Commencing at a point on the boundary line of the city of Pittsburgh, and running, by way of Westview, Perrysville, and Wexford, to a point on the dividing line between Allegheny and Butler Counties; thence, by way of Zelienople, to Portersville; thence over route seventy-nine¹ to a point at the intersection of State highway route seventy-nine¹ and the Pittsburgh and Erie road, about one and one-half miles east of Rose Point; thence to a point on the dividing line between Butler and Lawrence Counties; thence to Harlansburg; thence to a point on the dividing line between Lawrence and Mercer Counties; thence, by way of Leesburg, to the borough of Mercer, in Mercer County.