A brief review of the mining industry of Mexico
Economic Geology and The Bulletin of the Society of Economic Geologists
Mexico possesses a physiographic outline so characteristic and so generally familiar that it need not be described at length in an article like the present. It is sufficient to remind the reader that it is the tapering southern end of North America, terminating itself in an isthmus and having two peninsulas, one projecting into the Gulf of Mexico, the "American Mediterranean"--and the other separating the Gulf of California from the Pacific Ocean. The larger portion of its area and the one
... ea and the one forming its central part from the boundaries with the United States southward, is a great plateau which is cut off from the llanos of Texas by the Rio Grande del Norte. This great plateau rises gradually as one goes south and southeast, as far as north latitude x9 ø 3x'-The surface of the plateau is broken by two great groups of mountain ranges, with a depression between which is itself blocked out by many spurs. The two great mountain systems tend to unite toward the south, and the depression between them is largely filled by detritus from the ranges. Especially in the southern regions vast volcanic flows and deposits of tuffs have contributed to the same result, and indeed are chiefly responsible for the present altitude of the surface. This combination of mountain and plateau is known among the Mexicans 677 678 EZEQ UIEL ORDONEZ. as "Sierras Madres y la Mesa Central," yet they constitute a physiographic unit. The present outline has been in part produced by block faults of extraordinary length and in part by the huge piles of volcanic ejectments. We find deep valleys as well as lofty cones. Outside of the relatively limited areas of the Archean and Paleozoic formations which appear in the coastal regions along the Pacific, fronting the great ocean in Sonora and Lower California, all the rest of the country consists of the following: Mesozoic sediments, chiefly Cretaceous; Tertiary eruptions, both plutonic and volcanic, and detrital rocks derived from all the above. The Mesozoic strata occupy all the eastern part of the country, beginning with the edge of the coastal plain. They constitute as well the eastern system of the Sierra Madre, many of the interior ranges, and extend to the western edge of the great tableland. The Tertiary eruptives are, however, the chief contributors to the great mountain system of the western Sierra Madre.