Then both boys kept very quiet for a little while, and sure enough, over in the darkness, they heard an occasional snapping, like the breaking of dry twigs beneath the feet.
The process which the miners call “working” was going on. The pressure of the overlying mass of rock upon the pillars of coal left to support it was becoming so great that it could not be sustained, and the gradual yielding of the pillars to this enormous weight was being manifested by the crackling noises that proceeded from them, and the crumbling of tiny bits of coal from their bulging surfaces.
The sound of working pillars is familiar to frequenters of the mines, and is the well-known warning which precedes a fall. The remedy is to place wooden props beneath the roof for additional support, and, if this is not done, there comes a time, sooner or later, when the strained pillars suddenly give way, and the whole mass comes crashing down, to fill the gangways and chambers over an area as great as that through which the working extended, and to block the progress of mining for an indefinite time.
Tom had been too long about the mines to be ignorant of all this, and so had Bennie; but they knew, too, that the working often continued weeks, and sometimes months, before the fall would take place, though it might, indeed, come at any moment.
That afternoon Tom told the slope boss about the working, and he came and made an examination, and said he thought there was no immediate danger, but that he would give orders to have the extra propping of the place begun on the following day.
“Jimmie Travis said he seen rats goin’ out o’ the slope, though, when he come in,” said Tom, after relating to Bennie the opinion of the mine boss.
“Then ’twon’t be long,” replied Bennie, “’fore the fall comes.”
He was simply echoing the belief of all miners, that rats will leave a mine in which a fall is about to take place. Sailors have the same belief concerning a ship about to sink.
“An’ when the rats begin to go out,” added Bennie, “it’s time for men an’ boys to think about goin’ out too.”