aminae, 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.

(PLATE: CHARLES DARWIN, Cir. 1854. Maull & Fox, photo. Walker &
Cockerell, ph. sc.)

LETTER 540. TO C. LYELL. Down, January 10th, 1855.

I received your letter yesterday, but was unable to answer it, as I had
to go out at once on business of importance. I am very glad that you
are reconsidering the subject of foliation; I have just read over what
I have written on the subject, and admire it very much, and abide by it
all. (540/1. "Geological Observations on South America," Chapter VI.,
1846.) 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] (1) the foliation forming great symmetrical curves, and (2)
the proof from effects of form of shell (540/2. This refers to the
distortion of shells in cleaved rocks.) 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 is very odd, but I suspect that great metamorphic
areas are generally derived from the metamorphosis of clay-slate, and
not