The Complete Work of Charles Darwin Online

RECORD: Darwin, C. R. n.d. Cleavage / I much doubt whether any rocks have true cleavage. CUL-DAR42.69. Edited by John van Wyhe (Darwin Online, http://darwin-online.org.uk/)

REVISION HISTORY: Transcribed by Christine Chua and edited by John van Wyhe 1.2022. RN1

NOTE: See record in the Darwin Online manuscript catalogue, enter its Identifier here. Reproduced with permission of the Syndics of Cambridge University Library and William Huxley Darwin. The volume CUL-DAR42 contains notes for Darwin's book South America (1846).

[69]

Cleavage

I much doubt whether any rocks have true cleavage, (that is like stalactite of Sulp of lime), but all depend on separation of ingredients, even clay slate. I believe depends on this. (Hence quartz has not cleavage & the layers of homogeneous materials have their crystals lengthways – why do crystals radiate in splendid concretions.

[69v]

does the cleavage in stalactites obey any particular law.

I presume the position of each action is determined by that of it neighbour but yet why should all be in one plane.

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