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 H uel 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 by another fracture 

 49 



