(b. Bårschwyl, Switzerland, 17 July 1814; d. Bern, Switzerland, 13 April 1865)
Born at La Verrerie, a glassworks of Bärschwyl established by his grandfather, Gressly was first educated at home, then at Laufon, Solothurn, Lucerne, and Fribourg. As a medical student at Strasbourg, he came under the influence of Phillipe Louis Voltz and Jules Thurmann of Porrentruy in the Swiss Jura. Their interest inspired him to become a geologist. This was during the period of subdivision of major units of the geological column. Some of the geological column (A.G. Werner’s Secondary and Tertiary) had been subdivided earlier in relatively undisturbed sedimentary sequences, such as those of southern England (William Smith, Robert Bakewell) and the Paris basin (Georges Cuvier, Alexandre Brongniart).
To reach this stage of geological chronology, simple petrography and the principle of faunal succession had been sufficient. The extensions of the subdivisions to the disturbed sequences of mountainous regions required a new geometric perspective which the engineer Voltz could well appreciate and which in the hands of his protégé Thurmann (1832) were to begin the science of tectonics. But beyond the application of new mechanical and architectural considerations, the theoretical framework of geology required the abandonment of simplistic Wernerian doctrines of simultaneous worldwide depositions of lithologically similar formations—the “onionskin” view of stratigraphy. Gressly made a major contribution to this development, by his identification and definition of the concept of facies or “aspects de terrain,” an accomplishment of his first significant work, “Observations géologiques sur le Jura Soleurois” (1838), written at the age of twenty-two. This work and his extensive collections of fossils (Rollier mentions 25,000 specimens  brought him to the attention of Louis Agassiz, who engaged him as assistant at Neuchâtel. Agassiz made free use of Gressly’s abilities and fossils for his own monographs. When Agassiz departed for America in 1846, he carried with him a substantial part of Gressly’s fossil collections. This departure aggravated Gressly’s state of melancholia; already by 1845, he had spent time in a sanitarium. Nevertheless, Agassiz was always profuse in his published acknowledgments of Gressly’s high abilities.
Gressly’s close associations with Agassiz’s other abandoned assistants, Eduard Desor and Carl Vogt, continued, although his employment after the departure of Agassiz was in what would now be described as engineering geology for the construction of the alpine railroads. In this capacity he described the geologically rewarding tunnels of Hauenstein, des Loges, and Mont-Sagne. In 1859 he experienced what Wegmann described as immense pleasure in finding, on the modern coast of Sète on the French Riviera, the ecological zones he had deduced from his studies of the Jura while a student. In 1861 Gressly accompanied Vogt on a six-month voyage to the high latitudes. An indefatigable field geologist and collector in his native Jura, Gressly was described perhaps romantically as something of a folk figure. The painter Auguste Bachelin was one of his few close friends and sketched him often at Combe-Varin, which he made headquarters with Desor. A rapid mental decline began in 1864, and he died within a year.
The chronostratigraphic rock unit of Thurmann’s researches in the Bernese Jura had been the terrain, a term roughly equivalent to formation, which Gressly used (as one example) for the Portlandian series of the Upper Jurassic group of strata. Recognizing the striking variations within the horizontal extensions of the terrains of the Solothurn Jura, he characterized the facies as a distinguishable petrographic aspect always accompanied by the same faunal assemblage and rigorously excluding some of the genera and species common to other facies. Twenty-three years before he ever saw the sea, he described this law of dissociation as reflecting conditions at the time of sedimentation, with modern processes as a guide to the ancient environment. He proposed as a general law that every facies of a terrain presents quite distinct petrographic and geognostic or paleontologic characteristics in marked contrast with those of other facies, either on the same stratigraphic level or generally characteristic of the terrain. Further, petrographically and geognostically similar facies of distinct terrains are characterized by analogous faunal assemblages, even succeeding each other vertically through a series of superposed terrains.
Gressly derived a series of paleoecological rules from his observations, noting, for example, that the diversity of facies increases vertically with a rising series and decreases with a sinking series (corresponding to conditions of receding and advancing seas, respectively). This work of 1838 alone establishes Gressly as a pioneer in, if not the founder of paleogeography. Wegmann wrote of him, “In creating this vision of superposed paleogeographies, he added a fourth dimension to his perspective.
I. Original Works. Gressly’s own publications were very few. Among them are “Geognostische Bemerkungen über den Jura der nordwestlichen Schweiz, besonders des Kantons Solothurn und der Grenz-Partien der Kantone Bern, Aargau und Basel,” in Neues Jahrbuch für Mineralogie, Geognosie, und Petrefactenkunde (1836), pp. 659-675, short version in Bibliothèque universelle (1837), pp. 194-197; “Résumé d’observations géologiques sur les modifications du Jura des cantons de Soleure et d’Argovie,” in L’Institut, 4 (1836), 92-93; “Description géologiques des montagnes du Jura Soleurios et Argovien,” ibid., 126-128; “Note sur les restes de mammiteres trouvés dans le portlandien de Soleure,” ibid., 165-166.
Also see “Observations géologiques sur les terrains des chaînes Jurassiques du canton de Soleure et des contrées limitrophes,” in Verhandlungen der Schweizerischen naturforschenden Gesellschaft (1837), pp. 126-132; “Observations géologiques sur le Jura Soleurois,” in Neue Denkschriften der Schweizerishen naturforshcenden Gesellschaft, 2 (1838), 1-112; 4 (1840), 113-241; 5 (1841), 235-349; “Uebersicht der Geologie des nordwestlichen Agargau’s” in Neues Jahrbuch fur Mineralogie Geognosie, und Petrefactenkunde (1844), pp. 153-163, short version in Bulletin de la Société neuchâteloise des sciences naturelles, 1 (1844-1846), 166-168; “Nouvelles données sur les faunes tertiaires d’Aljoi, in Actes de la Société helvétique des sciences naturalles (1835), pp.; 251-261; “Ossements fossiles d’un saurien gigantesque de la famille des Dinosauriens,” in Bulletin de la Société neuchâteloise des sciences naturelles, 4 (1856-1857), 13-16; “Étudies géologiques sur le Jura Neuchâtelois,” in Mémoirés de la Société neuchâteloise des sciences naturlles, 4 (1859), 1-159, written with E. Desor; Briefe aus dem Norden. Der Bund (Bern 1861). PP. 246-251, 281-284; “Erinnerungen eines Naturforschers aus Südfrankreich,” In Album von Combe-Varin (Zurich, 1861), pp. 201-296: “Differenzialheber (Wasserstandsmesser),” in Mitteilungen der Naturforschenden Gesellschaft in Bern (1866), 228-233; and “Uebersicht der geologischen Verhaltnisse der Umgebungen Oltens in Bezug auf den Hauenstein Tunnel (1853),” in Mitteilungen der Naturforschenden Gesellschaft in Solothurn, 8 (1928), 1-40.
II. Secondary Literature. For works on Gressly, see Kurt Meyer, “Amanz Gressly, ein Solothurner Geologe (1814-1865),” in Mitteilungen der Naturforschenden Gesellschaft in Solothurn, no.22 (1966), 1-79; L. Rollier, “Lettres d’Amand Gressly, le géologue jurassien (1814–1865),” in appendices, Actes de la Société Jurassienne d’émulation, 16 (1911), 17 (1912), 18 (1913); and Imprimerie de petit Jurassien (Moutier, 1911), with biographical and bibliographical sketch and portrait.
Also see Emil Kuhn-Schnyder, in Neue deutsche Biographie; J. Thurmann. “Essai sur les soulèvements jurassiques du Porrentruy,” 2 vols., I (Porrentruy, 1832), 1-84; II (Strasbourg, 1836), 1-51; and Eugene Wegmann, L"exposé original de la notion de faciés par A. Gressly (1814-1865),” in Sciences de la terre, 9 , no. 1 (1962-1963), 83-119, with facsimile reproductions of critical parts of Gressly’s 1838 definition of facies.
Cecil J. Schneer