The President of the United States is authorized, in his discretion, to add by Executive proclamation to Yellowstone National Park any or all of the lands within a certain territory or tract in township 9 south, ranges 7 and 8 east, Montana principal meridian, to wit: Beginning at a point on the north line of said Yellowstone National Park where said line crosses the divide between Reese Creek and Mol Heron Creek, thence northeasterly along said divide to the junction of said divide with the branch divide north and west of Reese Creek; thence along said branch divide in a northeasterly and easterly direction around the drainage of Reese Creek, to the Yellowstone River; thence southerly and southeasterly along the west bank of the Yellowstone River to the line marking the western limits of the town of Gardiner, Montana; thence south on said town limits line to the northern boundary of Yellowstone National Park; thence west along the north boundary of Yellowstone National Park to the point of beginning, which are unappropriated lands of the United States or which may be acquired by the United States under the provisions of sections 37 to 40 of this title, within the territory described in this section, subject, however, to all valid existing claims and to reservations such as are authorized by section 39 of this title; but, with the exception of valid existing claims, no land so added to Yellowstone National Park shall be subject to entry under the mining laws of the United States: Provided, That the Secretary of the Interior for such lands as are added to Yellowstone National Park may provide by rules and regulations for the management and use of the added lands as may in his discretion be necessary to accomplish the purposes of sections 37 to 40 of this title: And provided further, That the lands of the United States acquired by donation or purchase within the area described in section 37 of this title shall not be subject to location and entry under the mining laws of the United States nor the Act of June 11, 1906, authorizing homestead entries in national forests.