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Darwin Correspondence Project

To John van der Weyde   29 September 1876

Down, | Beckenham, Kent. | Railway Station | Orpington. S.E.R.

Sep 29 1876

Dear Sir

I am much obliged for the photographs which you were so kind as to send me. I have sent them to Prof. Flower (one of the most capable judges in England) of the R. Coll. of Surgeons, where my specimens from the R. Plata were deposited. He admires the fine specimen of Toxodon & says that all the others apparently belong to Mylodon.1 I am extremely glad that you & your friends intend collecting the fossil Mammals. I will make two or three suggestions tho’ perhaps superfluous.

Judging from a distance, the Barrancas de Gregorio seemed to me worth investigating; & it wd be adviseable to ascertain where these cliffs are contemporaneous with the Pampean formation.2 Secondly, as far as I know the bones of the smaller mammals have not been collected, & these might be as valuable as those of the gigantic mammals: at M. Hermosa near Bahia Blanca I found the remains of small species.3 Thirdly, it wd be of paramount importance to find mammalian remains in the tertiary strata, such as those at Sta Fè Bajada beneath & older than the Pampean Formation.4 Near the mouth of the Uruguay I found such strata with great extinct oysters, & beneath these a formation in character quite like the Pampean, & which therefore it is probable wd contain Mammalian remains.5

Heartily wishing you success, | I remain, dear Sir | yours faithfully | Charles Darwin


The letter and photographs from Van der Weyde have not been found, but see the letter to W. H. Flower, 24 September [1876], and letter from W. H. Flower, 27 September 1876 and n. 3. Flower was in charge of the Hunterian Museum of the Royal College of Surgeons. The Río de la Plata is an estuary separating Argentina and Uruguay. Toxodon is a genus of rhinoceros-like mammals of the extinct order Notoungulata; Mylodon is a genus of giant ground sloth of the extinct family Mylodontidae.
In Geological observations 2d ed., pp. 102, 245, CD had noted that the Pampean deposit overlay and filled up furrows in coarse sand at the Barrancas de San Gregorio and suggested that the loose sand could not be contemporaneous with the old Tertiary strata of the more western parts of the province. He further suggested that a period of subsidence had occurred during which mud was deposited over the coarse sand, and that the area had been uplifted again to its present level.
CD had found fossils of rodents at Monte Hermoso, a city on the Atlantic coast of Argentina (see Geological observations 2d ed., p. 106).
CD had found mammalian fossils near Santa Fè Bajada (Paraná) in Entre Rios, Argentina (see Geological observations 2d ed., p. 106).
See Geological observations 2d ed., pp. 92–3; the oyster was Ostrea patagonica.


Geological observations 2d ed.: Geological observations on the volcanic islands and parts of South America visited during the voyage of H.M.S. ‘Beagle’. By Charles Darwin. London: Smith, Elder & Co. 1876.


Thanks JVdW for photographs of fossils; [W. H.] Flower has identified them as Toxodon and Mylodon.

Sends suggestions for collecting fossil mammals in Argentina and Uruguay.

Please cite as

Darwin Correspondence Project, “Letter no. 10626,” accessed on 27 October 2021,

Also published in The Correspondence of Charles Darwin, vol. 24