The Secretary of the Interior is authorized to accept donations of land, interest in land, buildings, structures, and other property within the boundaries of said park as determined and fixed hereunder and donations of funds for the purchase and/or maintenance thereof, the title and evidence of title to lands purchased to be satisfactory to the Secretary of the Interior: Provided, That the Secretary of the Interior is authorized, in his discretion, to accept on behalf of the United States other lands, easements, and buildings of Revolutionary War interest in Morris and adjacent counties in New Jersey as may be donated for the extension of the Morristown National Historical Park.