depth of metallic veins.

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nous, it may fairly be inferred that theydiffer in this respect in different situations.Veins are seldom rich in ore near the surface,but increase in richness as they descend, andat greater depths become poorer again. WhenPryce wrote the Mineralogy of Cornwall , itwas believed that the richest state of a mine ofcopper in that county was from 80 to 100yards deep, and for tin from 40 to 120 yards.This account by no means agrees with thepresent state of the Cornish mines. Copperand tin are procured in considerable quantitiesat the depth of400yards in the Dolcoath mine.The Eeton copper mine in Staffordshire is nowworked at the depth of 472 yards: it is thedeepest mine in England. The deepest minethat has been worked in Europe , or in anypart of the world, is one at Truttenbergin Bohemia , which is 1000 yards below thesurface.

Metallic veins frequently contain differentores at various depths. Iron ore, copper ore,cobalt ore, and silver ore succeed each otherin some of the mines in Saxony .

In France there are mines which contain

copper