Page:A Treatise on Geology, volume 2.djvu/195

 CHAP. VIII.

The ordinary explanation is that the tin vein, now appearing in four parts, a, a″, a″, a‴, is the oldest vein, and was formed in one straight line; after its formation the copper vein b b″ was formed by filling a straight continuous fissure, which was made by violent fracture of the mass of the rocks across the tin vein. This was accompanied by a dislocation of the rocks in closing the tin vein; so that the line was broken and