Beginning at a point in the middle of the main channel of the Missouri River, where a prolongation south of the line between ranges four and five, west, would intersect the same; thence north on the said range line to the southwest corner of section seven, township forty-seven, range four, west; thence east with the subdivisional lines to the southeast corner of section eight, township forty-seven, range three, west; thence north with the subdivisional lines to the northeast corner of section five, township fifty, north, range three, west; thence with the township line between townships fifty and fifty-one to the northwest corner of township fifty, range six, west; thence south with the range line between ranges six and seven to the middle of the main channel of the Missouri River; thence down said river, in the middle of the main channel thereof, to the place of beginning.