Rising from the _tierra caliente_, the road enters upon the more temperate zone, the _tierra templada_, extending upwards towards the Great Plateau. The limit of this climatic zone is at the elevation of 6,000 feet above sea-level, and here are evergreen oaks, pine, and the extraordinary forms of the organ cactus, as well as orchids. It is, indeed, a transition zone from the hot to the cold climates, and the zone embraces the greater part of the area of Mexico. Rising rapidly thence up to and over the escarpments of the Sierra Madre and the high plains, we shall enter upon the _tierra fria_ or cold lands, ranging from 6,000 feet to 8,000 feet above sea level. Above this rise the high summits of the Mexican Cordilleras, with their culminating peaks, some few of which penetrate the atmosphere above the limit of perpetual snow. Thus, three diverse climatic zones are encountered in Mexico, which, ever since the advent of the Spaniards, have been designated as the _tierra fria_, _tierra templada_, and _tierra caliente_ respectively. These conditions, as will be seen later, are also encountered upon the Pacific slope. We now ascend the steep upper zone of the Sierra Madre, and cross it, descending thence to the Great Plateau or _mesa central_, the dominating topographical feature of the country. Here lies the real Mexico of history, and here is the main theatre of the new land of industrial awakening. Within the mountain ranges--that which we have crossed, and those which intersect this vast tableland and bound it on three sides--lies the great wealth of minerals--gold, silver, and others--which have attracted men of all races and all times since Cortes came. Here the true fairy tales of long ago, of millions won by stroke of pick, had their setting, and indeed, have it still. Upon these hills the thankful miner reared temples to his saints, and blessed, in altar and crucifix, the mother of God who graciously permitted his enrichment! And as if such devotion were to be unstinted, he also places his shrines within the bowels of the mines, and pauses as he struggles through the dark galleries, with heavy pack of silver rock upon his back, to bend his knee a moment before the candle-lighted subterranean altar.