To Leonard Horner 29 August 
Down near Bromley | Kent
My dear Mr. Horner
I am greatly obliged for your kind note & much pleased with its contents. If one third of what you say, be really true & not the verdict of a partial judge (as from pleasant experience I much suspect), then should I be thoroughily well contented with my small volume,1 which small as it is, cost me much time.— The pleasure of observation amply repays itself; not so that of composition, & it requires the hope of some small degree of utility in the end, to make up for the drudgery of altering bad English into sometimes a little better & sometimes worse.
With respect to Craters of Elevation, I had no sooner printed off the few pages on that subject, than I wished the whole erased.— I utterly disbelieve in Von Buch & de Beaumonts views, but on the other hand in the case of the Mauritius & St Jago, I cannot, perhaps, unphilosophically persuade myself, that they are merely the basal fragments of ordinary volcanoes, & therefore I thought I would suggest the notion of a slow circumferential elevation, the central part being left unelevated, owing to the force from below being spent & relieved in eruptions.2 On this view, I do not consider these so-called craters-of Elevation, as formed by the ejection of ashes lava &c &c but by a peculiar kind of elevation, acting round & modifyed by a volcanic orifice.—
I wish I had left it all out; I trust that there is in other parts of the volume more facts & less theory.— The more I reflect on volcanoes, the more I appreciate the importance of E. de Beaumont’s measurements3 (even if one does not believe them implicitly) of the natural inclination of lava-streams & even more the importance of his view of the dikes or upfilled fissures in every volcanic mountain being the proofs & measures, of the stretching & consequent elevation which all such mountains must have undergone:4 I believe he thus unintentionally explains most of his cases of lava-streams being inclined at a greater angle, than that at which they could have flowed.
But excuse this lengthy note & once more let me thank you for the pleasure & encouragement you have given me,—which together with Lyells never-failing kindness, will help me on with S. America, & as my Books will not sell, I sometimes want such aid.—
I have been lately reading with care A. d’Orbigny work on S. America,5 & I cannot say how forcibly impressed I am with the infinite superiority of the Lyellian school of Geology over the Continental. I always feel as if my books came half out of Lyell’s brains & that I never acknowledge this sufficiently, nor do I know how I can, without saying so in so many words—for I have always thought that the great merit of the Principles, was that it altered the whole tone of one’s mind & therefore that when seeing a thing never seen by Lyell, one yet saw it partially through his eyes— it would have been in some respects better if I had done this less—but again excuse my long & perhaps you will think presumptuous discussion.
Enclosed is a note from Emma to Mrs Horner to beg you, if you can, to give us the great pleasure of seeing you here— we are necessarily dull here & can offer no amusements, but the weather is delightful & if you could see how brightly the sun now shines you would be tempted to come—
Pray remember me most kindly to all your family & beg of them to accept our proposal & give us the pleasure of seeing them.— Emma will tell how feasible the coming here is by a coach, which puts down by our door at dinner-time.
Believe me | dear Mr Horner | Yours truly obliged | Charles Darwin
Thanks Horner for his letter [about Volcanic islands].
Discusses craters of elevation with respect to the views of Leopold von Buch and Élie de Beaumont. Compares Lyell’s views to those of continental geologists. Mentions reading A. D. d’Orbigny [Voyage dans l’Amérique méridionale (1835–47)].
Encloses note from Emma to Mrs Horner, inviting the Horners to visit Down.