For the purpose of determining the descent of land to the heirs of any deceased Indian under the provisions of section 348 of this title, whenever any male and female Indian shall have cohabited together as husband and wife according to the custom and manner of Indian life the issue of such cohabitation shall be, for the purpose aforesaid, taken and deemed to be the legitimate issue of the Indians so living together, and every Indian child, otherwise illegitimate, shall for such purpose be taken and deemed to be the legitimate issue of the father of such child: Provided, That the provisions of this Act shall not be held or construed as to apply to the lands commonly called and known as the “Cherokee Outlet.”