Charles Darwin: manuscript letter to W.B. Carpenter concerning South American rock specimens, 25th Dec. 1844: Darwin, Charles R. (1809-1882) This important letter forms a crucial part of the correspondence between Charles Darwin and the invertebrate zoologist, William Benjamin Carpenter, regarding the structure of tertiary period rock specimens from the Pampas region of northern Patagonia, and their comparison with specimens taken from Chilean tuff [volcanic deposits]. The two scientists exchanged letters on the subject during the latter half of 1844. Single sheet folded into 4pp octavo, manuscript letter, written on four sides, from Charles Darwin, Down, near Bromley, Kent, Dec. 25th [1844], to [William Benjamin Carpenter, 1813-1885], signed C. Darwin. The letter is complete, clean and legible; the lower edge of the original vertical fold at the centre has a small amount of loss; there is a short perforation towards the upper edge of this fold, and a faint trace of reinforcing tape mid-way along it, but the document is stable and none of these minor fl aws affect the legibility of Darwin's handwriting in any way. There are light horizontal and vertical fold lines where the letter was folded by Darwin to fit inside a postal envelope; the manuscript is presented in a frame, in such a way that the recto (first two pages) is visible in a window mount on the left, alongside a reproduction of the verso on the right