My dear Darwin,—

I write this to you, at least I am beginning it, in a steamboat on the Rhine, so make allowance for the tremulous motion. We came in a steamer from Copenhagen to Lübeck, then in a hired carriage to Hamburgh, across the sand and boulder formation of the Baltic, which for the most part we have been on ever since, although we have crossed the Weser, and Ems, and Lippe. The blocks of red syenitic granite, which I hammered away at in Norway, and which I saw there in situ, sending its veins into the trilobite and orthoceratite schist, have been carried with small gravel of the same, by ice of course,² over the south of Norway, and thence down the south-west of Sweden, and all over Jutland and Holstein down to the Elbe, from whence they come to the Weser, and so to this or near this. But it is curious that about Münster and Osnabruck, the low secondary mountains have stopped them; hills of chalk, Muschelkalk, old coal &c., which rise a few hundred feet in general above the great plain of north and north-west Germany, effectually arrest their passage.

This then was already dry land when Holstein, and all from the Baltic as far as Osnabruck or the Teutoberger³ Wald hills, was submerged. At Bremen I saw Olbers, aged seventy-two, the astronomer who discovered Pallas and Vesta,⁴ and there and at Osnabruck and Münster I met a warm and German reception from men of whom I had never heard, but who had read my paper on Sweden⁵ or something else. I mean by German, that kind of frank expression of enthusiasm for science, or of any emotion, which a well-bred Englishman tries to suppress, at least all outward expression of it, from the dread of being thought ridiculous, or of affecting to feel more than he does, or from mauvaise honte. If you ever get sick of that fashionable nonchalance which would blush to admire anything, or at least to confess it, I advise you to plunge into Germany, and you will be soon refreshed, and brought back to a right tone again, whether it be literature, science, or any other pursuit you are following.

I hope to write to Horner a full account of my surprise to find that there is no truth in overlying granite in Norway—no exception to the rule, as I will tell you presently—that he may read it at the British Association.⁶ Be it known then to you and others who have read what Von Buch wrote on Norway in the days of his youth, and of his Wernerianism and Neptunianism, that his notion of the granite overlying the transition rock arose from this, that whenever he found schist dipping towards granite regularly up to the point of contact, he assumed that it went under.⁷ The granite may lean over a little here and there, but this is accidental, and in general it sends veins only into the transition beds, changing the limestone into marble near the junction, and the shale into micaceous schist, and other metamorphosis, the fossils often escaping in the white marble, and some traces in some crystalline schists.

Now what I have seen in several places, I take Keilhau’s word to be the universal fact.⁸ Had Von Buch believed as he afterwards did in the igneous origin of granite, he would have found the veins, but without this, somehow or other, he came by false reasoning to the true conclusion, that the granite is newer than the Silurian beds. This is lucky for him. What struck me forcibly was this: after seeing proofs innumerable and beautifully clear of the order of age being first gneiss, then secondly, unconformable transition beds, then granite, and after seeing that the granite was the newest, I then found that the granite not only sent veins into both transition and gneiss, but actually sometimes passed by imperceptible gradation into gneiss. This gneiss, so ancient that it had been crystallised and then thrown into vertical and curved stratification even before the trilobites flourished,⁹ this most ancient rock is so beautifully soldered on to the granite, so nicely threaded by veins large and small, or in other cases so shades into the granite, that had you not known the immense difference of age, you would be half staggered with the suspicion that all was made at one batch!

Paris, September 5.— Last year when Charlesworth spoke at Bristol about Crag,¹⁰ and the numerical percentage of recent tertiary shells, Sedgwick and Buckland gave some useful impromptu replies, stating that I was aware some modifications would be required, &c., but they would not affect this classification in the main. Now if he should again, as I expect, speak on this subject, and if he should again cite Beck,¹¹ will you state that you happen to know from correspondence which you have had with me this summer, that I have been engaged with Dr. Beck in a careful examination of the species of fossil shells of the Crag and other tertiary formations which have been identified with recent species; that you have learnt from my letters that Dr. Beck by no means denies the absolute identity of a certain number of Crag species, though he thinks a large proportion of those identified by Deshayes to be distinguishable.¹² Also that I consider that Dr. Beck’s views of the conchological fauna of the Crag, drawn from the consideration of 260 species, tend to confirm the classification which places the Crag as older Pliocene and on a parallel with the Sub-Apennine beds, and distinct from and more modern than the Touraine, Bordeaux, and other Miocene deposits. Also, that I am convinced that independently of the relative percentage of recent shells, about which naturalists may differ according to their notions of what constitutes a specific difference, there are other characters in the entire assemblage of forms of shells belonging to each great tertiary epoch, which will enable us to classify the deposits according to the approach which they make to the type of organisation now existing in the neighbouring seas; and that this approach will serve as a chronological test of the eras to which tertiary deposits may respectively belong. I mean the degree of approach to or departure from the assemblage of living shells in the neighbouring seas will be a test of the relative newness or antiquity of the several deposits; also that I consider the terms Eocene, Miocene, and Pliocene to be as convenient and (if I the inventor may say so) happy, in reference to this view, as when they were made to refer more exclusively to the proportion of fossil species identified with recent. For the Pliocene and Miocene will always express greater and less degrees of approximation to the existing fauna, and the Eocene that first dawn of resemblance which characterises the oldest tertiary shells when compared with those of the newest secondary formations. As I have not yet finished my examination of disputed points, and not even begun to hear the pleadings on one side, I will not risk any statement as to how far the identification of fossil with recent shells may have been pushed too far, for I certainly suspect that the error has been chiefly on this side; but I wish you to know that my conviction is stronger than ever, that rules may be given for measuring the approximation of different groups of tertiary shells, and that the degree of this approximation may be used as a test of age, and may lead to the same classification as that which I have adopted in the ‘Principles.’ I am fully prepared to defend all that is essential in my system of tertiary classification as founded on fossil shells.

Believe me ever most truly yours, | Charles Lyell.