58 STEVENSON— FORMATION OF COAL BEDS. [April 18, 



Bifurcation of Coal Beds. 



Parallelism of coal beds seems to be regarded as a fundamental 

 principle by some of those who have discussed the origin and forma- 

 tion of coal beds. It has been the subject of many papers in the 

 United States, based on studies in the Appalachian and Mississippi 

 coal fields. With one exception, the authors rejected the doctrine 

 of parallelism, but most of them recognize that, in some extended 

 areas there is parallelism along definite lines. 



The partings between benches of coal beds are usually extremely 

 variable but in some beds they show amazing persistence. The 

 bearing-in bench of the Pittsburgh bed is from 3 to 6 inches thick 

 and is bounded by partings which rarely exceed one half inch ; yet 

 these are present under more than 2,000 square miles, changing little 

 in thickness or in composition. Ordinarily they consist of mineral 

 charcoal and almost impalpable inorganic matter, but occasionally 

 they have so little inorganic material that the coal appears to be con- 

 tinuous — ^but the partings are there and the benches retain their 

 peculiarities. This persistence in character is, however, a strange 

 exception and in most beds the variation is extreme. 



The splitting or division of the Mammoth coal bed in the anthra- 

 cite area has been proved not only by measured sections and drill 

 cores but also by continuous workings, which often extend for many 

 miles. In the northern part of the Eastern Middle, the Mammoth 

 and the next bed below, the Wharton or Skidmore, are in contact, 

 but within a short distance the parting has become 114 feet; in 

 another part of the same field, the interval between the beds increases 

 from 35 to 200 feet, the workings on each bed being continuous ; the 

 same beds are but 6 feet apart in the southern part of the Western 

 Middle, but farther south, on the north border of the Southern, the 

 interval increases gradually to 80 feet. The Mammoth itself divides. 

 Near Shenandoah in the Western Middle it is a single bed, 40 to 60 

 feet thick, but within a short distance it is in 2 and then in 3 " splits " 

 in a vertical space of 150 to 200 feet. In the Southern, the bed 

 breaks up, reunites and breaks up again. Sometimes it is a single 

 bed but within a mile it may be in 2 or 3 splits in a vertical space 



