i877.] MR. ALLEN'S WORKS. 409 



ronment. I have some excuse for not having formerly in- 

 sisted more strongly on this head in my ' Origin of Species,' 

 as most of the best facts have been observed since its publi- 

 cation. 



With my renewed thanks for your most interesting essay, 

 and with the highest respect, I remain, dear Sir, 



Yours very faithfully, 



Charles Darwin. 



C. Darwin to E. S. Morse. 



Down, April 23, 1877. 



My dear Sir, — You must allow me just to tell you how 

 very much I have been interested with the excellent Address * 

 which you have been so kind as to send me, and which I had 

 much wished to read. I believe that I had read all, or very 

 nearly all, the papers by your countrymen to which you refer, 

 but I have been fairly astonished at their number and im- 

 portance when seeing them thus put together. I quite agree 

 about the high value of Mr. Allen's works,! as showing how 

 much change may be expected apparently through the direct 

 action of the conditions of life. As for the fossil remains in 

 the West, no words will express how wonderful they are. 

 There is one point which I regret that you did not make clear 

 in your Address, namely what is the meaning and importance 

 of Professors Cope and Hyatt's views on acceleration and 

 retardation. I have endeavoured, and given up in despair, 

 the attempt to grasp their meaning. 



Permit me to thank you cordially for the kind feeling 

 shown towards me through your Address, and I remain, my 

 dear Sir, 



Yours faithfully, 

 • Ch. Darwin. 



* " What American Zoologists have done for Evolution," an Address 

 to the American Association for the Advancement of Science, August, 

 1876. Vol. XXV. of the Proceedings of the Association. 



f Mr. J. A. Allen shows the existence of geographical races of birds 

 and mammals. Proc. Boston Soc. Nat. Hist. vol. xv. 

 42 



