of geology in Vienna, Suess published his important work on structural geology, Das Antlitz der Erde (‘Face of the Earth’), between 1833 and 1909. He studied mountain building, especially the Alps which he believed to have been formed in a geosyncline, which he named Tethys. He opposed the concept of isostasy, arguing that subsidence of the ocean floors had caused what he termed ‘eustatic’ changes in sea level. See orogeny; eustatic.