To Charles Lyell 10 January [1855]
Down Farnborough Kent
Jan 10th
My dear Lyell
I received your letter yesterday, but was unable to answer it, as I had to go out at once on business of importance. I am very glad that you are reconsidering the subject of foliation;1 I have just read over what I have written on the subject, & admire it very much!!! & abide by it all.2 You will not readily believe how closely I attended to the subject & in how many & wide areas I verified my remarks. I see I have put pretty strongly the mechanical view of origin; but I might even there, but was afraid, have put my belief stronger. Unfortunately I have not D. Sharpe’s paper here to look over; but I think his chief points is (1st) the foliation forming great symmetrical curves & (2d) the proof from effects of form of shell of mechanical action in cleaved rocks.3 The great curvatures wd be, I think, a grand discovery of Sharpes; but I confess there is some want of minuteness in statement in Sharpe which makes me wish to see his facts confirmed. That the foliation & cleavage are parts of curves, I am quite prepared from what I have seen to believe, but the simplicity & grandeur of Sharpe’s curves rather stagger me.— I feel deeply convinced that where, (& I & Sharpe have seen several most striking & obvious examples) great neighbouring or alternating regions of true metamorphic schists & clayslate, have their foliation & cleavage parallel, there is no way of escaping the conclusion that the layers of pure quartz feldspar, mica, chlorite &c &c are due not to original deposition, but to segregation; & this I consider the point which I have established.
It is very odd but I suspect that great metamorphic areas are generally derived from the metamorphosis of clay-slate, & not alternating layers of ordinary sedimentary matter.— I think you have exactly put the chief difficulty in its strongest light, viz what would be the result of pure or nearly pure layers of very different mineralogical composition being metamorphosed.4 I believe even such might easily be converted into an ordinary varying mass of metamorphic schists; I am certain of the correctness of my account of patches of chlorite schists enclosed in other schist, & of enormous quartzous viens of segregation being absolutely continuous & contemporaneous with the folia of quartz; & such I think might be the result of the folia crossing a true stratum of quartz. I think my description of the wonderful & beautiful laminated volcanic rocks at Ascension5 wd. be worth your looking at.
I have found Sharpe’s Paper but have nothing to add. I fear this letter will be of very little use to you.—
Our children are recovering capitally.6 We are going to take a House in London for 4 weeks, if we can get one, which seems exceedingly doubtful.7
Most truly yours | C. Darwin
Footnotes
Bibliography
Sharpe, Daniel. 1852. On the arrangement of the foliation and cleavage of the rocks of the north of Scotland. Philosophical Transactions of the Royal Society of London, pp. 445– 61.
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.
Volcanic islands: Geological observations on the volcanic islands, visited during the voyage of HMS Beagle, together with some brief notices on the geology of Australia and the Cape of Good Hope. Being the second 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. 1844.
Summary
Discusses views of Daniel Sharpe on foliation and cleavage. Recalls his own previous discussion [in South America].
Letter details
- Letter no.
- DCP-LETT-1626
- From
- Charles Robert Darwin
- To
- Charles Lyell, 1st baronet
- Sent from
- Down
- Source of text
- American Philosophical Society (Mss.B.D25.110)
- Physical description
- ALS 3pp
Please cite as
Darwin Correspondence Project, “Letter no. 1626,” accessed on 28 March 2024, https://www.darwinproject.ac.uk/letter/?docId=letters/DCP-LETT-1626.xml
Also published in The Correspondence of Charles Darwin, vol. 5