19".] STEVENSON— FORMATION OF COAL BEDS. 27 



thick. Perhaps one may regard layers containhig great abundance 

 of plants as equivalent to deposits in which the plants do not 

 form beds, because in the latter case the plants were brought in con- 

 temporaneously with the sand and mud masses. He is convinced 

 that the coal and the enclosing sandstone or shale beds are wholly 

 independent deposits. And this belief is strengthened by the fact 

 that the material, filling stems in coal, clay or sandstone, differs 

 from that which surrounds them — an additional evidence of the 

 extreme quiet prevailing during deposition. Goeppert was the first 

 to recognize that the coating of the filled stems is the converted 

 bark. The roots of Sigillaria and Lcpidodcndron were feeble, as 

 are those of related plants to-day, and the trees were overthrown 

 easily ; and thus it happens that the stems, as in Upper Silesia, con- 

 tribute to the formation of the coal. When overthrown, their cel- 

 lular interior was squeezed out and converted into coal, as is seen 

 near Dombrowa. All the phenomena indicate that the coal deposits 

 were made during conditions of quiet, which would be impossible 

 unless the plants grew where the coal is found. 



The vast extent and constancy in structure exhibited by coal beds 

 is important. He cannot think that such a mass could be floated in 

 at once, yet how could it be deposited so regularly by any other 

 means? He agrees with Lindley and Hutton and wath Burat that 

 the mass is too great for transport. He is unable to believe that 

 the coal was the product of forests, because the amount is so vast ; 

 but the evidence satisfies him that the plants have not come from a 

 distance. He prefers to accept the opinions presented by v. Berold- 

 ingen, De Luc, Ad. Brongniart, Link, and to believe that, if not all 

 coal beds, at least the thickest originated as peat bogs — the more so 

 because of the resemblance which a buried peat bog has to a coal bed. 



He conceives that on the damp floor there grew lycopods, cala- 

 mites, ferns, stigmaria and other plants, corresponding to the crypto- 

 gams and monocotyledons of present day bogs. Tree-like Sigillarice 

 and Lcpidodcndra grew on the borders of the bog and at times were 

 uprooted by floods. He laid great stress on the preservation of the 

 plants, as precluding the possibility of transportation ; he finds the 

 mode of decay of tree stems equally important, for the conditions 

 observed in Calamitcs are the same with those found in his experi- 



27 



