50 ICHTHYOLOGIA OHIENSIS 



first section of which terminates at the end of the 

 narrow valley above Troy in Indiana, and the second 

 which includes the broad and flat valleys reaches to 

 the inouth. The upper part of the river is the long- 

 est, being about seven hundred miles long. 



Breadth. At Pittsburgh the Ohio is about one 

 quarter of a mile wide, above the falls and near the 

 mouth it is over one mile : its average breadth may 

 be reckoned at half a mile or rather two thousand 

 five hundred feet. 



Depth. Very variable according to places and 

 times. The mean depth at low water may be reck- 

 oned at three feet, and at high water at about thirty 

 feet. Average medium fifteen feet. 



Velocity. The current of the Ohio is generally 

 gentle, except at the falls and ripples. Its average 

 at low water may be stated at two miles an hour and 

 at high water at four miles an hour. 



Bulk. The quantity of waters flowing in the Ohio 

 may be therefore calculated, upon a general medium 

 of the above breadth, depth, and velocity, at about 

 forty millions of cubic feet, during an hour at low 

 water, and at more than eight hundred millions of 

 such feet at high water. Average medium three 

 hundred and eighty millions in an hour, nine thou- 

 sand one hundred and twenty millions in a day, and 

 more than three millions of millions of feet in one 

 year. 



Waters. They are slightly turbid, and become 

 much more so in the rises. At a low stage they are 

 almost clear, and at all times very salubrious. The 

 Monongahela has the same character, while the Alle- 

 ghany is almost perfectly clear. The turbidity of 

 the waters is produced by very fine particles of earthy 



