“ Whether the tracts as to which the swamp land claim is still pending were such as came within the terms of the swamp land grant is a question of fact the decision of which is expressly committed to the Land Department; and this also is true of the question whether the tracts covered by the railroad company's lieu land selections were when the selections were tendered so occupied and appropriated as not properly to be subject to acquisition in that way. The approval or disapproval by the Secretary of the Interior of such lieu selections is not merely a formal act. ”

“ Ct. 385, 57 L. Ed. 623) ; but it does not enable him to complain on behalf of the United States or to assail the patent collaterally (Hoofnagle v. Anderson, 7 Wheat. 212, 214, 215, 5 L. Ed. 437; Smelting Co. v. Kemp, 104 U.S. 636, 647, 26 L. Ed. 875; Bohall v. Dilla, 114 U.S. 47, 51, 5 Sup. Ct. 782, 29 L. Ed. 61; Sparks v. Pierce, 115 U.S. 408, 6 Sup. Ct. 102, 29 L. Ed. 428; Fisher v. Rule, 248 U.S. 314, 318, 39 Sup. Ct. 122, 63 L. Ed. 263) . ”