gang?" he said. "The perfectly correct gentleman of the road never has a 'gang'. He believes thoroughly in the old theory that 'he travels fastest who travels alone'."

"So they pinched you for being a.s.sociates of ours, did they?" asked the other outlaw.

"That's what they said," replied Tommy.

"And that was the truth, too!" roared Katz.

"You seem to know all about these boys, and they know all about you.

You've been seen at their camp, and one of the boys at the camp stole my property, too!" he went on with another roar of indignation.

"Chester stole his official star!" chuckled Tommy.