CHAPTER IX.

MINERA L DYKES AND METALLIC V LIN'S.

Dykes intersecting primary and secondary Moun-tains. —Their structure , contents, and extent .—Dislocations of the Strata caused by Dykes .—Structure of Metallic Veins.—Their depth andthickness .— Substances found in Veins.—PipeVeins. —Fluor Mine at Castleton.—Position ofVeins.—Extent of Veins. —Opinions respectingthe manner in which Metallic Veins were filed .—Theory of IVerner proved to be erroneous, bystriking appearances in different English Mines.—Facts elucidating the Formation of MetallicVeins.

JT hat the surface of the earth has beenfractured since its consolidation, is proved bythe dislocations which rocks and strata inmany situations present. It is further provedby the existence of vertical seams intersect-ing them, and filled with mineral matter of adifferent kind. When the substance found inthese vertical seams is stone or earth, and theyare of considerable thickness, they are calleddykes, or faults. When filled with metallic

ores,