STEVENSON— INTERRELATIONS OF THE FOSSIL FUELS. 193 



conditions is shown very frequently by a faux-toit ; but not rarely the 

 passage from coal to roof is abrupt, which may indicate, perhaps, 

 that peat-making had ceased for some time prior to the burial under 

 transported material. 



The coal beds are rarely single ; they are divided by partings into 

 benches, which differ greatly in thickness and in composition, though 

 there are beds which are remarkably uniform in composition through- 

 out. The coal may be hard or soft, massive or laminated, and the 

 several types may be in separate benches or even in the same bench. 

 Generally, the coal is hard enough to require the use of heavy tools 

 in mining so that it comes out in lumps, Knabben- or Knorpelkohle 

 of the Germans. This type is especially characteristic in the United 

 States. But in somewhat extensive areas within Germany one finds 

 abundantly the other type. Form-, Fein-, Rieselkohle of the various 

 localities, fine-grained, earthy in appearance and but slightly coherent. 

 All types of coal, enumerated by authors, may be found in a single 

 bed or even in a single bench. Fragments of wood are numerous, 

 lignite at one end where the annual rings are distinct, while at the 

 other end they have been converted in shining Pechkohle, apparently 

 without trace of vegetable texture. A similar condition is seen in 

 many cases of replacement, for one part of a stem may be wholly 

 silicified while the other remains wood. In such cases, the original 

 structure frequently remains distinct, whereas in replacement with 

 dissolved carbon compounds, as in Pechkole, the structure disappears. 

 The distribution of Formkohle in a bed is indefinite ; it may occupy 

 the whole space from floor to roof, interrupted only by partings; it 

 may be at the bottom or at the top, or it may alternate with benches 

 of other coals. Its mode of origin is discussed elsewhere by the 

 writer. 



Macroscopically, the coal consists of various fragments of organic 

 and of inorganic origin, embedded in a structureless mass, in which 

 the unaided eye can find no trace of texture; but under the micro- 

 scope, this structureless mass proves to be minutely divided plant 

 debris. Woody materials are often predominant, occasionally more 

 than three fourths of the mass. Logs are reported from all locali- 

 ties, but they are distributed irregularly through the deposit, at least 



