1/15 A FINAL THREAT. In the distance could be heard the crash of great charges of dynamite, by which the carboniferous rocks were blasted. Draughts of air rushed along the ventilating galleries, and the wooden swing-doors slammed beneath their violent gusts. In the lower tunnels, trains of trucks kept passing along at the rate of fifteen miles an hour, while at their approach electric bells warned the workmen to cower down in the refuge places. |