Beginning in the middle of the main channel of the Missouri River, at a point where the western boundary line of the state intersects the same; thence south to the line between townships forty-six and forty-seven; thence east with the said township line to the southeast corner of section thirty-three of township forty-seven, range twenty-nine, west; thence north with the subdivisional lines to the middle of the main channel of the Missouri River; thence up said river, in the middle of the main channel thereof, to the place of beginning.