most able discussion on coral reefs. I thank you most
sincerely for the very honourable mention you make of me. (561/1.
"United States Exploring Expedition during the Years 1839-42 under the
Command of Charles Wilkes, U.S.N." Volume X., "Geology," by J.D. Dana,
1849.) This day I heard that the atlas has arrived, and this completes
your munificent present to me. I have not yet come to the chapter
on subsidence, and in that I fancy we shall disagree, but in the
descriptive part our agreement has been eminently satisfactory to me,
and far more than I ever ventured to anticipate. I consider that now
the subsidence theory is established. I have read about half through
the descriptive part of the "Volcanic Geology" (561/2. Part of Dana's
"Geology" is devoted to volcanic action.) (last night I ascended the
peaks of Tahiti with you, and what I saw in my short excursion was most
vividly brought before me by your descriptions), and have been most
deeply interested by it. Your observations on the Sandwich craters
strike me as the most important and original of any that I have read
for a long time. Now that I have read yours, I believe I saw at the
Galapagos, at a distance, instances of those most curious fissures of
eruption. There are many points of resemblance between the Galapagos and
Sandwich Islands (even to the shape of the mound-like hills)--viz., in
the liquidity of the lavas, absence of scoriae, and tuff-craters. Many
of your scattered remarks on denudation have particularly interested me;
but I see that you attribute less to sea and more to running water than
I have been accustomed to do. After your remarks in your last very kind
letter I could not help skipping on to the Australian valleys (561/3.
Ibid., pages 526 et seq.: "The Formation of Valleys, etc., in New South
Wales."), on which your remarks strike me as exceedingly ingenious and
novel, but they have not converted me. I cannot conceive how the great
lateral bays could have been scooped out, and their sides rendered
precipitous by running water. I shall go on and read every word of your
excellent volume.

If you look over my "Geological Instructions" you will be amused to
see that I urge attention to several points which you have elaborately
discussed. (561/4. "A Manual of Scientific Enquiry, prepared for the use
of Her Majesty's Navy, and adapted for Travellers in General." Edited by
Sir John F.W. Herschel, Bart. London, 1849 (Section VI., "Geology." By
Charles