Darwin Correspondence Project

Down Farnborough Kent

March 21st—

Sir

Permit me to thank you for your extremely kind letter: I have no doubt my small volume on S. America will reach you soon, as I directed my publishers to send it, at the same time that I addressed you: I fear you will find little in it that will interest you, except perhaps the short discussion on cleavage & foliation. Had I known that you were so well acquainted with English, I should have taken the liberty of writing to you at rather greater length respecting your interesting views on the structure of the Alpine metamorphic schists;—but so far from knowing that you had done me the very great honour of making others acquainted with my volume on Coral Reefs, I did not suppose that you would ever have heard my name.— I am glad to hear of your paper in the Bulletin & will take an early opportunity of consulting. I beg to call your attention to a paper in the last number of the Journal of our Geolog. Soc., by Mr D. Sharpe, on cleavage, which strikes me as very important. It is a difficult paper, I find, to understand, but the leading idea appears capital,—namely the proof from the distortion of known fossil-shells, that there has been regular & great displacement along the planes of cleavage.— In a small volume on Volcanic Islands published by me about two years ago, I have described in detail some curious laminated volcanic rocks, composed of crystals of feldspar, quartz & diopside & oxide of iron, in parallel & excessively thin layers,—so as to resemble some gneisses. these layers, no doubt, have been produced by the flowing movement of the lava, just before consolidation, in the same manner as the blue & white layers are produced in a glacier, according to Prof. Forbes.

I am greatly tempted to extend this view to the foliation of the metamorphic schists, not that I suppose that these ever flowed as lava, but that they have been stretched in uniform planes, by widely-extended elevatory movements. The planes of “tearing” or “of lesser & greater tension” determining the planes of crystallization & separation of the constituent minerals. The parallelism in direction or strike, though not in dip of the principal axes of elevation with the strike of the planes cleavage in almost every country points towards this conclusion. And now we know from Mr Sharpe that there has been actual movement along the planes of cleavage in clay-slate;— Whatever explanation is applicable to cleavage, I <am> satisfied, in accordance with your statements, mu<st> include the foliation of the metamorphic schists.—

But I ought to apologise for troubling you with so long a letter; & I can only plead the kindness of your note as my excuse.— I beg to thank you cordially for your offer of your work “sur la physique du globe”; I do read German but most imperfectly & with much difficulty & without making any progress towards facility (a remark made by many Englishmen who seldom can boast of a turn for languages), & therefore, if you will permit me speak quite frankly, I should be extremely much pleased to receive it, if it is not a very large & expensive work; for in this latter case, it would, I grieve to say, be almost thrown away on me.

Pray believe me, dear Sir, with much respect, your faithful & obliged servant | C. Darwin

My address in London, for parcels is 7. Park Stt | Grosvenor Square