Sea in culture of barbarian invaders and knowledge of geography took a backward step. In the seventh century, Isidore of Seville produced a "wheel map" in which Asia, Africa and Europe were arranged like segments in an orange, separated by the "Mare Mediterranean", "Nilus" and "Tanais" and surrounded by "Oceanus". It was not until the fifteenth century that Ptolemy's maps were used again and Henry the Navigator of Portugal initiated ocean exploration and maritime research. Encouraged by him, Portuguese navigators explored, mapped and charted the west coast of Africa and the Eastern Atlantic and this knowledge prepared the way for the great voyages
Plymouth Sound, Shores and Cliffs Plymouth Sound, Shores and Cliffs Plymouth Sound, Shores and Cliffs is a Site of Special Scientific Interest (SSSI) around the Plymouth Sound, a large area of water where the River Plym and Tamar meet. It stretches across the two ceremonial counties of Devon and Cornwall and the unitary authority area of Plymouth. It contains fossils of plants and sea creatures and its cliffs show a timeline of the Middle to Early Devonian period hundreds of millions of years ago. Lower to early Middle Devonian units of rock are visible from sections through the coastal cliffs and intertidal zones, which were