426 STEVENSON— THE FORMATION OF COAL BEDS. [Nov. i. 



Appalachia by additions along the western side from New England 

 through Virginia, thus giving a great area on which erosion could 

 work and did work, as evidenced by clastic sediments in the northern 

 part of the basin. The Cincinnati uplift of authors, occurring at 

 the same time, led to the elevation of Cincinnatia (of Schuchert), 

 the western boundary of the basin. Contemporaneously, as indi- 

 cated by Schuchert, a less conspicuous land area, Alleghania, ap- 

 peared within the basin, rudely parallel to Appalachia and extend- 

 ing southwardly across western Pennsylvania and eastern Ohio. It 

 was separated from Cincinnatia by the Ohio basin. During the 

 Silurian, there was occasional communication across Cincinnatia 

 with the Mississippi region beyond and the faunas indicate that the 

 basin opened northwardly to the Atlantic ocean. The same type of 

 evidence shows that the basin was divided by a land area in southern 

 Virginia, so that there was a northern sea extending into New York, 

 as well as a southern sea in Tennessee and Alabama. 



Studies by many geologists make clear that the southern portion 

 of Appalachia was unstable. Southward from central Pennsyl- 

 vania, the early Devonian rocks are wanting along the eastern side, 

 while in southern Virginia and thence southward only the lower 

 beds of the Middle Devonian are found. In Alabama the Devonian, 

 more than 8,000 feet thick in central Pennsylvania, is represented by 

 only dark shale rarely exceeding 100 feet and, near its southern 

 limit, varying from 3 to 30 feet. 



The area embraced in Schuchert's Alleghania was of decided 

 instability. It received deposits during the Chemung, for that 

 formation with its characteristic conglomerates crossed the area, 

 though with reduced thickness ; but all the principal elements of 

 the section observed in central Pennsylvania are present. The 

 intervals decrease toward this area and there is notable thinning 

 above the upper conglomerate. The Catskill beds, following the 

 Chemung, thin out against Alleghania, showing that once more it 

 was above water. That formation, as defined by Vanuxem, the 

 first to assign a definite meaning to the term, is 3,900 feet thick in 

 Fulton county of Pennsylvania; 3,000, in the eastern portion of 

 Bedford; 1,980 in western Bedford; it is concealed in Somerset, 



