“We might as well go,” said Lambert, at last. “There won’t be anything more to see here for a good while. They’ve got to cut that groove about two feet deep all the way across the face before they can begin blasting again. You see, the bottom layer of coal is slaty, and the powder needed to blast it out would break the good coal above it into little bits. So they take out the good coal first. That’s just one of the tricks of the trade—there’s a thousand more.”
He was busy guiding her safely down the chamber, and Mr. Bayliss, left to his own devices, suddenly found himself stumbling wildly over the high caps in which the wooden rails of the track were laid. Lambert rescued him, laughing, and they reached the foot of the room just in time to see a driver-boy bring in his mule, hitch it to the loaded car, pull it out to the main track, and attach it to his trip. The door closed behind them instantly as they went out.
“What is the door for?” asked Miss Andrews.
“To keep the air-current from going along that entry. If it wasn’t closed, the current would take a shortcut through there back to the airway, and the rooms farther on wouldn’t get any. The door shuts off the in-current, and so the air doesn’t get to those rooms over there till it’s on its way out.”
“And how many of these rooms are there?”
“We’re working about thirty now.”
“With four men in each one?”
“Yes; there’s nearly a hundred and fifty men and boys at work. We’ve worked out about a hundred rooms to the right, here, drawn back the ribs, and closed them up.”
“‘Drawn back the ribs’?”
“Yes; you see, when the rooms are first opened we have to leave pillars about twelve feet thick between them to hold up the roof. Well, when the seam has been worked out to the limit, or as far as we can go profitably from the main entry, we take out these pillars, too, before we close up the working. That’s called ‘drawing back the ribs.’”