LOWER ALLEGHENY DRAINAGE SYSTEM. 145 



Height ahove tide of f/uvial plains along the Lotoer Allegheny River. 



The interesting series of channels connecting the Lower Allegheny 

 with an old oxbow of the Monongahela River at Pittsburg were mentioned 

 in the discussion of the old Monongahela system, but it may be of interest 

 to consider them in more detail. An old channel of the Monongahela 

 leaves the present stream near Hondestead and passes northward to East 

 Liberty (now a part of Pittsburg). It there curves around to the southwest 

 through Oakland and Schenley Park, coming to the Monongahela again 

 about 3 miles below Homestead. This channel, like the gradation plain of 

 the Monongahela, is nearly a mile in average breadth. Its rock floor 

 stands 175 to 200 feet above the present stream, or about the same as 

 the gradation plain. Its northernmost part is only 1 to 2 miles from the 

 Allegheny Valley, but is separated from it by a chain of hills which in 

 places rise 200 to 300 feet above the old channel. There are, however, 

 three gaps in the chain of hills which were sufficiently low to permit the 

 waters of the Allegheny to enter the old oxbow of the Monongahela and 



MON XLI 10 



