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.255
Sir Charles Lyell (1837). “Principles of Geology: Being an Inquiry how Far the Former Changes of the Earth's Surface are Referable to Causes Now in Operation”, p.244