Boletín de la Sociedad Geológica Mexicana
Volumen 68, núm. 2, 2016, p. 215-230
Early 19thCentury Geologic Studies of the Zimapán Region, Central Mexico
1 Independant Scholar, Tucson, Arizona, USA; formerly at Instituto de Geología, Universidad Nacional Autónoma de México, Estación Regional del Noroeste, Hermosillo, Sonora.
The region of Zimapán, central Mexico, was the focus of much geologic interest during the early 19thcentury because of its metal mining operations. As a result, some of the earliest published geological observations made in Mexico are of this region. The first ones were by scholars from the Real Seminario de Minería and coincided with Alexander von Humboldt's visit to Mexico in 1803–1804. All of their authors were graduates of the Freiberg mining school in Saxony and adherents of Abraham Gottlob Werner's theory of earth history, in which rocks were successively deposited in a primordial ocean as universal formations that can be recognized around the whole globe on the basis of lithology and superposition. The major contribution is the textual survey by Friedrich Traugott Sonneschmid in 1804, covering minerals, rocks, and ore deposits, which is based on field work and assaying of samples with a blowpipe and provides a nascent understanding of the regional lithostratigraphy based on the principles by Werner.
A second group of publications appeared in the 1820s and 1830s. These are also lithological studies by graduates of the Freiberg Bergakademie, based on Wernerian geognosy, and motivated by economic interests. The study about central Mexico by Friedrich Karl Joseph von Gerolt and Carlos de Berghes in 1827, which includes the Zimapán area, contains the earliest published geologic map and sections of any region in Mexico. The authors roughly define the distribution of volcanic, sedimentary, and ore-bearing rocks using five map units and follow Werner's concepts in their identification of the stratigraphic sequence. The geologic knowledge is much improved on the local level in 1836 by Joseph Burkart, who published a cross section of the Zimapán area based on his fieldwork there in 1828. The section provides much structural and stratigraphic detail such as map-scale folds, the red conglomerate of Zimapán, and detail in the sequence of volcanic rocks.
The earliest local geological map of the Zimapán region, a hand-colored lithograph with ten rock units, was published by Henri Guillaume Galeotti in 1838 based on field work there in 1836. Contrary to the researchers studying the Zimapán area before him, who all had a background in mining, Galeotti was a graduate of the Etablissement géographique Vandermaelen in Brussels and had a wide range of interests in natural history, mostly in biostratigraphy and botany. He assumes the limestone of the Zimapán area to be of Cretaceous age and interprets the texture of the limestone in the La Encarnación area to be the result of metamorphism. No further geologic studies seem to have been published about the Zimapán area after Galeotti's until the geologic maps by Mariano Bárcena.
Keywords: Geognosy, Friedrich Traugott Sonneschmid, Joseph Burkart, Henri Guillaume Galeotti, Alexander von Humboldt, Deutsch-Amerikanischer Bergwerksverein.