West of this line the rocks are chiefly Tertiary and Quaternary; east of it they are mostly Palaeozoic or gneissic.
A fine-grained rock of gneissic structure having a faint pink color.
1757, from German Gneiss "type of metamorphic rock," probably from Middle High German gneist "spark" (so called because the rock glitters), from Old High German gneisto "spark" (cf. Old English gnast "spark," Old Norse gneisti).
