Min. Also 8 trapp. [a. Swed. trapp (Bergman, 1766), so named from the stair-like appearance often presented by the rock, f. trappa stair: see TRAP sb.3] A dark-colored igneous rock more or less columnar in structure: now extended to include all igneous rocks that are neither granitic nor of recent volcanic formation.
[1794. Sullivan, View Nat., II. 165. This is what the Swedes call trapp, or trapas, from stairs.)
1794. Schmeisser, Syst. Mineral., I. 184. Trapp…. Its name originates from the Swedish language. The term trapp describes a stone, which breaks in pieces of a rhomboidal figure, and consequently exhibits … steps like a stair case.
1796. Kirwan, Elem. Min. (ed. 2), I. 227. Common Trap. Basalt or Werner.
1811. Pinkerton, Petralogy, I. 62. The volcanic eruptions, which are supposed to have produced the mountains of trap.
1863. A. C. Ramsay, Phys. Geog., ix. (1878), 124. The rocks are pierced by ., a white felspathic-looking trap, which has charred the coals at the points of junction.
1872. W. S. Symonds, Rec. Rocks, v. 146. A dyke of trap penetrates the rocks by means of a fissure.
b. attrib. and Comb., as trap-dike (DIKE sb. 9 b), -granulite, -porphyry, -rock, -shale, -stone, -tuff.
1796. Kirwan, Elem. Min. (ed. 2), I. 355. Trap Porphyry … sometimes … abounds … in quartz and felspar.
1811. Sir A. Boswell, Poet. Wks. (1872), 102. Beneath his feet the trap-stone rung.
1813. Bakewell, Introd. Geol. (1815), 118. Rocks in which hornblende forms predominating ingredient, have been denominated trap rocks.
1821. R. Jameson, Man. Mineral., 401. Secondary Trap…. The following are the different kinds of these rocks,… Greenstone;… Syenite;… Amygdaloid;… Wacke;… Basalt; and … Trap tuff.
1842. Sedgwick, in Hudson’s Guide Lakes (1843), 241. Plumbago … has … been found among coal strata near the sides of ‘trap dykes.’
1853. in J. Phillips, Man. Geol. (1855), 102. Roofing-slate,… alternating with porphyry, trappean conglomerate, trap-shale.
1855. J. Phillips, Man. Geol., 187. There are no trap dikes in this coal field.
1867. Burton, Hist. Scot. (1873), I. ii. 57. It is a small bar of trapstone.
1881. Prevost, in Knowledge, No. 5. 85. The trap rocks, divisible into two great classes, called diorite and dolerite, contain soda, lime, magnesia, and potash.
