My dear Mr Darwin—

The arrival of your photograph has given me great pleasure, and I thank you warmly for it.¹ I value it all the more that it was made by your son. He must be a proficient in the photographic art; for I have never seen a finer black tint on such a picture.—

I hope that ere this you have the copy of the Geology** (and without any charge of expenses, as was my intention)²   I have still to report your book unread; for my head has all it can now do in my college duties.³

I have thought that I ought to state to you the ground for my assertion on page 602, that Geology has not afforded facts that sustain the view that the system of life has been evolved through a method of development from species to Species.—⁴ There are three difficulties that weigh on my mind, and I will mention them.

1. The absence, in the great majority of cases, of those transitions by small differences required by such a theory.— As the life of America & Europe has been with few exceptions independent, one of the other, it is right to look for the transitions on each Continent separately.— The reply to this difficulty is that the Science of Geology is comparatively new and facts are daily multiplying. But this admits the proposition that Geology does not yet afford the facts required.—⁵

2. The fact of the commencement of types in some cases by their higher groups of species instead of the lower.— As fishes began with the Selachians or Sharks (the highest order of fishes & the Ganoids, which are above the true level of the fish between fishes & Reptiles. In the introduction of land plants, there were Acrogens & Conifers and intermediate types, but not the lower grade of mosses—seemingly the natural stepping-stone from the Seaweeds. The fishes, Lepidodendron, Sigillarids, are examples of those intermediate or comprehensive types, with which great groups often began, and seem to explain the true relations of such types:—that they were not transitional forms in the system of life, but rather the commencing forms of a type.— If I advocated your theory, I think I should take the ground that there were certain original points of divergence from time to time introduced into the System, as indicated by the Comprehensive types.⁶

3. The fact that with the transitions in the strata & formations, the exterminations of species often cut the threads of genera, families & tribes, and sometimes, also, of the higher groups of Orders, classes and even Subkingdoms; and yet the threads have been started again in new species. The transition after the Carboniferous age was one apparently of complete extermination both in America & Europe, where all threads were cut; & yet life was reinstated and partly by renewing with species old genera in all the classes & subkingdoms, besides adding new types.⁷

You thus see that I have not spoken positively on page 602, without thinking I had some foundation for it. I speak merely of the geological facts that bear on the or any theory of development, not of facts from other Sources.—

You say in your letter that according to Mr Falconer, Prof. Owen has not done his work well with the Reptilian bird.⁸ I should be very glad to know what are Mr Falconer’s views.⁹ I should like also to have his present opinions with respect to the Mesozoic mammals of England, or at least, to be informed whether he sustains the conclusions he first published on the subject. I have quoted from Owen in my book because his publications were more recent, not that I have greater confidence in his opinions or knowledge.—¹⁰

With earnest wishes for your health and happiness, I remain | Sincerely yours | James D. Dana

** It was sent through Trubner & Co. 60 Paternoster Row¹¹