The Secretary of the Interior is authorized and directed to make an examination of Jamestown Island, parts of the city of Williamsburg, and the Yorktown battlefield, all in the State of Virginia, and areas for highways to connect said island, city, and battlefield with a view to determining the area or areas thereof desirable for inclusion in the said Colonial National Historical Park, not to exceed two thousand five hundred acres of the said battlefield or five hundred feet in width as to such connecting areas, and upon completion thereof he shall make appropriate recommendations to the President, who shall establish the boundaries of said national park by proclamation: Provided, That the boundaries so established may be enlarged or diminished by subsequent proclamation or proclamations of the President upon the recommendations of the Secretary of the Interior, any such enlargement only to include lands donated to the United States or purchased by the United States without resort to condemnation.