MINEKAL VEINS. 
605 
CHAPTER XXXVI, 
MINERAL VEINS. 
Different Kinds of mineral Veins.—Ordinary metalliferous Veins or Lodes. 
—Their frequent Coincidence with Faults.—Proofs that they originated 
in Fissures in solid Kock.—Veins shifting other Veins.—Polishing of their 
Walls or “Slicken sides.”—Shells and Pebbles in Lodes.—Evidence of the 
successive Enlargement and Reopening of Veins.—Examples in Cornwall 
and in Auvergne.—Dimensions of Veins.—Why some alternately swell 
out and contract.—Filling of Lodes by Sublimation from below.—Sup¬ 
posed relative Age of the precious Metals.—Copper and lead Veins in Ire¬ 
land older than Cornish Tin.—Lead Vein in Lias, Glamorganshire.—Gold 
in Russia, California, and Australia.—Connection of hot Springs and min¬ 
eral Veins. 
The manner in which metallic substances are distributed 
through the earth’s crust, and more especially the phenomena 
of those more or less connected masses of ore called mineral 
veins, from which the larger part of the precious metals used 
by man are obtained, are subjects of the highest practical 
importance to the miner, and of no less theoretical interest 
to the geologist. 
On different Kinds of Mineral Veins. —The mineral veins 
with which we are most familiarly acquainted are those of 
quartz and carbonate of lime, which are often observed to 
form lenticular masses of limited extent traversing both hyp- 
ogene strata and fossiliferous rocks. Such veins appear to 
have once been chinks or small cavities, caused, like cracks in 
clay, by the shrinking of the mass, during desiccation, or in 
passing from a higher to a lower temperature. Siliceous, 
calcareous, and occasionally metallic matters have sometimes 
found their way simultaneously into such empty spaces, by 
infiltration from the surrounding rocks. Mixed with hot 
water and steam, metallic ores may have permeated the 
mass until they reached those receptacles formed by shrink¬ 
age, and thus gave rise to that irregular assemblage of veins, 
called by the Germans a “ stockwerk,” in allusion to the dif¬ 
ferent floors on which the mining operations are in such cases 
carried on. 
The more ordinary or regular veins are usually worked in 
vertical shafts, and have evidently been fissures produced by 
mechanical violence. They traverse all kinds of rocks, both 
