552 THEORIES OF METALLIC VEINS. 
during the contraction and consolidation of the 
originally soft substances of the rocks themselves; 
and more frequently into fissures produced by 
the fracture and dislocation of the solid strata. 
Segregation of this kind may have taken place 
from electro-chemical agency, continued during 
long periods of time.* 
The total quantity of all metals known to 
exist near the surface of the Earth (except- 
ing Iron,) being comparatively small, and their 
value to mankind being of the highest order, 
as the main instruments by the aid of which he 
emerges from the savage state, it w^as of the 
utmost importance, that they should be disposed 
in a manner that would render them accessible 
by his industry ; and this object is admirably 
attained through the machinery of metallic veins. 
* The observations of Mr. Fox on the electro-magnetic pro- 
perties of metalliferous veins in Cornwall, (Phil. Trans. 1830, &c.) 
seem to throw new light upon this obscure and difficult subject. 
And the experiments of M. Becquerel on the artificial production 
of crystallized insoluble compounds of Copper, Lead, Lime, &c. 
by the slow and long continued reaction and transportation of 
the elements of soluble compounds, (see Becquerel, Traite de 
TElectricite, T. i. c. 7, page 547, 1834,) appear to explain many 
chemical changes that may have taken place under the influence 
of feeble electrical currents in the interior of the earth, and more 
especially in Veins. 
I have been favoured by Professor Wheatstone with the fol- 
lowing brief explanation of the experiments here quoted. 
" When two bodies, one of which is liquid, react very feebly 
on each other, the presence of a third body, which is either a 
conductor of electricity, or in which capillary action supplies the 
