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Down, Farnborough,

10th October (1846).

Dear Sir

Having just read your excellent Memoir on Denudation, I have taken the liberty to send you a copy of my volume on South America, finding that we have discussed some related questions. I wish I had profited by your memoir before publishing my volume. I see that we entirely agree on the sea's great power compared with ordinary alluvial action, and likewise on the frequency of grand oscillations of level and on several other points. If you had time to read parts of my volume, I should much like to discuss with you many cases, such as my notion of subsidence being necessary for the formation of high sea-cliffs, as inferred from the nature of the sea's bottom off them, likewise the horizontal elevation of the Cordillera as inferred from the sloping gravel fringes in the valleys; on the non-horizontality of lines of escarpments round old bays, etc. etc.

I grieve to see how diametrically opposite our views are (I being a follower of Lyell) on the probability of great and sudden elevations of mountain-chains; I cannot but think, that you would have estimated existing forces, as more than 'petty and entertained some doubt about their being 'conflicting' had you inspected with your own eyes the wide area of recently elevated and similarly affected districts in South America. There is much which I could say on this head, but I will not intrude on you.

May I ask whether you do not admit Mr Hopkin's views of mountain-chains being the subordinate effects of fractures consequent on changes of level in the surrounding areas; and does not all the evidence, which we possess, tend to show that widely-extended elevations are slow, and may we not infer from this that the formation of mountain-chains is likewise probably slow? I cannot see any difficulty, after a line of fracture has been once formed, in fluidified rock being pumped in by as many strokes, as it is pumped out in a common volcano, and yet producing a symmetrical effect. But I much fear that I have cause to apologise for having written at such unreasonable length; the interest excited in me by your Memoir, must plead my excuse, and trusting that you will forgive the liberty I have taken I remain, dear sir, yours faithfully,

C. Darwin