For the purpose of carrying out the provisions of this section and the Secretary of the Interior is authorized to accept donations of land or right-of-way, or to acquire title to any land along or adjacent to the said Point Lookout Road as may be deemed desirable by him for the protection of said road, by exchange for any unappropriated public lands within sections 29 and 32, township 36 north, range 14 west, New Mexico principal meridian, of equal value; the value of the lands offered for exchange hereunder and the value of the lands of the United States to be selected therefor shall be ascertained in such manner as the Secretary of the Interior may direct; and the owners of lands offered to the United States pursuant hereto shall, before the exchange is effective, furnish the Secretary of the Interior evidence satisfactory to him of title to the lands offered in exchange.section 111a of this title