ARTICLE 3.--The boundary line between the two countries west of the Mississippi shall begin on the Gulf of Mexico, at the mouth of the River Sabine, in the sea, continuing north, along the western bank of that river, to the 32d degree of latitude; thence, by a line due north, to the degree of latitude where it strikes the Rio Roxo of Natchitoches, or Red River; then, following the course of the Rio Roxo westward, to the degree of longitude 100 west from London and 23 from Washington; then crossing the said Red River, and running thence, by a line due north, to the River Arkansas; thence following the course of the southern bank of the Arkansas, to its source in latitude 42 north; and thence, by that parallel of latitude, to the South Sea; the whole being as laid down in Melish's map of the United States, published at Philadelphia, improved to the 1st of January, 1818. But, if the source of the Arkansas River shall be found to fall north or south of latitude 42, then the line shall run from the said source due south or north, as the case may be, till it meets the said parallel of latitude 42, and thence, along the said parallel, to the South Sea; all the islands in the Sabine, and the said Red and Arkansas Rivers, throughout the course thus described, to belong to the United States; but the use of the waters and the navigation of the Sabine to the sea, and of the said Rivers Roxo and Arkansas, throughout the extent of the said boundary, on their respective banks, shall be common to the respective inhabitants of both nations. The two high contracting parties agree to cede and renounce all their rights, claims, and pretensions, to the territories described by said line; that is to say, the United States hereby cede to his Catholic Majesty, and renounce forever, all their rights, claims, and pretensions, to the territories lying west and south of the above-described line; and, in like manner, his Catholic Majesty cedes to the said United States all his rights, claims, and pretensions, to any territories east and north of the said line; and for himself, his heirs, and successors, renounces all claim to the said territories forever. (No. 9) _Convention between the United States and Great Britain, signed at London, August 6th, 1827._ ARTICLE 1. All the provisions of the third article of the convention concluded between the United States of America and his majesty the king of the United Kingdom of Great Britain and Ireland, on the 20th of October, 1818, shall be, and they are hereby, further indefinitely extended and continued in force, in the same manner as if all the provisions of the said article were herein specifically recited.