i845.] LYELL'S 'NORTH AMERICA.' 307 



as new, though it has so struck me, and has placed in my 

 mind all the difficulties with respect to the causes of extinc- 

 tion, in the same class with other difficulties which are gener- 

 ally quite overlooked and undervalued by naturalists ; I ought, 

 however, to have made my discussion longer and shewn by 

 facts, as I easily could, how steadily every species must be 

 checked in its numbers. 



I received your Travels * yesterday ; and I like exceed- 

 ingly its external and internal appearance ; I read only about 

 a dozen pages last night (for I was tired with hay-making), 

 but I saw quite enough to perceive how very much it will in- 

 terest me, and how many passages will be scored. I am 

 pleased to find a good sprinkling of Natural History ; I shall 

 be astonished if it does not sell very largely. . . . 



How sorry I am to think that we shall not see you here 

 again for so long; I wish you may knock yourself a little bit 

 up before you start and require a day's fresh air, before the 

 ocean breezes blow on you. . . . 



Ever yours, 



C. Darwin. 



C, Darwin to C. Lyell. 



Down, Saturday [August ist, 1845]. 



My dear Lyell, — I have been wishing to write to you for 

 a week past, but every five minutes' worth of strength has 

 been expended in getting out my second part.f Your note 

 pleased me a good deal more I dare say than my dedication 

 did you, and I thank you much for it. Your work has in- 

 terested me much, and I will give you my impressions, 

 though, as I never thought you would care to hear what I 

 thought of the non-scientific parts, I made no notes, nor 

 took pains to remember any particular impression of two- 

 thirds of the first volume. The first impression I should say 



* 'Travels in North America,' 2 vols., 1845. 



f Of the second edition of the ' Journal of Researches.' 



