Veins, in Geology, are crevices or fissures—regular or irregular, and inclined at any angle to the horizon—caused by contraction during consolidation or by mechanical disturbance, and filled up with materials different from the adjacent rocks.
Veins occupied by ores and other minerals are termed lodes (see ORE, MINING, GOLD, &c.). These very often occur on lines of fracture (see DISLOCATIONS). Some veins, again, consist of intrusions of Igneous Rock (q.v.). See DYKES, GEOLOGY.