RECORD: Darwin, C. R. Geological diary: The more I reflect on Stratification & Cleavage the more difficulties I find. [nd] CUL-DAR34.179-180 Transcribed by Kees Rookmaaker, edited by John van Wyhe (Darwin Online, http://darwin-online.org.uk/)

REVISION HISTORY: Transcribed by Kees Rookmaaker, corrections and editing by John van Wyhe 4.2011. RN1

NOTE: This document, part of the largest scientific document composed by Darwin during the voyage of the Beagle, is written mostly in ink. Marginal notes are here integrated into the text.

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Reproduced with the permission of the Syndics of Cambridge University Library and William Huxley Darwin.

See the introduction to the Geological Diary by Gordon Chancellor.


179

The more I reflect on stratification & cleavage, the more difficulties I find in the subject: The following contradiction has often come nearly [necessary] in hypothesis — By stratification I mean planes formed originally by changes in nature & time horizontally in a horizontal front:

By cleavage — the slaty structure which I have so often noticed. — by fissure, parallel planes at wider intervals & meeting which divide the rocks into masses & meets those of cleavage at different angles. — by direction this bearing up or nearly [illeg] & horizontal plain. —

The first question one asks oneself is, what is cleavage? is the present position of the plains their original one or have they been disturbed. — It t is often said that the direction of cleavage & stratification is the same. this must require I do not see how this can be possible without these being deposited in the same place: but with different dips: I do not see how stratification can be evident: I can understand that from some unknown law in the original beds & slightly inclined (for if horizontal no direction would be visible) beds. cleavage might have the same range: but suppose these beds elevated with the cleavage & stratified dipped to same point, but at different angle, tilted on one side; there they will let a line of elevation cross these beds in any direction & this excepting it should happen to be that of original deposition, it will destroy all identity of dip: — And this must happen in the greater number of mountain chains: instance Tierra

But even

179 verso

this case the upheaved line new direction of stratified strata would be that of elevation cleavage very different. — Yet observations in any district on the cleavage would point the extent of a common cause; if not its actual direction: Tierra del

Everyone acknowledges the difficulty of observing stratification in a slate country: Tierra del but smaller

Suppose we leave it out of the question which is obscure: it will then be most necessary to find original position of the planes of cleavage

If we suppose it horizontal, it will explain the dir its similarity, when elevated with line of elevation; but in contra Humboldt argument are strong against. this & the general very great angle of dip in the case mentioned in Navarin Isd where at 38 miles distance the plains were precisely vertical & running to same point, puts out of the question the thought that a mass of a rock should be raised through 90° & not disturbed. — the country is more level than in other parts: Are we to suppose them originally vertical; the argument against horizontally will apply forcely in favor of this exception 1 to uniformity explained by [trouble] at the bottom of page put this (: if a coincidence of line of elevation & cleavage is proved & line of land is proved we must give up original verticality or any position excepting the horizontal:

Both in the East & West side of Navarin Island proceeding from the North to the South, we meet with first a SSW dip, then a N by E. & 3d a vertical plain. — now if we suppose the inclination to arise from either vertical or horizontal plain being disturbed, this order of dip does way with any good common cause. — A SSW dip elevated would be vertical before dipping to N by E. it is the same with vertical one little to one side:

180

(1) In Tierra del Fuego there is however a connection between direction of cleavage & form of land: the great mountain again made up (if not entirely to a great extent of unknown granite rock, runs in a WNW:

The whole form of the peninsula leaving out the eastern modern formation is nearly that & many of the channels (excepting the Beagle) such as West part of Magellan St Gabriel Channel: Admiralty: also although more doubtful, the tendency on the West side to dip to the West of SSW as on the East to the contrary direction: if we suppose the mountains & leading vallies & new form of land to be created by elevations, we must see a close (a) connection between this line & direction of cleavage:

But there is a difficulty in this view. if we imagine Sarmiento chain to be the line of upheaval all the beds should, as we found them, dip to the SSW. — but [illeg; text on sheet appears folded obscuring part of the text] to dip to the NNE — in the West East end of Beagle Channel, we yet see them with the SSW dip: —

(a) The direction of cleavage is also that of grand mineralogical change, for instance, the northern arm of Beagle Channel runs WNW & separate. an escarpement of clayslate. from a blue great lofty one of mica slate, which probably rests on granite: (mention it in evidence on moonstone supposition)

180 verso

(2) In Tierra Navarin Island I have noticed horizontal planes having bands of a white colour: which must originate in some chemical change to be horizontal — on the mountain chain it dipped at small angle to the SSW. — This certainly have looks like stratification. — But the former the planes of cleavage dipped nearly vertically to same point — which on the mountains about 60. that is less — It is impossible to reconcile this these facts, as the upheaval of the white bands must cause the cleavage to dip at a higher angle to this SSW: <e which would be vertical or to the N by E.

(1) Conclusion — This would show identity of elevation & cleavage, which on the supposition of cleavage originally exactly in the rock at a different in a inclined position & it must be so to be different five strata. I have shown to be rare as to depend on line of elevation & cleavage being the same: —


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Citation: John van Wyhe, editor. 2002-. The Complete Work of Charles Darwin Online. (http://darwin-online.org.uk/)

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