Facies in stratigraphy: from 'terrains' to 'terranes'.

Concepts of lateral variation in sedimentary rocks and fossil assemblages developed in France from the 1760s; the definitive definition of facies was provided in 1838 by the Swiss geologist Amanz Gressly (1814-65) in his detailed field study of the eastern Jura. His maps and cross-sections of variations in Jurassic and Triassic rocks are illustrated. He believed that variations reflected environmental conditions, as in modern seas, and would eventually permit former depths to be reconstructed. Gressly studied at Strasbourg under Voltz and Thurmann: he collaborated with L.Agassiz, E.Desor and C.Vogt. His work influenced German and French geologists and provided a basis for interpretations of the Alps. But the facies concept was not deeply rooted in American geology until around 1884 (H.S.Williams) and in Britain and Russia until around 1900. I.S.Evans