Beginning in the middle of the main channel of the Missouri River, where the prolongation south of the line between ranges twenty-five and twenty-six would intersect the same; thence north with said range line to the northeast corner of township fifty-four, range twenty-six, west; thence west with the township line to the northwest corner of township fifty-four, range twenty-nine; thence south with the range line to the middle of the main channel of the Missouri River; thence down the Missouri River, in the middle of the main channel thereof, to the place of beginning.