The opinion then proceeds to the consideration of the Act of Congress relied upon by Gibbons. This, Ogden's attorneys contended, merely conferred the American character upon vessels already possessed of the right to engage in the coasting trade; Marshall, on the contrary, held that it conferred the right itself, together with the auxiliary right of navigating the waters of the United States; whence it followed that New York was powerless to exclude Gibbons's vessels from the Hudson. Incidentally Marshall indicated his opinion that Congress's power extended to the carriage of passengers as well as of goods and to vessels propelled by steam as well as to those driven by wind. "The one element," said he, "may be as legitimately used as the other for every commercial purpose authorized by the laws of the Union." Two years later, in the case of Brown vs. Maryland, ¹ Marshall laid down his famous doctrine that so long as goods introduced into a State in the course of foreign trade remain in the hands of the importer and in the original package, they are not subject to taxation by the State. This doctrine is interesting for two reasons. In the first place, it implies the further principle that an attempt by a State to tax interstate or foreign commerce is tantamount to an attempt to regulate such commerce, and is consequently void. In other words, the principle of the exclusiveness of Congress's power to regulate commerce among the States and with foreign nations, which is advanced by way of dictum in Gibbons vs. Ogden, becomes in Brown vs. Maryland a ground of decision. It is a principle which has proved of the utmost importance in keeping the field of national power clear of encumbering state legislation against the day when Congress should elect to step in and assume effective control. Nor can there be much doubt that the result was intended by the framers of the Constitution. ¹ 12 Wheaton, 419.