All stocks, bonds, or other securities or evidences of indebtedness held by the Secretary of the Interior on June 10, 1876, in trust for the benefit of certain Indian tribes shall, within thirty days from that date, be transferred to the Treasurer of the United States, who shall become the custodian thereof; and it shall be the duty of said Treasurer to collect all interest falling due on said bonds, stocks, and so forth, and deposit the same in the Treasury of the United States, and to issue certificates of deposit therefor, in favor of the Secretary of the Interior, as trustee for various Indian tribes. And the Treasurer of the United States shall also become the custodian of all bonds and stocks which may be purchased for the benefit of any Indian tribe or tribes after the transfer of funds herein authorized, and shall make all purchases and sales of bonds and stocks authorized by treaty stipulations or by acts of Congress when requested so to do by the Secretary of the Interior: Provided, That nothing in this section shall in any manner impair or affect the supervisory and appellate powers and duties in regard to Indian affairs which may be vested in the Secretary of the Interior as trustee for various Indian tribes, except as to the custody of said bonds and the collection of interest thereon as hereinbefore mentioned.