IRON-ORE OF THE COAL-MEASURES. 385 



sociated with the absence or presence in smaller or larger quantities of 

 changing organic matter : 1. It may be universally diffused as a color- 

 ing-matter of rocks and soils, and unavailable for industries ; in this 

 case there has been no organic matter to leach it out and accumulate it. 

 2. It may be accumulated as ferric oxide ; in this case there has been 

 organic matter only sufficient to do the work of accumulation, and was 

 all consumed in doing that work. 3. It may be accumulated as ferrous 

 carbonate ; in this case there is excess of organic matter, usually in the 

 form of coal. 



This much is certain ; but, as to the exact mode and time of the 

 leaching and accumulation, there is some difference of opinion. There 

 are two ways in which the accumulation may have occurred : It may 

 have accumulated in the coal-marshes during the Coal period, being at 

 that time leached out of the surrounding soils, which were therefore 

 left in a decolorized condition, and in this condition subsequently washed 

 down as sediments into the coal-marshes. Or, it may have been brought 

 down as the coloring-matter of red sands and clays; and afterward, 

 perhaps after the Coal period, leached out by percolating waters con- 

 taining organic matter from the coal-beds, carried downward until 

 stopped by an impervious clay-stratum, and accumulated there. The 

 former mode is the more probable.* 



But, in any case, organic matter has been the agent ; and, there- 

 fore, in this case, as in all other cases, iron-ore is the sign of organic 

 matter, and the measure of the amount of organic matter consumed in 

 its accumulation. There are, therefore, three signs of the previous 

 existence of organisms used by geologists ; they are coal, iron-ore, and 



We can not dismiss this subject without making one passing reflec- 

 tion suggested by the mention of these three signs of life : 



The organic kingdom is so much matter taken from the atmosphere, 

 embodied for a brief space in individual living forms, to be again dis- 

 solved by death, and returned to the atmosphere whence it came. The 

 same material is again taken by the next generation, embodied and 

 again returned at its death. The same small quantity of matter in the 

 atmosphere is embodied and disembodied, again embodied and disem- 

 bodied, and thus worked over and over again by constant circulation 

 thousands, yea, millions of times, in the history of the earth. Now, in 

 this constant circulation of the elements of organic matter, besides the 

 work done in the fact of circulation itself, viz., the wonderful but fleet- 

 ing phenomena of vegetable, animal, yea, of human life, there was an- 

 other work, the results of which accumulated from age to age — a work, 

 too, of the greatest importance to the well-being of the human race. 



* Bischoff, Chemical Geology, vol. i, p. 315. 

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