When the channel has been cut a sufficient depth and distance the coal above it is brought down either by wedging or blasting. If blasting is to be resorted to it will be unnecessary to cut the vertical groove. If the bearing-in channel was cut above the floor, the bottom coal is then lifted by wedging, and broken up. The miners do the cutting and blasting, the laborers break up the coal and load it into the mine wagons, and the scraper is kept busy cleaning the cuttings away from the channels and attending to the lamps. The mine car track that is extended up into the room is of wooden rails, and the empty wagon is pushed in to the face by the laborers, and loaded and run out by them to the entry. Each wagon will hold a little more than a ton, and a mule will draw four wagons to the mouth of the drift. The wheels of the mine car are set close to each other, near the middle of the car, to facilitate its movement around sharp curves; the doors at the ends of the car are swung from a bar hinge at the top, and the cars are dumped in the same manner as those in the anthracite region. In some of the bituminous mines a small locomotive is used to draw the trains of mine wagons from the working parts of the mine to the opening. It will draw from twelve to sixteen wagons at a time, and will do the work of twenty mules. There is usually a separate split of the air current to supply the locomotive road in order to keep the smoke out of the working rooms. When a set of rooms has been driven to its limit the miners then “draw back the rib;” that is, take out the pillars between the rooms, beginning at the face and working back. Posts must be used freely to support the roof while this work is in progress, about sixty or seventy being necessary in drawing a rib. Ventilation here is obtained by both the fan and the furnace systems. In mines that are worked below water level fire damp often accumulates, but where the coal does not descend at any point below the water-level line, there is no probability that mine gases will be found.