Emily Dickinson Lexicon

TRAP, n.² [Sw. trappa, Dan. trappe, a stair or stairs.]

In mineralogy, a name given to rocks characterized by a columnar form, or whose strata or beds have the form of steps or a series of stairs. Kirwan gives this name to two families of basalt. It is now employed to designate a rock or aggregate in which hornblend predominates, but it conveys no definite idea of any one species; and under this term are comprehended hornblend, hornblend slate, greenstone, greenstone slate, amygdaloid, basalt, wacky, clinkstone, porphyry, and perhaps hypersthene rock, augite rock, and some varieties of sienite. Cleaveland.