Shaft- A primary vertical or non-vertical opening through mine strata used for ventilation or drainage and/or for hoisting of personnel or materials; connects the surface with underground workings.

Shaft mine�C An underground mine in which the main entry or access is by means of a vertical shaft.

Shale- A rock formed by consolidation of clay, mud, or silt, having a laminated structure and composed of minerals essentially unaltered since deposition.

Shearer- A mining machine for longwall faces that uses a rotating action to "shear" the material from the face as it progresses along the face.

Shift- The number of hours or the part of any day worked.

Shortwall�C An underground mining method in which small areas are worked (15 to 150 feet) by a continuous miner in conjunction with the use of hydraulic roof supports.

Shuttle car�C A self-discharging truck, generally with rubber tires or caterpillar-type treads, used for receiving coal from the loading or mining machine and transferring it to an underground loading point, mine railway or belt conveyor system.

Sinking- The process by which a shaft is driven.

Skid- A track-mounted vehicle used to hold trips or cars from running out of control. Also it is a flat-bottom personnel or equipment carrier used in low coal.

Skip- A car being hoisted from a slope or shaft.

Slack- Small coal; the finest-sized soft coal, usually less than one inch in diameter.

Slag- The waste product of the process of smelting.

Slate- A miner's term for any shale or slate accompanying coal. Geologically, it is a dense, fine-textured, metamorphic rock, which has excellent parallel cleavage so that it breaks into thin plates or pencil-like shapes.

Slate bar- The proper long-handled tool used to pry down loose and hazardous material from roof, face, and ribs.

Slickenside- A smooth, striated, polished surface produced on rock by friction.

Slip- A fault. A smooth joint or crack where the strata have moved on each other.

Slope- Primary inclined opening, connection the surface with the underground workings.

Slope mine�C An underground mine with an opening that slopes upward or downward to the coal seam.

Sloughing- The slow crumbling and falling away of material from roof, rib, and face.

Solid- Mineral that has not been undermined, sheared out, or otherwise prepared for blasting.

Sounding- Knocking on a roof to see whether it is sound and safe to work under.

Spad�C A spad is a flat spike hammered into a wooden plug anchored in a hole drilled i

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