apers "On Glaciers," and "On some Physical Properties of Ice" ("Proc.
R. Inst." 1854-58) before the date of this letter. In 1856 he wrote
a paper entitled "Observations on 'The Theory of the Origin of Slaty
Cleavage,' by H.C. Sorby." "Phil. Mag." XII., 1856, page 129.)

Sorby read a paper to the Brit. Assoc., and he comes to the conclusion
that gneiss, etc., may be metamorphosed cleavage or strata; and I
think he admits much chemical segregation along the planes of division.
(543/2. "On the Microscopical Structure of Mica-schist:" "Brit. Ass.
Rep." 1856, page 78. See also Letters 540-542.) I quite subscribe to
this view, and should have been sorry to have been so utterly wrong, as
I should have been if foliation was identical with stratification.

I have been nowhere and seen no one, and really have no news of any kind
to tell you. I have been working away as usual, floating plants in salt
water inter alia, and confound them, they all sink pretty soon, but at
very different rates. Working hard at pigeons, etc., etc. By the way,
I have been astonished at the differences in the skeletons of domestic
rabbits. I showed some of the points to Waterhouse, and asked him
whether he could pretend that they were not as great as between species,
and he answered, "They are a great deal more." How very odd that no
zoologist should ever have thought it worth while to look to the real
structure of varieties...

2.IX.VI. AGE OF THE WORLD, 1868-1877.

LETTER 544. TO J. CROLL. Down, September 19th, 1868.

I hope that you will allow me to thank you for sending me your papers
in the "Phil. Magazine." (544/1. Croll published several papers in
the "Philosophical Magazine" between 1864 and the date of this letter
(1868).) I have never, I think, in my life been so deeply interested
by any geological discussion. I now first begin to see what a million
means, and I feel quite ashamed of myself at the silly way in which I
have spoken of millions of years. I was formerly a great believer in the
power of the sea in denudation, and this was perhaps natural, as most of
my geological work was done near sea-coasts and on islands. But it is a
consolation to me to reflect that as soon as I read Mr. Whitaker's paper
(544/2. "On Subaerial Denudation," and "On Cliffs and Escarpments of
the Chalk and Lower Tertiary Beds," "Geol. Mag." Volume IV., page 447,
1867.) on the escarpments of England, and Ramsay (544/3. "Quart. Journ.
Geol. Soc." Volume XVIII