STEVENSON— INTERRELATIONS OF FOSSIL FUELS. 449 



according to Dannenberg, i8 to 32 per cent., selected specimens 

 having as much as 22 per cent. The water is from 4 to 8 per cent. 

 A thin coal seam is present in the basal portion of the Middle Roth- 

 liegende, but is without value. 



In all areas, the Rothliegende is unconformable to the Coal Meas- 

 ures. Fragments of Coal Measures rocks are common in the basal 

 conglomerate and Siegert saw in the Lugau area large blocks of 

 coal torn from exposed coal seams. Grains of coal occur commonly. 



In 1881, Sterzel discussed the origin of coal seams and in 1901 

 a revised edition of his paper was published. He sums up in thor- 

 oughly judicial manner the features which, for him, appear to sug- 

 gest autochthonous origin of the materials, and then presents the 

 features which indicate allochthonous origin. These are : 



(a) The often very distinct lamination of the coal; (b) the 

 Bergmittel, which at times occurs abundantly within coal seams and 

 consists of the same rock material as the Hangende and Liegende 

 of the seam, is evidence of quiet deposition, as must be accepted for 

 the plant material itself. Bergmittel may be in form of increased 

 ash in the coal, or as conformable deposits, plates or benches of 

 clay shale, or iron ore, varying in extent and often splitting the 

 coal bed into an extraordinary number of thin plates. A new vege- 

 tation for each of these many thin coal layers appears inadmissable ; 

 (c) Stigmaria occurs frequently in the roof; (d) vertical stems in 

 the roof of beds are only local and occasional. He concludes that 

 the majority of facts speak for allochthonous origin of the Zwickau 

 coal seams. 



All observations lead him to the belief that the coal seams were 

 formed in a lake basin, into which the plant material was carried 

 from the widely extending swampy surrounding land, which was 

 fitted for Waldmoors with luxuriant vegetation, as well as from the 

 higher slopes, on which were plants, loving a drier region. The in- 

 floating was done by quiet waters, which carried very little inorganic 

 matter. Plant materials predominated, so that great masses of more 

 or less rotted organic matter were heaped up on the lake bottom, 

 where afterward they were converted into coal. Occasionally, the 

 watercourses were swollen and brought down rock material, which 



