Sedgwick, Adam (1785–1873)

English geologist who contributed greatly to understanding the stratigraphy of the British Isles, using fossils as an index of relative time. Together with Scottish geologist Roderick Murchison, he identified the Devonian system in southwest England.

Sedgwick was born in Dent, Yorkshire, and studied mathematics at Cambridge, where he became professor of geology in 1818.

An energetic champion of field work, Sedgwick explored such diverse districts as the Isle of Wight, Devon and Cornwall, the Lake District, and northeast England. In the 1830s, he unravelled the stratigraphic sequence of fossil-bearing rocks in North Wales, naming the oldest of them the Cambrian period (now dated at 500–570 million years ago). In South Wales, his companion Murchison had concurrently developed the Silurian system. The question of where the boundary lay between the older Cambrian and the younger Silurian sparked a dispute that was not resolved until 1879, when Charles Lapworth (1842–1920) coined the term Ordovician for the middle ground.