"That's evidence enough that there's a cave under the island, and the column of smoke shows that Mason and the valet have started a fire to cook their breakfast. When we get in, we are likely to find them at that occupation. Are you ready for the attempt?"

"Certainly," a.s.sented Young King Brady.

They walked over to the hut, and entered.

Nick had explained where the trap was located, and they soon found a cunningly hidden ring, and pulled it upward.

A door, covered with earth, was raised.

It revealed a flight of damp stone stairs.

The Bradys drew their pistols, got their dark lanterns ready for use, and descended the stairs for a distance of fifteen feet.

They found themselves in a big natural cavern, and as they flashed their lantern lights around in the gloom, a cry of the most intense astonishment burst from their lips.

CHAPTER XV.

THE PRISONER IN THE CAVE.

"Harry, this is the most astonishing place I ever was in in all my life."

"It certainly is wonderful, Old King Brady."

The detectives were gazing in amazement where the lights of their lanterns rested, and beheld a wonder of nature very seldom seen.

In the first place, they were in a huge cavern of circular shape.

The flight of stairs wound around one of the walls, and beside the bottom step there was a yawning hole in the ground fifty feet in diameter.

It seemed to go straight down into the earth.

Harry picked up a big stone and dropped it into the opening.

They listened intently, but failed to hear it strike bottom in the pit.

"This hole must be of enormous depth!" the boy exclaimed, "else we would have heard that stone hit the bottom."

"Look at the church organ rising up from the depths against that side of the abyss," said Old King Brady, pointing across the chasm.

His light rested upon a number of stalact.i.tes forming what looked exactly like the pipes of an enormous organ.

Beneath them was a bank of keys.

The silence of death prevailed.

Nature had wrought a wonderful formation there.

The entire interior of the cave was pure white, looking like camphor.

Huge pendants like great icicles hung from the ceiling, and similar formations rose from the floor.

In some cases the ends of the pendants nearly touched the points of the stalagmites rising from the bottom, and not a few were dropping pure, clear water, which formed little pools that ran in rivulets to the great well, and there vanished in the bowels of the earth.

It was quite cold there, yet there was a strong, fresh, invigorating taste to the air, which was agreeable to the lungs.

At various parts of the walls were other natural formations, and among them, in a niche, the figure of a woman holding a child.

"For beauty, the Mammoth Caves of Kentucky cannot compare with this place," said Young King Brady, in tones of delight.

"We are forgetting our object," said the old officer.

"True. But no one is in this place."

"Let us see if there are not adjoining caverns."

"Explore those openings in the wall."

He pointed at an arched aperture, and they crept into it on their hands and knees, and went ahead a dozen yards, then paused.

They were on the brink of another chasm.

A rift split the pa.s.sage in two crosswise.

It looked as if some convulsion of nature had ripped the earth apart, and they crept back to the main cavern and tried another opening.

It was possible to stand upright in this place.

The pa.s.sage wound and zigzagged.

Following it for some distance, they suddenly caught view of a lurid glare ahead as they turned an abrupt bend, and halted.

"Put out your light," whispered Old King Brady, in warning tones.

"See them?" asked the boy, complying.

"No, but they must have kindled that fire."

"Advance carefully now."

They got down on their hands and knees again, and went on to the spot where the pa.s.sage opened into a smaller cave.

Here the sight was prettier.

The floor, walls and ceiling were a delicate shade of pink, and the icicles formed many fantastic shapes that sparkled in the firelight.