SECTION 7. Jurisdiction over land acquired by United States; reversion

The United States shall have jurisdiction over any tract of land within the commonwealth acquired by it in fee for the following purposes: for the use of the United States bureau of fisheries, or for the erection of a marine hospital, custom office, post office, life-saving station, lighthouse, beacon light, range light, light keeper's dwelling or signal for navigators; provided, that a suitable plan of such tract has been or shall be filed in the office of the state secretary within one year after such acquisition of title thereto. But the commonwealth shall retain concurrent jurisdiction with the United States in and over any such tract of land to the extent that all civil and criminal processes issuing under authority of the commonwealth may be executed thereon as if there had been no cession of jurisdiction, and exclusive jurisdiction over any such tract shall revest in the commonwealth if such tract ceases to be used by the United States for such public purpose.