and transporting down Grand River, goods destined and marked for other States than Michigan, and in receiving and transporting up the river goods brought within the State from without its limits; * * * So far as she was employed in transporting goods destined for other States, or goods brought from without the limits of Michigan and destined to places within that State, she was engaged in commerce between the States, and however limited that commerce may have been, she was, so far as it went, subject to the legislation of Congress. She was employed as an instrument of that commerce; for whenever a commodity has begun to move as an article of trade from one State to another, commerce in that commodity between the States has commenced."[355] Turning then to counsel's _reductio ad absurdum_, the Court added: "We answer that the present case relates to transportation on the navigable waters of the United States, and we are not called upon to express an opinion upon the power of Congress over interstate commerce when carried on by land transportation. And we answer further, that we are unable to draw any clear and distinct line between the authority of Congress to regulate an agency employed in commerce between the States, when the agency extends through two or more States, and when it is confined in its action entirely within the limits of a single State. If its authority does not extend to an agency in such commerce, when that agency is confined within the limits of a State, its entire authority over interstate commerce may be defeated. Several agencies combining, each taking up the commodity transported at the boundary line at one end of a State, and leaving it at the boundary line at the other end, the Federal jurisdiction would be entirely ousted, and the constitutional provision would become a dead letter."[356] In short, it was admitted inferentially, that the principle of the decision would apply to land transportation; but the actual demonstration of the fact still awaited some years.[357] See _infra_. HYDROELECTRIC POWER