salt, clays, and building-stone. The rainfall of the Ohio Valley is so
great as to give the river a mean discharge at its mouth (according to
the report of the United States government engineers) of one hundred
and fifty-eight thousand cubic feet per second. This is the drainage
of an area embracing two hundred and fourteen thousand square miles.

The head of the Ohio River, at Pittsburgh, has an elevation of eleven
hundred and fifty feet above the sea, while in the long descent to its
mouth there is a gradual fall of only four hundred feet; hence its
current, excepting during the seasons of freshets, is more gentle and
uniform than that of any other North American river of equal length.
During half the year the depth of water is sufficient to float
steamboats of the largest class along its entire length. Between the
lowest stage of water, in the month of September, and the highest, in
March, there is sometimes a range of fifty feet in depth. The spring
freshets in the tributaries will cause the waters of the great river
to rise twelve feet in twelve hours. During the season of low water
the current of the Ohio is so slow, as flatboat-men have informed me,
that their boats are carried by the flow of the stream only ten miles
in a day. The most shallow portion of the river is between Troy and
Evansville. Troy is twelve miles below the historic Blennerhasset's
Island, which lies between the states of Ohio and Virginia. Here the
water sometimes shoals to a depth of only two feet.

Robert Cavelier de la Salle is credited with having made the discovery
of the Ohio River. From the St. Lawrence country he went to Onondaga,
and reaching a tributary of the Ohio River, he descended the great
stream to the "Fa1ls," at Louisville, Kentucky. His men having
deserted him, he returned alone to Lake Erie. This exploration of the
Ohio was made in the winter of 1669-70, or in the following spring.