Mexico is one of the richest countries in the world. Nowhere else do we find and enrichment of ores. Nowhere else is there such fertility of soil coupled with such possibilities of crop cultivation as in the wedge-shaped southern end of the North American continent. The United States of Mexico do not represent a physical unity with their two million square kilometres. The Isthmus of Tehuantepec separates the States of Chiapas, Tabasco, Campeche and Yucatan from the northern part of the country. In their geological structure, climate, regetation and fauna they belong to Central America. The country to the north of the Isthmus is chiefly a high plateau. Along the Rio Grande del Norte it is merely the continuation of the stone and waste deserts of Arizona and New Mexico with their wide table-mountains. To the south of the 28° latitude the grouping of the mountain ranges becomes clearly evident. The high plateau or Mesa Central is limited in the west by the Sierra Madre Occidental with its wealth of recent volcanic extrusions, and in the east by the folded chains of the Sierra Madre Oriental, chiefly built up of limestone and flattening out northward to the "Llanos estacados" of Texas. Steep slopes deeply-incised by mountain torrents, the beds of which are dry during most of the year, give both of the bordering ranges a young and wild appearance. In its northern part, the Mesa Central is an enormous broad folded basin-area consisting of waste-plains, without exterior drainage, showing in the Bolson of Mapimé an altitude lower than a thousand metres above sea level. This steppe like boundary district was once the battle-field of nomadic Indian tribes against whose attacks European settlers had long to defend themselves.
Between the 25 and 19° latitude the high plateau rises again to 1.800 and 2,000 metres, and is divided up into several broad and fertile vallevs, separated by ridges or timbered mountain ranges, running as a rule parallel to the edge of the plateau, but in places with a somewhat oblique trend.
Further to the south the country rises to the zone of high volcanos where lava-streams have blocked the valleys in which, as in the valley of Mexico and further west in the states of Michoacan and Jalisco, great lakes were formed. most of which were salty. These parts of the country have long been densely populated. The strata of the soil show the remains of at least three pre- Spanish cultures superimposed one on the other: here on the surface we set foot on historic ground full of memories of recent Aztec or Spanish times. The highest volcanoes are the Pic of Orizaba (Citlaltepetl. Star Mountain).
5.594 metres: Popocatepetl (the Smoking Mountain), 3,452 metres (which after
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