586 STEVENSON— FORMATION OF COAL BEDS. [November 3, 



This is placed beyond doubt in his later work/'" where he modifies 

 the broad statements made in his earlier work and shows that the 

 difference is formal rather than real. He says that dopplerite origi- 

 nates, as does the peat, out of a varying mass of colloid substances, 

 free humus acids, salts of humus acids, inorganic substances and 

 some nitrogen. So one may regard dopplerite as an ulmate, a hu- 

 mate, a crenate or a mixture of them all, with in addition some inor- 

 ganic salts. The essential point is that, during the process of peat- 

 making, a greater or less portion of the vegetable material is brought 

 into a condition admitting of flowage, so that it may remain distrib- 

 uted throughout the mass or may be collected into cavities. When 

 the pores of the peat are filled, farther drainage is possible only to a 

 limited degree and the material will find its way to the tissues, be- 

 coming the Carbohumin of v. (iiimbel. To this absorption of Car- 

 bohumin is due the different effect of pressure upon peat and brown 

 coal ; in peat the porosity is very great, in brown coal it is small. 



Variations in structure or appearance of the peat have been 

 observed in recent bogs, which are as notable as those found in the 

 Schieferkohle. Griffith'^'* in describing the Irish peat bogs, said that 

 bases of the bogs consist of clay covered with a layer of peat, which 

 is composed of rushes and flags. Above this is another bed of peat, 

 closely resembling cannel coal, with conchoidal fracture and hard 

 enough to be worked into snuffboxes. It yields 25 per cent, of ash 

 and much oxide of iron. This, in turn, is covered with black peat 

 containing twigs and branches of fir or pine, oak, yew and hazel, 

 only the bark remaining. Where whole trees were found, the roots 

 had disappeared. 



Lesquereux"'' relates that on the border of the valley of the 

 Locle, a considerable mass of marl covers a bed of peat, which has 

 become converted into lignite, hard, fragile and with brilliant frac- 

 ture. The thickness on the border is barely 3 inches. Farther 

 downward toward the bottom of the valley, the marl is only 4 feet 



°' J. J. Friili, in " Die Moore der Schweiz," 1904, pp. 164, 165, 166, 167. 



°* Griffith, cited by S. S. Haldeman in Introduction to 2d Ed. of R. C. 

 Taylor's " Statistics of Coal," Philadelphia, 1855, p. 166. 



°' L. Lcsquerenx. " Quclques rccherches sur les marais tourbeux," Neu- 

 chatcl, 1845, p. 95. 



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