"What is this?"
"It is the support that rested under the post holding up the old trap," answered the lad.
"Then—then——"
"Someone had sawed it partly through, so the support would give way and let someone else down. I happened to be the one who was let down."
The smile vanished from the eyes of the general superintendent and the lines of his face hardened perceptibly.
"How do you know this piece supported the post?"
"You will find the mark of the post on it. We fitted the post to the mark to make sure. Whoever did the job, entered the skip shaft from sub-level seventeen. I am sure of this, because I found fresh mud on the rungs of the ladder. No one is supposed to go down there, is he, sir?"
"No; no one does go down there. This is very serious. Why did not my men discover all these things?"
"I guess they did not look very sharply. The evidence was there to be found if one looked hard enough."