Elements of geology, or, The Elements of geology, or, The ancient changes of the earth and its inhabitants as illustrated by geological monuments elementsofgeolog00lyel Year: 1868 Oh. XXXVIII.] ORIGIN' OF METALLIFEROUS VEINS. 769 Fig. 762. That Metalliferous Veins were Fissures.—As some intelligent miners, after an attentive study of metalliferous veins, have been unable to reconcile many of their characteristics with the hypothesis of fissures, I shall begin by stating the evidence in its favor. The most striking fact, perhaps, which can be ad- duced in its support, is the coincidence of a c
Elements of geology, or, The Elements of geology, or, The ancient changes of the earth and its inhabitants as illustrated by geological monuments elementsofgeolog00lyel Year: 1868 Oh. XXXVIII.] ORIGIN' OF METALLIFEROUS VEINS. 769 Fig. 762. That Metalliferous Veins were Fissures.—As some intelligent miners, after an attentive study of metalliferous veins, have been unable to reconcile many of their characteristics with the hypothesis of fissures, I shall begin by stating the evidence in its favor. The most striking fact, perhaps, which can be ad- duced in its support, is the coincidence of a con- siderable proportion of mineral veins with faults, or those dislocations of rocks which are indispu- tably due to mechanical force, as above explained (p. 61). There are even proofs in almost every mining district of a suc- cession of faults, by which the opposite walls of rents, now the receptacles of me- tallic substances, have suf- fered displacement. Thus, for example, suppose a a, fig. 762, to be a tin lode in Cornwall, the term lode being applied to veins con- taining metallic ores. This lode, running east and west, is a yard wide, and is shift- ed by a copper lode (b b), of similar width. The first fissure (a a) has been filled with vari- ous materials, partly of Chemical -Origin, Such as Yertieal Bections oftlie mine of Huel Peever, Redruth, quartz, fluor-spar, peroxide Cornwall, of tin, sulphuret of copper, arsenical pyrites, bismuth, and sulphuret of nickel, and partly of mechanical origin, comprising clay and angular fragments or detritus of the intersected rocks. The plates of quartz and the ores are, in some places, parallel to the vertical sides or walls of the vein, being divided from each other by alter- nating layers of clay, or other earthy matter. Occasionally the metallic ores are disseminated in detached masses among the vein- stones. It is clear that, after the gradual introduction of the tin and other substances, the second rent (b b) was produced b
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