Arnold Henry Guyot (1807-1884) was a Swiss-American geologist and geographer. He was the first to point out certain important observations relating to glacial motion and structure. Among other things he noted the more rapid flow of the center than of the sides, and the more rapid flow of the top than of the bottom of glaciers; described the laminated or ribboned structure of the glacial ice; and ascribed the movement of glaciers to a gradual molecular displacement rather than to a sliding of the ice mass as held by de Saussure. He subsequently collected important data concerning erratic boulders. in 1854, he was appointed professor of physical geography and geology at Princeton University, which office he retained until his death.