of St. Bernard and the Louisiana Marshes constitute a peninsula in the true sense of the word, but insists that they constitute an archipelago of islands. Certainly there are in the body of the Louisiana Marshes or St. Bernard peninsula portions of sea marsh which might technically be called islands, because they are land entirely surrounded by water, but they are not true islands. They are rather, as the Commissioner of the General Land Office wrote the Mississippi land commissioner in 1904, "in fact, hummocks of land surrounded by the marsh and swamp in said townships.

And when the Louisiana act used the words: "thence bounded by the said Gulf to the place of beginning, including all islands within three leagues of the coast," the coast referred to is the whole coast of the State, and the peninsula of St. Bernard formed an integral part of it. Lake Borgne and Mississippi Sound are bodies of salt water and as such parts of the sea or Gulf, and as the coast of Louisiana began along the north shore of the peninsula, it is not to be supposed that the islands referred to by Congress in the Louisiana act were solely those islands to the south of that State.

The contention of Mississippi is based upon an assumed inconsistency between the Louisiana and the Mississippi acts, but we think upon a true interpretation, in the light of the facts, that no such inconsistency can be imputed. The maps show that there is a chain, not of alluvial but of sea sand islands running from the west shore of Mobile Bay in the State of Alabama, westward to and inclusive of Cat Island in the State of Mississippi. This chain forms the southern boundary of Mississippi Sound, and the islands are all relatively the same. distance from the shore of the States of Mississippi and of Alabama. They, beginning at the eastern end, are Dauphin, Petit Bois, Horn, Ship and Cat Islands, and there are some other islands lying within this chain. If Congress referred to these islands as being thus within six leagues of the shore, when the act creating the State of Mississippi was passed, it follows that there would be no conflict with prior existing boundaries of

the State of Louisiana, particularly if the deep water sailing channel line be taken as the correct boundary between the States. And when Congress created a separate territorial government for the eastern part of Mississippi Territory and called it Alabama, by the act of March 3, 1817, it used the same language concerning the western and southern boundary of the Territory: "thence due south to the Gulf of Mexico, thence eastwardly, including all islands within six leagues of the shore to the river Perdido and thence up same to the beginning." It seems obvious to us that it was to this chain of islands that Congress referred when it admitted Mississippi into the Union, and that it had no intention whatsoever of giving Mississippi any claim of ownership in the sea marsh islands, which had been previously granted to the State of Louisiana.

We are of opinion that the peninsula of St. Bernard in its entirety belongs to Louisiana; that the Louisiana Marshes at the eastern extremity thereof form part of the coast line of the State; and that the islands within nine miles of that coast are hers, except as restricted by the deep water sailing channel regarded as a boundary. Cat Island, for instance, is within the nine miles, but it is north of the deep water channel, is not alluvial, and is conceded by both States to belong to Mississippi.

3. That there is a deep water sailing channel line emerging from the mouth of Pearl river, and extending east between Lower Point Clear and Grand Island, is shown by the numerous maps, surveys and sketches in the record. It separates into two branches, one of them passing betwen Cat Island and Isle à Pitre.

Among the maps put in evidence by Louisiana is one prepared by George Gauld, M. A., for the British Admiralty in the year 1778, and, from the relative depths of water given, the existence of this same channel, extending out into the Gulf, southwest of Cat Island, is shown and is the same as noted on maps of subsequent years.

February 14, 1839, an act of the legislature of Mississippi was

approved, providing for a survey of the Mississippi coast. The survey and report are given in full in the record, and the deep water channel above referred to is traceable in detail on the sketch. The channels indicated on this survey and on the United States Coast and Geodetic Survey map are the same channels. It may be noted, in passing, that the body of water now known as "Mississippi Sound," is not so designated on this sketch, and the first map which uses this name, to which our attention has been called, was issued in 1866.

Louisiana lies between the States of Mississippi to the east and Texas to the west. The southern portion of Louisiana is geologically of an alluvial formation, containing the delta of the Mississippi river. The peninsula of the parish of St. Bernard is practically a part of this delta formation.

Mississippi's mainland borders on Mississippi Sound. This is an inclosed arm of the sea, wholly within the United States, and formed by a chain of large islands, extending westward from Mobile, Alabama, to Cat Island. The openings from this body of water into the Gulf are neither of them six miles wide. Such openings occur between Cat Island and Isle à Pitre; between Cat and Ship Islands; between Ship and Horn Islands; between Horn and Petit Bois Islands; between Petit Bois and Dauphin Islands; and between Dauphin Island and the mainland on the west coast of Mobile Bay. The maps show all this, and, among others, reference may be made to Jeffrey's map of 1775, given in the record, and which in reduced form is reproduced from Jeffrey's Atlas of 1800 as the frontispiece of vol. II Adams' History of the United States.

Now to repeat, the boundary of Louisiana separating her from the State of Mississippi to the east is the thread of the channel of the Mississippi river, and this extends south until it reaches the thirty-first degree of north latitude and then runs directly east along that degree until Pearl river is reached; thence south along the channel of that river to Lake Borgne. Pearl river flows into Lake Borgne, Lake Borgne into Mississippi Sound and Mississippi Sound into the open Gulf of Mexico,

through, among other outlets, South Pass, separating Cat Island from Isle à Pitre.

If the doctrine of the thalweg is applicable, the correct boundary line separating Louisiana from Mississippi in these waters is the deep water channel.

The term "thalweg" is commonly used by writers on international law in definition of water boundaries between States, meaning the middle or deepest or most navigable channel. And while often styled "fairway" or "midway" or "main channel, the word itself has been taken over into various languages. Thus in the treaty of Luneville, February 9, 1801, we find "le Thalweg de l'Adige," "le Thalweg du Rhin," and it is similarly used in English treaties and decisions, and the books of publicists in every tongue.

In Iowa v. Illinois, 147 U. S. 1, the rule of the thalweg was stated and applied. The controversy between the States of Iowa and Illinois on the Mississippi river, which flowed between them, was as to the line which separated "the jurisdiction of the two States for the purposes of taxation and other purposes of government. Iowa contended that the boundary line was the middle of the main body of the river, without regard to the "steamboat channel" or deepest part of the stream. Illinois claimed that its jurisdiction extended to the channel upon which commerce on the river by steamboats or other vessels was usually conducted. This court held that the true line in a navigable river between States is the middle of the main. channel of the river.

Mr. Justice Field, delivering the opinion of the court, said: “When a navigable river constitutes the boundary between two independent States, the line defining the point at which the jurisdiction of the two separates is well established to be the middle of the main channel of the stream. The interest of each State in the navigation of the river admits of no other line. The preservation by each of its equal right in the navigation of the stream is the subject of paramount interest. It is, therefore, laid down in all the recognized treatises on interVOL. CCII-4

national law of modern times that the middle of the channel of the stream marks the true boundary between the adjoining States up to which each State will on its side exercise jurisdiction. In international law, therefore, and by the usage of European nations, the term 'middle of the stream,' as applied to a navigable river, is the same as the middle of the channel of such stream, and in that sense the terms are used in the treaty of peace between Great Britain, France, and Spain, concluded at Paris in 1763. By the language, 'a line drawn along the middle of the river Mississippi from its source to the river Iberville,' as there used, is meant along the middle of the channel of the river Mississippi."

This judgment related to navigable rivers. But we are of opinion that, on occasion, the principle of the thalweg is applicable, in respect of water boundaries, to sounds, bays, straits, gulfs, estuaries and other arms of the sea.

As to boundary lakes and landlocked seas, where there is no necessary track of navigation, the line of demarcation is drawn in the middle, and this is true of narrow straits separating the lands of two different States; but whenever there is a deep water sailing channel therein, it is thought by the publicists that the rule of the thalweg applies. 1 Martens (F. de), 2d ed. 134; Hall, § 38; Bluntschli, 5th ed. §§ 298, 299; 1 Oppenheim, 254, 255.

Thus Martens writes: "What we have said in regard to rivers and lakes is equally applicable to the straits or gulfs of the sea, especially those which do not exceed the ordinary width of rivers or double the distance that a cannon can carry.'

So Pradier Fodéré says (Vol. II, p. 202), that as to lakes, "in communciation with or connected with the sea, they ought to be considered under the same rules as international rivers. The same view is confirmed by decisions of this court and of many arbitral tribunals.

In Devoe Manufacturing Company, 108 U. S. 401, the question at issue was in regard to the boundary line between New York and New Jersey under an agreement between the two