The extension of the federal judicial power "to all cases of admiralty and maritime jurisdiction" can better be understood if it is stated that in England admiralty courts have jurisdiction of matters on the high seas which are beyond the jurisdiction of the ordinary courts. The purpose of giving such a jurisdiction to the federal courts was to enable them to exercise the powers of admiralty courts in England. But as a matter of fact the jurisdiction has been extended by construction, so that it is broader in scope than that of the English admiralty courts. Admiralty cases are those brought for breaches of contract relating to maritime affairs, or for torts committed on the high seas or other waters within the admiralty jurisdiction, or for the enforcement of the peculiar liens recognized by courts of admiralty. The admiralty law is distinct in its rules and methods of procedure from both the law and equity systems, and as a separate branch of the law, it is exclusively administered in the federal courts; that is to say, an admiralty case cannot be tried in the state courts. It is true, the state courts may give the ordinary legal or equitable relief between the parties as to subject-matter which might have been the basis for a proceeding in admiralty; but an admiralty case as such cannot be tried save in the federal courts upon which admiralty jurisdiction is conferred by acts of Congress.

In England the admiralty jurisdiction is limited to the high seas and navigable waters within the ebb and flow of the tide; but this limitation has been deemed inapplicable in this country, because of the existence of lakes and rivers capable of navigation, and over which extensive foreign commerce is conducted, in which the tide does not ebb and flow. As now construed, the admiralty jurisdiction extends not only over the high seas, but over all of the navigable waters of the United States which constitute avenues for foreign or interstate commerce (The Steamboat Magnolia). Thus, the Great Lakes, the navigable rivers, such as the Mississippi and the Hudson, and even the canals, are within the admiralty jurisdiction, and the powers of the admiralty courts extend to the determination of cases relating to maritime rights or transactions on all such waters.