United States. Congress

“ Section 3 And be it further enacted, That in the making of any such exchange or exchanges, it shall and may be lawful for the President solemnly to assure the tribe or nation with which the exchange is made, that the United States will forever secure and guaranty to them, and their heirs or successors, the country so exchanged with them; and if they prefer it, that the United States will cause a patent or grant to be made and executed to them for the same: Provided always, That such lands shall revert to the United States, if the Indians become extinct, or abandon the same. ”