"The exercise of these powers would not conflict with any State authority. Most of the States have laws forbidding the killing, capture or pursuit of different kinds of game during specified portions of the year. This makes such killing, etc., lawful at other times, but only lawful because not made unlawful. And it is lawful only when the State has power to make it lawful, by either implication or direct enactment. But, except in those cases already referred to, such as eminent domain, service of process, etc., no State has power to authorize or make lawful a trespass upon private property. So that, though Congress should prohibit such killing, etc., upon its own lands, at all seasons of the year, this would not conflict with any State authority or control. That the preservation of game is part of the public policy of those States, and for the benefit of their own people, is shown by their own legislation, and they cannot complain if Congress upon its own lands goes even further in that direction than the State, so long as the open season of the State law is not interfered with in any place where such law is paramount. [Illustration: MOUNTAIN SHEEP AT REST] "It has always been the policy of the Government to invite and induce the purchase and settlement of its public lands; and as the existence of game thereon and in their localities adds to the desirability of the lands, and is a well-known inducement to their purchase, it may well be considered whether, for this purpose alone, and without reference to the protection of the lands from trespass, Congress may not, on its own lands, prohibit the killing of such game."