It has been attempted to present in this paper, for the first time, an idea of the tectonics of Mexico as a whole, based on the concepts developed mainly by Alpine geologists for the study of orogenic processes.

With this object in view, the paper was divided in two parts; the first, in which was established the meaning of the concepts in order to fix the sense in which they will be used and to point out in a general way the orogenic processes to which the region of Mexico was subjected; the second part in which are described the major structural units, from a tectonic point of view, especially as to the character and orientation of their folds, since the character of the major units is mainly established from the character of the folds.

There have been established in the foreland of the Mexican geosyncline, three shelves, a large massif, two small ones, and four basins. There have been postulated for the hinterland a great massif or continent, two large massifs, two medium and four small massifs, and three basins. The foredeep of the geosynclinal fold has been indicated in three regions, as established by the flysch sediments deposited therein.

It is considered that the geosyncline of the Mexican Cordillera begins west of Ciudad Juarez extending southward to Torreon, where it turns eastward to Monterrey, and from there, southeastward to the Coatzacoalcos River, thence northeastward to the Chalchijapan River, and upon reaching the narrowest part of the Isthmus of Tehuantepec, it turns east-southeastward into Guatemala.

It is established that the principal orogeny which gave rise to this folding started at the end of the Cretaceous in the northern part of Mexico and at the beginning of the Eocene in the rest of the country, and ended at the end of the Eocene excepting in the southeast where it lasted until the beginning of the Oligocene. Furthermore, there were embryonic and posthumous movements, the last of which is very important, in the Isthmus and the Macuspana and Pichucalco basins.

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Fig. 1. TECTONIC MAP OF THE REPUBLIC OF MEXICO

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