Ch. XXXVUL] RELATIVE AGE OF METALS. 7^7 



and vice versd, The same observation applies to killas and the gran- 

 itic porphyry called elvan. Sometimes, in the same continuous vein, 

 the granite will contain copper, and the Mllas tin, or vice versa." * 

 Mr. Fox, after ascertaining the existence at present of electric currents 

 in some of the metalliferous veins in Cornwall, has speculated on the 

 probability of the same cause, having acted originally on the sulphnrets 

 and muriates of copper, tin, iron, and zinc, dissolved in the hot water 

 of fissures, so as to determine the peculiar mode of their distribution. 

 After instituting experiments on this subject, he even endeavored to 

 account for the prevalence of an east and west direction in the prin- 

 cipal Cornish lodes by their position at right angles to the earth's 

 magnetism ; but Mr. Henwood and other experienced miners have 

 pointed out objections to the theory ; and it must be owned that the 

 direction of veins in different mining districts varies so entirely that it 

 seems to depend on lines of fracture, rather than on the laws of vol- 

 taic electricity. Nevertheless, as different kinds of rock would be 

 often in different electrical conditions, we may readily believe that 

 electricity must often govern the arrangement of metallic precipitates 

 in a rent. 



" I have observed," says Mr. E. Fox, " that when the chloride of 

 tin in solution is placed in the voltaic circuit, part of the tin is de- 

 posited in a metallic state at the negative pole, and part at the positive 

 one in the state of a peroxide, such as it occurs in our Cornish mines. 

 This experiment may serve to explain why tin is found contiguous to, 

 and intermixed with, copper ore, and likewise separated from it, in 

 other parts of the same lode." f 



Relative Age of the Different Metals. — After duly reflecting on the 

 facts- above described, we cannot doubt that mineral veins, like erup- 

 tions of granite or trap, are referable to many distinct periods of the 

 earth's history, although it may be more difficult to determine the. 

 precise age of veins ; because they have often remained open for 

 ages, and because, as we have seen, the same fissure, .after having 

 been once filled, has frequently been reopened or enlarged. But 

 besides this diversity of age, it has been supposed by some geologists 

 that certain metals have been produced exclusively in earlier, others 

 in more modern times — that tin, for example, is of higher antiquity 

 than copper, copper than lead or silver, and all of them more ancient 

 than gold. I shall first point out that the facts once relied upon in 

 support of some of these views are contradicted by later experience, 

 and then consider how far any chronological order of arrangement 

 can be recognized in the position of the precious and other metals in 

 the earth's crust. 



In the first place, it is not true that veins in which tin abounds are 

 the oldest lodes worked in Great Britain. The Government survey of 

 Ireland has demonstrated, that in Wexford veins of copper and lead 



* R. W. Fox on Mineral Veins, p. 10. f Ibid., p. 38. 



