n up
them.

Out into the big auditorium they emerged, weak and faint, and toward
the hidden dirigible balloon they rushed.

"Quick!" cried Tom, as he climbed into the car, followed by Mr.
Damon and Eradicate. "Shove it right under the broken dome, Ned, and
I'll turn on the gas machine. It's partly inflated."

A moment later the balloon was right below the big opening. The blue
sky showed through it--a welcome sight to our friends. The hiss of
the gas was heard, and the bag distended still more.

"Hop in!" cried Tom. "She'll go up I guess."

"There they come!" shouted Ned, as he spoke the foremost of the
head-hunters emerged from the hole beneath the stone altar. He was
followed by Delazes.

"Stop them! Get them! Spear them!" cried the contractor. They
evidently thought our friends had all the gold from the underground
city.

Fortunately the temple was so large that the balloon was a good
distance from the hole leading to the tunnel, and before the
foremost of the head-hunters could reach it the dirigible began to
rise.

"If they throw their spears, and puncture the bag in many places
we're done for," murmured Tom. But evidently the savages did not
think of this, though Delazes screamed it at them.

Up went the balloon, and not a moment too soon, for one of the
head-hunters actually grabbed the edge of the car, and only let go when
he found himself being lifted off the temple floor.

Up and up it went and, as it was about to emerge from the broken
dome, Tom looked down and saw a curious sight.

Mr. Foger and Andy, who brought up in the rear of the pursuing and
attacking party, had just emerged from the hole by the great stone
altar when there suddenly spouted from the same opening a solid
column of water. A cry of wonder came from all as they saw the
strange sight. A veritable geyser was now spurting in the very
middle of the temple floor, and the head-hunters, the Mexicans and
the Fogers ran screaming to get out of the way.

"Look!" cried Ned. "What happened?"

"The underground river must be running the wrong way!" answered Tom,
as he prepared to set in motion the motor. "Either they accidentally
turned some hidden lever, or when they raised the stone door they
did it. The tunnel is flooded and--"

"Bless my match box! So is the underground city!" cried Mr. Damon.
"I guess we've seen the last of it and its gold. We were lucky to
escape with our lives, and these fellows might have been drowned
like r