Beginning at a point in the middle of the main channel of the Missouri River, where the prolongation north of the subdivisional line dividing equally into two parts range four would intersect the same; thence south to the northeast corner of section sixteen, township forty, range four, west; thence west with section lines to the range line between five and six; thence south with said range line to the township line between townships thirty-nine and forty; thence west with said township line to the southwest corner of township forty, range six, west; thence north 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.