To Charles Lyell [16 December 1843]
Down. nr. Bromley Kent
Saturday
My dear Lyell
I have been looking over my huge bundle of notes & I find that the proposition that the Tosca was a diluvial mud is monstrous.—1 It is distinctly stratified in some parts & often shows differences in the upper & lower parts. It is not the last deposit; at least a grand formation of absolutely similar character, underlies in Banda Oriental a great formation of red sandstone & conglomerate. At the mouth of the Uruguay, we have the following section, in a vertical cliff. diag A
———
Limestone, often cellular &
crystalline or impure, with
numerous sea-shells.
———
seams of white sand
———
Limestone
———
30 feet of pale clay with
many layers of oysters
———
unideniable tosca or
pampæan mud
———ramme And near this place, I found tosca, resting on the limestone, (at A) with the bones of Mammalia.2 —. In fact we have everywhere proofs, that in the midst of a grand estuary formation of an intercalation of a pure marine one.—3 A little higher up the Uruguay, we have this section.— diag —————————
oddly variegated agate &
limestone
—————————–
coarse comglomerate
—————————–
gritstone with more or less
calcareous matter
—————————–
a thin bed of the ordinary red
tosca
—————————–
calcareuous gritstone &
limestone
———ramme This is the uniform diluvian mud.!4
In fact there appears to be an older & newer tosca. The upper tosca no doubt retains same character over wide spaces, though to the East in the granitic districts it gets very sandy & this upper tosca bed chiefly contains mammal bones.—5
Even at the Rio Negro, (D’Orbigny’s own country) I find in a cliff 200 ft high of various sandstones, two thin beds of perfectly characterized tosca.—6 I find that the conglomerate of pumice in sandstone in the Patagonian Tertiary is apo-cryphal.— I found merely great fragments & could not in the high overhanging cliffs find the actual bed, which in my notes, I regret.— I daresay I have given you more details, than you care to hear.
So farewell | Ever yours | C. Darwin
Footnotes
Bibliography
Falconer, J. D. 1937. Darwin in Uruguay. Nature 140: 138–9.
Journal of researches: Journal of researches into the geology and natural history of the various countries visited by HMS Beagle, under the command of Captain FitzRoy, RN, from 1832 to 1836. By Charles Darwin. London: Henry Colburn. 1839.
Orbigny, Alcide Charles Victor Dessalines d’. 1835–47. Voyage dans l’Amérique Méridionale (le Brésil, la République orientale de l’Uruguay, la République Argentine, la Patagonie, la République du Chili, la République de Bolivia, la République du Pérou), exécuté pendant les années 1826 … 1833. 6 vols. in 7 and 4 atlases. Paris and Strasbourg: Pitois-Levrault et Cie, P. Bertrand.
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.
Summary
Description and defence of his view of the tosca in Banda Oriental, along the Rio Uruguay and at the Rio Negro, taking issue with A. D. d’Orbigny. Refers to the pumice in the Patagonian Territory. Two tables show the layered tosca formation along the Uruguay.
Letter details
- Letter no.
- DCP-LETT-724
- From
- Charles Robert Darwin
- To
- Charles Lyell, 1st baronet
- Sent from
- Down
- Source of text
- American Philosophical Society (Mss.B.D25.33)
- Physical description
- ALS 3pp
Please cite as
Darwin Correspondence Project, “Letter no. 724,” accessed on 24 April 2024, https://www.darwinproject.ac.uk/letter/?docId=letters/DCP-LETT-724.xml
Also published in The Correspondence of Charles Darwin, vol. 2