I913.] STEVENSON— FORMATION OF COAL BEDS. 93 



by Renault, made the capital discovery that bacilli existed in Coal 

 Measures time. Renault elaborated this observation afterwards in 

 some memoirs which are captivating in style. The studies of bog- 

 heads and related types by C. E. Bertrand and Renault fully con- 

 firmed the results presented by von Giimbel, while more recently 

 new confirmation has come through the investigations by Potonie. 



For the most part conclusions reached after microscopic study of 

 coal concern chiefly the question as to the origin of the coal ; some 

 of them will find place on a later page. It is well, however, to con- 

 sider the origin of the mineral charcoal or fusain, as that material 

 has been deemed important in some of the hypotheses which will 

 demand attention. It is present throughout the series of fossil fuels, 

 •even in peats, sometimes scattered in fragments, minute or consider- 

 able, scattered through the mass, at others forming distinct layers 

 more or less persistent and up to 2 or 3 inches thick. Two partings 

 in the Pittsburgh coal bed, continuous in an area of not less than 

 2,000 square miles, consist in most of that area of mineral charcoal 

 mingled with impalpable mineral matter. The term mineral char- 

 coal well describes the material ; the vegetable structure is distinct, 

 the substance is soft and soils the fingers. 



Rogers"'^ thought that leaves and fronds were brought to the 

 marsh by winds or tides and that such parts as were not reduced 

 quickly to condition of pulp, might remain as mineral charcoal, if 

 the volatile constituents were removed rapidly. Three years later, 

 Daubree''^ studied fibrous coal from Saarbruck near Altenkirchen. 

 Some specimens are pure black, with the fibers very fine, and resem- 

 ble charcoal but are more tender ; the fragments are irregular, 

 angular and show little rounding of the edges. There is no transi- 

 tion between this and the surrounding coal and, according to 

 Schimper, the fibers suggest those of coniferous wood. At the same 

 locality is a dense type, less black, less brittle but very hke charcoal ; 

 it contains 48 per cent, of ash. The material bears no resemblance 



" H. D. Rogers, " Origin of Appalachian Coal Strata," etc., p. 462. 



"' A. Daubree, " Examen de charbons produits par voie ignee a I'epoque 

 houillere et a I'epoque liasique," Bull. Soc. Geol. de France, II., Vol. III., 1846, 

 pp. 153-157. 



