Among the more important subjects which, it has been held, may, in the absence of federal legislation, be controlled by the States, because they lend themselves to local regulation, are ferries, bridges,, pilotage, and harbor regulations.

The purpose of this treatise which is the determination and statement of the general principles of United States constitutional law does not require us to review in any detail the adjudications of the Supreme Court as to these several subjects. As has been said, each case has to be decided upon its own merits.

The general rule governing all the cases is, perhaps, best stated and the authorities summarized, in Covington, etc., Bridge Co. v.

55 Thayer in a note in his Cases on Constitutional Law. p. 2190. points out that this question as to the need for local or national regulation is, inherently, a legislative and not a judicial one.

56 L54 U.. S. 204; 14 Sup. Ct. Rep. 1087; 38 L. ed. 962. "The adjudications of this court with respect to the power of the States over the general subject of commerce are divisible into three classes. First, those in which the State is exclusive; second, those in which the States may act in the absence of legislation by Congress; third, those in which the action of Congress is exclusive and the States, cannot interfere at all. The first class, including all. those wherein the States have plenary power, and Congress has no right to interfere, concern the strictly internal commerce of the State, and while the regulations of the State may affect interstate commerce indirectly, their