To Daniel Sharpe [1 November 1846]
Down Farnborough Kent
My dear Sir
I have been much interested with your letter & am delighted that you have thought my few remarks, worth attention. My observations on foliation are more deserving confidence than those on cleavage;1 for during my first year in clay-slate countries I was quite unaware of there being any marked difference between cleavage & stratification; I well remember my astonishment at coming to the conclusion that they were totally different actions, & my delight at subsequently reading Sedgwicks views;2 hence at that time I was only just getting out of a mist. With respect to cleavage-laminæ dipping inwards, on mountain-flanks I have certainly often observed it, so often that I thought myself justified in propounding it as usual; I might perhaps have been some degree prejudiced by Von Buch’s remarks,3 for which in those days I had a somewhat greater deference than I now have.— The mount at M. Video (p. 146 of my Book) is certainly an instance of the cleavage laminæ of an hornblendic schist dipping inwards on both sides; for I examined this hill carefully with compass in hand & note book. I entirely admit, however, that a conclusion drawn from striking a rough balance in one’s mind, is worth nothing, compared with the evidence drawn from one continuous line of section. I read Studer’s Papers carefully & drew the conclusion stated, from it;4 but I may very likely be in an error. I only state that I have “frequently” seen cleavage-laminæ dipping inwards on mountain-sides; that I cannot give up, but I daresay a general extension of the rule, (as might justly be inferred from the manner of my statement) would be quite erroneous.5
Von Buch’s statement is in his Travels in Norway; I have unfortunately lost the reference & it is a high crime, I confess, ever to refer to an opinion, without a precise reference. If you never read these Travels, they might be worth skimming, chiefly as an amusement; & if you like, & will send me a line by the Gen. Post on Monday or Tuesday, I will either send it up with Hopkins on Wednesday, or bring it myself to Geolog. Soc. I am very glad you are going to read Hopkins;6 his views appear to me eminently worth well comprehending: false views & language appear to me to be almost universally held by geologists on the formation of fissures, dikes & mountain-chains. If you would have the patience, I shd be glad if you wd read in my “Volcanic Islands” from page 65, or even 54 to 72, viz on the lamination of volcanic rocks: I may add that I sent the series of specimens there described to Prof. Forbes of Edinburgh, & he thought they bore out my views.7
There is a short extract from Prof. Rogers’ in the last Eding. New Phil. Journ. well worth your attention on the cleavage of the Appalachian Chain,8 & which seems far more uniform in direction of dip, than in any case, which I have met with: the Rogers’ doctrine of the ridges being thrown up by great waves I believe is monstrous; but the manner in which the ridges have been thrown over (as if by a lateral force acting on one side on a higher level than on the other) very curious, & he now states that the cleavage is 〈parallel〉9 to the axis-plane of these thrown over ridges.— Your case of the limestone beds to my mind is the greatest difficulty on any mechanical doctrine; though I did not expect ever to find actual displacement, as seems to be proved by your shell-evidence.—10 I am extremely glad you have taken up this most interesting subject in such a philosophical spirit; I have no doubt you will do much in it;—Sedgwick let a fine opportunity slip away.— I hope you will get out another section like that in your letter; these are the real things wanted.
Believe me Yours very sincerely | C. Darwin
Discusses foliation and cleavage. Comments on dip of cleavage laminae in mountains. Mentions views of Sedgwick and Studer. Suggests reading C. L. von Buch [Travels through Norway and Lapland (1813)] "as an amusement". Praises views of William Hopkins. Suggests reading paper by H. D. Rogers ["On cleavage of slate-strata", Edinburgh New Philos. J. 41 (1846): 422–3)]. Comments on the paper.
Please cite as
Darwin Correspondence Project, “Letter no. 1016,” accessed on 23 July 2016, http://www.darwinproject.ac.uk/DCP-LETT-1016