braces within equal latitudinal limits so great a variety of climate, soil, and vegetation—a variety whose important bearing on the native development can be understood in some degree, and which would doubtless account satisfactorily for most of the complications of progressional phenomena observed within the territory, were the connection between environment and progress fully within the grasp of our knowledge. All the gradations from a torrid to a temperate clime are here found in a region that lies wholly within the northern tropic, altitudinal variations taking the place of and producing all the effects elsewhere attributable to latitude alone. These variations result from the topography of the country as determined by the conformation given to the continent by the central cordillera. The Sierra Madre enters this territory from the north in two principal ranges, one stretching along the coast of the Pacific, while the other and more lofty range trends nearer the Atlantic, the two again uniting before reaching the isthmus of Tehuantepec. This eastern branch between 18° 40´ and 20° 30´ opens out into a table-land of some seventy-five by two hundred miles area, with an altitude of from six to eight thousand feet above the sea level. This broad plateau or series of plateaux is known as the tierra fria, while the lower valleys, with a band of the surrounding slopes, at an elevation of from three to five thousand feet, including large portions of the western lands of Michoacan, Guerrero, and Oajaca, between the two mountain branches, constitute the tierra templada. From the surface of the upper table-land rise sierras and isolated peaks of volcanic origin, the highest in North America, their summits covered with eternal snow, which shelter, temper, and protect the fertile plateaux lying at their base. Centrally located on this table-land, surrounded by a wall of lofty volcanic cliffs and peaks, is the most famous of all the valley plateaux, something more than one hundred and sixty miles in circuit, the valley of Mexico, Anáhuac, that is to say, 'country by
