I9I3-] STEVENSON— FORMATION OF COAL BEDS. 69 



Phillips,*'^ referring to his studies in Yorkshire, states that toward 

 the southwest the hmestones thicken, while sandstones and shales 

 become thin. The sandstones thicken toward the north, while shales 

 thicken toward the west, in which direction certain sandstones and 

 limestones vanish. With those sandstones, the coals also vanish. 

 Where the sandstones thicken and grow numerous, toward the 

 north, in which direction the limestones change from an undivided 

 mass to many members, the coal beds augment in number and 

 in thickness. A similar condition is apparent in eastern Oklahoma. 

 Coal beds seem to be wholly wanting in the Mississippi lime- 

 stones of the Appalachian basin. Their absence from this mass, at 

 times more than 2,000 feet thick, including the calcareous shales, can 

 hardly be due to lack of vegetation on the land, for the underlying 

 Pocono or Logan sandstone and shales show definite coal beds from 

 central Pennsylvania to Wythe county- of Virginia, a distance of not 

 less than 400 miles ; while the sandy division of the Chester, equiva- 

 lent to the highest part of the Mississippian, contains thin coal beds 

 at many places west from the old Cincinnatian land. The writer 

 has not been able to make sufficient study of conditions elsewhere to 

 justify him in offering a generalization; but in the Appalachian 

 basin, every observation indicates that conditions favoring deposi- 

 tion of marine limestone or of fine detritus in extended areas are 

 not favorable to the accumulation of coal beds. 



Mx\CR0SC0PicAL Structure of Coal in Beds. 



The several benches of a coal bed may show marked dififerences 

 aside from those already mentioned. The coal from one may be 

 impure, containing large percentage of ash or sulphur ; that from 

 another may be hard, breaking into more or less regular blocks ; 

 that from a third may be brilliant, tender ; that from a fourth may be 

 prismatic, the rude prisms or columns being readily separable with 

 the fingers ; that from a fifth may be a solid coal, yet not hard enough 

 to bear rough handling; while any one of the five benches may show 

 saucer-shaped inclusions of cannel. These variations are shown in 



'^ J. Phillips, " A Treatise on Geology,"' new ed., London, 1852, Vol. L, 

 p. 190. 



