That the boundary line dividing and separating the counties of Marshall and Washington, state of Kansas, shall hereafter be as follows: Commencing at a point on the north line of the state where said line is intersected by the range line dividing ranges five and six east of the sixth principal meridian; running thence south on said range line, to a point forty feet north of the line between sections six and seven, in township four south, of range six east; thence east parallel with said section line, to the middle of the Little Blue river; thence south eighty feet; thence west, to the said range line; thence south along said range line, to the southeast corner of said county of Washington as now constituted: Provided, That this portion of sections 6 and 7 so added to the territory of Washington county shall only be used as a public highway to reach the Little Blue river, and to give the county of Washington authority to join with the county of Marshall and build a bridge over said stream, and that in case such bridge shall not be built within five years from the passage of this act, or that after the building of said bridge it shall ever be abandoned as a public highway, then the territory hereby annexed to Washington county shall revert and become again a part of the territory of Marshall county, and the boundary line restored the same as though this act had not passed.