the experiment, and Mr. Damon and Eradicate went with Tom and Ned. It was no easy work to make their way over the ruins to the inner auditorium. Wreckage and ruin was all around, and they had to avoid the yawning holes on every side. But when they got to the main, or sacrificial chamber, as Ned insisted on calling it, they found the floor there solid. In the centre was a great altar, but to their chagrin there was not a sign of a tunnel opening.
"Fooled again!" said Tom bitterly.
"Maybe some of those holes outside is the entrance," suggested Mr. Damon.
"I don't believe so," objected Tom. "They seemed to go only to the cellar, if a temple has such a thing."
Bitterly disappointed, Tom strolled over and stood in front of the big stone altar. It seemed that he must give up the search. Idly he looked at the sacrificial stone. Projecting from it was a sort of a handle.
Tom took hold of it, and to his surprise he found that it could be moved. Hardly knowing what he was doing, he pulled it toward him.
The next instant he uttered a cry of horror, for the immense stone altar, with a dull rumbling, rolled back as though on wheels, and there, over where it had stood was a hole of yawning black-
