"Gaither's Dictionary of Scientific Quotations" edited by Carl C. Gaither, Alma E. Cavazos-Gaither, Springer Science & Business Media, (p. 863), January 5, 2012.
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