MINES AND STREAM-WORKS. 109 



of metalliferous regions, as those of Derbyshire, Wales, and 

 Cornwall. 



The great value of primary districts lies, as already men- 

 tioned, in their metalliferous lodes and veins, or in the 

 stream-drifts that have been weathered and worn in course 

 of ages from the cliffs and precipices above. The vein lies 

 in the solid rock, and must be mined with great labour and 

 outlay; the stream-drift, on the other hand, is but the 

 water-borne debris from the veins above, and demands 

 merely sorting and washing. The stream-work is the ready 

 and primitive method of obtaining the ores and metals ; 

 the mine is the laborious but more certain appliance of 

 modern times and modern requirements. In conducting a 

 stream-work, little more is needed than manual labour and 

 care in managing a mine, mechanical appliances, engineer- 

 ing skill, and correct geological deduction are indispensable 

 at every stage of the undertaking. 



Such is a brief, and necessarily sketchy, outline of the 

 nature and origin of veins and vein-stuffs. The rents or 

 fissures originally produced by subterranean convulsion are 

 subsequently filled by infiltrations of mineral and metallic 

 matter, and thence become the veins which seem to ramify 

 and reticulate through the earth's crust like the veins 

 through vegetable and animal structures. A fissure may be 

 produced in an instant by earthquake convulsion, but ages 

 may pass before it be completely filled by sparry minerals 

 and metallic ores the slow depositions from aqueous per- 

 colation and solution. As water is ever percolating the 

 earth's crust, so it is ever dissolving from one part and re- 

 depositing in another ; and this power of dissolving is no 

 doubt greatly augmented by heat, just as rapidity of pre- 

 cipitation and crystallisation may be facilitated by electro- 

 magnetic currents which are incessantly traversing the 



