142 J. J. STEVENSON CARBONIFEROUS OF APPALACHIAN BASIN 



places in Eoane county; for, though only 13 to 24 inches thick it is 

 the only coal bed in the region. It is hardly probable that the succes- 

 sion will ever be worked out. The limestones and coal beds, with the 

 exception of the Washington, have all disappeared, the sandstones are 

 indefinite, and the red beds are inconstant to the last degree. To follow 

 the section with any degree of certainty seems almost impossible. In 

 this part of the field there are no natural division planes above the 

 Alleghenv. 



"&' 



Geographical Changes during the Pennstlvanian* 



Toward the close of the Devonian, the Appalachian water area had 

 decreased to a basin at the east, 70 to 80 miles wide at most, extending 

 from the Catskill mountains of New York across Pennsylvania, Mary- 

 land, and Virginia to a short distance beyond New river, in the last 

 state. The Catskill beds, deposited in this narrow basin, which in south- 

 ern Pennsylvania reached westwardly only to Laurel hill, about 60 miles 

 east from the western boundary of the state, are red to green shales and 

 sandstones, fine grained and argillaceous, many of them little more than 

 indurated clay beds.f 



The close of the Devonian was marked by elevation at the east and 

 slow sxibsidence toward the west and south — a reversal of the conditions 

 prevailing during the later Devonian. The earlier Mississippian deposits, 

 comparatively coarse on the easterly side to beyond New river, in Vir- 

 ginia, eventually reached far into Ohio. The subsidence toward the 

 west was not of long continuance in the northern part of the basin and 

 was followed by elevation on that side, so that the western limit of each 

 Mississippi formation in Ohio and northern Kentucky is east from 

 that of its predecessor ; but the subsidence continued toward the south for 

 a much longer period, and the later Mississippian overlaps even the 

 earlier Devonian, while its limestones pass into sandstone in approaching 

 the old land area of eastern and southern Alabama, though even there 

 some elevation occurred before this time closed. The narrowing of the 

 basin brought about conditions at the close of the Mississippian resem- 

 bling those at the close of the Devonian. 



* As the writer is preparing anotlier work, in which the facts thus far gathered will 

 be discussed in their bearing upon the origin of coal and the accumulation of coal 

 beds, it is necessary here only to summarize the varying relations of land and water 

 during Pennsylvanian time. 



t The term Catskill Is used here as by Vanuxem, who first defined and named the 

 "Catskill group." It has no reference to color of the beds, which is due to a condition 

 beginning in New York at the close of the Hamilton and thence gradually extending 

 southward until, at the close of the Devonian, it prevailed throughout the area of 

 deposit. 



