A close examination of the floor revealed no marks save those put there by the treasure-hunter’s knife.

“This house seems to be built on the solid ground.  I do not think you will find anything under it,” protested the Professor.

“There are houses under every one of these buildings,” answered Mr. Marquand.  He held a short, keen edged bar in place, while Kris Kringle swung the maul.  Gradually they cut a ring about two feet in diameter about the cross.  The material of which the floor had been made had been tempered with the years and was almost as hard as flint.

The steady thud of the heavy maul, accompanied by the click, click of the cutting bar, the dim light, the silent, expectant faces, formed a weird picture in this silent desert place.

After a full half hour of this the two men paused, and stood back, drawing sleeves across their foreheads to wipe away the perspiration.

Stacy Brown walked pompously over to the circle.

“Maybe I can fall through it.  If I can’t, nobody can,” he said, jumping up and down on the spot where they had been cutting.

There followed a rambling sound, and with a yell, Stacy Brown suddenly disappeared from sight.  In place of the circle in which he had been standing was a black, ragged hole, from which particles of the mortar were still crumbling and rattling to the bottom of the pit.

“Are you there?” cried Kris Kringle, leaping to the spot, thrusting the lantern down through the opening.  “Master Stacy!”

“Wow!” responded the boy from the depths.

“Did it hurt you?”

“How far did you fall?”

This and other questions were hurled at the fat boy, as his companions crowded about the opening.

“I’m killed.  That’ll answer all your questions,” replied Stacy.  “Hurry up!  Get my remains out of this place.”

The rays of the lantern disclosed a short stairway, built of the same material of which the house itself had been constructed.

Mr. Marquand forced himself past the guide and was down the steps in a twinkling.  He was followed by the wondering Pony Rider Boys, Professor Zepplin and Kris Kringle in short order, for all crowded down through the narrow opening.

Chunky had hit the top step and rolled all the way down.  He had scrambled to his feet and was rubbing his shins by the time his friends reached him.  His clothes were torn and he was covered with dust.

“Fell down the cellar, didn’t I?” he grinned.

But no one gave any heed to him now.  Mr. Marquand had snatched at the lantern and was running from point to point of the chamber in which they found themselves.  He was laboring under great excitement.

“Here’s another opening,” he shouted.  “We haven’t got to the bottom yet.”

Another flight of stairs led to still another and smaller chamber below.  Mr. Marquand let out a yell the moment he reached the bottom.  The others rushed pell-mell after him.