236 



expect of the character of currents set np by chemical action going on 

 between oxygenated saline solutions, and the veins themselves in which 

 these experiments were conducted. The direction of these currents would 

 vary according to the position of the positive element of the natural pair 

 generating such current in relation bo the other element, while, as a rule, 

 in the case of stations connected at different levels, the current would be 

 downwards, from the simple reason that the oxydizing of vein matters is 

 more rapid and general as we approach the surface. 



This is quite a different theoiy to either of those generally adopted to 

 explain the origin of these currents ; but the whole question of these 

 " eai'th currents is involved in so much obscurity," so little data having been 

 obtained in this direction, that no decided expression of opinion has been 

 educed. On the other hand, scientific opinion seems to oscillate between the 

 acceptance of two theories, attributing them either to magnetism or to thermal 

 causes. 



It is difficult, however, to account for these deep-seated currents by either 

 of these theories ; on the other hand, it is certain that in the natural decom- 

 position of our metallic sulphides, we have a supply of electro-motive force 

 amply sufficient to generate such currents ; and, besides, currents so deiived 

 would, as before said, have those particular characters indicated by their 

 first discoverer. 



That each separate pyritous vein or mass with surrounding walls and exciting 

 solution, may constitute, in fact, a true voltaic pair on a grand scale, competent 

 for the development of various electric phenomena, including that of electro- 

 deposition, has been more particularly the object of this 2:)aper to demonstrate. 



In these sulphides, abundantly diffused in our rocks, we have immense 

 stores of electro-motive force locked up, or now being liberated or developed 

 by natural infiuences. So far as we Jcnow, they are the only source of 

 chemico-electricity we have in nature, or, at least, of chemico-electricity of 

 such intensity as to be able to deposit any of the metals instanced from 

 their solutions. 



I have only to add as a suggestion, that possibly a table like that 

 above given, when amended and enlarged by further researches, may be' 

 useful to chemical geology in its attempts to ascertain the manner and order 

 in which changes have been effected among the various constituents of our 

 metalliferous lodes ; since it shows by a tliorouglily reliable and simple process, 

 the relative tendency of certain sulphides to decompose as compared with 

 others, in the solutions most likely to have had contact with them in the 

 situations where they generally occur. 



