“We’re on top of the safe-deposit vault,” he said.  “That’s why we didn’t fall all the way to the floor below.  I wonder how we’re going to get down?”

Estelle followed him, still frightened for fear of the building falling upon them.  Some of the long floor-boards stretched over the edge of the vault and rested on a tall, bronze grating that protected the approach to the massive strong-box.  Arthur tested them with his foot.

“They seem to be pretty solid,” he said tentatively.

His strength was coming back to him every moment.  He had been no more than stunned.  He walked out on the planking to the bronze grating and turned.

“If you don’t get dizzy, you might come on,” he said.  “We can swing down the grille here to the floor.”

Estelle followed gingerly and in a moment they were safely below.  The corridor was quite empty.

“When the crash came,” Estelle explained, her voice shaking with the reaction from her fear of a moment ago, “every one thought the building was coming to pieces, and ran out.  I’m afraid they’ve all run away.”

“They’ll be back in a little while,” Arthur said quietly.

They went along the big marble corridor to the same western door, out of which they had first gone to see the Indian village.  As they emerged into the sunlight they met a few of the people who had already recovered from their panic and were returning.

A crowd of respectable size gathered in a few moments, all still pale and shaken, but coming back to the building which was their refuge.  Arthur leaned wearily against the cold stone.  It seemed to vibrate under his touch.  He turned quickly to Estelle.

“Feel this,” he exclaimed.

She did so.

“I’ve been wondering what that rumble was,” she said.  “I’ve been hearing it ever since we landed here, but didn’t understand where it came from.”

“You hear a rumble?” Arthur asked, puzzled.  “I can’t hear anything.”

“It isn’t as loud as it was, but I hear it,” Estelle insisted.  “It’s very deep, like the lowest possible bass note of an organ.”

“You couldn’t hear the shrill whistle when we were coming here,” Arthur exclaimed suddenly, “and you can’t hear the squeak of a bat.  Of course your ears are pitched lower than usual, and you can hear sounds that are lower than I can hear.  Listen carefully.  Does it sound in the least like a liquid rushing through somewhere?”

“Y-yes,” said Estelle hesitatingly.  “Somehow, I don’t quite understand how, it gives me the impression of a tidal flow or something of that sort.”

Arthur rushed indoors.  When Estelle followed him she found him excitedly examining the marble floor about the base of the vault.

“It’s cracked,” he said excitedly.  “It’s cracked!  The vault rose all of an inch!”

Estelle looked and saw the cracks.

“What does that mean?”

“It means we’re going to get back where we belong,” Arthur cried jubilantly.  “It means I’m on the track of the whole trouble.  It means everything’s going to be all right.”