XII] OEIGIN OF METALLIFEEOUS DEPOSITS. 229 



is illustrated "by the destructive action of rusting iron bolts 

 on moist wood, and the effect of iron stains in impairing the 

 strength of linen fibre. 



We see in the coal formation that the vegetable matter 

 necessary for the production of the iron-ore beds was not 

 wanting ; but the question has been asked me, Where are the 

 evidences of the organic material which was required to pro- 

 duce the vast beds of iron-ore found in the ancient crystalline 

 rocks 1 I answer that the organic matter was, in most cases, 

 entirely consumed in producing these great results ; and that 

 it was the large proportion of iron diffused in the soils and 

 waters of these early times, which not only rendered possible 

 the accumulation of such great beds of ore, but oxidized and 

 destroyed the organic matters which in later ages appear in 

 coals, lignites, pyroschists, and bitumens. Some of the carbon 

 of these early times is, however, still preserved in the form of 

 graphite, and it would be possible to calculate how much car- 

 bonaceous material was consumed in the formation of the great 

 iron-ore beds of the older rocks, and to determine of how much 

 coal or lignite they are the equivalents. 



In the course of ages, however, as a large proportion of the 

 once diffused iron-oxide has become segregated in the form of 

 beds of ore, and thus removed from the terrestrial circulation, 

 the conditions have grown more favorable for the preservation 

 of the carbonaceous products of vegetable life. The crystalline 

 magnetic and specular oxides, which constitute a large propor- 

 tion of the ores of this metal, are almost or altogether indiffer- 

 ent to 'the action of organic matter. When, however, these 

 ores are reduced in our furnaces, and the resulting metal is 

 exposed to the oxidizing action of a moist atmosphere, it is 

 again converted into iron-rust, which is soluble in water hold- 

 ing organic matters, and may thus be made to enter once more 

 into the terrestrial circulation. 



There is another form in which iron is frequently concen- 

 trated in nature, that of sulphide, and most frequently as the 

 bisulphide, known as iron-pyrites. This substance is found 

 both in the oldest and the newest rocks, and, like the oxide of 



