The date range is set by the publication of the first volume of Lady Willoughby’s diary in May 1844 (Literary Advertiser) and the completion of South America. This letter is associated with two covers addressed to CD by E. A. Darwin, both with further calculations by E. A. Darwin: 14$\frac{1}{2}$ miles 188 feet, rise gives 7′ 20’ 486 feet rise in 35^miles (2025^yards to mile) gives an angle 0^o 7′ 52’ 100 feet in 14$\frac{1}{2}$ miles gives 0^o 3′ 5’ CD has annotated these covers: 7′ 20’] ‘p 182, p. 185’ added pencil 486 feet … 35^miles] ‘((842 is the rise of the bottom of the lava in the 35 miles))’ added ink 0^o 3’ 5’] ‘1’ [’’‘ over ’^o‘]. 22’ (77 & 85 fathoms)’ added ink The calculations relate to the inclination of lava flows in the valley of the Santa Cruz River described by CD in South America, pp. 116–17. According to CD’s ‘Journal’ (Correspondence vol. 3, Appendix II) he worked on the book from 27 July 1844 to 1 October 1846.

Ralph and William H. Swale, Booksellers, 21 Great Russell Street, London.

[Rathbone] 1844–8, a fictitious diary.

The Hensleigh Wedgwoods lived at 16 Gower Street.

Susan Darwin, CD’s sister.