Rib- The side of a pillar or the wall of an entry. The solid coal on the side of any underground passage. Same as rib pillar.

Rider- A thin seam of coal overlying a thicker one.

Ripper- A coal extraction machine that works by tearing the coal from the face.

Rob- To extract pillars of coal previously left for support.

Robbed out area- Describes that part of a mine from which the pillars have been removed.

Roll- (1) A high place in the bottom or a low place in the top of a mine passage, (2) a local thickening of roof or floor strata, causing thinning of a coal seam.

Roll protection- A framework, safety canopy, or similar protection for the operator when equipment overturns.

Roof- The stratum of rock or other material above a coal seam; the overhead surface of a coal working place. Same as "back" or "top."

Roof bolt- A long steel bolt driven into the roof of underground excavations to support the roof, preventing and limiting the extent of roof falls. The unit consists of the bolt (up to 4 feet long), steel plate, expansion shell, and pal nut. The use of roof bolts eliminates the need for timbering by fastening together, or "laminating," several weaker layers of roof strata to build a "beam."

Roof fall- A coal mine cave-in especially in permanent areas such as entries.

Roof jack- A screw- or pump-type hydraulic extension post made of steel and used as temporary roof support.

Roof sag- The sinking, bending, or curving of the roof, especially in the middle, from weight or pressure.

Roof stress- Unbalanced internal forces in the roof or sides, created when coal is extracted.

Roof support�C Posts, jacks, roof bolts and beams used to support the rock overlying a coal seam in an underground mine. A good roof support plan is part of mine safety and coal extraction.

Roof trusses- A combination of steel rods anchored into the roof to create zones of compression and tension forces and provide better support for weak roof and roof over wide areas.

Room and pillar mining�C A method of underground mining in which approximately half of the coal is left in place to support the roof of the active mining area. Large "pillars" are left while "rooms" of coal are extracted.

Room neck- The short passage from the entry into a room.

Round- Planned pattern of drill holes fired in sequence in tunneling, shaft sinking, or stopping. First the cut holes are fired, followed by relief, lifter, and rib holes.

Royalty- The payment of a certain stipulated sum on the mineral produced.

Rubbing surface- The total area (top, bottom, and sides) of an airw

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