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FORMATION OF VEINS.

at different times, a number of these metallicsolutions would succeed each other, and weshould find regular strata of ore in all primaryand transition rocks; and the quantity formedbv these deep seas of metallic matter wouldbe inconceivably great*.

This theory is decidedly invalidated by thefollowing facts. When a metallic vein, passesthrough different kinds of rock, it is generallyobserved that the quality of the ore varieswith that of the rock through which it passes;and even different beds of the same rock aremore productive than others, and are calledby miners bearing measures. This is the casein Durham , in Derbyshire , and probably inevery part of England and Wales .

Mr. Werner quotes one instance, as if itwere extraordinary, of the quality and quan-tity of the ore being changed by the nature of

* Metallic ores may, in some instances, have been form-ed in fissures which were once open at the top, or veins mayhave been reopened by a subsequent convulsion. Tiie roundpebbles which are sometimes found in veins prove thatthere must in such instances have been a connection withthe surface.

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