hich led to the coast. At one
time in the history of the country one large glacier had completely
covered that section. But now, thousands of subordinate canyons and
hollows on the mountains were filled with independent masses of ice.

All that section of Alaska, from smoking Wrangell to the Pacific coast,
shows volcanic peaks. There are many dead craters, and some which are
not so dead! There are still peaks of fire as well as rivers of ice.

After the departure of the two boys, Will and the others devoted
considerable attention to the wounded lad. They did their best with the
simple means at hand, but never, for an instant, did the boy regain
consciousness.

"I don't think we can do anything for him until the surgeon comes," Will
said as he threw himself disconsolately into a chair.

"If we only knew whether he was forced to translate the code message for
the benefit of the man who robbed him," Sandy suggested, "there wouldn't
be so much doubt as to what course we ought to take."

"The code message," Will argued, "may change the whole scheme."

"Yes," Sandy complained, "and we won't know what to do until Frank comes
back with the duplicate."

"We won't know what to do then unless Will loosens up!" laughed George.

"Referring, of course," Sandy laughed, "to the prospective story of the
mark of the human thumb. Will was about to tell us all about it when we
saw the signals sent up by Frank."

"That's a fact," Will replied. "I didn't get any further than the
mention of the human thumb, did I?"

"We're waiting to hear the rest of it now!" declared Sandy.

"Well," Will began, "there was a safe robbed in Chicago one night, and
two men were accused of the crime. The accused men were in the employ of
the manufacturing concern whose safe was entered. They admit that they
were in the private office of the firm during the night, but they deny
that they opened the safe."

"Of course!" laughed George.

"Now don't form any hasty conclusions," Will went on. "There was a third
person in the office that night, according to the stories told by the
two men who are accused, but this third person says he wasn't there!"

"Then this third person may be the one who opened the safe."

"That is the theory of the defense," Will explained.

"But what's all this got to do with the mark of a man's right thumb?"
asked George.

"I'm coming to that," Will went on. "The three men who were in the
office that night--we are supposing