Pursuant to the turning over to the state of Michigan, for use as a state park, and for no other purpose, the military reservation, lands and buildings of the national park on Mackinac Island, subject to a reversion to the United States whenever the state ceases to use the lands for the purpose described in this section, by the secretary of war, under the authorization of an act of congress, the lands and buildings shall be used as a state park and shall be known as the Mackinac Island state park.