Sir

I hope you will excuse the liberty I take in addressing you, but I trust that our several common acquaintances may be some excuse & M^r Lyell¹ has been so good as to say that I might use his name as an introduction to you. My object in writing is to ask you to confer a favour on me by examining a specimen of calcareous rock. The great deposit of the Pampas, in which so many strange mammiferous remains are embedded, in its southern parts, passes into an indurated, calcareous, tuff-like stone. Comparing a specimen of this, with a specimen from a post-pleiocene calcareous bed from the coast of Chile, which has resulted from the attrition of recent shells, of which many are embedded in it, I was struck with the general resemblance between them, and especially in some minute, rounded, included fragments.—²

I am most anxious to know, whether these minute fragments, which are very indistinct, are really pieces of shells, like those in the Chilian stone, because the origin of the Pampæan formation has been lately disputed & attributed to a debacle, & is in many points of view of considerable interest.—³ Having seen some of your curious researches on the microscopical structure of shells,⁴ it has occurred to me, that perhaps you would be willing to confer this great favour on me;⁵ and would be so kind, if you think the little fragments in their matrix would stand cutting & polishing, to have it done at my expence.— Should you have time to spare to look at my specimen, I would send it (carriage free) either to anywhere in London, or perhaps better, direct to Ripley, if you would tell me by what conveyance is best—

Hoping that you will excuse the liberty which I am taking Pray | Believe me, dear Sir | Yours faithfully | Charles Darwin