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 hoarsely.

"To our gang?" he said. "The perfectly correct gentleman of the road
never has a '