Any company desiring to secure the benefits of sections 687a, 687a–2 to 687a–5,¹ and 942–1 to 942–9 of this title and sections 607a and 615a of title 16, shall, within twelve months after filing the preliminary map of location of its road as hereinbefore prescribed, whether upon surveyed or unsurveyed lands, file with such officer as the Secretary of the Interior may designate of the land office for the district where such land is located a map and profile of at least a twenty-mile section of its road or a profile of its entire road if less than twenty miles, as definitely fixed; and shall thereafter each year definitely locate and file a map of such location as aforesaid of not less than twenty miles additional of its line of road until the entire road has been thus definitely located, and upon approval thereof by the Secretary of the Interior the same shall be noted upon the records of said office, and thereafter all such lands over which such right of way shall pass shall be disposed of subject to each right of way: Provided, That if any section of said road shall not be completed within one year after the definite location of said section so approved, or if the map of definite location be not filed within one year as herein required, or if the entire road shall not be completed within four years from the filing of the map of definite location, the rights herein granted shall be forfeited as to any such uncompleted section of said road, and thereupon shall revert to the United States without further action or declaration, the notation of such uncompleted section upon the records of the land office shall be canceled, and the reservations of such lands for the purposes of said right of way, stations, and terminals shall cease and become null and void without further action.