For hundreds of millions of years the rocks of North Wales have been subjected to earth-movements, volcanic activity and erosion. They have altered and contorted so much by heat and pressure that it is difficult to make out their original form and structure. The credit for tracing the history of these rocks and unravelling their structure belongs primarily to Adam Sedgwick. Before his time, the rocks of much of Wales, the lake district, and Scotland were labelled Transition rocks. Werner gave them this name because they appeared intermediate in character between the Primitive rocks (granites, etc.) and the layered rocks (sandstone, limestones, etc.). We now call the Transition rocks the lower Palaeozoics. Adam Sedgwick was the first man to study them in detail. They are mainly hard, fine sandstones, slates, and shales, together with some volcanic rock.
Adam Sedgwick was born in Dent, in the West Riding of Yorkshire, in 1785. He embarked upon a career in the Church and, after graduating from Trinity College, Cambridge, he became a lecturer of theology. In 1818 he was ordained as a priest and, at about the same time, was offered the Chair of Geology in the University of Cambridge. Adam Sedgwick accepted this honour with the remark Hitherto I have never turned a stone, now I shall leave no stone unturned.
Adam Sedgwick spent more than fifty years as Professor of Geology and during this period worked hard to establish the subject on a sound, scientific basis. He took a leading part in the Cambridge Philosophical Society and in the London Geological Society. Most of his writings are to be found in the records of these societies. His most important contributions are those concerning the Palaeozoic rocks of Britain.
Some of Adam Sedgwicks early work was done in the Lake District , close to his home. By paying close attention to the nature of the rocks, and by careful mapping, he was able to follow the changes that had taken place and to work out the original structure of the area. After this, Adam Sedgwick turned his attention to North Wales. He found the base of the Transition rocks lying on a platform of Primitive rocks. Again, by paying close attention to details of faults and changing rock types, he was able to unravel the history of the area, and produce accurate maps. He named the rocks with which he worked Cambrian, after Cambria, the Roman name for Wales. Adam Sedgwick was not primarily interested in fossils but he understood their value and kept all those that he found for identification. Many of them bear his name. When these fossils were compared with those found by Murchison further south, it was realised that there were three distinct populations. The Transition rocks thus became divided into Cambrian, Ordovician and Silurian systems.
Throughout his life Adam Sedgwick maintained his religious connections and was, for some time, Canon of Norwich. This may have been responsible for his strong opposition to Darwins theory of natural selection and The Origin of Species. Adam Sedgwick died in 1873. His name is remembered in the Sedgwick Museum and the Sedgwick Club in the University of Cambridge.