All lands and easements heretofore and hereafter conveyed to the United States by the States of Mississippi, Alabama, and Tennessee for the right-of-way for the projected parkway between Natchez, Mississippi, and Nashville, Tennessee, together with sites acquired or to be acquired for recreational areas in connection therewith, and a right-of-way for said parkway of a width sufficient to include the highway and all bridges, ditches, cuts, and fills appurtenant thereto, but not exceeding a maximum of two hundred feet through Government-owned lands (except that where small parcels of Government-owned lands would otherwise be isolated, or where topographic conditions or scenic requirements are such that bridges, ditches, cuts, fills, parking overlooks, and landscape development could not reasonably be confined to a width of two hundred feet, the said maximum may be increased to such width as may be necessary, with the written approval of the department or agency having jurisdiction over such lands) as designated on maps heretofore or hereafter approved by the Secretary of the Interior, shall be known as the Natchez Trace Parkway and shall be administered and maintained by the Secretary of the Interior through the National Park Service, subject to the provisions of the Act of Congress approved August 25, 1916 (39 Stat. 535), entitled “An Act to establish a National Park Service, and for other purposes”,1