Cil XXXVI1I.J MINERAL VEINS. 707 



CHAPTER XXXVIII. 



MINERAL VEINS. 



Werner's doctrine that mineral veins were fissures filled fioin above — Veins of 

 segregation — Ordinary metalliferous veins or lodes- — Their frequent coincidence 

 with faults — Proofs that they originated in fissures in solid rock — 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 — Four- 

 net's observations in Auvergne — Dimensions of veins — Why some alternately 

 swell out and contract — Filling of lodes by sublimation from below — Chemical 

 and electrical action — Relative age of the precious metals — Copper and lead 

 veins in Ireland older than Cornish tin — Lead vein in lias, Glamorganshire — 

 Gold in Russia, California, and Australia- — Connection of hot springs and min- 

 eral veins — Concluding remarks. 



The manner in which metallic substances are distributed through 

 the earth's crust, and more especially the phenomena of those nearly 

 vertical and tabular masses of ore called mineral veins, from which 

 the larger part of the precious metals used by man are obtained — 

 these are subjects of the highest practical importance to the miner, 

 and of no less theoretical interest to the geologist. 



The views entertained respecting metalliferous veins have been 

 modified, or, rather, have undergone an almost complete revolution, 

 since the middle of the last century, when Werner, as director of the 

 School of Mines at Freiburg, in Saxony, first attempted to generalize 

 the facts then known. He taught that mineral veins had originally 

 been open fissures which were gradually filled up with crystalline and 

 metallic matter, and that many of them, after being once filled, had been 

 again enlarged or reopened. He also pointed out that veins thus formed 

 are not all referable to one era, but are of various geological dates. 



Such opinions, although slightly hinted at by earlier writers, had 

 never before been generally received, and their announcement by one 

 of high authority and great experience constituted an era in the sci- 

 ence. Nevertheless, I have shown, when tracing, in another work, 

 the history and progress of geology, that Werner was far behind some 

 of his predecessors in his theory of the volcanic rocks, and less en- 

 lio-htened than his contemporary, Dr. Hutton, in his speculations as to 

 the origin of granite.* According to him, the plutonic formations, 

 as well as the crystalline schists, were substances precipitated from a 



* Principles of Geology, chap. iv. 



