My dear Darwin

Please sign the memorial & return it by return of post as no time is to be lost.¹ I have had Hooker’s letter copied.² I feel sure that the whole globe must at times have been superficially cooler— Still I think that during extreme excentricity the sun would make great efforts to compensate in perihelion for the chill of a long winter in aphelion in one hemisphere & a cool summer in the other—³

I think you will turn out to be right in regard to meridianal lines of mountain chains by which the migrations across the equator took place while the was contemporaneous tropical heat of certain low lands, where plants requiring heat & moisture were saved from extinction, by the heat of the earth’s surface, which was stored up in perihelion being prevented from radiating off freely into space by a blanket of aqueous vapour caused by the melting of ice & snow.⁴ But though I am inclined to profit by Croll’s maximum excentricity for the glacial period, I consider it quite subordinate to geographical causes or the relative position of land & sea & the abnormal excess of land in polar regions.⁵ It is a vast subject & if one applies to the astronomer there is no end to the number of uncertain data which it has never been worth their while to calculate for their own purposes. The worst of all the uncertainties is that which relates to the temperature of space⁶

believe me | ever most truly yrs | Cha Lyell