WCP4982

[1]¹ [p. 358]

Pen-y-bryn, St. Peter's Road, Croydon,

19^th July 1880.

James Croll, Esq.

Dear Mr. Croll,—Many thanks for your interesting letter. The facts you mention are most curious and startling, and I shall look with great interest to Professor Geikie's detailed account of them. My chapter on "Glacial Epochs and Warm Polar Climates" has passed through the press some months back, and I am now near the end of my book. I can hardly venture to hope that my conclusions will satisfy you, but I may say here that they have been reached mainly by giving greater weight to your admirable views on ocean currents as affecting climate, than you seem to do yourself. I have endeavoured to show that a comparatively slight increase of the warm tropical waters carried to the Arctic regions, combined with somewhat less high land in those regions, would render glacial conditions impossible there, and this being done, there would necessarily result the state of climate that the Miocene Arctic vegetation showed did exist. I have further attempted to prove that the geological evidence shows that there was, during the greater part of the Secondary and Tertiary periods, such terrestrial conditions as would cause this great transference of equatorial heat northwards, and I have further argued, I hope soundly, that, such a condition of things existing, neither high eccentricity nor the changing phases of aphelion and perihelion would alter the general character of the climate, though it might affect the nature of the seasons. I also show that the changing phases of perihelion, etc., would only reverse the Polar glaciation when that glaciation was of small extent. When it was extensive and excessive, the change to winter in perihelion would not do away [2] [p. 359] with the Glacial epoch, but only cause a slight fluctuation of its southern limits.

This will enable you to form some idea of the nature of my argument, which I am sure you will weigh carefully when I have the pleasure of sending you a copy of the book, as I hope to do in a few months.—Believe me, yours very faithfully,

Alfred R. Wallace.