The earth science content of two late medieval encyclopedias, the Mirrour of the World and Higden's Polychronicon, both printed by William Caxton in the 1480's, is examined in relation to fifteenth century ideas about the physical nature of the earth and the universe. Such topics as the four elements, the earth and the spheres, location of Hell and Paradise, the arrangement of , continents and oceans, the unity of waters, earthquakes and volcanoes, erosion, fossils and mountain building, climatic zones and weather phenomena are summarized and reference made to the Biblical and Classical Greek sources of these ideas.