Without them there'd be more fires and explosions than there are.

And by each one there's a trapper, who's to open and close them as the pony drivers with their lurches that carry the mined coal to the hoists go in and out.

Easy work, ye'll say.

Aye--if a trapper did only what he was paid for doing.

He's not supposed to do ought else than open and close gates, and his orders are that he must never leave them.