512 STEVENSON— THE FORMATION OF COAL BEDS. [Nov. i, 



The use of the term currents to explain local conditions is apt to 

 be misleading. There is no good reason for supposing that there 

 were any currents in the Appalachian basin. The close succession 

 of often coarse sandstones upon marine limestones, even upon 

 sapropelic limestone, shows that the deposits were near a shore. 



A review of the conditions leads to conclusions the same as 

 those suggested by deposits of other materials. The marine lime- 

 stones are local, are in areas which, for the most part, can be de- 

 termined closely. Those of the earlier formations are found on 

 both sides of the Alleghenia ridge, but the localities, at which 

 observations have been made, are too widely separated to admit of 

 an attempt to determine their relations. The Beaver and Allegheny 

 limestones, however, have been traced in detail. On the western 

 side, within the Ohio basin (of Schuchert), they followed in a 

 general way the direction of the pre-Beaver valley in Ohio but as 

 they approached the Pennsylvania line, they turn eastward into that 

 state. This variation becomes notable in the Vanport, which seems 

 to have followed rather closely in Pennsylvania the lines of valleys 

 eroded during the immediately preceding times. There can be no 

 question that the early drainage line, established prior to Beaver 

 time, persisted until the middle of the Allegheny and that it de- 

 termined the area of sea-invasion, as the old river valleys along the 

 Atlantic coast have done in recent times. The extent of the lime- 

 stones, though they follow the same line in great part, shows that 

 the estuaries, due to drowning of the valleys, were not of equal 

 length. When one examines the conditions on the eastern side, he 

 finds that, in the Beaver and Allegheny, the marine limestones 

 occur within a small area in West Virginia. Erosion has removed 

 the Pennsylvanian from a great expanse on the eastern side so that 

 the relations of these limestones cannot be determined beyond the 

 present exposures, but the deposits seem to mark the upper portion 

 of successive estuaries along the same general course. The sea- 

 invasion on this side may not have reached so far north as on the 

 western. 



In the early Conemaugh, the conditions were somewhat dififerent. 



