620 



ORIGIN OF METALLIFEROUS VEINS. [Ch. XXXVIII. 



Fig. 710. 



feet. They hold their course continuously in a certain prevailing direc- 

 tion for miles or leagues, passing through rocks varying in mineral com- 

 position. 



That metalliferous veins were fissures. — As some intelligent miners, 

 after an attentive study of metalliferous veins, have been unable to re- 

 concile many of their characteristics with the hypothesis of fissures, I 



shall begin by stating the 

 evidence in its favour. The 

 most striking fact perhaps 

 which can be adduced in its 

 support is, the coincidence 

 of a considerable proportion 

 of mineral veins with faults, 

 or those dislocations of rocks 

 which are indisputably due 

 to mechanical force, as above 

 explained (p. 61). There 

 are even proofs in almost 

 every mining district of a 

 succession of faults, by 

 which the opposite walls of 

 rents, now the receptacles 

 of metallic substances, have 

 suffered displacement. Thus, 

 for example, suppose a a, 

 fig. 7 10, to be a tin lode in 

 Cornwall, the term lode be- 

 ing applied to veins contain- 

 ing 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 various ma- 

 terials, partly of chemical 

 origin, such as quartz, fluor- 

 spar, peroxide of tin, sul- 

 phuret of copper, arsenical 

 pyrites, bismuth, and sul- 

 phuret 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 alternating layers 

 of clay, or other earthy matter. Occasionally the metallic ores are dis- 

 seminated in detached masses among the vein-stones. 



Vertical sections of the mine of Huel Peever, Redruth, 

 Cornwall. 



