from The Century Dictionary.
- noun Mineral matter, often metalliferous, filling a preëxisting fissure, not formed by simple shrinkage of the rock itself, but resulting from deep-seated or crust movements, and which therefore may be expected to extend indefinitely downward, instead of ending in the particular stratum or group of strata in which it began. See vein, deposit, true vein (under vein), and gash-vein.
Sorry, no etymologies found.
The possibility that they extend to immense depths is increased when we reflect that mineral veins occur in parallel groups that run with great regularity for hundreds of miles; and further by the fact that, in all the changes of the earth's surface, by which deep-seated rocks have been brought up and exposed by denudation, no instance is known of the bottom of a fissure-vein having been brought by such movements within the reach of man.