468 STEVENSON— THE FORMATION OF COAL BEDS, [^'"v. i, 



to their last exposure in West Virginia. They are coarse, loosely 

 cemented and weather into caverns. The area in which they remain 

 is too narrow to afford information respecting the local conditions 

 of deposit. Their presence along the middle line of the area, where 

 the lower formations have little aside from fine materials, marks the 

 approaching close of deposition in the Appalachian basin. 



It is evident that the materials for these sandstones had not a 

 common source. The Bonair, east from Alleghania, received its 

 sand and pebbles from the east, from Appalachia ; it becomes less 

 coarse as it approaches Alleghania but beyond that ridge it is again 

 coarse, even pebbly. The sands and pe'bbles of this western prong 

 must have come from the north as did those of the still newer beds 

 of the New River. The Homewood like the Bonair is very coarse 

 in eastern parts of the basin but the pebbles decrease in size as well 

 as number toward the northwest. But in much of western Penn- 

 sylvania, the rock is coarse and more or less pebbly. Here again 

 one must look to the north for the source of coarse material ; none 

 could come even from the line of the present Allegheny mountains, 

 for there the rock is without coarse elements except along narrow 

 easterly-westerly lines, marking filled valleys, cut probably in the 

 sandstone itself. The fine sands and argillaceous shales, so com- 

 monly marking the horizon in Ohio, point unmistakably to the low 

 Cincinnatia at the west as their place of origin. The sandstones of 

 the higher formations extend successively farther toward the in- 

 terior of the area of deposit, and for the most part become coarser 

 and less firmly cemented as one ascends in the series. The area of 

 deposit was contracting throughout and elevation along the borders 

 permitted the streams to cut down to the coarse beds of earlier 

 formation. 



The abrupt variations in structure and composition, laterally 

 and vertically, seem to find explanation in the phenomena of actual 

 river deposits. River phenomena are distinct in the Bonair west 

 from Alleghania. Along the middle line of the old channel way 

 the rock is coarse, usually with abundant pebbles of considerable 

 size, "but on each side the coarseness diminishes so that, at the east, 

 one finds sandstone with pebbly layers and, at the west, merely 



