Grier: Morphological Features of Mussel-shells. 155 



Physical Conditions of the Drainage Basin of the Upper Ohio. 



The drainage basin of the Upper Ohio River (19, 28, 44) lies in the 

 central part of the eastern part of the United States. The river is 

 formed by the junction of the Allegheny and Monongahela Rivers 

 at Pittsburgh, Pennsylvania. From that point the Ohio flows in a 

 generally southwestern direction and joins the Mississippi at Cairo, 

 Illinois. The principal tributaries with which this investigation is 

 concerned (beginning at the source and following down the right or 

 north bank) are the Allegheny and Beaver Rivers; on the left are the 

 Monongahela River, Raccoon Creek and Chartiers Creek. The total 

 length of the Ohio River is 767 miles and the total area drained is 

 about 210,000 square miles. The portion of the drainage basin with 

 which we are concerned lies in the states of New York, Pennsylvania, 

 Ohio, West Virginia, and Maryland. The source of the tributaries 

 from the north lies in the glaciated area, the sources of the southern 

 tributaries are located in the steep and rocky slopes of the western 

 side of the Appalachian Mountains. The topography varies from flat 

 and rolling in the western and northern portions, to rough and moun- 

 tainous in the southern and eastern sections. 



The Allegheny River, which unites with the Monongahela River at 

 Pittsburgh to form the Ohio, drains the western slopes of the Alle- 

 gheny Mountains. The Allegheny is the larger stream, as its drainage 

 area is nearly fifty per cent, greater than that of the Monongahela. 

 The drainage of the Allegheny lies in the states of Pennsylvania and 

 New York. The river rises in the central part of Potter County in 

 the northern part of Pennsylvania; flows in a generally northwestern 

 direction across the state line into New York, thence southward back 

 into Pennsylvania. At Franklin in Venango County the river turns 

 and' flows southeastward to the mouth of Mahoning Creek in Arm- 

 strong County, thence it turns to the southwest and joins the Ohio 

 at Pittsburgh. The upper Allegheny and its tributaries are plateau 

 streams, originating upon the Allegheny plateau at an elevation of 

 300 feet above the main stream. The tributaries above the Clarion 

 descend by rapids and cascades from only a height of 150 to 200 feet 

 above the river. 



The tributaries with which we are concerned beginning at the source 

 and following down the right bank as follows: Conewango, Broken- 

 straw, and French Creeks; on the left bank are Potato Creek, Clarion 

 River, Red Bank, Mahoning, and Crooked Creeks, and the Kis- 



