James Dwight Dana (1869). “Manual of Geology: Treating of the Principles of the Science, with Special Reference to American Geological History, for the Use of Colleges, Academies, and Schools of Science”, p.9
"Gaither's Dictionary of Scientific Quotations" edited by Carl C. Gaither, Alma E. Cavazos-Gaither, Springer Science & Business Media, (p. 863), January 5, 2012.