Roderick Impey Murchison (1792-1871) The most politically powerful geologist of the 19th century. Developed the modern classification of the Paleozoic, which previously consisted only of the Greywacke and Coal Measures (Carboniferous). He first defined the Silurian system to distinguish his Welsh rocks from Sedgwick's older, Cambrian territory ; he then defined the Devonian to resolve a ...

Trilobites in Murchison's Siluria Sir Roderick Impey Murchison published a comprehensive work on the Silurian System in Great Britain and elsewhere in 1838. Initially comprising rocks approximately the interval now known as Silurian, Murchison's definition of Silurian later expanded to encompass much of the pre-Old Red Sandstone (i.e. pre-Devonian) Paleozoic rocks in Great Britain, including ...