"9i-'.J STEVENSON— THE FORMATION OF COAL BEDS. 439 



midway in the great sandstone mass filling the valley just described. 

 It occupies a trough in that sandstone, showing that, during migra- 

 tions of the stream in its valley, portions of the flood plain remained 

 exposed long enough to permit accumulation of an important coal 

 bed. 



A valley of notable extent existed in western Pennsylvania 

 during the early Allegheny. There is good reason for believing 

 that it reached as far east as the border of Cambria county, but 

 connected observations begin only in JefTerson county, somewhat 

 more than 40 miles farther northwest ; thence the course can be 

 followed across southern Clarion, northern Armstrong, northern 

 and western Butler into northern Beaver, — almost to the Ohio 

 River, a distance of about 90 miles in direct line. The interval 

 from the \^anport limestone down to the Homewood sandstone — ^the 

 last member of the Beaver — is filled with coarse to pebbly sand- 

 stone in a strip, 8 to 10 miles wide, on each side of which the normal 

 section is exposed. To trace this valley southward along the Ohio 

 valley is not possible, as the horizon passes quickly under cover, 

 but there are good reasons for supposing a southward extension. 

 Borings at Wheeling, West Virginia, on the Ohio, report the interval 

 filled with sandstone; at Aloundsville. 10 miles south, a line of bor- 

 ings begins, which is continuous across Wetzel countv of West Vir- 

 ginia into Greene county of Pennsylvania, in all of which sandstone 

 fills the interval, thus indicating the existence of a long tributary 

 from the east. It may be that the stream's course lay well west 

 from the Ohio, nearer that of the pre-Beaver valley and that even 

 the top member of the Beaver was invaded. Hodge reports that 

 in Coshocton county of Ohio, a sandstone begins at 25 feet below 

 the A'anport limestone and continues downward 280 feet to a thin 

 coal bed resting on the New River conglomerate, thus passing 

 through the whole of the Beaver. i' 



The portion of the column, beginning with the Vanport lime- 



'■'The observations by W. G. Piatt, I. C. White, H. M. Chance, J. F. 

 Carll and J. J. Stevenson, on which this summary is based, are recorded in 

 "Carboniferous of the Appalachian Basin," Bull. Geol. Soc. Amer., Vol. 

 17, 1906, pp. 65-228; J. T. Hodge, Ohio Geol. Survey, Vol. HI., 1878, p. 572. 



PROC. AMER. PHIL. SOC., I I, 207 B, PRINTED DEC. I3, I9I2. 



