To C. G. Ehrenberg 21 May 
Down near Bromley Kent
Dear and highly honoured Sir
I do not know how to thank you enough for your last most valuable letter.1 I am particularly obliged for your examination of the Pampas mud, which I fear you undertook entirely for my sake. Your results have quite confirmed my view of its origin.2 Considering the number & strangeness of the mammifers embedded in it (more different from our present quadrupeds, than are the Eocene fossil mammifers of Europe) the history of the Pampæan deposit is really interesting. I presume you did not examine the infusoria sufficiently to know whether the species are extinct or recent; as that would throw light on its age, which, as well as the manner of its formation, is disputed by the French Geologists.3 In case you should ever further investigate the subject, I hope you will kindly inform me of the result; & I will endeavour to send you a few more & good samples. The Bahia Blanca is the least interesting part of the Pampæan Formation.
—. In the many volcanic districts, which I visited, I found obsidian only at Ascension; I will send some chips, though probably you will already have got them from this well-known island.—
As you seem interested with the great, chalk-like, Patagonian tufaceous formation, I will send soon to you through the Chevalier Bunsen,4 a set of specimens from every station which I visited; & I will label them outside, so as to give you little trouble by sending you duplicates of those already sent. Santa Cruz is the most southern spot, where I collected specimens, though I saw the formation still further S.: Rio Negro is the most northern part where it occurs, & there only in thin beds in sandstone. The gypsum occurs in vast quantity in plates or veins, running in every direction, especially at P. St Julians: some gypsum is disseminated throughout the mass.— My specimens are small, but I will send you half of my largest, which I think will be an inch square as you desire. I shall publish a small volume on the geology of S. America this ensuing winter & how greatly will your Researches add to its value!
I have looked through all the accounts given by those on board vessels, where the Atlantic dust has fallen; & I find the wind has generally been between NE & East, & sometimes SE.—and it has always fallen during the same four months, when the harmattan blows from NE & ENE.—5 I will detail all the facts in my little paper, which I will immediately send to the Geological Soc.— The dust to which I allude, which fell on the Princess Louise, was not during Meyen’s voyage, but subsequently:6 I doubt whether Meyen’s dust was our infusorial dust, for it fell during a different month from any other case, & (as far as I can judge) further off the African coast.— I am sorry to find that I have misled, though in so unimportant point, as hardly to be worth your correcting. The packets marked by you IA & IB are same: I had so little expectation of the the first packet, which I sent, interesting you, that I did not describe it fully & gave only the approximate latitude & did not specify that it was not collected by myself. That collected by myself, fell on our ship, when 10 miles NW of St. Jago, (& is marked in your list ‘St. Jago’) as I stated in the M.S. which I sent you. But these inaccuracies are quite unimportant.
Believe me, Sir, with many thanks | Yours very faithfully & obliged | C. Darwin.
CGE’s account of Pampas mud confirms CD’s view of its origin. Will send Patagonian specimens. Discusses dust-carrying winds in the Atlantic.
Was not referring to F. J. F. Meyen’s voyage.
Corrects error concerning samples.
Please cite as
Darwin Correspondence Project, “Letter no. 870,” accessed on 13 February 2016, http://www.darwinproject.ac.uk/DCP-LETT-870