That mainland comprises, with the two peninsulas, 765,762 square miles, and the 1,561 square miles of coastal islands under Mexican sovereignty bring the total area of the country up to 767,323 square miles. The greatest width of the mainland is 750 miles, and the greatest length is 1,942 miles, from the northwestern tip of Lower California, where it joins the United States, to the southernmost point in the jagged Guatemalan border in the Mexican state of Chiapas. The narrowest point in Mexico is 120 miles, at the Isthmus of Tehuantepec, once discussed as the possible site of an interoceanic canal, and in the time of Diaz the route of a great transshipping railway between the Pacific and the Gulf of Mexico. The Atlantic (Gulf of Mexico) coastline of Mexico is 1,727 miles long, that of the Pacific (including the long border of Lower California) 4,574 miles. Lying between 32° 30′ and 14° 30′ North Latitude and 86° 30′ to 117° Longitude west from Greenwich, the triangular form of the Mexican territory places it about equally in the temperate and torrid zones. This is a primary factor in Mexican climate, but far more significant is the contour of the country itself. This is largely mountainous, for if we include the high but fertile table-lands, nearly two-thirds of the country is covered with mountain ranges. The Rocky Mountains of the United States, the great backbone of the Western Hemisphere, cross the Mexican border into Sonora, in a low, narrow range. Almost immediately south of the international line they begin spreading eastward. A long, slowly rising valley a hundred miles wide continues southward from El Paso, narrowing rapidly, while to the eastward of this valley rises an apparently new range of mountains, obviously a part of the great Rocky Mountain range, but unconnected with it in the United States and south, indeed, of the broad flat plains of Texas. This is the _Sierra Madre Oriental_, or Eastern Mother Range, the continuation of the Rockies in Sonora and Durango being called the _Sierra Madre Occidental_, or Western Mother Range. Further south, these two join together, and spread to virtually the whole width of Mexico, excepting for the Gulf coastal plain, some 300 miles wide, to the east. All of Central Mexico is mountainous, flattened only by vast plateaus which, according to the accepted geological theory, were created by alluvial deposits and lava dust from the mountains which rise still above them. At the Isthmus of Tehuantepec, the Sierra Madre flattens out till, save for the relatively easy grades which climb from the Gulf and from the Pacific to the summit of the low divide (less than 300 feet above sea level) the mountains might be all but gone. The narrow plane of the Isthmus passed, the mountains rise again until the center of the state of Chiapas is once more a vast plateau accented with towering peaks, a formation which continues southward through