191 1] STEVENSON— FORMATION OF COAL BEDS. 579 



exposure, the solution becomes darker and a flocculent deposit is 

 produced. If the yellowish solution be evaporated to dryness and 

 the residue be heated to redness, this becomes black and, when treated 

 with water, yields potassium carbonate. Evidently, boiling water 

 extracts a substance which owes its solubility to alkaline salts con- 

 tained in plants. Leibig says, on authority of Sprengel, that humic 

 acid becomes insoluble when dried in air or when frozen in moist 

 condition. 



Hunt^^ has remarked that organic matters in solution acting on 

 insoluble peroxide of iron form the protoxide, which is soluble in 

 carbonic acid and in excess of the organic (acid) matter. In this 

 way, great quantities of iron may be removed and white clay or sand- 

 stone may be produced. The iron salts become oxidized and go 

 down as hydrated peroxide. Manganese deposits are formed in 

 similar fashion. He is inclined to believe that hydrated alumina 

 may originate in the same way. Organic matter dissolved by sur- 

 face waters reduces sulphates to sulphides and these, decomposed 

 in turn by carbonic acid, yield alkaline and earthy carbonates as well 

 as hydrogen sulphide. 



One finds in bogs some types of peat to which the descriptions 

 thus far given do not apply. Examined in detail, these in some 

 cases suggest original differences due to mode of accumulation or to 

 character of material, while in others they appear to be due to sec- 

 ondary processes. 



Long ago, Caspary described the Lebertorf obtained at Purpes- 

 seln, near Gumbinnen in east Prussia. This material was studied 

 very carefully by v. Giimbel.*- his specimens being from the type 

 locality. The deposit is 5 feet thick and at 10 feet below the sur- 

 face. When damp, it is liver-brown in color and dense, but when 

 dry it divides into paper-like laminae. Under the microscope it 

 proves to be composed of very fragmentary parts of plants within 

 a felt-like, flocky mass, in which are insects, recognizable grass and 

 moss, scattered black wood cells, many spores and an immense quan- 



*' T. Sterry Hunt, " Chemical and Geological Essays," Boston, 1875, pp. 



97-99- 



''^ C. W. V. Giimbel, op. cif.. pp. 131, 132, 133. 



177 



