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Darwin Correspondence Project

To Trenham Reeks   [before 8 February 1845]1

☞Besides numbers on the labels, they are scratched on the glass.

(Please to keep this paper for me) 1312.A bed of recent upraised shells from Peru falling into fragments & decaying. The shells are often filled with common salt, & have their surfaces, deeply & peculiarly corroded; therefore I suspect double decomposition has slowly taken place: if so there shd be in this mixture some carbonate of soda & traces of muriate of lime:2 is this so?

I should esteem it a great favour, to be informed, or referred to any work whether muriate of soda & carbonate of lime, when mixed in large masses & damp, will partially decompose each other. I see some Agriculturists recommend mixing salt & chalk for this purpose, but they do not state positively the result.3 1313 The same continuous bed at a greater height, in which the shells have absolutely decayed— does this contain carbonate of soda, or muriate of soda, or carbonate of lime or muriate of lime, or some of all four? 763 is this sulphate of Soda? it was originally in long pure crystals: 1633(paper packet) superficial incrustation; what is this? is it sulphate & muriate of Soda? or both? 1227.Nitrate of soda as quarried: does it contain any muriate of lime? this is the only point, which I want to know. this soil damp from muriate of lime? the surrounding soil under the Peruvian climate, was impregnated with muriate of soda, but was not damp. this anhydrite or gypsum?: does it contain any carbonate of Soda or lime? a superficial crust over the country.— 1264.What is the opake, white, saline crust on the common salt? 759.Salt from great salt-lake of the R. Negro: it does not serve well for curing meat. What does it contain, or not contain, that makes it different from sea-salt? 762.Salt from salt-lake of Chiquitos: how does it differ from sea-salt? 954.Saline matter, abundant. In veins with gypsum in a tertiary sediment; what is it? 25 Bone of head of Glossotherium, from the Pampas;4 it had an extraordinarily fresh appearance & even emitted a flame:; what percentage of animal matter does it contain? Mr. Trenham Reeks, | of the Museum of Economic Geology.5

CD annotations

1.1 Besides … so? 2.6] crossed pencil
3.5 The same … four? 3.7] crossed pencil; ‘Whether any Carbonate of lime?’ added pencil
3.24 Bone … contain? 3.26] crossed pencil


Apparently enclosed with a lost covering letter and returned with Reeks’s letter of 8 February. The questions were not necessarily addressed to Reeks and may have been forwarded to Reeks by a third party, see n. 5, below.
See CD’s second letter to the Gardeners’ Chronicle and Agricultural Gazette, [before 14 September 1844].
The passage ‘I should esteem … result.’ was added on the verso of the first page with the symbol ‘*a)’ used to indicate its position in the text.
In South America CD identified the bone as from a Mylodon, stating in a footnote that Richard Owen had at first considered the head to be that of Glossotherium, a closely related but distinct genus (South America, p. 92).
The last sentence is not in CD’s hand. Reeks was a mineralogist employed in the laboratory of the Museum of Economic Geology.


South America: Geological observations on South America. Being the third part of the geology of the voyage of the Beagle, under the command of Capt. FitzRoy RN, during the years 1832 to 1836. By Charles Darwin. London: Smith, Elder & Co. 1846.


CD sends queries on chemical composition of various Beagle mineral specimens.

Letter details

Letter no.
Charles Robert Darwin
Trenham Reeks
Sent from
Source of text
DAR 39: 51–2
Physical description

Please cite as

Darwin Correspondence Project, “Letter no. 823,” accessed on 21 April 2021,

Also published in The Correspondence of Charles Darwin, vol. 3