The method of working coal-seams most commonly practiced in this country is known as the “room-and-pillar” system. One or more tunnels, or “entries,” are first driven from the bottom of the shaft or the mouth of the drift. These are the main thoroughfares of the mine, and are usually provided with tracks, over which the mine cars are hauled by mules or by some other method of traction--locomotives, endless chains, etc. Secondary entries (“headings,” “butt entries,” etc.) branch off from the main entries. Finally, the work of extracting the coal consists of excavating open spaces, or “rooms,” adjoining the entries. [Illustration: Courtesy of “Coal Age” MODEL COAL BREAKER Note the neat and careful “upkeep” of the place] The actual mining is done in the rooms, and different methods are in use. Anthracite is generally “shot from the solid”; that is, blasted out from the face of the coal without any preliminary cutting. This method is objectionable, especially in bituminous mines (where it is, however, much practiced), because the large charges of powder it requires produce a great deal of coal-dust and weaken the roof and pillars, often leading to falls of coal and fatal accidents. A better plan consists of “undercutting” the coal before it is blasted out. A long groove is made at the level of the floor, either with a pick or with a coal-cutting machine. Holes are then drilled some distance above the groove for the insertion of the blasting charges, and the coal is blasted down. A single shot will sometimes dislodge a ton or two of coal. The next step is to shovel the coal from the floor into a mine car, which is then pushed into the adjacent entry. The miner attaches a numbered tag to the car, so that he will be duly credited for his work, which is paid for by the ton. The loaded cars are eventually hoisted or hauled out of the mine, to be weighed and discharged above ground. The final step in working a coal-seam by the room-and-pillar method is to mine out the thick walls or pillars of coal, which are originally left between adjacent rooms to support the roof. As this work proceeds the worked-out sections are filled with waste rock, or the roof is allowed to fall. The object is to leave as little coal in the mine as possible, but practically it is rare that more than 60 or 70 per cent. is recovered.