8 PHYSICAL GEOGRAPHY OF 



And such is also the characteristic of many of the smaller ramifications of the 

 head waters of the Alleghany, which do not rise on the borders of Lake Erie. 

 They still descend so gradually and uniformly that they may be safely traversed 

 by rafts and boats when reduced to a width of only 12 or 15 feet. 



The elevation of the Alleghany at Olean Point, 250 miles above Pittsburg, 

 as determined by the surveys of the writer, is 1,403 feet above tide. Steamboats 

 have ascended to this point in sufficient water — 2,300 miles from the mouth of 

 the Mississippi— and might, by a little labor, be capable of running there at all 

 times. 



The following figure is a profile of the Alleghany and the outlet of Chautau- 

 que lake, one of its tributaries, showing the physical formation of the district 

 connecting the head waters of the Ohio with Lake Erie. 



Horizontal scale — 20 miles to the inch. 



Vertical scale — 800 feet to the inch. 



FIG. I. 



CHAUTAUQUE L.AKE. 



An inspection of this diagram will exhibit the plain along which flow some of 

 the noi'thern tributaries of the Ohio, and the sudden depression below that plain 

 of the basin which contains Lake Erie. It is a correct representation, drawn 

 from the actual surveys of the writer. 



The upper Alleghany and its tributaries, traced towards their sources, rise 

 very uniformly at the rate of about 3 feet per mile, and terminate in a number 

 of small lakes, of which the Chautauque is the most important, and separated 

 like the others by a narrow ridge from the basin of Lake Erie. An excavation 

 only 60 feet deep through this ridge would turn one of the principal tributaries 

 of the Ohio into Lake Erie and the St. Lawrence. 



Tracing the Ohio river from Coudersport, which is some 40 miles above the 

 extreme limit of the natural steamboat navigation of the Alleghany, to the 

 entrance of the Mississippi into the Gulf of Mexico, we find the following rate 

 of descent from point to point : 



