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. The director of the Dpt des Cartes of the Marine and Colonies, at Paris, in 1872 possessed a rich mass of historical documents, the collection of which had covered thirty years of his life. This material related chiefly to the French rule in North America, and its owner had offered to dispose of it to the French government on condition that the entire collection should be published. The French government was, however, only willing to publish parts of the whole, and the director retained possession of his property. Through the efforts of Mr. Francis Parkman, the truthful American historian, supported by friends, an appropriation was made by Congress, in 1873, for the purchase and publication of this valuable collection of the French director; and it is now the property of the United States government. All that relates to the Sieur de la Salle--his journals and letters--has been published in the original French, in three large volumes of six hundred pages each. La Salle discovered the Ohio, yet the possession of the rich historical matter referred to throws but little light upon the details of this important event. The discoverer- -of the great west, in an address to Frontenac, the governor of Canada, made in 1677, asserted that he had discovered the Ohio, and had descended it to a fall which obstructed it. This locality is now known as the "Falls of the Ohio," at Louisville, Kentucky.