I9I1.] STEVENSON— FORMATION OF COAL BEDS. 105 



been the low country to yield humic material for the coal beds of 

 that basin. He thinks that to accept the land conditions necessary 

 would require too great draft on one's credulity. But the case is 

 wholly different with the peat bog theory. 



Schmitz concludes that the coal systems consist of allochthonous 

 rocks and autochthonous coal beds. The underclay is not a special 

 sediment; it is a sediment modified by the establishment of vegeta- 

 tion. There must have been some allochthonous deposits of carbon- 

 aceous matter, but they were merely local. The accumulation as a 

 whole was autochthonous, after the manner of the forested swamps. 



Sterzel"^ thinks that very probably no theory of formation is of 

 universal application, the conditions being unlike in dififerent regions, 

 even in dififerent parts of the same region. In studying the Zwickau 

 region area, he became convinced that plants embedded in shales 

 accompanying the coal are not in their original place, for they are 

 broken, they are in different stages of decomposition, their remains 

 are mostly parallel to the stratification, and they show distinct evi- 

 dence of sorting due to currents of water. Plants in situ occur only 

 locally. 



Some features favor belief in the autochthony of coal ; the narrow 

 variations in thickness of important beds within great areas ; the 

 small proportion of ash in many beds ; the localization of Stigmaria 

 in the Liegenden ; the occurrence of erect stems in the Hangenden. 

 But there are others equally favoring allochthony ; the distinct lami- 

 nation of the coal ; the mineral matter, often forming a considerable 

 part of the bed, is mostly clay, the same with that of the roof and 

 floor, and it tells of quiet deposition ; Stigmaria occurs abundantly in 

 the roof of coal beds ; erect stems are of exceptional occurrence. 



The greater number of phenomena favor allochthonous origin of 

 the Zwickau coal beds. They were deposited in a lake basin sur- 

 rounded by forested swamps. The gently inflowing waters carried 

 little mineral matter and the plant material accumulated long time 

 on the bottom, where it was converted slowly into coal. When the 



"'^ T. Sterzel, " Palaeontologische Character der Stcinkohlenformation 

 und des Rothliegenden von Zwickau in den Erlauterung zur geologischen 

 Specialkarte," Section Zwickau, 1891, pp. 87-142; " Mittheil. aus d. Naturw. 

 Sammlung d. Stadt-Chemnitz," 1903, 22 pp. 



105 



