Coal Mining, etc. Obs. [History obscure; app. connected with the continental words trap, trappe step: see prec. (Perh. introduced by foreign miners in 16th c.)] A ‘fault’ in a seam of coal, also in a mineral vein or in any stratum; an up-throw or down-throw of the stratum (usually trap-up or trap-down). (Cf. step-faults applied to a series of faults in the same direction.)
1719. Strachey, in Phil. Trans., XXX. 971. As … they are dug near the same Depth, it follows there must be a Trap, or several Traps down, which in all must amount to that Depth between the said Works.
1883. Gresley, Gloss. Coal-Mining, Trap-down [in Bristol Coal-field], a fault which is a down-throw one…. Trap-up, a fault which is an up-throw one.
Hence Trap v.3 in to trap up or down, to be found at a higher or lower level after dislocation by a dike or fault: see quots.; whence Trapping vbl. sb.
1719. Strachey, in Phil. Trans., XXX. 969. They observe, as they work to the South West, when they meet with a Ridg it Causeth the Coal to trap up, that is … they find it over their heads, when they are thro’ the Ridg: but … when they work thro’ a ridg to the North East, they say it traps down, that is, they find it under their feet.
1757. Da Costa, in Phil. Trans., L. 233. The heavings, displacings, trappings, and breaks of the metallic veins.
1811. W. Taylor, in Monthly Mag., XXXI. 448. Where there is a trapping down of the strata.
