Lodes. 595 



various kinds of mineral matter, such as layers and 

 nests of quartz, carbonate of lime, carbonate of copper, 

 sulphide of copper, sulphide of lead, oxide of tin, or 

 with other kinds of ores. Various theories have been 

 formed to account for the presence of ores in these 

 cracks. Formerly, the favourite hypothesis was, that 

 they were formed by sublimation from below, somehow 

 or other connected with the internal heat of the earth ; 

 and the ores were supposed to have been deposited in 

 the cracks through which the heated vapours passed. 

 A great deal also has been said on the effect of electric 

 currents passing through the rocks, and aiding in de- 

 positing along the sides of fissures the minerals which 

 were being carried up by sublimation, or were in solu- 

 tion in waters that found their way into the fissures. I 

 dare not utter any positive statement on the question, 

 but my opinion is that the ores of metals in lodes have 

 generally been deposited from solutions. 



We know that water, especially when warm, can 

 take up silica in solution and deposit it, as in the case 

 of the Greysers in Iceland ; and we also know that 

 metals may, in some states, be held in solution in water, 

 both warm and cold. This is proved by the accurate 

 results of chemists, who, it is said, have detected silver, 

 gold, and copper in solution in sea water. We must 

 remember that when the lodes or cracks were originally 

 formed, those parts of them that we explore were not 

 so near the surface as we now see them ; but in a 

 great many cases they lay deep underneath, covered 

 by thousands of feet of rock that have since been 

 removed by denudation. They were probably, in all 

 cases, channels of subterranean filtration, both in their 

 upper portions that have been removed by denudation, 

 and in the parts originally deeper that now remain. 



QQ2 



