Place, Baker Street [1855].

I have received your letter from Down, and I have been studying my S.
American book.

I ought to have stated [it] more clearly, but undoubtedly in W. Tierra
del Fuego, where clay-slate passes by alternation into a grand district
of mica-schist, and in the Chonos Islands and La Plata, where glossy
slates occur within the metamorphic schists, the foliation is parallel
to the cleavage--i.e. parallel in strike and dip; but here comes, I am
sorry and ashamed to say, a great hiatus in my reasoning. I have assumed
that the cleavage in these neighbouring or intercalated beds was (as in
more distant parts) distinct from stratification. If you choose to
say that here the cleavage was or might be parallel to true bedding,
I cannot gainsay it, but can only appeal to apparent similarity to
the great areas of uniformity of strike and high angle--all certainly
unlike, as far as my experience goes, to true stratification. I have
long known how easily I overlook flaws in my own reasoning, and this is
a flagrant case. I have been amused to find, for I had quite forgotten,
how distinctly I give a suspicion (top of page 155) to the idea, before
Sharpe, of cleavage (not foliation) being due to the laminae forming
parts of great curves. (542/1. "I suspect that the varying and opposite
dips (of the cleavage-planes) may possibly be accounted for by the
cleavage-laminae...being parts of large abrupt curves, with their
summits cut off and worn down" ("Geological Observations on S. America,"
page 155). I well remember the fine section at the end of a region where
the cleavage (certainly cleavage) had been most uniform in strike and
most variable in dip.

I made with really great care (and in MS. in detail) observations on
a case which I believe is new, and bears on your view of metamorphosis
(page 149, at bottom). (Ibid., page 149.)

(FIGURE 7.)

In a clay-slate porphyry region, where certain thin sedimentary layers
of tuff had by self-attraction shortened themselves into little curling
pieces, and then again into crystals of feldspar of large size, and
which consequently were all strictly parallel, the series was perfect
and beautiful. Apparently also the rounded grains of quartz had in other
parts aggregated themselves into crystalline nodules of quartz. [Figure
7.]

I have not been able to get Sorby yet, but shall not probably have
anything to write on it. I am delighted you have taken up the subject,
even