384 



PALiEOZOIC SYSTEM OF KOCKS. 



IKON" AND STEEL. 



1845. 



1856. 



1864. 



1871. 



1873. 



1884. 



Great Britain. . . . 

 United States. . . . 

 France 



2,200,000 

 '502,000 

 450,000 



3,500,000 

 1,000,000 



5,000,000 

 1,200,000 

 1,217,000 



5,667,000 

 1,664,000 



6,566,000 

 2,560,000 

 1,381,000 



14,485,000 



10,600,000 

 6,200,000 

 2,600,000 

 4,500,000 



27,300,000 



Germany 



World 





7,000,000 



























Theory of the Accumulation of the Iron-Ore of the Coal-Measures. — 



We have already explained (p. 144) how iron-ore is now accumulated 

 by the agency of decaying organic matter. We have also shown that 

 if the organic matter is consumed in doing the work of accumulation, 

 the iron-ore is left in the form of iron peroxide ; but if it is accumu- 

 lated in the presence of excess of organic matter, it retains the form 

 of ferrous carbonate. We will now give additional evidence, taken 

 from the occurrence of iron-ore in the strata of the earth, that the 

 same agency has accomplished the same results in all geological times : 



1. Immense beds of iron-ore are found in the strata of all geological 

 ages ; but, wherever we find them, we find also associated a correspond- 

 ing amount of strata, decolorized or leached of their iron coloring-mat- 

 ter. Contrarily, wherever we find the rocks extensively red, we usually 

 find also an absence of valuable beds of iron-ore. We are thus led to 

 conclude that the iron-ore of iron-beds has been washed out of the 

 strata, which are thereby left in a decolorized condition. 



2. That this has been done by the agency of organic matter is shown 

 by the fact that, wherever we find evidences of organic matter, whether 

 in the form of fossils or of coal, we find the sandstones and shales are 

 white or gray — i. e., leached of coloring-matter. Conversely, red rocks 

 are usually barren of fossils or of coal. For example, all the sand- 

 stones of the coal-measures, or of all other strata containing coal, are 

 gray, while the Old Red sandstone below the coal, and the New Red 

 sandstone above the coal, and, in fact, all red sandstones, are very poor 

 in fossils or evidences of organic matter of any kind. Thus, evidences 

 of organic matter, and the decoloring of the strata, and the accumula- 

 tion of iron-ore, are closely associated as cause and effect. 



3. In all the strata, whether older or newer, in which there is no 

 coal, i. e., in which there is no excess of organic matter in a state of 

 change, the iron-ore is peroxide {ferric and magnetic oxide) ; while in 

 coal-measures of all periods, whether Carboniferous, or Jurassic, or Cre- 

 taceous, or Tertiary, or in all cases where there is organic matter in ex- 

 cess in a state of change (not graphite), the iron-ore is in the form of 

 carbonate protoxide, or ferrous carbonate (FeC0 3 ). 



Therefore, we conclude that both noiv and alivays iron-ore is, and 

 has been, accumulated by organic agency ; again, that both now and 

 always there are, and have been, three conditions of iron-ore, each as- 



