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Darwin Correspondence Project

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

Lyell was probably revising his Manual of elementary geology for the fifth edition (C. Lyell 1855), published in March 1855 (Publishers’ Circular, 2 April 1855, p. 133). Chapters on metamorphic rocks, cleavage, and foliation were extensively revised for this edition (C. Lyell 1855, p. ix).
Lyell had been unconvinced by CD’s view, first discussed in South America (pp. 162–8), that cleavage and foliation were the result of processes entirely different from stratification. See letters to Charles Lyell, [November–December 1851], nn. 25 and 30, and to Daniel Sharpe, 12 November [1854].
Sharpe 1852 and 1855 discussed foliation in symmetrical curves or arches. Sharpe described the distortion of shells and other fragments in cleaved rocks in Sharpe 1847 and 1849.
See C. Lyell 1855, pp. 605–6.
Volcanic islands, pp. 69, 70. Lyell evidently followed CD’s advice, for he referred to CD’s account of Ascension Island in C. Lyell 1855, pp. 612–13.

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
3pp

Please cite as

Darwin Correspondence Project, “Letter no. 1626,” accessed on 5 August 2020, https://www.darwinproject.ac.uk/letter/DCP-LETT-1626.xml

Also published in The Correspondence of Charles Darwin, vol. 5

letter