BOG IRON-ORE I 35 



The bogs of northern latitudes are due principally to the bog 

 moss Sphagnum, which forms dense and tangled masses of vege- 

 tation, dead and decaying below, green and flourishing above. 

 As these mosses hold water like a sponge, they will develop bogs 

 in any shallow depression, or even on a flat surface, where they 

 may get a foothold. The depth of peat is sometimes as much as 

 fifty feet, and its density and fineness of grain increase with the 

 depth and the length of time it has been macerating in water. 



Fire-clay is frequently found at the bottom of peat bogs, and is 

 directly connected with the processes of vegetable decomposition, 

 though not itself of organic origin. Fire-clay contains a large 

 admixture of siliceous sand, but is free from lime, magnesia, the 

 alkalies, and any high percentage of iron ; it is thus a mixture of 

 nearly pure clay and sand, which may be heated very highly with- 

 out melting or crumbling. The iron, alkalies, and alkaline earths 

 are gradually leached out of the clay by the action of the peaty 

 water, which is charged with humous acids, and thus an ordinary 

 clay is converted into a fire-clay. Fire-clay occurs frequently 

 beneath coal seams ; as the percentage of silica becomes very high, 

 fire-clay passes over into gannister, which is largely used for the 

 lining of iron furnaces. 



Bog Iron-ore is another substance which is indirectly due to the 

 decay of plants ; it is found at the bottom of bogs, or lakes, in 

 deposits which are sometimes many feet thick. Iron is a very 

 widely disseminated substance, occurring in almost all rocks and 

 soils, though usually in very small quantities. Immediately at or 

 very near the surface of the ground the ordinary iron ingredient 

 is the red oxide Fe 2 3 , an exceedingly stable compound. In 

 contact with decomposing organic matter, and protected from 

 the air, Fe 2 3 is deoxidized and converted into FeO (Fe 2 3 — O 

 = Fe 2 2 = FeO); this in its turn takes up C0 2 , which is present 

 in all such waters, and becomes FeC0 3 , which is soluble in carbo- 

 nated water. Solutions of FeC0 3 accumulate under peat bogs and 

 deposit their mineral by concentration ; but when the iron-bearing 

 waters evaporate in contact with the air, the carbonate is recon- 

 verted into the red oxide, by the loss of C0 2 and absorption of O. 



