Read it through once

'It is only when you ascend the mighty current for fifty or a hundred miles, and use the eye of imagination as well as that of nature, that you begin to understand all his might and majesty. You see him fertilizing a boundless valley, bearing along in his course the trophies of his thousand victories over the shattered forest--here carrying away large masses of soil with all their growth, and there forming islands, destined at some future period to be the residence of man; and while indulging in this prospect, it is then time for reflection to suggest that the current before you has flowed through two or three thousand miles, and has yet to travel one thousand three hundred more before reaching its ocean destination.'