steep ravines, or barrancas, formed by the slow action of rivers, and by occasional highland lakes, such as Chapala, Pazcuaro and Mexico. Much of the ground is volcanic, and the names of the volcanoes Popocatepetl and Iztacciuatl in Mexico province, and of Orizaba on the Puebla-Vera Cruz border, are familiar to everyone. The Mexican valley forms the apex of the triangular plateau, and the natural route thence to the south lies via Tehuacan and Teotitlan del Camino, a fact which should be kept in mind in studying the tribal migrations. The height of the mountain-chains and their proximity to the coast explain the fact that there are but few important rivers in Mexico; most of the streams on the plateau drain into land-locked basins, and practically the only rivers which pierce the mountain barrier are the Panuco on the east, and the Lerma and Rio de las Balsas on the west. Climate and vegetation are dependent upon elevation; the coast is tropical, but the elevation is so abrupt that the traveller passes with remarkable rapidity from palms, bananas, coconuts and rubber, according to locality, to slopes clad with fir and oak and plains of wheat and maize. In the same way, table-lands rise in successive terraces from Tehuantepec through Oaxaca and Puebla to Mexico which has an elevation of nearly 7500 feet above the sea-level, and enjoys a more temperate climate than New York or Chicago fourteen to sixteen hundred miles further north. The country is conveniently divided into three zones, according to its elevation; the so-called "tierra caliente" (hot country) runs from the sea-level to 3000 feet, the "tierra templada" (temperate country) from 3000 to 6000 feet, and the "tierra fria" (cold country) thence to the 9000 foot level. The most important vegetable product from the economic point of view was maize, which constituted the chief food of the natives. The varieties and development of the maize-plant as we know it imply centuries of settled
