226 MINERAL VEINS. 



ever, very good evidence that these local currents have, 

 of themselves, many peculiar influences. It not unfre- 

 quently happens that owing to some great disturbance 

 of the crust of the earth, a mineral vein is dislocated, 

 and one part either sinks below, or is lifted above its 

 original position 5 the fissures formed between the two 

 being usually filled in with clay or with crystalline 

 masses of more recent formation than the fissure itself. 

 It is frequently found that these "cross courses" as 

 they are called in mining language, contain ores of a 

 different character from those which constitute the 

 mineral vein ; for instance, in them nickel, cobalt, and 

 silver are not unfrequently discovered. When these 

 metals are so found, they almost invariably occur be- 

 tween the ends of the dislocated lode, and often take a 

 curvilinear direction, as if they were deposited along a 

 line of electrical force.* 



In the laboratory such an arrangement has been 

 imitated, and in a mass of clay fixed between the gal- 

 vanic plates, after a short period a distinct formation of 

 a mineral vein has taken place.f By the action, too, of 

 weak electrical currents, Becquerel, Crosse, and others, 

 have been successful in imitating nature so far as to 

 produce crystals of quartz and other minerals. In addi- 

 tion to this evidence, in support of the electrical theory 



results at Frlsch Gliick, Neue Hoffnung, Gottlob, and in other mi- 

 neral veins in the mining districts of Saxony: Edinburgh New 

 Philosophical Journal, vol. xxviii. 1839. The irregularities are all 

 to be explained by the presence or absence of chemical excitation. 



* This was remarkably the case at Huel Sparnon, near Redruth, 

 where the cobalt was discovered betweed two portions of a dislo- 

 cated lode ; and the same was observed by Mr. Percival Johnson 

 in a small mine worked for nickel, near 8t. Anstell. 



f On the process used for obtaining artificial veins in clay : by 

 T. B. Jordan ; Sixth Annual Report of the Royal Cornwall Poly- 

 technic Society. See also my memoir, already referred to, in the 

 Memoirs of the Geological Survey and Museum of Practical Geo- 

 logy, vol. i. 



