To Charles Lyell 5 March [1869]
Down. | Bromley. | Kent. S.E.
March 5
My dear Lyell
Your point seems to me a very good one.1 When reading Croll, I thought of the perfectly preserved glaciation of the rocks in Scotland & N. Wales, & of the preservation of the turf-covered shelves of Glen Roy & of all turf-covered surfaces; but I vaguely supposed that Croll would say that the wear & tear was confined chiefly to the valleys & ravines & was much less than average when rocks hard.— But when the wear & tear is put into figures, as you have done, it seems scarcely possible that the water channels could supply detritus enough.—2
It wd be most interesting to visit Glen Roy for this sole purpose, & estimate how large an area, consisted of naked rock or naked detritus. Certainly my impression is strong that the shelves themselves are now, except when crossed by a rill, just as they were when they bordered the lake or water.—3 One is led to suspect that Crolls & Geikies estimate of the amount of surface degradation, is much too high, even supposing that the amount of loose matter now carried away by the rivers is correct.—4 Somehow I cannot persuade myself that the Glacial period was much more recent than hitherto supposed. I shd like to hear what Croll wd say to your line of argument—5
I am sorry to hear about the Amazonian shells.—6
My dear Lyell | Yours most sincerely | Ch. Darwin
Footnotes
Bibliography
Croll, James. 1868. On geological time, and the probable date of the Glacial and the Upper Miocene Period. Philosophical Magazine 4th ser. 35: 363–84; 36: 141–54, 362–86.
Geikie, Archibald. 1868b. On modern denudation. Transactions of the Geological Society of Glasgow 3: 153–90.
Herbert, Sandra. 2005. Charles Darwin, geologist. Ithaca and London: Cornell University Press.
Lyell, Charles. 1867–8. Principles of geology or the modern changes of the earth and its inhabitants considered as illustrative of geology. 10th edition. 2 vols. London: John Murray.
Rudwick, Martin John Spencer. 1974. Darwin and Glen Roy: a ‘great failure’ in scientific method? Studies in History and Philosophy of Science 5 (1974–5): 97–185.
Summary
Discusses wear and tear due to glaciation and significance of this evidence for dating the glacial period. Mentions views of James Croll and Archibald Geikie on the issue.
Letter details
- Letter no.
- DCP-LETT-6692
- From
- Charles Robert Darwin
- To
- Charles Lyell, 1st baronet
- Sent from
- Down
- Source of text
- American Philosophical Society (Mss.B.D25.364)
- Physical description
- ALS 4pp
Please cite as
Darwin Correspondence Project, “Letter no. 6692,” accessed on 28 March 2024, https://www.darwinproject.ac.uk/letter/?docId=letters/DCP-LETT-6692.xml
Also published in The Correspondence of Charles Darwin, vol. 24 (Supplement)