Letter 901 – Lyell, Charles to Darwin, C. R., (after 2 Aug 1845), Darwin Correspondence Project, archived from the original on 1 September 2007, retrieved 9 October 2009 Bunbury, Charles James Fox (1906) Recollections of Darwin. The life of Sir Charles J. F. Bunbury, Bart. Edited by his sister-in-law Mrs Henry Lyell [Katharine Murray Lyell]; with an introductory note by Sir Joseph Hooker. 2 vols. London: John Murray.
Freeman 2007, pp. 107, 109. Freeman, R. B. (2007). Charles Darwin: A companion (2nd online ed.). The Complete Works of Charles Darwin Online. Archived from the original on 25 December 2014. Retrieved 25 December 2014.
Letter 901 – Lyell, Charles to Darwin, C. R., (after 2 Aug 1845), Darwin Correspondence Project, archived from the original on 1 September 2007, retrieved 9 October 2009 Bunbury, Charles James Fox (1906) Recollections of Darwin. The life of Sir Charles J. F. Bunbury, Bart. Edited by his sister-in-law Mrs Henry Lyell [Katharine Murray Lyell]; with an introductory note by Sir Joseph Hooker. 2 vols. London: John Murray.
Letter 901 – Lyell, Charles to Darwin, C. R., (after 2 Aug 1845), Darwin Correspondence Project, archived from the original on 1 September 2007, retrieved 9 October 2009 Bunbury, Charles James Fox (1906) Recollections of Darwin. The life of Sir Charles J. F. Bunbury, Bart. Edited by his sister-in-law Mrs Henry Lyell [Katharine Murray Lyell]; with an introductory note by Sir Joseph Hooker. 2 vols. London: John Murray.
Freeman 2007, pp. 107, 109. Freeman, R. B. (2007). Charles Darwin: A companion (2nd online ed.). The Complete Works of Charles Darwin Online. Archived from the original on 25 December 2014. Retrieved 25 December 2014.