CORRESPONDENCE WITH CHARLES DARWIN 



DANA TO DARWIN 



" NEW HAVEN, February 5, 1863. 



" The arrival of your photograph has given me great 

 pleasure, and I thank you warmly for it. 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 expense, as was my intention). 

 I have still to report your book [ The Origin of Species] 

 unread ; for my head has all it can now do in my college 

 duties. 



" 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. There are three 

 difficulties that weigh on my mind, and I will mention 

 them: 



" i. The absence, in the great majority of cases, of 

 those transitions by small differences required by such a 

 theory. As the life of America and Europe has been 

 with few exceptions independent, one of the other, it is 

 right to look for the transitions on each continent sepa- 

 rately. The reply to this difficulty is that the science of 

 geology is comparatively new and facts are daily multiply- 

 ing. But this admits the proposition that geology does 

 not yet afford the facts required. 



" 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, and the ganoids, which are 

 above the true level of the fish, between fishes and rep- 

 tiles. In the introduction of land plants, there were 

 acrogens and conifers and intermediate types, but not 

 the lower grade of mosses, seemingly the natural step- 

 ping-stone from the seaweeds. The species, Lepidodendra, 

 sigillarids, are examples of those intermediate or compre- 

 hensive types with which great groups often began, and 

 seem to explain the true relations of such types; but they 

 were not transitional forms in the system of life, but rather 

 the commencing forms of a type. If I advocate your 



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