64 STEVENSON— FORMATION OF COAL BEDS. [April i8, 



seen rhizomas of ferns and creeping roots of Cordaites making part 

 of the coal, thus binding the beds to the vegetation of the mur — 

 which, as he says, contradicts one of his former determinations. 

 The lower portion of the coal in such cases is irregular in structure 

 but the passage from one grade of coal to the other is gradual and 

 the coal throughout is composed of the same plants. His belief is 

 that the running rhizomas at the bottom of the marsh have formed 

 coal in place, along with the fossil humus, which he regards as for- 

 mation of peat, by which the rooted plants were killed, the stems and 

 adventive roots being found in the coal above. 



The thickness of a coal bed is from a film to many feet. Definite 

 coal beds, not more than 6 inches to a foot thick, sometimes mark a 

 horizon over hundreds or even thousands of square miles. A thick- 

 ness of more than 8 feet is unusual in the bituminous regions of this 

 country but very much greater beds are reported from some fields 

 in Europe. The Grande Couche of les Pegauds in the Commentry 

 l^asin attains, according to Fayol, a maximum of I2 meters while the 

 main bed of the other subbasin reaches, at one place, 20 meters. The 

 vast deposits at Decazeville are in each case at least 70 feet thick 

 near that city and apparently about 100 feet at a few miles south. 

 Dannenberg gives the thickness of one bed in Saarbruck as 5 meters 

 and of the great bed in the Upper Silesian field as from 10 to 20 

 meters. The Mammoth bed of the southern anthracite field attains 

 a maximum of 114 feet at the easterly end, including only 9 feet of 

 partings. In this case, as also in that of the great Reden bed of 

 Upper Silesia, the enormous thickness is due to union of several 

 beds by disappearance of the intervening rocks. Coal in any field 

 makes up but a small part of the total section. In the middle divi- 

 sion of the Saarbruck measures, there are said to be 132 coal beds, 

 in all 32 or 33 meters thick, within a column of 850 meters ; in the 

 bituminous region of Pennsylvania, the column is somewhat more 

 than 4,000 feet and contains perhaps 30 coal beds with total thick- 

 ness of no feet. 



