., page 185, 1862. "On the Glacial Origin of
certain Lakes in Switzerland, the Black Forest, Great Britain, Sweden,
North America, and elsewhere.') and Jukes' papers (544/4. "Quart. Journ.
Geol. Soc." Volume XVIII., page 378, 1862. "On the Mode of Formation of
some River-Valleys in the South of Ireland."), I gave up in my own mind
the case; but I never fully realised the truth until reading your papers
just received. How often I have speculated in vain on the origin of the
valleys in the chalk platform round this place, but now all is clear. I
thank you cordially for having cleared so much mist from before my eyes.

LETTER 545. TO T. MELLARD READE. Down, February 9th, 1877.

I am much obliged for your kind note, and the present of your essay.
I have read it with great interest, and the results are certainly most
surprising. (545/1. Presidential Address delivered by T. Mellard Reade
before the Liverpool Geological Society ("Proc. Liverpool Geol. Soc."
Volume III., pt. iii., page 211, 1877). See also "Examination of a
Calculation of the Age of the Earth, based upon the hypothesis of the
Permanence of Oceans and Continents." "Geol. Mag." Volume X., page 309,
1883.) It appears to me almost monstrous that Professor Tait should
say that the duration of the world has not exceeded ten million years.
(545/2. "Lecture on Some Recent Advances in Physical Science," by P.G.
Tait, London, 1876.) The argument which seems the most weighty in favour
of the belief that no great number of millions of years have elapsed
since the world was inhabited by living creatures is the rate at which
the temperature of the crust increases, and I wish that I could see this
argument answered.

LETTER 546. TO J. CROLL. Down, August 9th, 1877.

I am much obliged for your essay, which I have read with the greatest
interest. With respect to the geological part, I have long wished to see
the evidence collected on the time required for denudation, and you have
done it admirably. (546/1. In a paper "On the Tidal Retardation Argument
for the Age of the Earth" ("Brit. Assoc. Report," 1876, page 88), Croll
reverts to the influence of subaerial denudation in altering the form of
the earth as an objection to the argument from tidal retardation. He had
previously dealt with this subject in "Climate and Time," Chapter
XX., London, 1875.) I wish some one would in a like spirit compare
the thickness of sedimentary rocks with the quickest estimated rate of
depos