CHAPTER I. Geological and Geographical Structure of Mexico—Extent.

According to the convention of Mr. Trist, the boundary between the republics commences in the Gulf of Mexico, three leagues from land, opposite the mouth of the Rio Grande, otherwise called Rio Bravo del Norte, or opposite the mouth of its deepest branch, if it should have more than one branch emptying directly into the sea; from thence it passes up the middle of that river, following the deepest channel, when it has more than one, to the point where it strikes the southern boundary of New Mexico, thence, westerly, along the whole southern boundary of New Mexico, which runs north of the town of El Paso, to its western termination;—thence northward, along the western line of New Mexico, until it intersects the first branch of the river Gila, or, if it does not intersect any branch of that river, then to the point on the said line nearest to such branch, and then in a direct line to the same;—thence down the middle of the said branch and of said river, until it empties into the Rio Colorado;—thence across the Rio Colorado, following the division line between Upper and Lower California, to the Pacific Ocean.