2O4 GEOLOGY [CHAP. IX 



Letter 539 the metamorphic schists, so unlike common cleavage laminse, 

 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 Rogers' Law, as he reiterates 

 it, of cleavage being parallel to his axes-planes of elevation ? 



If you know beforehand, will you tell me when your 

 paper is read, for the chance of my being able to attend ? 

 I very seldom leave home, as I find perfect quietude suits 

 my health best. 



Letter 540 To C. Lyell. 



Down, Jan. zoth, 1855. 



I received your letter yesterday, but was unable to answer 

 it, as I had to go out at once on business of importance. 1 

 am very glad that you are reconsidering the subject of folia- 

 tion ; I have just read over what I have written on the subject, 

 and admire it very much, 1 and abide by it all. You will not 

 readily believe how closely I attended to the subject, and in 

 how many and wide areas I verified my remarks. I see I 

 have put pretty strongly the mechanical view of origin ; 

 but I might even then, but was afraid, have put my belief 

 stronger. Unfortunately I have not D. Sharpe's paper here 

 to look over, but I think his chief points [are] (i) the foliation 

 forming great symmetrical curves, and (2) the proof from 

 effects of form of shell 2 of the mechanical action in cleaved 

 rocks. The great curvature would be, I think, a grand 

 discovery of Sharpe's, but I confess there is some want of 

 minuteness in the statement of Sharpe which makes me wish 

 to see his facts confirmed. That the foliation and cleavage 

 are parts of curves I am quite prepared, from what I have 

 seen, to believe ; but the simplicity and grandeur of Sharpe's 

 curves rather stagger me. I feel deeply convinced that when 

 (and I and Sharpe have seen several most striking and obvious 

 examples) great neighbouring or alternating regions of true 

 metamorphic schists and clay-slate have their foliations and 

 cleavage parallel, there is no way of escaping the conclusion, 

 that the layers of pure quartz, feldspar, mica, chlorite, etc., etc., 

 are due not to original deposition, but to segregation ; and 

 this is I consider the point which I have established. This 



1 Geological Observations on South America, Chapter VI., 1846, 



2 This refers to the distortion of shells in cleaved rocks. 



