There is reserved and excepted from the unallotted lands now embraced within the Flathead Indian Reservation, in the State of Montana, a parcel not to exceed twenty thousand acres of said lands, near the confluence of the Pend d’Oreille and Jocko Rivers, for a permanent National Bison Range for the herd of bison presented by the American Bison Society. The Secretary of the Interior is authorized and directed to inclose said lands with a good and substantial fence and to erect thereon the necessary sheds and buildings for the proper care and maintenance of the said bison.