Olark v. Smith, 13 Pet. 19.5; Hurt v. HoUingworth, 100 U. S.100, These cases 'were mostly founded on state statutes, and were all commenced by bill in equity; and there are expressions in the opinions in most of them indicating that the appropriate mode of proceeding in such cases in the (lourts of the United States, when the land is unoccupied, is by bill in equity.