My dear Lyell

I have been deeply interested in your letter, & so far at least worthy of the time it must have cost you to write it.— I have not much to say: I look at the whole question as settled, Santorin² is splendid; it is conclusive—it is perfect.— You have read Dufrenoy³ in a hurry, I think, & added to difficulty; it is the whole hill or “colline” which is composed of tuff with cross stratification; the central boss or “monticule” is simply trachyte.— Now I have described one tuff crater at Galapagos (p. 108).⁴ which has broken through a great solid sheet of basalt; why should not an irregular mass of trachyte have been left in middle after the explosions & emission of mud which produced the overlying tuff— Or again I see no difficulty in a mass of trachyte being exposed by subsequent dislocations & bared or cleaned by rain.— At Ascension, p. 40, subsequent to the last great aeriform explosion, which has covered the country with fragments, there have been dislocations & a large circular subsidence.— As far as size of Astroni⁵ is concerned it is nothing— do not quote Banks’ cove (for there has been some denudation there) but the “elliptic one”⁶ (p. 105) which is 1500 yards ($\frac{3}{4}$ of naut: mile) in internal diameter, & therefore larger than Astroni; & is the very one, the inclination of whose mud=streams or tuff strata I measured (before I had ever heard the name Dufrenoy) & found varying from 25^o to 30^o.—

Albemarle Isl^d instead of being a Crater of Elevation as Von Buch foolishly guessed⁷ is formed of 4 great sub-aerial, basaltic volcanos, (p. 103) of one of which, you might like know, the external diameter of the summit or crater was above 3 nautical miles— There are no “Craters of Denudation” at Galapagos;.

I hope you will allude to Mauritius;⁸ I think this is the instance on largest scale of any known,—though imperfectly known. If I were you, I w^d give up consistency (or at most only allude in note to your old Editions) & bring out the Craters of Denudation as a new view which it essentially is, & you cannot, I think, give it prominence as a novelty, & yet keep to consistency & passages in old Editions.— I sh^d. grudge this new view being smothered in your Address, & sh^d. like to see a separate Paper.—⁹

The one great channel to Santorin & Palma &c. &c.—is just like the one main chanel being kept open in atolls & encircling barrier reefs, & on same principle of water being driven in, through several shallow breaches.—

I of course utterly reprobate very wild notion of circular elevation: it is a satisfaction to me to think that I perceived there was a screw loose in old view, & so far I think I was of some service to you.—¹⁰

Depend on it, you have for ever smashed, crushed & abolished Craters of Elevations.— There must be Craters of engulfment & of explosion mere modifications of craters of Eruption—but Craters of Denudation are the ones which have given rise to all the discussions

Ever yours | C. Darwin

Pray give my best thanks to Lady Lyell for her translation¹¹ which was as clear as daylight to me, including “leglessness”

I shall be up on Wednesday¹² & want to speak one word to you about Royal Medals,¹³