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 rats in a trap, if they hadn’t followed us.  The underground city will never be discovered again.”

“And now for home!” cried Tom, when they had eaten and drunk sparingly until they should get back their strength, and had seen to their slight wounds.

“And our trip wasn’t altogether a failure,” said Mr. Damon.  “We’d have had more gold if the stone door hadn’t trapped us.  But I guess we have enough as it is.  I wonder how the Fogers ever found us?”

“They must have followed our trail, though how we’ll never know and they came up to where Delazes and his men were, joined forces with them, and hunted about until they found the temple,” remarked Tom.  “Then they saw the opening, went down, and found the stone door.”

“But how did they get it open? and what were they doing with the head-hunters, and why didn’t the head-hunters attack them?” Ned wanted to know.

“Well, I guess perhaps Delazes knew how to handle those head-hunters,” replied Tom.  “They may be a sort of lost tribe of Mexicans, and perhaps their ancestors centuries ago owned the city of gold.  At any rate I think some of them knew the secret of raising the door.”  And later Tom learned in a roundabout way from the Fogers that this was so.  The father and son had after much hardship joined forces with Delazes and he, by a promise of the heads of the party of our friends, and much tobacco, had gained the head-hunters as allies.

On and on sailed the balloon and our friends regained their strength after partaking of the nourishing food.  They looked at their store of gold and found it larger than they had thought.  Soon they left far behind them the great plain of the ruined temple, which, had they but known it was a lake now, for the underground river, perhaps by some break in the underground mechanism that controlled it, or a break in the channel, overflowed and covered temple, plain and underground city with water many fathoms deep.

“Are we going all the way home in the balloon?” asked Ned on the second day of their voyage in the air, when they had stopped to make slight repairs.