Sir Charles Lyell, Gérard Paul Deshayes (1830). “Principles of Geology: Being an Attempt to Explain the Former Changes of the Earth's Surface, by Reference to Causes Now in Operation”, p.4
Charles Lyell (1863). “The Geological Evidences of the Antiquity of Man with Remarks on Theories of the Origin of Species by Variation by Charles Lyell”, p.421