The Secretary of the Interior is authorized to acquire, in such manner as he shall consider to be in the public interest, any land or interests in land situated within sections 15, 22, 27, 34, block 234, Brewster County, Texas, which he shall consider to be suitable for addition to the Big Bend National Park: Provided, however, That the aggregate cost to the Federal Government of properties acquired hereafter and under the provisions hereof shall not exceed the sum of $10,000. Properties acquired pursuant to this section shall become a part of the park upon acquisition of title thereto by the United States.