To Daniel Sharpe 16 October [1851]1
Down Farnborough Kent
Oct 16th.
My dear Sharpe
I am very much obliged to you for telling me the results of your foliaceous tour2 & I am glad to hear you are drawing up an account for the Royal Soc.3 I hope you will have a good illustration or map, of the waving line of junction of the slate & schist with uniformly directed cleavage & foliation. It strikes me as crucial.4 I remember longing for an opportunity to observe this point. All that I say is that when slate & the metamorphic schists occur in the same neighbourhood, the cleavage & foliation are uniform: of this I have seen many cases, but I never observed slate actually overlying mica-slate.— I have, however, observed many cases of glassy clay-slate included within mica-schist & gneiss.
All your other observations on the arches &c seem very interesting. From conversations with Lyell &c, I recommend you to describe in a little detail the nature of the metamorphic schists;5 especially whether there are quasi-sub-strata of different varieties of mica-slate or gneiss &c.; & whether you traced such quasi-beds into the cleavage-Slate. I have not the least doubt of such facts occurring, from what I have seen (& described at M. Video) of portions of fine Chloritic schists being entangled in the midst of a gneiss district.6 Have you had any opportunity of tracing a bed of marble? this I think from reasons given at p. 166 of my S. America would be very interesting.7
A suspicion has sometimes occurred to me (I remember more especially when tracing the clay-slate at the C. of Good Hope,8 turning into true gneiss) that possibly all the metamorphic schists necessarily once existed as clay-slate, & that the foliation did not arise or take its direction in the metamorphic schists, but resulted simply from the preexisting cleavage.— The so-called beds in the metamorphic schists, so unlike common cleavage laminæ, seems the best, or at least, one argument against such a suspicion. Yet I think it is a point deserving your notice.— Have you thought at all over Roger’s Law, as he reiterates it, of cleavage being parallel to his axes-planes of Elevation?9
If you know before hand, will you tell me when your Paper is read; for the chance of my being able to attend.10 I very seldom leave home, as I find perfect quietude suits my health best.
Pray believe me, dear Sharpe | Your’s sincerely | C. Darwin
Footnotes
Bibliography
Correspondence: The correspondence of Charles Darwin. Edited by Frederick Burkhardt et al. 29 vols to date. Cambridge: Cambridge University Press. 1985–.
Rogers, Henry Darwin. 1846. On cleavage of slate-strata. Edinburgh New Philosophical Journal 41: 422–3.
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
Thanks DS for writing about his research on foliation and cleavage. Discusses nature of slate and metamorphic schists.
Makes suggestions for the paper DS is preparing for the Royal Society and raises questions for his consideration; CD hopes he can attend the Society meeting when the paper is read ["On foliation and cleavage of Scotland", Philos. Trans. R. Soc. Lond. 142 (1852): 445–62].
Letter details
- Letter no.
- DCP-LETT-1458
- From
- Charles Robert Darwin
- To
- Daniel Sharpe
- Sent from
- Down
- Source of text
- American Philosophical Society (Mss.B.D25.)
- Physical description
- ALS 3pp
Please cite as
Darwin Correspondence Project, “Letter no. 1458,” accessed on 20 April 2024, https://www.darwinproject.ac.uk/letter/?docId=letters/DCP-LETT-1458.xml
Also published in The Correspondence of Charles Darwin, vol. 5