LIFE OF JAMES DWIGHT DANA 



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 compre- 

 hensive types. 



" 3. The fact that with the transitions in the strata and 

 formations, the exterminations, of species often cut the 

 threads of genera, families, and 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 carbonif- 

 erous age was one apparently of complete extermina- 

 tion both in America and Europe, when all threads were 

 cut ; and yet life was reinstated, and partly by renewing 

 with species old genera in all the classes and subkingdoms, 

 besides adding new types. 



1 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. Fal- 

 coner, Professor Owen has not done his work well with 

 the reptilian bird. I should be very glad to know what 

 are Mr. Falconer's views. 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 sus- 

 tains the conclusions he first published on the subject. 

 I have quoted from Owen in my book because his pub- 

 lications were more recent, not that I have greater con- 

 fidence in his opinions or knowledge." 



DARWIN TO DANA 



" DOWN, BROMLEY, KENT, February 20 [1863]. 



" I received a few days ago your book, and this morn- 

 ing your pamphlet on Man and your kind letter. I am 

 heartily sorry that your head is not yet strong, and what- 

 ever you do, do not again overwork yourself. Your book 

 [Manual of Geology] is a monument of labor, though I 

 have as yet only just turned over the pages. It evidently 

 contains a mass of valuable matter. 



' With respect to the change of species, I fully admit 

 your objections are perfectly valid. I have noticed them, 



314 



