My dear Lyell

It certainly seems to me safer to rely solely on slowness of ascertained up & down movement. But you could argue length of probable time before the movement became reversed as in your letter.² And might you not add that over whole world it would probably be admitted that a larger area is now at rest than in movement? & this I think would be tolerably good reason for supposing long intervals of rest. You might even adduce Europe, only guarding yourself by saying that possibly (I will not say probably, though my prejudices would lead me to say so) Europe may at times have gone up & down all together.—   I forget whether in former letter you made a strong point of upward movements being always interrupted by long periods of rest.—   After writing to you, out of curiosity I glanced at the early Chapt^s. in my Geology of S. America; & the areas of elevation on E. & W. coasts are so vast, & proofs of many successive periods of rest so striking that evidence becomes to my mind striking.

With respect to Astronomical causes of change, in ancient days in the Beagle, when I reflected on the repeated great oscillations of level on very same area; & when I looked at symmetry of mountain-chains over such vast space, I used to conclude that the day would come when slow change of form in the semi-fluid matter beneath the crust would be found cause of volcanic action & of all changes of level. And the late discussion in Athenæum by Sir H. James (though his letter seemed to me mighty poor, & what Jukes wrote good) reminded me of this notion.³ In case astronomical agencies sh^d ever be proved or rendered probable, I imagine, as in nutation or precession, that an upward movement or protrusion of fluidified matter below might be immediately followed by movement of opposite nature. This is all that I meant.—   I have not read Jamieson, or yet got the number.—⁴

I was very much struck with Forbe’s explanation of N. of Soda beds & the saliferous crust, which I saw & examined at Iquique.—⁵ I often speculated on greater rise inland of Cordillera, & c^d. never satisfy myself.

How far to lump & split species is indeed a hopeless problem.—   It must in the end, I think, be determined by mere convenience.—

I have not read Stur,⁶ & am awfully behind hand in many things.

I am very glad to hear that you continue to stir them up at Zoolog. Soc.—⁷

I get on slowly with my new Edition; I find that your advice was excellent; I can answer all Reviews, without any direct notice of them, by a little enlargement here & there, with here & there a new paragraph.—   Bronn alone I shall treat with the respect of giving his objections with his name.—⁸ I think I shall improve my Book a good deal, & add only some 20 pages.—

I hear that there is article in Macmillan on the Origin—⁹

Ever yours | C. Darwin

I have not yet read Phillips.—¹⁰