_Fire damp._ Light carbureted hydrogen. _Fissure._ A separation of rock or coal across the measures. _Floor._ The upper surface of the stratum immediately underlying a coal seam. _Gangway._ An excavation or passageway, driven in the coal, at a slight grade, forming the base from which the other workings of the mine are begun. _Gas._ Fire damp. _Gob._ The refuse separated from the coal and left in the mine. _Guides._ Narrow vertical strips of timber at each side of the carriage way in shafts, to steady and guide the carriage in its upward or downward movement. _Gunboat._ A car used for hoisting coal on steep slopes. _Head-frame._ The frame erected at the head of a shaft to support the sheaves and hold the carriage. _Heading._ Synonymous with gangway. Any separate continuous passage used as a traveling way or as an airway. _Hopper._ A feeding shute or pocket in a breaker. _Horseback._ A small ridge in the roof or floor of a coal seam. _Inside slope._ An inclined plane in a mine, on which coal is hoisted from a lower to a higher level. _Jacket._ One of the sections or frames of wire mesh of which a revolving screen is made up. _Keeps._ Projections of wood or iron on which the carriage rests while it is in place at the head of the shaft. _Lagging._ Small timbers or planks driven in behind the legs and over the collars to give additional support to the sides and roof of the passage. _Legs._ The inclined sticks on which the collar rests in gangway, tunnel, drift, and slope timbering. _Lift._ All the workings driven from one level in a steep-pitching seam. _Loading place._ The lowest extremity of the breaker, where prepared coal is loaded into railway cars. _Lump coal._ The largest size of prepared anthracite. _Manway._ A passageway in or into the mine, used as a footway for workmen. _Mouth._ The opening, at the surface, of any way into the mines. _Needle._ An instrument used in blasting coal, with which a channel is formed through the tamping for the entrance of the squib. _Nut coal._ One of the regular sizes of bituminous coal. _Opening._ Any excavation in or into a mine. _Operator._ The person, firm, or corporation working a colliery. _Outcrop._ That portion of any geological stratum which appears at the surface. _Output._ The amount of coal produced from any mine, or from any area of country. _Parting._ The layer of slate or bony coal which separates two benches of a coal seam. _Pea coal._ One of the regular sizes of prepared anthracite. _Picking shute._ A shute in the breaker from which the pieces of slate are picked out by a boy as they pass down with the coal. _Pillar._ A column or body of coal left unmined to support the roof. _Pillar and breast._ The name of a common mining method. _Pinch._ See Crush. _Pitch._ See Dip. _Plane._ Any incline on which a track is laid for the purpose of lowering or hoisting coal.